Remediation of Heavy Metals

Contamination of agricultural soil is becoming an increasingly serious problem because of long-term exposure to pollutants in irrigation water, sludge, fertilizers, and pesticides. Cadmium (Cd) is one of the most dangerous and potentially toxic metals. Pollution by Cd is especially significant as contaminated soils are used for agriculture; this metal is easily absorbed from soils into crops, inhibiting plant growth and nutrient uptake. So, the present study aimed to elucidate the effect of accumulation Cd over the permissible limits on growth of higher plants, e.g., alfalfa and soil microorganisms, e.g., rhizobium bacteria and arbuscular mycorrhiza fungi. In this study we also attempted to find an optimum solution for the problem of soil pollution with Cd through the application of biochar (BC) as bioadsorbent, rhizobia, (Rh) and arbuscular mycorrhizal fungi (AMF) as biofertilizers. CdCl 2 was applied in a pot experiment in presence and absence of BC, AMF and Rh. Cd negatively affected alfalfa growth and yield, content of essential minerals such as N, P, K, Ca and Mg in leaves and roots, activity of nodules nitrogenase and rhizosphere dehydrogenase. AMF colonization % and the total microbial count decreased under Cd stress. Application of BC, AMF and Rh individually or in combination improved alfalfa growth, leaf and root content of essential minerals, fungal population and the microbial count. On the other side, these treatments reduced Cd uptake and translocation from roots to seeds. Solo application of BC contributed in Cd immobilization through the metal adsorption and increasing soil alkalinity. Application of BC together with AMF and Rh significantly promoted alfalfa growth and yield, the leaf and root content of mineral ions, the fungal populations and the microbial count compared to control and Cd-stressed plants.

Trace metal contamination of soil and surface waters arising from increased emissions from industries,traffic,
auto-mechanic activities and agriculture raise concern on human health and environmental quality. The aim of
this study was to find practical and cost-effective measures to reduce metal uptake in crops grown on metal
contaminated soils. A laboratory batch experiment using 6 potential mineral–organic amendment combinations
in the ratio 1: 2, (a)composted Farm yard manure (cFYM) + Gravel sludge ( GrS), (b) Vemicompost ( VC) + GrS, (c)
composted sewage sludge (cSS)+ GrS , ( d) Red mud (RM)+ cFYM), (e) RM + VC, (f) cSS+ RM, were used to treat
trace metal contaminated soil in a completely randomized pot experiment using Amaranthus viridis as a test
crop. Result showed that all the amendment combinations had varied potential to reduce metal uptake by
Amaranthus viridis when compared to control. There was appreciable reduction in metal leachability across all
the amendments: Cd (<51%), Cu (<67%), Zn (<34%) and Pb (<69%) on the average when compared to controls,
with a concurrent reduction of uptake into Amaranthus viridis root and shoot tissues (Cd < 62%, Pb < 68%, Cu<
66% and Zn 56%) on the average. Dry matter yield in the amendments is in the order cFYM + GrS> cFYM +RM>
cSS+GrS>cSS+RM>Control>VC+RM >VC+GrS.Acid extractable (DTPA) fractions of Cd, Pb, Cu and Zn were reduced
by up to 76%, 79%, 65% and 49%, respectively in amended soils. Investigations on long term effects of metal
mobility is recommended