Contaminated soils are typically rated according to their ‘bioavailable’ metal content – the amount of metal dissolved or suspended in water percolating through the soil that could be absorbed by living organisms. The proportion of pollutants that bind tightly to soil particles is presumed to be inaccessible to organisms feeding on soil.
But according to a paper to be published in Environmental Science and Technology, Renaud Scheifler and colleagues at the University of Franche-Comté in France have found that snails are able to absorb cadmium bound to soil particles. In a two week experiment studying snails living in cadmium-contaminated soil from a disused lead and zinc smelter, the team found that the snails had adsorbed 16% of the soil-bound cadmium.
The findings, reported in New Scientist, suggest other heavy metals could also be more bioavailable than was previously assumed. But more work is needed to establish whether risk assessment procedures for contaminated soils need rethinking, says Scheifler. His team will now investigate other metals such as zinc, copper, lead and mercury using a range of organisms. “We have to work with other invertebrates to find whether the snail is a particular case,” he says.