TRACE-METAL LEVELS IN WATER, SEDIMENTS AND CHIRONOMUS GR THUMNI, FROMDIFFERENT WATER COURSES IN FLANDERS (BELGIUM)

Fourth instar larvae of the midge, Chironomus gr. thumni were collecte d at 12 sampling stations, belonging to 8 watercourses of different ty pes. Trace metal levels (cadmium, lead, copper and zinc) were measured in water, sediment and chironomids. Although high metal levels were m easured in water and/or sediment at many of the sample sites,no sedime nt-larvae, nor water-larvae relationship was found, except for cadmium . Only at one sampling site with very high surface water trace metal l evels, elevated metal concentrations were measured in the chironomids. Even when sampling sites of the same water quality composition and sa me substrate are considered independently from the other sites, no rel ationship was found. The results indicate that metal analysis of insec t-larvae is not only invaluable in the quality assessment of surface w ater, but is even more usefull as a means of monitorring heavy metal c ontamination in freshwater ecosystems than water or sediment analysis.