**5. Conclusions**

The motivation for this study emanated from our previous findings, which observed elevated ERC incidence in Nebraska counties with the highest atrazine usage. Given that groundwater is one of the significant exposure routes of atrazine to humans, we were puzzled by the low-level atrazine concentration frequently observed in the groundwater of these counties. As we unraveled the potential reasons for low-level groundwater atrazine in the counites of elevated ERC incidence and high atrazine usage, we found a negative correlation between well depth and groundwater atrazine, D.E.A., and D.I.A. concentrations. This suggests that shallow wells are more atrazine-contaminated than deeper wells. Further analysis among water supply wells with equal depths showed that excessive groundwater abstraction, reduced precipitation, high population, metropolitan areas, and water discharge areas were potential reasons for Nebraska's observed low groundwater atrazine in high atrazine usage counties. Hence, this makes it difficult to rely on groundwater atrazine measurement as a good predictor for potential health implications of atrazine. Therefore, as we aim to determine the toxicity and health implications of atrazine in this field, groundwater atrazine may not sufficiently explain potential pathological implications; studies aimed at understanding the potential toxicity of atrazine in water should utilize atrazine measurement of already abstracted groundwater. They may be better predictors of health outcomes.

**Author Contributions:** Conceptualization, M.N.-A. and O.A., methodology, M.N.-A. and O.A.; software, M.N.-A., O.A. and Z.N.; validation, M.N.-A., O.A., R.M., O.F., Z.N., A.A., J.E.B., S.B.-H. and E.G.R.; formal analysis, M.N.-A., O.A. and Z.N.; investigation, M.N.-A., O.A., R.M., O.F., Z.N., A.A., J.E.B., S.B.-H. and E.G.R.; resources, M.N.-A., O.A., Z.N., J.E.B. and E.G.R.; data curation, M.N.-A., O.A. and Z.N.; writing—original draft preparation, M.N.-A. and O.A.; writing—review and editing, M.N.-A., O.A., R.M., O.F., Z.N., A.A., J.E.B., S.B.-H. and E.G.R.; visualization, M.N.-A., O.A., R.M., O.F., Z.N., A.A., J.E.B., S.B.-H. and E.G.R.; supervision, J.E.B., S.B.-H. and E.G.R.; project administration, E.G.R.; funding acquisition, M.N.-A. and E.G.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the College of Public Health Sparks Student Research Award.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Please refer to https://clearinghouse.nebraska.gov/Clearinghouse. aspx, for Quality Assessed Agrichemical Contaminant Nebraska Groundwater Database, Omaha Nebraska, USA and https://waterdata.usgs.gov/ne/nwis/wu for Water Use Data obtained from United States Geographical Survey (USGS).

**Acknowledgments:** We want to acknowledge the Department of Environmental Health, Occupational Health and Toxicology, College of Public Health, University of Nebraska Medical Center for supporting this project.

**Conflicts of Interest:** The authors declare no conflict of interest.
