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Physico-chemical properties & ecotoxicology

The term chlorinated paraffins is usually taken to encompass a wide range of liquids and solids from C₁₀ to >C₂₄ and containing 30-72% chlorine content. Properties (including ecotoxicology) differ significantly across this range and for this reason, they are best considered in three separate groups.

a) The C_10-13 liquid products from 40-72% C₁₂ content.

b) The C_14-17, C_18-20 and chlorinated paraffin wax liquids from 40-60% C₁₂ content.

c) The powder chlorinated paraffin waxes of >69% C₁₂ content.

• CPs have very low vapour pressure with the most volatile (C_10-13 types) < 10^-3 mbar. They are chemically very stable but dehydrochlorinate on heating at high temperatures (or for prolonged periods). Dehydrochlorination also occurs on prolonged exposure to light.

• All CPs have low solubility in water but C_10-13 types at up to 150 �g/l are significantly more soluble than the other classes which show decreased solubility with increasing chain length (down to below 5 �g/l).

• Studies have confirmed that CPs adsorb strongly onto suspended materials or sediments in an aqueous environment. True solutions (at the low solubility limit) do degrade without added reagents.

• Laboratory studies often fail to indicate biodegradation occurring, but longer-term studies in biological effluent treatment plants do reveal substantial degradation and the undegraded residue is removed by adsorption onto the biological sludge.

• The short-chain grades have been shown, in laboratory tests, to have toxic effects on fish and other forms of aquatic life after long-term exposure to concentrations close to their water solubility, and significantly higher than those found typically in the environment.

• Mid-chain chlorinated paraffins show a significantly-reduced spectrum of toxicity compared with the short-chain grades, as would be expected from their lower bioaccumulation. No measureable short or long term toxicity has been found in studies with numerous species of fish. Only one of several aquatic invertebrate species that have been tested 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 mg/kg (parts per million), whilst others are unaffected at thousands of mg/kg.

• 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.

June 2005