Assessment Of Pesticide Residue Levels In Water, Wastewater Lagoons, Fish Ponds And Farmed Fish In The Catchment Of River Kuja, Kenya

Abstract

Environmental contamination by pesticides is a matter of great concern worldwide. In Kenya, anthropogenic activities involving the use of pesticides in horticulture, cash crop farming and raising of livestock continue to contribute to the pollution load in Lake Victoria Basin. Whereas limited accounts concerning the pesticides distribution such as in the River Nyando catchment have been reported, there exist huge knowledge gaps on the subject in the highly populated areas of River Kuja watershed. Quantities of pesticide remains in cultured fish, wastewater lagoons, fish pond effluents, and river waters in the region have been scantly studied. This study investigated the distribution of organochlorine pesticide residues in water and sediment samples from fish ponds and their river waters as well as in fish from the fish ponds and wastewater lagoons in September 2016 to December 2017, in some selected parts of Kericho, Nyamira, Kisii and Homa Bay counties. Water quality parameters were obtained In situ and analysed. The study used a purposeful and multistage stratified sampling design with wards being the basic sampling units. Consequently, four wards were sampled in Kisii, three in Nyamira and one each in Kericho and Homabay counties. The former two counties were emphasized in the sampling because they are more densely populated than the latter two. Fish and sediment samples were obtained from the field and transported in cooler boxes packed in ice and later frozen to -200C. 2.5 L water samples were collected in amber bottles and preserved, transported and kept at 4C in the laboratory. Pesticides in water samples were solvent-extracted using acetone-hexane, concentrated by rotary evaporation and cleaned up using liquid-liquid and solid-phase extraction method for water and solids. The SPE column were eluted with the appropriate solvent system followed by Gas Chromatography (GC) analysis and GC-Mass Spectroscopy (MS) for identification of pesticide chromatograms. Data sets were analyzed using Excel spreadsheet program 2013 and GraphPad Prism software version 5.03 with results presented in frequency tables and bar graphs. Determination of variations in organochlorine pesticides mean value concentration between sampling stations was performed using one-way ANOVA (Analysis of Variance) statistical method, at the 95% confidence level, while independent sample T-test was performed in determination of significant variation in OCPs mean values between wet and dry seasons. Tukey’s post hoc test was applied when significant differences between means were observed to identify the specific stations that differed from one another (p < 0.05). Correlation analysis was done on levels of organochlorines and physico-chemical parameters to determine the associations among the variables. Pesticide contamination levels in fish and water samples were compared with those from NEMA, WHO, FAO, EU and US EPA water quality standards and mitigation measures suggested. Chromatographic analysis identified seventeen different organochlorine pesticides known to occur in three major groups namely, hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs) and cyclodienes. HCHs constituted of four isomers: α-HCH, -HCH, -HCH and -HCH. DDTs constituted of three metabolites: p,p’-DDD, p,p’-DDE and p,p’-DDT while cyclodienes comprised of ten compounds: aldrin, dieldrin, endrin, heptachlor, heptachlor epoxide, endosulfan I, endosulfan II, endrin aldehyde, endosulfan sulfate and methoxychlor. Mean (± SE) physico-chemical parameters results varied significantly viz; dissolved oxygen (DO) (6.96±0.897 mgL-1), temperature (25.39±1.201 ⁰C), conductivity (62.03±8.123 μScm-1), pH (7.57±0.314), and TSS (193±5.462), TP (0.127±0.005) and TN (3.25±0.24) which contributed significantly to variations in organochlorine pesticide residue levels observed. Results of DDTs, cyclodienes and HCHs in fish ponds ranged below detection limit (BDL) to 0.27±0.03 μgL-1, BDL to 0.11±0.00 μgL-1, and 4.39±1.01 μgL-1 respectively; and BDL to 0.23±0.01 μgL-1, 1.20±0.005 μgL-1, and 1.71±0.02 μgL-1 in river water respectively. Mean OCPs sediment contents were significantly (p < 0.05) higher for dieldrin (3.043±0.43 μgKg-1), endrin (2.56±0.460 μgKg-1), heptachlor (3.61±0.02 μgKg-1); DDT (2.97±1.32 μgKg-1), endosulfan (6.31.27±1.051μgKg-1), ix methoxychlor (2.15±1.641 μgKg-1) and lindane (2.96±1.32 μgKg-1), respectively. Mean pesticides residue levels in fish ranged from 0.229 to 2.541 gKg-1 for Nile tilapia (Oreochromis niloticus). Most dominant isomer in target species was lindane (-HCH) with (3.417 ± 0.983 gKg-1) and endosulfans. Mean endosulfan sulfate was 2.499 ± 0.071 gKg-1 d.w. and frequently detected, and methoxychlor (2.235 ± 1.459 gKg-1), respectively. Mean aldrin and dieldrin was 2.028 and 0.574 gKg-1 d.w. Concentration for DDT and its metabolites was 0.27-3.71 gKg-1 for p,p’-DDE (dichlorodiphenyldichloroethene), BDL - 1.098 for p,p’-DDD (dichlorodiphenyldichloroethane), and 0.105-3.518 gKg-1 for p,p’-DDT (dichlorodiphenyltrichloroethane) with significant differences in mean values ranges. The study revealed overall mean residue values for HCHs to be between BDL to 0.571 ±0.62 μgL-1 values that were below NEMA and WHO of 2.0 μgL-1 in water. Overall, the concentrations of all the DDT metabolites were below WHO maximum acceptable standards of 2.0 μgL-1 and below NEMA locally maximum acceptable thresholds in natural drinking water (1.5 mgL-1). However, some sampling stations recorded scores above EPA (0.2 μgL-1) and WHO maximum acceptable standards, with an implication of potential risk to public health and environment, as some sampled sediment and fish results showed higher residue values implying that prolonged exposure would be of public health concern. Available results indicate organochlorine pesticides (OCPs) exist in our environment, and their recent use in the sampled area. The study recommends regular aquatic monitoring in upstream catchment areas to detect persistency and changes in target environment for informed policy decisions and management in order to safeguard human and environmental health.