Department of Plant Sciences, University of California-Davis, 387 North Quad, Davis, CA 95616, USA.
Department of Land, Air and Water Resources, University of California-Davis, 387 North Quad, Davis, CA 95616, USA.
Sci Total Environ. 2019 Feb 1;649:300-307. doi: 10.1016/j.scitotenv.2018.08.216. Epub 2018 Aug 18.
The accumulation of arsenic (As) in rice grain is a public health concern since As is toxic to humans; in particular, inorganic As can cause many chronic diseases including cancer. Rice crops are prone to accumulating As, in part, due to the anaerobic soil conditions triggered by the traditional continuously flooded irrigation practice. The objective of this study was to determine how the severity and the timing (i.e. crop stage) of a single soil drying period impact total As concentration and As speciation within the rice (both white and brown) grain, compared to a continuously flooded (CF) control. Drying the soil until the perched water table reached 15 cm below the soil surface (same severity as in the "Safe Alternate Wetting and Drying"), which in this study corresponded to a soil (0-15 cm) water potential of ~0, did not decrease grain As concentrations, regardless of timing. Drying the soil to Medium Severity [MS: soil (0-15 cm) water potential of -71 kPa] or High Severity [HS: soil (0-15 cm) water potential of -154 kPa] decreased total As by 41-61%. However, inorganic As did not always decrease because the severity and the timing of soil drying affected As speciation within the grain. Overall, the soil had to be dried to HS and/or late in the growing season (i.e., at booting or heading instead of at panicle initiation) to decrease inorganic As concentration in the rice grain. This study indicates that the imposition of a single soil drying period within the growing season can mitigate As accumulation in rice grain, but it depends on the severity and timing of the drying period. Further, irrigation management affects As speciation within the rice grain and this must be considered if regulations on inorganic As are based on a percentage of total As measured.
砷（As）在水稻中的积累是一个公共卫生关注点，因为 As 对人体有毒；特别是无机 As 可导致许多慢性疾病，包括癌症。水稻作物容易积累 As，部分原因是传统的连续淹水灌溉实践引发的厌氧土壤条件。本研究的目的是确定单次土壤干燥期的严重程度和时间（即作物阶段）如何影响糙米（白米和糙米）和糙米中总 As 浓度和 As 形态，与连续淹水（CF）对照相比。将土壤干燥至地下水位达到距土壤表面 15cm 处（与“安全交替湿润和干燥”中的严重程度相同），在本研究中，这对应于土壤（0-15cm）水势约为 0，无论时间如何，都不会降低谷物 As 浓度。将土壤干燥至中度严重程度[MS：土壤（0-15cm）水势为-71kPa]或高度严重程度[HS：土壤（0-15cm）水势为-154kPa]可降低总 As 浓度 41-61%。然而，无机 As 并不总是降低，因为土壤干燥的严重程度和时间影响了谷物中 As 的形态。总体而言，必须将土壤干燥到 HS 并/或在生长季节后期（即在抽穗或扬花期而不是在颖花分化期），才能降低水稻籽粒中的无机 As 浓度。本研究表明，在生长季节内施加单次土壤干燥期可以减轻水稻籽粒中 As 的积累，但这取决于干燥期的严重程度和时间。此外，灌溉管理会影响水稻籽粒中 As 的形态，这在基于总 As 测量百分比制定无机 As 法规时必须考虑。
