College of Architecture and Environment, Sichuan University, No. 24 South Section 1 First Ring Road, Chengdu 610065, Sichuan, PR China.
College of Architecture and Environment, Sichuan University, No. 24 South Section 1 First Ring Road, Chengdu 610065, Sichuan, PR China.
Sci Total Environ. 2020 Dec 1;746:141248. doi: 10.1016/j.scitotenv.2020.141248. Epub 2020 Jul 25.
There are large areas of moderately Cd-contaminated rice paddies (Cd content was less than risk intervention value) in southwest China, under natural conditions, the effect of irrigation water system's distribution on the Cd contamination in soil and rice is still less accurate. In this study, a survey of paired soil-rice (n = 1520) samples was conducted in a large paddy of about 7000 ha in southwest China that originated from the same parent material and grew with the same rice varieties. Specially, three representative characteristic regions (area A, B, C) were selected from north to south to thoroughly investigate the reasons for pollution characteristics. Background soil, irrigation water and sediment, atmospheric deposition, fertilizer were sampled to study the causes of pollution. Results showed the biological accumulation factor (BAF = C /C ) of area C in the south reached 1.34, which was about 8 times higher than that of area A in the north. The uneven distribution of irrigation water due to geographical reasons was the most important factor leading to this pollution characteristics. The Cd content in soil of north was much higher than that in the south due to the history of Cd-contaminated irrigation and background content of Cd. During farmland formation, river impinges resulted in a gradual decrease in both Cd content and pH in the background soil from north to south. Both of historical polluters and major irrigation systems were distributed in area A. However, when sewage irrigation stopped about 30 years ago, long-term weakly alkaline irrigation increased the pH of the soil from acidic to neutral in area A. Meanwhile, flooding irrigation in area A reduced the absorption of Cd by roots compared area C where was rarely flooded during the rice planting process due to the lack of irrigation water.
在中国西南地区，存在着大面积中度镉污染的稻田（镉含量低于风险干预值），在自然条件下，灌溉水系的分布对土壤和水稻中镉污染的影响仍不够准确。在本研究中，对中国西南地区一个约 7000 公顷的大型稻田中采集的 1520 对土壤-水稻（n=1520）样本进行了调查，这些样本源自同一母质，种植相同的水稻品种。特别地，从北到南选择了三个具有代表性的特征区域（A、B、C 区），以彻底调查污染特征的原因。采集背景土壤、灌溉水和沉积物、大气沉降物、肥料等样本，以研究污染原因。结果表明，南部 C 区的生物积累因子（BAF=C/C）达到 1.34，是北部 A 区的约 8 倍。由于地理位置的原因，灌溉水的不均匀分布是导致这种污染特征的最重要因素。北部土壤中的镉含量远高于南部，这是由于历史上的镉污染灌溉和背景镉含量造成的。在农田形成过程中，河流的冲击导致从北到南背景土壤中镉含量和 pH 值逐渐降低。历史污染源和主要灌溉系统都分布在 A 区。然而，大约 30 年前，污水灌溉停止后，由于缺乏灌溉水，A 区长期的弱碱性灌溉使土壤的 pH 值从酸性变为中性。同时，由于 A 区在水稻种植过程中很少发生洪水，淹没灌溉减少了根对 Cd 的吸收，而 C 区则很少发生洪水。
