PRINCIPLES OF TOXICOLOGY - Biology East Borneo

22.4 CASE STUDIES 543The study was designed to minimize exposure by the ingestion route; workers were required to washtheir hands before eating, smoking, or putting a plug of chewing tobacco in their mouths. However,dose from the ingestion route was estimated by subtracting the estimate from a dermal absorptionpharmacokinetic model from the corrected amount found in the urine and subtracting away theestimated inhalation dose.In addition to the herbicide, creatinine was measured in the urine samples to assess whethervolunteers collected all their urine. Creatinine is a byproduct of metabolism and is excreted fairlyuniformly from one day to the next by the same individual. Excretion levels will vary betweenindividuals. The herbicide was quantified in each of the samples and then fitted to a pharmacokineticmodel developed from the laboratory study. The model estimate of dose and the sum of the amountsfound in the urine samples were compared, and the higher number was used for further calculations.A number of differences had been noted at each site. The first application site had low growth, andthe undergrowth was sparse. The second site had moderate vegetation. The third site had much highervegetation and was fairly dense. The fourth site was similar to the second site.Another difference between sites involved the method used to mix the herbicide. The workers atthe first and fourth sites mixed the herbicide and water into a 50-gallon container (nurse tank).Backpacks were filled by gravity feed through a hose. This allowed only one worker to handle theconcentrate, and he had to handle it only once. Workers at the second site mixed by adding theconcentrate into each of the 3-gallon backpacks at each fill-up and handled the concentrate each timethe backpacks were filled (about 6 times per day). The third group mixed into a 5-gallon container andthen poured from the container into the backpacks; they had to handle the concentrate at each fill-up,and then had to pour the mix into the backpacks.The equipment used at the three sites may also have affected exposure. Workers that used pistonpumps, which generate a higher pressure inside the backpack, had a higher rate of leaks at seals, andclothing was soaked with herbicide. Their exposure levels were greater than those of workers whoused diaphragm pumps, which generate a lower pressure. None of the diaphragm pumps leaked. Theworkers at the first site used wands to apply the material, while gunjets were used at the other twosites. The potential for exposure appeared to be much greater using the gunjet since it was held muchcloser to the body when sprayed. During walking, it could rub against the thigh where droplets fromthe tip could soak into the clothing. The gunjets also malfunctioned more often so workers had tohandle them while contaminated with herbicide. A comparison of these and other factors is presentedTABLE 22.2 Comparison of Herbicide Doses Across SitesSource Number Geometric Mean of Dose (g)BackpackDiaphragm 19 0.09Piston 3 2.34Handle concentrateYes 11 1.26No 11 0.93Use tobaccoYes 11 0.93No 11 1.35Regularly applyYes 20 0.91No 2 8.71ApplicatorWand 13 0.71Gunjet 9 1.51