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, altering the bioavailability and subsequent toxicity of cadmium to ecologically important species such as Daphnia magna. The toxicity of cadmium to D. magna has been well-described; however, what is not known, and what this study aimed to address was how the addition of polyethylene microplastics altered cadmium toxicity. Using high-throughput feeding assays and size assessments, this study quantified effects of exposure to cadmium, microplastics, or their mixture on daphnids from neonate to adult. Exposure to cadmium inhibited feeding efficiency while exposure to microplastics inhibited growth rates of juveniles. Daphnia magna co-exposed to cadmium and microplastics showed significant decreases in both feeding and pre-reproductive 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 co-contamination of microplastics and cadmium has additive effects on feeding and growth rates, resulting in a greater energy allocation shift. This article is protected by copyright. All rights reserved. Environ Toxicol Chem 2023;00:0-0. © 2023 SETAC.