With the enactment of California's Toxic Air Contaminant Act (Assembly Bill 1807, Tanner, Chapter 1047, Statutes of 1983; amended by Tanner, Chapter 1380, Statutes of 1984), the Legislature created the statutory framework for the evaluation and control of chemicals as toxic air contaminants (TACs). The statute defines TACs as air pollutants that may cause or contribute to increases in serious illness or death, or that may pose a present or potential hazard to human health. Included in the definition are substances listed as Hazardous Air Pollutants (HAPs) under section 7412 of Title 42 of the United States Code. The Department of Pesticide Regulation (DPR) is responsible for the evaluation of pesticides as TACs.

In general, the law focuses on the evaluation and control of pesticides in ambient community air. In implementing the law, DPR must: 1) conduct a review of the physical properties, environmental fate and human health effects of the candidate pesticide; 2) determine the levels of human exposure in the environment; and 3) estimate the potential human health risk from those exposures. The law requires DPR to list in regulation those pesticides that meet the criteria to be TACs. DPR must then determine the appropriate degree of control measures for the pesticide. DPR may conduct compliance monitoring to assure that users adhere to the control measures as appropriate.

DPR's TAC Program consists of two phases: risk assessment (evaluation and identification) and risk management (control). The program's first phase involves an extensive evaluation of the candidate pesticide to assess the potential adverse health effects and to estimate levels of exposure associated with its use. As part of this evaluation, California's Air Resources Board (ARB) conducts monitoring studies to measure the air concentrations of pesticides. Typical pesticide applications (and thus exposures) differ from exposures to other types of air pollutants, such as automobile exhaust. Therefore, different strategies must be used to monitor levels of pesticides in ambient air. Because most of California's pesticide applications normally occur in agricultural areas and are seasonal in nature, ARB conducts the monitoring studies to collect data during the worst-case situation-in the areas of high use during the season of peak use-instead of collecting samples throughout the State. This "worst-case" information can then be used to determine the ambient exposures of those people living near places where pesticides are used.

In general, for each candidate pesticide, two types of studies are conducted; ARB collects samples in ambient community air and in air near an application. For ambient community air measurements, ARB collects samples at three to five locations (usually schools or other public buildings) in communities near agricultural areas expected to receive applications of the pesticide being monitored. Samples of 24 hours in duration are collected for four days per week for four or more consecutive weeks. For application-site monitoring (e.g. sampling before and after a specific application), samples are collected immediately before, during and for approximately 72 hours following a pesticide application. Samples are normally collected less than 50 feet from the treated area and represent the short-term peak air concentrations (acute exposure).

Continuing the evaluation, for each pesticide the law requires the preparation of a report that includes: an assessment of exposure (PDF, 153 kb) of the public to ambient concentrations of the pesticide; a risk assessment (PDF, 153 kb), which includes data on health effects, including potency, mode of action, and other biological factors; an overview of the environmental fate and use of the pesticide; and the results of air monitoring studies conducted in California to measure the levels of the candidate pesticide present in ambient air. The report is reviewed by the Office of Environmental Health Hazard Assessment, the ARB, and is made available for public review. Based on the results of these reviews, the draft report is revised as appropriate. The draft undergoes a rigorous peer review for scientific soundness by the Scientific Review Panel, a panel of experts representing a range of scientific disciplines. Based on the results of this comprehensive evaluation, the Director of the DPR determines whether the candidate is a TAC. If the Director determines the pesticide meets the criteria to be a TAC, DPR declares the pesticide a TAC in regulation, and adds it to the TAC list.

Once a candidate pesticide has been declared a TAC, it enters phase two of the program-the mitigation, or control, phase. In the mitigation phase, DPR investigates the need for, and appropriate degree of, control for the TAC. If reductions in exposure are needed, DPR must develop control measures to reduce emissions to levels that adequately protect public health. DPR must use the best practicable control techniques available, which may include, but are not limited to: 1) product label amendments; 2) applicator training; 3) restrictions on use patterns or locations; 4) changes in application procedures; 5) reclassification of the pesticide as a restricted material; or 6) product cancellation. In developing control measures, the law requires DPR to coordinate with the agricultural commissioners, air pollution control districts, and air quality management districts in the counties where the pesticide is used. Control measures may be implemented by several methods, including regulatory actions, local permit conditions, and product cancellation, to name a few.