Methyl Bromide Poisoning

State's Internal Study Showed Danger of Drifting Fumigant One Year Before Victim Died of Methyl Bromide Poisoning

On March 20, 1996, eight days after Gov. Pete Wilson signed a bill overturning the state ban on methyl bromide, the California Department of Pesticide Regulation (DPR) published an internal report showing that when the poison gas is used to fumigate homes, unsafe levels of hazardous vapors can drift through empty pipes into neighboring houses. The study also found that methyl bromide levels outside homes under fumigation can be more than seven times higher than the state safety standard, and that methyl bromide can be detected inside closed houses up to 100 feet away from the fumigated structure, even if the two buildings are not connected by pipes of any kind (DPR 1996a, 1996b).

The study, conducted at the same time that Legislature was debating the overturn of the ban, constituted explosive but unpublicized evidence to support arguments against methyl bromide's continued use in structural fumigation. In 1995, almost 600,000 pounds of methyl bromide was used to fumigate thousands of California homes and businesses (DPR 1995). In Los Angeles and Orange counties alone, more than 500,000 pounds of methyl bromide was used that year, enough to fumigate 8,400 single-family homes (Table 1). But DPR made no effort to publicize the study or warn lawmakers, local authorities or fumigators of the threat to public health.

Table 1. Methyl Bromide applied in structural fumigations in California in 1995. (All counties with 1,000 pounds or more.)

County Methyl
Bromide (lbs.)
Home Fumigation capacity*
Los Angeles 389,346 6,489
Orange 114,320 1,905
Riverside 13,990 233
Sacramento 9,504 158
San Bernardino 9,060 151
San Joaquin 7,792 130
Sonoma 7,696 128
San Mateo 5,231 87
Marin 5,148 86
Monterey 4,645 77
Alameda 4,610 77
Santa Cruz 3,196 53
Stanislaus 3,083 51
San Diego 2,294 38
Contra Costa 2,075 35
San Luis Obispo 1,739 29
Napa 1,458 24
Fresno 1,210 20
Mendocino 1,145 19
Placer 1,101 18
Solano 1,094 18
STATEWIDE 598,656 9,978

Source: Californians for Pesticide Reform/Environmental Working Group, from California Department of Pesticide Regulation, Pesticide Use Reporting System.

*Estimate based on 2,500 sq. ft. house fumigated with 3 lbs. per 1,000 cu. ft. of methyl bromide as described in DPR HS-1717.

Almost exactly one year later -- March 25, 1997 -- Sandra Mero, 36, died in a Burbank hospital. She had fallen into a coma after a building near her house was fumigated with methyl bromide and the chemical drifted through empty pipes connecting the building to her home. Mero's doctor told the victim's family that blood tests found evidence of methyl bromide well above lethal levels (Berry 1997). Mero was the 19th person to die in California from methyl bromide poisoning since 1984 -- the same year the original law was passed to phase out the chemical.

In an interview two days before Mero died, DPR Director James Wells acknowledged that methyl bromide is "acutely toxic," adding: "That's why we're so careful about how we control its use" (Bernstein 1997). But an investigation by Environmental Working Group and Californians for Pesticide Reform found no evidence DPR tightened controls on structural fumigation with methyl bromide after the1996 study, or since Mero's death.

An acute toxin

Methyl bromide is a colorless, odorless gas, classified by the U.S. Environmental Protection Agency as a Category I acute toxin -- a designation reserved for the most deadly substances. Human exposure to small amounts can produce nausea, headaches and other flu-like symptoms. In larger amounts, methyl bromide has been linked to birth defects and nerve damage in laboratory animals. Methyl bromide is also a powerful destroyer of the earth's ozone layer, and under the U.S. Clean Air Act is scheduled to be banned nationally in 2001.

As a soil and harvested crop fumigant, methyl bromide is used in California on strawberries, grapes, flowers and other crops. In 1995, nearly 17.6 million pounds were applied statewide. Although the great majority is used in agriculture, 3.4 percent of the 1995 total was used to fumigate homes and businesses for termites or powder-post beetles. More than 86 percent of the structures fumigated with methyl bromide were in Los Angeles, Orange and Riverside counties (Table 1).

