Copper, Zinc, and Organotin as Long-Term Factors Governing the Distribution of Organisms in the Fal Estuary in Southwest England

Abstract

Evidence of long-term metal pollution in the Fal Estuary is provided by analyses of Cu in oyster (Ostrea edulis) communities extending over more than 120 yr and by analyses of Cu and Zn in sediments dating back to 1921. Indications are that levels of Cu pollution from mining have declined very slowly but that Zn pollution has not. In Restronguet Creek, the most heavily polluted area, metal levels in waters and sediments are elevated by orders of magnitude. The invertebrate fauna of the creek is limited, but far richer than might be predicted from laboratory toxicity data. The cockleCerastoderma edule exemplifies organisms that are excluded from the creek owing to the toxicity of dissolved Cu, whereasOstrea edulis, by virtue of its innate tolerance to Cu and Zn, grown in the Iower reaches. On the other hand, the population of the ragwornNereis diversicolor, which penetrates into the most heavily polluted areas, is demonstrably far more tolerant of Cu and Zn than population from clean areas and appears to be a tolerant strain. To a considerable degree, therefore, the distribution of species is dependent not only on the innate ability of some species to tolerate Cu and Zn, but on the capacities of other populations to develop metal resistance and thereby maintain their original range of distribution. Present-day problems in the Fal Estuary appear to stem not only from mining wastes but also from the increased usage of tributyltins in antifouling paints. In the dogwhelkNucella lapillus, the incidence of imposex (the appearance of a penis and other male characters in females) is virtually 100% at sites along the English Channel coast of southwest England. The degree of imposex is related to the body concentration of hexane-extractable organotin, which includes both tributyltin and dibutyltin fractions. The highest degree of imposex, where the female penis approaches that of the male in size, occurs in the Fal Estuary; also, in some males the penis becomes deformed. Populations of dogwhelks have declined dramatically in this estuary, and are also characterised by the presence of relatively fewer females and by the absence of juveniles and egg capsules. Reproductive failure in females is now known to be caused by blockage of the pallial oviduct during the development of imposex.