Assessing levels of E-coli and heavy metals in green vegetables grown in the Nakivubo wetlands

Abstract

Provision of adequate food for the increasing population is one of the major concerns of urban areas. In the case of Kampala city, urban agriculture is increasingly practiced in wetlands. Different studies have established that a wide range of crops cultivated in the wetlands is contaminated with various heavy metals and pathogenic microorganisms. This study was therefore carried out to determine the extent of heavy metal and E. coli contamination in edible parts of green amaranth in the Nakivubo wetland. Wastewater samples were collected from Nakivubo channel and from various pollution sources in the catchment. Soil and fresh green amaranth samples were collected from the Nakivubo wetlands. These samples were analyzed for heavy metal and E.coli contaminants using standard procedures in the Ministry of Water and Environment (MWE) and the Makerere University School of Food Science microbiology laboratories respectively. Physico-chemical parameters of wastewater were also determined instantly using the automatic multi water quality checker U53 HORIBA. Except for mean lead concentration of 2.28 ± 1.10 mg/L in Nakivubo channel wastewater, laboratory results established that all mean lead, cadmium and E.coli concentrations in the catchment area wastewater, Nakivubo channel wastewater, Nakivubo wetlands and in green amaranth were above NEMA and WHO permissible limits. However, PCF values for both metals were below the WHO acceptable limit of 0.2, implying that PCF is not a reliable indicator of safety levels of crops contaminated with heavy metals. The close proximity of sampling point W1 to a former solid waste dumping site accounts for the high RI values at this point. A high proportion of H8+ at P1 (effluent of Bugolobi WWTP), confirms that much of the E.coli that gets into the treatment facility is human associated and also suggests that much of it is not removed or destroyed during the treatment process. This implies that the treatment facility may not be efficient with respect to microorganism removal. It can therefore be concluded that at the time of this study, there was considerable lead, cadmium and E.coli pollution in the sampled areas. Agricultural activities in the wetlands may have to be stopped with the authorities taking immediate steps to restore the Nakivubo wetlands to save L. Victoria from pollution. Measures need to be put in place to limit amount of pollutants reaching the cultivated parts of the wetlands. Regulatory bodies like NEMA should exercise their mandated authority of monitoring upstream activities and enforce punitive measures against potential polluters.