Microplastic contamination from surface waters and commercially valuable fishes of Karachi Coast, Pakistan

Microplastic (MPs) pollution is a major concern due to extensive human plastic dependency that is deteriorating ecological health of the world’s oceans. This study was conducted to observe MPs contamination in surface water samples and gastrointestinal tracts of 127 fishes attributed to 15 species from Karachi coast, the busiest port of Pakistan. Total of 6319 MPs/m3 were recorded during this study from water samples where 73% MPs recorded from Manora channel (Karachi harbor) and 27% from open ocean. The most dominant MPs were fibers (42%), pellets (27%), and fragments (20%) respectively. MPs abundance differed significantly among species and ranged between 20.833 ± 2.522–76.400 ± 7.869 item ind.−1. Fibers were the most dominant type in all samples (53.39–90.0 %) followed by pellets (4.88–20.22 %) and blue (21.60–66.23 %) was the most common color. The mean size of MPs ranged between 0.34 mm (Otolithus ruber) to 2.1 mm (Terapon jarbua). The mean highest number of MPs were recorded from shallow coastal fishes (440 item ind.−1) followed by estuarine and shallow coastal fishes (385 item ind.−1). MPs abundance differed significantly among species from different habitat type (Kruskal–Wallis Test, P < 0.0001) with negative correlation between MPs abundance in GITs of fishes and their habitat (Spearman’s rho, r = -0.143) whereas MPs abundance was not significantly correlated with body weight (F = 0.002, p = 0.963), suggesting that MPs ingestion is independent of body weight. There is a need to work about origin, composition, interaction of MPs with biota and impacts of consuming fishes contaminated with high levels of MPs on human health. This is the preliminary study from the Karachi coast and will be a gateway for future studies in this area.