MERCURY CONTAMINATION OF THE BELGIAN AVIFAUNA 1970-1981

Birds (200) found dead in Belgium between 1970-1981, and belonging to 30 spp., were analyzed for total Hg contamination. The contamination of aquatic birds ranged between 0.11-35 .mu.g/g wet wt. For terrestrial birds, the extreme values were: not detectable-14 .mu.g/g. In both cases, differences in diet explained the differences in contamination. The order of diets associated with increasing Hg contamination for aquatic birds was invertebrates, zooplankton and garbage and fish, and for terrestrial birds this consisted of plants, invertebrates, mammals and birds. For raptors and owls, this effect of diet included geographical variations within species. A higher Hg contamination level in the winter and early spring was noted for 2 spp. of owls. For aquatic birds, the contamination of liver was higher than that of kidney, with ratios varying between 1.2-2.5. For terrestrial birds, the ratio was closer to 1. A few determinations were also made for muscle and heart, giving, respectively, 0.25 and 0.6 of the liver contamination. Among the birds analyzed for their liver contamination, 15% showed levels > 3 .mu.g/g and could have been affected in their reproduction; 3% had levels > 10 .mu.g/g and could have died from Hg poisoning; and 6% showed an abnormally high liver:kidney ratio, which could have reflected an acute intoxication. There existed a striking parallelism between the levels of Hg and of organochlorine residues (DDT) in birds of prey, suggesting the existence of common ecotoxicological mechanisms.