Seasonal rainfall affects occurrence of organohalogen contaminants in tropical marine fishes and prawns from Zanzibar, Tanzania

Seasonal differences in precipitation may affect contaminant dynamics tropical coastal regions due to terrestrial runoff of contaminants the marine environment after rainy seasons. To assess effect seasonal rainfall on occurrence organohalogen a ecosystem, fishes and prawns were collected off coast Zanzibar, Tanzania January August 2018, representing pre- post-rainy season, respectively. Samples analyzed for organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs) emerging BFRs, as well dietary descriptors stable isotopes carbon (δ13C) nitrogen (δ15N). Across all species seasons, mean concentrations ranged from below limit detection (LOD) 129 ng/g lipid weight (lw) ΣPCBs; 5.6–336 lw ΣOCPs; < LOD –22.1 ΣPBDEs. Most BFRs LOD. Contaminant generally increased with higher pelagic signal relative trophic position The ratio DDE/ΣDDTs was lower than January, suggesting non-degraded DDT into system during or rainfall. patterns OCPs PCBs, differed between seasons species. A concentration-increase halogenated, more mobile PCB PBDE congeners, compared halogenated congeners mobility, aligns following season.