While the combined presence of global climate change and nanosized plastic particle (i.e., nanoplastic) pollution is clear, the potential for interactions between climate-change-shifting environmental parameters and nanoplastics is largely unknown. Here, we aim to understand how nanoplastics will affect species in concert with climate change in freshwater ecosystems. We utilized a high-throughput full-factorial experimental system and the model photosynthetic microorganism Scenedesmus obliquus to capture the complexity of interacting environmental stressors, including CO2, temperature, light, and nanoplastics. Under a massive number of conditions (2000+), we consistently found concentration-dependent inhibition of algal growth in the presence of polystyrene nanoparticles, highlighting a threat to primary productivity in aquatic ecosystems. Our high-treatment experiment also identified crucial interactions between nanoplastics and climate change. We found that relatively low temperature and ambient CO2 exacerbated damage induced by nanoplastics, while elevated CO2 and warmer temperatures reflecting climate change scenarios somewhat attenuated nanoplastic toxicity. Further, we revealed that nanoplastics may modulate light responses, implying that risks of nanoplastic pollution may also depend on local irradiation conditions. Our study highlights the coupled impacts of nanoplastics and climate change, as well as the value of full-factorial screening in predicting biological responses to multifaceted global change.

Hydrogen peroxide (H2O2) is a common control measure for cyanobacterial harmful algal blooms (cyanoHABs), but local contaminants may alter its effects. Here, we aim to understand the control of cyanoHABs by H2O2 in light of nanoplastic contamination using a multistressor framework. We utilized a high-throughput full-factorial experiment to capture the multistressor impacts of H2O2, nanoplastics, temperature, and light on a toxigenic strain of the freshwater cyanobacterium Microcystis aeruginosa. In addition to revealing independent inhibitory effects of H2O2 and nanoplastics on cell abundance and microcystin production, our high-throughput system also identified non-additive, interactive effects. Specifically, we found that nanoplastics weakened the inhibitory effects of H2O2 on cell abundance and microcystin production. In addition, we discovered that nanoplastics restricted the degradation of H2O2, partially explaining this non-additive effect. Because combined H2O2 and nanoplastic still curbed growth, we expect H2O2 will remain an effective control measure even with background nanoplastic pollution. Our findings illustrate the importance of taking local stressors, including anthropogenic contaminants such as nanoplastics, into account before H2O2 is applied to control cyanoHABs.

We now know that nanoplastics can harm aquatic organisms, but understanding ecological risk starts with understanding fate. We coupled population balance and fugacity models to predict the conditions under which nanoplastics remain as single particles, aggregate, or sediment and to predict their capacity to concentrate organic pollutants. We carried out simulations across a broad range of nanoplastic concentrations, particle sizes, and particle−particle interactions under a range of salinity and organic matter conditions. The model predicts that across plastic materials and environmental conditions, nanoplastics will either remain mostly dispersed or settle as aggregates with natural colloids. Nanoplastics of different size classes respond dissimilarly to concentration, ionic strength, and organic matter content, indicating that the sizes of nanoplastics to which organisms are exposed likely shift across ecological zones. We implemented a fugacity model of the Great Lakes to assess the organic pollution payload carried by nanoplastics, generating the expectation that nanoplastics would carry nine times more pollutants than microsized plastics and a threshold concentration of 10 μg/L at which they impact pollutant distribution. Our simulations across a broad range of factors inform future experimentation by highlighting the relative importance of size, concentration, material properties, and interactions in driving nanoplastic fate in aquatic environments.