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Effects of organic enrichment, oxygen availability and the presence of contaminants on three sediment-dwelling invertebrates, the polychaete Nereis (Hediste) diversicolor, the bivalve Abra alba and the brittle star Amphiura filiformis, were assessed using growth, arm regeneration and biomarkers (metallothionein-like proteins, glutathione reductase, glutathione S-transferase) in a 93-day microcosm experiment. Moderate organic enrichment (approx. 40 g C m-2) increased growth and hypoxia (2.4-3.5 mg l-1) decreased growth in all three species. Effects of organic enrichment and low oxygen availability were additive for growth in N. diversicolor and A. filiformis, whereas there was an interaction between hypoxia and organic enrichment in their effects on growth in A. alba, reflecting a decreased ability of this species to utilize the available organic material under hypoxic conditions. Sediment-bound contaminants (4.8 mg kg-1 Cd and 1.32 mg kg-1 benzo[a]pyrene) had minor effects ongrowth and arm regeneration. Some biomarkers in N. diversicolor and A. filiformis reflected tissue contaminant concentrations, whereas there was no response of biomarkers in A. alba to any treatment or contaminant. [ABSTRACT FROM AUTHOR]

A major environmental issue is to understand how eutrophication processes, such as organic enrichment and hypoxia may act on the distribution patterns and bioavailability of contaminants to benthic organisms. An experiment with sediment organic C content (control vs enrichedwith concentrated phytoplankton) and oxygen level (normoxia vs 2-3 mg O2 l-1) as fixed factors, and 14C-B(a)P in benthic organisms and sediment as dependent variable, was conducted for 93 days. Three species of sediment-dwelling organisms with different feeding strategies (Amphiura filiformis, Nereis diversicolor and Abra alba) were chosen. Blue mussels (Mytilus edulis), kept in separate aquaria, were exposed to the outflowing water of the microcosms. Concentration of 14C-B(a)P in the sediment surface at the end of the experiment was significantly higher in the organically enriched sediments than in the control sediments. Accumulation of14C-B(a)P in A. filiformis and N. diversicolor was also higher in the presence of organic enrichment. Concentrations of 14C-B(a)P in M. edulis placed downstream of aquaria treated withorganic matter were also higher, indicating a higher leaching of bioavailable 14C-B(a)P from the enriched sediments. Hypoxia had no significant effect on the sediment distribution and bioaccumulation of 14C-B(a)P, and there was no significant interaction between hypoxia and organic enrichment. Our results support the concept of selective feeding on labile organic matter as a major exposure route of organic contaminants in benthic organisms. [ABSTRACT FROM AUTHOR]

In marine environments influenced by human activities, the sea-bed is a major recipient of both contaminants and organic matter. Deposition and recycling of contaminants from bottom sediments may be affected by the eutrophication status of the area. Contaminants and eutrophication factors may also interact to affect bioaccumulation as well asthe growth, health and reproduction of benthic organisms. Consequently, from an environmental management point of view, these interactions should be considered when decisions are made about input of contaminants and organic matter to the aquatic environment. In order to elucidate interaction patterns between eutrophication and contaminants, radio-labeled contaminants were applied in a large scale experiment performed at Marine Research Station Solbergstrand, situated by the Oslofjord, Norway. The continuous flow through experiment was performed in glass aquaria containing three sediment-dwelling species (Abra alba, Nereis diversicolor and Amphiura filiformis) placed in marine claysediments. Blue mussels (Mytilus edulis) were kept in separate downstream aquaria and exposed to the outflowing water from the sediment aquaria. In 12 contaminated aquaria the sediment was spiked with 203Hg (0.23 mg Hg kg-1 dry sediment), 109Cd (5 mg Cd kg-1) and 14C-benzo[a]pyrene (1 mg BaP kg-1). In 12 organically enriched aquaria, phytoplankton (2 mg C kg-1 dry sediment) was initially mixed into thesediment and two months later another batch corresponding to 20 g C m-2 was added to the aquaria. Finally, the concentration of oxygen was continuously lowered from 7-9 mg O2 l-1 in 12 well-oxygenated aquaria to 2.4-3.5 mg O2 l-1 in 12 low-oxic aquaria by purging the source water with nitrogen. Allowing three replicate aquaria for each treatment, all combinations of the two levels (high/low) of the three factors (contaminants, [ABSTRACT FROM AUTHOR]

Partitioning of 14C-2,2',4,4'-TCB (tetrachlorobiphenyl) between sediment, and water and suspended particles was studied in eutrophic and oligotrophic benthic microcosms, respectively. Microcosms consisted of glass aquaria with homogenized clay sediment, circulatedwith natural seawater (60 m, 340/00). Organic enrichment in the eutrophic treatment was obtained by adding a phytoplankton culture of themarine diatom Phaeodactylum tricornutum into the water column; the oligotrophic aquaria received only filtered seawater. 14C-TCB was added to the water using a generator column technique. Phytoplankton and TCB were continuously added during an exposure phase of 8 days, followed by a semi-static phase in which TCB and phytoplankton were left to equilibrate and sediment during one month. Presence of phytoplankton induced a higher concentration of TCB in the water column. Higher concentration of TCB in the water was not caused by higher amounts of TCB bound to algal cells but due to an association of TCB with an increased production of dissolved organic matter and bacteriain the eutrophic treatment. TCB concentration in the sediments was not significantly different between treatments. The observed partitioning of TCB between water and sediment was in accordance with a predicted distribution, based on the equilibrium partitioning model. [ABSTRACT FROM AUTHOR]