The Effect of Organic Matter Application on the Availability of As in the As-Contaminated Paddy Soils.

The increase of As uptake into rice (Oryza sativa L.) plants has become a potential dietary risk to human health. This study investigates the effects of application of three kinds of organic matter on the As release in soil solutions and accumulation in paddy rice grown in As-contaminated soils. Two As-spiked soils (Pc and Cf) and a geogenically As-contaminated soil (Gd) collected from Taiwan were used. The soils were amended with, 0% (control), 1%, and 4% organic matters [soybean meal (SB), cattle-dung compost (CD), and sugarcane dregs compost (SC)] respectively. The results of soil flooding incubation study indicated that organic matter applications enhanced the release of As into soil solutions, and the extent of enhancement was higher in the SB (easily decomposable organic matter) treatments than CD and SC treatments, due to the concentrations of dissolve organic carbon in soil solutions were higher in the SB application. The accumulation of As in rice plants was enhanced by organic matter amendments compared with control treatments, and the SB treatments had the higher As accumulation due to the higher As concentrations in soil solutions. This effect of application of organic matter on As release into soil solutions could be more notable in soils with high pH and low As sorption capacity (such as Cf soil), thus resulting in the increase of As toxicity to rice plants. Therefore, it is important to evaluate the properties of organic matters and soils carefully before adding organic materials into As-contaminated soils.