title: Effect of sediment-chemical contact time on availability of sediment-associated pyrene and benzo
abstract: Hydrophobic organic chemicals achieve equilibrium in sediments and soils by adsorption and desorption processes driven by diffusion into organic material of particle aggregates. Exposure of benthic animals to contaminated sediments results in bioaccumulation and, in theory, a steady state is established between sediment organic carbon and the organism lipids. The purpose of this study was to test the importance of sediment-chemical contact time in bioaccumulation of pyrene and benzo[a]pyrene to the freshwater oligochaete, Lumbriculus variegatus. Also, the applicability of semi-permeable membrane devices (SPMDs) in mimicking accumulation of sediment-associated chemicals by benthic invertebrates was evaluated. Feeding and nonfeeding animals were exposed to dual spiked lake sediment in five consecutive 144 h accumulation tests. SPMDs were exposed in five consecutive single point 12 h exposures to test the effect of aging of sediment on accumulation. SPMDs were also exposed in a 28 day accumulation test to determine uptake rate coefficients. Increase in sediment-chemical contact time decreased pyrene and benzo[a]pyrene uptake clearance coefficients of successive exposures for both feeding and nonfeeding animals. This decrease in bioavailability was strongest at the start of contact and slowed down with time. Ingestion of sediment considerably increased accumulation of both compounds indicating the importance of feeding behavior in bioaccumulation of sediment-associated chemicals. The significance of ingested sediment as uptake route for pyrene varied between exposures. This was probably due to combined effect of variable ingestion rate and decreasing bioavailable fraction of chemical. Availability of PAHs decreased also for SPMDs with increasing sediment chemical contact time. SPMDs reached curvilinear portion of overall uptake curve in 28 days and calculated uptake clearance constants (k(s), g sediment/g SPMD per hour) corresponded to constants calculated for nonfeeding organisms. The results of this work emphasize the significance of sediment-chemical contact time in bioaccumulation and the importance of feeding behavior of deposit feeders in bioaccumulation of sediment-associated contaminants. Both should be taken into account when performing and modeling bioaccumulation of sedimented contaminants. Furthermore, uptake of sediment-associated PAHs by SPMDs appeared to mimic uptake by nonfeeding organisms. However, more research is needed to compare the uptake of artificial devices to sediment-dwelling species in sediment exposures.
authors.affiliation: Department of Biology, University of Joensuu, PO Box 111, FIN-80101, Joensuu, Finland
authors.initials: MT
authors.lastname: Leppänen
authors.initials: JV
authors.lastname: Kukkonen