Multilevel toxicological impacts of industrial settleable particulate matter in a freshwater crustacean, Macrobrachium rosenbergii

As integral components of aquatic food webs, crustaceans serve as pivotal conduits for energy transfer and sensitive bioindicators of environmental quality. This study characterizes the toxicological consequences of settleable atmospheric particulate matter (SePM)-a byproduct of industrial iron-ore processing-utilizing the freshwater shrimp Macrobrachium rosenbergii as a model organism. Experimental exposure demonstrated that SePM significantly enhances the aqueous solubility of both conventional (Fe, Al, Zn, Cu, Mn) and emergent (Cr, Ni, Sr, Sn, La, Ce) metals, establishing it as a potent vector for multi-elemental contamination. Exposed individuals bioaccumulated 24 metals, with predominant enrichment of Fe, Ba, Sr, Cu, and Zn; these accumulation profiles were modulated by both external concentration and element-specific uptake kinetics. Notably, ultrastructural characterization revealed significant metal sequestration within the exoskeleton, identifying an incidental pathway for contaminant cycling through discarded carapaces (ecdysis). Biochemical assessments indicated impairment of redox homeostasis, characterized by the exhaustion of enzymatic (CAT, SOD, GPx, GST) and non-enzymatic (GSH) defenses, alongside elevated lipid peroxidation and DNA strand breaks. While bioaccumulation had a dose-dependent progression, oxidative distress was manifest even at the lowest exposure levels, underscoring that the toxicity of SePM as a complex mixture cannot be accurately predicted by the additive impacts of its individual constituents. These findings highlight SePM as a critical, yet largely overlooked, driver of air-to-water cross-contamination. Our results underscore the urgent need to incorporate such atmospheric deposition into environmental monitoring frameworks and to expand regulatory criteria to address emergent metals and potential synergistic effects of metallic mixtures.