Degree Granting Department
Civil and Environmental Engineering
Qiong Zhang, Ph.D.
James R. Mihelcic, Ph.D.
Ismael Hoare, Ph.D.
ecotoxicity, fate and transport, risk assessment, rural gravity-fed water systems, sustainable development, watershed protection
In 2014, the global pesticide industry's projected worth is $52 billion and by 2020, the developing world will make up one-third of the world's chemical production and consumption. Pesticides can have unintended negative consequences for human health and the environment, especially in the developing world where regulations are loose or nonexistent. One country with unrestricted use of pesticides is Panam[aacute], especially in Santa Rosa de Cucunatí. In this indigenous village, small-scale farmers and ranchers spray paraquat, glyphosate, picloram, and 2,4-D at higher elevations than the spring water source of a gravity-fed water system, the river, and the village. The objective of this study was to estimate the concentration of these pesticides in the water system and the river and to perform a human health and ecological risk assessment.
Pesticide fate and transport models in the graphical user interface EXAMS-PRZMS Exposure Simulation Shell (EXPRESS), which was developed by the United States Environmental Protection Agency, were used to predict concentrations of the four mentioned pesticides in drinking water and the river using chemical properties, data from Food and Agriculture Organization and Smithsonian Tropical Research Institute, and the author's experience as a Peace Corps Volunteer. The results from Tier I model FQPA Index Reservoir Screening Tool (FIRST) were used to compare immediate and delayed rain events, noting minimal difference. The Tier II PRZM-EXAMS shell provided estimated drinking water concentration (EDWC) profiles. The paraquat profile was much lower than picloram, glyphosate, and 2,4-D, which had almost identical profiles with peak concentrations around 12 ppm and the average annual concentration 100 ppb.
Average Daily Dose (ADD) via drinking water was calculated for men, women, and children using model results and compared to the oral reference dose (RfD). ADDs only exceeded the RfD with maximum peak EDWCs, implying low risk. However, RfD was used to calculate a breakpoint concentration, the concentration at which each pesticide presents a risk to the consumer. This was then compared to the maximum peak (highest, i.e. worst-case scenario) and annual (lowest, i.e. best-case scenario) EDWC profiles. In the best-case scenario, glyphosate and picloram did not pose a threat, paraquat posed a moderate threat and 2,4-D posed a high threat, with the concentration exceeding the breakpoint for 90 percent of the years. With respect to the worst-case scenario, all four chemicals posed high threats to the consumer. Individual exposure via consumption of fish from the river was calculated using a calculated bioconcentration (BCF) factor and calculated breakpoint concentrations. For the best case scenario, picloram presented a low risk and 2,4-D presented a high risk but for the worst case, both of these chemicals presented a very high risk. An additive exposure of these two human health pathways found that for the best case scenario, exposure from most of the four chemicals did not approach the RfD. However, for the worst-case scenario the exposures were significantly higher than the oral RfD--therefore, between the lowest and the highest concentrations, the general population is at risk.
For the ecological risk assessment, the 96-hour peak profile was compared to the 96-hour lethal dose (LD50); glyphosate posed a high risk to fathead minnows and low risk to bluegills and 2,4-D presented a high risk to fathead minnows, low risk to channel catfish, and very high risk to bluegills. A more general risk assessment compared maximum peak and annual concentrations to the US EPA's aquatic life benchmarks. Glyphosate presented no threat and 2,4-D only presented a threat to plants. For picloram, fish were at very high risk at the chronic level and low risk at the acute level, and plants were at moderate risk. Paraquat presented the most significant threat to aquatic life, exceeding benchmarks for all plants and invertebrates at the chronic level 100 percent of the time. It presented no threat to fish in the best-case scenario, but a high risk for fish at the chronic level in the worst case scenario, as well as very high risk for all invertebrates and plants. Improvements in application and watershed protection as part of a multi-disciplinary approach are proposed in place of technological mitigation strategies. Recommendations for future studies include the development of a developing-world context model and experimental studies in the developing world to compare to model results, where possible.
Scholar Commons Citation
Watson, Sarah Louise, "Assessing the Impacts of Unrestricted Pesticide Use in Small-Scale Agriculture on Water Quality and Associated Human Health and Ecological Implications in an Indigenous Village in Rural Panam[aacute]" (2014). USF Tampa Graduate Theses and Dissertations.