Single and combined toxicity of amino-functionalized polystyrene nanoparticles with potassium dichromate and copper sulfate on brine shrimp Artemia franciscana larvae

The increasing use and disposal of plastics has become a persistent problem in the marine environment, calling for studies that refer to realistic scenarios to understand their effects on biota. Particularly, the understanding about the effects of co-exposure with nanoplastic particles and metals on aquatic organisms is still limited. The present work aimed to investigate the acute toxicity of amino-functionalized polystyrene nanoparticles (PS-NH2; 50 nm) as proxy for nanoplastics on brine shrimp Artemia franciscana larvae under different culture conditions and at different stages of development, as well as the combined effect with two reference toxicants - potassium dichromate (K2Cr2O7) and copper sulfate (CuSO4). Nauplii (instar II or III larval stages) were exposed to different concentrations of PS-NH2 (0.005 to 5 μg mL-1) for up to 48 h, with or without agitation in order to mimic a more realistic environmental scenario. Larval mobility and PS-NH2 accumulation were monitored under microscopy. PS-NH2 alone showed toxicity only at the highest concentration tested (5 μg mL-1) regardless the incubation method used (61.2 + 3.1% and 65.0 + 4.5% with and without agitation, respectively). Moreover, instar III stage was the most sensitive to PS-NH2 exposure (38.2% immobility in 24 h of exposure; 5 μg mL-1). Evidence of PS-NH2 retention in the gastrointestinal tract in a concentration- and time-dependent manner was also obtained. Mixtures of PS-NH2 (0.005 and 5 μg mL-1) with different concentrations of K2Cr2O7 increased the immobilization rate of the larvae after 48 h of exposure, when compared to the K2Cr2O7 alone. Similar results were observed for CuSO4 in the co-exposure conditions at different concentrations. However, exposing nauplii to a mixture of PS-NH2 (0.005 μg mL-1) and CuSO4 decreased immobilization rate, in comparison to the group exposed to CuSO4 alone. The present work highlights the potential risk posed by nanoplastics to zooplanktonic species through their interaction with other toxicants.