Action of Surfactants in Driving Ecotoxicity of Microplastic-Nano Metal Oxides Mixtures: A Case Study on Daphnia magna under Different Nutritional Conditions

Abstract

The series of experiments presented in the paper served to clarify the effects of contemporary exposure to surfactant, microplastics (polyethylene and polyvinyl chloride), and nanoparticles (TiO2 and ZnO) on the model organism Daphnia magna. Exposure was evaluated with respect to the age of the organisms (“young”, 24 hours old, and “aged” 10 days old specimens), trophic status (feeding or fasting), and the simultaneous presence of a surfactant. All the above-mentioned substances are present in the wastewater coming from various environmental sources from cosmetic products. The experiments were conducted in compliance with the OECD 202:2004 guideline, which is also a reference for ecotoxicity tests required by REACH. The results showed that surfactants enhance effects of toxicity produced by the exposure to the microplastic + nanoparticle mixtures. The influence due to factors such as nutrition (effect in fasting >> feeding conditions) and the age of individuals (effects in older >> younger animals) is essential. Concerning young individuals, exposure to PE-TiO2 is the most significant in terms of effects produced: it is very significant, especially in the presence of surfactant (both under fasting and feeding conditions). On the contrary, exposure to the PE-Zn mixture shows the minor effects. The comparison with the literature, especially as regards the possibility of interpreting the toxicity trends for the various mixtures with respect to the individual elements that compose them, leads to hypothesize additive effects still to be investigated and confirms the greatest toxicity contribution of TiO2.

Methods for controlled preparation and dosing of microplastic fragments in bioassays

“…Additionally, many previous studies coated microplastics in a thin layer of surfactant to achieve a homogenous distribution of particles in solution [46][47][48] . Surfactants can have toxic effects on aquatic organisms 49,50 and may also increase the proliferation of bacterial growth on the surface of microplastics 51 . Here, we introduce a novel ice cap dosing technique capable of producing accurate microplastic concentrations for experimental use.…”