Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2004
Publication Date: February 20, 2004
Citation: Potter, T.L., Wauchope, R.D., Bosch, D.D. 2004. Pesticide fate and transport assessment in coastal plain watersheds. Weed Science Society of America Meeting Abstracts. Technical Abstract: The Environmental Protection Agency (EPA) is required by the 1996 Food Quality Protection Act (FQPA) to reassess food tolerances for all currently registered pesticides. During FQPA implementation a risk-based process has evolved. Its simplest form involves exposure assessment and dose comparisons to reference-dose metrics. Exposure routes include food, drinking water and residential. Their cumulative sum dictates the dose. A controversial part of FQPA implementation is the manner in which drinking water exposure is assessed. EPA relies on the field scale numerical model PRZM to predict potential pesticide concentrations in reservoirs and rivers at watershed scales. Widespread concern has been expressed about this approach because the model was not designed to do this and watershed scale calibration is lacking. Preliminary assessments by EPA staff have indicated that predicted environmental concentrations may be high by >100X or more. This has the potential to overstate exposures and in so doing human and ecological risks. A related concern is that drinking water exposure assessments do not effectively take into account regional differences in pesticide fate and transport processes. Most risk assessors would agree that it is inappropriate to use degradation rate data obtained with soils collected in the mid-West Corn-Soybean Belt to assess rates for the same chemical in cotton soils in the Southeast. However, in the absence of region specific data, approximations must be made. This includes using the data available. In recognition of related technical problems and issues, SEWRL has committed to collecting data which can be used to more accurately assess pesticide fate and transport in agricultural watersheds in the southern portion of the Atlantic Coastal Plain. Peanuts and cotton are produced intensively in the region. The 334-km2 Little River Watershed (LRW) is our principal experimental unit. We are intensively monitoring pesticide residue levels at the watershed outlet, developing pesticide use estimates, and assessing land cover. This is in addition to on-going precipitation and stream-flow monitoring that has been conducted for >35 years. The goal is to develop comprehensive data sets to calibrate watershed scale pesticide and fate models that reflect Coastal Plain conditions. Initial findings show that residue levels in surface water are extremely low (part per trillion) even though estimated pesticide use rates exceed 1kg ha-1yr-1 conventional active ingredient over the entire watershed.