Although chronic contamination by silver ions (Ag+) can persist in aquatic systems over long periods of time and can therefore have an impact on population developments, regulatory testing commonly relies on single-generation endpoints. Here, we used Daphnia magna to quantify long-term effects of pg/L to ng/L concentrations of Ag+ across generations and to test whether recovery depends on exposure history. Using 21 d life-cycle assays over up to seven consecutive generations, we quantified survival, key life-history traits, and population fitness (intrinsic rate of natural increase, r). In our study, low environmental concentrations of Ag+ caused minimal mortality, but sublethal effects persisted or multiplied over generations. Notably, continuous exposure led to significant reductions in body length and r at 50 pg/L (nominal LOEC) by the fourth generation exposed, representing population-relevant effects of Ag+ at very low concentrations which should be given consideration in the assessment of both water quality and the chemical itself. Recovery was concentration-dependent: low-concentration-exposed lineages recovered within a few generations, whereas 15 ng/L exposure resulted in persistent deficits even through the recovery period of three generations. Exposure-history patterns indicated that long-term outcomes were dominated by the cumulative number of exposed generations. These findings highlight the limitations of acute and single-generation assays and emphasize the importance of considering information on the effects of chemicals, including Ag+, across multiple generations in risk assessments. They also highlight the need to include expectations regarding recovery after the removal of pollutants in these assessments.
Ding et al. (Thu,) studied this question.