Chlorinated paraffins (CPs), identified collectively under the CAS number 63449-39-8, are chlorinated linear hydrocarbons with between 10 and 30 carbon atoms. They contain varying numbers of chlorine atoms, with a maximum of one chlorine per carbon. There are an array of commercially available CPs with each CP corresponding to a mixture of isomers and congeners whose carbon skeletons belong to one of three main groups (in terms of chain length) C10-13, C14-17, C18-26. Commercial CPs are usually identified by a trade name followed by a number reflecting the chlorine percentage. Commercial products have a chlorine content of 40 - 70% (Hardie 1964, cited in Howard et al 1975).

CPs are physically homogeneous, viscous yellowish liquids or low melting solids. They are described as having a colour ranging from light amber to yellow (the actual shade will depend on the storage conditions and the manufacturing process with the colour darkening with prolonged heating due to the evolution of hydrogen chloride gas) and a slightly unpleasant odour due to the presence of small quantities of lower molecular weight products. CPs with a chlorine content higher than 40% are non-flammable, while those with a lower chlorine percentage will burn with difficulty (Mukherjee 1990).

CPs have similar properties to polychlorinated biphenyls (PCBs), although not as thermally stable, and have replaced PCB compounds in many applications (Howard et al 1975). Chlorinated paraffins have a variety of uses, depending on the carbon chain length. Short chain chlorinated paraffins (C10-13) are used as lubricants, additives and sealants, medium chain length (C14-17) as secondary PVC plasticisers and long chain length (C20-30) in paints, lubricants and additives (Campbell and McConnell 1980).

At present, the main uses of chlorinated paraffins are as fire retardants and secondary plasticisers. Secondary plasticisers are used as a substitute for primary plasticisers, such as phthalates, usually through cost considerations. However, the addition of chlorinated paraffins to PVC, for example, also provides flame retardancy whilst maintaining the low temperature properties, e.g. strength of the plastic. Chlorinated paraffins are also used as an additive in cutting oils to improve the surface roughness of the cutting surface.

In the UK, the manufacture of CPs is presently carried out by ICI Chemicals and Polymers Group. ICI has stated that the bulk of their Cereclor production in Europe, some 80 KT annually, is in the UK (approximately 50KT). Of this, about 70% is exported (BRE 1992).

The major source of environmental contamination is more likely to be via the use or disposal of products containing CPs. CPs have a very low volatility and are therefore not expected to be present at any significant level in the atmosphere, although minor inputs into the atmosphere from secondary plasticisers (where the CPs are not chemically bound up into plastics and are thus able to volatilise to some extent) and flame retardant applications may occur.

Chlorinated paraffin containing products such as plastics, building materials and oils are likely to be disposed of in dumps or landfills and, to a lesser extent, by incineration. Due to the relatively low thermal stability of CPs, the latter process should result in the destruction of CP material. Removal of CPs in landfills due to leaching is likely to be slow due to their low water solubility and their high log Kows which infers that CPs becoming dispersed in the environment will tend to be adsorbed onto solids and sediments, thus reducing their availability for uptake by biota. Madeley and Birtley (1980) predicted that the main input of CPs to the aquatic environment was likely to remain adsorbed to the sediment.

It can be concluded that there is unlikely to be a significant input of CPs into the aquatic environment from the atmosphere or via leaching from landfills. Instead, entry is more likely to originate from direct emissions into the aquatic environment via industrial and sewage treatment plant effluents in areas where CPs are used.

Investigations into the environmental concentrations of CPs are currently limited to old studies carried out by Campbell and McConnell (1980).

Campbell and McConnell (1980) investigated the concentration of CPs in the environment and reported concentrations for marine and freshwaters and sediment, using a thin-layer chromatographic technique. This technique enabled the authors to differentiate between CPs of C10-20 and C20-30 chain length but not between 45 and 52% chlorination, nor between C10-13 or C14-17 chain length.

In UK marine waters, CP concentrations were found in the range non-detected to 4 µg l^-1 for C10-20 CPs and not detected to 2 µg l^-1 for C20-C30 CPs. CP concentrations in marine sediments from coinciding sites were in the range not detected to 0.5 mg l^-1 for C10-20 CPs and not detected to 0.6 mg l^-1 for C20-30 CPs. CP levels in non-marine waters, freshwaters and sediments in industry free areas ranged from 0-1 µg l^-1 of either CP type. While 65% of samples contained no CPs (almost twice that found for seawaters), when CPs were detected, levels were close to that found in marine waters. Sediment levels in freshwater were also found to be comparable with marine sediments.

