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Arsenic (As)-contaminated paddy soil could result in elevated levels of As in rice plants and sequentially harm human health. The Fe3O4-modified biochar (NBC-Fe) prepared by the coprecipitation method was applied in a pot experiment to investigate its effect on mobility and bioavailability of As in soil and to reduce As accumulation in rice tissues (brown rice, husks, spikelets, leaves, stems, and roots). Compared with non-application (CK), application of NBC-Fe significantly increased the cation exchange capacity (CEC), decreased As availability, and raised the As concentration of crystalline hydrous oxide–bound fraction in the soil. The addition of 0.05–1.6% (w/w) NBC-Fe significantly reduced the As concentrations in brown rice by 9.4–47.3%, which was lower than the level set by the National Food Safety Standards of China (0.2 mg/kg). The NBC-Fe treatment decreased As concentrations in iron plaque (DCB-As), and the DCB-As had the very significant correlations (P

Cadmium (Cd) is a ubiquitous environmental pollutant, and rice (Oryza sativa L.) is the main staple food in China. Water regimes are promising, controllable, and environment-friendly agricultural measures for remediation Cd contaminated soil. The optimum water regime for ensuring high rice yield with low Cd contents in brown rice was investigated. A pot experiment was conducted to study the effects of Cd migration and accumulation from paddy soil to rice plants under four water regimes with three growth stages of two rice cultivars, ‘Xiangwanxian 12’ (X12) and ‘Weiyou 46’ (W46) grown in a polluted soil with 5 mg kg−1 of Cd. The relationship between Cd accumulation amounts in rice plant and soil Eh was also investigated. The four regimes were moisture throughout growth (M), moisture before the filling stage and flooding after filling (M-F), flooding before filling and moisture after filling (F-M), and continual flooding (F). Water regimes effectively reduced Cd accumulation in rice at the three growth stages, whereas the filling stage was suggested to be as the key stage for interventions to prevent Cd transport and accumulation. Compared with M, the M-F, F-M, and F regimes significantly reduced Cd contents of rice tissues (root, stem, husk, and brown rice) at the maturity stage. Under the M, F-M, M-F, and F regimes, Cd contents were 2.17, 2.10, 0.21, 0.06 mg kg−1 in X12 brown rice and 3.27, 0.47, 0.19, 0.10 mg kg−1 in W46 brown rice, respectively. Importantly, Cd contents of brown rice of X12 (0.06 mg kg−1 under regime F) and W46 (0.19 mg kg−1 under regime M-F and 0.10 mg kg−1 under regime F) did not exceed China’s food safety standard of 0.20 mg kg−1 (GB 2762–2017). Moreover, there were significant positive exponential relationships between soil Eh and Cd accumulation amounts in belowground and aboveground parts of rice. The M-F regime (W46) and F regime (X12) could ensure high rice yield with low Cd contents in brown rice and could be recommended as the irrigation management in rice production. Simultaneously, keeping soil Eh under 50 mV is also necessary after the rice filling stage.

Rice (Oryza sativa L.) planted in cadmium (Cd)- and arsenic (As)-contaminated soil is considered the main source of dietary Cd and As intake for humans in Southeast Asia and thereby poses a threat to human health. Minimizing the transfer of these pollutants to rice grain is an urgent task for environmental researchers. The main objective of this study was to investigate the effects and the mechanisms of a combined amendment (hydroxyapatite + zeolite + biochar, HZB) on decreasing Cd and As accumulation in rice. In situ remediation and aqueous solution adsorption experiments were conducted. The results showed that after application of HZB, Cd and As concentrations of the exchangeable fraction and TCLP extraction in soil decreased with the growth of rice plants. Cd concentrations in rice tissues were decreased at the tillering, filling and maturing stages after in situ remediation, while As concentrations in rice tissues were decreased only at the maturing stage. When 8 kg·plot−1 (9000 kg ha−1) HZB was applied, concentrations of Cd and inorganic As in brown rice were decreased to 0.18 and 0.16 mg kg−1, respectively, lower than the levels permissible for grain in China, i.e., 0.2 mg kg−1. Application of HZB reduced Cd accumulation in rice tissues, and the suppression of Cd accumulation was significantly greater than that of As. Furthermore, HZB significantly increased rice grain yield. An aqueous solution adsorption experiment demonstrated that HZB could adsorb and covalently bind Cd and As (V) via -OH, -COOH, -Si-O-Si and CO32- groups to produce carboxylates, silicates and carbonates, thereby promoting in situ immobilization of Cd and As in soil solution.

