Heavy M etal a nd M icrobial C learance of R aft cultivated G reen M ussels Perna viridis from T he S outheast C oast of T he Bay of Bengal: Salinity and S ize D riven D epuration S trategies for S eafood S afety

Abstract

Maintaining the microbial and chemical safety of tropical bivalves is diff icult beca use estuarine environments are often heavily contaminated and post harvest purification processes are not yet fully understood. This study offers the first detailed assessm ent of depuration performance in the green mussel Perna viridis ) from Ban gladesh, f ocusing on the roles of salinity, depuration duration, and mussel size in reducing microbial contamination and heavy metal loads. Depuration experiments were carried out fo r 72 hours using a static fill and drain system with UV sterilized, filter ed seawate r at salinities ranging from 15 to 30 ppt and across three size categories (small, medium, and large). Pathogenic bacteria were identified and quantified through selective culture methods followed by PCR confirmation, while ten trace metals (Cr, Mn, Fe, Ni , Cu, Zn, As, Se, Hg, Pb) were analyzed using Energy Dispersive X ray Fluorescence (EDXRF). Statistical analysis using generalized linear mixed effects models demonstrated that depuration time (p < 0.001) and its interaction with salinity signifi cantly aff ected microbial reduction. Complete removal of Salmonella Shigella Escherichia coli , and Vibrio cholerae was achieved within 48 72 hours at salinities of 25 ppt or higher . Larger mussels showed more efficient microbial clearance, likely due to greater fi ltration efficiency. The removal of heavy metals varied among elements, with notable decreases observed for Fe (43.2%), Cu (43.1%), Zn (33.0%), Pb (50.4%), Cr (56.6%), and Hg (41.0%). In contrast, Ni, As, and Se remained largely unchanged, possib ly due to strong binding within tissues and limited biological regulation. Although total arsenic levels slightly exceeded recommended safety limits, concentrations of most metals de clined to well below international standards. Overall, depuration for 72 h ours at sa linities between 25 and 30 ppt effectively improves both microbial and chemical safety of P. viridis , establishing a practical post harvest depuration strategy for shellfis h harvested from tropical estuaries.