dod tactical herbicide sites - United States Department of Defense

Summary of Assessment of Site ExposureThe issue of “meaningful exposure” to Tactical Herbicides is a subject of debate in thescientific literature. The most reliable information has shown that the esters of theherbicides, 2,4-D and 2,4,5-T, that made up Herbicide Orange, and its associated dioxincontaminant (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) rapidly dried within minutesof being sprayed on vegetation, rendering them unavailable for absorption. The processof drying involved the chemicals being absorbed within the waxy layer of the plantcuticle, where they were not readily dislodged [1]. Studies of Herbicide Orange and theassociated TCDD on both leaf and soil surface demonstrated that photolysis rapidlydecreased the concentration of TCDD (within hours), and this process even continued inshade [2]. Studies of ‘dislodgeable foliar residues’ (the fraction of a substance that isavailable for cutaneous uptake from the plant leaves) showed that only 8% of werepresent 1 hour after application. This dropped to 1% 24 hours after application [3].Moreover, studies in human volunteers confirmed that after 2 hours of saturated contactwith bare skin, only 0.15-0.46% of 2,4,5-T entered the body and was eliminated in theurine [4]. The implications of these studies and observations are that individuals whoentered a sprayed area one day after application of Herbicide Purple, Herbicide Green,Herbicide Pink and Herbicide Orange received essentially no “meaningful exposure.”These are important findings because military and civilian personnel from Fort Detrick,United States Department of Agriculture (in Puerto Rico and Texas), and the Air ForceLogistics Command that participated in the evaluation of the spray and monitoringoperations were not likely to have been exposed. Certainly, any local civilians whoentered the spray area days after spraying were at no risk of exposure.What is meant by a “measurable” human exposure to Tactical Herbicides is difficult toestimate for personnel who were not monitored by non-evasive blood or urine techniques.In the years before and during Vietnam, these techniques were not available [5]. Thecomponents of the Tactical Herbicides, 2,4-D, 2,4,5-T, cacodylic acid and picloram cannow be measured in the urine. The excellent studies by Lavy [5] and Hood [6] haveprovided convincing evidence that in forestry and brush control programs mixers andapplicators of the phenoxy herbicides, picloram or cacodylic acid would have had“measurable”, albeit generally very low, levels in their urine. However, these studies alsoindicated that individuals who walked through the sprayed areas even 2 hours afterapplication did NOT have measurable levels of herbicides in their urine. Thus, it wasunlikely that either short term or prolonged time spent in sprayed areas 24 hours afterspraying would have resulted in any “measurable” levels of exposure.Testing of serum dioxin levels has been widely regarded as the gold standard forepidemiological studies of TCDD from Herbicide Orange since its development in thelate 1980s [7]. Studies conducted on the men that actually handled the liquid HerbicideOrange showed measurable levels of TCDD in their blood serum [8,9]. Moreover, themajor industrial studies since the 1980’s have relied upon it to validate estimation ofexposure [7]. The significance of these studies and observations is that those ActiveDuty military personnel who mixed, loaded, and participated in the actual spray programsduring the development of the tactical phenoxy-related herbicides and spray equipment,77