Chemical contaminants and microplastics in bivalves from São Paulo coast: A systematic approach supporting management strategies

Bivalves are widely used as sentinels of chemical and microplastic contamination in coastal environments. The coastline of São Paulo State, is one of the most densely populated and industrialized coastal regions in the Southern Hemisphere, overlapped with a mosaic of marine protected areas. Evidence on contamination of resident bivalves remains fragmented across chemical classes, species, and geographic sectors. Here, we present a systematic review of chemical and microplastic contaminants based on bivalves along the São Paulo coast, synthesizing 30 peer-reviewed studies published between 2000 and 2025. The review encompasses toxic metals and metalloids, hydrocarbons, persistent organic pollutants, microplastics, and drugs of abuse, complemented by an assessment of bibliometric patterns and knowledge gaps. Metals dominated the literature (54.6%) and spanned the longest temporal range (analysis period: 1995–2023), whereas hydrocarbons, microplastics, and persistent organic pollutants were investigated less frequently and were largely restricted to estuarine and port-influenced environments. Sentinel use was strongly based in few mussel and oyster species, while research effort was highly concentrated in the Santos–São Vicente Estuarine System. Although fewer studies were conducted within marine protected areas, contaminant levels were generally lower than in unprotected sites, suggesting localized mitigation effects but not complete protection. Overall, the findings reveal a compartmentalized monitoring landscape characterized by limited integration among contaminant classes and uneven spatial coverage. This review provides the first consolidated synthesis of bivalve contamination along the São Paulo coast and identifies priority gaps to support the development of harmonized, multi-contaminant biomonitoring frameworks in highly urbanized coastal systems.