Occurrence of Pesticides Residues in Feeds, the Pond Environment and Farmed Fish. A case Study of Uasin Gishu County, Kenya

Abstract

The use of pesticides in crop production and preservation poses a risk of contaminating aquaculture facilities and fish, through water and feed raw materials. This study investigated the use of pesticides on crop production and preservation, and residue occurrence in aquaculture ponds, fish feeds, and fish tissues. Questionnaires were used to ascertain the types and factors governing the use of pesticides. In addition, the following samples were analysed for the concentrations of pesticide residues using Gas Chromatography Mass Spectrometry (GC-MS): a) three distinct samples [i.e. pond water, sediment and Nile tilapia muscle tissues from four farms; b) feed raw materials; and c) formulated feeds from fish farmers and traders]. The study was conducted between April and June, 2021, and showed that 82 % of 178 respondents used 30 different pesticides in crop production and for preserving cereals during storage. Pesticides with Atrazine as the active ingredient were commonly used by over 50% of the farmers. The choice of pesticides was governed by the gender, level of education, training and knowledge on the negative effects associated with pesticides residues to fish and humans. Eleven (11) pesticide residues, namely: Atrazine, Carbofuran, Acetochlor, Aldrin, Dichlorodiphenyltrichloroethane (DDT), Heptachlor, Lindane, Malathion, Metalaxyl, Pirimiphos Methyl and Profenofos were recorded in water, fish and feed samples. The concentrations of pesticide residues in mashed fish feeds were six to seven times higher than in pelleted feeds. Carbofuran pesticide residues were recorded in all fish-feed raw materials and most of the feeds. In pond water, Atrazine was reported in half of the samples analysed to be above the WHO maximum residue limits (MRLs) of 2 μg l-1 for drinking water. Within sediments, Profenofos and DDT were the most prevalent. Although DDT was not recorded among the pesticides applied in the study area, its presence in sediment may suggest continued unreported usage or persistence in the environment. In fish tissues, three pesticide residues were reported: Aldrin, γ-HCH and Profenofos, with Aldrin being above FAO MRL of 0.1 μg kg-1. The occurrence of pesticide residues in farmed fish suggests possible transfer of pesticide residues from any of the three sample types analysed (feeds, water or sediments) to farmed fish. The study concludes that there is potential health risk for humans as a result of continuous exposure to pesticides through the consumption of farmed fish from Uasin Gishu county.