Assessment of hazardous microplastic polymers and phthalic acid esters in an invasive mollusk (Mytella strigata) from the Cochin estuary, southwest coast of India: Unraveling ecosystem risks

This paper characterizes the abundance, chemical characteristics, and potential hazards of microplastics (MPs) in water, sediment, and Mytella strigata from the Cochin Estuary (CE). In parallel, concentrations of plastic additives such as PAEs were measured in M. strigata to explore a possible relationship with MP contamination levels. A 100 % prevalence of MPs was observed with abundances ranging from 900 ± 100 to 1850 ± 150 particles/m in water and 540 ± 90 (CBM) to 1180 ± 320 particles/kg in sediment respectively. Marked spatial variations in abundance and composition of MPs were noted within the study area in relation to the hydrodynamic conditions and geographic location. Microplastic (MP) abundance in M. strigata varied from 3.8 ± 3 to 9.3 ± 5 particles/ind. in digestive (D) and 3.1 ± 2 to 7.8 ± 4 particles/ind. in non-digestive (ND) parts; and was related to the ambient concentration and composition. The abundance of MPs also showed a positive relation with the size of the organism. Fiber was the most abundant morphotype in the water and the organisms, while fragments dominated in sediment. Transparent, red, black, and blue were the dominant colors recovered from the study. The prevalence of smaller-sized (<2 mm) MPs indicates greater bioavailability to biota. The low pollution load index (PLI) implies a lower risk level (level I) in the study area, while the high polymer risk index (PHI>100) underlines the ecological risk associated with polymers, even at minimal concentrations. The study analyzed over 70 % of MPs qualitatively and identified 38 diverse polymers such as PVC, PAM, PA 6, UP, PVAL, PC. The ∑14 PAE congeners were quantified in the tissue of M. strigata; among them, DnBP, DIBP, DEEP, DMPP, DPP, DBEP, DEHP, and DEP are the dominant PAEs. This study illustrates that a major portion of PAEs in M. strigata are derived from MPs, considerably impacting the quality and quantity of such bioresources. This study is the first of its kind from the region, and the species selected (M. strigata) is found to be an ideal species for the in-situ and ex-situ studies of MPs, owing to its cosmopolitan distribution, sedentary and suspension feeding habit, and tolerance to a wide range of environmental conditions. Furthermore, quantitative estimation of PAEs is proposed as an indicator of MP contamination in the aquatic environment.