Policy paper

Annex D: summary of UK proposal to list Chlorinated paraffins with carbon chain lengths in the range C14-17 and chlorination levels at or exceeding 45% chlorine by weight

Updated 7 June 2021

1. Introduction

1. This Proposal document is a summary of a more detailed assessment (Support document), which should be referred to for more comprehensive information regarding the underlying data.

2. Chlorinated paraffins (CPs) are manufactured substances consisting of predominantly linear chloroalkanes, with different degrees of chlorination and chain length distributions depending on the application and feedstock. This proposal is for any CP product that has constituents with 14 to 17 carbon atoms (C14-17) and a chlorination level at or exceeding 45% chlorine by weight (Cl wt.). These congeners are the principal constituents of substances called “medium-chain chlorinated paraffins” (MCCPs) in Europe, North America and Australia, and major constituents of several products manufactured in Asia (e.g. CP-52). Due to the possible confusion regarding different product names, the proposal for listing is based on specific chain lengths and degrees of chlorination. Nevertheless, most of the available hazard and monitoring information is available from assessments on the substance called MCCPs, and so the term “MCCPs” is used in these instances.

2. Chemical identity

2.1. CAS number, chain length and chlorination

3. Key information for CPs with C14-17 chain lengths is provided in Table 1, based on Environment Agency (2019). A non-exhaustive list of relevant CAS numbers is provided in Appendix 3 of the Support document, together with further information (such as additives). Around forty CAS numbers have been used to describe the CP family at various times. Some of these clearly cover CPs in the C14-17 range, and it is possible that some of the remainder may be used for products containing CPs in this range too.

Table 1: Substance identity

IUPAC name	Alkanes, C14-17, chloro
CAS number	85535-85-9
EC number	287-477-0
Molecular formula	CxH(2x - y+2)Cly, where x = 14 to 17 and y = ≥5 to 17
Molecular weight range	370 - 826 g/mole (approximately)
Synonyms	Medium-chain chlorinated paraffins (MCCPs); Chlorinated paraffins, C14-17 (used in Annex VI of the CLP Regulation)

4. The predominant chain length of “MCCPs” is in the range C14-17, with a significant proportion being the C14 carbon chain length. CPs produced in Asian countries such as India and China are differentiated based on their chlorine content (or viscosity) rather than by the carbon chain lengths of their constituent congeners. These may have a broader range of carbon chain lengths (e.g., C9-30 chain lengths), but may still potentially contain significant levels of C14-17. The chlorine content of commercial products (e.g. “MCCPs” and CP-52) varies according to the applications they are used for, but is generally within the range 40% to 63% by weight; the majority of products have a chlorine content between 45% and 52% by weight. The chlorination process is random, and so all of these products contain many thousands of constituents. The main constituents in the majority of product types have between five and seven chlorine atoms per molecule. Nevertheless, it should be noted that percentage chlorine content only represents an average level of chlorination, and so a wider range of constituents may be present in any particular product. Commercial products may also contain some constituents outside of the C14-17 range. Chain lengths below C14 are structurally analogous to the range described as short-chain chlorinated paraffins (SCCPs).

2.2. Structural formula

5. An image of two example structures (hydrogen atoms removed for simplicity) of CPs with C14 and C17 chain lengths can be found on page 4 of the support document.

2.3. Analogues

6. SCCPs (containing C10-13 carbon chain lengths) and long-chain chlorinated paraffins (LCCPs, containing C18 30 carbon chain lengths) are structural analogues registered under EU REACH. SCCPs was listed as a Persistent Organic Pollutant (POP) in 2017. An earlier report assessing LCCPs (Environment Agency, 2009) is currently being updated by the UK following the substance evaluation of “MCCPs” in the EU (Environment Agency, 2021 in prep.). Further details of the analogues are provided in the Support document.

3. Persistence

7. The key data are the absence of transformation of a C14 chlorinated n-alkane, 50% Cl wt. substance after 120 days at 12 °C in a reliable OECD TG 308 study performed to GLP (Unpublished, 2019c and 2019d). The absence of degradation at 120 days in the study suggests that it is very unlikely that significant degradation would subsequently occur between 120 and 180 days. This hypothesis is supported by sediment core monitoring data (Iozza et al. (2008), Chen et al. (2011), Muir et al. (2002), Yuan et al. (2017), Zeng et al. (2017a), Zhang et al. (2019)) where levels of “MCCPs” are at similar orders of magnitude in horizons representing deposition from 8 or more years ago older and surface sections of the same core.

