Occurrence and distribution of arsenic in soils and plants

Abstract

Inorganic arsenicals have been used in agriculture as pesticides or defoliants for many years and, in localized areas, oxides of arsenic have contaminated soils as a result of fallout from ore-smelting operations and coal-fired power plants. Use of inorganic arsenicals is no longer permitted in most agricultural operations, and recent air pollution controls have markedly reduced contamination from smelters. Thus, this paper will concentrate on the effect of past applications on arsenic accumulation in soil, phytotoxicity to and uptake by plants as influenced by soil properties, and alleviation of the deleterious effects of arsenic. Once incorporated into the soil, inorganic arsenical pesticides and arsenic oxides revert to arsenates, except where the soil is under reducing conditions. The arsenate ion has properties similar to that of orthophosphate, and is readily sorbed by iron and aluminum components. This reaction greatly restricts the downward movement (leaching) of arsenic in soils and the availability of arsenic to plants. Several methods of estimating plant available arsenic in soils have been developed. They involve extraction of the soil with reagents used to estimate phosphorus availability. This extractable arsenic is reasonably well correlated with reduced plant growth by, and plant uptake of arsenic. For most plants, levels of arsenic in the edible portion of the plant are well below the critical concentration for animal or human consumption, even when severe phytotoxicity occurs. Alleviation of arsenic phytotoxicity has been attempted by increasing the soil pH, by use of iron or aluminum sulfate, by desorbing arsenate with phosphate and subsequent leaching, and by cultural practices such as deep plowing. Only limited benefits have accrued from these procedures the cost of which is often prohibitively high. Since attempts to reduce arsenic toxicity have not been very successful, its excessive accumulation in soils should be avoided.

Effect of arbuscular mycorrhizal fungi on growth of Gmelina arborea in arsenic-contaminated soil

“…Subjection of arsenic toxicity to human and animal health can result from ingestion of surface residues of arsenic in plant. The amount of arsenic in soil is directly correlated with the amount of arsenic in the whole plant (Walsh et al 1977). Plants show variable tolerance limit to arsenic toxicity.…”

The Effects of Soil Amendments on the Growth of Atriplex halimus and Bituminaria bituminosa in Heavy Metal-Contaminated Soils

“…Regarding As, the shoot tissue concentrations measured in B. bituminosa sown and cultivated in soil LB (>3.5 μg g −1 ; Table 6) were probably phytotoxic (Chaney 1989), particularly as members of the Fabaceae may be more sensitive to As (Walsh et al 1977). This was likely another factor, which limited its growth in this soil.…”

Metallurgy, environmental pollution and the decline of Etruscan civilisation

“…In groundwater systems, arsenic can also be derived from the dissolution of arsenic-bearing iron oxides in unconsolidated aquifers' (Madhavan and Subramanian 2000). 'In less reduced environments, such as those in flooded soils, the relatively toxic arsenite (MasO 2 ) can be formed' (Walsh et al 1977). 'Soluble arsenic has been observed to increase in flooded rice soils' (Deuel and Swoboda 1972).…”

“…[NB-up to 3 miles from the Obuasi mine]'Plant growth stimulation has been observed as a result of low levels of arsenic additions to soils, perhaps as a result of the displacement of phosphate by arsenate from solid surfaces, thereby increasing phosphate availability' (Walsh et al 1977). 'Plants vary considerably in their tolerance to high levels of soil arsenic.…”

“…'Plants vary considerably in their tolerance to high levels of soil arsenic. Cabbage, carrots, rye and grapes are highly tolerant; corn, beets and squash are moderately tolerant, whilst onions, cucumbers and legumes have low tolerance' (Walsh et al 1977).…”