Mining activities have increased the accumulation of heavy metals in farmland soil and in food crops. To identify the key soil properties influencing heavy metal bioavailability and accumulation in food crops, 81 crop samples and 81 corresponding agricultural soil samples were collected from rape, wheat, and paddy fields. Heavy metal (copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), iron (Fe), and manganese (Mn)) concentrations in soils and rape, wheat, rice grains were determined using inductively coupled plasma atomic emission spectroscopy, and soil physicochemical properties (pH, organic matter, total nitrogen, total phosphorus, available phosphorus, and available potassium (AK)) were analyzed. Soil extractable metals were extracted using various single extractants (DTPA, EDTA, NHOAc, NHNO, and HCl). The average concentrations of Cu, Zn, Pb, Cd, and Mn in the soil samples all exceeded the local geochemical background value (background values of Cu, Zn, Pb, Cd, and Mn are 43.0, 81.0, 28.5, 0.196, and 616 mg/kg, respectively), and Cd over-standard rate was the highest, at 98%. Furthermore, soil total Cd concentrations (0.1-24.8 mg/kg) of more than 86% of the samples exceeded the soil pollution risk screening value (GB 15618-2018). The sources of Cu, Zn, Pb, Cd, and Mn in soils were mainly associated with mining activities. The key factors influencing heavy metal bioavailability were associated with the types of extractants (complexing agents or neutral salt extractants) and the metals. Cd and Pb concentrations in most wheat and rice grain samples exceeded the maximum allowable Cd and Pb levels in food, respectively, and Cd concentrations in approximately 10% of the rice grain samples exceeded 1.0 mg/kg. Furthermore, rice and wheat grains exhibited higher Cd accumulation capacity than rape grains, and despite the high soil Cd concentrations in the rape fields, the rape grains were safe for consumption. High soil pH and AK restricted Cd and Cu accumulation in wheat grains, respectively. Soil properties seemed to influence heavy metal accumulation in rice grains the most.© 2022. The Author(s).

为探究不同叶面肥阻控水稻富集镉的机制,以期为解决农田重金属镉污染和食品安全问题提供科学的依据。本研究归纳了镉对水稻的生长危害,水稻叶与叶面肥的特征包括水稻叶与水稻的养分吸收、叶面肥的种类、叶面肥的特点及叶面肥阻控水稻富集镉的机理。指出影响叶面肥阻控水稻富集镉的效果因素,如天气、温度、利用率、喷施次数和浓度等,提出与其他阻控措施相结合、开展其他种类叶面肥研究、继续叶面肥理论基础研究及加强统一管理和规范操作技术等一系列展望。

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimizing Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we designed three Cd concentration stress treatments (Cd1: 0.20 mg·kg, Cd2: 0.60 mg·kg, and Cd3: 1.60 mg·kg) and two foliar silicon (Si) treatments (CK: no spraying of any material, and Si: foliar Si spraying) to conduct pot experiments on soil Cd stress. The results showed that spraying Si on the leaves reduced the Cd content in brown rice by 4.79-42.14%. Si application increased net photosynthetic rate (Pn) by 1.77-4.08%, stomatal conductance (Gs) by 5.27-23.43%, transpiration rate (Tr) by 2.99-20.50% and intercellular carbon dioxide (CO) concentration (Ci) by 6.55-8.84%. Foliar spraying of Si significantly increased the activities of superoxide dismutase (SOD) and peroxidase (POD) in rice leaves by 9.84-14.09% and 4.69-53.09%, respectively, and reduced the content of malondialdehyde (MDA) by 7.83-48.72%. In summary, foliar Si spraying protects the photosynthesis and antioxidant system of rice canopy leaves, and is an effective method to reduce the Cd content in brown rice.© 2024. The Author(s).

Rice is a worldwide staple food and heavy metal contamination is often reported in rice production. Heavy metal can originate from natural sources or be present through anthropogenic contamination. Therefore, this review summarizes the current status of heavy metal contamination in paddy soil and plants, highlighting the mechanism of uptake, bioaccumulation, and health risk assessment. A scoping search employing Google Scholar, Science Direct, Research Gate, Scopus, and Wiley Online was carried out to build up the review using the following keywords: heavy metals, absorption, translocation, accumulation, uptake, biotransformation, rice, and human risk with no restrictions being placed on the year of study. Cadmium (Cd), arsenic (As), and lead (Pb) have been identified as the most prevalent metals in rice cultivation. Mining and irrigation activities are primary sources, but chemical fertilizer and pesticide usage also contribute to heavy metal contamination of paddy soil worldwide. Further to their adverse effect on the paddy ecosystem by reducing the soil fertility and grain yield, heavy metal contamination represents a risk to human health. An in-depth discussion is further offered on health risk assessments by quantitative measurement to identify potential risk towards heavy metal exposure via rice consumption, which consisted of in vitro digestion models through a vital ingestion portion of rice.

为明确施用纳米硅和活性硅在不同镉污染条件下的降镉效应，选取轻度污染的稻田土壤，盆栽设置双因素试验，即设3个镉水平（Cd1，不添加镉，低镉；Cd2，添加5 mg/kg镉，中镉；Cd3，添加10 mg/kg镉，高镉）和3个硅肥水平（Si0，不施硅肥；Si1，叶片喷施纳米硅20 mg/pot；Si2，叶喷纳米硅20 mg/pot+土施活性硅120 mg/kg）共9个处理。结果表明，随着土壤镉浓度的增加，水稻根系和茎叶生物量降低，有效穗数减少，产量显著下降，与Cd1处理相比，Cd2和Cd3处理水稻产量分别降低7.1%和20.0%；施用硅肥能够降低根系和茎叶镉含量，促进根系和地上部分干物质积累，提高有效穗数，进而增加水稻产量，与Si0处理相比，Si1和Si2处理水稻产量分别增加12.3%和15.4%；与Si0处理相比，Si1和Si2处理还能够降低镉从颖壳向糙米和精米转运，糙米镉含量分别降低26.0%和42.3%，精米镉含量分别降低25.2%和42.0%，Si2处理的降镉效果要优于Si1处理。综上，在中镉和高镉胁迫下，水稻叶片喷纳米硅+土壤施活性硅的处理增产和降镉效果显著，可以作为镉污染稻田降镉的有效措施进一步研究。

为了实现水稻的安全生产，降低土壤Cd生物有效性及糙米Cd含量，以4种炭基复合改良剂为材料，开展田间小区试验，研究其对土壤Cd生物有效性以及水稻植株吸收、累积及转运Cd的影响。结果表明，施用4种炭基复合改良剂（生物炭+沸石BZ、生物炭+沸石+有机肥BZM、生物炭+铁粉BFe、生物炭+钙镁磷肥BP）后，早稻和晚稻产量提高了4.41%~21.18%，其中BZM和BP表现较好，早稻增产更为显著。晚稻中Cd富集系数(BCF)总和大大超过早稻（1.07~3.75倍）。施用4种复合改良剂可使糙米Cd含量降低到0.03~0.23 mg/kg，除了施用BZ的晚稻糙米超标外，其余均符合国家食品安全标准，其中BP的效果最好。该研究表明炭基复合改良剂在Cd污染土壤修复中具有一定的应用价值，其中BP在中性或弱碱性土壤中的潜力更大一些。