Trimethoprim and Sulfamethoxazole Residues in Untreated Wastewater Used for Irrigation in Peri-Urban Farms in Nairobi County, Kenya

Untreated wastewater is often recycled in peri-urban subsistence farming. This water may contain residues of pharmaceutically active compounds discharged into the wastewater. Of concern are the residues of trimethoprim and sulfamethoxazole which are administered synergistically under the brand name septrin or cotrimoxazole. These two antibiotics are administered to both humans and livestock and belong to the group of medicines called ‘anti-infectives’. This being the case, they are administered routinely to HIV-AIDS patients and to poultry and livestock as growth promoters, prophylaxis and to control microbial infections. Application of irrigation water with pharmaceutically active compounds may predispose microbial life to significant doses of the antibiotics for a non-limited span of time. This has been known to induce microbial resistance and thus minimize the drug sensitivity upon administration, an outcome that is harmful to human health and the environment. This study was carried out to determine if there are pharmaceutically active residues of these antibiotics by the use of high performance liquid chromatography coupled to spectroscopy. Untreated wastewater used for irrigation was collected during the dry season from various peri-urban farms in Ruai and Njiru from small scale farms along Ngong River. In the untreated wastewater, sulfamethoxazole levels ranged from 62.09 to 88.66 ng/L while trimethoprim levels ranged from 24.71 to 27.52 ng/L. In all cases the results in the farms upstream were higher than in those downstream. From these findings, it is recommended that wastewater should be treated prior to recycling in farms.