Como o fotoenvelhecimento modula a adsorção de contaminantes por microplásticos? Uma síntese quantitativa baseada em meta-análise de três níveis

Abstract

Microplastic pollution is a significant environmental challenge, especially in aquatic ecosystems, due to its ability to act as a vector for emerging contaminants such as heavy metals, pesticides, and pharmaceuticals. Among the processes that modulate this interaction, photoaging stands out, mainly induced by ultraviolet radiation exposure, which promotes physicochemical changes in polymers, such as increased surface roughness, oxidation, and the formation of carbonyl and hydroxyl groups. These alterations can either enhance or reduce the adsorption potential of Mps, depending on environmental conditions, thereby impacting their role as pollutant vectors. This study aimed to quantify the effects of photoaging on contaminant adsorption by Mps and to identify the main experimental and environmental factors modulating this response. A multilevel meta-analysis was conducted based on 30 independent studies and 256 quantitative comparisons. The log-transformed ratio of means (lnRR) was used as the effect size, applied in three-level random-effects hierarchical models to account for the high heterogeneity between studies (I² = 81.64%) and to identify significant moderators. Results showed that photoaging increased, on average, contaminant adsorption by 132%, with this effect present in 72% of the comparisons analyzed. Three moderators had a statistically significant impact: polymer type, hydrophobicity (even when reduced by oxidation), and medium pH. Acidic pH favored the adsorption of cations (e.g., metals), while basic pH favored the adsorption of anions (e.g., pesticides). In contrast, factors such as salinity, UV exposure time, and contaminant class showed no relevant isolated effect. These findings indicate that tropical regions, with high UV radiation and acidic pH, are particularly vulnerable, since polymers such as PE, PP, and PS—the most common in the environment—become significantly more effective at adsorbing pollutants after photoaging. The study highlights the need to standardize photoaging and surface characterization protocols to enhance the understanding of isolated phenomena. It is concluded that identifying the factors that modulate this interaction is essential to anticipate ecotoxicological risks and to guide public policies aligned with Sustainable Development Goals (SDGs) 6, 12, and 14.