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Brief Report: Illness Associated with Drift of Chloropicrin Soil Fumigant into a Residential Area --- Kern County, California, 2003

Chloropicrin is the fourth most commonly used soil fumigant in California. Exposure to chloropicrin causes eye and respiratory tract irritation, vomiting, and diarrhea (1). This report describes an investigation by the California Department of Pesticide Regulation (CDPR) and the Kern County Agriculture Commissioner (KCAC) into illnesses associated with the offsite drift of chloropicrin in Kern County. A total of 165 persons experienced symptoms consistent with chloropicrin exposure. The findings underscore health risks associated with fumigants and the usefulness of procedures adopted in California to ensure both prompt identification of exposure events and timely notification of the affected public.

On October 3, 2003, an agricultural pest control service began applying 100% chloropicrin at a concentration of 80 pounds/acre to 34 acres of fallow land in Kern County. Chloropicrin was injected 17--18 inches into the soil; a weighted board was used to compact the soil, treating 18 acres. That evening, residents living one quarter mile west of the application site experienced irritant symptoms. The Kern County Fire Department (KCFD) was contacted to investigate; however, darkness, distance from the treated field, and absence of chloropicrin odor prevented firefighters from identifying the source of the irritation. Records from a weather station approximately 7 miles southeast of the application site indicated low wind speeds and stable atmospheric conditions but also that the wind direction had changed that evening, blowing from the field toward the residential dwellings.

The next day, chloropicrin was applied to the remaining 16 acres. A 60-foot, chloropicrin-free buffer was maintained around the perimeter of the field because workers noted a persistent odor when they arrived. Residents one quarter mile west and south of the field complained about irritant symptoms that evening. Residents notified KCFD; several responding firefighters experienced eye irritation. The wind had changed again that evening and begun blowing from the field toward the residential dwellings. Suspecting a pesticide release, KCFD notified KCAC. The field was recompacted, and the odor ceased.

On October 6, KCAC notified CPDR about the incident. KCAC and CDPR conducted in-person interviews at 35 households located approximately one quarter mile west and south of the field and at a day care center; additional interviews were conducted on October 15. The 35 households and day care center had a total of 172 persons present during the exposure period. Representatives from each household and the day care center were interviewed by using a standardized questionnaire (2). In addition, five workers involved with the fumigation were questioned informally, and KCFD records were reviewed to identify affected firefighters.

The investigation determined that 165 persons reported symptoms compatible with illness caused by chloropicrin; median age of the persons was 16 years (range: 3 months--63 years). Nearly all (99%) had irritant symptoms (e.g., eye or upper respiratory) (Table); nine (5%) received medical evaluations. Seven had persistent respiratory symptoms when interviewed 11 days after the event. Follow-up medical care was limited because most of the affected persons lacked health insurance.

Exposures were retrospectively estimated by using a standard air dispersion model (3). Estimated 1-hour average chloropicrin air concentrations in areas south and west of the field ranged up to 0.20 parts per million (ppm). Peak-to-mean extrapolations indicated that peak concentrations might have exceeded 1 ppm. The Occupational Safety and Health Administration permissible exposure limit and the National Institute for Occupational Safety and Health (NIOSH)-recommended exposure limit is 0.10 ppm averaged during 8 hours. However, extrapolations from animal studies suggest 0.0044 ppm as a safe level for a 1-hour environmental exposure (4).

According to KCAC, a possible cause of the offsite drift was failure to contain the chloropicrin adequately after application. After the incident, KCAC imposed new restrictions on chloropicrin applications, including prohibition of applications within one quarter mile of an occupied structure and mandatory use of a heavy-duty tarp or water seal for applications within one half mile of such structures.

The findings in this report are subject to at least two limitations. First, this report is limited by an imprecise estimate of reported cases. Some affected persons likely were not interviewed, leading to an underestimation. Conversely, false-positive cases cannot be excluded because some self-reported symptoms might not have been related to exposure. Second, environmental measurements were not conducted to confirm chloropicrin exposure.

Adequate chloropicrin containment measures are needed to prevent similar community outbreaks. In addition, when outbreaks occur, measures are needed to prevent the community distress that arises when government authorities do not provide timely information regarding the emergency response and follow-up investigation findings. In 2003, CDPR developed procedures to respond to incidents involving offsite drift of pesticides (2). This approach might be useful in other jurisdictions where offsite pesticide drift can occur.

Reported by: MA O'Malley, MD, Univ of California, Davis; S Edmiston, D Richmond, M Ibarra, T Barry, M Smith, California Dept of Pesticide Regulation. GM Calvert, MD, Div of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, CDC.


  1. Prentiss AM. Chemicals in War: A Treatise on Chemical Warfare. New York, New York: McGraw-Hill, 1937.
  2. California Department of Pesticide Regulation. Responding to non-occupational pesticide use-related exposure episodes. Sacramento, California: California Department of Pesticide Regulation, 2003. Available at
  3. U.S. Environmental Protection Agency. User's Guide for the Industrial Source Complex (ISC3) Dispersion Models for Use in the Multimedia, Multipathway and Multireceptor Risk Assessment (3MRA) for HWIRR99, Volume II: Description of Model Algorithms. Washington, DC: U.S. Environmental Protection Agency, 1999. Available at
  4. Alexeeff GV, Budroe JD, Collins JF, et al. Air Toxics Hot Spots Program Risk Assessment Guidelines. Part I. The Determination of Acute Reference Exposure Levels for Airborne Toxicants. Sacramento, California: California Office of Environmental Health Hazard Assessment, 1999. Available at


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