A global tool for terrestrial risk assessment
The Threshold Calculator is a versatile risk assessment tool for metals in soil that can be used worldwide to determine ecotoxicological thresholds for different protection objectives. This tool calculates ecotoxicological threshold concentrations for Cd, Co, Cu, Pb, Mo, Ni, and Zn based on chronic toxicity data for their direct effects on soil-dwelling organisms (plants, invertebrates, and microbial processes) and, where applicable, for secondary poisoning to mammals and birds through bioaccumulation in the food chain. All threshold values are expressed as (pseudo-)total (i.e., aqua-regia extractable) metal concentrations in soil (mg/kg dry weight). The aim of this tool is to make the most efficient use of available toxicity data and bioavailability models for the derivation of soil quality standards for specific protection objectives, jurisdictions, regions, or sites.
The Threshold Calculator for metals in soil (v3.0) includes a wide range of chronic toxicity data for direct effects on soil organisms, covering all major groups of soil organisms, and allows for the use of a statistical extrapolation approach to derive a threshold concentration using a species sensitivity distribution (SSD). The soils used for ecotoxicity testing for each metal cover a wide range of soil properties, making the results globally representative. The tool offers several options to calculate metal soil threshold concentrations for various goals, such as risk assessment or setting remediation thresholds for different land uses. These options include the selection of organism groups or species to be considered, the selection of effect levels of original toxicity data (EC10, EC20, NOEC, LOEC, MATC, etc.), the selection of protection level (probability level in distribution of effect levels), etc. In addition, except for Cd, specific toxicity thresholds can be calculated based on information about the soil properties of a specific site of interest. The input parameters depend on the metal under consideration and are soil parameters that are likely to be determined in routine soil analyses (metal background concentrations, pH, % organic matter, % clay and eCEC).
The potential for secondary poisoning of mammals and birds via the food chain is only considered for Cd, Pb, and Ni in the Threshold Calculator for metals in soil (v3.0) because this pathway is not relevant for Co, Cu, Mo, and Zn due to their essentiality and the strong homeostatic control of their internal concentrations in organisms. Soil quality standards for this pathway are all expressed as total metal concentrations, and calculated using two approaches: either based on the critical metal concentration in food (in mg/kg diet) and the metal-specific bioaccumulation factor in earthworms or based on the critical metal intake rate (mg/kg body weight/day) and assumptions on food intake rate and the bioaccumulation factor in earthworms. For Pb, sufficient information is available to allow the selection of effect level (x in ECx), the use of NOEC, MATC, or LOEC values in cases where reliable ECx values are not available, and the selection of probability level in the species sensitivity distribution (p in HCp) to determine the thresholds for metal concentration in food and the metal intake rate. The bioaccumulation of Pb in earthworms varies with soil properties, and a soil-specific bioaccumulation factor for Pb is calculated based on information on the soil properties of the site of interest.
The Threshold Calculator for metals in soil (v3.0) is freely accessible to all users. When requesting the tool, please provide complete contact information, as you will be automatically notified when a new version becomes available. Note that each request for the tool is subject to review and approval before it is released. To ensure proper functionality, please enable macros when using the tool.
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