Accurate derivation and modelling of criteria of soil extractable and total cadmium for safe wheat production.

It is significant to establish an accurate model to predict cadmium (Cd) criteria for safe wheat production. More importantly, for better evaluation of the risk of Cd pollution in high natural background areas, the soil extractable Cd criteria are needed. In the present study, the soil total Cd criteria were derived using the method of cultivars sensitivity distribution integrated with soil aging and bioavailability as affected by soil properties. Firstly, the dataset that meet the requirements was established. Dataset from thirty-five wheat cultivars planted in different soils published in literature of five bibliographic databases were screened using designated search strings. Then, the empirical soil-plant transfer model was used to normalize the bioaccumulation data. Afterwards, the soil Cd concentration for protecting 95 % (HC5) of the species was calculated from species sensitivity distribution curves, and the derived soil criteria were obtained from HC5 prediction models that based on pH. The process of derivation for soil EDTA-extractable Cd criteria was the same way as the soil total Cd criteria. Soil total Cd criteria ranged from 0.25 to 0.60 mg/kg and soil EDTA-extractable Cd criteria ranged from 0.12 to 0.30 mg/kg. Both the criteria of soil total Cd and soil EDTA-extractable Cd were further validated to be reliable using data from field experiments. The results suggested that the criteria of soil total Cd and soil EDTA-extractable Cd in the study can ensure the safety of Cd in wheat grains and thereby enable local agricultural practitioners to develop appropriate management for croplands.

Integrating bioavailability and aging in the criteria derivation of cadmium for the safe production of rice in paddy soils.

It is significant to derive an appropriate cadmium (Cd) threshold for the rice to ensure that the Cd concentration of rice grains meets the food safety standards. In the present study, soil thresholds for Cd were derived using the method of species sensitivity distribution based on aging time, cultivars, and soil properties. Dataset from thirty-nine rice cultivars planted in different soils published in literature of five bibliographic databases were screened using designated search strings to explore their differences in Cd accumulation capacity in paddy soil. The empirical soil-plant transfer model was used to normalize the bioaccumulation data. Later, the soil Cd concentration for protecting 95% (HC5) of the cultivars was calculated using species sensitivity distribution curves 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 the combination of soil pH and organic carbon in soil. Soil Cd criteria ranged from 0.34 to 1.18 mg/kg. The prediction model for HC5 was applied to field experimental data to validate its validity and applicability. The predicted Cd thresholds were less than the field experiment Cd thresholds. In conclusion, this study provided valuable and scientific bases for setting soil Cd criteria for paddy soils.

Integrating bioavailability and soil aging in the derivation of DDT criteria for agricultural soils using crop species sensitivity distributions.

Although the agricultural use of dichlorodiphenyltrichloroethane (DDT) has been banned for decades in many countries around the world, the detection of DDT and its metabolites in soils is very common due to their persistence. DDTs (sum of DDT and its metabolites) in farmland soils can be absorbed by crops at different levels and accumulate in the edible parts of agricultural products, posing threats to the health of human being. However, no information on the species sensitivity distribution (SSD) of crops with regard to DDTs has been reported due to the lack of enough bioavailability data and models to normalize the bioavailability data from different sources. Based on the bioconcentration factors of 17 crop species in Chinese soils obtained from previous studies, the criteria of DDTs in soils was derived according to the quality standard of agricultural products using the SSD method. Corrections for water content and aging time were conducted to normalize the data from different sources. The risk values of agricultural products at different concentration levels of DDTs in soils were also evaluated. It was found that oil crops are able to take up more DDTs than non-oil crops, so the soil criteria were calculated separately for oil crops and non-oil crops, which were 0.083 mg/kg and 0.29 mg/kg, respectively. With the residual concentrations of DDTs in soils at the range of 0.01-0.5 mg/kg, 0-8% of the agricultural products exceeded the permissible limits for DDTs which were set in the National Food Safety Standard of China. The results also demonstrated the feasibility for applying SSDs to derive the soil criteria of DDTs in order to ensure the safety of agricultural products. This work will provide information for the risk assessment and the establishment of soil environmental quality standards to ensure safe agricultural production.

Derivation of Soil Criteria of Cadmium for Safe Rice Production Applying Soil-Plant Transfer Model and Species Sensitivity Distribution.

