DEPURATION PROCESSES AFTER EXPOSURE OF BURROWING MAYFLY NYMPHS (HEXAGENIA-RIGIDA) TO METHYLMERCURY AND CADMIUM FROM WATER COLUMN OR SEDIMENT - EFFECTS OF TEMPERATURE AND PH

An experimental study, based on a complete experimental design, was se t up in order to analyse depuration processes after exposure of the bu rrowing mayfly nymphs Hexagenia rigida to cadmium (Cd) and methylmercu ry (MeHg) from the sediment or water column as initial contamination s ources. Actions and interactions of two abiotic factors (temperature a nd water column pH) were also quantified, from the combinations of two modalities for each parameter: temperature, 15 and 25 degrees C; pH, 5.0 and 7.5. Marked differences were observed in depuration kinetics i n relation to the metal studied and also to the exposure source during the contamination phase: results revealed a rapid and total eliminati on of Cd after 24 days whereas depuration of MeHg was progressive. The combined effects of temperature and water column pH were very weak on these phenomena, per opposition to their combined effects during the contamination phase.