Heavy metals levels in Spinacia oleracea and Daucus carota harvested from soil treated with different amounts of sewage sludge in Pretoria, South Africa

Abstract

This study investigated the effects of four different rates of sewage sludge amendment (100, 200, 300, and 400g) on Spinacia oleracea (Leafy vegetable) and Daucus carota (Root vegetable) on the growth and the accumulation of heavy metals. The yield of S. oleracea and D. carota was measured in terms of weight while heavy metals levels at harvest were measured using ICP-MS. The growth and yield at harvest in S.oleracea were in following order 300g > 400g > 200g > 100g while in D.carota the order for the yield was 400g > 200g > 300g > 100g. Elemental concentrations showed that iron (Fe) had the highest average concentration for both plants and ranged between 68.60 ± 2.82mg/kg − 1503.00 ± 82.31mg/kg. Differences obtained as a result of the amendments were significant for heavy metals such as Fe, Pb, Cd from the different plant parts. Concentrations of Pb and Cr recorded in the leaves of S. oleracea were above the recommended limit for human consumption with the exception from leaves of S. Olereacea harvested from soil treated with 400g of sewage sludge. There was no particular trend of heavy metals accumulation noted in the experiment except for the values obtained for trace elements in the roots of D. caraota where, roots parts harvested either from soil treated with 300g or 400g recorded the highest concentrations of these elements. The bioaccumulation factor showed that the elements were bioaccumulated from the soil.