Down the River: Glyphosate Use in Agriculture and Birth Outcomes of Surrounding Populations

This paper documents an externality from the agricultural use of the most widely applied herbicide in human history—glyphosate—on birth outcomes of surrounding populations. We focus on the subclinical effects of water contamination in areas distant from the original locations of application. Our identification relies on: (i) the regulation allowing the introduction of genetically modified seeds in Brazil; (ii) the potential gain in municipality-level productivity from adoption of genetically modified soybean seeds; (iii) the strong complementary between glyphosate and genetically modified soybean seeds; and (iv) the direction of water flow within water basins. We document a deterioration in birth outcomes for populations downstream from locations that exogenously expanded glyphosate use, with no effect for populations upstream from these locations. We provide several pieces of evidence indicating that this effect is related to water contamination from expansions in soybean production and rule out alternative channels other than glyphosate. Despite ongoing controversy, little is known about the externality imposed by pesticides on the health of human populations at large. This externality, nevertheless, is essential for assessing the net benefit from the adoption of new agricultural technologies. We provide a first piece of evidence on this type of externality.