Researchers at the School of Public Health at the University of California Berkeley have been working to improve the Toxic Equivalency Potentials (TEPs) used to weight chemical releases by toxicity and exposure potential.
Three types of changes are responsible for differences between the current scores displayed on Scorecard (TRI 2002 Version) and earlier versions.
1) RISK ASSESSMENT VALUES HAVE BEEN UPDATED
The risk assessment values used to generate TEPs are occasionally updated by regulatory agencies. For example, a recent change to the oral cancer potency factor for arsenic (from 1.5 to 9.45 kg-d/mg) has increased the cancer TEP for air releases of arsenic compounds by a factor of 6, compared to previous years.
2) THE CALTOX MODEL HAS BEEN UPDATED
In 2001, noncancer air TEPs were developed for a small set of conventional air pollutants, based on the assumption of a linear relationship between atmospheric concentrations and emissions, uniform mixing, and an equal atmospheric scale height for all chemicals. These calculations are based only on exposure to airborne pollutants and do not include exposure through routes other than inhalation. They were developed to be used together with the TEPs for organic and inorganic pollutants.
Reference: Hertwich, E.G., 2001. Human Toxicity Potentials for conventional air pollutants. Draft. LCA Laboratory, Inst. for Product Design, Norwegian University of Science and Technology.
In 1999, improvements were made to the CALTOX model to better handle soil-air and soil-plant interactions, removal from the system with rain, breakdown by UV of certain chemicals in the stratosphere, and unavailability of metals in the soil after aging. In 2000, the model was changed to more accurately correlate exposure concentrations in meat, eggs, and milk to changes in plant concentrations and to limit reaction half-lives to 100 years for metals as well as for organic compounds.
3) PHYSICAL-CHEMICAL DATA GAPS HAVE BEEN FILLED
In earlier Scorecard versions, a number of substances lacked the chemical-specific data required for environmental fate and exposure modeling and were therefore assigned TEPs based on default values for important parameters such as half-lives. A major effort has been made to obtain information to fill these data gaps with chemical-specific data (and a number of manufacturing companies have provided missing data). Current TEP values reflect less reliance on default values and greater incorporation of chemical-specific data.