MSc Chemistry
The Science for Energy and Sustainability
Literature Thesis
Analysis of Replacement Chemicals of Several Persistent
Organic Pollutants
Ad lib.: Working Towards Developing a Trend to Prevent
Regrettable Substitutions
by
Cooper Crippen
11985186
January 2020
12 Credits
Period 1 - 2
The Institute for Biodiversity and Ecosystem Dynamics
Supervisor/Examiner:
Dr. Thomas ter Laak
Examiner:
regulations of past, current and future persistent organic pollutants (POPs) and the chemicals that subsequently replace them after regulations are imposed upon them. This research aims to provide the basis of understanding what contributes to chemicals being labelled as POPs and how the resulting chemicals that replace these regulated POPs are no better for the environment than those that have come before them. This understanding will then work to stop this cycle from repeating itself and make the effort to stop POPs from being regulated, just to be replaced by a new, future POP. This will be accomplished by analyzing several POPs and regulatory frameworks that allow for this type of cycle to continue from various angles. Several main findings resulted from this literature research. Such as the correlation between strong carbon halogen bonds leading to high environmental persistence; leaving such chemicals predisposed to becoming a persistent organic pollutant. Additionally, lack of change on behalf of the regulatory frameworks, such as the Environmental Protection Agency, continue to facilitate the easy replacement of regulated POPs with new chemicals equally as inadequate for the environment, through poor chemical grouping and lax laws on environmental persistence testing of chemicals before production.
2 The Chemicals ... 5 2.1 PCBs ... 5 2.2 PBDEs ... 9 2.3 PFCs ... 12 3 Comparison ... 15 3.1 Persistence ... 20 3.1.1 Is Persistence Dangerous? ... 23 3.2 Future Chemicals... 25 4 Conclusion... 28 5 Bibliography ... 31
deca-brominated diphenyl ethers decaBDE(s)
Dichlorodiphenyltrichloroethane DDT
Environmental Protection Agency EPA
European Union EU
National Institute of Health NIH
octa-brominated diphenyl ethers octaBDE(s)
penta-brominated diphenyl ethers pentaBDE(s)
perfluorinated compounds PFC(s)
perfluoroalkyl substances PFAS(s)
perfluorooctane sulfonate PFOS
perfluorooctanoic acid PFOA
persistent organic pollutants POP(s)
polybrominated diphenyl ethers PBDE(s)
polychlorinated biphenyls PCB(s)
polychlorinated triphenyls PCT(s)
1 Introduction
This literature thesis seeks to further the understanding of persistent organic pollutants (POP’s) and how this understanding can be used to analyze chemical substitutions that are made to replace chemicals that have either been banned or subject to strict regulations. The analysis will be done in order to determine if replacement chemicals are any less harmful or dangerous than those who came before it. By looking at the characteristics of persistent organic pollutants, there are hopes to establish a trend that allows for early identification of dangerous and persistent replacement chemicals before they are used. However, even though the chemicals that are being studied have been subject to bans or regulations, they cannot only be viewed as prolific mistakes made by the chemical industry. These chemicals were developed and ultimately succeeded within the chemical industry and the market, due to their exceptional chemical properties. Given the wide array of consumer and industry applications, many of these chemicals became widely used and successful. However, these same exceptional properties of these chemicals are also their downfall. This issue truly is a double-edged sword.
A persistent organic pollutant (POP) is a chemical that is persistent in the environment. The word pollutant in POPs already gives an idea on the toxicity of these persistent chemicals. This word pollutant at the end tells us that these chemicals have a negative toxicity effect on the environment. The National Institute of Health (NIH) in the United States (US) defines a persistent organic pollutant as “a group of toxic chemicals that don’t break down easily in the environment.”1 The NIH also notes that POP’s are able to travel not only regionally, but also worldwide, bioaccumulate in fat of humans and animals, biomagnify and are persistent within the environment.2 All of these facts are reasons that POP’s are of interest in this literature thesis. They are known to be harmful to the environment, pose a threat to both animals and humans and can persist in the environment for long periods of time without being removed. Also accounting for the fact that they are able to travel around the world, areas that are not directly
1 National Institute for Health. (2017, May 31). Persistent Organic Pollutants (POPs): Your Environment, Your
Health | National Library of Medicine. Retrieved October 22, 2019, from https://toxtown.nlm.nih.gov/chemicals-and-contaminants/persistent-organic-pollutants-pops.
exposed to POP’s are also at risk. This risk was eventually realized by many people around the world, which resulted in the Stockholm Convention. The Stockholm Convention is a global treaty, that was signed in 2001 and entered into force three year later, in 2004. Its aim is to protect humans and the environment from the negative effects of POP’s3 by requiring the member countries of the treaty “to take measures to eliminate and reduce release of POP’s into the environment”.4
There are several examples of persistent organic pollutants that have been subject to strict regulations and due to this, a replacement chemical came along to fill this new chemical void. The first of these examples, and possibly the most infamous, are polychlorinated biphenyls (PCB’s). The Environmental Protection Agency (EPA) in the United States describes, “PCBs as a group of man-made organic chemicals consisting of carbon, hydrogen and chlorine atoms with the location and number of chlorines determining the properties.”5 PCB’s were used world-wide for a whole host of industrial purposes since as early as 1929.6 The discovery of PCB accumulation in nature was discovered by accident, as Swedish researchers were investigating the accumulation of another persistent organic pollutant, Dichlorodiphenyltrichloroethane more commonly known as DDT.7 PCB’s at the time were an unknown chemical that was being detected during the DDT research and was only correctly identified as PCB, two years later, in 1966.8 After being recognized as a very harmful and persistent chemical to the environment, both DDT and PCB had the honor of being added to the ‘dirty dozen’; the first 12 chemicals to be listed as persistent organic pollutants under the 2001 Stockholm Convention.9
3 Stockholm Convention. (2008). Overview. Retrieved October 21, 2019, from
http://chm.pops.int/TheConvention/Overview/tabid/3351/Default.aspx.
4 ibid.
5 Environmental Protection Agency. (2019, August 23). Learn about Polychlorinated Biphenyls (PCBs). Retrieved
October 10, 2019, from https://www.epa.gov/pcbs/learn-about-polychlorinated-biphenyls-pcbs.
6 Jensen, S. (1972). The PCB story. Ambio, 123-131. 7 ibid.
8 ibid.
9 Stockholm Convention. (2008). The 12 initial POPs under the Stockholm Convention. Retrieved October 1, 2019,
Following PCBs were polybrominated diphenyl ethers (PBDE’s), a chemical that is very similar to PCBs in many ways. PBDEs were chemicals that came into the market quite strong and had a wide array of uses, such as those of PCBs. Due to the new regulations that were being put upon PCB’s, PBDE’s began to flourish as the PCB replacement chemical. Dr. Vonderheide et al. states, “In 1978, brominated flame retardants (BFRs) were established as the new major chemical flame retardant and within this group, the polybrominated diphenyl ethers took a prominent role (about 40% of the global market of flame retardants).”10 After the widespread use in the US and other locations around the world began in the 1970’s, concerns about their persistence and impact on the environment began to grow.11 This concern led to discoveries of accumulation of PBDE’s worldwide and subsequent regulations were imposed after several attempted directives by the European Commission were withdrawn due to ‘uncertainty in the scientific community’.12 The failed directives by the European Commission can most likely be explained by a push back from the industry due to the amount of products PBDEs were used in and its important use as a flame retardant. This essentially entails that there was a lot to lose if they made the wrong choice in regulating PBDEs without having an absolute need to regulate them. Evidence of the industry pushing against the regulations of PBDEs is still seen today, as one of the major PBDEs managed to escape regulation until as late as 2017 due to industrial lobbying, a topic that will be discussed at a later point.
