Impact of bioturbation by Arenicola marina on the fate of particle-bound fluoranthene

Abstract

The fate of particle-bound 14C-fluoranthene deposited at the sediment-water interface in microcosms with different densities (0 to 300 m-2) of Arenicola marina was followed for 28 d. Worms had a pronounced effect on the degradation rate of fluoranthene. Defecated material quickly buried the surface layer of 14C-fluoranthene into deeper layers of the sediment, where degradation of fluoranthene was much slower than at the more reactive surface sediment in microcosms without A. marina. Only 0.3 and 2.9% of 14C-fluoranthene was mineralised to 14CO2 after 28 d in treatments with and without A. marina, respectively. There was no significant difference between degradation rates among different densities of A. marina, although the mixing of fluoranthene into deeper sediment layers was enhanced at higher worm densities. The DO14C and PO14C (particulate and dissolved organic 14C) in the overlying water were negatively related with worm density. The ventilating currents of A. marina may have repositioned 14C-activity from the water into deeper sediment layers, which then acted to filter both dissolved and bound fluoranthene. 14C-activity was high in worms after 28 d, approximately an order of magnitude higher than that mineralised to 14CO2 during this period. The removal of deposited organic contaminants on sediment surfaces through degradation at the highly reactive sediment-water interface or through local transport by currents or wave action can be reduced as a result of burial of contaminants by bioturbating organisms. Contaminants may thus persist longer in the sediment environment and will be released from the sediment over a prolonged period of time. Enhanced biological transport of contaminants to depth can lead to increased exposure of infauna.