Levels, bioaccumulation and biomagnification of pesticide residues in a tropical freshwater food web

The study assessed pesticide contamination transfer in Ikpoba River, an important tropical freshwater ecosystem in Southern Nigeria. The study quantified concentrations, bioaccumulation and biomagnification of pesticides in Ikpoba River's food web, with emphasis on less frequently assessed lower trophic-level organisms. Concentrations of pesticides were quantified in water, sediment and biota (phytoplankton, green algae (Cladophora), macrophyte (Commelina erecta), macrobenthic invertebrates (Lestes species, Caridina africana, Enallagma species, Gerris lacustris, Culex species, Pentaneura species, Sympetrum species, Argyroneta aquatica, Lecane species (Cladocera) and pelagic fish (Tilapia zilli)). Samples were collected at two separate stations and were analyzed using gas chromatography equipped with electron capture detector. Aldrin was the dominant pesticide in the Ikpoba River food web with concentrations accounting for 14.4% of the total pesticide residues in the assessed matrices. Sediment samples had significantly higher pesticide concentrations among the matrices assessed, with a total mean concentration of 0.095 +/- 0.02 mu g/kg dw. Among the biota samples, total pesticide levels were significantly higher (p < 0.05) in Commelina erecta. BAF and BSAF values were also highest in this species indicating that Commelina erecta may represent a greater reservoir for pesticides and may be a principal factor in subsequent transfer of pesticides along the food web of Ikpoba River. The BMF values for alpha-HCH, gamma-HCH, beta-HCH, glyphosate, heptachlor, aldrin, heptachlor epoxide, endosulfan I, endrin, carbofuran and diazinon showed that these pesticides have the potential to biomagnify along the trophic levels. The persistence of these pesticides in Ikpoba River supports the need for continuous monitoring.