Reduction of Arsenic Uptake by Lettuce with Ferrous Sulfate Applied to Contaminated Soil

Abstract

Soil contamination by arsenic (As) presents a hazard in many countries and there is a need for techniques to minimize As uptake by plants. A proposed in situ remediation method was tested by growing lettuce (Lactuca sativa L. cv. Kermit) in a greenhouse pot experiment on soil that contained 577 mg As kg(-1), taken from a former As smelter site. All combinations of iron (Fe) oxides, at concentrations of 0.00, 0.22, 0.54, and 1.09% (w/w), and lime, at concentrations of 0.00, 0.27, 0.68, and 1.36% (w/w), were tested in a factorial design. To create the treatments, field-moist soil, commercial-grade FeSO4, and ground agricultural lime were mixed and stored for one week, allowing Fe oxides to precipitate. Iron oxides gave highly significant (P < 0.001) reductions in lettuce As concentrations, down to 11% of the lettuce As concentration for untreated soil. For the Fe oxides and lime treatment combinations where soil pH was maintained nearly constant, the lettuce As concentration declined in an exponential relationship with increasing FeSO4 application rate and lettuce yield was almost unchanged. Iron oxides applied at a concentration of 1.09% did not give significantly lower lettuce As concentrations than the 0.54% treatment. Simultaneous addition of lime with FeSO4, was essential. Ferrous sulfate with insufficient lime lowered soil pH and caused mobilization of Al, Ba, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sr, and Zn. At the highest Fe oxide to lime ratios, Mn toxicity caused severe yield loss.

Availability to Lettuce of Arsenic and Lead from Trace Element Fertilizers in Soil

“…Another reason could be related to the high content of soluble Fe. The role of ferrous or ferric iron in reducing the solubility and availability of soil As has been demonstrated (Moore et al, 2000;Warren and Alloway, 2001;Kim and Davis, 2003).…”

The influence of arsenic speciation (AsIII & AsV) and concentration on the growth, uptake and translocation of arsenic in vegetable crops (silverbeet and amaranth): greenhouse study

“…When we compared with the control, a significant decline was observed at both low (0.5 mg/l) and high Fe doses (10 mg/l). However, we found the effect of Fe was more predominant at low concentrations than at high, probably because Fe-As binding sites become saturated and therefore excess Fe cannot achieve a similarly significant effect on As uptake (Warren and Alloway 2003). The low Fe dose is so effective in reducing As uptake that it can reduce nearly half (45%) of the As content in the shoots when compared with control; this suggests that iron salts might be a useful remediation tool in contaminated soils, but a neutral pH of the growth media needs to be maintained.…”

Phytoremediation of Soil Trace Elements

“…Reduced phytoavailability was shown for Fe additions to soils [233]. Reduction of in vitro bioavailable or bioaccessible soil As has been demonstrated by Subacz et al [234], by Beak et al [235], and by Smith et al [236] by adding Fe to soils.…”