Terrestrial isopods: useful biological indicators of urban metal pollution

Environmental pollution by toxic metals is widespread in urban areas. In contrast to many industrialized sites, however, metal pollution in most urban regions occurs at low or moderately elevated levels. Reliable criteria of environmental quality have therefore to be established, with the consequence that there is an increasing need for sensitive monitoring of pollution. In this present study, the isopod species Porcellio scaber was used as a bioindicator of lead and cadmium pollution in Innsbruck, Austria. During May 1988, isopods were collected at 356 points over the whole city area; lead and cadmium in whole animals were measured using flame atomic absorption spectrophotometry. Lead and cadmium contamination of urban districts were correlated with traffic density, the only exception being higher cadmium contamination of one district in which several factories are situated. Concentrations of lead, but not of cadmium, increased along the main arterial roads with increasing traffic density and with decreasing distance from the city centre. On a large scale, concentrations of lead and cadmium increased in the direction of the prevailing wind, from south-west to north-east. On a small scale, the variability of metal concentrations can be explained by the irregular distribution of active business centres, by different degrees of contamination between exposed and non-exposed sites, and by contamination gradients depending on wind direction. Compared to highly polluted sites around industrial factories and metal smelting works, lead contamination in Innsbruck can be considered as moderately elevated, whereas cadmium contamination is low.