Determining the appropriate soil cadmium (Cd) criteria for vegetable production is important for ensuring that the Cd concentrations of the vegetables meet food safety standards. The soil extractable Cd criteria for vegetable production are also essential for both food safety and environmental management, especially in areas with a high natural background level. In the present study, soil total and extractable Cd criteria were derived using the approach of species sensitivity distribution integrated with soil aging and bioavailability as affected by soil properties. A dataset of 90 vegetable species planted in different soils was compiled by screening the published in literature in five bibliographic databases using designated search strings. The empirical soil–plant transfer model was applied to normalize the bioaccumulation data. After normalization, the intra-species variability was reduced by 18.3 to 84.4%. The soil Cd concentration that would protect 95% (HC₅) of the species was estimated by species sensitivity distribution curves that were fitted by the Burr III function. The soil Cd criteria derived from the added approach for risk assessment were proposed as continuous criteria based on a combination of organic carbon and pH in the soil. Criteria for total Cd and EDTA-extractable Cd in the soil ranged from 0.23 to 0.61 mg kg^–1 and from 0.09 to 0.25 mg kg^–1, respectively. Field experimental data were used to validate the applicability and validity of these criteria. Most of the predicted HC₅ values in the field experimental sites were below the 1:1 line. These results provide a scientific basis for soil Cd criteria for vegetable production that will ensure food safety.

Cadmium (Cd) is one of the most toxic heavy metals in the environment.  Atmospheric deposition has been found to be the main source of Cd pollution of soil on a large scale in China, and identification of the relationships between anthropogenic emission, atmospheric deposition, and Cd accumulation in soil is important for developing ways to mitigate Cd non-point pollution.  In this study, the relationship between atmospheric emission, atmospheric deposition, and soil Cd accumulation in the Middle-Lower Yangtze Plain in China was investigated using datasets of atmospheric emission, deposition, and soil accumulation from the literatures published between 2000 and 2020.  The results showed that the soil Cd accumulation rate in the study area exceeded the national average (4.0 μg kg^–1 yr^–1) and continued to accumulate in recent decades, although the average accumulation rate decreased from 9.45 μg kg^–1 yr^–1 (2000–2010 period) to 8.86 μg kg^–1 yr^–1 (2010–2020 period).  The contribution of atmospheric deposition flux to Cd increment in the soil was in the range of 22–29%, with the atmospheric deposition flux decreasing from 0.54 mg m^–2 yr^–1 (2000–2010) to 0.48 mg m^–2 yr^–1 (2010–2020), both values being greater than the national average.  Atmospheric Cd deposition and emission were highly correlated in a provincial administrative region, which is close to a ratio of 1.0.  Emission factors may be in a state of dynamic change due to the influences of new Cd emission control technologies and environmental policies.  As the main sources of Cd emissions, dust, and smoke emissions per ton of non-ferrous metal production decreased by 64.7% between the 2000–2010 and 2010–2020 periods.  Although new environmental policies have been instigated, atmospheric emission of Cd is still excessive.  It was hoped that the findings of this work would provide a scientific basis for the rational control of atmospheric emissions and Cd pollution of soil.

   The variations of grain cadmiun (Cd) concentrations, translocation factors (TFs) of Cd from roots to shoots/grains of six rice cultivars, characterized with different Cd-sensitivities in polluted soil were studied, the selected rice cultivars were Xiangzao 17 (R1), Jiayu 211 (R2), Xiangzao 42 (R3), Zhuliangyou 312 (R4), Zhuliangyou 611 (R5), and Jinyou 463 (R6), respectively. The Cd subcellular distribution and Cd binding characteristics on subcellular fractions of rice root cell wall (CW) were further investigated. The results showed that the rice grain Cd contents varied significantly, with a maximum variation of 47.0% among the cultivars, the largest grain Cd content was observed with cultivar R1 (Cd-sensitivity cultivar) and the smallest with R5 (Cd-tolerance cultivar). The translocation factors of Cd from roots to shoots (TF_shoot) and roots to grains (TF_grain) varied greatly among the cultivars. In general, the TF_grain of the cultivars followed the order of R1>R2>R3>R4> R6-R5. The Cd concentration (mg kg^–1 FW) in the fraction of root CW, the fraction of cell wall removing pectin (CW-P) and the fraction of cell wall removing pectin and hemicellulose (CW-P-HC) of the cultivars generally followed the order of CW-P>CW>CW-P-HC; the ratios of Cd concentration (mg kg^–1 FW) in the fraction of CW-P to that of CW were mostly more than 1.10, while the ratios of Cd concentration in the fraction of CW-P-HC to that of CW were mostly less than 0.60, indicating that Cd was mainly stored in the hemicellulose of the root CW. The ratios of Cd of CW-P-HC to CW generally followed the descending order of R1~R2>R3>R4>R5~R6 for the cultivars, which implied that hemicellulose is probably the main subcellular pool for transferring Cd into rice grain, and it restrains the translocation of Cd from shoot to the grain, especially for the Cd-tolerance cultivars (R5 and R6), the compartmentation of more Cd in hemicellulose in root CW is probably one of the main mechanisms for Cd tolerance of rice cultivars.

Ecological risk assessment of metals in soils is important to develop the critical loads of metals in soils. Phytotoxicity is one of the endpoints for ecological risk assessment of soils contaminated with metals. The sensitivity of eight Chinese plant species (bok choy, mustard, tomato, green chilli, paddy rice, barley, spinach and celery) to copper (Cu) and nickel (Ni) toxicity in two Chinese soils was investigated to assess their potential use for ecological risk assessment in the region. The results showed that bok choy and mustard were the two most sensitive species to Cu and Ni toxicities. Assessment of metal accumulation by the plants demonstrated that bok choy shoot had the highest bioconcentration factor (BCF, the ratio of metal concentration in plant shoots to metal concentration in soil). Given the importance of bok choy to agricultural production in Asia, it is therefore important that these sensitive plant species are included in species sensitivity distributions for ecological risk assessment of Cu and Ni in soils.

A field plot experiment in a calcareous soil with wheat and maize rotation was carried out for 2 yr. The study aimed to investigate the effects of biosolids (sewage sludge or chicken manure) application on nitrogen (N) and phosphorus (P) accumulation in soils and to develop a model for the effects of biosolids application on available P (Olsen-P) accumulation in soils, by which the quantities of biosolids that can be safely applied to agricultural soils were estimated. The results showed that heavy application of biosolids to agricultural soils based on the N requirement of a wheat-maize rotation cropping system will oversupply P. Soil total N was increased by 0.010 g kg-1 at application rate of 1 ton sewage sludge per hectare. The high ratio of N to P in grains of wheat and maize (from 4.0 to 7.6) and low ratio of N to P in biosolids (<2) led to more surplus P accumulated in soils. Although plant yields and P uptake by plants increased with increasing quantities of applied biosolids in soils, there was still an average 2.87 mg kg-1 increase in Olsen-P in the plough layer treated with biosolids for every 100 kg P ha-1 surplus. A predictive model was developed based upon the initial Olsen-P in soils, P input rates, crop yield, soil pH, and cultivation time. From the model, it is suggested that sewage sludge could be applied to calcareous soils for 12 yr using the recommended application rate (9 tons ha-1 yr-1). The field results will be helpful in achieving best management of biosolids application for agricultural production and environmental protection.