The effect of benthic invertebrates on the clearance of mercury from sediments

Tubificid worms caused a significant loss of radiolabeled inorganic mercury and methyl-mercury from contaminated sediments over a 3-week period. The fractional clearance rate of mercury from the sediments was linearly related to worm density. The most significant loss was from the first 1 cm of sediment. The presence of worms changed the appearance, and caused some redistribution, of fine sediment. Loss of mercury could be contained by a sand overlay but the upward movement of mercury into the sand overlays when worms were present suggested that their effectiveness in preventing such movement would be limited over longer periods of time. While a number of considerations prevent the direct application of the clearance coefficient to natural systems, it was possible to demonstrate, on the basis of certain simplifying assumptions, that the benthic macrofauna could be entirely responsible for the clearance of mercury from the bed sediments of flowing water systems.