Determination of Arsenic and Mercury in Seafood from Coastal Markets in Lagos State

Mercury and arsenic are highly toxic metalloids that bioaccumulate through marine food chains and represent significant dietary exposure risks for coastal populations with high seafood consumption. This study determines arsenic and mercury concentrations in five categories of seafood, including shrimp, crab, mackerel, catfish, and tilapia, purchased from coastal markets in Lagos State, South West Nigeria. Samples were collected over two months, homogenised, and digested by microwave-assisted acid digestion. Mercury was determined by cold vapour atomic absorption spectrophotometry, while arsenic was analysed by hydride generation atomic absorption spectrophotometry. Total and inorganic arsenic species were differentiated by selective reduction techniques. Results show that total arsenic concentrations in shrimp and crab exceeded 5 milligrams per kilogram in several samples, with inorganic arsenic accounting for approximately 30 to 45 percent of total arsenic. Mercury concentrations in mackerel and catfish ranged from 0.05 to 0.38 milligrams per kilogram, with no samples exceeding the EU regulatory limit of 0.5 milligrams per kilogram. Estimated weekly intakes for high-consuming adults approached provisional tolerable weekly intakes for inorganic arsenic in some consumption scenarios. The study recommends targeted monitoring of arsenic in crustaceans and periodic mercury surveillance in predatory fish species from Lagos coastal waters. Keywords: arsenic, mercury, seafood, Lagos State, dietary exposure