Abstracts Biological Sciences

Chlorinated fatty acids in freshwater fish and some biological effects of dichlorostearic acid

by Gastons Vereskuns

Chlorinated fatty acids (CFAs), major constituents of extractable, organically bound chlorine in biota, are found in almost all fish studied in this respect. The concentration of CFAs in fish varies considerably from some micrograms per gram of lipids in fish from remote areas up to more than two thousand micrograms per gram of lipids in fish from the vicinity of chlorine bleached kraft mills. CFAs were liberated from fish lipids as the corresponding methyl esters and subjected to enrichment. The methylated CFAs were studied by gas chromatography with electrolytic conductivity detection and/or mass spectrometry. A considerable diversity of CFAs were found in fish, e.g. more than twenty were indicated in pike from Latvian lakes. However, only part of the CFAs could be identified. Pattern of CFAs differ considerably between fish from different areas. Thus, the patterns of CFAs in previously studied eel caught in Idefjord differ from the CFA patterns of pike from Latvian lakes and also from that of perch from Latvian rivers. The main CFAs in pike are likely chlorohydroxy fatty acids and in perch chlorinated, possibly sulphur containing carboxylic acids. In the study of pike, CFAs were released from all lipid classes considered: steryl esters, triacylglycerols, and phospholipids. Because an enrichment is usually needed to make CFAs in lipids detectable, their quantification may be difficult. A method to facilitate quantitative studies was developed, where the enrichment factor is calculated using cholesterol. Dichlorostearic acid was taken up by rats via food and were distributed within different organs with the highest concentration in heart lipids and the lowest in muscle lipids. Dichlorostearic acid was metabolised in rats yielding dichloropalmitic and dichloromyristic acids. Some shorter-chain metabolites, possibly including dichlorotridecanoic acid were found in the liver lipids. CFAs in the lipid extracts of rat tissues were studied also by liquid chromatography with electrospray ionisation mass spectrometry. In a test for mutagenicity, the Ames test, dichlorostearic acid did not show any adverse effects. In contrast, dichlorostearic acid caused inhibition of mutagenicity of some indirectly-acting mutagens, possibly by the inactivation of Cytochrome P450 enzymes. Certain effects on the ability of rat enzymes to activate indirectly acting mutagens by the same acid was found also in in vivo studies. A possible explanation to this observation might be an interaction of dichlorostearic acid with membrane bound enzymes or changes in the membrane lipid composition resulting from the exposure to dichlorostearic acid.