The scientific application of stabilized materials has been considered an effective method for the in situ remediation of Cd-contaminated soil. This study aimed to investigate the persistence of the effect of a combined amendment of limestone and sepiolite (LS) on soil Cd availability and accumulation in rice grown in a mildly Cd-contaminated paddy field (0.45 mg/kg of Cd) over three consecutive rice seasons. 1125–4500 kg/ha of LS was applied to the soil before the first rice planting season and 562.5–2250 kg/ha of LS was supplemented before the third rice planting season. The application of LS (1125–4500 kg/ha) increased the soil pH by 0.44–1.09, 0.18–0.53, and 0.42–0.68 in the first, second, and third season, respectively, and decreased the soil acid-extractable Cd content by 18.2–36.4%, 17.7–33.5%, and 9.6–17.6%. LS application significantly decreased the Cd contents in the rice tissues. The application of 4500 kg/ha of LS decreased the Cd content in brown rice to below the National Food Limit Standard of 0.2 mg/kg (GB 2762-2017) in the three consecutive rice seasons. However, the effect of LS on the soil-rice system was significantly weakened in the third season. The supplementary application of 562.5–2250 kg/ha of LS further decreased the Cd content in brown rice by 26.1–56.5% and decreased the health risk index by 23.7–43.8%. Therefore, it was recommended to apply 4500 kg/ha of LS in the first season and to supplement 2250 kg/ha of LS in the third season to effectively guarantee the clean production of rice in three consecutive rice seasons.

Planting sweet potato (Ipomoea batatas (L.) Lam.) instead of rice in the area contaminated with heavy metals is one of the measures to ensure people's health and agricultural economy. Therefore, it is important to screen the low accumulation cultivars of sweet potato and to find out the concentration rule of cadmium (Cd) and lead (Pb) in edible parts along with the associated health risks to humans. A field experiment was performed with fourteen of three main types (starch, purple, and edible-type) of sweet potato cultivars grown on farmland polluted with Cd and Pb in eastern Hunan Province, China. The Cd and Pb concentrations in the sweet potato tissues as well as the yield were measured. The yield of the shoot and tuberous root of the fourteen sweet potato cultivars ranged from 14.59 to 68.57 and 26.35-50.76 t ha-1 with mean values of 33.09 and 33.46 t ha-1, respectively. Compared with purple and edible-type cultivars, the starch-type cultivar had lower Cd and Pb concentrations in the flesh, but higher in the shoot. The Cd and Pb concentrations in the flesh of cultivars Shangshu 19, Sushu 24, Yushu 98, and Xiangshu 98 were lower than MCL provided in Chinese National Food Safety Standards GB2762-2017. Based on the hazard index (HI), the consumption of sweet potato flesh is lower health risk, while shoots pose a greater health risk to local people and Cd is the main cause of the risk. As a result, sweet potato cultivars Shangshu 19, Sushu 24, Yushu 98 and Xiangshu 98 can be plant in serve Cd and Pb contaminated soils with the advantages of easy cultivation, high yield and economic benefits without stopping agricultural production.

A pot experiment was carried out to investigate the remediation of paddy soils contaminated with both Cd and As. The effects of a soil additive (HZB: hydroxyapatite + zeolite + biochar) on the chemical speciation of Cd and As in the soil and on the accumulation and translocation of these two elements in rice plants were studied. The application of HZB decreased the concentration of acid-extractable Cd in the soil by 7.3–32.6% by promoting the transformation of soil Cd from soluble to insoluble species; as a result, the concentration of organically bound Cd in the soil increased by 6.8–49.5%. The application of HZB also promoted the transformation of soil As from soluble to insoluble species, thus increasing the concentration of Ca-bound As by 34.1–93.4% and reducing the concentration of soil-exchangeable As by 12.2–55.1%. However, when the application rate of HZB was greater than 4.0 g kg−1, the concentration of soil-exchangeable As increased again. It was found that the application of HZB decreased the Cd and As bioaccumulation capacity of rice root, and among various rice organs, rice husk was the highest in Cd transferring capacity, whereas rice root was the highest in As transferring capacity. When the amount of HZB applied was 0.05–0.2%, the Cd and As concentrations in the various parts of the rice plants decreased significantly.

