Twenty years after federal officials recommended phasing out methyl bromide due to serious health risks, the toxic pesticide remains in widespread use across California, with some communities facing exposure levels nearly double state safety recommendations, according to new University of California research.
The pesticide, a known developmental, neurologic and respiratory toxin, is currently used in 36 of California's 58 counties — home to more than 35 million people — primarily for fumigating shipping containers at ports and freight facilities, researchers from UCLA and UC Irvine found.
The study, published in the peer-reviewed journal Environmental Research Communications, reveals that port communities face the highest exposure risks. In western Long Beach, air monitoring between 2023-24 showed average methyl bromide levels of 2.1 parts per billion, nearly double the state's 1.2 ppb recommendation. On at least two occasions, hourly levels exceeded 900 ppb.
"These levels translate to a 'hazard quotient' of 1.6; values greater than 1.0 suggest an increased risk of negative health effects," said study co-author Dr. Yoshira Ornelas Van Horne, assistant professor in the UCLA Fielding School of Public Health's Department of Environmental Health Sciences.
The affected Long Beach neighborhood is home to an elementary school, 600 residences and parks, and already ranks in the top 25% of California communities for environmental hazards, according to state assessments.
Children face uniformly higher risks than adults due to greater inhalation rate-to-body weight ratios, yet research on fumigation pesticide exposure in children remains limited, the researchers noted.
"Research in rural, agricultural communities have seen an association between proximity to agriculturally applied methyl bromide and restricted fetal growth," said Dr. Jill Johnston, study co-author and associate professor at UC Irvine's Joe C. Wen School of Population and Public Health. "Additionally, studies in California have found that an increase in the ambient air concentration of methyl bromide is associated with increased risk of emergency department visits for asthma among children."
When asked about potential long-term health impacts, Van Horne said, "For children, potential long-term effects on respiratory health are a concern. Additionally, there is concern that prenatal exposure could increase the risk of lower birth weight."
The U.S. government recommended phasing out methyl bromide in 2005 because of known health and environmental impacts, including cancer, respiratory issues, and damage to kidneys, skin and livers. Agricultural use in California largely ended in 2015, but exceptions allowed for freight container fumigation continue today.
Between 2016-22, the top counties reporting methyl bromide applications were Siskiyou, Merced, Stanislaus, San Joaquin and Los Angeles. In predominantly agricultural counties, primary uses included soil fumigation and nursery operations. In Los Angeles County, the main application was non-agricultural fumigation for shipping purposes.
"Freight transported in containers is typically fumigated as a means to reduce potential infestations or inhibit the spread of pests," Johnston said. "In the United States, foreign freight containers with certain produce, such as grapes, must be treated for pests, and in most cases, methyl bromide use is allowed at permitted facilities."
Johnston noted that safer alternatives exist but have not been widely adopted.
"These are important precautions, but the reality is there are potential alternatives to methyl bromide that pose lower health risks," she said.
According to Van Horne, integrated pest management approaches can reduce reliance on methyl bromide, while non-chemical alternatives like inert-gas treatments or cold treatments show potential for pest control. Fumigant alternatives such as ethyl formate have demonstrated effectiveness and are considered less harmful to humans and the environment.
The researchers acknowledged data limitations in their analysis. In Long Beach, only one air quality monitor has tracked methyl bromide levels, and only since 2023.
Van Horne expressed particular concern about notification systems: "There are no systems in place to alert residents or schools nearby that fumigation activities are taking place."
Despite these limitations, the authors called for better coordination between federal, state and local agencies, improved monitoring and warning systems, and expedited replacement of methyl bromide with less toxic materials.
"This work highlights the ongoing challenge of addressing community health concerns due to fumigation activities, and the lack of comprehensive health and safety assessments," Van Horne said. "It is clear the potential health burdens for continued methyl bromide use are concentrated in areas near fumigation activities, like Long Beach and the port areas, but it is equally clear there are gaps in information and oversight that need to be addressed; people's health is at risk."
The research was funded by the National Institutes of Health through the Southern California Center for Children's Environmental Health Research and the JPB Environmental Health Fellowship.