Unveiling the Toxic Impact and Biodegradation Products of Anionic Surfactants in an Edible Clam <i>Meretrix casta</i> Through Tandem Mass Spectrometry

ABSTRACT Shellfish, being filter feeders, are susceptible to bioaccumulating environmental contaminants. This study examines the occurrence, bioaccumulation, and in vivo transformation of linear alkylbenzene sulfonates (C 10 –C 13 LAS) and their degradation products, sulfophenyl carboxylic acids (C 10 –C 11 SPCs), in the edible clam Meretrix casta from the estuary of Goa, India. Using electrospray ionization‐quadrupole time‐of‐flight tandem mass spectrometry (ESI‐QTOF MS/MS), diagnostic fragment ions formed enabled detection and structural characterization of LAS and their biodegradation intermediates in clams under natural conditions. Acute toxicity assays revealed 100% lethality of commercial LAS at 3.5 mg/L, with an LC 50 of 2.67 mg/L. Laboratory exposure experiments demonstrated in vivo biotransformation of LAS into oxidized saturated and unsaturated biodegraded products, SPCs, and dicarboxylates (SPdCs) with carbon chains of C 4 , C 6 , C 8 , C 10 , and C12 for C 12 LAS and methylated C 13 SPdCs for C 13 LAS. This was confirmed by fragment ions analysis using ESI‐triple quadrupole (TQ) MS/MS. The study provides the first direct evidence of detailed tandem mass spectrometric data used for characterizing the structure of LAS biodegraded products. These compounds hold potential as biomarkers for pollutant exposure. Their MS‐based metabolite detection with the proposed biodegradation pathway can be applied for environmental monitoring and ecological risk assessment. The investigation reveals its metabolic capacity to transform and detoxify, contributing to our understanding of bivalve biotransformation mechanisms and their role in pollutant cycling in coastal ecosystems.