Houses to be fumigated are enclosed with a tent before the gas is pumped in and for at least 24 hours afterward. The amount applied varies from 1.5 pounds to 3 pounds per 1,000 cubic feet of enclosed volume (DPR 1996). The state's Pesticide Use Reporting database does not disclose the number of fumigated structures. Based on the maximum application rate for a 2,500 sq. ft. house, enough methyl bromide was used in California in 1995 for 9,978 home fumigations.

The politics of poison

In January 1996, Gov. Wilson called a special session of the Legislature to revoke a ban on methyl bromide scheduled for the end of March 1996. After an intense battle marked by heavy lobbying from chemical interests, the Legislature extended the deadline until the end of 1997, when the pesticide's manufacturer is supposed to complete long-delayed studies on methyl bromide's health effects.

It was the third time, since enactment of the California Birth Defects Prevention Act of 1984 (SB 950) that the deadline for methyl bromide had been extended in the absence of the requisite health studies. If the studies are submitted by the latest deadline, DPR must decide whether the findings require a ban on methyl bromide -- an action DPR has taken against only one pesticide covered by SB 950 in the agency's history.

Under the 1986 state law called Proposition 65, chemicals known to cause birth defects or cancer fall under a special set of restrictions that include giving written warnings to anyone who may come into contact with them, and allowable levels of exposure are much lower. Methyl bromide was placed on the Prop. 65 list in 1993. After an appeal from agribusiness interests, who saw that the tighter restrictions would severely limit agricultural use, the Wilson Administration did an about-face: Methyl bromide was listed under Prop. 65 for structural fumigation, but not for crops.

Double standard

This double standard means that Californians must be warned before methyl bromide is used in their homes, but not when it is applied to agricultural fields near their homes, schools or businesses. It also means that while the state's safety standard for exposure to methyl bromide from an agrigultural application is 210 parts per billion(ppb), averaged over 24 hours, the target safety level for exposure in a structural fumigation is 15.5 ppb. The practical effect is that Californians can legally be exposed to 13 times more methyl bromide on their back porches than in their living rooms.

But are the stricter Prop. 65 standards for structural fumigation adequate to protect the public? Between 1984 and 1996, 18 people died in California after entering fumigated homes. In 1992, a Redwood City man died even though post-fumigation tests showed "safe" levels of methyl bromide in his apartment. DPR found that the poison gas was "hiding" in the wall spaces and woodwork, only to seep out later in lethal amounts (DPR 1992..) Like Mero, he was in a coma for more than two weeks before dying.

To its credit, in 1992 DPR imposed new regulations that increased the waiting period before re-entering a fumigated house, lowered the acceptable level of methyl bromide allowed before re-entry and requred monitoring for methyl bromide lurking in wall spaces. Under the new restrictions, the use of methyl bromide in structural fumigation dropped dramatically -- from 5 million pounds in 1990 to 600,000 pounds in 1993.

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.

A needless tragedy

Sandra Cornwall Mero, a native of Dublin, Ireland, moved to Los Angeles in 1983. An aspiring actress with several television credits, she worked at Alliance Communications, a film distributor. She lived in a cottage in the Toluca Lake district, on a property including several other residential buildings. (Unless otherwise attributed, information about the Mero case is taken from personal communication between her family and friends and Environmental Working Group.)

On Friday, March 7, 1997, a studio in a building near Mero's was fumigated with methyl bromide. Mero returned home that evening. On Sunday night, her landlord found her on the floor of the cottage, comatose and having convulsions. At St. Joseph Medical Center in Burbank, her illness was a mystery until her landlord remembered the fumigation. The landlord then learned that at some prior time, seven 1-to-2-inch underground conduits had been installed to carry wiring between the studio and Mero's cottage.

The owner of the company that carried out the fumigation of the studio said the building was inspected before fumigation and was completely enclosed with a tent as required by law. (Berry 1997). Mero's friends insist no tent was used. But a tent would not have prevented the gas from drifting into the cottage through the pipes, which the fumigator said he did not see because they were hidden by a chair.

At the hospital, Mero's blood was tested for methyl bromide poisoning. Although a family member was quoted as saying doctors found 27 parts per million of methyl bromide (Berry 1997), the standard blood test measures levels of bromine, a breakdown product of methyl bromide. No definitive lethal level of bromine in blood has been established.

