Current-use fumigants: Health effects of prenatal and early childhood exposures

Bradman, Asa

Abstract

In a risk assessment of air monitoring data by the California Health Department, the top four pesticides ranked by non-cancer health risk, based on respiratory and neurological toxicity, were metam sodium, methyl bromide (MeBr), 1,3-dichloropropene (1,3-DCP) and chloropicrin. These fumigants, which are used to sterilize soils prior to planting many crops, account for ~20% of the 78 million kilograms (kg) of pesticides used annually in California. In the U.S., approximately 50 million kg of fumigants are applied each year, primarily in California, Florida, Washington, Idaho and Oregon, representing about half of worldwide fumigant use. Soil fumigants are a concern for nearby residents due to their toxicity and potential for drift. All four of these fumigants are known respiratory toxicants, and MeBr, chloropicrin and metam sodium are also neurotoxic and genotoxic. Due to concerns about the Earth's ozone layer, MeBr was banned by the Montreal Protocol in 2005. However, under an EPA exemption, MeBr is still used in large quantities in California. Since 2005, use of replacement fumigants, including chloropicrin, 1,3-dichloropropene (1,3-DCP) and metam sodium has increased by 20% in the state, and this trend is expected to continue. There are no biomarkers available to assess non-occupational exposures to fumigants. Thus, geospatial methods must be used to estimate exposure from nearby applications. The California Pesticide Use Reporting (PUR) system, considered the best in the world, requires reporting of all agricultural pesticide use. For this proposal, we will use neurodevelopmental assessment and respiratory health data from the CHAMACOS cohort to determine the association of residential proximity to MeBr, chloropicrin, 1,3-DCP and metam sodium applications during pregnancy and early childhood with cognition, motor functioning, attention and pulmonary function in 7-year-old children. Further, we will confirm our findings of an association between prenatal MeBr exposure and adverse birth outcomes (birth weight and gestation length) with statewide geocoded PUR information and vital statistics data (n~750,000). This will be the first study to: 1) Examine the relationship between in utero and early childhood fumigant exposure and neurodevelopment and respiratory health in school-age children;and 2) Utilize statewide fumigant use and vital records information to determine the association between prenatal residential proximity to fumigant applications and birth outcomes in a large population. Virtually nothing is known about pregnant women's and children's exposures to these chemicals or their long-term health effects in children. This research will generate new information about the health effects of fumigants in school-age children that will inform the design of future epidemiological and risk assessment studies as well as on-going policy decisions regarding the replacement of MeBr and the implementation of new strategies to reduce fumigant exposure in agricultural communities.

Public Health Relevance

Soil fumigants are heavily used in California and other U.S. agricultural regions, often in close proximity to homes and schools. Virtually nothing is known about prenatal and early childhood exposures to these chemicals or their long-term health effects in children. The proposed research will generate new information about pregnant women and children's exposure to methyl bromide (MeBr), chloropicrin, 1,3-dichloropropene (1,3-DCP), and metam sodium and consequent health impacts on birth outcomes, as well as neurodevelopment and respiratory health in school-age children, information needed for future policy decisions.