Phytoextraction assessment of green amaranth (Amaranthus viridis Linn.) grown on soil amended with sewage sludge

Abstract

Disposal of sewage sludge is the major challenge facing wastewater treatment facilities. Several reports claimed that land application is the best option to manage sludge disposal. However, there is perception that sludge contains heavy metals that are potentially harmful to the living organisms. Thus, the study assessed heavy metals uptake of Amaranthus viridis grown on soil amended with sludge sourced from three wastewater treatment facilities. The vegetable was chosen because it is mostly planted by the farmers who could replace NPK fertiliser which is expensive with readily and freely available sludge from the facilities in Lagos State. The plant shoot harvested at 42 days and the amended soil after harvest were analysed for 5 selected heavy metals (Cu, Zn, Cd, Cr and Pb) using standard methods. To know which portions of the vegetable the metals were accumulated, transfer factor, bioconcentration factor and translocation index were computed for phytoextraction test. The results showed that the transfer factor of Zn > 1 but of Cu < 1. Both bioconcentration factor and translocation index were < 100. The Cd, Cr and Pb were below the machine detection limits. The study observed that the levels of heavy metals absorbed by the vegetable were insignificant when compared to the amount remaining in the soil.

Keywords: Sewage sludge, Green amaranth, Phytoextraction, Heavy metals