The final example that will be looked at are perfluorinated compounds and perfluoroalkyl substances (PFC’s or PFASs). PFC’s have been around for a long period of time, although they are one of the newest compounds to be discovered as a potential persistent organic pollutant. There are a various number of PFC’s that exist, but the two main types are the perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which are known for their widespread
10 Vonderheide, A. P., Mueller, K. E., Meija, J., & Welsh, G. L. (2008). Polybrominated diphenyl ethers: causes for
concern and knowledge gaps regarding environmental distribution, fate and toxicity. Science of the Total Environment, 400(1-3), 425-436.
11 Cooke, M. Technical Fact Sheet – Polybrominated Diphenyl Ethers (PBDEs), Technical Fact Sheet –
Polybrominated Diphenyl Ethers (PBDEs) (2017).
12 Noelle Eckley & Henrik Selin (2004) All talk, little action: precaution and European chemicals regulation, Journal
environmental distribution.13 Having been developed since the 1950’s, these PFASs have been used in a wide array of industrial and commercial applications14 and even though they have been produced for more than 50 years, PFASs were not seriously identified as an environmental threat until the early 2000’s.15 However, once this threat was recognized, the EPA claims that PFOAs and PFOSs have been voluntarily phased out by the industry.16 Unfortunately, this is not the end of PFASs chemicals threating the environment. The older PFOA and PFOS chemicals that have been phased out, are still present in the environment today and a new generation of PFAS chemicals, such as GenX and PFBS are slated to take their place and are currently being produced and used.17
These three different examples of persistent organic pollutants can be seen as a timeline. Things began with one of the first identified POPs, PCB. From there, PBDEs were adopted in order to fill the void that was left by PCBs. Once the true affects of PBDEs were known, they were also heavily regulated and seen as unsafe for most uses. Then PFASs came along. Now, PFASs are not a direct replacement in terms of uses for PCBs or PBDEs, however the line if thinking is the same. With PFOA and PFOS being used and eventually being phased out due to the realization of their environmental unsafety, another subset of PFASs are next in line to fill the gap that was left when PFOA and PFOS were phased out.
Due to these circumstances, it is necessary to ask: when discussing PCB, PBDEs, and PFC chemicals, are the chemicals that replace them any better for the environment and can a trend be developed to determine if a chemical is likely to be harmful for the environment? There must be a shift in the paradigm, otherwise things will continue how they have in the past.
13 Kannan, K. (2011). Perfluoroalkyl and polyfluoroalkyl substances: current and future perspectives. Environmental
chemistry, 8(4), 333-338.
14 cf Kannon (n 13).
15 Interstate Technology Regulatory Council. (2017, November). History and Use of Per- and Polyfluoroalkyl
Substances (PFAS). Retrieved October 19, 2019.
16 Environmental Protection Agency. (2018, December 6). Basic Information on PFAS. Retrieved October 15, 2019,
from https://www.epa.gov/pfas/basic-information-pfas.
This thesis will first provide an analysis of the structures and properties of the above-mentioned chemicals, as well as the taking a look into the future about some of the new emerging chemicals that are set to replace existing chemicals. Following this, other issues, paradoxes and laws will be discussed to give a full understanding of the situation, as it is much larger than it appears.
2 The Chemicals
To fully understand the connection between all these different persistent organic pollutants that were discussed up to this point, we must take a deep look into the specific uses, chemical structures and chemical properties. Doing this will provide insight into any potential connections that might be made between the chemicals. Using these potential clues given by the chemical properties and structures, a trend may be established that allows for the identification of a potentially ‘regrettable substitution’ of a chemical, before it is even made.
2.1 PCBs
Beginning with one of the original ‘dirty dozen’ chemicals to be listed as persistent organic pollutants, PCB. As mentioned before, PCBs had a very wide variety of uses around the world within the industry and for a long period of time. Some of the most important uses of PCBs were as dielectric fluid in power transformers and capacitors, hydraulic fluid in machinery and underground mining, heat exchanger fluid and plasticizers in paints, plastics and sealants.18 Now, PCBs had such an extensive list of uses in the industry for a good reason. This was because PCBs have a number of properties than make them very desirable for various industrial uses, such as a high heat capacity, chemical stability, and great dielectric properties.19 Consequently, PCBs were essentially a very stable chemical that did not break down easily, could withstand a large amount of heat, and work
18 Global Asset Protection Services LLC. (2015) DIELECTRIC FLUIDS CONTAINING PCBs. GAPS Guidelines, GAP.5.4.5.1 19 Stratton, C. L., & Sosebee, J. B. (1976). PCB and PCT contamination of the environment near sites of manufacture
and use. Environmental science & technology, 10(13), 1229-1233.
Figure 1 - Structure of PCB (A) and PCT (B)
impeccably to insulate electrical energy. With all of these main properties listed out, it is understandable why the industry had adopted the use of PCBs so heavily.
Now that the uses and the chemical properties of PCBs were discussed, we can illustrate the chemical structure of a PCB to identify why PCBs have their certain properties. Figure 1 shows the structure of both, PCB and PCT. 20 PCT is another chemical of interest, which as seen has a very similar structure to PCB; not only this but PCT also has many of the same physical properties discussed before and yields PCB is very small quantities (~0.5%).21 PCTs have also been known to be used as chemical substitutes to PCBs in certain instances.22 Looking at the structure of both PCB and PCT, there is a great number of similarities, in fact they are almost identical except for the fact that PCT has an additional, third phenyl group. Both PCB and PCT also have a large amount of chlorines that attach to each of the phenyl groups. For PCB this can range from 1 – 10 chlorines23 and for PCT it can range from 1 – 14 chlorines.24 This variation in the number of chlorines allows for a vast number of different congeners of PCBs, 209 to be exact.25 And with the larger number of chlorines available to place on PCT; there is even a larger number of congeners for PCT. This carbon to chlorine bond is one of the main reasons these PCB and PCT chemicals are so stable. Thinking back to some basic chemistry, halogens in general are quite electronegative atoms, while carbons are less so. This difference in electronegativity leads to a polarized bond with a positive charge on the carbon and a negative charge on the chlorine. This resulting polarized carbon – chlorine bond is very stable and requires quite a lot of energy to break. Chlorine is also quite a bulky atom, which imparts steric hinderance, making attack from reactive species unlikely. These two elements are what give these PCB and PCT chemicals their unbridled strength. Proof of this can be seen when analyzing the destruction temperature of PCBs from various studies. When looking at these studies, extremely high temperatures used to
20 cf Stratton & Sosebee (n 19).
