Microplastome visualizations: From spatiotemporal distribution to risk assessment

The microplastic pollution issue is infamous for its enormous multidimensionality and the intricate combination arising from plastics themselves and "plastic-associated chemicals". Interactions between microplastic particles with multiple chemicals can affect biological health and alter the toxicity of the primary environmental pollutants. These complex combinations raise great challenges to experimental design for toxicity evaluation, going beyond the investigation of individual or dual contaminations. Systematic research and an integrated visualization strategy are needed to decipher these biochemical processes and molecular mechanisms.

The role of microplastic particles as vectors for the cycling and bioaccumulation of plastic-associated chemicals, especially hydrophobic organic chemicals, is a topic of much debate. Scientists propose the “microplastics vector effect,” namely that the desorption of chemicals from microplastics after particle uptake may promote chemical exposure and pose chemical risks to various organisms. These chemicals involve sorbed environmental pollutants (POPs, bisophenols, metals, etc.) and additives (brominated flame retardant, etc.). However, further ample evidence is required to clarify the transfer vector effect of microplastics into animals or for plastic additives like flame retardants. First, experimental designs need to consider the total chemical exposure from both the transport or uptake of microplastics and other parallel ingestion pathways. Second, a realistic chemical concentration gradient between plastics and organisms should be considered because these exogenous additives are subject to obvious dilution in the natural environment. More specifically, it would be inappropriate to investigate potential toxicity effects using in vitro models with extracts exhibiting a high plastic-to-water ratio. Third, it will be best to comprehensively evaluate the enrichment characteristics of microplastic particles and plastic-associated chemicals at the (sub-)organ level, including spatiotemporal distribution, and the correlation between contents and distributions. Above all, multiple factors should be taken into account in plastics analysis from different in vivo and in vitro models, including the dilution of pollutants, ingestion from various media, and spatial distribution.