Purpose

Recently, the cadmium (Cd) accumulation in the black shale area has attracted increasing attentions, due to its extensive distribution and extremely high background values. The aim of our study is to explore the impacts of soil properties on Cd uptake by rice, and identify the key factors of Cd transfer from soil to rice in the black shale area.

Materials and methods

A total of 40 pairs of topsoil and rice samples were collected from the paddy fields in the black shale area and the control area. The relevant parameters in the soils, as well as the Cd concentrations in different rice tissues, were analyzed.

Results and discussion

The results show that 87.5% of the soil samples in the study area exceed the risk screening values of Cd, and 42% of the rice grain samples exceed the allowable limit of Cd. The key factor influencing Cd uptake by rice in this area is the soil phytoavailable Cd concentration. Compared to those in the control area, the soils in the black shale area have a much higher Cd level but a lower phytoavailability due to the higher pH, which is caused by carbonate. Even so, the level of Cd in the rice from the black shale area indicates a much higher ecological risk.

Conclusions

Soil pH and iron (Fe) are the most important variables exhibiting direct effects on Cd fractions in soils. In light of the neutral or weakly alkaline soil in the black shale area, we concluded that increasing the soil pH was not a feasible way to reduce Cd levels in the rice in this area.

中文翻译：

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黑色页岩引起地球化学背景高的土壤-水稻系统中地源镉生物利用度评价

目的

近来，由于其广泛分布和极高的背景值，黑色页岩中镉（Cd）的积累引起了越来越多的关注。我们研究的目的是探讨土壤性质对水稻吸收Cd的影响，并确定黑页岩地区Cd从土壤向水稻转移的关键因素。

材料和方法

从黑页岩区和控制区的稻田中收集了总共40对表土和水稻样品。分析了土壤中的相关参数以及不同水稻组织中的Cd浓度。

结果和讨论

结果表明，研究区87.5％的土壤样品超过了镉的风险筛选值，而42％的稻谷样品超过了镉的允许限量。影响该地区水稻吸收Cd的关键因素是土壤中植物有效Cd浓度。与对照地区相比，黑色页岩地区的土壤镉含量高得多，但由于碳酸盐引起的pH值较高，其植物利用率较低。即便如此，黑页岩地区大米中的镉含量仍显示出更高的生态风险。

结论

土壤pH和铁（Fe）是最重要的变量，对土壤中的Cd分数具有直接影响。根据黑页岩地区中性或弱碱性土壤，我们得出结论，提高土壤pH值不是降低该地区稻米中Cd含量的可行方法。