21 Filyk, G. (n.d.). POLYCHLORINATED TERPHENYLS (PCTs). PDF. Hull, Quebec. 22 Ibid.
23 cf Stratton & Sosebee (n 19). 24 cf Filyk (n 21).
25 IARC Working Group on the Evaluation of Carcinogenic Risk to Humans. Polychlorinated Biphenyls and Polybrominated
Biphenyls. Lyon (FR): International Agency for Research on Cancer; 2016. (IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 107.) 1. EXPOSURE DATA. Available from: https://www.ncbi.nlm.nih.gov/books/NBK361688/
completely destroy PCBs can be seen. The lowest of these report destruction temperatures is 800°C and other temperatures range from 1000°C to 2000°C for about 99.9999% destruction.26 However, due to PCBs being one of the most stable organic substances in the world, and because of its ability to bioaccumulate, it also poses a great threat to the environment and living organisms.27
Having a chemical that is very stable under high heat and other conditions is always a good property in the sense of usability and practical application. However, this same property makes it incredibly undesirable for the environment. The author of The PCB Story, Jensen, says, “The stability of the substance that makes it so attractive for industrial use is the same property that causes the accumulation of the substance in ecosystems and the food chains.”28 Chemicals which such high stability, such as PCBs or PCTs, are very desirable by the industry, because they can solve many problems. But once these chemicals find their way into the environment, they are so stable that natural processes and organisms in the environment are not able to break them down. This leads to an accumulation of PCB in the environment, which in turn will lead to biomagnification of PCBs within animals as it moves up the food chain. This poses a real threat to not only environmental organisms and animals, but also to humans, as we may also be exposed. The EPA states that human exposure can come from poorly maintained waste sites, leaks from electrical transformers, burning of certain waste and even from the consumption of fish that has been exposed to PCBs through bioaccumulation.29
The discovery of PCB in the environment, as stated before, was a surprise to everyone. As no one was looking for it and most people were concerned with the effects of DDT at the time. It has even been stated that the DDT contamination in the environment was over-estimated due to overlapping of major peaks in gas chromatography analysis of samples while researching DDT
26 Hutzinger, O., Choudhry, G. G., Chittim, B. G., & Johnston, L. E. (1985). Formation of polychlorinated
dibenzofurans and dioxins during combustion, electrical equipment fires and PCB incineration. Environmental health perspectives, 60, 3-9.
27 cf Jensen (n 6). 28 cf Jensen (n 6).
29 Environmental Protection Agency. (2019, August 23). Learn about Polychlorinated Biphenyls (PCBs). Retrieved
contamination.30 Following the discovery of PCBs as a toxic chemical that was accumulating in the environment in 1966, subsequent action taken on PCBs were quick to follow. In 1979 the EPA released an official statement that prohibited the manufacture, processing, distribution, and ‘non-enclosed’ uses of PCBs, unless specifically authorized and also disallowed the manufacture of new electrical PCB equipment.31 This prohibition has been upheld to this day, with the manufacture or use of any PCB that is not totally enclosed being disallowed, unless an exception is met by meeting very strict criteria.32 The European Union (EU) was late to the party, heavily restricting PCBs six years after the US in 1985 and then furthering its restrictions in 2010 to remove PCTs and all PCB containing equipment as soon as possible.33 Once PCBs had been heavily restricted there was an empty place in the market where PCBs once were and PBDEs began to take that place.
30 cf Jensen (n 6).
31 US Environmental Protection Agency. (2016, August 8). EPA Bans PCB Manufacture; Phases Out Uses. Retrieved
October 15, 2019, from https://archive.epa.gov/epa/aboutepa/epa-bans-pcb-manufacture-phases-out-uses.html.
32 eCFR - Code of Federal Regulations. (2019). Retrieved October 16, 2019, from
https://www.ecfr.gov/cgi-bin/text-idx?SID=bdd48b3291c37e2ca417103619fa040f&mc=true&node=se40.34.761_120&rgn=div8.
33 European Commission. (2019, June 8). Polychlorinated biphenyls and polychlorinated terphenyls (PCBs / PCTs).
2.2 PBDEs
Once PCBs had been heavily regulated, they could no longer be used for the wide variety of uses that they had once been used. This led to the search for a substitution or a replacement that would be able to fill the gap that had been left. Ultimately polybrominated diphenyl ethers (PBDEs) became the main substitute for PCBs and PCTs. PBDEs, like PCBs, have a very large range of uses. Gaining widespread adoption in the 1970s, PBDEs were used as a flame retardant and a flame-retardant additive to materials such as paints, foams, textiles, and plastics.34 This use of PBDEs was also largely concentrated in the US, with the US using about 98% of the global PDBE demand in 1999.35 The use as not limited to these products alone and in general had a much more widespread release into the environment than PCBs did. This is since PCBs mostly had a use in industrial settings, while PBDEs did have industrial uses as well, there was a large number of consumer products that contained PBDEs, meaning that they were able to reach the environment from more locations.36 This increased commercial use is because of fire safety standards that needed to be met by household and commercial products.37 This made PBDEs the chemical of choice to add to various commercial products to meet these standards.
It is necessary to look at the physical and chemical properties of PBDEs to discover why this widespread use was a problem for the environment. Figure 2 shows the general structure of a penta-brominated PBDE.38 During the production and use of PBDEs, there were three main types that were used, pentaBDEs, octaBDEs, and decaBDEs; each having 5, 8, or 10 bromines
34 Center for Disease Control and Prevention. (2017, April 7). Biomonitoring Summary. Retrieved October 1, 2019,
from https://www.cdc.gov/biomonitoring/PBDEs_BiomonitoringSummary.html.
35 Siddiqi, M. A., Laessig, R. H., & Reed, K. D. (2003). Polybrominated diphenyl ethers (PBDEs): new pollutants–old
diseases. Clinical Medicine & Research, 1(4), 281-290.
36 Ibid.
37 Shaw, Susan. (2009). Polybrominated Diphenyl Ethers in Marine Ecosystems of the American Continents:
Foresight from Current Knowledge. Reviews on environmental health. 24. 157-229. 10.1515/REVEH.2009.24.3.157.
38 National Center for Biotechnology Information. PubChem Database. CID=36159,
https://pubchem.ncbi.nlm.nih.gov/compound/1_2_4-tribromo-5-_2_4-dibromophenoxy_benzene (accessed on Oct. 30, 2019)
Figure 2 - General structure of a penta-brominated PBDE.
attached to the phenyl rings respectively.39 PBDEs are very strong chemicals, requiring a temperature of greater than 400°C to be destroyed, with some studies using temperatures as high as 900 - 1000°C.40 After looking at the general structure of a PBDE, there are a lot of interesting aspects that we can learn and a lot of similar themes that seem to be carried over from PCBs. PBDEs, like PCBs, have carbon to halogen bonds centered around a phenyl ring. However, in PBDEs the halogen is a bromine atom and not a chlorine atom. This means that there will still be a dipole moment, making it a polar bond, but the dipole moment will be smaller than that of a carbon chlorine bond. This is due to the difference in electronegativity of chlorine and bromine. While the difference in electronegativity is not much (3.16 vs 2.96), it is enough to make the carbon halogen bond in PBDEs less polar and slightly weaker than the carbon chlorine bonds of PCBs. The relative difference in bond strength is significant though. With the carbon chlorine bond having a bond strength of 397 kJ/mol and the carbon bromine bond having a bond strength of 280 kJ/mol.41 This lower bond strength is one of the key reasons that PBDEs are such effective flame retardants. When combustion happens, very high energy OH and H radicals are created by the intense heat.42 At this point the relatively weak carbon bromine bonds come into play. Also, when under heat by combustion, the carbon bromine bond breaks via a radical mechanism to from a bromine radical. This newly formed bromine radical then reacts with the high energy OH and H radicals to effectively remove energy from the system and therefore making PBDE containing products less flammable.
