The Environmental Risk Threshold (Hc5) for Cd Remediation in Chinese Agricultural Soils

Abstract

Given the increasing concern over Cd contamination of agricultural soils in China, reducing the availability of the toxic metal has become an important remedial strategy. However, the lack of a unified evaluation framework complicates the assessment of remediation efficiency of different practices. Here, we evaluated the general extraction method (GEM) of available Cd in nine typical soil types by comparing extraction agents, including CaCl2, EDTA, Mehlich-III, HCl and DTPA. The safe grain concentration of different agricultural products from National Food Safety Standards Limits of Contaminants in Food (GB 2762-2022) was then applied to understand soil limited available Cd concentration based on dose-response curves. We also derived environmental risk threshold (HC5) values for Cd remediation in agricultural soils by constructing species sensitivity distribution (SSD) curves. The results showed that Mehlich-III best predicted Cd accumulation in crops (with 76.5% of explanation of grain Cd) and was selected as the GEM of soil available Cd for subsequent analyses. The derived limit concentration of soil available Cd based on GB 2762-2022 for 30 different agricultural products was 0.18 - 0.76 mg‧kg‒1. An HC5 of 0.19 mg‧kg‒1 was then calculation, meaning that a concentration of available Cd in agricultural soil below 0.19 mg‧kg‒1 ensures that 95% of agricultural products meet the quality and safety requirements of GB 2762-2022. This study provides a robust scientific framework for deriving the risk threshold for Cd remediation in agricultural soils and could be quite useful for establishing soil remediation standards.

Keywords: Cadmium, Chemical extraction methods, Species sensitivity distribution (SSD), Hazard concentration for 5% of species (HC5), Remediation standard