Changes in Organochlorine Contamination of the Marine Environment of Eastern Britain monitored by Shag Eggs

Abstract

A SURVEY of the residues of organochlorine insecticides in the marine environment of north-east England and south-east Scotland in 1965 and 1966 showed that dieldrin and pp′-DDE (a metabolite of DDT) occurred inthe highest amounts¹. The highest concentrations of residues were found in tissues and eggs of the shag and cormorant (Phalacrocorax aristotelis and P. carbo), with, for example, the eggs of the former possessing on average almost 1 p.p.m. of dieldrin and about 2 p.p.m. of pp′-DDE. All other organochlorine insecticides including DDT were present at concentrations of less than 0.02 p.p.m. As a result of this survey it was concluded that shags' eggs were the most suitable material for continuing the monitoring of residues in that environment. The criteria used in selecting the indicator species were, first, that the concentration in the indicator should be sufficiently large to allow changes to be readily detected; second, that the movement of the organism from which the sample was to be taken should be restricted to the area under study; third, that the diet (and source of contamination) should be known; fourth, that the relationship between variations in age of the organism and the concentration of insecticide should have been determined.