Microplastics and heavy metals in shrimp Litopenaeus vannamei from the SAMARE lagoon, Gulf of California: Is it a case of combined MPs-Zn pollution in gills?

Microplastic (MPs) pollution studies in the coastal environment are increasing, as observed in the growing number of documents published yearly. However, studies regarding the combined effect of MPs and heavy metal (HMs) pollution are scarce, particularly in marine biota. Microplastics and HMs were investigated in the exoskeleton (EX), gills (GI), gastrointestinal tract (GT), and muscle (MU) of the shrimp Litopenaeus vannamei from the Santa María-La Reforma (SAMARE) lagoon, Mexico. Results showed that shrimp ingest mainly MPs of the fiber type (74.7%) and fragments (22.7%). The most frequent MP colors in the four tissues were transparent (61.4%-72.2%) and blue (3.2-36.4%) fibers. Microplastic abundance in the four tissues was 5.5 ± 0.5 MPs per individual. The predominant polymers found in most tissues were cotton and synthetic polyethylene-terephthalate (PET). Heavy metals exhibited wide variability depending on the tissue and metal; the highest Cu concentration in the GI was 138 ± 16 μg/g, while the highest Cd value was 0.40 ± 0.11 μg/g, Ni was 17.0 ± 8.3 μg/g, and Zn was 120 ± 18 μg/g in the GT. The relationship between MPs and HMs was significant and positive (p < 0.05) between MPs and Zn in the GI. This reveals a possible MPs-Zn interaction due to cotton and PET reactivity or is related to polymer manufacture. This study implies that an essential part of the world fisheries is a potential route for MPs and HMs. The problem is exacerbated due to the consumption of whole shrimp tissues consumed by humans. Considering Mexican shrimp consumption, and MPs in this study, the estimated intake was 594 MPs/capita/year. Future research requires MP monitoring in coastal lagoons that support wildlife and important fisheries and assess their effects combined with HMs.