CalTOX: Multimedia Fate and Exposure Model

Developed by Dr. Thomas McKone (LBNL retired) and maintained by Dr. Shin

The CalTOX model is a mature and widely used multimedia fate and transport and exposure model – with an extensive history of model evaluation exercises and case studies. First issued in 1993 and updated in 1995 and 2002, with continued enhancements ongoing, CalTOX consists of two component models – a multimedia transport and transformation model and a multi-pathway human exposure model. The CalTOX model provides a broad assessment of the partitioning of chemicals between the air, water, soil, and biota. CalTOX includes an eight-compartment fugacity model. For all chemicals, fugacity and fugacity capacities are used to represent mass potential and mass storage within compartments. CalTOX accounts systematically for gains and losses in each compartment and for the whole system in concert.

CalTOX derives environmental concentrations by determining the likelihood of competing processes by which chemicals (a) accumulate within the compartment of origin, (b) are physically, chemically, or biologically transformed within this compartment (i.e., hydrolysis, oxidation, etc.), or (c) transported to other compartments by cross-media transfers that involve dispersion or advection (i.e., volatilization, precipitation, etc.).

To download CalTOX template, click here.

FINE: Fugacity-based Indoor fate and Exposure Model

Developed by Dr. Deborah Bennett (UC Davis) and updated by Dr. Shin

The model accounts for indoor chemistry (e.g., sorption to indoor surfaces, gas-particle partitioning, and reaction with OH radical) and various transport and removal processes (e.g., removal via vacuum cleaning, ventilation, deposition, and resuspension). The model simulates the concentrations of organic compounds in various indoor compartments (e.g., gas phase, airborne particles, dust, carpet, vinyl flooring, and walls).

The model includes four compartments that capture the major indoor reservoirs for chemicals – air, carpet, vinyl flooring, and walls. Each compartment in the model is comprised of multiple phases, such as gases and particles in the air compartment. A set of differential equations accounts for gains and losses in each compartment as well as transfers between compartments.

Integrated CalTOX and WWTP Fate Model

Integrated and programmed by Dr. Shin

Low vapor pressure-volatile organic compounds (LVP-VOCs) are exempt from the VOC content limits for consumer products and are defined in the California Code of Regulations. To evaluate the availability of LVP-VOCs that may contribute towards ozone formation from the use of consumer products, we deleloped modeling tools for two potential modes of releases during the use of consumer products (i.e., direct release to the outdoor air and disposed down the drain). For the fate of LVP-VOCs found in some consumer products used in down-the-drain applications (e.g., laundry detergents, fabric softeners, dishwashing detergents, and other laundry products), we applied a wastewater treatment plant (WWTP) fate model to predict the fraction of LVP-VOCs that may volatilize at WWTPs. For the portion of the LVP-VOCs volatilized to air during product use, we applied a multi-compartment mass-balance model (CalTOX) to track the fate of LVP-VOCs in a multimedia urban environment.