CADMIUM, LEAD, MERCURY AND CESIUM-137 IN FRUTICOSE LICHENS OF NORTHERN QUEBEC

Cadmium, lead and mercury concentration averaged 0.171, 4.09 and 0.09-mu-g . g-1 (dry wt.) respectively, in terrestrial lichens over a 640 000-km2 study area of northern Quebec; the average cesium level reached 378 Bq . kg-1 (dry wt.). Cadmium and lead were the most closely related pollutants in lichens, while there was little relationship between 137 cesium and the three trace metals. The distribution of the elements over the territory was not uniform and the altitude influenced three of them. The cesium concentration increased along with this variable, while lead levels were higher in the middle altitude class (200-400 m) than in the two other classes. There was a significant interaction between attitude and biome for mercury concentration, this element being almost twice more abundant in the tundra below 400 m than in the forest tundra and the boreal forest. The mercury level was related to percent ground cover by Alectoria ochroleuca, Cornicularia divergens and Cetraria nivalis, three lichen species typical of a wind-exposed habitat. Lead concentration was related only to Cornicularia divergens ground cover. In general, the concentrations of cadmium, lead and mercury were higher in the northwest quarter of the study area than elsewhere, while cesium contamination was highest in the southeast quarter. It seems preferable that caribou should be harvested at low elevation when they are taken in winter in order to minimize the risk associated with cesium consumption by humans.