August 21, 1997

Methyl Bromide Poisoning: DPR's structural fumigation studies

In the winter of 1995-96, DPR conducted a series of studies on structural fumigation with methyl bromide at an abandoned housing development on the decommissioned Mather Air Force Base in Sacramento. Two internal reports were produced from these experiments: Methyl Bromide Concentrations in Air Downwind During Aeration of Fumigated Single-Family Houses (HS 1713) and Methyl Bromide Concentrations in Air Near Fumigated Single-Family Houses (HS 1717).

These studies were designed to measure the levels of methyl bromide typically found in the air in neighborhoods of fumigated houses. DPR wrote it initiated these studies because the agency was "concerned about the magnitude of airborne methyl bromide levels in the vicinity of fumigated single-family dwellings during the aeration phase, in light of new toxicology data received for this fumigant. . . . [P]resent fumigation work practices may not provide an adequate margin of safety in close proximity to a fumigated house" (DPR 1996, 1996 b.)

This concern emerged after DPR established the 210 ppb standard for agricultural applications and set up buffer zones intended to protect farm workers and neighbors. Fumigators are required to give the occupants of fumigated homes written health warnings on the symptoms of methyl bromide poisoning and the consequences of exposure. But no buffer zones designed to protect neighbors of fumigated houses have been established.


In these studies, a DPR contractor conducted seven separate fumigations of a house in the center of a cluster of one-story, three-bedroom, ranch-style houses. They set up monitoring stations at varying distances around the fumigated house and within five surrounding houses., at distances 50 to 100 feet from the fumigated house. All of the monitored houses surrounding the fumigated structure were closed securely. No fences separated the houses.

Air samples to measure methyl bromide were taken during the 24-hour fumigation, and again during aeration of the fumigated houses after the tent was removed. Samples were taken in 1-, 12-, and 24-hour increments.

  • The hidden pipe: The most alarming finding was made by mistake. In one house next to one under fumigation, 24-hour levels of methyl bromide were detected well in excess of the 210 ppb safety standard, during both fumigation and aeration One-hour levels in that house ranged up to 1,139 ppb. Upon inspection, DPR discovered an empty drain pipe linking the houses. The drain traps in the kitchen and bathroom fixtures were also empty, allowing methyl bromide to flow freely between the houses. In the neighboring house "a shower in a bathroom. . . was found to be emitting methyl bromide" (DPR 1996b). After filling the sewer pipes with liquid, the experiment was repeated and methyl bromide levels in the house were reduced.
  • Other neighboring houses: Aside from the house with the connecting pipe, other neighboring houses were also penetrated by methyl bromide during the experiments, despite having windows and doors closed. During fumigation, DPR measured 24-hour average levels of methyl bromide in neighboring houses at levels ranging from 20 to 81 ppb in the three houses 50 feet from the fumigated structure and 22 to 203 ppb in the two houses 100 feet away. Levels were highest downwind.
  • Sheltered pockets: A spot where consistently higher levels of methyl bromide were detected was an area flanked by the outside wall of the fumigated house and its attached garage, sheltered from the wind. 24-hour levels during fumigation at this site averaged 619 ppb, and one sample measured 1,495 ppb, more than seven times the safety standard. In the first hour of aeration, this spot had levels of more than 7,400 ppb. This finding has significant implications for fumigations in dense neighborhoods or houses fumigated on windless days.
  • Air downwind: DPR's report said that during fumigation, the safety standard was "routinely exceeded" 10 feet outside the treated house. During the first hour of aeration, regardless of aeration method, outdoor levels in the vicinity of the house rose well above the standard. During the first hour, outdoor levels up to 30 feet from the treated house were as high as 3,182 ppb. One-hour average levels 50 feet from the house ranged up to 778 ppb, and 100 feet from the house, from 27 ppb to 575 ppb.

DPR's reaction to these findings was to do almost nothing. According to one of the authors, who asked not to be identified, the two studies were distributed only as internal reports as part of an ongoing DPR study scheduled to be completed this year. The studies were "public" only in the sense that they were conducted by a state agency with taxpayers' money and were available if a member of the public asked for them by name or number. A computer-assisted search of DPR records finds no press release on the studies. There is no evidence that any warning was issued to local pesticide authorities or fumigation companies, or that any changes were ordered in methyl bromide structural fumigation procedures. In November 1996, when DPR issued a special report to the Legislature on methyl bromide regulations, as required by the bill extending the deadline, the agency mentioned the ongoing study in passing but said nothing of the threat to neighbors:

. . . DPR conducted additional monitoring of structural fumigations focusing on off-site methyl bromide concentrations. The results of this work are being used by DPR staff to develop methods that will provide greater control over off-site movement of methyl bromide, both during the treatment phase and the aeration phase. These changes may benefit fumigation crew workers by increasing control over the entire fumigation process, thereby further decreasing potential worker exposure. DPR is currently developing additional regulations covering structural fumigation with methyl bromide to carry out these changes (DPR 1996c).

The existence of the structural fumigation studies became known outside DPR after Assemblyman Fred Keeley, chair of the subcommittee that oversees the agency's budget, requested in March 1997 that DPR Director James Wells provide documents regarding methyl bromide use, standards and monitoring studies. The structural fumigation studies were included in a file of hundreds of documents Wells sent Keeley, and uncovered during research by the California Rural Legal Assistance Foundation.