Active uptake of aluminium, copper and manganese by the freshwater amphipod Paramelita nigroculus in acidic waters

Experiments were performed on the freshwater amphipod Paramelita nigroculus to determine the route of uptake for Al, Cu and Mn. The extent of correlation between the concentrations of Al, Cu and Mn and those of macro-cations Na, Ca and Mg was investigated in order to determine appropriate strategies of water quality management. Indeed, active uptake of toxicants can be controlled by disturbing the active pump used. After 21 days of exposure to different combined concentrations, survivors were analysed chemically by ICP-S after depuration, drying, ashing and digestion with concentrated nitric acid.The results showed significant correlations between the concentrations of major cations and the three metals under study (i.e. Al, Cu and Mn) at p < 0.05. These are Ca vs Al, Ca vs Mg, Na vs Mg, Na vs Mn, Al vs Mg, Al vs Cu, and Mg vs Mn. No other combination showed significant correlation. High r-values for Na vs Mg (r=0.7194) and for Na vs Mn (r=0.6253), as well as low concentrations of Mg and Mn, suggest interactions between the active uptake of Mn and Mg, although there may be interferences due to the use of Na pump. Additional experiments examined the type of interaction occurring when Mn and Mg were present in 1:1 mixtures in water. The Student's t test showed that observed differences in bioaccumulation of Mn, when alone and when combined, were not statistically significant at p < 0.05. These differences may be attributed to chance but not to the presence of Mg in the medium; while differences in bioaccumulation of Mg, when alone and when combined, were statistically significant at p < 0.002. These were attributed to Mn, which lowers Mg uptake by P. nigroculus.