Modeling Full Life-Cycle Effects of Copper on Brook Trout (Salvelinus fontinalis) Populations

Population models are increasingly used to predict population-level effects of chemicals. For trout, most toxicity data are available on early-life stages, but this may cause population models to miss true population-level effects. We predicted population-level effects of copper (Cu) on a brook trout (Salvelinus fontinalis) population based on individual-level effects observed in either a life-cycle study or an early-life stage study. We assessed the effect of Cu on predicted trout densities (both total and different age classes) and the importance of accounting for effects on the full life cycle compared with only early-life stage effects. Additionally, uncertainty about the death mechanism and growth effects was evaluated by comparing the effect of different implementation methods: individual tolerance (IT) versus stochastic death (SD) and continuous versus temporary growth effects. For the life-cycle study, the same population-level no-observed-effect concentration (NOEC_pop) was predicted as the lowest reported individual-level NOEC (NOEC_ind; 9.5 µg/L) using IT. For SD, the NOEC_pop was predicted to be lower than the NOEC_ind for young-of-the-year and 1-year-old trout (3.4 µg/L), but similar for older trout (9.5 µg/L). The implementation method for growth effects did not affect the NOEC_pop of the life-cycle study_. Simulations based solely on the early-life stage effects within the life-cycle study predicted unbounded NOEC_pop values (≥32.5 µg/L), that is, >3.4 times higher than the NOEC_pop based on all life-cycle effects. For the early-life stage study, the NOEC_pop for both IT and SD were predicted to be >2.6 times higher than the lowest reported NOEC_ind. Overall, we demonstrate that effects on trout populations can be underestimated if predictions are solely based on toxicity data with early-life stages. Environ Toxicol Chem 2024;43:1662-1676. © 2024 SETAC.