Occurrence of selected antibiotics in sediments and surface water of river sosiani, Eldoret, Kenya and their sorptive removal using biochars

Abstract

Antibiotics as therapeutics have been widely used in both human and veterinary medicine. Their indiscriminate use and improper disposal have led to environmental pollution, exerting adverse effects on non-target organisms. Various methods have therefore been developed to remove antibiotics from environmental matrices. Adsorption using bio-based adsorbents has been a preferred method for the removal of antibiotics from water as it is eco-friendly, cost effective and relatively simple. The general objective of this study was to assess the occurrence of selected antibiotics in water sediments, and surface water of River Sosiani, Eldoret, Kenya, and their sorptive removal using modified and unmodified biochar materials derived from water hyacinth and millet husks. The specific objectives of the study were; to quantify selected antibiotics in sediments and surface water from Sosiani River in Eldoret, to prepare and characterize chemically modified and unmodified biochar materials from water hyacinth and millet husks; to determine the sorption capacity of ciprofloxacin (CIP), sulfamethoxazole (SMX) and penicillin G (PNG) antibiotics from water using the prepared biochars, and to establish sorption isotherms and kinetics for adsorption of CIP, SMX and PNG by the biochar materials. The biochars were prepared by slow pyrolysis at 350 °C and 500 °C, modified using potassium hydroxide and characterized using Fourier Transform-Infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). Batch sorption equilibrium experiments were used to determine the capacity and efficiency of adsorption and data was fitted into different isotherm and kinetic models. Quantification of the antibiotics was done using liquid chromatography tandem mass spectrometry. The results showed that 30 compounds belonging to eight antibiotics classes: fluoroquinolones, sulfonamides, macrolides, penicillins, nitroimidazoles, lincosamides, diaminopyrimidines, and salfones were present in surface water and sediments from River Sosiani. Detectable concentrations of antibiotics in water samples ranged from 0.1 - 247 ng L -1 and 0.01 - 974 μg kg -1 in the sediments. Compared to other classes of compounds, fluoroquinolones were found in higher amounts in both water (56.02 ng L -1 ) and sediment samples (16 μg kg -1 ). Sulfamethoxazole had the highest concentration in water (247 ng L -1 ), whereas penicillin G showed the highest concentrations in sediments (414 - 974 μg kg -1 ). The results of FT- IR and SEM showed that there were differences in the physical and chemical properties of the biochar pyrolyzed at 350°C and 500 °C; hence differences in observed sorption characteristics. Biochar prepared at high temperature (BC500) had high adsorption capacity (> 80%) for the three antibiotics, while activated biochar showed high removal efficiency (83-88%) compared to non-activated biochar (50-70%). Sorption kinetics was best described by pseudo-second-order kinetics (R 2 > 0.99), while the sorption process could be best described by the Freundlich isotherm (R 2 > 0.97), and intra-particle diffusion models. Therefore, multilayer sorption of tested antibiotics on heterogeneous biochar surfaces was the most plausible sorption mechanism. The study showed a high prevalence of pharmaceuticals in surface water and sediments, and are therefore potential ecological hazards. Biochar from both feedstocks showed potential as alternatives to commercial activated carbon for the removal of CIP, PNG and SMX from water. The occurrence of antibiotics in surface water and sediments of the river differed widely according to classes of the pharmaceuticals and was mainly influenced by anthropogenic activities within the sampled location. Continuous monitoring of these pollutants is imperative to inform the public on their fate in the environment and for the enactment of policies for interventions, and sustainable mitigation strategies.