Toxicity of nanoplastics to zooplankton is influenced by temperature, salinity, and natural particulate matter

Abstract

Plastic pollution is ubiquitous and understanding its environmental effects is a matter of urgency. Nanoplastics (NPs) are the smallest class of plastic pollution, and may elicit more detrimental biological effects than larger plastic particles. However, nanoplastic toxicity may depend on variable environmental parameters, such as temperature, salinity and the presence of other particulate matter—a parameter set too large for conventional toxicity measurement approaches. We applied a high-throughput approach to examine toxic effects of NPs on A. franciscana across 112 combinations of temperature (three levels, 15–29 °C), salinity (four levels, 35–261 g L⁻¹ salts), and particulate matter (humic acids or natural colloids at 5 g L⁻¹, or none) and NP particles (4 levels, 0–100 mg L⁻¹). The influence of experimental conditions on toxicity to A. franciscana strongly depended on NP surface charge. We did not observe any effects from negatively charged NPs over 48 hours. There was not any mortality caused by positively charged NPs below 100 mg L⁻¹ at room temperature (22 °C), but there was decreased survival and motility by more than 50% at higher salinities and warmer temperature. The extent to which natural particulates mitigated nanoplastic toxicity to A. franciscana (up to 20%), and the retention of NPs inside A. franciscana were also temperature- and salinity-dependent. In sum, we found nanoplastic toxicity to A. franciscana varies greatly across ecologically relevant ranges of temperature and salinity, highlighting the importance of environmental conditions to nanoplastic effects on this species. Our findings hinged on the combinatorial experimental treatments that our automated system enabled, demonstrating the power of high-throughput platforms for ecotoxicology.