Sewage sludge land application: Balancing act between agronomic benefits and environmental concerns

Abstract

Land disposal of sewage sludge has become an attractive practice worldwide. However, ubiquitous presence of toxic metals raises environmental and public health concerns regarding subsequent plant uptake. This study was intended to determine the suitability of sewage sludge application under hot environmental condition using tomato crop. A greenhouse experiment was conducted to investigate various levels of heavy metals as well as potential health risks associated with the consumption of tomato fruit grown in sludge amended soil. Plant samples were collected on four different growth stages: beginning of the experiment before planting, twice during growing period, and at the end of the experiment (post-harvest). Samples were analyzed for commonly occurring heavy metal contaminants (Cd, Cr, Cu, Pb and Zn). In this study, we did not observe consistent relationship between metal concentrations in tomato plant and various sludge ratio. Heavy metal levels were consistently greater in roots than other parts of tomato plant, followed by stem. The most salient finding from our study was that Cd and Pb, two very important metals because of their solubility and subsequent mobility, were not detectable in tomato fruits under any of the sludge treatments, compared to other parts of tomato plants. The trend in transfer factors (TF) followed the sequence Zn > Cu > Cr > Cd for roots and Zn > Cu > Cr for fruits, suggesting the risk of heavy metal TF to tomato fruits is minimal. It can be inferred from these results that potential risk may be greater through consumption of leafy vegetables and tuber crops.