Effect of temperature on nickel uptake and elimination in Daphnia magna

Abstract

It is well known that temperature can affect the ecotoxicity of chemicals (including metals) to aquatic organisms. It was recently reported that nickel (Ni), a priority substance under the European Water Framework directive, showed decreasing chronic toxicity to Daphnia magna with increasing temperature, between 15 and 25 °C. We performed a toxicokinetic study to contribute to an increased mechanistic understanding of this effect. More specifically, we investigated the effect of temperature on Ni uptake and elimination in D. magna (in 4 clones) using an experimental design that included Ni exposures with different stable isotopic composition and using a one‐compartment model for data analysis. Both Ni uptake and elimination were affected by temperature, and some clear interclonal differences were observed. On average (across all clones), however, a similar pattern of the effect of temperature was observed on both Ni uptake and elimination, that is, the uptake rate constant (ku) and elimination rate constant (ke) during 72 h of Ni exposure were lower at 25 than at 19 °C, by 2.6‐fold and 1.6‐fold, respectively, and they were similar at 19 and 15 °C. This pattern does not correspond to the effects of temperature on chronic Ni toxicity reported previously, suggesting that Ni compartmentalization and/or toxicodynamics may also be affected by temperature. The data gathered with our specific experimental design also allowed us to infer that 1) the ku was up‐regulated over time, that is, the ku after 2 d of Ni exposure was significantly higher than the initial ku, by 1.5‐ to 2.3‐fold, and 2) the ke decreased significantly when the external Ni exposure was stopped, by 1.2‐ to 1.9‐fold. These 2 findings are in contrast with 2 commonly used assumptions in toxicokinetic models, that is, that ku is constant during exposure and ke is independent of external exposure. We suggest that future toxicokinetic studies consider these factors in their experimental designs and data analyses. Overall, our study contributes to the growing body of evidence that temperature affects toxicokinetics of metals (and chemicals in general), but at the same time we emphasize that knowledge of toxicokinetics alone is not necessarily sufficient to explain or predict temperature effects on (chronic) toxicity. Environ Toxicol Chem 2019;38:784–793. © 2019 SETAC

Extrapolating Metal (Cu, Ni, Zn) Toxicity from Individuals to Populations Across Daphnia Species Using Mechanistic Models: The Roles of Uncertainty Propagation and Combined Physiological Modes of Action

“…Populations were predicted to be equally or less sensitive than individuals. This prediction is in line with experimental evidence of the population‐level sensitivity of D. magna to metals (Pereira, Blust, et al, 2019; Vlaeminck et al, 2021). Our modeling study therefore suggests that standard individual‐level chronic endpoints (cumulative reproduction and survival) are conservative for single‐metal population effects across Daphnia species under the scenario that was considered in our simulations.…”

“…The simulations of population dynamics mimicked a laboratory microcosm experiment with daily food addition (0.4 mg dry mass L −1 day −1 ) in 500 ml of medium, a constant loss rate of food due to algal cell sinking (0.5 $${\mathrm{day}}^{-1}$$) and bi‐weekly 25% renewals of test medium (=proportional removal of residual food in the test medium). The capacity of DEB‐IBM models to predict population dynamics and effects of metals in similar scenarios has been demonstrated previously for Ni (Pereira, Blust, et al, 2019), Cu, and Zn (Vlaeminck et al, 2021) in D. magna . As population‐level endpoints, we used a carrying capacity (daphnids L −1 , approximated as population density averaged from day 49 to 56) and the initial growth rate.…”