Derivation of preliminary ecological thresholds for lead to protect terrestrial organisms based on toxicity testing in artificially spiked soils.

Lead (Pb) is one of the most severe soil pollutants and poses a serious threat to terrestrial organisms by affecting the growth and reproduction of plants and soil fauna. However, Chinese soil quality standards primarily focus on food safety and human health, without addressing ecological risks, and research on ecological thresholds for Pb remains limited. In this study, toxicological data for both added Pb (EC₁₀) and DTPA-extractable Pb (EC_10-DTPA) were collected from bioassays using artificially spiked soils, supplemented by literature data. Normalization models with soil properties were established, and applied to normalize all data to representative soil scenarios. Species sensitivity distribution (SSD) curves were subsequently constructed, from which scenario-specific thresholds protecting a certain proportion of terrestrial organisms within acceptable hazard levels were derived for added Pb (HC_x) and DTPA-extractable Pb (HC_x-DTPA). Continuous thresholds were developed using regression equations linking HC_x/HC_x-DTPA to soil properties. Finally, soil environmental criteria (SEC) were determined based on the proposed thresholds and soil background levels, and validated using field Pb-contaminated soils. It should be noted that the proposed thresholds are preliminary, and uncertainties remain due to limited data availability. Future research should focus on expanding toxicity datasets across diverse soil types and test organisms, and conducting long-term field validations to improve the reliability and applicability of the thresholds.