Residue analysis of organochlorine pesticides in water and sediments from Agboyi Creek, Lagos

Microlayer water, mixed layer water, epipellic and benthic sediments were collected from Agboyi Creek, Lagos to analyse organochlorine 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 sediments were subjected to cold extraction with petroleum ether/acetone (1:1 v/v) mixture and cleanup on silica gel adsorbents. The samples were analyzed for aldrin, dieldrin, endrin, DDT, heptachlor, HCH, endosulfan, chlordane and methoxychlor. The detection and determination of the pesticide residues were performed by injecting 1 μL of purified extract into the injection port of a gas chromatograph with a 63Ni electron capture detector (GC-μECD Agilent 7890A) equipped with ChemStation software. Pesticide residues in the epipellic and benthic sediments were higher than the residues in the water. The mixed layer water showed enhanced levels of residues when compared with the microlayer water. The residue levels were higher during the dry season than the wet season. The levels of residues in the water and sediments were below the maximum permissive residue limits.Key words: Agboyi Creek, organochlorine pesticides, microlayer water, mixed layer water, epipellic sediment, benthic sediment