The widespread commercial use of PBDEs has made them of great concern to the environment. Due to the more commercial use of PBDEs, there are concerns that the contamination in the environment is greater than that of PCBs and that there are far more ways
39 cf Cooke (n 11).
40 Yang, Y., Huang, Q., Tang, Z., Wang, Q., Zhu, X., & Liu, W. (2012). Deca-brominated diphenyl ether destruction
and PBDD/F and PCDD/F emissions from coprocessing deca-BDE mixture-contaminated soils in cement kilns. Environmental science & technology, 46(24), 13409-13416.
41 T. L. Cottrell, The Strengths of Chemical Bonds, 2d ed., Butterworth, London, 1958; B. deB. Darwent, National
Standard Reference Data Series, NationalBureau of Standards, no. 31, Washington, 1970; S. W. Benson, J. Chem. Educ. 42:502 (1965); and J. A. Kerr, Chem. Rev. 66:465 (1966).
42 Rahman, F., Langford, K. H., Scrimshaw, M. D., & Lester, J. N. (2001). Polybrominated diphenyl ether (PBDE)
for PBDEs to enter the environment, potentially making them a larger threat the environment than PCBs.43 The extent that PBDEs have entered not only the environment, but everyday human life is problematic, as they are found in the air, soil, sediment, water, buildings, sewage, automobiles and more indoor environments that were never accessible by PCBs.44 Additionally, in several studies, the concentration of PBDEs is equal to if not greater than that of PCBs, in indoor environments, cars, and environmental settings.45 This may be explained in part to discoveries made showing similar PBDE bioaccumulation to that of PCBs.46 However, there is a small amount of good news that accompanies how PBDEs react in the environment. Several studies claim that biomagnification of PBDEs only happens with PBDEs that are up to 6 – 7 bromine atoms and that heavier PBDEs do not biomagnify at all or another study that claims PBDEs exhibited negligible biomagnification.47
The topic of biomagnification of lighter PBDEs introduces the next area of discussion; regulations. Although the three main PBDEs that were produced – penta, octa, and decaBDE – are all known to be harmful to the environment and bioaccumulate, only the pentaBDE and octaBDE have been subject to regulations. Within the US pentaBDE and octaBDE were subject to regulations on their use in 2006 in order to phase out the chemicals.48 However, this ban was not carried over to the heavier PBDE, decaBDE. The producers and main importers of decaBDE did agree to phase out the use of decaBDE by the end of 2013, however comments from the industry in 2012 stated that there still may be a use of decaBDE in the industry.49 This means that the use of decaBDE may still be continuing within the US. The EU followed roughly the same path, with early regulations on the use of pentaBDE and octaBDE and with no regulations on decaBDE until
43 cf Siddiqi (n 35).
44 Vonderheide et al. (n 10). 45 Vonderheide et al. (n 10).
46 Wu, J. P., Luo, X. J., Zhang, Y., Luo, Y., Chen, S. J., Mai, B. X., & Yang, Z. Y. (2008). Bioaccumulation of
polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in wild aquatic species from an electronic waste (e-waste) recycling site in South China. Environment international, 34(8), 1109-1113.
47 Burreau, S., Zebühr, Y., Broman, D., & Ishaq, R. (2006). Biomagnification of PBDEs and PCBs in food webs from
the Baltic Sea and the northern Atlantic Ocean. Science of the Total Environment, 366(2-3), 659-672 : Kelly, B. C., Ikonomou, M. G., Blair, J. D., & Gobas, F. A. (2008). Bioaccumulation behaviour of polybrominated diphenyl ethers (PBDEs) in a Canadian Arctic marine food web. Science of the Total Environment, 401(1-3), 60-72.
48 cf Cooke (n 11). 49 cf Cooke (n 11).
2017, where production and use of decaBDE was also regulated.50 The continued use of decaBDE was lobbied for by many parties within the industry during the time that penta and octaBDE were being subjected to regulations; many believed that some of the chemical properties discussed before of decaBDEs, such as increased stability over less brominated species and their lesser ability to biomagnify, made them less of a danger to the environment.51 This lesser ability to biomagnify is most likely due to the low bioavailability of PBDEs, as if they are not readily bioavailable, then it is difficult for them to biomagnify. Therefore, their use continued for several years after other PBDEs were subject to regulations. This proved to be problematic, as decaBDEs still accumulate in the environment, which based on research done about decaBDEs, accumulation itself is not a health risk. The issue arises with deca-BDEs ability to be transformed into a lower brominated BDE species. This process can happen in both aerobic and anerobic environments in sludge, sediment and other environmental settings.52 Given the toxicity information about penta and octaBDEs, this fact is a big cause for concern over the prolonged and continued use of decaBDEs. The issue of PBDEs had become enough of a concern as early as 2003, for PBDEs to be referred to as “PCBs of the future”, but with a more widespread pollution in the environment and a more diverse set of sources for PBDEs to enter the environment.53 2.3 PFCs
The final persistent organic pollutant that will be analyzed is one of the newest ones to be added to the POP list. This POP is a group of chemicals called perfluorinated compounds or perfluoroalkyl substances (PFCs or PFASs). These compounds are a bit
different than PCBs or PBDEs are in terms of the structure and usage, but still share many similarities. Nevertheless, they are POP of interest due to their chemical properties and wide array of usages. The most important
50 The European Commission. (2017). COMMISSION REGULATION (EU) 2017/227. Official Journal of the European
Union, 35, 6–9. Retrieved from https://eur-lex.europa.eu/eli/reg/2017/227/oj
51 Vonderheide et al. (n 10).
52 Deng, D., Guo, J., Sun, G., Chen, X., Qiu, M., & Xu, M. (2011). Aerobic debromination of deca-BDE: isolation and
characterization of an indigenous isolate from a PBDE contaminated sediment. International Biodeterioration & Biodegradation, 65(3), 465-469.
53 cf Siddiqi (n 35).
Figure 3 - General structure of PFCs
use of PFCs is its use in firefighting foams, while they are also present in many consumer products as a coating, such as stain and water repellents in fabric, non-stick coating on cookware, paints, waxes, etc.54 The firefighting foam use is the most important, as it is the most direct entrance PFCs have into the environment and where large quantities may be introduced into the environment at once, where as other commercial uses are a much more gradual introduction into the environment. And due to this wide array of uses, there are many ways that PFCs can enter the environment which is problematic.
