Ecotoxicidade de parabenos em organismos aquáticos: a Interação entre microplásticos de polietileno e metilparabeno nos estágios iniciais de desenvolvimento do zebrafish (Danio rerio)

Abstract

Emerging contaminants are substances of anthropogenic origin detected in the environment in various concentrations, but without a clear ecotoxicological profile and outside the scope of environmental legislation. Growing industrialization introduces more and more substances and materials into environmental matrices, raising concern about the possible harmful effects on biota and human health. Of particular note are microplastics, particles smaller than 5 mm and ubiquitous in aquatic environments. Their predominantly hydrophobic structure is capable of adsorbing organic substances and heavy metals, concentrating them and potentially increasing their toxicity to aquatic organisms. Parabens, esters of p-hydroxybenzoic acid, are preservatives found in low concentrations in aquatic environments, and their toxicity could be increased when adsorbed by microplastics. The toxicity of microplastics and parabens, along with their possible interactions, were addressed throughout this dissertation. Firstly, a literature review was carried out on the state-of-the-art knowledge on the bioaccumulation and ecotoxicity of parabens in aquatic organisms of different phyla. This revealed a small number of field studies evaluating bioaccumulation and biomagnification of parabens in aquatic organisms, with underrepresentation of certain groups and results that varied according to the location, type of organism and tissue analyzed. In addition, there was great heterogeneity in the experimental protocols and concentrations used, a predominance of a few model species and low use of analytical controls. There was also an increase in the number of studies over time, especially between 2020 and 2023, as well as in the variability of biomarkers and metabolic pathways analyzed. Subsequently, the zebrafish embryotoxicity test (ZELT) tested the hypothesis that exposure of zebrafish (Danio rerio) embryos and larvae to a combination of three different environmentally relevant concentrations of methylparaben (MeP — 0. 01, 0.1 and 1 µM) with polyethylene microplastics (MPPE — ~35 µM, 3 mg/L) would lead to more pronounced embryotoxic effects, 01, 0.1 and 1 µM) with polyethylene microplastics (MPPE, ~35 µM, 3.4 mg/L) would lead to more pronounced embryotoxic effects than with isolated exposure to each of the two contaminants, as well as the hypothesis that MeP toxicity is concentration-dependent. The ZELT results suggest that environmentally relevant concentrations of MeP are capable of eliciting cardiotoxicity in zebrafish embryos, although the hypothesis that mixing with MPPE amplifies its toxicity has not been confirmed. In addition, the relevance of the size of MPPE in its ecotoxicological effects and the possibility of a reduction in the toxicity of MeP in zebrafish embryos with the use of larger particle sizes are highlighted. Attention is drawn to the need for further studies using realistic concentrations and exposure routes, in order to obtain a more accurate picture of the consequences of the presence of such contaminants in aquatic environments.