Evaldo Luiz Gaeta Espíndola

The presence of microplastics (MPs) in freshwater environments represents a growing environmental concern due to their persistence and ability to interact with contaminants such as pesticides. This study evaluated the influence of photodegradation on the toxicity of polyethylene microplastics (PE-MPs), alone and combined with the pesticide Imidacloprid (IMI), on the cladoceran Daphnia similis . Microparticles of polyethylene were aged under UV-C radiation for 94 days and subsequently characterized by Scanning Electron Microscopy (SEM) and Fourier-Transform Infrared Spectroscopy (FTIR). Surface analysis indicated polymer degradation through cracks and cavities, and increased surface roughness, while FTIR analyses showed polymer oxidation. Ecotoxicological results revealed that pristine MPs significantly reduced survival by 90% at 80 mg L ⁻¹ , while photodegraded MPs caused more pronounced sublethal effects, particularly on reproduction, with a 69.8% reduction in neonates at 140 mg L ⁻¹ . When associated with IMI, significant reductions in reproduction were observed, with a decrease of up to 75.7% in the number of neonates. However, the presence of IMI attenuated the toxicity of PE-MPs, evidencing an antagonistic interaction between the contaminants, particularly at concentrations of 80 and 140 mg L ⁻¹ of pristine PE-MPs. Taken together, these results demonstrate that the interactions between MPs and pesticides, as well as the state of particle degradation, significantly modulate ecotoxicological effects, posing a potential risk to the ecological integrity of aquatic ecosystems.

Metal discharges from anthropogenic activities are of great concern, and the effects of metallic mixtures in aquatic environments are still not fully understood. This study aimed to evaluate the effects of cadmium (Cd) and copper (Cu), isolated and combined, in the growth and photosynthesis – photosystem II (PSII) activity (Φ _PSII = F _v /F _M ), effective quantum yield, photochemical (qP) and non-photochemical quenching (qN and NPQ), and quenchings of regulated ((Y(NPQ)) and non-regulated ((Y(NO)) non-photochemical energy loss in photosystem II, in addition to the rapid light curves of the freshwater green microalga Ankistrodesmus densus . Both metals affected algal physiology and when combined most of the responses were antagonists, i.e., the observed effects were lower than those predicted for the mixture. The contaminants decreased the chlorophyll a production, photosynthetic activity, and increased heat dissipation, suggesting activation of the photoprotection mechanisms and with no evidence of photoprotection damage in the algae. Except for Y(NO), all evaluated photosynthetic parameters were sensitive indicators of the changes observed in microalgae under Cd and Cu exposure, isolated or combined. In addition, we suggest that algal protective mechanisms were efficient to decrease the impact of the combination of metals, reinforced by the increases in qN, NPQ and Y(NPQ), resulting mainly in antagonism in photosynthetic parameters.

Pesticides such as 2,4-dichlorophenoxyacetic acid (2,4-D) and fipronil pose potential risks in agricultural soils, and phytoremediation is a promising alternative to mitigate their ecotoxicity. In this study, the potential of three green manure species, Canavalia ensiformis, Dolichos lablab, and Mucuna pruriens, was assessed in terms of their ability to reduce soil ecotoxicity by examining the uptake of 2,4-D and fipronil, both individually and in a mixture. The experiments were performed with 20 µg kg^-1 of each pesticide, lasting 30 days, and the contaminants were quantified in soil and plant biomass (shoots and roots). However, the plants did not significantly reduce pesticide concentrations, and only fipronil residues were detected in plant biomass. Elutriate samples (1 soil: 4 water) were prepared with soil samples after the exposure period, and their ecotoxicity was evaluated using tests with the cladocerans Ceriodaphnia silvestrii, Ceriodaphnia dubia, and Daphnia similis, the larvae of the insect Chironomus sancticaroli, and the germination of Eruca sativa. Bioindicators were sensitive when exposed to elutriate samples, particularly E. sativa to 2,4-D, while the other species to fipronil. While the phytoremediation potential was limited, the uptake of fipronil indicates the possibility for further improvement in soil remediation.