Risk Assessment of Soil Exposure to Antibiotic Residues in Manure in Livestock Rearing Farms of Rongai Sub-County, Nakuru County, Kenya

Abstract

Limited spaces within urban centers have forced farmers to practice intensive livestock farming within very small spaces, contributing to the prevalence of livestock diseases and increased veterinary drug use. In order to meet the growing demands for animal products, farmers have embraced intensive livestock production and thus heavy reliance on veterinary drugs for therapeutic, disease prevention and growth promotion purposes that introduce the risk of antibiotics in the environment from manure application. Antibiotic contaminated manure reaches agricultural ecosystems exerting antimicrobial resistance selection and toxicity pressure in soils and the environment. The main aim of this study was to assess the risk of soil exposure to antibiotic residues in livestock manure from livestock rearing farms in Rongai sub-county, Nakuru County. The study used a mixed method design consisting of cross-sectional survey, ecological survey and laboratory analysis. Questionnaires were used to obtain information on livestock reared, farm and farmer practices. Livestock manure samples were picked from compost heaps in farms while soil samples were collected from soil (0-10cm depth) in farms. Analysis for antibiotic drug residues in livestock manure and manure amended soils was done using HPLC-DAD.The common class of antibiotics used among poultry farmers were tetracyclines (35%), sulfonamide (40%), quinolones (20%) and others (5%). Tetracyclines (60%), sulfonamide (8%), penicillin’s (20%) and, macrolides (12%) were the most consumed class of antibiotics among cattle farmers. Concentration of tetracycline and sulphonamide antibiotics ranged from 1105-16240 μg/kg and 375.5-4955 μg/kg in poultry manure. In cattle manure, the concentrations ranged from 60-15231 μg/kg for tetracycline and 8.9-3940 μg/kg for Sulfonamide. In, manure-amended soils, antibiotic concentrations for tetracyclines ranged from 1880-29396 μg/kg in poultry and 1532-14237 μg/kg in cattle. Sulfonamide in soils had concentrations of 64.2-10556 μg/kg in poultry and 11.74-7752 μg/kg in cattle manure. Most of the risk quotient values calculated in this study presented low and medium risk. Sulfadiazine presented a higher ecological risk quotient value above the recommended value of ≤1. Most of the manure and soils were contaminated with antibiotic residues indicating a significant threat to environmental and human health. Sensitization on proper antibiotic use and healthy manure management practice is recommended in order to reduce antibiotic residues released into the environment from livestock rearing farms. Ministry of Agriculture, livestock and fisheries and NEMA, should set and monitor maximum residues limits of antibiotics in manure to protect the environment.