Rice as a paddy field crops, iron-containing materials application could induce its iron plaque formation, thereby affecting cadmium (Cd) transportation in the rhizosphere and its uptake in root. In this study, a hydroponic experiment was conducted to investigate the effects of three exogenous iron materials, namely nano-Fe3O4-modified biochar (BC–Fe), chelated iron (EDTA-Fe), and ferrous sulfate (FeSO4), on the iron plaque formation on the surface of rice root, and to investigate the effects of formed iron plaque on the absorption, migration, and transportation of Cd and Fe in rice plant. The results showed that yellow-brown and brown iron plaque was formed on surface cells of the Fe-treated rice root, and some black particles were embedded in the iron plaque formed by BC-Fe. The proportion of crystallized iron plaque (31.8%–35.9%) formed by BC-Fe was much higher than that formed by EDTA-Fe and FeSO4. The Cd concentrations in the crystallized iron plaque formed by BC-Fe were 7.64–13.0 mg·kg−1, and increased with the increasing of Fe concentrations in the plaque. The Cd translocation factor from root to stem (TFr-s) and the Cd translocation factor from stem to leaf (TFs-l) with BC-Fe treatment decreased by 84.7% and 80.0%, respectively. The results demonstrated that application BC-Fe promoted the formation of iron plaque and enhanced the sequestration of Cd and Fe in roots, thus reduced the transportation and accumulation of Cd in aerial rice tissues.

The main objectives of the present study were to investigate the levels of arsenic (As) in 23 vegetable species planted on As-polluted soil and assess the human health risks of contaminated vegetable consumption. The target hazard quotient (THQ) and target cancer risk (TR) methods were employed to evaluate the human health risks posed by exposure to As through vegetable consumption. Our results indicate substantial As contamination of the experimental soil. Significant differences were detected in the concentrations of total and inorganic As in the edible parts of the various vegetables grown on contaminated soil, which were generally in the following order: leafy vegetables > stem vegetables > root vegetables > melon and fruit vegetables. The total THQ value for As due to vegetable consumption for children (4.81) was higher than that for adults (3.66), the TR values for As due to vegetable ingestion for adults (1.65 × 10−3) and children (2.17 × 10−3) were significantly beyond the range of accepta...

The objectives of the present study were to investigate the mitigation of lead (Pb), cadmium (Cd), and arsenic (As) in a multi-metal contaminated soil and their accumulation in rice plants (Oryza sativa L., cv II You 93) using a combined amendment (CMF, calcium carbonate + metakaolin + fused calcium–magnesium phosphate fertilizer). The results showed that application of CMF was effective in reducing the acid-extractable concentrations of soil Pb and Cd. The exchangeable concentrations of soil As showed an initial decrease followed by a gradual increase. The application of 0.2% CMF notably reduced the concentrations of Pb, Cd, and As in brown rice by 46.5%, 43.6%, and 32.0%, respectively. The concentration of As in brown rice was 0.179 mg kg−1 at 0.2% CMF, which met the maximum levels of contaminants in foods of China (MLs) (the ML of Pb, Cd, and As is 0.2 mg kg−1 according to the China national standard GB 2762-2012). At 1.6% CMF, the concentrations of Pb and Cd in brown rice were 0.002 and 0.185 ...

The use of Napier grass to remediate heavy metal-contaminated soil is a new phytoremediation technique. The objective of this study was to evaluate the ability of Napier grass (Pennisetum purpureum Schumach.) to remediate Cd- and Zn-contaminated cultivated soil under nonmowing and mowing and the possibility of safe utilization of the stem and leaf after detoxification by liquid extraction. Three Napier grass varieties, P. purpureum cv. Mott (PM), P. purpureum cv. Red (PR), and P. purpureum cv. Guiminyin (PG), were planted in a field with 3.74 mg kg−1 Cd and 321.26 mg kg−1 Zn for 180 days. The maximum amounts of Cd and Zn removed by PG were 197.5 and 5023.9 g ha−1, respectively, almost equaling those of hyperaccumulators. Compared with nonmowing, mowing did not decrease the Cd and Zn contents in various tissues but increased the biomasses of PM, PR, and PG by 86.6%, 18.9%, and 26.1%, respectively. Compared with nonmowing, the amounts of Cd removed by PM, PR, and PG under mowing increased by 110.5%, 40.0%, and 107.9%, respectively, and that of Zn increased by 63.0%, 53.1%, and 71.6%. The dominant Cd and Zn chemical fractions in Napier grass were the pectate- and protein-integrated fractions. After liquid extraction, although the nutrient element (Ca, K, Mg, and Mn) contents in the stem and leaf were reduced significantly, the Cd and Zn contents decreased below the limit of the Chinese Hygienic Standard for Feeds, and the crude protein content was largely retained. Such detoxified stems and leaves can be safely used as feeds or as raw materials for energy production.

