Chlorinated paraffins: synopsis

Synopsis

Chlorinated paraffins (CPs) are chlorinated derivatives of n-alkanes with carbon chain lengths from 10 to 38 carbon atoms, and with varying chlorine contents. CPs include short-chain chlorinated paraffins (SCCPs) (CPs with 10 - 13 carbon atoms), medium-chain chlorinated paraffins (MCCPs) (CPs with 14 - 17 carbon atoms) and long-chain chlorinated paraffins (LCCPs) (CPs with ≥ 18 carbon atoms).

CPs were included on the first Priority Substances List (PSL1) under the 1988 Canadian Environmental Protection Act (CEPA 1988) for assessment of potential risks to the environment and human health. With the data available at that time, it was concluded that SCCPs were “toxic” because they constitute or may constitute a danger in Canada to human life or health as defined under paragraph 11(c) of CEPA 1988. However, as outlined in the PSL1 assessment report released in 1993, relevant data identified before August 1992 were considered insufficient to conclude whether SCCPs, MCCPs or LCCPs could have immediate or long-term harmful effects on the environment as defined under paragraph 11(a) of CEPA 1988 and whether MCCPs or LCCPS could be considered “toxic” to human health as defined under paragraph 11(c) of CEPA 1988.

Research to address data gaps relevant to the assessment of impacts of CPs on the environment was funded; an industry survey on the Canadian manufacture, import and uses of CPs was conducted for the years 2000 and 2001 through a Canada Gazette Notice issued pursuant to section 71 of the Canadian Environmental Protection Act (1999) (CEPA 1999); and literature was also reviewed for new exposure and toxicological data on CPs on human and non-human organisms in Canada and elsewhere.

Total reported annual usage of CPs in Canada (production + imports - exports) was approximately 3,000 tonnes in 2000 and 2001. MCCPs accounted for a large majority of CP usage in Canada, followed by smaller proportions of SCCPs and LCCPs. The major uses of CPs in Canada are in plastics, in lubricating additives and in metalworking. There was only one manufacturer of CPs in Canada, and only MCCPs and LCCPs were produced at this facility. In 2000, their production capacity was reported to be 8.5 kilotonnes; however, there is no production in Canada at present.

There are no known natural sources of CPs. The major sources of release of CPs (SCCPs, MCCPs and LCCPs) into the Canadian environment are likely the formulation and manufacturing of products containing CPs and use in metalworking fluids. The possible sources of releases to water from manufacturing include spills, facility wash-down and drum rinsing/disposal. CPs in metalworking/metal cutting fluids may also be released to aquatic environments from drum disposal, carry-off and spent bath. These releases are collected in sewer systems and often ultimately end up in the effluents of sewage treatment plants. When released to the environment, CPs tend to partition primarily to sediment or soil.

Environmental assessment

SCCPs have been detected in the following Canadian environmental media: Arctic air, sediments from remote northern lakes, sewage treatment plant effluents from southern Ontario, surface water, sediments, plankton, invertebrates and fish from Lake Ontario and marine mammals from the Canadian Arctic and the St. Lawrence River. SCCPs have also been detected in plankton, invertebrates and fish from Lake Michigan. MCCPs have been detected in effluent from a CPs manufacturing facility near Cornwall, Ontario, and also in sediments near this facility (which has since ceased operation), in fish from Lake Ontario and in beluga from the St. Lawrence River. Maximum Canadian concentrations of SCCPs and MCCPs were observed in aquatic biota and sediments from the St. Lawrence River and also in sediments and fish from southwestern Ontario. No data on environmental concentrations in Canada exist for LCCPs. They have been detected in marine sediments, crabs and mussels near a CPs manufacturing facility in Australia.

Atmospheric half-lives for many CPs are estimated to be greater than 2 days. In addition, SCCPs have been detected in Arctic biota and lake sediments in the absence of significant sources of SCCPs in this region, which suggests that long-range atmospheric transport of SCCPs is occurring. SCCP and MCCP residues have been detected in Canadian lake sediments dating back over 25 years at concentrations suggesting that the half-lives of SCCPs and MCCPs in sediment are greater than 1 year. There are no data available for LCCPs in Canadian lake sediments; however, based on their physical/chemical properties, which are similar to those of MCCPs, LCCPs are expected to be persistent in sediments. Several biodegradation studies have also found that biodegradation is hindered by increasing carbon chain length. It is, therefore, concluded that SCCPs, MCCPs and LCCPs are persistent as defined in the Persistence and Bioaccumulation Regulations of CEPA 1999.