PFCs are organofluorine compounds, consisting of a carbon chain ranging from 6 – 16 long with almost all of the hydrogens have been replaced by fluorine atoms and a hydrophilic end group.55 This is detailed in figure 3, where the general formula of PFCs can be seen.56 There are two main PFCs that are of interest for this study, which are Perfluorooctanoic acid (PFOA) and Perfluorooctanesulfonic acid (PFOS). The structure of both PFOA and PFOS can be seen in figures 4 and 5, respectively.57 The reason that these two specific PFC’s are of interest is because they are some of the most commonly produced PFC’s and are known to be persistent in the environment. Although these chemicals have been heavily studied, there are many more classes PFCs and new generations of PFCs successors that are currently being used and thus are being released into the environment.
The displayed structures lead to PFCs having quite unique physical and chemical properties, some of which are shared with PCBs and PBDEs. These properties include:
54 US Environmental Protection Agency. (2018, December 6). Basic Information on PFAS. Retrieved October 13,
2019, from https://www.epa.gov/pfas/basic-information-pfas.
55 Surma, M., & Zieliński, H. (2015). What do We Know about the Risk Arising from Perfluorinated
Compounds. Polish Journal of Environmental Studies, 24(2).
56 Ibid.
57 National Center for Biotechnology Information. PubChem Database. Perfluorooctanoic acid, CID=9554,
https://pubchem.ncbi.nlm.nih.gov/compound/Perfluorooctanoic-acid (accessed on Oct. 17, 2019) : National Center for Biotechnology Information. PubChem Database. Perfluorooctanesulfonic acid, CID=74483, https://pubchem.ncbi.nlm.nih.gov/compound/Perfluorooctanesulfonic-acid (accessed on Oct. 17, 2019)
Figure 4 - Structure of PFOA
lipophobicity and hydrophobicity, high heat resistance, and friction reduction.58 While the heat resistance is not as good as the other persistent organic pollutants that have been discussed before, but they can still withstand high heats, with temperatures higher than 1000°C usually used for complete destruction of PFCs.59 Like the other POPs discussed before, PFCs have a carbon halogen bond, which in this case is the carbon fluorine bonds. This bond in particular is the strongest of the carbon halogen bonds and is actually one of the strongest bonds that exists in organic chemistry. This may be one of the reasons that PFCs are able to withstand such temperatures and most definitely is the reason that PFCs are so stable. However, this stability also finds its way into the environment, where PFCs are very persistent due to this stability.
Unfortunately, just as PCBs and PBDEs before it, PFCs are also not good for the environment. As stated before, there are many studies on specifically PFOAs and PFOSs and the scientific community is continuing to broaden its knowledge on the environmental impact of more and more PFCs. Through these various studies, the scientific community has been able to determine that PFCs are mobile, persistent, bioaccumulative, and do not degrade in the environment.60 If this already was not problem enough, there is even more bad news in terms of the environmental concerns related to PFCs. Other studies have shown that with the use of current waste-water treatment processes and methods are not capable of removing PFCs from waste-water streams.61 The problem here is obvious, once the PFCs have entered the environment and begun to contaminate water streams, the way that waste-water is currently treated cannot sufficiently remove the PFCs. This will lead to an ever-increasing amount of PFCs in the environment and water, because there is no possibility of getting it out. In fact, PFCs are most likely to be found in water. As a result of their properties, once they enter water, lighter PFCs will not sorb to solid material, while many of the larger PFCs will and both have little to no volatilization or degradation.62
58 cf Interstate Technology Regulatory Council (n 15).
59 Kucharzyk, K. H., Darlington, R., Benotti, M., Deeb, R., & Hawley, E. (2017). Novel treatment technologies for
PFAS compounds: A critical review. Journal of environmental management, 204, 757-764.
60 15
61 cf Kannon (n 13). 62 cf Kannon (n 13).
This brings us to one of the newest developments in the area of PFCs. This development is the new GenX chemical. The original development of the GenX was due to a ban and voluntary phase out of PFOA because of health concerns.63 This ban was made within the EU in 2017. Thus,
there needed to be a new development in PFCs for the continuation of products that previously used PFOA.64 This ban lead to a search for a chemical that could replace PFOA in the industrial
applications but be better and less persistent in the environment. This led to the development and use of GenX, a mixture of several PFC chemicals. However, this chemical was not as environmentally friendly as it was claimed.
3 Comparison
Now a comparison will be made based on the various POPs displayed above. This comparison aims at providing an insight into a pattern that may give an idea into what is the problem and why all these various chemicals have become listed as POPs. This information will then be analyzed to see if it is possible to preemptively know if a chemical is going to be persistent in the environment or not and whether it is possible to create a balance between the properties of chemicals like these. Is it possible to have a balance where a chemical is useful enough for it to be used in the market, but its properties don’t lead to damage in the environment? Another comment that should be addressed is: if a chemical is only persistent, but has no harmful properties, should it be regulated and is persistence alone dangerous?
63 Ahearn, A. (2019, March 14). A Regrettable Substitute: The Story of GenX. Retrieved November 19, 2019, from
https://ehp.niehs.nih.gov/doi/10.1289/EHP5134.
64 Brandsma, S. H., Koekkoek, J. C., van Velzen, M. J. M., & de Boer, J. (2019). The PFOA substitute GenX detected in
To begin with this comparison, the properties and chemical composition of the three POPs that we have discussed, PCBs, PBDEs, and PFCs, need to be summarized, so that they can
be analyzed. Table 1 shows a comprehensive list of the key information that was discussed during earlier sections in this thesis.
Table 1 - Comparison of PCBs, PBDEs, and PFCs
Chemical Uses Use Type Destruction
Temp. (°C) # of halides Structure PCB dielectric fluid in transformers/capaci tors, hydraulic fluid, heat exchanger fluid, plasticizers in paints, plastics and sealants
Industrial 800 - 1400 1 - 10 PBDE flame retardant, flame-retardant additive to materials such as paints, foams, textiles, and plastics
Industrial or
Commercial <400 - 1000 5, 8, 10
PFC
firefighting foams, coatings, stain and water repellents, non-stick coatings for cookware, paints, waxes Industrial or Commercial <1000 11 - 31
First, based on the uses of all three of the chemicals, we can determine if the chemicals in question are appearing in the environment because their use is inherently putting them at risk to enter the environment. However, by looking at the uses of these chemicals it can quite clearly be stated that this is not the case. While there are some uses with these three chemicals that overlap, such as the use a firefighting foam and or flame retardants, there is not much correlation between the uses of each of these chemicals and their occurrence in the environment. Whether it is the use of PCB as a heat exchanger fluid in machinery or PBDE a flame-retardant additive to textiles or PFC present in the non-stick coating of a pan; they all show up in the environment and in large enough quantities and locations for them to be listed at POPs. The type of use does not seem to be a factor either, with both chemicals that are mostly used in the industry and chemicals that were used in both industry and commercial still appear in the environment.
The next area of comparison between all these chemicals is their destruction temperature or their resistance to heat in general. Looking at the table we can determine that PCBs run the race with the highest boiling point by quite a margin, followed by PBDEs and then PFCs in third. This is an important property of these chemicals to analyze, as when these chemicals enter the environment, they will not be reaching temperatures nearly this high. This means that if there were any opportunity for the chemicals to break down under high heats, this will not be possible in the environment as the boiling points are just far too high. In this respect the destruction temperatures may be quite different. But the similarity lies in the fact that they are all high destruction temperatures, which make them more stable chemicals and thus are all able to survive in the environment without being broken down by processes that involve heating.
