Heavy metals in various Belgian benthic invertebrates

Context of the study

In the Belgian coastal waters comes most of the contamination from dredging disposals. Many species (flatfish, mussels,...) are studied continuously as part of monitoring programs. In addition to this the benthic communities are monitored as well.

Content of the study

This study analyzed heavy metal contents in benthic invertebrates between 1981 and 1996. The animals were caught at 10 locations in the Belgian part of the North Sea. The study aimed to detect trends in the concentrations of mercury (Hg), cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn) and chrome (Cr) in the benthic organisms. The sampled animals were: starfish, brown shrimp, hermit crab, swimming crab and cut through shell.

Main results of the study

In almost all locations the concentrations for all heavy metals in the animals showed a decreasing trend over the 15 year study period. At one location (the Bligh bank) however an increase in copper and zinc concentrations was observed in brown shrimp and hermit crabs. The reason for this increase in unclear, but might be related to the dumping of wast products in the Bligh bank. The overall decrease in contamination is very likely to have been caused by both the lesser input of form the Scheldt river and by reduced contamination by dredging activities. Concentrations for most metals were also comparable between the different sampling sites. Chromium however did seam to have lower concentrations in 3 of the 5 species sampled at the Bligh bank. In contrast, copper concentrations in brown shrimp appeared to be higher at this location. The reason for not finding higher concentrations in animals at dumping sites of dredged soils might be that these soils are dumped over a large area and are dispersed widely by strong ocean currents.