8. Environment Agency (2019) summarises a number of modified and enhanced ready biodegradation tests performed using various substances that are representative of “MCCPs”. Several, for example a 55% and a 60% Cl wt., were shown to be less degradable than C14 chlorinated n-alkane, 50% Cl wt. C14 chlorinated n-alkane. C15-17 constituents with similar or higher chlorine contents to C14 chlorinated n-alkane, 50% Cl wt. will also be equally or more adsorptive to sediment (and therefore have a lower bioavailability to micro-organisms). They are therefore highly likely to be equally or more persistent in sediment than the C14 (50% Cl wt.) congener block (i.e. their sediment half-lives will exceed 180 days), even though no definitive test information is available for them.

9. C14 chlorinated n-alkanes with a low chlorine content (≤45% Cl wt.) are readily biodegradable, although it is noted that a C14-17 chlorinated n-alkane, 45.5% Cl wt. was not readily biodegradable despite extensive mineralisation. It is possible that adsorption could cause these substances to have longer sediment half-lives than expected, but no robust data are available to allow a conclusion to be drawn. Given that the test results for these specific C14 constituents would meet the OECD definition of “readily biodegradable”, chain lengths below 45% Cl wt. are excluded from this proposal. Whilst it is possible that more highly chlorinated (persistent) constituents might be present in the <45% Cl wt. fraction used in the screening studies, the high level of mineralisation attained in these specific screening studies suggests that the concentration of any potentially persistent constituents present is likely to be extremely low, and therefore not considered relevant.

10. Overall, the Annex D criteria for persistence 1b(i) are considered to be met as the half-life for sediment is assessed to exceed 180 days for C14 constituents, and by analogy C15-17 constituents, with chlorination levels ≥45% Cl wt. C14-17 constituents with lower chlorination levels are not considered to be persistent based on the currently available information.

4. Bioaccumulation

11. The constituents of CPs with C14-17 chain lengths have a range of log KOW values, but all measured values exceed 5 (Unpublished (2019b), Fisk et al. (1998a), Renberg et al. (1980)).

12. Two reliable fish bioaccumulation studies conducted according to OECD TG 305 and to GLP show that a C14 chlorinated n-alkane, 45% Cl wt. product has a measured bioconcentration factor (BCF) value significantly in excess of 5 000 L/kg in Rainbow Trout (Oncorhynchus mykiss) (Unpublished, 2010a and b), and that a C14 chlorinated n-alkane, 50% Cl wt. substance has a calculated BCF from dietary exposure significantly in excess of 5 000 L/kg (Unpublished, 2019e and 2019f).

13. Supporting laboratory evidence indicates that there may be a high bioaccumulation potential in fish for CPs with chain lengths longer than C14. They are an aqueous exposure test performed with a C15 chlorinated n-alkane, 51% Cl wt. substance and a series of dietary bioaccumulation studies using C14, C16 and C18 chain lengths with different levels of chlorination (Fisk et al. (1996, 1998b and 2000), Thompson et al. (2000)). The measured and estimated BCF values range from around 2 000 L/kg to above 5 000 L/kg. Additionally, all substances had long depuration half-lives (consistent with a BCF exceeding 5 000 L/kg). Invertebrate data also suggest that other taxonomic groups might bioaccumulate C14-17 CPs significantly (Castro et al. (2019), Renberg et al. (1986), Madeley & Thompson (1983), Fisk et al. (1998a)). However, these studies are all of lower and mixed reliability and are therefore considered to carry a lower weight in this assessment.

14. Despite the general uncertainty in the available aquatic and terrestrial monitoring data due to the analytical challenges discussed in the Support document, CPs with C14 17 chain lengths are present (often based on the detection of “MCCPs”) in a wide range of organisms living and feeding in locations that are close to input sources (i.e. industrial and urban areas). The data are summarised in Appendix 5 of the Support document. Whilst more limited in number, “MCCPs” have also been detected in samples from remote regions, including the Arctic, as well as in top predators (Iozza et al. (2009a and 2009b), Glüge et al. (2018), Vorkamp et al. (2019), Reth et al. (2006), NILU (2013)). Only limited information is available on the actual carbon chain length distribution and chlorine contents of “MCCPs” detected in most environmental samples, although advances in analytical methodologies have meant that this has been possible in some of the more recent studies. C14 chain lengths are frequently the predominant constituents of “MCCPs” when more detailed information is available. This chain length is a significant constituent of commercial product types (see paragraph 4).