From there we can take a look into one of the most important aspects of all of these chemicals, the carbon to halides bonds. This is one of the most important, if not the most important, comparisons that can be made because these carbon to halide bonds are largely responsible for the stability properties of the chemicals. Looking at table 1, it can be seen that all of the chemicals being discussed can have a wide variety of halogens in their structure; anywhere from 1 – 16. Each of the chemicals has a different carbon to halogen bond, but nevertheless the strength of each of the bonds is quite strong. PBDEs have the weakest bond with carbon bromine
bonds, followed by PCBs with carbon chlorine bonds, and finally PFCs with carbon fluorine bonds. This is an area in this comparison that shows a large amount of similarities between all the chemicals. While the exact carbon halogen bond for each of the chemicals is with a different halogen, the fact that they all have carbon halogen bonds is where the problem arises. The idea that the carbon halogen bonds within these chemicals are partially responsible for the environmental persistence of these chemicals is not very far-fetched. Carbon halogen bonds are inherently strong bonds, with the carbon fluorine bond being one of the strongest bonds that can be formed. The strengths of these bonds require quite a lot of energy to break, thus making them difficult for any kind of environmental process to break down or deal with. Further support of this shows when investigating the number of carbon halogen bonds in each of the chemicals and the respective temperature to destroy these chemicals. When looking at PCBs, this temperature ranges from 800 - 1400°C, presumably increasing as the PCBs become more halogenated. This trend continues when looking at PBDEs, but to a slightly lesser extent. DecaBDE, the highest bromine substituted BDE, has a destruction temperature of 900 - 1000°C. However, this destruction temperature varies a bit with temperatures as low as 400°C being reported as sufficient to destroy 99% of PBDEs. With PFCs, this statistic is a bit more difficult to measure, as there a large variation in the classes of PFCs. PFCs also have an end group on the end of the carbon chain that will also have an influence on the properties. Additionally, for more fluorines to be added to a PFC, there has to be an addition of carbons, making the chain longer, which also may impact the properties. Regardless of this, looking at the two main PFCs being addressed in the paper, PFOA and PFOS, there is a difference in the number of carbons and therefore the number of fluorines as well in these two chemicals. PFOA has an 8 long carbon chain with 15 carbon fluorine bonds, while PFOS also have an 8-carbon long chain, but with 17 carbon fluorine bonds. Regardless, the destruction temperatures of PFCs is greater than 1000°C. The stability of these PFCs seems to increase with longer carbon chains, as the longer the carbon chain, the higher the temperature required to destroy the PFC.65 The only other difference in PFOA and PFOS is the end group. So, this change in boiling point cannot be wholly contributed to
65 cf Kucharzyk et al. (n 59).
the additional carbon fluorine bonds, however, due to the strength of carbon-fluorine bonds it is safe to say that this increase in boiling point is due in part to the additional carbon-fluorine bonds. Based on this information it maybe be a possible hypothesize that in this situation, the carbon halogen bonds play a part in the environmental persistence of these chemicals. And that the more carbon halogen bonds each chemical has may not necessarily make it more persistent in the environment, but it can be stated that the more carbon halogen bonds undoubtedly do not make the chemicals any less environmentally persistent. Hence, in my belief, the carbon halogen bonds are a large contributor to the environmental persistence of these chemicals.
The next place that we can try to draw similarities is in the structures of each of the chemicals. The structures of both PCB and PBDEs involve phenyl rings, with the halogens around the outside of those rings. In fact, the structures of PCBs and PBDEs are eerily similar. With the only differences in the physical structure being the oxygen linking to two phenyl rings together and the different halide being used, chlorine vs. bromine. I think that an important lesson can be learned here. After PCB was known to be a persistent organic pollutant, the development and marketing of PBDEs should have immediately set off red flags for the potential environmental persistence of PBDEs just by analyzing the structures. A new chemical is brought to market that has a very similar structure and properties as PCB and also has halogen bonds. Due to these reasons there should have been extensive research into the environmental impact of PBDEs far before they were used at such the extent that they were. If we continue on to look at the structure of PFCs, we see a slightly different story. PFCs, rather than having rings, have a long chain of carbons as their main backbone and with an end group. This is the major difference in PFCs over PCBs or PBDEs.
Another interesting difference between PCBs and PBDEs against PFCs is the carbon backbone of the molecule. As seen in figures earlier, PCBs and PBDEs have a carbon backbone composed of ring structures, while PFCs have a linear structure. This is another important distinction to mention, because this difference determines the number of carbon halogen bonds these chemicals can have. PCBs and PBDEs are limited in the number of carbon halogen bonds because the 6-membered ring can only hold so many carbon halogen bonds. While a linear
carbon chain can add two carbon halogen bonds per carbon that is added to the chain. This gives the PFCs the ability to have many more carbon halogen bonds than PCBs or PBDEs can have. This difference probably plays into how persistent PFCs are. As discussed earlier, the longer the carbon chain of a PFC, the higher the temperature that is requires to destroy the PFCs. This gives us an indication as to the influence of carbon halogen bonds on the stability of at the very least PFCs, if not also PCBs and PBDEs. The addition of a single carbon to a PFC, introduces two more carbon halogen bonds, which is enough to increase the required temperature to destroy the PFC. This implies at the carbon halogen bonds being heavily responsible for the stability, meaning that the more carbon halogen bonds there are, the more stable the chemical will be. And I believe that this trend will also stand from PCBs and PBDEs.
3.1 Persistence
With other similarities of these three persistent organic pollutants briefly discussed, the true chemical-killing similarity can be addressed. There are many similarities connecting these chemicals; and these similarities are contributing to the environmental problems. But the most important similarity in these chemicals and other POPs is their persistence. When objectively looking at all of the information that is has been gather and presented about theses chemicals in this thesis, it can be said that many of these chemicals may not pose as much of a problem to the environment if they were not as persistent as they are or if there was a way to easily remove these chemicals from the environment. The negative health effects of many of these chemicals would be less relevant if they could leave the environment easily. Now, I’m not advocating for the development and production of chemicals that aren’t environmental persistent so that they can be put into the environment with care. But rather saying that the removal of the environmental persistence property of these chemicals might be enough to remedy the problem. Additionally, ways of removing these chemicals needs to be addressed. If we take PFCs for example, they cannot be removed from water using current wastewater treatment procedures. Now, if there was a way to easily remove PFCs from the environment, the persistence of these chemicals would not be such a problem, as the problem could be mitigated. But the issue of these chemicals being able to enter the environment would still exist.
