Physico-chemical properties & ecotoxicology
The term chlorinated alkane (CA) covers a wide range of liquids and solids from C10 to >C24 and containing 30-72% chlorine content. Properties differ significantly across this range and for this reason, they are best considered in three separate groups.
- The C10-13 liquid products from 40-72% Cl content.
- The C14-17, C18-20 and chlorinated alkane wax liquids from 40-60% Cl content.
- The powdered chlorinated alkane waxes of >69% Cl content.
CAs have very low vapour pressure with the most volatile (C10-13 types) < 10-3 mbar. They are chemically very stable but dehydrochlorinate on heating at high temperatures (or for prolonged periods). Such dehydrochlorination can also occur upon prolonged exposure to sunlight.
All CAs have a low solubility in water but C10-13 up to 150 μg/l is significantly more soluble than other classes, which show decreasing solubility with increasing chain length (down to <5 μg/l).
Studies have confirmed that CAs adsorb strongly onto suspended materials/ sediments in an aquatic environment. However, unabsorbed or solutions at the lower solubility limit will degrade without added reagents.
Assessing the environmental impact
It is noteworthy that only very low levels of chlorinated alkanes have ever been found in the environment. Analysis of rivers in industrialised parts of the UK has shown levels in the range 0 to 2 µg/l with short-chain chlorinated alkanes typically accounting for one-quarter to one-third of the total amount present. Higher levels (typically 0 to 10 mg/kg) have been found in those sediments collected from areas closer to industry.
In areas that are further from industry, chlorinated alkanes were either found at signifcantly lower levels or could not be detected at all. The overall assessment of environmental impact is often based on measures of persistence, bioaccumulation and toxicity (PBT).
Some chlorinated alkanes are considered to be relatively persistent. However, many have been shown to bacterially degrade. The rate of 'biodegradation' was found to be higher for grades with lower chlorine content and where bacteria had become 'acclimated' to chlorinated alkanes.
When looking at these chemicals in the environment, degradation rates of upto 80% are observed within 42 days in closed bottle tests.
Laboratory tests have been carried out to measure the levels present in fish exposed to chlorinated alkanes versus the water content; this ratio is called the bioconcentration factor (BCF).
In tests carried out with trout, the BCF was found to be approximately 8,000 for short-chain grades and approximately 1,000 for medium-chain grades, whilst for long-chain grades it wasaround 50 (>2000 is the limit to be considered a bioaccumulating substance under REACh). These values are very much lower than for substances such as polychlorinated biphenyls (PCBs) and chlorine-based pesticides (dieldrin, DDT etc).
Studies have also shown that there is no biomagnification of chlorinated alkanes by fish (i.e. the levels in fish eating food dosed with the product were no higher than those in their normal diet).
In laboratory tests, short-chain grades have been shown to have toxic effects on fish and other aquatic life after long-term exposure to concentrations close to their water solubility, but at significantly higher than those typically found in the environment.
Mid-chain chlorinated alkanes show a significantly reduced spectrum of toxicity compared with the short-chain grades, as would be expected due to their lower bioaccumulation (see previous paragraph).
No measureable short or long term toxicity has been found in studies of several species of fish. Only one tested aquatic invertebrate species showed any sensitivity, but again at levels considerably higher than those found in the environment.
Similarly, certain soil and sediment organisms are affected, but only at levels of hundreds of parts per million (ppm), others remain unaffected at concentrations of thousands of ppm.
Long-chain grades, because of their large molecular size and very low solubility, have shown no toxicity to fish and other forms of aquatic life at, and above, their solubility limit.
Do chlorinated alkanes act as oestrogen mimics?
There is nothing in the biological profile or currentl literature on CAs suggesting that they would have this effect.
Reducing the environmental impact
From the information presented in this section, it can be concluded that only short chain chlorinated alkanes present a potential environmental risk. In 1999, the UK government prepared (revision 2005) a risk assessment report on short-chain chlorinated alkanes within the framework of the EU Existing Substances Review. At that time, work on medium-and-long chain chlorinated alkanes started, which has continued under the "REACH" legislation, during which time, both substances were registered (in 2010).
