Pesticides residues in soil and mountain gorilla food plants in and around Bwindi Impenetrable National Park
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Pesticides are widely used to control pests but may have detrimental effects on non-targeted species. This study aimed at establishing pesticides types used by farmers and determining their levels in the soils and plant leaves consumed by gorillas along the forest edges of Bwindi Impenetrable National Park (BINP). The study areas were Nkuringo, Buhoma and Ruhija. The areas were selected because they are located in the vicinity of the park with agricultural activities taking place. A structured questionnaire was used to establish the types of pesticides used by the farmers to control pests. Samples of soil and plant leaves were also randomly collected from the study areas and analyzed in a laboratory for cypermethrin and selected organochlorine. The residue levels were analyzed by a gas chromatography coupled to a mass spectrometer, and samples were considered positive when their pesticide residue levels were greater than or equal to the limits of detection. This study has established five mainly used pesticides namely glyphosate cypermethrin, macozeb, dimethoate and 2,4 amine. Glyphosate and cypermethrin were commonly used (50% and 37% for Ruhija, 52% and 36% for Buhoma and 44% and 40% for Nkuringo). The study also determined organochlorine (OCPs) in soil and plant leaves eaten by gorillas. The mean concentrations of DDTs ranged from 0.03 – 0.34 mg kg-1 in soil while those in plant leaves varied from 0.03 to 3.15 mg kg-1. o,p’-DDD was the most predominant DDT metabolite in the soil (contributed 58.3% to ΣDDTs). The ratio of o,p’-DDE to o,p’-DDT in the soils from Ruhija was 2.61, suggesting past input of DDT. Some of the concentrations of DDTs in the leaves were higher than the maximum residue limits (MRL) set by FAO/WHO codex Alimentarius commission (0.2 mg kg-1) in leafy vegetation and thus could pose health risks to mountain gorillas that inhabit the park. The concentrations of endosulfans were 1.18 – 2.18 mg kg-1 in soil and 1.26 to 8.07 mg kg-1 in the plant leaves respectively. However, the endosulfalfans residues in the leaves were lower than the set (MRL) by FAO/WHO codex Alimentarius commission (10 mg kg-1) suggesting no health risks to mountain gorillas. Principal component analysis (PCA) was used to explore variation in the mean concentration of pesticides in soil plant leaves. The results from PCA indicated that the first principal component (PC1), which was related to the endosulfans, explained 64.3% of the total variation. The next four components (PC2–PC5), which were related to DDT and its metabolites, explained the remaining percentage (35.7%) of the total variation. Component PC6 that was related to cypermethrin explained none of the variation.