Contribution for the derivation of a soil screening level (SSV) for cadmium using a natural reference soil

The risk assessment of metal-contaminated soils demands the establishment of soil screening values (SSVs) for metals. Cadmium(Cd) is a very toxic metal resulting from anthropogenic wastes/activities. However, ecologically relevant Cd SSVs are often unavailable for several European countries, including Portugal, due to the lack of ecotoxicological datasets on regional natural soils. Therefore, this work aims to generate an ecotoxicological dataset in a dominant type of Portuguese natural soil for the preliminary derivation of Cd SSVs. A battery of terrestrial ecotoxicological tests focusing on microbial parameters, reproduction of invertebrates (Eisenia andrei, Enchytraeus crypticus, Folsomia candida), seed germination and growth of terrestrial plants (Avena sativa, Zea mays, Lactuca sativa, Lycopersicon esculentum) was carried out in a natural soil contaminated with Cd. The Assessment Factor approach was followed to determine the predicted no effect concentrations (PNECs) after correcting the toxicity values used for PNEC calculation for leaching-aging processes, as to harmonize toxic effects in freshly spiked soils to those in field soils. The obtained PNECs will be the preliminary derivation of SSVs for Cd. Urease was slightly compromised (EC20 = 47.8 mg Cd kg(-1) (dw)), whilst acid phosphatase and cellulase activities, and nitrogen mineralization were the most inhibited parameters (LOEC = 13.4 mg Cd kg(-1) (dw)). Invertebrates reproduction was constrained, being E. crypticus the most sensitive species (EC50 = 8.3 mg Cd kg(-1) (dw)). The phytotoxicity of Cd was effective on the seed germination of L. sativa and L. esculentum for an EC50 of 460.0 and 919.0 mg Cd kg(-1) (dw), respectively. The dry mass was the most sensitive endpoint for plant growth effects, providing significant inhibitions at a LOEC = 35.0 mg Cd kg(-1) (dw) for most species. Based on these data, the PNECs ranged between 3.7 (EC20-based) and 3.5 (NOEC-based) mg Cd kg(-1) (dw). Towards a precautionary decision we proposed an SSV of 3.5 mg Cd kg(-1) (dw). When comparing our results with the literature, a direct influence of soil properties on Cd toxicity was likely, hence highlighting the importance of using regional natural soils in the derivation of SSVs. Overall, this work is a good contribution for the establishment of national soil quality guideline values, while at the same time is providing a working path for other European countries.