MAGNITUDE AND DISTRIBUTION OF CONTAMINANTS IN SALT-MARSH SEDIMENTS OF THE ESSEX COAST .4. ORGANOCHLORINE INSECTICIDES AND POLYCHLORINATED-BIPHENYLS

The concentrations of 14 organochlorine insecticides (HCB, alphaHCH, betaHCH, gammaHCH, aldrin, dieldrin, endrin, op' and pp' DDT, op' and pp' DDE, op' and pp' DDT) and polychlorinated biphenyls (as Aroclor 1248) have been determined in sediments of five salt marsh sites along the Essex coast, UK. The extent and distribution of contamination was found to be dependent upon the nature of the sources. The results indicate a ubiquitous but low level of contamination throughout all these salt marsh sediments. The greatest level of contamination was found on the more urban site at Two Tree Island (situated on the outer Thames Estuary). Both the organochlorine insecticides and PCB exhibited intra-site variations with enhancement in vegetated areas at depths of between 10-30 cm, which was probably indicative of historical inputs. In mud flat and creek areas contaminants displayed a more even distribution to greater depth which was related to physical and biological factors. Core profiles of DDT and DDD concentrations indicated that the extent of reductive dehalogenation was dependent upon depth within the sediment.