A QUANTITATIVE RISK ASSESSMENT WITH ATTENDANT UNCERTAINTY ESTIMATIONS FOR IRRIGATED FARMLANDS IN OKLAHOMA

Agricultural chemical use has increased dramatically in the post World War II era. Benefits to society include greater crop production and lower manpower requirements. Detriments include environmental and public health impacts. The subject research presents the results of a risk assessment which examined potential impacts of agricultural pesticide use. The two phase assessment focused in Phase 1 upon the projected risks associated with using six pesticides on four crop types within three hydrological soil groupings. Irrigation was compared with the dry land farming base case. The hypothetical target receptors were a “typical” farm family in Caddo County, Oklahoma; an area undergoing significant change from dry land farming to irrigated agriculture. Phase 2 addressed some of the uncertainties associated with the Phase 1 risk assessment. Both Phases utilized available transport and exposure codes to determine the probability of exceeding the U.S. Environmental Protection Agency’s supported Reference Dose (RfD). Of the six pesticides evaluated only 2,4-D when used on peanuts presented potentially significant risk. Selection among the other variables such as other crops, the hydrologic soil groupings or the use of irrigation did not contribute consistently to this elevated risk. There was much uncertainty in these estimates. Phase 2 efforts showed that the exposure variables of receptor body weight and drinking water ingestion rate, together with the estimated pesticide concentration had the greatest impact on this uncertainty determination. 125 2003, Baywood Publishing Co., Inc. INTRODUCTION Background Increasingly the agricultural community in the United States and worldwide has become more dependent upon various chemicals to control farm pests and increase production [1]. It has been reported that over 4.5e8 kilograms of active ingredients were applied in 1991 to U.S. farms [2] representing a 100 percent increase from the previous seven years [3]. Concerns have long been expressed regarding the unintended, adverse impacts resulting from the use of these chemicals. Ecological as well as public health concerns have been cited [4]. As an example, 67,000 non-fatal pesticide poisonings were reported in 1990 [2]. Finding ways to identify and subsequently reduce the hazards associated with these chemicals has been the subject of much research [5, 6]. The problem is made more complicated by the complex interactions between these chemicals, various irrigation techniques, and other agronomic practices, different soils, and uncertainties in levels of exposure to potential human receptors. This research attempts to address some of these questions by applying fundamental risk assessment techniques to the problem of pesticide exposures at the individual farm level. In this way, the uncertainties associated with pesticide use over a range of potential environments and use practices can be addressed. A review of risk assessment in general follows. Risk Assessment Paradigm As defined by the United States National Academy of Sciences and the U.S. Environmental Protection Agency, an environmental risk assessment (RA) consists of the following four elements: • Hazard Identification; • Dose-Response Assessment; • Exposure Assessment; and • Risk Characterization [7]. The Hazard Identification and Dose-Response Assessment comprise the medical or public health elements of the RA process and serve to determine if a chemical or other environmental agent is capable of inducing adverse public health effects to a potential receptor population. Chemicals can have hazardous attributes while simultaneously exhibiting minimal, adverse dose-response properties. This occurs when the chemical is poorly incorporated into the respective receptor tissues over the period of exposure. This condition results in reduced environmental risk regardless of inherent hazard or exposure to the subject chemical. These two elements combine to quantitatively identify which chemicals pose a significant hazard to exposed individuals. 126 / HANSON AND MCTERNAN