Abstract
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.