To investigate the differences in cadmium (Cd) and lead (Pb) uptake and translocation among rape cultivars and genotypes and select suitable rape cultivars for both safe production and soil remediation, a field experiment was carried out with 39 rape cultivars of three genotypes on a farmland polluted with Cd and Pb in eastern Hunan Province, China. The Cd and Pb contents in rape tissues were measured, and the amount of Cd and Pb removed was calculated. The results showed that Cd in rape plants accumulated mostly in stems, while Pb accumulated mostly in roots. The Cd accumulation in various rape tissues followed the sequence stem > root > husk > rapeseed, while the Pb accumulation followed the sequence root > stem > husk > rapeseed. The total Cd and Pb removed by planting rape were 4.50–23.6 g ha−1 and 5.85–13.7 g ha−1, respectively, and the Cd and Pb contents in rapeseeds were in the range 0.11–0.47 mg kg−1 and 0.03–0.84 mg kg−1, respectively. Only the Pb content in rapeseed of “Youyan 9” exceeded the limit of the maximum levels of contaminants in foods (GB2762-2017, Pb ≤ 0.2 mg kg−1). In this experiment, the roots of most rape cultivars showed a greater capacity for Cd transport, while the stems showed a greater capacity for Pb transport. Except for the TFstem-husk for Cd, there were no significant differences in the TFs and BAFs of 39 rape cultivars, and clear variations in Cd content were found in the stems of the three genotypes, while there was no significant difference in the Cd and Pb contents in the other tissues. In the farmland polluted with Cd and Pb, planting “Xiangzayou 695” and “Youyan 2013” not only reduced soil pollution but also allowed the production of safe rapeseed.

Rapeseed (Brassica napus L.) is a winter oil crop and biodiesel resource that has been widely cultivated in the southern part of China. Applying rapeseed residue (RSD) to summer rice fields is a common agricultural practice under rice-rapeseed double cropping systems. However, in Cd-contaminated paddy fields, the influence mechanisms of this agricultural practice on the migration and distribution of Cd fractions in soil are not clear. Therefore, a field experiment was carried out to analyse the changes in soil pH, organic matter (OM), microbial biomass carbon (MBC) and nitrogen (MBN), enzyme activity (urease (UA), acid phosphatase (ACP), and dehydrogenase (DH)), Cd distribution fractions, and Cd concentration in rice tissues after RSD application. The results showed that RSD treatment significantly increased the soil OM and MBC concentrations and UA, ACP, and DH activities, decreased the soil acetic acid-extractable fraction of Cd (ACI-Cd), and increased the reducible fraction of Cd (Red-Cd). The formation of stable organic complexes and chelates upon application of RSD is a result of the high affinity of Cd for soil OM. The activities of soil ACP, DH and MBC can well reflect Cd ecotoxicity in soil, particularly the DH activity. In addition, RSD application was helpful in inducing iron plaque formation. The "barrier" effect of iron plaque resulted in reduced Cd accumulation in different tissues of rice. The health risk of rice consumption also decreased as a result of RSD application; it decreased by 0.89-30.0% and 24.1-51.7% in the two tested fields. Overall, the application of RSD was increased soil OM, microbial biomass, and enzyme activity, and these changes was instrumental in reduce the risk of cadmium pollution in rice fields.

The objective of the present study was to investigate the effects of rapeseed dregs (RSD, a commonly organic fertilizer in rural China) at application rates of 0, 0.75, 1.5, and 3.0 % on Cd availability in soil and its accumulation in rice plants (Oryza sativa L., Xiangwanxian 12#, and Weiyou 46#) by means of a pot experiment. The results showed that application of RSD resulted in a sharp decrease in the soil TCLP-extractable Cd content. However, the soil TCLP-extractable Cd content in amended soil gradually increased during the rice growing period. Application of RSD significantly increased Cd transport from root to shoot and the amount of Cd accumulated in the aerial part. RSD was an effective organic additive for increasing rice grain yield, but total Cd content in rice grain was also increased. At an application rate of 1.5-3.0 % RSD, the total Cd content in Weiyou 46# brown rice was 0.27-0.31 mg kg-1, which exceeded the standard safe limit (0.2 mg kg-1) and was also higher than that of Xiangwanxian 12# (0.04-0.14 mg kg-1). Therefore, Weiyou 46# had a higher dietary risk than Xiangwanxian 12# with RSD application. We do not recommend planting Weiyou 46# and applying more than 0.75 % RSD in Cd-contaminated paddy fields.

