Cadmium threshold for acidic and multi-metal contaminated soil according to Oryza sativa L. Cadmium accumulation: Influential factors and prediction model

Cadmium (Cd) contamination in soil-rice systems has become a global public concern. However, influencing factors and the contamination threshold of Cd in soils remain largely unknown owing to soil heterogeneity, which limits our ability to assess the risk to human health and to draft appropriate environmental policies. In this study, we selected the soil-rice system of Longtang and Shijiao town in southern China, which was characterized by multi-metal acidic soil contamination due to improper electronic waste recycling activities, as a case to analyze the influence of different soil properties on the Cd threshold in the soil and Cd accumulation in rice. The results showed that soil organic matter (SOM) was the main factor regulating Cd accumulation in the soil-rice system. Moreover, compared with the total Cd concentration, the DTPA-extractable Cd concentration in the soil was a better predictor of Cd transportation in the soil-rice system. According to the prediction model, when SOM was < 35 g kg(-1) , the Cd-DTPA threshold was 0.16 mg kg(-1) with a 95% likelihood of Cd-rice accumulation above the Chinese food standard limit (0.2 mg kg(-1)). Conversely, when SOM was >= 35 g kg(-1), the Cd-DTPAY threshold was only 0.03 mg kg(-1). This study of the influence of SOM on Cd accumulation in a soil-rice system confirms that SOM is a crucial parameter for better and safer rice production, especially in multi-metal contaminated acidic soils.

Automated summary

Soil organic matter is the key factor regulating Cd accumulation in soil-rice systems, with DTPA-extractable Cd concentration being a better predictor of Cd transportation in the system. When soil organic matter is <35 g kg(-1), the Cd-DTPA threshold is 0.16 mg kg(-1) with a likelihood of Cd-rice accumulation above the Chinese food standard limit.