There is growing concern regarding human dietary exposure to arsenic (As) via consumption of rice. The concentration and speciation of As in rice are highly variable, and models describing rice As speciation as a function of environmental covariates remain elusive. We conducted a survey of paddy rice and soil in the Mekong Delta with the objective of linking patterns in rice As content to soil chemical variables or hydrogeological parameters. The sum of As species (ΣAs) in husked rice averaged 243 μg/kg and the average inorganic As (iAs) content was 84%. There was no relationship found between rice As concentration or speciation and As levels in soil. However, mean As concentrations in groundwater near rice sampling locations were strongly correlated with grain ΣAs and iAs over a large part of the study region, despite the fact that groundwater is not commonly used for rice paddy irrigation in this region. We hypothesize that surficial sediments with high concentrations of soluble and plant-available As also serve as sources of arsenic to downgradient shallow aquifers, explaining the observed associations between rice and groundwater As. This study suggests that shallow groundwater As concentrations may serve as a useful indicator for locations at risk of elevated iAs concentrations in rice.

人们通过食用大米而在饮食中暴露于砷（As）的问题日益引起人们的关注。水稻中砷的含量和形态高度可变，描述将水稻形态作为环境协变量的函数的模型仍然难以捉摸。我们对湄公河三角洲的水稻和土壤进行了一项调查，目的是将稻米中砷的含量与土壤化学变量或水文地质参数联系起来。糙米中砷的总和平均为243μg/ kg，无机砷的平均含量为84％。水稻中砷的含量或形态与土壤中的砷含量之间没有关系。但是，在研究区域的大部分地区，稻米采样地点附近的地下水中的平均砷浓度与谷物ΣAs和iAs高度相关，尽管该地区并不普遍使用地下水灌溉稻田。我们假设可溶性和植物有效砷含量高的表层沉积物也可作为砷的来源，从而使浅层含水层降级，从而解释了水稻与地下水砷之间的相关关系。这项研究表明，浅层地下水砷的浓度可以作为水稻中iAs浓度升高风险的有用指标。