Metal uptake by woodlice in urban soils

This study evaluated the uptake of bioavailable metal (Cd, Cr, Cu, Fe, Pb and Zn) by woodlice (Isopoda) collected from public open spaces in urban areas of Renfrewshire, Central West Scotland, UK. The species Oniscus asellus and Porcellio scaber were collected at 13 different locations together with associated surface soil samples. Soils were subject to sequential extraction to evaluate metal availability and analyzed by ICP-AES and flame AAS for Cd, Cr, Cu, Fe, Pb and Zn concentrations. The soil samples had metal concentrations typical of general urban environments and the potentially toxic elements were well below published guideline values for contaminated sites. The metal concentration showed differing inputs of natural and anthropogenic sources. Metals were bioconcentrated in the order Cu>Cd>Pb>Cr>Zn>Fe for O. asellus and Cu>Zn>Cd>Cr>Fe for P. scaber. Principal Component Analysis of soil geochemical properties and Isopoda metal concentration identified metal to metal variation in uptake. Multiple linear regression analysis was applied in order to investigate the metal uptake in relation to soil properties (total metal concentration, pH and organic matter (OM)). The results showed that factors affecting metal concentration were both species and site specific. The most available forms of metals were generally poorly related to metal accumulation by woodlice, with the only exception being for Cu, which was related to the exchangeable soil fraction. Soil conditions e.g. pH and OM, influenced metal association within the soil and OM played a significant role in restricting uptake of Cr and Pb in particular. For most of the metals studied, despite differences in the environmental availability of the metals, accumulation from ambient soil concentration is controlled by ecological and physiological factors influencing metal assimilation, storage and excretion and that the two biological species vary considerably in their regulation of individual metals.