Arsenic accumulation and metabolism in rice (Oryza Sativa L).

The use of arsenic (As) contaminated groundwater for irrigation of crops has resulted in elevated concentrations of arsenic in agricultural soils in Bangladesh, West Bengal (India), and elsewhere. Paddy rice (Oryza sativa L.) is the main agricultural crop grown in the arsenic-affected areas of Bangladesh. There is, therefore, concern regarding accumulation of arsenic in rice grown those soils. A greenhouse study was conducted to examine the effects of arsenic-contaminated irrigation water on the growth of rice and uptake and speciation of arsenic. Treatments of the greenhouse experiment consisted of two phosphate doses and seven different arsenate concentrations ranging from 0 to 8 mg of As L-1 applied regularly throughout the 170=day post-transplantation growing period until plants were ready for harvesting. Increasing the concentration of arsenate in irrigation water significantly decreased plant height, grain yield, the number of filled grains, grain weight, and root biomass, while the arsenic concentrations in root, straw, and rice husk increased significantly. Concentrations of arsenic in rice grain did not exceed the food hygiene concentration limit (1.0 mg of As kg-1 dry weight). The concentrations of arsenic in rice straw (up to 91.8 mg kg-1 for the highest As treatment) were of the same order of magnitude as root arsenic concentrations (up to 107.5 mg kg-1), suggesting that arsenic can be readily translocated to the shoot. While not covered by food hygiene regulations, rice straw is used as cattle feed in many countries including Bangladesh. The high arsenic concentrations may have the potential for adverse health effects on the cattle and an increase of arsenic exposure in humans via the plant−animal−human pathway. Arsenic concentrations in rice plant parts except husk were not affected by application of phosphate. As the concentration of arsenic in the rice grain was low, arsenic speciation was performed only on rice straw to predict the risk associated with feeding contaminated straw to the cattle. Speciation of arsenic in tissues (using HPLC−ICP-MS) revealed that the predominant species present in straw was arsenate followed by arsenite and dimethylarsinic acid (DMAA). As DMAA is only present at low concentrations, it is unlikely this will greatly alter the toxicity of arsenic present in rice

Arsenic-speciation in arsenate-resistant and non-restistant populations of the earthworm Lumbricus rubellus.

In this study, the earthworm, Aporrectodea longa, was used as a model soil organism to assess the impact of ageing upon the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in soil. The objectives were to characterise the temporal changes in the extractability/availability of PAHs amended into soil and to examine how the decline in PAH availability to earthworms related to the decline in chemical availability as determined by solvent extraction. Two PAHs (pyrene and benz[a]anthracene) were spiked into sterilised soil and aged in microcosms for up to 240 days. The earthworms were incubated in the PAH spiked soils, at 0, 30, 60, and 240 days after spiking, for a period of 28 days. After exposure, the earthworm-PAH tissue concentrations were measured. Change in chemical extractability of the soil-PAHs was monitored throughout the incubation by employing a sequential extraction technique with two solvents of different polarities. The chemical extractability and bioavailability of both PAHs reduced with increased soil contact time. Pyrene and benz[a]anthracene both displayed biphasic profiles in chemical extractability and earthworm bioavailability, but the rates and extents differed. Thus, chemical extractability does not accurately predict the bioavailable fraction of PAHs in the soil and does not agree with work reported earlier using Eisenia fetida, hence it follows that the earthworm species may be important in determining the bioaccumulation of soil-associated PAHs. Further, the ecological niche occupied by the experimental species will influence feeding behaviour and thus, perhaps, the degree of accumulation. Therefore, the use of the manure earthworm, E. fetida, in screening of contaminated soils (as recommended by the USEPA) may underestimate toxicity or accumulatory potential