Campbell and McConnell (1980) also reported CP concentrations in UK waters and sediments receiving industrial/domestic effluents. CP levels in water were found to be 1-6 µg l^-1 and 1-10 mg l^-1 in sediments (CPs of C10-20 chain length predominated).

Campbell and McConnell (1980) investigated CP concentrations in plaice Pleuronectes platessa pouting Trisopterua luscus mussel Mytilis edulis pike Esox lucius and the liver and blubber of grey seal Halichorus grypus. C20-30 CPs were barely detectable in tissues (a maximum of 0.2 mg/kg) and CPs of C20-30 were seen only at 0.4 mg/kg in organisms from waters not receiving effluent from CP plant effluents. However, mussels from water receiving a CP manufacturing plant effluent had, in general, concentrations of up to 1 mg/kg C10-20 CPs with concentrations of 6 - 12 mg/kg close to the effluent discharge.

When comparing sediment CP levels with aquatic organism tissue levels, Campbell and McConnell (1980) found little or no accumulation. Tissue levels were found to be similar to those in the sediment near where organisms lived. In addition, the authors found no indication of biomagnification in any food chain, aquatic or on land, including the human food chain.

Since CPs are heterogeneous (i.e. a particular sample may contain from ten to one hundred different molecular species), the chemical properties of CPs are the average of the chemical properties of the different molecules. The properties vary with the nature of the paraffinic raw materials, the temperature of chlorination and the chlorine content.

Chlorinated paraffins are virtually insoluble in water and lower alcohols but partially soluble in higher alcohols, such as octanol. They are stable mixtures but can undergo slow hydrolysis or dehydrochlorination in aqueous solution. When subjected to high temperature, the substances release HCl. Commercial CPs are often stabilised against decomposition by the addition of small quantities of substances that can act as acid acceptors. The high log Kow values for chlorinated paraffins (Lyman 1982, cited in Mukherjee 1990), calculated log Kows in the range of 5.06 or a CP of formula C10 H18 Cl4 to 12.68 for a CP of formula C26 H44 Cl10) suggest that they will adsorb onto sediments rather than remain in water.

Under ambient and neutral conditions, CPs hydrolyse very slowly (Howard et al 1975). The short chain CPs (C10-13) appear to be rapidly degraded by acclimatised micro-organisms. Sewage treatment organisms also brought about significant breakdown of these short chain CPs. For longer chain paraffins chlorinated up to 45%, the biodegradation, although slower and reduced, indicated substantial breakdown by acclimatised organisms. Similarly, a wax-grade CP (C20-30, 42% Cl w/w) was also degraded when organisms were previously acclimatised.

It can be concluded that chlorinated paraffins are chemically stable under ambient temperatures and will not undergo hydrolysis, photolysis or oxidation at any significant rate. Micro-organisms have been found to biodegrade chlorinated paraffins and acclimatisation increases the ability of micro-organisms to degrade long chain CPs. However, the longer the carbon chain in the molecule and the greater the percentage of chlorination, the more recalcitrant the compound.

In view of the highly complex composition of CPs, it is difficult to distinguish between desirable (i.e. straight chain derivatives) ingredients and structurally related compounds (a factor that may be important when investigating the ecotoxicity of these compounds). However, while few investigations into the presence of such impurities have been conducted, available information indicates that their presence is only likely at low concentrations. Stabilisers are frequently added to CPs to inhibit decomposition, especially when the product is intended for elevated temperature use. Stabilisers used cover a wide range of compounds and include: hydrocarbons; alcohols; ethers; epoxy compounds; organometallic compounds; organic nitrogen compounds, and inorganic compounds (Svanberg 1983).

An exhaustive literature review on the toxicity of chlorinated paraffins to marine organisms has not been carried out for the purposes of this profile. The information provided in this section is taken from existing review documents (BRE 1992). The most sensitive groups of organisms have been identified.

Data on the toxicity of chlorinated paraffins to marine organisms indicate that toxicity increases as the chain size decreases. High sensitivity is exhibited by marine invertebrates and fish exposed to short chain molecules.

