A survey of the gastropod Nucella lapillus around the south-west peninsula of England has revealed that the incidence of ‘imposex’, the induction of male sex characters in the female, is widespread, that all populations are affected to some degree and that the phenomenon is most prevalent along the south (Channel) coast. Populations close to centres of boating and shipping activity show the highest degrees of imposex, especially those within the vicinities of the Helford, Fal, Salcombe and Dart estuaries and in Plymouth Sound and Tor Bay. Within Plymouth Sound the degree of imposex increased markedly between 1969 and 1985, coinciding with the introduction and increasing usage of antifouling paints containing tributyltin (TBT) compounds.

The concentration of copper in Nereis diversicolor O. F. Miiller is roughly related to the total concentration in the sediment and particularly high concentrations are found where mining pollution occurs. In contrast, the concentration ofzinc in Nereis remains remarkably constant despite wide variations in the environment and appears to be accurately regulated.

Concentrations of copper, zinc, lead, manganese and iron in the brown seaweed Fucus vesiculosus have been measured in samples collected over its range of distribution in four estuaries having different degrees of metal contamination. Factors controlling the concentrations in the weed have been studied and include the concentrations of metals in the water, seasonal changes, the position of the weed in the intertidal zone and the particular portion of the plant which is analysed. It is concluded that analysis of the weed gives a reasonable indication of average conditions in the water at points along an estuary and provides a method of making comparisons with the same estuary in subsequent years or with other estuaries. I N T R O D U C T I O NIn the brown seaweed Fucus vesiculosus, the combined results of Black & Mitchell (1952), Young & Langille (1958) and Gutnecht (1965) have suggested that the concentration of zinc changes with that in the sea water. This was confirmed experimentally for zinc, copper and lead in Laminaria digitata, another brown weed, by Bryan (1969Bryan ( ,1971, although the relationship is not one of direct proportionality since at higher metal concentrations the concentration factor, relating the level in the weed to that in the water, is reduced. However, the weed would still be expected to reflect the average availability of metals in the water and, since concentration factors greater than 1000 to 1 are generally found, this property can be used for practical purposes.Fucoid seaweeds from the intertidal zone have been used as indicators of heavy metals in inshore waters around the British Isles by Preston et al. (1972) and in the Bristol Channel by Nickless, Stenner & Terrille (1972). It seems to be a reasonable technique, although one which it might be possible to refine by taking into account some of the factors which affect the relationship between metals in the seaweed and in the water. On open shores this relationship may be influenced by factors such as the time of year and the level of the weed in the intertidal zone, but, in estuaries, additional factors such as the variable salinity and the presence of high concentrations of particulate material may need to be considered. This paper compares the concentrations of heavy metals in Fucus vesiculosus from four estuaries in south-west England -the Tamar, the Restronguet Creek branch of the Fal, the Dart and the Camel. These drain parts of the mineralized zone which extends across Cornwall and into West Devon and differ markedly in the degree to which they are contaminated with metals such as zinc and copper.

Following treatment of the shells of adult Nucella lapillus with different marine paints under field conditions, the development of 'imposex' (the growth of a penis and vas deferens in females) was promoted by three TBT-based antifouling paints but not by a tin-free copper-based paint nor by yacht enamels.When adult animals were exposed to a range of sea-water leachates from TBT copolymer antifouling paint the initial rate of tin accumulation was approximately proportional to the ambient concentration over the range < 1-107 ng/1 of tin in the TBT fraction. In experiments of between 8 and 14 months duration, concentration factors (dry tissue/water) for tin (as TBT) reached about 10 5 at sea water concentrations of 1-5-18-7 ng/1. At 107 ng/1, however, the factor fell to about 3 x 10 4 owing probably to the accelerated degradation of TBT to DBT by the tissues. The bioaccumulation data from the laboratory experiments compare favourably with field data from populations around south-west England.At all experimental sea water concentrations, the bioaccumulation of tin by adult females was accompanied by increased development of imposex. However, the sterilisation of adult females through blockage of the oviduct by the vas deferens (as observed in declining field populations) occurred only after at least 12 months exposure to 107 ng/1 of tin as TBT: it also occurred after more than 18 months in some adults transplanted to a rocky shore exposed to a mean concentration of about 28 ng/1. Growing juveniles, on the other hand, are far more sensitive and may be sterilized at concentrations of only a few ng/1 before reaching maturity.The depuration of tin was followed for up to 9 months and, depending on the conditions, half-times for loss of the TBT fraction from the tissues ranged between about 50 days and more than 100 days. There was no evidence that loss of tin leads to any remission of imposex. I N T R O D U C T I O NPopulations of the gastropod, Nucella lapillus (L.), normally one of the commonest of rocky-shore macroinvertebrates, have recently suffered from declining numbers at many sites along the south coast of England. Bryan et al. (1986) showed that these declining populations exhibited a high degree of imposex (the induction of a penis and vas deferens in females) and that imposex was almost certainly caused by tributyltin (TBT) compounds leached from ships' antifouling paints. Evidence implicating TBT compounds in the development of imposex included: (1) a good relationship between the degree of imposex and the proximity of affected populations to harbours and marinas; (2) in Plymouth Sound, the degree of imposex increased dramatically between its discovery in 18-2