Agricultural-Related Chemical Exposures, Season of Conception, and Risk of Gastroschisis in Washington State

Abstract

A number of studies have linked agrichemical exposure in pregnancy to a remarkable increase in the incidence of gastroschisis and other birth defects. Several organic chemicals, solvents, teratogens, and cyclooxygenase inhibitors, specifically related to agricultural exposure, may be associated with the reported 2-fold increase in the prevalence of gastroschisis over the last 30 years. One of these agents, atrazine, is an organic compound used mainly to stop the spread of weeds among agricultural crops. This chemical has been shown to have embryotoxic and embryolethal effects in rodents, and to be associated with hermaphroditism and retarded gonadal development in male frogs exposed to polluted surface water. This retrospective, case-controlled study investigated whether periconceptional exposure to agrichemical herbicides and increased exposure in utero was associated with the development of gastroschisis. Pregnancies were evaluated for maternal periconceptional and first-trimester exposure to atrazine and other agricultural chemicals. Information obtained from Washington State birth certificate and hospital discharge data on all live-born singleton infants with gastroschisis was linked to US Geological Survey data on surface water concentrations of agricultural pollutants. The investigators calculated the distance between each woman's residence, using her zip code and the closest geographic site of increased exposure to each individual agrichemical. The association between exposure to contaminated surface water and risk of gastroschisis was analyzed, using multivariate logistic regression. The control group was selected randomly from all Washington State singleton live births. The study population was comprised of 4421 infants: 805 infants with gastroschisis and 3616 control subjects. The data showed that gastroschisis occurred more frequently among infants whose mothers resided <25 km from a site of high surface water contamination with atrazine (odds ratio = 1.6; 95% CI = 1.1―2.3). There was an inverse relationship between the risk of gastroschisis and the distance between maternal residence and the closest site with increased atrazine (P = 0.049). A seasonal variation in the prevalence of gastroschisis was noted, with a peak during spring conception, a time of high use of agrichemicals. Multivariate analysis showed that spring conception, nulliparity, and tobacco use were independent predictive factors for gastroschisis. These findings indicate a clear relationship between exposure to surface water atrazine and increased prevalence of gastroschisis, especially when conception occurs in the spring.