Heavy metals in isopods from the supra-littoral zone on the Southern shore of the Severn Estuary, UK

The concentrations of zinc, cadmium, lead and copper in the tissues of the littoral isopod Ligia oceanica from three sites near to a primary zinc, lead and cadmium smelting works on the southern shore of the Severn Estuary and an unpolluted site in the Menai Strait, Anglesey, were determined. The concentrations of zinc, cadmium and copper in whole L. oceanica from the contaminated sites were significantly higher than in specimens from the uncontaminated site, although the levels were only about one-and-a-half, three to four and twice as great, respectively. The amounts of lead in L. oceanica from all four sites were very small. The hepatopancreas was the most important storage organ of heavy metals and, at all sites, contained more than 50% of the total zinc, cadmium and copper in the body.

The concentrations of heavy metals were compared in the tissues of L. oceanica and in two ‘more terrestrial’ isopods, Oniscus asellus and Porcellio scaber, collected from the same habitat at one of the contaminated sites. The mean concentrations of copper were the same in the hepatopancreas of all the isopods. However, there were large differences in the extent to which zinc, cadmium and lead had been accumulated by this organ in the three species. Analysis of the gut contents of the isopods revealed that all three species had been feeding on leaf litter derived from nearby trees, rather than on seaweed washed up onto the shore. Therefore, it was concluded that the extent to which zinc, cadmium and lead were assimilated by L. oceanica, O. asellus and Porcellio scaber must have been related to differences in their digestive physiology, rather than to choice of food material containing different concentrations of metals.