PERSISTENT ORGANOCHLORINE CONTAMINANTS IN THE FIRTH-OF-CLYDE IN RELATION TO SEWAGE-SLUDGE INPUT

The concentrations of faecal sterols, chlorobiphenyls and several orga nochlorine pesticides have been determined in surface sediment and sed iment col es fi om the Firth of Clyde, Scotland. Faecal sterols and el evated organochlorine levels were present over the entire Firth. Sedim ent from the current sewage sludge clump ground contained the highest concentrations of organic carbon (11.9%), coprostanol (176 mg/kg), 4,4 '-DDE (19 mu g/kg), chlordanes (39 mu g/kg) hexachlorobenzene (12 mu g /kg), lindane (11 mu g/kg) and pentachloro-amino-diphenylether (12 mu g/kg). The concentrations of chlorobiphenyls (500 mu g/kg), dieldrin ( 62 mu g/kg), 4,4'-DDT (171 mu g/kg) and 4,4'-DDD (228 mu g/kg) were hi ghest in sediment from the former sludge dump ground. Chlorobiphenyl a nd faecal sterols levels on the former dump ground were similar to tho se measured 20 years ago. Examination of (1) the spatial distribution of contaminants, (2) the relative concentrations of faecal and natural sterols in sediment, and (3) the relative proportions of organochlori ne contaminants by cluster analysis suggests that the sludge disposal operation is the major source of these compounds to the entire Firth. A quantitative estimate of the degree of sludge dispersion obtained fr om faecal sterol measurements suggests that sludge constitutes 100% of the sediment organic input up to 2 km and 60% up to 4 km from the cen tre of the present dump ground. Only 10% of the reported input of chlo robiphenyls to the current damp ground is present within the designate d area. The concentrations of certain compounds on the dump grounds ex ceed proposed 'sediment safe levels'.