15. Monitoring studies demonstrate widespread contamination of wildlife by CPs with C14-17 chain lengths at all trophic levels (including predatory species). The available (limited) field bioaccumulation studies are equivocal: trophic magnification factors (TMFs) below and above 1 have been derived for “MCCPs”, and although most biomagnification factors (BMFs) are below 1, BMF values above 1 have been derived for some specific feeding relationships. The data collected in more recent studies, while still limited, do not contradict the possibility of bioaccumulation up the food chain. It should be noted that all of the available field magnification studies have methodological limitations. The data are taken from the following references: Swedish Environmental Protection Agency (1998), Jansson et al. (1993), Muir et al. (2002) Houde et al. (2008). Du et al. (2018), Du et al. (2019, 2020), Liu et al. (2020), Wang et al. (2021), Zeng et al. (2017b), Yuan and de Wit (2018), Yuan et al. (2019), Casa et al. (2019), Bennie et al. (2000), Reth et al. (2006), Heimstad et al. (2018), Ruus et al. (2018), Green et al. (2018)).

16. “MCCPs” are detected in human breast milk, and other tissue such as blood, with the substance estimated to have a long half-life in humans (Greenpeace (1995), Thomas and Jones (2002), Thomas et al. (2006), Hilger et al. (2011), Darnerud et al. (2012), Xia et al. (2017a), Xia et al. (2017b), Zhou et al. (2020), EFSA (2020), Li et al. (2017), Wang et al. (2018), Dong et al. (2020)).

17. Overall, the Annex D criteria for bioaccumulation 1c(i) are considered to be met as BCF values exceed 5 000 L/kg for at least the C14 constituents with a chlorination level in the range 45-50%. Less reliable data suggest that the C15-17 constituents may also meet the criteria. This is supported by monitoring data for “MCCPs” indicating widespread uptake by biota.

5. Potential for long-range environmental transport

18. The predicted atmospheric half-life for two relevant C14 and C17 constituents (C14H24Cl6 (52.6% Cl wt.) and C17H29Cl7 (51.6% Cl wt.), both with and without terminal chlorine atoms) are between 37 and 62 hours using AOPWIN v1.92 (US EPA, 2020). It is difficult to validate these estimated values due to the lack of experimental data, and so they are considered uncertain. The two modelled C14 constituents are at or above the 48 hour threshold in Annex D. The two modelled C17 constituents are below 48 hours. The C17 constituents are less relevant for (gaseous) atmospheric photodegradation as a greater fraction will be adsorbed to aerosols. More highly chlorinated constituents will be more photolytically stable and more adsorptive.

19. Using the OECD POV and LRTP Screening Tool (OECD, 2006), the long-range transport potential (LRTP) for these constituents. based on Characteristic Travel Distance (CTD) and Transfer Efficiency (TE), are comparable to, but slightly below those for SCCPs, which is a POP (UNEP, 2015). It also falls within the range of other listed POPs. CPs with C14-17 chain lengths have low volatility and are expected to adsorb strongly to particulates. Given the relatively high gaseous fraction predicted for the C14 constituents in the OECD Screening Tool, it is not clear how well the adsorption of the constituents is actually modelled. Several lines of evidence from other models and experimental data suggest that the fraction adsorbed to aerosols could be higher (see, AEROWIN v1.0 (US EPA, 2020), Jiang et al. (2021), Al Saify et al. (2021)). The atmospheric transport of airborne particulates provides a potential route for long range transport, and this is supported by the detection of “MCCPs” at low levels in air samples taken in remote locations. These include 5 years’ monitoring in the Arctic and Antarctica, and recent sampling at the Tibetan Plateau (Bohlin-Nizzetto et al. (2014, 2015, 2017, 2018, 2019, 2020), Bohlin-Nizzetto & Aas (2016), Jiang et al. (2021), Ma et al. (2014), Wu et al. (2019)). “MCCPs” monitoring at Svalbard suggests levels in air are increasing at this remote location. The ratio of “MCCPs” to SCCPs is also observed to be increasing in Antarctic air. The levels of “MCCPs” observed in both these remote locations was noted to be higher than some listed POPs such as polybromodiphenyl ethers (PBDEs).

