Influence of bioturbation by the amphipod Corophium volutator on fluoranthene uptake in the marine polychaete Nereis virens

The uptake kinetics of fluoranthene in the polychaete worm Nereis virens we re investigated in the presence and in the absence of amphipods to examine the effects of sediment bioturbation by the benthic amphipod Corophium volu tator on the uptake in worms. Worms only and worms together with two differ ent densities of amphipods were exposed to fluoranthene-spiked sediment for 12 d. Worms and overlying water samples for fluoranthene analyses were tak en and total suspended solids in water column were measured after 1, 2, 5, 8, and 12 d. Results showed that in all treatments fluoranthene was rapidly accumulated by N. virens during the first two days and a steady state was reached within five days of exposure. Biota to sediment accumulation factor s normalized to lipid concentration and to sediment organic carbon (BAF(loc )) of worms exposed with the highest number of amphipods were significantly higher (two to three times) compared to worms exposed with fewer or withou t amphipods after one and two days of exposure. Bioconcentration factors (B CFs), calculated as the ratio between the uptake (k(1)) and elimination (k( 2)) rate constants were not significantly different among treatments. When BCFs were calculated on the basis of dissolved fluoranthene concentrations (BCFdiss), values of the treatments where worms were exposed with 100 and 3 00 amphipods were slightly higher than those calculated on the basis of tot al (dissolved + particle-bound) aqueous fluoranthene (BCFtot). However, the presence of fluoranthene bound to dissolved organic matter could have acco unted for lower than expected BCFdiss values. The results suggest that biot urbation by amphipods affected the concentration of fluoranthene in the wor ms not by changing the worm to water partitioning (k(1)/k(2)) but by changi ng the worm to sediment partitioning (BAF(loc)). In the treatments with wor ms a higher mortality of amphipods was found compared to those without worm s. The presence of worms might have contributed to lower BCF values than ex pected.