The induction of metallothioneins during pulsed cadmium exposure to Daphnia magna: Recovery and trans-generational effect

• Exposure duration played a decisive role in MT induction.
• There was a delayed effect in MT induction.
• The tolerance recovered in exposed generation, but that of offspring was reduced.
• Although the MT levels of F1 were higher than that of F0, the more detoxification effect of them have not been found.

Although the importance of pulse exposure has gained ground in recent years, there were few studies on recovery and trans-generational effect of it. Two successive generations Daphnia magna were exposed to cadmium (Cd) pulses for 6 h at the concentrations from 40 to 100 µg/l. The changes of tolerance and induction of MTs in exposed D. magna and their offspring were measured. The reduced tolerance of exposed D. magna was returned to levels similar to control after about 9 days in a generation. The level of MT still increased up to 3 days after exposure. In the experimental range, exposure duration played a decisive role in MT induction. The tolerance of F1 was lower than F0 and decreased with increasing pulsed concentrations of F0. Exposed to the same pulse, the MT levels of F1 were higher than the MT levels of F0, but the more obvious detoxification of MT in F1 had not been found. Our results suggest that pulsed cadmium exposure had impact on offspring of exposed organism and the risk assessment should take trans-generational effect into account.