Any risk in consuming home grown vegetables irrigated with a mixture of wastewater and sludge?

Background/Question/Methods

We studied potential health risks of heavy metals in two cultivars of Swiss chart commonly consumed in one of the South African Development Community (SADC) countries. The experiment was conducted in a greenhouse and the design was 2 x 2 x 4 factorial experiment with four replicates. The treatments were: two soil types and Swiss chart cultivars (Ford hook Giant and Star 1801) and three sources of wastewater and sludge (WWS) and a control replicated four times. Results indicated that soils and wastewater and sludge used in the investigation had very low levels of heavy metals (Cu, Zn Cd, Cr and Ni) compared to the tolerable levels proposed by the Joint FAO/WHO Expert Committee on Food Additives (1999). In addition, application of wastewater and sludge (WWS) significantly affected height and leaf number/plant of these vegetable cultivars compared with the control (de-ionized water). However, with regard to the dry matter yield (DMY) of these two vegetables, results showed that there were no significant differences compared with the control, though it ranged between 1.1 to 1.30 kg/pot (Ford hook Giant) and 1.80 to 1.50 kg/pot (Star 1801). Results/Conclusions Results of the tissue analyses showed that heavy metals (Cr, Cd and Ni) and Cu were not detectable in the tissues of these two cultivars at 2, 4 and 6 weeks after planting (WAP). However, at 4 and 8 WAP, Zn was detected and it ranged between 0.35 and 0.45 mg/kg though not significantly different across weeks and between cultivars. This study concludes that although the contents of the heavy metals did not reach toxic levels in both WWS and even in the tissues of vegetables, its continuous consumption over a long period of time may result in potential health risks for consumers. It may be pointed-out that regular monitoring of the ponds be conducted in order to prevent excessive build-up of these metals in the food chain.