INFLUENCE OF WATER HARDNESS ON ACCUMULATION AND ELIMINATION OF CADMIUM IN 2 AQUATIC MOSSES UNDER LABORATORY CONDITIONS

This study investigated the effect of water hardness on the accumulati on and elimination of cadmium (Cd) by two aquatic mosses, Fontinalis d alecarlica and Platyhypnidium riparioides, under laboratory conditions . The two mosses were exposed to nominal Cd concentrations of 0, 0,8, 2, and 10 mu g.L-1, which includes the concentration range generally f ound in nature. The influence of three levels of water hardness (very soft: 11.7 mg.L-1; soft: 44.2 mg.L-1; and hard water: 92.3 mg.L-1 as C aCO3) was measured while maintaining the alkalinity and pH constant du ring the 28-day exposure, The Cd accumulation by the aquatic mosses wa s rapid, showing the potential of accumulation and the sensitivity of this biomonitor. Even if the actual Cd concentration in the water was low (concentration <0.15 mu g.L-1 to 6.82 mu g.L-1 of Cd), the uptake of Cd was very fast and mostly linear. This study was conducted in wat er hardness comparable to that found in the Canadian shield (hardness was (100 mg.L-1 as CaCO3). When the actual Cd concentration in the wat er was as high as 6.82 mu g.L-1, the uptake of Cd was mostly linear an d the steady state condition was not reach. Accumulation rates of Cd w ere significantly different when the mosses were in very soft (11.7 mg .L-1) as compared to hard water (92.3 mg.L-1 as CaCO3). The eliminatio n of Cd followed a very slow process for the two species studied. The elimination rates of Cd from the mosses were not influenced by water h ardness.