SPECIES-SPECIFIC DIFFERENCES IN THE NET ASSIMILATION OF ZINC, CADMIUM, LEAD, COPPER AND IRON BY THE TERRESTRIAL ISOPODS ONISCUS-ASELLUS AND PORCELLIO-SCABER

Specimens of these woodlice were collected from a contaminated deciduous woodland (Haw Wood) 3 km downwind of a primary Zn, Pb and Cd smelting works on the Severn Estuary, Avon, and from a similar but uncontaminated site (Wetmoor Wood), and maintained on leaves of field maple Acer campestre collected from the litter layer at the sites. Zinc was retained by contaminated P. scaber fed on uncontaminated leaf litter but was lost rapidly from the hepatopancreas of O. asellus fed on the same diet. Cadmium and Pb were accumulated to a much greater extent in O. asellus. After 20 wk mean concentrations of Cd and Pb in the hepatopancrease of O. asellus were at least 5 times higher than in the hepatopancreas of P. scaber. Copper was accumulated by the hepatopancreas of both species in all experimental situations. Concentrations of Fe increased in all the woodlice during the experiment but the metal was stored predominantly in the gut, not in the hepatopancreas. Death of individual woodlice in the laboratory was due to Zn poisoning. Critical concentrations of Zn in the hepatopancreas (dry weight basis) were 15 000 μg g-1 in O. asellus and 25 000 μg g-1 in P. scaber. Populations of the two species collected from sites <3 km from the smelting works at Avonmouth, occasionally contain moribund individuals in which these critical concentrations of Zn in the hepatopancreas are exceeded. -from Author