Widespread soil contamination is hazardous to agricultural products, posing harmful effects on human health through the food chain. In China, Cadmium (Cd) is the primary contaminant in soils and easily accumulates in rice, the main food for the Chinese population. Therefore, it is essential to derive soil criteria to safeguard rice products by assessing Cd intake risk through the soil-grain-human pathway. Based on a 2-year field investigation, a total of 328 soil-rice grain paired samples were collected in China, covering a wide variation in soil Cd concentrations and physicochemical properties. Two probabilistic methods used to derive soil criteria are soil-plant transfer models (SPT), with predictive intervals, and species sensitivity distribution (SSD), composed of soil type-specific bioconcentration factor (BCF, Cd concentration ratio in rice grain to soil). The soil criteria were back-calculated from the Chinese food quality standard. The results suggested that field data with a proper Cd concentration gradient could increase the model accuracy in the soil-plant transfer system. The derived soil criteria based on soil pH were 0.06-0.11, 0.33-0.59, and 1.51-2.82 mg kg-1 for protecting 95%, 50% and 5% of the rice safety, respectively. The soil criteria with soil pH further validated the soil as being safe for rice grains.

Proper management of lead-contaminated agricultural lands against the exceedance of lead in agricultural produce: Derivation of local soil criteria.

The Measures for Management of Soil Environment in Agricultural Land (Trial, Nov. 01, 2017, China) recently came into effect and highlighted the proper management of contaminated croplands to lower risks of exceedances of contaminants, especially toxic trace metals in agricultural produce. We aimed to develop local soil criteria for lead (Pb) in Hezhang county of southwestern China by the inverse use of reliable models linking Pb contamination levels between soils and vegetables. Dilute nitric acid (0.43 M) extraction, a new ISO standard (ISO-17586:2016) for extracting the geochemically reactive Pb fraction (PbNA), and calcium chloride (0.01 M) extraction (ISO-14255: 1998) for estimating the plant-available Pb (PbCC) were performed in fifty historically polluted and newly Pb-spiked soils with differing soil types, properties (pH 4.1-8.0), and total soil Pb levels (PbT, 20-6153 mg kg-1). Greenhouse experiments for Brassica pekinensis L., and in-situ soil porewater measurement for Pb were conducted to investigate the mechanism of Pb uptake, and to establish reliable Pb soil-plant relationships. The results indicated that about 83% of the variation for Pb concentrations in vegetable (PbCL, 0.009-1.06 mg kg-1) was contributable to free Pb2+ activity in soil porewater, which was mainly influenced by pH and dissolved organic matter. PbCL was satisfactorily predicted using PbNA and key soil properties (adj. R2 0.852). Soil Pb criteria for PbT and PbNA are then derived based on food standard. The full implementation of criteria derived for PbNA (i.e., 27-127 mg kg-1, soil pH 5.5-8.0) can avoid the exceedance of Pb in 95% of cabbage samples in this study, 95% of cabbage cultivars by model extrapolation, and one widely cultivated root vegetable, radish, in the study region. We provide a successful case study that has effectively tackled the challenge for the complexity of the soil management in contaminated croplands.

Geochemical cadmium anomaly and bioaccumulation of cadmium and lead by rapeseed (Brassica napus L.) from noncalcareous soils in the Guizhou Plateau.

The cruciferous crop, oil rapeseed (Brassica napus L.), may bioaccumulate excessive cadmium (Cd) and lead (Pb) as well, from Cd-enriched noncalcareous soils in Guizhou province of southwestern China. Field paired soil-rapeseed sampling and greenhouse experiment were performed to characterize the Cd anomaly in rapeseed-planting soils and to predict the bioaccumulation of Cd and Pb in raw seeds using soil variables. The results indicated that total soil-Cd concentrations averaged 0.43 mg kg-1 (range 0.11-1.41 mg kg-1) from field investigation; and a soil type dependent Cd anomaly was observed. Besides, cumulative frequency of total soil-Cd was plotted to be helpful in delimitation of regional Cd anomalies. Rapeseeds readily bioaccumulated Cd from soils as validated by greenhouse experiment and field data. Contrary results were observed in relation to rapeseed Pb levels measured from greenhouse experiment (very low) and field (very high) which was likely due to soil particle contamination as indicated by the considerably higher ratio of Pb to Cd level in seeds harvested from fields. Based on multiple stepwise regression analysis, reliable Cd soil-rapeseed relationships, but less reliable for Pb, were derived using either total or (bio)available metal concentrations and were further inversely used to derive local soil Cd criteria (e.g., total soil-Cd based, 2.5 mg kg-1) based on Hygienic Standard for Feeds (GB13082-2001). Although seed Cd levels (