Contaminants of concern in Dutch marine harbor sediments.

The status of the contamination of Dutch marine harbor sediments was reevaluated after a period in which emissions from point sources had been greatly reduced. Data on sediment chemistry from 1999 and 2000 were assessed against screening levels (SLs) selected from available sediment quality guidelines and representing a low probability of adverse biological effects. This yielded a ranking of the environmental hazard of 22 contaminants. Most of the sediments were silty material; every year 15 to 25 million m3 of such material is dredged from Dutch harbors. Some 34% of the volume exceeded one or more SLs. The contaminants of concern were tributyltin (TBT), mineral oil (petroleum hydrocarbons), polychlorinated biphenyls (PCBs), and mercury. The PCB and mercury contamination is the legacy of historic inputs; the TBT and mineral oil contamination is related to present-day shipping activity. Concentrations of trace metals, rare earth elements, organochlorine pesticides, and polycyclic aromatic hydrocarbons (PAHs) were low and apparently of minor environmental concern. It is concluded that the risk assessment would be improved by laboratory testing of adverse biological effects.

Environmental impact and recovery at two dumping sites for dredged material in the North Sea.

The environmental impact and recovery associated with the long and uninterrupted disposal of large volumes of moderately contaminated dredged material from the port of Rotterdam was studied at nearby dumping sites in the North Sea. Observations were made on sediment contamination, ecotoxicity, biomarker responses and benthic community changes shortly after dumping at the 'North' site had ceased and at the start of disposal at the new dumping site 'Northwest'. During the period of dumping, very few benthic invertebrates were found at the North site. Concentrations of cadmium, mercury, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs) and tributyltin (TBT) in the fine sediment fraction (<63 microm) from this site were 2-3 times higher than at the reference site. In four different bioassays with marine invertebrates the sediments showed no acute toxic effects. In tissue (pyloric caeca) of resident starfish Asterias rubens, residual levels of mercury, zinc, PCBs and dioxin-like activity were never more than twice those at the reference site. Four different biomarkers (DNA integrity, cytochrome P450 content, benzo[a]pyrene hydroxylase activity and acetylcholinesterase inhibition) were used on the starfish tissues, but no significant differences were found between North and the reference site. Minor pathological effects were observed in resident dab Limanda limanda. One year after dumping had ceased at the North site, a significant increase in the species richness and abundance of benthic invertebrates and a concomitant decrease in the fine sediment fraction of the seabed were observed. After 8.2 million m3 of moderately contaminated dredged material had been dumped at the new dumping site Northwest, the species richness and abundance of benthic invertebrates declined over an area extending about 1-2 km eastwards. This correlated with a shift in sediment texture from sand to silt. The contamination of the fine sediment fraction at the Northwest location doubled. It is concluded that marine benthic resources at and around the dumping sites have been adversely affected by physical disturbance (burial, smothering). However, no causal link could be established with sediment-associated contaminants from the dredged spoils.

Ecotoxicity Assessment of Contaminated Dredged Material with the Marine Amphipod Corophium volutator

The incorporation of toxicological data from bioassays can improve the present system of sediment quality criteria in the Netherlands. The use of acute lethality toxicity tests alone does not however provide sufficient discrimination and sensitivity for predicting ecological effects of slightly and moderately contaminated dredged material. Sublethal endpoints are needed for the assessment of environmental hazards of such dredged material. In this study, two approaches were used to identify toxicity of marine sediments collected from 16 locations classified as "slightly and moderately contaminated" on the basis of chemical data: (1) a comparison of growth vs. mortality as different endpoints in the marine amphipod Corophium volutator (Pallas); (2) an investigation on the use of sediment dilutions to characterize the degree of toxicity. The influence of sediment storage time on toxicity was also evaluated. In four out of 16 locations, mortality over 10 days of exposure ranged 80-100%; in two out of 16 locations mortality ranged 40-60%. In the other 10 locations, mortality was below 15%. Results on growth showed that in all locations final dry weight values were significantly lower (a factor of 1.5 to 3) than in controls. Results of dilution experiments showed that if sediments were diluted with a reference sediment of similar physicochemical characteristics, total concentrations of metals, mineral oil, and PAHs decreased as expected and so did the effects on C. volutator. In the 100% contaminated sediments growth was reduced by 32-60% compared to controls. The dilution rate necessary to reduce toxicity to the EC10 value for growth of C. volutator was considered an appropriate endpoint for the evaluation. When sediments were stored for a period of 3-5 months at 4 degreesC and retested, effects on mortality and growth decreased, although some effects on growth were still measured after 5 months of storage. The experiments illustrate the usefulness of ecotoxicity assessment to evaluate contaminted dredged material.