Expansion of 2,4-D Use on U.S. Farmland and Rising 2,4-D Urine Concentrations in the U.S. Population, 1999 to 2012

Abstract

Background/Aim: Multiple studies in the 1990s reported associations between agricultural 2,4-dichlorophenoxyacetic acid (2,4-D) use and reproductive problems, birth defects, and sperm quality. In 2018, the International Agency for Research on Cancer classified 2,4-D as a possible human carcinogen. Over the past decade, the spread of weeds resistant to glyphosate-based herbicides began driving herbicide use upward. In response, seed and biotechnology companies developed genetically engineered crops resistant to glyphosate and legacy herbicides, 2,4-D or dicamba. In 2018, the Enlist® program, comprised of crops able to tolerate application of 2,4-D, was approved and sold commercially. About 4 million acres of Enlist® soybeans were planted in 2019 and 25+ million are projected in 2021. As a result, 2,4-D use will dramatically increase in the next few years. In order to determine if 2,4-D exposure corresponds to increased 2,4-D use, we compared 2,4-D agricultural trends with 2,4-D urine levels in the U.S. population between 1999 to 2012. Methods: 2,4-D use data comes from Hygiea Analytics' Pesticide Use Data System, which draws on publicly accessible data at the state and national levels. 2,4-D urine concentrations were obtained from NHANES cycles 1999/2000 to 2011/2012. Results: Soybean farmers applied 1.6 million pounds of 2,4-D in 2000, 6.3 million in 2012, and 8.9 million in 2018. Despite the relatively short half-life of 2,4-D in the environment and quick elimination of 2,4-D after human exposure, 2,4-D urine concentrations in the general U.S. population increased from GM= 0.11 ug/L (1999/2000) to GM=0.33 ug/L (2011/2012). Conclusion: Use of Enlist® soybean crops will nearly triple 2,4-D use from 2018 levels through 2023. With the upsurge in 2,4-D use and the concern for health effects from 2,4-D exposure, it is imperative that epidemiological studies investigate human health effects from long-term exposure to 2,4-D.