20. The modelled comparability to SCCPs is further supported by the detection of “MCCPs” in environmental samples from remote regions, including in top predators (Iozza et al. (2009a and 2009b), Glüge et al. (2018), Vorkamp et al. (2019), Reth et al. (2006), NILU (2013)). In some instances, the levels of “MCCPs” appear to be similar to SCCPs. There is also environmental monitoring data showing the detection of “MCCPs” in different matrices at locations in the following countries: Australia, Belgium, Canada, China, Czech Republic, Denmark, France, Germany, India, Ireland, Japan, Norway, Pakistan, Sweden, Switzerland, UK and USA, as well as various marine locations such as the Baltic Sea, Irish Sea, North Sea in Europe and Chinese Bohai Sea (refer to Appendix 5 of the Support document).

21. Overall, the Annex D criteria for Long Range Transport 1d(i), (ii) and (iii) are considered to be met. Limited biota monitoring data indicate detection of “MCCPs” in remote areas, with similar concentrations to SCCPs suggested in some studies. Air sampling data are also limited to specific locations, but the available information confirms the potential for transport via this medium. The predicted atmospheric half-life of the modelled constituents is around 2 days with values above and below the threshold. It remains unclear how accurate these predictions are, and to what degree the gaseous transport of CPs with C14-17 chain lengths is relevant compared to adsorption to particles. Other monitoring data indicate that “MCCPs” are widely detected in the environment.

22. In conclusion, the limited data indicate that there is both a pathway and delivery of CPs with C14-17 chain lengths to remote locations. The concern is that the characteristics of these constituents, while slightly less efficiently transported over long distances than SCCPs, appear to be similar to that POP.

6. Adverse effects

23. A C14-17 chlorinated n-alkane, 52% Cl wt. has a 48-h EC50 of 0.0059 mg/L for Daphnia magna (Thompson et al., 1996). The 21-day NOEC for the same species and substance is 0.0087 mg/L (Thompson et al., 1997a). These two results, from reliable laboratory studies performed to recognised OECD test guidelines and to GLP, indicate that constituents of CPs with C14-17 chain lengths are very toxic to aquatic invertebrates in the environment.

24. The concern for adverse effects is supported by the internal haemorrhaging and death observed in rodent offspring in the mammalian reproduction study resulting in a harmonised EU classification for “MCCPs” as H362 (May cause harm to breast-fed children) (IRDC (1985), CXR Biosciences Ltd (2003 & 2004)). Potential adverse effects could therefore occur in mammalian wildlife.

25. Overall, the Annex D criteria 1e(i) for adverse effects are considered to be met.

7. Conclusion and need for action

26. For CPs with C14-17 chain lengths, there are reliable laboratory data clearly indicating that constituents with a C14 chain length and chlorination levels around 45-50% Cl wt. meet all of the Annex D screening criteria for persistence, bioaccumulation and adverse effects. Data for C15, C16 and C17 constituents suggest that these also meet the persistence and toxicity screening criteria. These longer chains may meet the bioaccumulation criteria, but fully reliable data to confirm this are not available. Long range transport potential is considered to be shown for all chain lengths.

27. The persistence information indicates that the concern is for all constituents with chlorination levels at or exceeding 45% chlorine by weight.

28. The C14 constituents are a major congener group in commercial CP products currently being supplied. This indicates that CPs with C14-17 chain lengths will contain a significant fraction of constituents that meet the Annex D screening criteria. Of the remaining fraction, a significant proportion meets three out of the four criteria, with weaker evidence for the bioaccumulation endpoint. Given the potential bioaccumulation concern from the available data for these longer chains together with the evidence for the other criteria, it is proposed to include all four carbon chain lengths in the listing.

29. It is noted that laboratory bioaccumulation data of limited reliability are available for a C18 constituent. The focus of this proposal is the C14-17 chain lengths, and this reflects the data available for the other endpoints and generally the monitoring data. Therefore chain lengths longer than C17 are not included within the proposal. As noted in paragraph 7 an update of a national assessment of “LCCPs” is currently in progress by the UK, which will assess C18 chain lengths (and above).

30. As a result of its persistent, bioaccumulative and toxic (PBT) properties, “MCCPs” is of regulatory concern in the UK, EU, Switzerland, Australia and Canada (Environment Agency (2019), ECHA (2021a), NICNAS (2020), Environment Canada (2008)). As shown in the Support document, the different applications and ongoing use of CPs with C14-17 chain lengths globally is estimated to result in around 2 800 to 28 000 tonnes being potentially emitted to the environment each year. Due to the hazard concerns for the substance, and the estimated level of environmental emissions, global action is required to manage the risks from CPs with C14 17 chain lengths.

31. In conclusion, it is proposed to list carbon chain lengths in the range C14-17 and chlorination levels ≥45% chlorine by weight in the Convention.  

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