Bioaccumulation factors (BAFs) of 9900 - 51200 wet weight in sculpin, smelt and trout from Lake Ontario indicate that SCCPs are bioaccumulating to a high degree in aquatic biota in Canada, this is supported by very high laboratory-derived bioconcentration factors (BCFs). Despite the lack of valid studies of BCFs, MCCPs have been found to have significant potential to bioaccumulate in aquatic food webs: field BAFs for MCCPs in some Lake Ontario fish were calculated to be approximately 5450 wet weight. In addition BAF values calculated using the Modified Gobas BAF Model are >5000 for all SCCP and MCCP congeners.

While biomagnification factors (BMFs) are not considered in the bioaccumulation regulations, they are supporting evidence for bioaccumulation when substantially above 1. Both SCCPs and MCCPs were found to have biomagnification factors (BMFs) greater than one in various food webs. MCCPs also had BMFs greater than one. The liquid LCCP C₁₈H₃₀Cl₇ had BMF values greater than one in rainbow trout in laboratory studies, and its half-life in rainbow trout was found to be similar to those of recalcitrant compounds that are known to accumulate in organisms and magnify in food chains. In addition, SCCPs, MCCPs and LCCPs have octanol-water partition coefficient (log KOW) values greater than five. Elevated concentrations of MCCPs have been measured in aquatic biota from the St. Lawrence estuary, the United States and Australia. While all of the available published BCF studies for LCCP have found values <5000, some elevated concentrations of LCCPs have been found in marine benthic organisms in Australia. In addition the Gobas BAF Model predicts that 44% of liquid C_18-20 LCCP congeners have BAF ≥ 5000. On the other hand, none of the C_>20 LCCP congeners had modeled BAFs ≥ 5000. Therefore, based on the weight of evidence, it is concluded that SCCPs, MCCPs, and liquid C_18-20 LCCPs are bioaccumulative as defined in the Persistence and Bioaccumulation Regulations of CEPA 1999. However based on the limited information available (particularly BAF estimates), C_>20 liquid and solid LCCPs are not bioaccumulative as defined under the Persistence and Bioaccumulation Regulations.

The available toxicity data indicate that SCCPs , MCCPs and C_18-20 LCCPs may be harmful to certain aquatic species (e.g., Daphnia magna) at low concentrations (for example, chronic no-observed-effect concentrations (NOECs) < 100 µg/L).

SCCPs, MCCPs and C_18-20 LCCPs are considered to be both highly persistent and bioaccumulative. In addition, there is evidence that SCCPs, MCCPs and C_18-20 LCCPs are released into the Canadian environment and have the potential to cause harm to sensitive aquatic organisms at relatively low concentrations. Substances that are persistent remain in the environment for a long time, increasing the magnitude and duration of exposure. Releases of small amounts of bioaccumulative substances may lead to high internal concentrations in exposed organisms. Highly bioaccumulative and persistent substances are of special concern, since they may biomagnify in food webs, resulting in very high internal exposures, especially for top predators.

Human health assessment

For SCCPs, critical data relevant to both estimation of exposure of the general population in Canada and assessment of the weight of evidence for the mode of induction of specific tumours were identified following release of the PSL1 assessment and prior to February 2001, although most of this information has been reported in incomplete published summary accounts or abstracts. These data suggest that several tumours observed in carcinogenicity bioassays in rats and mice exposed to SCCPs are induced by modes of action either not relevant to humans (kidney tumours in male rats) or for which humans are likely less sensitive (in rats, liver tumours related to peroxisome proliferation and thyroid tumours related to thyroid-pituitary disruption). Complete documentation of available studies and consideration in additional investigations of the reversibility of precursor lesions in the absence of continued exposure is lacking. However, reported data on mode of induction of tumours in addition to the weight of evidence that SCCPs are not DNA reactive are at least sufficient as a basis for consideration of a tolerable daily intake (TDI) for non-cancer effects as protective for carcinogenicity for observed tumours. Upper-bounding estimates of daily intake of SCCPs approach or exceed the TDI for these compounds, which, on the basis of available information, is likely also protective for potential carcinogenicity.

For MCCPs and LCCPs, critical data relevant to both estimation of exposure of the general population in Canada and assessment of effects were identified following release of the PSL1 assessment and prior to December 2000. Based upon these semi-quantitative data, upper-bounding estimates of daily intake for MCCPs and LCCPs are within the same order of magnitude of, or exceed, the TDIs for these substances.

Conclusion

Based on the information available, it is concluded that CPs containing up to twenty carbon atoms are entering, or may enter, the environment in quantities or concentrations or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity and that all chlorinated paraffins constitute or may constitute a danger in Canada to human life or health. CPs containing up to twenty carbon atoms are persistent and bioaccumulative as defined in the Persistence and Bioaccumulation Regulations.