PLA Nanoplastics Accumulate but Do Not Cause Acute Toxicity to Marine Rotifers, Brine Shrimps, and Zebrafish Embryos

Conventional plastics are widely utilised across industrial sectors and in consumer products. However, the growing use of plastics has led to plastic pollution, including the formation of nanoplastics (NPs), which are harmful to aquatic organisms. Bioplastics are emerging alternatives. They are renewable and/or biodegradable and are supposed to be more environmentally friendly. However, the toxicity and environmental fate of bioplastics are not yet fully understood. This study evaluated the toxicity and fate of commercially available plain or fluorescent polylactic acid (PLA) NPs (250 nm) on aquatic organisms. Confocal microscopy demonstrated the uptake of fluorescent PLA NPs by the test organisms, marine rotifers (<i>Brachionus plicatilis</i>), brine shrimps (<i>Artemia salina</i>) and zebrafish (<i>Danio rerio</i>) embryos. However, the results of the bioassays indicate that plain PLA NPs did not induce acute toxicity in either of the two zooplankton species and did not cause substantial mortality, malformations, or hatching delays in zebrafish embryos at the tested concentrations (up to 100 mg/L). However, brine shrimp showed a significant decrease in ingestion capability. The biochemical biomarkers, catalase activity induction, as an indicator of oxidative stress, and acetylcholinesterase inhibition, as a marker of neurotoxicity, showed no significant alterations compared to the control of both zooplankton species and that of zebrafish embryos. Overall, the findings suggest a pattern of no acute and low sublethal toxicity for the tested plain PLA NPs in the studied organisms. Nonetheless, further research is imperative to comprehensively assess the environmental fate of bioplastics found in various consumer products, as these may contain harmful chemical additives, as well as the effects of prolonged exposure and their impact on physiological parameters, ensuring informed decisions before their widespread commercialisation and presence in the environment.