To understand the reasoning that persistence is the underlying problem, first the word persistence must be given a definition. Persistence should not be confused with a chemical that is often found in the environment or a chemical that is found over larger areas. Persistence is all about how long a chemical remains in the environment, regardless of how widespread or often the chemical enters the environment. Persistence is defined by Environment Canada as the length of time that a chemical remains in the environment and this time is usually measured through the half-live of the chemical.66 From this definition, we can gather that the half-life of a chemical in the environment is what determines persistence and does not take into consideration other potentially harmful properties of chemicals. This definition is a sufficient definition, however there is more to the persistence than just this, as it encompasses much more. First, it must be asked how the chemical entered the environment and into which environmental compartment. There are several different environmental compartments that the chemical can enter. These compartments being air, water, soil, sediment, and biota, if the chemical can be taken up by animals. For each of these different compartments there is a certain criterion that must be met in terms of time for it to be considered a persistent chemical. For each of the compartments that are available there is a minimum time period that must be met for air, water, soil, and sediment, which are equally to 2 days, 6 months, 6 months, and 1 year for each respective environmental compartment.67 So with this information we can see that to be labeled as a persistent chemical, is not something that happens overnight. The time periods for each of the environmental compartments is quite long and gives this issue some perspective on how long of times periods are being discussed when the term persistent is being used. However, if PCBs, PBDEs or PFCs had a half life in the range of 6 months to a year, that would be a luxury. In reality the half-lives of these chemicals in the environment is much longer than that. PCBs have an average half-live somewhere in the range of 10 to 20 years, meaning they surpass the time criteria for being considered persistent by at the very least 10 times.68 PBDEs show a bit more
66 Webster, E., Mackay, D., & Wania, F. (1998). Evaluating environmental persistence. Environmental Toxicology
and Chemistry: An International Journal, 17(11), 2148-2158.
67 Ibid.
68 Sinkkonen, S., & Paasivirta, J. (2000). Degradation half-life times of PCDDs, PCDFs and PCBs for environmental
promise, half-lives ranging from at best weeks in the air and months to years in the soil and sediment.69 These half-life determinations are made in a laboratory setting in specific conditions, while the environment is different with much more variation, generally leading to a longer half-life than the laboratory testing suggests. In general, the lighter PBDEs seem to be less persistent in the environment than the heavier PBDEs. As PFCs mostly exist in water and, as they are not likely to sorb to sediment or air, the half-life in water is estimated to be 5120 and 25,600 years for open and coastal ocean, respectively for specifically PFOA.70 This half-live is specific to PFOA and other PFCs will have half-lives that are shorter or even longer. So, the half-life of PFOA can be a representative for roughly how long PFCs can exist in the environment. The reason for these enormously long half-lives for PFCs is because of the extreme stability of the chemical. When in water PFCs can undergo photochemical reactions that break them down, however this only can occur up to a certain depth in the waters. If the PFCs fall below this depth where the photochemical reactions can occur, then the half-lives of PFCs will become even longer.71 This idea is also applicable to PFCs in soil as well, where under the surface the sun cannot penetrate, thus creating an increased half-life.
Undoubtedly, these chemicals far exceed the criteria for what makes a chemical persistent. They are chemicals that have been released into the environment that it will take decades to lifetimes for them to be truly removed from the environment. To me and I’m sure many others, this is unacceptable. Chemicals that have an environmental persistent, let alone a persistence of this long, will be detrimental to the environment and to people, as we are consuming these chemicals, whether it be in food, water or other means. There may be a few key elements that create a chemical that is persistent, such as high stability, high heat resistance, and strong carbon halogen bonds. But not one of these elements are unacceptable, they are useful and important properties to chemistry that allow for scientific development. The true problem is when these very useful properties come together to create a chemical that is highly
69 Gouin, T., & Harner, T. (2003). Modelling the environmental fate of the polybrominated diphenyl
ethers. Environment International, 29(6), 717-724.
70 Vaalgamaa, S., Vähätalo, A. V., Perkola, N., & Huhtala, S. (2011). Photochemical reactivity of perfluorooctanoic
acid (PFOA) in conditions representing surface water. Science of the total environment, 409(16), 3043-3048.
environmentally persistent. The structure, bonds, stability, properties, or anything else of a chemical, only become a worry when these things lead to a chemical that is of high environmental persistence.
3.1.1 Is Persistence Dangerous?
Now that it has been established that persistence is the basis of the issue of these chemicals, the question begs to be asked; is persistence dangerous to the environment? If you play devil’s advocate, then the answer would be quite easy. If the chemical at hand has no known negative health effects and is only a chemical that is persistent in the environment, then no, persistence is not dangerous. However, in the real world, many chemicals have health effects that are unknown to us. And many of the chemicals that end up entering the environment were never intended to be used in such a way that they get digested by animals or humans, so it is often that the health effects of chemicals such as these are unknown, until after they are found in the environment. For example, the new GenX chemical. GenX is a new type of PFC chemical that has not been in use for that long. However, there is already a large amount of concern about GenX in the environment and it is already being found in the environment near manufacturing plants in the Netherlands.72 And like other PFCs, GenX likes to reside in water, meaning that many people are subject to ingesting this chemical as it can be contaminating drinking water, which as seen by this study in the Netherlands, it already is.73 This is concerning enough, as having any kind of unwanted chemical in potential drinking water is never a good thing, however its arguably even worse when little is known about the potential health effects of the contaminating chemical. That is the case with GenX today. The EPA states that the only toxicity information available shows that the liver is sensitive to GenX chemicals and that in animals there are many different potential negative health effects.74 What this means is that there is a new chemical that is being released into the environment and contaminating the drinking water of populations, while nothing is known about the potential damage this chemical could cause to humans,
72 cf Brandsma et al. (n 64).
73 64
animals, or ecosystems. This is very problematic, and it is a trend that repeats itself, as even as far back as PCBs, the health effects of the chemical were not known until the discovery of vast number of PCBs in the environment. It was at this point that PCBs were then tested to determine the health effects. This, in and of itself, should be enough of a reason to say that persistence is dangerous. Precaution in this situation should always be taken, as no one can know what chemicals are capable of, until they have been thoroughly studied.
So, the question must then be asked, if a chemical is only environmentally persistent and does not have any negative health effects, should that chemical be regulated? Or another way to say it, is persistence alone a chemical problem that should be regulated? My answer to this is yes. Like with PCB, there may be chemicals that we are using now that we don’t know are persistent because we haven’t been able to detect or identify them in nature yet. And we do not know what potential health effects that chemicals like these can cause. Just like PFCs today, they are being found in various areas around the world and the health effects of them are not completely known. This trend continued with the development and use of GenX. Persistence leads to putting ourselves and the rest of the environment into a dangerous position that we have no reason to be in. This is something that is completely preventable and there is no reason for these types of problems to continue to occur. When chemicals are produced, they need to be heavily tested on their environmental persistence and if they do not meet certain standards, then there need to be heavy regulations on what a heavily environmentally persistent chemical can be used for. Additionally, there should be regulation on how the waste containing these chemicals should be treated to prevent emissions. An example of this would be PCBs, after PCBs were found to be persistent and regulations were imposed upon them, PCBs that existed in a totally enclosed manner, such as inside of a transformer or other type of enclosed equipment, were still allowed to be used. This regulation did not change how persistent PCBs are in the environment, but what it did do is create a much safer and predictable way to go about using PCBs. Due to the fact that the PCBs were totally enclosed in a piece of machinery, there was little to no way that they could find their way from that piece machinery into the environment. There is still risk of PCBs entering the environment when in these types of uses, such as from production
and potential accidents that open these totally enclose machines. But with this system, after a product containing a highly environmentally persistent chemical is fulfilled its lifetime use, then it can be properly disposed of in a manner that does not allow for the chemical to enter the environment. The use of stringent environmental persistence testing, with standards that must be met for a chemical to be put into production, and strict use regulations, if those standards are not met would be a good start for preventing these types of events from continuing to occur. This method should also be paired with very early environmental testing of a chemicals to determine if they are a threat to the environment or not. The author of The PCB Story, Jensen says, “It is necessary that responsible authorities invest in man-power and equipment to facilitate an unbiassed search for pollutants at an early stage by systematic analysis.”75 And I believe he is correct. Without the effort and the active safeguards to look for pollutants such as these, they will continue to appear.
