Fluorescent-tracer techniques

Estimation of Respiratory Exposure 23 Estimation of Dermal Exposure 23 Surrogate Skin Techniques 23 Chemical Removal Techniques 25 Fluorescent Tracer Techniques 27 Estimation of Exposure to Children in the Home 27 Biological Monitoring 28... 

Dermal exposure sampling methods fall into three general categories surrogate skin techniques, chemical removal techniques and fluorescent tracer techniques (Fenske, 1993a). 

Fluorescent tracer techniques hold the promise of improved accuracy in assessing dermal exposures, as they require no assumptions regarding the distribution of exposure across skin surfaces. However, this approach also has several limitations. First, it requires introduction of the tracer compound into the agricultural spray mix. Secondly, there must be demonstration of a correspondence between pesticide deposition and deposition of the fluorescent compound for the production, such that the fluorescence can indeed be considered a tracer of chemical deposition. Thirdly, range-finding and quality assurance studies may be needed to ensure the accuracy of tracer measurements. Fourthly, when protective clothing is worn by workers, the relative penetration of the pesticide and tracer needs to be characterized. All of these limitations make fluorescent tracer methods technically challenging. 

Epema AH, Gerrits NM, Voogd J (1990) Secondary vestibulocerebellar projections to the flocculus and uvulo-nodular lobule of the rabbit a study using HRP and double fluorescent tracer techniques. Exp. Brain Res., 80, 72-82. 

As methods of exposure estimation, neither the fluorescent tracer technique nor the patch technique have been validated. Nevertheless, it would be encouraging if a comparison of estimates by the two methods yielded roughly equivalent results. The only body region which can be reasonably compared is the head, as the patch method assumes no clothing penetration, and no hand wash was conducted in this study. Furthermore, four of the six workers must be excluded, as they wore face shields. Thus, the only comparison available is the head and neck exposure of workers 1 and 2. These data are presented in Table IX. Following the protocol outlined by Durham and Wolfe ( ) and Davis ( ), the amount of diazinon recovered from the dermal monitor on the chests of the two workers is employed to calculate exposure to the face and front of neck. A similar patch on the back allows calculation of exposure to the back of the neck. 

Unfortunately the Ideal situation does not exist and there are many difficulties which must be overcome before accurate risk assessments can be conducted. For pesticide applicators, the dermal route has been shown to be the most Important one. However, the methods used to measure the amount of pesticide landing on the skin are not very reliable and many studies conducted In the past did not try to estimate hand exposure. This omission Is a serious one because it has been shown that a very large percentage of the total dermal exposure Is to the hands. New methods using fluorescent tracer techniques are promising and will undoubtedly lead to more quantitative estimates of contact exposure. 

Morooka S, Kusakabe K, Ohnishi N, Gujima F, Matsuyama H. Measurement of local fines movement in a fluidized bed of coarse particles by a fluorescent tracer technique. Powder Technol 58 271-277, 1989. 

Davis SS, Walker 1.1983. Measurement of the yield of multiple droplets by a fluorescent tracer technique. Int J Pharm 17 203-213. 

Tanabe, T Ueda, S. Sano, Y. Combined method of fluorescence tracer technique and PAP immunohistochemistry for discrimination of the transplanted cells. Histochemistry 1989,91,191-194. 

PIV has become the most popular technique to measure velocity and turbulent properties (Figure 15.1). The movement of seed particles in a millimeter-thick laser sheet is measured by correlating two photos taken a few milliseconds apart. With two cameras, it is also possible to obtain a 3D vector of the velocity in that plane. The method gives, in general, very good resolution of the flow, but it requires optical access. Also, measurement close to walls can be problematic due to light reflections that disturb the measurements. One extension of PIV is the micro-PIV that uses fluorescent tracer particles, which allows all direct light, for example, reflections at the walls, to be filtered out [1]. 

Fenske, R.A., Wong, S.M., Leffingwell, J.T., and Spear, R.C. (1986b) A video imaging technique for assessing dermal exposure. II. Fluorescent tracer testing, Am. Ind. Hygiene Assoc.., 47 771-775. 

Flow cytometry (FCM) is a high-precision technique for rapid analysis and sorting of cells and particles. In theory, it can be used to measure any cell component, provided that a fluorescent tracer is available that reacts specifically and stoichiometrically with that constituent. The technique provides statistical accuracy, reproducibility, and sensitivity. 

Preliminary results using a fluorescent tracer, which was added to the spray tank at the same time as the pesticide (Guthion WP), indicated that the distribution of the tracer, and presumably the pesticide, was not uniform, emphasizing the difficulty in the placement of the patches (2) This tracer technique is currently being evaluated as a tool for quantitative exposure estimation. This could result in a more realistic measurement of pesticide contact on the skin and minimize the reliance on extrapolation from the patch data. 

In the gas-liquid two-phase flows illuminated by a laser sheet, for example, the intensity of light reflected from the gas-liquid interface (mostly the gas bubble s surface) not only saturate the CCD camera, but also overwhelm the intensity of light from the seeded tracer particles in its vicinity. Fluorescent particles are often used to realize the laser-induced fluorescence (LIF) technique together with PIV (e.g., Broder and Sommerfeld, 2002 Fujiwara et al., 2004a, b Kitagawa et al., 2005 Liu et al., 2005 Tokuhiro et al., 1998,1999), so that both images of gas-liquid interface (e.g., bubble s geometry) and velocity distribution in the liquid phase around the gas bubbles can be obtained. Issues on PIV measurement of gas-liquid two-phase flows will be further illustrated in the latter sections. 

Black, K.G. and R.A. Fenske (1996). Dislodgeability of chlorpyrifos and fluorescent tracer residues on turf Comparison of wipe and foliar wash sampling techniques. Arch. Environ. Contam. Toxicol, 31, 563-570. 

The rate of diffusion of molecules through intact tissues in an animal is difficult to measure, so the amount of information currently available is limited. Diffusion coefficients for size-fractionated dextrans, albumin, and antibodies have been measured in granulation tissue and tumor tissue [20, 21] similar measurements have been made in slices of brain tissue [87]. In both cases, the diffusion coefficient was estimated by fitting solutions to the diffusion equation, similar to Equation 3-36, to data obtained by direct visualization of fluorescent tracers in the interstitial space. These measurements, as well as others made by a variety of techniques, are compiled in... 

The feasibility of employing fluorescent tracers and video imaging analysis to quantify dermal exposure to pesticide applicators has been demonstrated under realistic field conditions. Six workers loaded a tracer with the organophosphate pesticide, diazinon, into air blast sprayers, and conducted normal dormant spraying in pear orchards. They were examined prior to and immediately after the application. UV-A illumination produced fluorescence on the skin surface, and the pattern of exposure was digitized with a video imaging system. Quantifiable levels of tracer were detected beneath cotton coveralls on five workers. The distribution of exposure over the body surface varied widely due to differences in protective clothing use, work practices and environmental conditions. This assessment method produced exposure values at variance with those calculated by the traditional patch technique. 

The impetus for this study came from a realization that the traditional patch technique ( ) was inherently limited in its ability to accurately measure dermal exposure, and from the great potential which a fluorescent tracer methodology appeared to hold. The ability to visualize exposure immediately provides valuable qualitative information regarding the exposure process. When combined with a video image processing system which quantifies fluorescence, the possibility of carefully characterizing dermal exposure seemed well worth the effort involved. 

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