Nano-Fe3O4-modified biochar (BC–Fe) was prepared by the coprecipitation of nano-Fe3O4 on a rice husk biochar surface. The effects of BC-Fe on cadmium (Cd) bioavailability in soil and on Cd accumulation and translocation in rice (Oryza sativa L. cv. ‘H You 518’) were investigated in a pot experiment with 7 application rates (0.05–1.6%, w/w). BC-Fe increased the biomass of the rice plants except for the roots and affected the concentration and accumulation of Cd and Fe in the plants. The Cd concentrations of brown rice were significantly decreased by 48.9%, 35.6%, and 46.5% by the 0.05%, 0.2%, and 0.4% BC-Fe treatments, respectively. Soil cation exchange capacity (CEC) increased by 9.4%–164.1% in response to the application of BC-Fe (0.05–1.6%), while the soil Cd availability decreased by 6.81%–25.0%. However, 0.8–1.6% BC-Fe treatments promoted Cd transport to leaves, which could increase the risk of Cd accumulation in brown rice. Furthermore, BC-Fe application promoted the formation of iron plaque and enhanced the root interception of Cd. The formation of iron plaque reduced the toxicity of Cd to rice roots, but this barrier effect was limited and had an interval threshold (DCB-Fe: 22.5–27.3 g·kg−1) under BC-Fe treatments.

Rice consumption is considered the main source of human dietary Cd intake in Southeast Asia. This study aimed to investigate Cd uptake, accumulation, and remobilization in iron plaque and rice (Oryza sativa L. cv. ‘Xiangwanxian 12′) tissues at different growth stages. A pot experiment was performed in two Cd-contaminated paddy soils. Cd concentrations in iron plaque and rice tissues at five different growth stages (tillering, booting, milky, dough, and maturing) were measured. Cd concentrations in iron plaque and rice tissues (roots, stems, leaves, spikelet, husks, and brown rice) varied with growth stage. Cd accumulation in rice plants increased with extending growth in both soils, reaching 15.3 and 35.4 μg/pot, respectively, at the maturing stage. The amounts of Cd in brown rice increased from the milky to maturing stages, with the greatest percentage uptake during the maturing stage. Cd amount in iron plaque significantly affected the uptake and accumulation of Cd in roots and aerial parts of rice plants. Accumulated Cd in leaves was remobilized and transported during the booting to maturing stages, and the contributions of Cd transportation from leaves to brown rice were 30.0% and 22.5% in the two soils, respectively. A large amount of Cd accumulated in brown rice during the maturing stage. The transportation of remobilized Cd from leaves was also important for the accumulation of Cd in brown rice.

A soil spiking experiment at two Cd levels (0.72 and 5.20 mg kg-1) was conducted to investigate the effects of rapeseed cake (RSC) at application rates of 0%, 0.75%, 1.5%, and 3.0% (w/w) on iron plaque formation and Cd uptake by rice (Oryza sativa L.) seedlings. The use of RSC did result in a sharp decrease in soil bioavailability of Cd and a significant increase in rice growth, soil pH and organic matter. Application of RSC increased the amount of iron plaque formation and this effectively inhibited the uptake and translocation of Cd into the rice seedlings. RSC was an effective organic additive for increasing rice growth and reducing Cd uptake by rice plant, simultaneously. These results could be used as a reference for the safety use of Cd polluted paddy soil.

The objectives of the present study were to investigate heavy metal accumulation in 22 vegetable species and to assess the human health risks of vegetable consumption. Six vegetable types were cultivated on farmland contaminated with heavy metals (Pb, Cd, Cu, Zn, and As). The target hazard quotient (THQ) method was used to assess the human health risks posed by heavy metals through vegetable consumption. Clear differences were found in the concentrations of heavy metals in edible parts of the different vegetables. The concentrations of heavy metals decreased in the sequence as leafy vegetables > stalk vegetables/root vegetables/solanaceous vegetables > legume vegetables/melon vegetables. The ability of leafy vegetables to uptake and accumulate heavy metals was the highest, and that of melon vegetables was the lowest. This indicated that the low accumulators (melon vegetables) were suitable for being planted on contaminated soil, while the high accumulators (leafy vegetables) were unsuitable. In Shizhuyuan area, China, the total THQ values of adults and children through consumption of vegetables were 4.12 and 5.41, respectively, suggesting that the residents may be facing health risks due to vegetable consumption, and that children were vulnerable to the adverse effects of heavy metal ingestion.