Arbejdsrapport fra Miljøstyrelsen, 29/2005 – Effekter af forurenet sediment på bundfauna

Effekter af forurenet sediment på bundfauna

Summary and conclusions

The report "Effects of contaminated sediments on bottom fauna" summarises the relevant literature and in addition contain new statistical analysis based on data collected under the EMAP prorgamme in USA.

Environmental risk of contaminated sediments can be evaluated using a number of approaches. This report focuses on studies that aim to establish links between concentration of contaminants in natural sediment and effects on resident fauna. In contrast to tests carried out using single species exposed to either natural contaminated or spiked sediment the changes in resident benthic fauna will reflect the toxic effects of all contaminants in the sediment and integrate responses due to the natural variation in sediment characteristics, water quality ect.

The inherent drawback using such an approach is a large natural variability in the composition of benthos. In addition, the presence of numerous contaminants in sediments makes it difficult to quantify the role of individual contaminants. Therefore, to be able to quantify the influence of contaminants extensive data sets are required and moreover, the methods to collect samples, analyse for concentrations and taxonomic identification must be comparable and comply with accepted standards. To that end 7 different studies were selected for a thorough analysis. They each included between 40 and 500 samples/stations with synoptic data on sediment characteristics, concentration of contaminants and composition of benthos. Five studies also included tests of sediment toxicity to single species.

Overall, the analysis demonstrated that the species composition within benthos was very sensitive to sediment contamination. In studies from the US east coast and from Los Angeles and San Diego organic contaminants dominated the predicted (from single species test data) toxicity, however, statistical analysis consistently showed that heavy metals were the most influential on the composition of benthos. In Chesapeake Bay PAH's along with heavy metals were the main contaminants affecting the fauna, while the influence of PCB-congeners, DDT (and degradation products) and pesticides was low irrespective of high concentrations at numerous stations.

It was noticeable that the influence of sediment-bound Hg was low despite concentrations often exceeding sediment quality criteria and that TBT seemingly did not affect the fauna suggesting a low availability of sediment-bound TBT, which was suggested in a transplantation study also reviewed. In two case studies the lowest observed effect concentration was around 0.3 μg TBT g^-1 sediment.

Based on the studies reviewed and a series of statistical analysis it is concluded that composition of benthic fauna is a sensitive indicator for sediment contaminations and generally more predictable than the single species toxicity. Among 80 to 100 individual contaminants in sediments heavy metals (Cu, Cd, Pb, Zn) followed by PAH's general were the most influential. Therefore the Danish EPA's focus on Cu, Cd, Pb and benzo(a)pyrene in regulating dredging activities is warrented.

The analysis failed to document effects of sediment-bound Hg and TBT on benthos composition, however. Besides toxic effects the environmental risks of Hg also must include food-chain accumulation. This issue was not dealt with in this study.