ASSESSING DIFFERENCES IN THE CONCENTRATIONS OF TRACE METALS FROM DIFFERENT TOMATO VARIETIES HARVESTED FROM SOILS TREATED WITH MUNICIPAL WASTE SLUDGE

This study investigated the differences in the concentrations of trace metals in four different tomato varieties cultivated on soil treated with municipal waste sludge in Pretoria, South Africa. Fruits were harvested at maturity and analyzed for trace metals content using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The study showed that different varieties of tomatoes bioaccumulated different trace metals from the soil: Rodade tomato bioaccumulated the highest concentrations of Mn, Cr, Cu and Ni, Roma bioaccumulated the highest concentrations of Cd, Fe and Pb while Heinz bioaccumulated the highest concentrations of As and Zn. The lowest concentrations for most trace metals was recorded in Cherry tomato. The calculated contamination factor values of trace metals like Cr, Cu, Pb and Zn were above the safe value of 1 which indicated that some of the tomato fruits may be unsafe for human consumption. However, the contamination factor values for the remaining trace metals were well below the safe value of 1. The tomato varieties used in the study, bioaccumulated the toxic trace metals in their fruits and values obtained for Zn, Pb, Cu, Cr, and Fe were higher than the acceptable limit set by the World Health Organization (WHO) and the Agency for Toxic Substances and Disease Registry (ATSDR) (2008). Using sewage sludge like the one used in this study may not be suitable for some crops. Hence, care should be taken when these tomato varieties are either cultivated or harvested for consumption and attention should be given to the growth medium used.