Effects of Exposure to Cadmium, Microplastics, and Their Mixture on Survival, Growth, Feeding, and Life History of Daphnia magna

There is concern that microplastics can act as a vector for cadmium (Cd), altering the bioavailability and subsequent toxicity of Cd to ecologically important species such as Daphnia magna. The toxicity of Cd to D. magna has been well described; however, what is not known, and what the present study addresses, was how the addition of polyethylene microplastic altered Cd toxicity. Using high-throughput feeding assays and size assessments, the present study quantified effects of exposure to Cd, microplastic, or their mixture on daphnids from neonate to adult. Exposure to Cd inhibited feeding efficiency, while exposure to microplastic inhibited growth rates of juveniles. Daphnia magna coexposed to Cd and microplastic showed significant decreases in both feeding and prereproductive growth rate. There were no differences in life-history traits across any treatments. The alterations of feeding and growth while maintaining reproductive endpoints (time to first brood, reproductive frequency, the number of neonates released at each reproductive event, and the size of neonates produced) might be the result of a shift in energy allocation away from somatic growth, allowing individuals to maintain reproductive output despite lower nutritional reserves. Our findings suggest that cocontamination of microplastic and Cd has additive effects on feeding and growth rates, resulting in a greater energy allocation shift. Environ Toxicol Chem 2023;42:1401-1408. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.