Tarkpea et al (1981 cited in Svanberg 1983) reported that the harpacticoid Nitocra spinipes appeared more sensitive to short chain than long chain CPs. Reported 96 hour LC50s for short chain CPs range from 0.06 - 9 mg l^-1, while for long chain CPs, the 96 hour LC50s are >1,000 mg l^-1.

Madeley and Birtley (1980) found no significant mortality in mussels fed for 47 days with dry yeast contaminated with 524 µg/g (dry weight) of Cereclor 42.

Svanberg et al (1978) reported sublethal effects in bleak Alburnus alburnus when exposed over a 14 day period to 1.0 and 0.1 microg l^-1 of Huls chloparaffin 70C (C10-13, 70%Cl w/w) (added to the test water from acetone solution). Fish showed signs of disorientation and tetanic spasm which may have led to the death of three individuals.

Linden et al (1979) also investigated the acute toxicity (96 hour) of CPs to bleak. The tests were carried out under static conditions in brackish water (7 ppt). No renewal, aeration or control analysis of the test solutions was carried out. Nine different trade name CPs were tested, with carbon lengths ranging from C10 - C26 and chlorine percentage ranging from 42 to 71. All 96 hour LC50 were greater than 5,000 mg l^-1.

Haux et al (1982) reported the effects of the CP preparations Witachlor 149 (C12, 49% chlorine w/w) and Hulz 70C (C12, 70% chlorine w/w) on the haematology, osmoregulation, ionic regulation, intermediary metabolism, hepatic mixed-function oxidase system and steroid metabolising enzymes in male and female flounder Platichthys flesus L. in brackish and marine water. CPs were administered orally via a stomach tube. The fish were fed twice (day 1 and day 4) to obtain a total exposure of 1,000 mg kg^-1 body weight of each CP. Sampling was at 13 and 27 days after the first administration of CP. Witachlor 149 and Hulz 70C caused some sublethal effects, mainly on the haematology, glucose metabolism and xenobiotic and steroid metabolising enzymes of female fish. However, the authors were unable to interpret the physiological and ecological significance of these findings.

Svanberg et al (1978) investigated the bioaccumulation of Chlorparaffin Huls 70C in bleak. The fish were exposed to concentrations of 0.1 or 1.0 mg CPl^-1 under semi-static conditions at 10°C in brackish waters (7 ppt) (test solutions were renewed every two or three days). During the experiment, individual fish exhibited signs of neurotoxic effects at the dose of 1 mg CPl^-1 after 14 days and some mortality occurred at both concentrations. The whole body chlorine content indicated that the CP was taken up but the uptake did not appear to differ significantly between the two concentrations. After 29 days, the mean whole body chlorine content (wet weight) of fish exposed to 0.1 mg CPl^-1 was 26.2 microg Cl g^-1 and 28.6 µg Cl g^-1 for fish exposed to 1.0 mg Cl l.^-1.

Svanberg (1983) reported some unpublished observations of Tarkpea and Renberg (1982). Mussels Mytilus edulis accumulated 14C-labelled C16-chloro-alkane when exposed via water, resulting in a bioconcentration factor of about 6,000.

Campbell and McConnell (1980) concluded from investigations into levels of CPs found in the environment that there was no evidence to suggest that aquatic organisms accumulated CPs to levels above those found in nearby sediments. The authors also concluded that there was no evidence of CP biomagnification through the food chain. However, it appears that CPs of low molecular weight maybe accumulated while those of high molecular weight are not. Madeley and Birtley (1980) proposed that CPs of high molecular weight would be limited in their potential for bioaccumulation in the aquatic environment due to their low water solubility and because their strong tendency to adsorb onto suspended particles would decrease their availability to food-chain organisms. Zitko and Arsenault (1974) concluded that the uptake of CPs decreased or was completely inhibited when the molecular weight of the CP exceeded 600 (this would correspond to a carbon chain length of 24 and a chlorination level just below 50%).

Potential effects include:

• toxicity of chlorinated paraffins (especially short chain, low molecular weight species) to invertebrates and fish in the water column (there is no EQS for chlorinated paraffins);
• accumulation in sediments and a largely unknown potential for low molecular weight chlorinated paraffins to bioaccumulate.

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