Glyphosate, the active ingredient of the herbicide RoundUp, has been subject to extensive scrutiny since the
introduction of genetically engineered glyphosate tolerant crops in 1995. However, both a lack of observational
studies and continued uncertainty around the toxicity of glyphosate emissions contribute to international political
controversy and numerous civil actions at a time when US rural health measures are worsening and youth cancer
rates are rising. Recent quasi-experimental studies using genetically engineered crop adoption as a source of exposure
variation found glyphosate applications caused deleterious infant health effects in rural US areas, but we are unsure
their exposure is truly exogenous. We reassess glyphosate’s effects on infant health using two sources of exposure
variation in two-stage least squares instrumental variable approaches for twelve different infant health measures.
We first similarly employ genetically engineered crop adoption but using seed sale marketing data, which is a more
accurate measure of adoption relative to previous attempts. We then use changes in glyphosate product characteristics
from the introduction of generic product types using product sales marking data, which is a novel separate source
of variation. We do not find any consistent significant health changes from glyphosate exposure, where estimates are generally precise, pass typical assumption tests, and are robust to alternative specifications. By investigating
the association between genetically engineered crop adoption and several rural co-occurring health and agricultural
trends, we obtain evidence exposure variation from genetically engineered crop adoption is probably not independent
from other agricultural production externalities. While this study provides evidence glyphosate did not contribute
to rural health problems from 1995 to 2013, we believe pesticide data limitations, continued glyphosate controversy,
and remaining potential for toxic agricultural emissions justifies evaluations of improved environmental monitoring.
