Bioaccumulation of Heavy Metals in Muscle and Exoskeleton of Shrimp from Karachi Coast, Pakistan

Abstract

Marine seafood like fish and shrimp is nutritionally valuable but increasingly contaminated by heavy metals from human activities, which bioaccumulate in aquatic organisms and pose ecological and human health risks.This study assessed the concentrations and size-related accumulation of selected heavy metals in two commercially important shrimp species, Fenneropenaeus merguiensis (banana prawn) and Fenneropenaeus penicillatus (redtail shrimp), collected from Karachi Fish Harbour, Pakistan. Muscle and exoskeleton tissues were classified into three size groups based on morphometric parameters and analyzed for aluminum (Al), lead (Pb), zinc (Zn), copper (Cu), and cadmium (Cd) using inductively coupled plasma optical emission spectrometry (ICP-OES). Mean metal concentrations (µg/g) in Fenneropenaeus merguiensis muscle were 4.59±1.63 (Al), 0.37±0.23 (Pb), 21.41±8.91 (Zn), 7.47±0.87 (Cu), and 0.17±0.04 (Cd), while corresponding values in the exoskeleton were 3.50±0.72, 0.39±0.23, 25.03±11.35, 7.34±1.75, and 0.19±0.03, respectively. In Fenneropenaeus penicillatus, higher concentrations were observed in muscle (11.18±1.27, 1.12±0.26, 60.04±25.07, 15.68±0.38, and 0.26±0.09 µg/g for Al, Pb, Zn, Cu, and Cd, respectively) and exoskeleton (9.58±1.42, 1.23±0.10, 61.59±25.45, 17.78±0.85, and 0.28±0.09 µg/g, respectively). A positive correlation between size and metal accumulation was evident in both species. Comparison with international permissible limits indicated that Pb and Cd levels in Fenneropenaeus penicillatus muscle approached or marginally exceeded recommended thresholds, whereas other metals remained within acceptable ranges. These findings demonstrate species- and size-dependent variation in metal accumulation and highlight potential food safety concerns associated with Fenneropenaeus penicillatus. Continuous monitoring of heavy metals in shrimp from this region is recommended to safeguard public health and support sustainable fisheries management.