Lead within ecosystems on metalliferous mine tailings in Wales and Ireland

A comparative study of the concentrations of lead in ecosystems developed on metalliferous mine tailings was undertaken. Mine soils, vegetation, ground-dwelling invertebrates and Apodemus sylvaticus from nine abandoned mines in Wales and a modern Irish mine site were sampled in order to evaluate and compare exposure risks to wildlife. The mine sites had a wide range of relatively high concentrations of total lead in their tailings (from 1058 to 46630 mg kg-1) but the extractable lead fractions were extremely variable and not clearly related or proportional to the total values. The high soil concentrations were reflected in vegetation collected from most of the sites with the exception of the modern mine, but there was no statistical relationship, on a site basis, between available soil lead and that in plant leaf samples. The highest plant concentrations were found in litter, which in all but one of the Welsh sites exceeded the threshold guideline value of 150 mg kg-1. Food-chain transfer was shown by high concentrations of lead in invertebrates and A. sylvaticus from the abandoned Welsh mines. A highly significant relationship existed between lead in grass and the grasshopper, Chorthippus brunneus. Adverse effects on soil invertebrates, essential to the decomposition processes and cycling of essential nutrients, were identified as probably the major obstacle to natural ecosystem development on the abandoned Welsh sites. Toxicological risk of lead to the small mammals from the Welsh sites, but not the modern Irish tailings, is indicated given the high lead concentrations in dietary items and the resultant residues in kidney with some evidence of renal oedema in animals from two sites. The absence of a significant relationship between the estimated dietary lead concentration, calculated on a site basis, and the total body concentration in A. sylvaticus, was attributed, in part, to the large size of the home range and the partial feeding of individual animals off the contaminated mine site. © 2002 Elsevier Science B.V. All rights reserved.