Anthropogenic microparticles and mercury co-occurrence in blue sharks from the Tropical Eastern Pacific

Abstract Anthropogenic microparticles derived from synthetic polymers and industrially modified natural materials have become persistent pollutants in marine ecosystems because of their capacity to adsorb and transport other contaminants. In this study, we quantified anthropogenic microparticles (AMPs) ingestion and evaluated its relationship with total mercury concentrations (THg; liver + muscle) in 23 blue sharks ( Prionace glauca ) from the northern Tropical Eastern Pacific (TEP), a key corridor for global fisheries and debris transport associated with the North Pacific Garbage Patch. All individuals contained AMPs (mean ± SD = 32 ± 37 particles per digestive tract). Most particles were < 5 mm, with fibers as the dominant shape (76%). Among synthetic polymers, polyethylene (PE) and polyethylene terephthalate (PET) were the most abundant. Microplastics (MPs) showed a mean abundance of 12 ± 11 particles per digestive tract, whereas more than 60% of FTIR-confirmed particles corresponded to non-plastic anthropogenic microparticles (NPAMPs), mainly cotton, rayon, and cellulose, with a mean abundance of 22 ± 27 particles per digestive tract. Generalized additive models (GAMs) identified NPAMP abundance as the strongest predictor of THg concentrations (mean ± SD = 1.08 ± 0.43 mg kg⁻ 1 ), revealing a significant non-linear relationship with higher Hg levels during the hot–rainy season. These findings suggest that NPAMPs may represent, together with diet, an additional pathway associated with Hg exposure in P. glauca . Risk indices (PLI, MPDI, and PHI) indicated low-to-moderate contamination levels; however, more than half of the individuals exceeded polymer hazard thresholds (PHI > 1000). Given the observational design, limited sample size, and the fact that seasons were sampled in different years, the NPAMP–THg relationship should be interpreted as co-occurrence rather than direct evidence of contaminant transfer. Furthermore, because particles were quantified only in non-edible tissues, these findings cannot be directly extrapolated to seafood safety risk. Nevertheless, NPAMPs emerge as a previously under-recognized component of contaminant exposure in pelagic predators and should be incorporated into future marine monitoring frameworks.