CONTAMINANT FLUXES FROM SEDIMENT DUE TO TUBIFICID OLIGOCHAETE BIOTURBATION

The release of the hydrophobic organic compounds pyrene, dibenzofuran and phenanthrene from bioturbated freshwater sediments was studied in laboratory microcosms. Initial Tubificid oligochaete densities of 0, 6 700 and 2.67 x 10(4) individuals . m(-2) were employed. Under oxygen s aturated conditions, the difference between the contaminant fluxes fro m the high-density bioturbated microcosms and controls remained essent ially constant at 37 and 70 ng . cm(-2). d(-1) for pyrene and phenanth rene, respectively, corresponding to effective mass transfer coefficie nts of 0.16 and 0.37 cm/y. Under hypoxic conditions, worm defecation o n the sediment surface increased and led to significantly increased fl uxes to a maximum of 380, 490 and 940 ng . cm(-2). d(-1), for pyrene, phenanthrene and dibenzofuran, respectively. Average bioturbation flux es in the high-density microcosms of 246, 258 and 310 ng . cm(-2). d(- 1) for the respective compounds corresponded to effective mass transfe r coefficients of 1.7, 3.2, and 7.5 cm/yr. Initial release rates from medium-density microcosms (25% of high density) were typically half th e release rate of the high-density microcosms, indicating greater orga nism activity per individual at the lower density. The increased flux with the more soluble compounds likely reflects more rapid release at the sediment surface and the increased importance of porewater pumping over sediment particle reworking for migration of these compounds.