Assessment Of Selected Antibiotics And Heavy Metals In Untreated Wastewater, Vegetables And Soils In Eastern Nairobi, Kenya

ABSTRACT

Untreated wastewater contains pharmaceutical compounds and heavy metals harmful to human health and the environment. People get access to untreated water through broken sewer pipes, blocked manholes and direct disposal into rivers. One such river is the Ngong River which passes through Nairobi County including Njiru and Ruai. People use untreated wastewater for growing of vegetables and washing cars. Soils and vegetables grown or irrigated with untreated wastewater may contain high levels of antibiotics and heavy metals that are detrimental to health. Sulfamethoxazole (SMX) and trimethoprim (TMP) antibiotics, administered in synergy for the management of pneumocystis carinii pneumonia, pneumocystis jiroveci pneumonia, toxaplasmosis and genitourinary tract infections in HIV-AIDS patients or in cases of oral thrush infections. The two drugs are also cheap and readily available in synergy over the counter even through self-prescription for management of upper respiratory tract and genitourinary tract infections under the brand name septrin or co-trimoxazole. In synergy, the two drugs are also administered to poultry and livestock as growth promoters, prophylaxis and to control microbial infections. Their presence in vegetables could induce microbial resistance and minimize drug sensitivity. The heavy metals may emanate from the waste water discharged by the small scale industries that are based in the study site. However, reports on levels of antibiotic residues and heavy metals in untreated waste water, vegetables and soils in Kenya are very scarce. Therefore this study aimed to determine the concentration of sulfamethoxazole (SMX) and trimethoprim (TMP), Cd, Pb, Zn, Mn, Fe and Cu in the soil, untreated waste water and vegetables irrigated with the untreated waste water in Ruai and Njiru. Untreated wastewater, soil and vegetables were collected during the dry season from various sites in Ruai and Njiru from small scale farms along Ngong River. The samples were also obtained from a control plot at the Kenyatta University. The samples for heavy metal analysis underwent wet digestion pre-analysis procedures while for antibiotics underwent solvent extraction pre-analysis. The heavy metals were determined by atomic absorption spectroscopy while antibiotic residues were determined by high performance liquid chromatography. The heavy metal concentrations in the vegetables ranged from 81.88 to 633.05 mg/kg. The mean concentration for Fe in the vegetables ranged between 481.24 to 1215.49 mg/kg for Mn, 1.94 to 4.58 mg/kg for Cd, 2.19 to 4.46 mg/kg for Pb, 3.19 to 8.70 mg/kg for Zn, 21.17 to 29.70 mg/kg for Cu, 24.71 to 27.52 ng/L for TMP, and 4.93 to 22.64 ng/L SMX. Some of these values were above the local and international safety limits. The concentrations (mg/L) of the heavy metals in untreated wastewater ranged from 3.09 to 3.54 for Mn, 0.01 to 0.03 for Zn, 0.21 to 0.28 for Pb, 4.79 to 8.07 for Fe, 0.17 to 0.22 for Cu and 0.42 to 0.47 for Cd. In the untreated wastewater SMX ranged from 62.09 to 88.66 ng/L. The vegetables TMP concentration ranged from 2.16 to 15.45 ng/L. The levels of some heavy metals and antibiotics were significantly higher than those from control samples. In all cases the results in the farms upstream were higher than in those downstream. The results from this work will be availed to relevant authorities for policy formulation and they can be used to sensitize the public, especially on the antibiotic residues