The effect of sediment characteristics on bioturbation-mediated transfer of lead, in freshwater laboratory microcosms with Lumbriculus variegatus

While it has been well established that sediment bioturbators can affect the fate of metals in aquatic systems and that the fate of metals there can depend on sediment characteristics, the interaction between these influences is not well known. The present study therefore investigated whether the influence of a sediment bioturbator on the fate of metals is affected by sediment characteristics. This was investigated using two laboratory microcosm experiments with lead-contaminated sediment and the oligochaete Lumbriculus variegatus. The first experiment used sediment collected from five Toledo Bend reservoir sites that differed in sediment characteristics, and analyses looked at the influence of sediment organic matter, sediment silt/clay content, sediment pH, and pore-water pH. In the second experiment, organic matter and silt/clay content of Toledo Bend reservoir sediment were varied experimentally using alpha-cellulose and clay, and Pb transfer to the water column and bioaccumulation were again quantified. Both experiments were conducted with sediment spiked with Pb to a concentration of 100 µg/g, at an oligochaete density of 6279 ind./m². In the first experiment, the Pb concentrations in the water column and those in the worms at the end of the 14-day experiment differed among sediment-collection sites. Silt/clay content and sediment pH were the two most important variables influencing Pb transfer from sediment to the water column. A multiple regression model with these variables explained 58% of the variability in this lead transfer. For Pb accumulation by the worms, sediment organic matter and pore-water pH were the two most important variables. This regression model explained 85% of the variability in tissue Pb levels. In the second experiment, where the individual effects of the organic matter and silt/clay content on Pb transport and distribution were assessed, the use of sediment with more organic matter resulted in a reduction in both the Pb transfer to the water column and the accumulation in worms. The increase in the sediment’s silt/clay content resulted in a reduction in Pb bioaccumulation only. Overall, the results of the present study demonstrate that sediment pH, pore-water pH, organic matter, and silt/clay content influence the bioturbation-mediated transfer and the environmental distribution of Pb.