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The objective of this study was to derive regional soil Cd criteria for cultivated land. Six representative soils were collected from Guizhou plateau and were spiked with Cd（NO3）2 in a pot experiment using Chinese cabbage. Two widely utilized extractants, 0.43 mol·L-1 HNO3 and 0.01 mol·L-1 CaCl2, were also included to evaluate the phytoavailability of Cd and were correlated to Cd concentrations in cabbage by either linear regression or multi-linear regression（log transformed）. Soil Cd risk screening values（RSVs）and risk intervention values（RIVs）were back calculated based on food quality standards. The results indicated that total Cd and available Cd could be used to establish a highly significant regression model or multiple regression model for the Cd content in the edible parts of Chinese cabbage. Within the pH range（5.5≤pH≤8.0）, the calculated soil Cd RSVs50（0.8~1.7 mg·kg-1）and RIVs95（2.8~8.4 mg·kg-1）were higher than the existing national standard（GB 15618—2018）. The 0.43 mol·L-1 HNO3-Cd based soil Cd criteria increased with increasing soil pH. The 0.01 mol·L-1 CaCl2-Cd based soil Cd criteria was independent of soil pH. RSVs95, RSVs50, and RIVs95 were 0.02, 0.078 mg·kg-1, and 0.09 mg·kg-1, respectively. Standard suitability assessment using field and literature data showed that the existing national soil Cd standard was rather conservative. The RSVs50 based on total Cd and two available Cd proposed in this study showed a high rate of correctness（>80%）. The present study confirmed that for better risk management of agricultural land, the establishment of regional soil environmental standards based on available concentration and specific crops is required.

By compilation of data from field sampling, pot experiment and literature, we evaluated the suitability of the existing national standards (GB 15618-2018 and GB/T 36783-2018) for the classification of soil environmental quality in potato producing areas of Guizhou. The results showed that both soil Cd standards were overly stringent as, for example, these for potatoes grown in mining areas were more likely to exceed food standard. Here, we summarized the inadequacy of the existing sampling methods for soil-crop synchronized monitoring and proposed a sampling theory-based Decision Unit-Multi Increment Sampling method (DUMIS) for soil-crop synchronized monitoring and remediation verification. We proposed that the criteria for safe soil utilization should be derived on a site-specific basis using bioavailable fractions. In order to facilitate the evaluation of soil environmental quality and safety for the agricultural production regions of China, we suggested that further research is needed regarding the use of DUMIS in soil-crop synchronized monitoring and bioavailable fractions based criteria for safe utilization of mild to moderately contaminated soils.

The objective of this study was to derive regional soil Cd criteria for cultivated land. Six representative soils were collected from Guizhou plateau and were spiked with Cd（NO3）2 in a pot experiment using Chinese cabbage. Two widely utilized extractants, 0.43 mol·L-1 HNO3 and 0.01 mol·L-1 CaCl2, were also included to evaluate the phytoavailability of Cd and were correlated to Cd concentrations in cabbage by either linear regression or multi-linear regression（log transformed）. Soil Cd risk screening values（RSVs）and risk intervention values（RIVs）were back calculated based on food quality standards. The results indicated that total Cd and available Cd could be used to establish a highly significant regression model or multiple regression model for the Cd content in the edible parts of Chinese cabbage. Within the pH range（5.5≤pH≤8.0）, the calculated soil Cd RSVs50（0.8~1.7 mg·kg-1）and RIVs95（2.8~8.4 mg·kg-1）were higher than the existing national standard（GB 15618—2018）. The 0.43 mol·L-1 HNO3-Cd based soil Cd criteria increased with increasing soil pH. The 0.01 mol·L-1 CaCl2-Cd based soil Cd criteria was independent of soil pH. RSVs95, RSVs50, and RIVs95 were 0.02, 0.078 mg·kg-1, and 0.09 mg·kg-1, respectively. Standard suitability assessment using field and literature data showed that the existing national soil Cd standard was rather conservative. The RSVs50 based on total Cd and two available Cd proposed in this study showed a high rate of correctness（>80%）. The present study confirmed that for better risk management of agricultural land, the establishment of regional soil environmental standards based on available concentration and specific crops is required.

By compilation of data from field sampling, pot experiment and literature, we evaluated the suitability of the existing national standards (GB 15618-2018 and GB/T 36783-2018) for the classification of soil environmental quality in potato producing areas of Guizhou. The results showed that both soil Cd standards were overly stringent as, for example, these for potatoes grown in mining areas were more likely to exceed food standard. Here, we summarized the inadequacy of the existing sampling methods for soil-crop synchronized monitoring and proposed a sampling theory-based Decision Unit-Multi Increment Sampling method (DUMIS) for soil-crop synchronized monitoring and remediation verification. We proposed that the criteria for safe soil utilization should be derived on a site-specific basis using bioavailable fractions. In order to facilitate the evaluation of soil environmental quality and safety for the agricultural production regions of China, we suggested that further research is needed regarding the use of DUMIS in soil-crop synchronized monitoring and bioavailable fractions based criteria for safe utilization of mild to moderately contaminated soils.