The SCCP Risk Assessment summary detailed, a requirement for risk reduction measures to be implemented on emissive uses in metalworking fluids and in leather treatment.
In the meantime, the Oslo and Paris Commissions (OSPAR) recommended the phase-out of the use of short-chain chlorinated alkanes in most applications in 1999 and in 2009 the UNECE decided to list SCCP on their POPs list. SCCP is also going through the Stockholm Convention process at present.
European producers of chlorinated alkanes have voluntarilyceased production and sale of SCCPs to the metalworking and leather treatment industries, which are believed to present the greatest potential environmental risk.
Toxicity to humans
Chlorinated alkanes are of very low, single exposure, acute toxicity. Various different grades have been tested and doses of 4-10 g/kg show no signs of toxicity to laboratory animals. An equivalent dose in humans would be an 'average' person drinking about 250-600 ml of liquid chlorinated alkane.
In longer-term studies on laboratory animals, short-chain chlorinated alkanes produce toxic effects on the kidney and liver. The highest dose that can be given without showing an adverse effect (the No Observed Effect Concentration - NOEC) is 10 mg/kg/day for rats. This amount is many orders of magnitude higher than the highest exposure likely to be encountered in industrial conditions or conditions under which people are likely to be exposed in everyday life.
Coming into contact with chlorinated alkanes
The three routes by which any chemical can enter the body are ingestion (via the mouth), inhalation and skin contact. During industrial use, inhalation and skin contact are therefore the main routes. Despite this, since the vapour pressure of chlorinated alkanes is very low, exposure to CA vapour by inhalation is minimal. However, there is potential exposure to aerosols of mixtures containing CAs. For most workers, skin contact is the most likely source of exposure to chlorinated alkanes. Studies have shown that skin and eye irritation is low and that they are not significantly absorbed through the skin.
There have been suggestions that workers exposed to metal working lubricants may suffer from allergic reactions or skin sensitisation. There is no evidence though that this effect is caused by the CA content of the lubricants. This was investigated further in animal studies which, together with evidence from humans, have confirmed that chlorinated alkanes do not have the potential to be skin sensitisers. Any effect seen is likely due to other components in the lubricant or to stabilisers that may have been added. As a precautionary measure, most CA suppliers use stabilisers which have been shown not to cause skin sensitization.
All chlorinated alkanes have very low vapour pressure. Under normal conditions of use, the quantity of chlorinated alkane likely to be inhaled is extremely small. However, if chlorinated alkanes were to be heated during handling, fuming may occur. These fumes may contain a small proportion of HCl (an irritant) and in such situations, adequate ventilation is recommended.
Aerosol mists may be produced during the use of metal working fluids in the engineering industry and these may contain chlorinated alkanes. It has been calculated that exposure in this way does not present a risk, provided that the Occupational Exposure Limit (OEL) for oil mists (e.g. 5 mg/ml in the UK) is met.
Lifetime animal studies have been carried out with two grades of chlorinated alkanes. A short-chain grade with 58% chlorine caused tumours in rats and mice. Male mice exposed to a long-chain grade with 40% chlorine showed an excess of tumours at one site but this was most deemed unlikely to be due to exposure to CAs. It has been shown that the mechanisms by which short chain chlorinated alkanes cause tumours to be formed is specific to rodents and, therefore of no relevance to human health. Furthermore, CAs have been shown clearly to be non-genotoxic. Based on this evidence it is concluded from the carcinogenic findings in animals, CAs do not give rise to concern for human health.
Despite this, as the basis for the regulatory classification of carcinogens differs from country to country, some systems give less weight to the more recent mechanistic studies which indicate that the animal results are of little relevance for man than others.
In the USA, the short-chain (C12), 58% chlorine product is the only CA to be classified and labelled as a carcinogen. However, some suppliers in the US have voluntarily decided to label other short-chain CAs in the same way as a precaution.
In Germany, the MAK Commission has classified almost all chlorinated alkanes as Category IIIB (i.e. suspected carcinogens). However, they have not been included in the list of substances (TRGS 905) required to be labelled.
All EU Member States have been required to implement the EU decision in 1998 to classify short chain chlorinated alkanes as Category 3 carcinogens.