Levels and distribution of chlorinated pesticide residues in water and sediments of Tarkwa Bay, Lagos Lagoon

Microlayer water, mixed layer water, epipellic and benthic sediments were collected from Tarkwa Bay end of Lagos Lagoon to analyse for chlorinated pesticide residues. Sampling was conducted between December 2008 and September 2009 during the dry and wet seasons to study effects of seasonal variation on the samples. Water samples were subjected to liquid-liquid extraction using dichloromethane while sediment samples were subjected to cold extraction with petroleum ether/acetone (1:1 v/v) mixture and clean-up on silica gel adsorbents. The water and sediment samples were analysed for aldrin, dieldrin; endrin, DDT, heptachlor and their metabolites; HCH and endosulfan isomers; α, γ-chlordane and methoxychlor. The detection and determination of the pesticide residues were performed by gas chromatography. Pesticide residues in the epipellic and benthic sediments were higher than residues in the water. The microlayer water showed reduced levels of residues when compared with the mixed layer water. The residue levels were higher during the dry season than the wet season and levels of residues in the water and sediments were within the permissible limits.