Multispecies Biomonitoring of Metal(loid) Contamination and Human Health Risk in a Peri-Urban Transboundary River System (Brazil–Paraguay)

Urban and peri-urban river systems subjected to intensive agriculture are vulnerable to diffuse metal(loid) inputs, yet the integration of hydrological compartments, bioindicators, and human health risk remains poorly explored. This study investigated the seasonal dynamics, bioaccumulation patterns, and potential human health risks associated with metal(loid)s in the Santa Virgem River (Brazil–Paraguay border), using water from backwater zones and three plant groups (Apiaceae angiosperms, mosses, and the liverwort Dumortiera sp.). Water and plant samples were collected during five seasonal campaigns (2019–2020) and analyzed by ICP OES. Multivariate analysis (PCA) was applied, and biological accumulation coefficients (BAC) and chronic daily intake (CDI) were estimated for adults and children under different ingestion scenarios. Results showed that Mg, Fe, K, S, and P dominated water chemistry, while As, Cd, Cr, Cu, Pb, and Se were mostly below detection limits. PCA explained 77.6% of total variance, distinguishing agricultural and hydrological phases. Bryophytes exhibited markedly higher BAC values, particularly for Mn (up to 2.3 × 105) and Fe, compared with Apiaceae. CDI and hazard assessment indicated negligible non-carcinogenic risk for most elements (HQ < 1), except phosphorus, which dominated the Hazard Index due to its low reference dose. Overall, the results demonstrate that hydrodynamic conditions and plant functional traits jointly control metal(loid) dynamics, highlighting the value of multispecies biomonitoring in peri-urban river systems.