After Mero spent 17 days in a coma, her family was advised that she had no brain function and life support was terminated. The coroner's office lists the official cause of death as methyl bromide poisoning (Los Angeles County 1997).

Conclusion and recommendations

In an interview two days before Mero died, DPR Director James Wells compared her situation to the people killed by carbon monoxide poisoning from kerosene heaters. "I don't think you should use [Mero's case] to ban methyl bromide just like you wouldn't ban all use of kerosene heaters," he said. "These things are all accidents." (Bernstein 1997).

But was it preventable? If DPR had properly warned fumigators and local authorities of its March 1996 study, greater precaution might have been exercised in the fumigation of the studio near Mero's house. DPR had authority to go beyond merely issuing a warning, and could have immediately imposed new regulations requiring inspection for hidden pipes.

Furthermore, if DPR had told state lawmakers about the study when it was completed, the Legislature might have kept the methyl bromide ban in place, enacted a ban on structural applications or at least imposed additional safety restrictions on methyl bromide's use. Methyl bromide was the subject of intense debate and front-page news coverage at the time, yet DPR neglected to disseminate information with major implications for state policy.

Californians for Pesticide Reform and the Environmental Working Group urge that the following regulatory action be taken:

  • An immediate statewide ban on all structural fumigations with methyl bromide. The DPR study provides further evidence that methyl bromide poses an acute health hazard, reinforcing the urgent need to ban all uses of the chemical. Methyl bromide must not be replaced with other toxic pesticides, but with proven non-chemical alternatives. (See "Safe Alternatives for Home Pest Control." below)

    In addition, we urge the following actions to hold the Department of Pesticide Regulation accountable for its failure to carry out its responsibility to protect public health and safety:

  • The appropriate committees of the Legislature should conduct oversight hearings into DPR's failure to disseminate the 1996 study, the agency's actions before and since Mero's death and its ongoing effort to dismiss the evidence that methyl bromide is unsafe under any conditions.
  • The Scientific Review Panel on Toxic Air Contaminants, a state panel made up of public-health scientists from leading California universities, should also receive an accounting from the agency.
  • The Legislature should transfer DPR's authority to regulate methyl bromide and other pesticides in air to the California Air Resources Board, which currently regulates all other airborne toxins except pesticides.

Safer Alternatives for Non-Toxic Pest Control

Instead of using methyl bromide, there are many alternative treatment methods for structural pest control. A number of pest control companies, including at least one multi-million dollar operation in Bakersfield, have switched to nontoxic alternatives like cooled liquid nitrogen that kills insects by freezing them. Safe use of cooled liquid nitrogen requires careful worker safety precautions and aeration but presents no drift or chronic toxicity problems.

Other pest control operators use propane heaters that raise house temperatures to 150 degrees and non-toxic dusts that kill pests through dehydration. These and other non-toxic alternatives are much safer than chemical pesticides (such as sulfuryl fluoride) that are often used instead of methyl bromide in structures.

We’re in this together

Donate today and join the fight to protect our environmental health.


California Department of Pesticide Regulation, 1992. Toxicology Review Prompts Changes in Structural Fumigations. Press Release No. 92-07. April 2, 1992.

California Department of Pesticide Regulation, 1995. California Pesticide Use Reporting Database.

California Department of Pesticide Regulation, 1996a. Methyl Bromide Concentrations in Air Downwind During Aeration of Fumigated Single-Family Houses (HS 1713). March 20, 1996

California Department of Pesticide Regulation, 1996b. Methyl Bromide Concentrations in Air Near Fumigated Single-Family Houses (HS 1717). March 20, 1996.

California Department of Pesticide Regulation, 1996c. Review of Restrictions on the Use of Methyl Bromide: A Report to the Legislature. November 1996.

Berry, Steve, 1997. Illness Probed for Possible Pesticide Link. Los Angeles Times. March 22, 1997.

Bernstein, Sharon, 1997. Use of Powerful Insecticide Fills Air With Controversy. Los Angeles Times. March 23, 1997.

Los Angeles County, 1997. Coroner's Department Medical Record 97-02247.

Learn about these issues