Heightened concerns regarding the protection of terrestrial ecosystems at a national level has increased the need to develop a suite of indicators capable of assessing the quality, integrity and fertility of soils. Of the assays currently available, tests that measure aspects of soil function and associated parameters are among the most promising, since these integrate effects on soil quality at the highest level of organisation. In this study we describe results of the deployment of an indicator of soil functional integrity (the bait lamina test) that is designed to measure the feeding activity of soil invertebrates. Bait lamina was used at six grassland sites located along a transect from a smelter at Avonmouth (South-West England) used in the EU funded BIOPRINT II project. Results indicated highest bait removal (feeding) at sites furthest from the factory, intermediate feeding activity at intervening sites and extremely low activities at the two sites closest to the smelter. The strong decline in activity for the group of sites closest to the smelter corresponded with increasing metal concentrations suggesting a clear impact of metals on detritivorous invertebrate feeding. Comparisons of the results of the bait lamina study to previous invertebrate survey work suggested that the differences in observed bait removal can be attributed to direct effects of metals on the abundance and biodiversity of key decomposer groups such as earthworms, isopods, molluscs, myriapods, springtails and mites.