Bioaccumulation and effects of anthropogenic microparticles in Brachidontes rodriguezii from the Southwestern Atlantic coast

• APs were higher in seawater and mussels at the less industrialized site. • Brachidontes rodriguezii is an effective bioindicator of AP pollution with high bioaccumulation. • APs <1 mm and fibers dominated all samples; fragments found only in mussel tissue. • Mussels with high concentration of APs showed digestive gland alterations. • Oxidative stress was not related to AP bioaccumulation. The bivalve Brachidontes rodriguezii , a species inhabiting the southwestern Atlantic coast, has emerged as an ideal bioindicator for environmental contamination due to its continuous water filtration, which exposes it to anthropogenic particles (APs), including microplastics (MPs). Although APs such as MPs have been shown to cause biological harm in bivalves, further research is essential to a deeper understanding of these impacts. This study investigates the concentrations and characteristics of APs in the soft tissue of B. rodriguezii and the surrounding water column at two contrasting sites in southern Buenos Aires Province, Argentina: Pehuen-Co (PC), a region with lower industrial activity, and Club Náutico (CN), a heavily industrialized and urbanized area. Our results indicate surprisingly higher AP concentrations at PC (22.0 ± 5.7 items/L in seawater; 4.2 ± 2.7 items/g w.w. in soft tissue) compared to CN (4.7 ± 1.2 items/L in seawater; 1.0 ± 0.3 items/g w.w. in soft tissue), with bioaccumulation factors exceeding 100 for both sites. APs smaller than 1 mm and fibers were predominant across all samples, while fragments were exclusively detected in the soft tissue of mussels. Interestingly, the APs from PC displayed greater color diversity than CN. Health assessments revealed significant site-specific differences: mussels from PC exhibited higher rates of digestive gland alterations (80 %) and parasite presence (15 %) but no evidence of eosinophilic bodies or hermaphroditism. Conversely, mussels from CN had lower rates of digestive gland alterations (50 %), no parasites, but a high incidence of eosinophilic bodies (61 %). At the molecular level, no site-specific differences were observed in the expression of genes related to oxidative stress markers such as superoxide dismutase (SOD), reactive oxygen species (ROS), or total thiols. However, protein carbonylation and lipid peroxidation were elevated in mussels from CN. In conclusion, B. rodriguezii bioaccumulates APs in its tissues, correlating with environmental levels, thus confirming its status as an effective bioindicator of AP contamination. The higher levels of APs in PC and the observed histological alterations, along with the lower oxidative stress response, may suggest that APs primarily affect tissue level rather than oxidative stress. These findings highlight the need to consider multiple health indicators in studies of AP contamination and underscore the importance of monitoring and managing pollution even in seemingly less-impacted areas.