Environmental Geochemistry Laboratory, University of Texas at San Antonio, San Antonio, TX, USA.
Chemosphere. 2011 Sep;84(11):1563-71. doi: 10.1016/j.chemosphere.2011.05.047. Epub 2011 Jun 30.
Although organoarsenical pesticides are being phased out, sites with high concentrations of organic arsenical residues still exist due to the long-term application of these pesticides. The biotic and abiotic speciation of dimethylarsinic acid (DMA) can result in the formation of inorganic arsenic (As) species. Oxidation state, retention, and thereby persistence, varies according to temporal changes, influencing the availability and toxicity of contaminants. The current greenhouse study aimed at evaluating temporal changes in the oxidation state of As, geochemical partitioning, and bioaccessibility. Four soils with varying physiochemical properties were contaminated with DMA at two concentrations (675 and 1,500 mg kg(-1) of As). Rice plants were grown for a 6 months period, following which, the soils were allowed to age. The operationally defined forms of As and its bioaccessibility was analyzed at 0, 6 months, 1 year, and 3 years. Changes in oxidation state of As were evaluated immediately after spiking and after 3 years of soil-pesticide equilibration. Results show that geochemical partitioning of As was affected significantly (P<0.05) by soil type, loading rates, and equilibration time. Arsenic was bound mainly to the poorly-crystalline Fe/Al-oxyhydroxides in the soil. However, these interactions did not affect As bioaccessibility, presumably due to the dissolution of the bound fractions of As in the acidic stomach. While 74-94% of the total bioaccessible As was transformed to As(V), 4-19% was transformed to the more toxic As(III). This study indicates that although aging affected the geochemical partitioning of As in the soil, bioaccesibility was controlled by the gastric pH.
虽然有机胂农药正在逐步淘汰，但由于这些农药的长期使用，仍存在高浓度有机胂残留的地点。二甲砷酸（DMA）的生物和非生物形态可以导致无机砷（As）形态的形成。氧化态、保留率以及因此的持久性因时间变化而变化，影响污染物的可用性和毒性。本温室研究旨在评估 As 的氧化态、地球化学分配和生物可利用性随时间的变化。四种具有不同物理化学性质的土壤用 DMA 以两种浓度（675 和 1500 mg kg(-1)As）污染。种植水稻 6 个月后，让土壤老化。在 0、6 个月、1 年和 3 年后分析 As 的操作定义形式及其生物可利用性。在添加后立即和土壤-农药平衡 3 年后评估 As 的氧化态变化。结果表明，As 的地球化学分配受土壤类型、加载率和平衡时间的显著影响（P<0.05）。砷主要与土壤中结晶度差的 Fe/Al 氢氧化物结合。然而，这些相互作用并没有影响 As 的生物可利用性，可能是由于酸性胃中结合态 As 的溶解。尽管总可生物利用的 As 中有 74-94%转化为 As(V)，但有 4-19%转化为更有毒的 As(III)。本研究表明，尽管老化会影响土壤中 As 的地球化学分配，但生物可利用性受胃 pH 值控制。
