Preliminary determinations of heavy metals in winkles Littorina littorea along a concentration gradient in the Fal Estuary suggested that whole body concentrations might be related to those of the water. When animals were transplanted to this heavily contaminated estuary, changes in tissue concentrations of As, Co, Cu and Zn were largely complete after 2 months.

Relations between the winkle and water concentrations may be indirect since its algal diet is thought to be the main source for most heavy metals. Data from a large number of United Kingdom estuaries were used to compare concentrations of 12 metals in L. littorea with those of the brown seaweed Fucus vesiculosus which forms part of its diet. Very significant relations were found for Ag, As, Cd and Pb, suggesting that since concentrations in the seaweed probably reflect those of the surrounding water, so also do those of the winkle. However, concentrations of Ag in the animal also appeared to be influenced by dietary Cu levels. In addition, significant relations between the two species were found for Cu, Fe, Hg and Zn, but the slopes were shallow, perhaps indicating regulation by the winkle. For Cr and Mn relations were not very significant and, for Co and Ni, concentrations in the winkle appeared to be influenced by those of Cu and Zn.

Compared with concentrations in L. littorea, those of L. littoralis from the same site were generally higher whilst in L. saxatilis they were usually of the same order or lower.

In assessing the winkle as an indicator of metal contamination the present results have been combined with those of other workers to produce comparisons between most estuaries in England and Wales. It is concluded that whilst the winkle is a useful indicator for Cd and a few other metals, it is certainly not a perfect indicator organism.

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.

Populations 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 1969 (Blaber, 1970) and 1985, thus coinciding with the introduction and increasing usage of TBT-based paints; (3) tissue concentrations of tin as TBT increased consistently with the degree of imposex; (4) animals transplanted from a ‘clean’ area to a harbour site absorbed TBT and developed imposex; (5) preliminary experiments showed that imposex was induced by exposure to 20 ng/1 of tin as TBT leached from a TBT-based paint; (6) TBT is implicated in the induction of imposex in other stenoglossan gastropods including Nassarius obsoletus (Say) (Smith, 1981) and Ocenebra erinacea (L.) (Féral & Gall, 1982).

In the first paper of this series (Bryan & Hummerstone, 1971) it was shown that in the estuarine polychaete Nereis diversicolor O. F. Müller the concentration of copper is roughly proportional to that of the surrounding sediment. On the other hand, concentrations of zinc appeared to be relatively independent of those in the sediment and it was suggested that the level of zinc in the worm is regulated.

A map of the Looe Estuary in south-east Cornwall is shown in Fig. 1. As it flows to the western branch of the estuary, the West Looe River passes through the Herodsfoot mining area which lies about 5 km above Sowden's Bridge. By Cornish standards, this was a productive area for lead and Dewey (1921) gives the output of Herodsfoot mine as 13470 tons of metal between 1848 and 1884 and more than 17 tons of silver between 1853 and 1884.

In a previous paper (Bryan & Hummerstone, 1971) the average concentrations of copper, zinc, lead, manganese and iron in the polychaete Nereis diversicolor O. F. Müller from several estuaries draining the mineralized areas of South-West England were compared with concentrations in the sediments. Although high levels of copper and zinc were encountered in some sediments none contained high levels of manganese and, in the worms, concentrations of manganese were low and relatively constant. Other estuaries in the area have since been examined, but although thousands of μg/g of copper, zinc, lead and arsenic have been found in some sediments, concentrations of manganese exceeding 1000, μg/g have rarely been encountered. Manganese ores occur quite widely in South-West England but the scale of mining appears to have been small by comparison with that for more obvious contaminants of estuaries such as copper, lead and arsenic (Dines, 1956). However, it is thought that the field observations and experimental results described in this paper can be extrapolated to situations where much higher concentrations of manganese occur.

Analysis of the deposit-feeding bivalve Scrobicularia plana (da Costa) has been proposed as a method of assessing the biological availability of heavy metals in estuarine sediments (Bryan & Hummerstone, 1977; Bryan & Uysal, 1978). Scrobicularia has a number of attributes which are useful in this type of indicator: (i) it is common in many British estuaries, particularly in the south, and often penetrates much farther upstream than other common bivalves such as Mytilus edulis; (ii) it is a convenient size for analysis and, during its life span of perhaps 10 years, reaches a shell length of 40-50 mm (Green, 1957; Hughes, 1970); (iii) it is a good accumulator of metals and appears to reflect changes in their biological availability.

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.

A study of tributyltin (TBT) uptake, tissue distribution and breakdown in dog-whelks, Nucella lapillus, was carried out using 14C-labelled tributyltin chloride. The compound was introduced into animals by exposure to sea-water, from a diet of labelled mussels and by injection. Measurements of 14C were made on tissue extracts containing total 14C, TBT+DBT and TBT. Organs examined included digestive gland, kidney, mantle, foot, viscera, gonads and blood. Absorption of dissolved TBT occurred primarily via tissues associated with the mantle: autoradiographic evidence showed that of these the ctenidium (gill) and osphradium were probably most important. Of non-reproductive tissues, mantle displayed least evidence of TBT degradation whereas kidney and digestive gland contained lower proportions of 14C as TBT (~60%) than other tissues. By virtue of its more rapid response, initially at least, the kidney had a primary role in degrading dissolved TBT that reached the blood. Dog-whelks feeding on labelled Mytilus edulis absorbed organotins very efficiently via the digestive gland, which then played a major role in TBT breakdown. However, the capacity for degradation is not sufficient to prevent, TBT concentration factors of the order of 100,000 (dry tissue/water) being attained in N. lapillus. Autoradiography revealed surprisingly high grain-counts in nerves, which may be significant in view of evidence in the literature that neurohormones are intermediaries in the chain linking TBT with imposex.

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.

Zinc is one of the most important of the essential trace metals and more than 90 zinc-containing enymes and proteins have been discovered: furthermore, zinc increases the activity of many other enzymes (Vallee, 1978). It is not surprising, therefore, that in some groups of animals the body concentration is regulated against fluctuations in intake. Decapod crustaceans comprise one such group, although the ways in which regulation is achieved vary from species to species. In the freshwater crayfish, Austropotamobius pallipes, excretion in the faeces is a major pathway for removing zinc (Bryan, 1967a) whereas in the shore crab Carcinus maenas losses over the body surface also assume considerable importance (Bryan, 1966). On the other hand, preliminary work on the lobster Homarus gammarus (formerly H. vulgaris) suggests that in this species urinary excretion plays a major role in regulation (Bryan, 1964). The present work continues the study of zinc regulation in lobsters and its main aims are: (1) to measure rates of absorption from sea water over a wide range of concentrations and study the uptake mechanism; (2) to examine absorption from the stomach under different conditions; (3) to determine the relative importance of different pathways for the removal of zinc in response to various levels of intake.