3.2 Future Chemicals
What does everything that has been discussed entail for the chemicals of the future? To begin with, it is quite easy to say, that if nothing changes in the way that chemicals are produced and regulated, then persistent chemicals will continue to find their way into the environment. There is clear pattern of history repeating itself with these persistent organic pollutants entering the environment. If we look at the list of persistent organic pollutants, originally it began with only 12 or the ‘dirty dozen’.76 If there was a shift in the way that chemicals were made and a more conscious effort was put into making sure that chemicals were made in a way that they were not as persistent in the environment, then the POP list should not be getting larger every year. However, meeting after meeting of the Stockholm convention, was and still is, a time of just adding more and more chemicals to this list. If the industry was making changes to how they produce chemicals or if the regulatory bodies were taking proper action against persistent chemicals, forcing the industry to make a change, then this list should not continue to grow. However, this is not the case, with meetings every two years, there has yet to be a meeting that
75 cf Jensen (n 6).
did not include new chemicals being added to the POP list.77 It was mentioned earlier in this paper that I believe one of the biggest causes behind the persistence of these chemicals is due to their very strong carbon halogen bonds. And when we look at the new chemicals that have been added to the POP list in the past years, we see that a very large number of these chemicals have carbon halogen bonds.78 And just like the chemicals being studied in this paper, the carbon halogen bonds in the chemicals that have been added to the POP list include chlorine, bromine and fluorine. It cannot be coincidence that the chemicals being studied in this paper and a large majority of the chemicals that have ended up on the persistent organic pollutant list both have carbon halogen bonds.
It is clear there has been a lack of change in the way that chemicals are being produced and how they are being regulated. This must change if the future of chemicals is to be any different than it has up until now. So how can this be accomplished? There are a several ways that a change can be made for the better. And the easiest way to make a change is to start with regulations and legislation around these chemicals to make them more difficult to produce and use if they are harmful to the environment. The idea is to regulate harmful environmental chemicals before they enter the environment, not after.
One positive change that could be made is to look at how chemicals are classified themselves. If we look at what the Toxic Substances Control Act (TSCA) considers a ‘new chemical substance’, then we see that a new chemical substance is just any chemical that is not currently listed on the inventory list that is kept by the TSCA.79 This means that a chemical that is only one or two atoms different would be considered a completely new chemical under the TSCA and thus would have to go through all environmental testing procedures, even if the base chemical that was only slightly changed was known to be incredibly bad for the environment. A similar scheme exists within the EU, with substances being manufactured or imported at 1 tonne or more per
77 Stockholm Convention. (2019). Information on the 16 chemicals added to the Stockholm Convention. Retrieved
November 23, 2019, from http://chm.pops.int/TheConvention/ThePOPs/TheNewPOPs/tabid/2511/Default.aspx.
78 Ibid.
79 US Environmental Protection Agency. (2017, May 18). Basic Information for the Review of New Chemicals.
Retrieved from https://www.epa.gov/reviewing-new-chemicals-under-toxic-substances-control-act-tsca/basic-information-review-new.
year needing to be reported to REACH with the properties of these substances.80 These areas of defining what a new chemical is, may be the starting point that changes could be made for the better. Rather than this system, classes of chemicals should have separate registration systems and environmental testing standards that need to be met. For example, substances that have carbon halogens bonds would need to be registered separately than other chemicals that don’t have these bonds. This would help to set standards and test that need to be met by each separate ‘registration class’, as many times a chemicals structure and bonds play heavily into the properties of the substance. It does not make sense for a highly fluorinated compound that is most likely environmentally persistent to undergo the same environmental testing as a new pesticide or food additive compounds. They are two different worlds and they must be treated as such.
This sense of change needs to come from both sides. The producers of chemicals need to be more conscience of the chemicals that they are making and recognize the signs of a potentially environmentally harmful chemical. This is the change that is more unlikely in this scenario, as the chemical companies are in this business to turn a profit. And if they are cutting out many chemicals due to them being persistent for the environment, then they will have high expenses to find a new chemical that is better for the environment. I believe that this is something that the chemical production industry is just not capable of. They have too much to lose. This change likely will have to come from the regulatory body side of this debate, as while they might have some financial interest in the volume of chemicals a company in their country can sell, it is not nearly as large of an interest as the company itself has. Nevertheless, if one of these two parties do not decide to change anything about their practice and how persistent chemicals are regulated, then there more than likely will be no change at all. Leading to history repeating itself and persistent chemicals being reintroduced into the environment simply under a new name.
80 European Chemicals Agency. (n.d.). Registration Process. Retrieved from
4 Conclusion
Using the facts, evidence and history as a guide, an analysis was done of several different persistent organic pollutants, starting with PCBs, then PBDEs and finally PFCs. These chemicals follow a rough timeline of being produced and then found to be environmentally persistent and then being replaced with another chemical, and this process is repeated. While these chemicals are not use for use replacements for each other, they share many similarities that made them an interesting subject for researching how these environmentally persistent chemicals are used and replaced.
After analyzing a brief history of the chemicals, a systematic trend of use, regulations and then replacement can be established with these chemicals, leading all the way up the newer GenX chemicals; where it looks like this trend is set to continue with regulations to be imposed on GenX chemicals. With this trend it become quite clear that something is wrong. If these chemicals did not have something that was wrong with them, this systematic placement of regulation would not continually plague these types of chemicals. So, it begs the question, what is the problem? To answer this an in-depth look at the composition, properties, and structure of these chemicals was performed, leading to some interesting facts that may give insight into what is making these chemicals persistent. The answer and problem, in short, is the stability of these chemicals. This stability was imparted onto these chemicals mainly through very strong carbon halogen bonds, which require a lot of energy to break. Other, lesser factors that increased the stability of these chemicals was also ring structure of PCBs and PBDEs and the hydrophilic end groups of various PFCs. However, the main element of these chemicals that I believe creates the most environmental persistence is the carbon halogen bonds. Further, in my opinion carbon halogen bonds can be used as a red flag for future chemicals to possibly pre-determine if they will persistent in the environment. While other elements play a factor in environmental persistence, this should be recognized as one of the most important factors to be considered.
While carbon halogen bonds point towards possible environmental persistence, the true trait that we should be afraid of is the persistence itself. If a chemical is able to have carbon halogen bonds and not be persistent, then these bonds are not a problem. But as long as a
