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Manganese oxides are naturally occurring powerful oxidants and scavengers, which can control the mobility and bioavailability of arsenic (As). However, the effect of synthetic nanostructured manganese oxides on the mobilization and transportation of As at actual paddy soils are poorly understood, especially in soils with low or medium background Mn concentration. In the present study, a novel nano manganese oxide with superior reactivity and surface area has been synthesized. A 90-d soil incubation experiment combined with pot and field rice cultivation trials were designed to evaluate the effectiveness of exogenous α-MnO

In order to study the role of mulberry (Moms alba L) as an economic crop for remediation of cadmium (Cd) contaminated soil, the transport of Cd from mulberry to silkworm were investigated. Three varieties of mulberry (Yuesang-11, Nongsang-14, and Qiangsang-1) with three planting densities were cultivated in two heavy metal-contaminated fields named Dongkou in Shaoyang city and Linxiang in Yueyang city in Hunan province respectively. The both field soils were contaminated by heavy metals, especially by Cd. The potential risks of heavy metals in Linxiang's soil were higher than those in Dongkou's because of higher concentrations of Cd. Since the promotion of Cd concentrations in aerial parts (stem, branch and leaf) resulted from the increase of planting density, the method of high planting density is beneficial to improve the efficiency of the remediation of Cd contaminated soil. The percentages of average Cd contents of mulberry in Dongkou accounted for 44%, 20%, 18% and 16% in roots, stems, branches and leaves respectively, while the Cd contents were 38%, 27%, 19% and 16% distributed in roots, stems, branches and leaves respectively. Mulberry leaves from contaminated soils was applied in food source of silkworms in this study. Although there is Cd uptake occurred in silkworm growth and its products (cocoons and chrysalis), Cd contents in cocoons are lower than the national standard (100 μg*kg-1) for textile industry of China. Therefore, mulberry can be regarded as an economical crop to control soil contamination with Cd.

Compared to other cereals, rice has particular strong As accumulation. Therefore, it is very important to understand As uptake and translocation among different genotypes. A field study in Chenzhou city, Hunan province of China, was employed to evaluate the effect of arsenic-contaminated soil on uptake and distribution in 34 genotypes of rice (including unpolished rice, husk, shoot, and root). The soil As concentrations ranged from 52.49 to 83.86 mg kg(-1), with mean As concentration 64.44 mg kg(-1). The mean As concentrations in rice plant tissues were different among the 34 rice genotypes. The highest As concentrations were accumulated in rice root (196.27-385.98 mg kg(-1) dry weight), while the lowest was in unpolished rice (0.31-0.52 mg kg(-1) dry weight). The distribution of As in rice tissue and paddy soil are as follows root ≫ soil > shoot > husk > unpolished rice. The ranges of concentrations of inorganic As in all of unpolished rice were from 0.26 to 0.52 mg kg(-1) dry weight. In particular, the percentage of inorganic As in the total As was more than 67 %, indicating that the inorganic As was the predominant species in unpolished rice. The daily dietary intakes of inorganic As in unpolished rice ranged from 0.10 to 0.21 mg for an adult, and from 0.075 to 0.15 mg for a child. Comparison with tolerable daily intakes established by FAO/WHO, inorganic As in most of unpolished rice samples exceeded the recommended intake values. The 34 genotypes of rice were classified into four clusters using a criteria value of rescaled distance between 5 and 10. Among the 34 genotypes, the genotypes II you 416 (II416) with the lowest enrichment of As and the lowest daily dietary intakes of inorganic As could be selected as the main cultivar in As-contaminated field.

A field experiment was conducted to investigate the effect of bean stalk (BBC) and rice straw (RBC) biochars on the bioavailability of metal(loid)s in soil and their accumulation into rice plants. Phytoavailability of Cd was most dramatically influenced by biochars addition. Both biochars significantly decreased Cd concentrations in iron plaque (35-81 %), roots (30-75 %), shoots (43-79 %) and rice grain (26-71 %). Following biochars addition, Zinc concentrations in roots and shoots decreased by 25.0-44.1 and 19.9-44.2 %, respectively, although no significant decreases were observed in iron plaque and rice grain. Only RBC significantly reduced Pb concentrations in iron plaque (65.0 %) and roots (40.7 %). However, neither biochar significantly changed Pb concentrations in rice shoots and grain. Arsenic phytoavailability was not significantly altered by biochars addition. Calculation of hazard quotients (HQ) associated with rice consumption revealed RBC to represent a promising candidate to mitigate hazards associated with metal(loid) bioaccumulation. RBC reduced Cd HQ from a 5.5 to 1.6. A dynamic factor's way was also used to evaluate the changes in metal(loid) plant uptake process after the soil amendment with two types of biochar. In conclusion, these results highlight the potential for biochar to mitigate the phytoaccumulation of metal(loid)s and to thereby reduce metal(loid) exposure associated with rice consumption.