Site Mitigation & Restoration Program

We protect and maintain California’s land and places
by setting strict standards for land restoration and cleanup

Human and Ecological Risk Office


CalTOX is designed to run in Microsoft Excel®

CalTOX Model Structure

CalTOX is an innovative spreadsheet model that relates the concentration of a chemical in soil to the risk of an adverse health effect for a person living or working on or near the contaminated soil. CalTOX computes site-specific health-based soil clean-up concentrations given target risk levels or human health risks given soil concentrations at the site.

The CalTOX spreadsheet contains a multimedia transport and transformation model that uses equations based on conservation of mass and chemical equilibrium. This model predicts the time-dependent concentrations of a chemical in the seven environmental compartments of air, water, three soil layers, sediment, and plants at a site.

After partitioning the concentration of the chemical to these environmental compartments, CalTOX determines the chemical concentration in the exposure media of breathing zone air, drinking water, food, and soil that people inhale, ingest and contact dermally. CalTOX then uses the equations found in the U.S. Environmental Protection Agency Risk Assessment Guidance for Superfund (US EPA RAGS) to estimate exposure and risk.

CalTOX has the capability of conducting Monte Carlo simulations with a spreadsheet add-in program. Used in this way, CalTOX will present a range of risks or health-based soil target clean-up levels that reflect the uncertainty/variability of the estimates.

Disclaimer:  The CALTOX fate and exposure model is for research use only.  CalTOX has not been fully tested for a broad range of applications or on all versions of Windows or Excel. There could be errors in the mathematical algorithms that we have not yet identified. Problems may occur in the execution of macros and in the display and printing of the spreadsheet output.  The toxicity criteria and exposure factors used by CalTOX may differ from those recommended by HERO, and HERO does not recommend use of this model. This program should be considered as a research tool, and not used for regulatory decision making.