Threshold calculator for metals in soil v3.0

A GLOBAL TOOL FOR TERRESTRIAL RISK ASSESSMENT

Threshold calculator for metals in soil

A new version of the Threshold calculator for metals in soil (v3.0) is publicly available since July 2020. This version also includes secondary poisoning exposure pathway to mammals and birds.

The Threshold Calculator is a flexible risk assessment tool for metals in soil and it can be used in various parts of the world to derive soil type-specific ecotoxicological thresholds for different protection goals. This tool calculates ecotoxicological threshold concentrations for the metals Cd, Co, Cu, Pb, Mo, Ni and Zn based on chronic toxicity data for their direct effects to soil dwelling organisms (plants, invertebrates and microbial processes) and, where relevant, 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 goal of this tool is to make maximal use of available toxicity data and bioavailability models for the derivation of soil quality standards for specific protection goals, jurisdictions, regions or sites.

All metals in this tool have a wide range of chronic toxicity data for direct effects to soil organisms, covering all major groups of soil organisms and allowing the use of a statistical extrapolation approach for derivation of a threshold concentration with 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. Several options are included to allow calculation of metal soil threshold concentrations for various goals (e.g. risk assessment or setting of remediation thresholds for different land uses): selection of organism groups or species to be considered, selection of effect levels of original toxicity data (EC10, EC20, NOEC, LOEC, MATC, …), 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 on the soil properties of a site of interest. The input parameters are dependent upon the metal under consideration, and are soil parameters 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 included for Cd, Pb and Ni 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 following 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 allowing selection of effect level (x in ECx), the use of NOEC, MATC or LOEC values in case no reliable ECx values are 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.

This tool is freely available for all users. Please fill in all your details when requesting the tool as you will be automatically warned when a new version becomes available. Also note that each request for the tool is evaluated for approval before release of the tool. Any feedback is highly appreciated (please send your comments to Dr Koen Oorts at koen.oorts@arche- consulting.be mentioning the operating system and office/excel version, thanks!!). Please enable macros for proper running of all functionalities in the tool.

Threshold calculator for metals in soil v3.0

Background document for version 3.0