Application rate exposure

Exposures of Children. Data need to be developed to properly assess the exposure of infants who eat processed baby foods containing residues of pesticides such as endosulfan. Several studies have estimated exposure based on endosulfan concentration found in foods typically eaten by infants however, no studies that directly studied infant exposure could be located. Attention should also be given to infant formulas and to the tap water used to prepare infant formulas from condensed or powdered forms. More data are also required to properly assess endosulfan exposure to children who live, play, or attend school near farmlands that are treated with endosulfan. Maps that catalog endosulfan use on crops and present average application rates would better allow an assessment of the potential for children in farming communities to be exposed. The possibility that farming parents work clothes and shoes may carry endosulfan residues into the home also should be studied. In addition, home use of endosulfan, which may result in exposure of children, needs to be investigated. 

Plant uptake is one of several routes by which an organic contaminant can enter man s food chain. The amount of uptake depends on plant species, concentration, depth of placement, soil type, temperature, moisture, and many other parameters. Translocation of the absorbed material into various plant parts will determine the degree of man s exposure—i.e., whether the material moves to an edible portion of the plant. Past experience with nonpolar chlorinated pesticides suggested optimal uptake conditions are achieved when the chemical is placed in a soil with low adsorptive capacity e.g., a sand), evenly distributed throughout the soil profile, and with oil producing plants. Plant experiments were conducted with one set of parameters that would be optimal for uptake and translocation. The uptake of two dioxins and one phenol (2,4-dichlorophenol (DCP)) from one soil was measured in soybean and oats (7). The application rates were DCP = 0.07 ppm, DCDD 0.10 ppm, and TCDD = 0.06 ppm. The specific activity of the com-... 

When a tracer is considered, it is important to evaluate its performance with respect to these criteria, especially stability during exposure and storage/analysis. Normal practice involves conducting weathering tests where field collectors are treated with known amounts of the tracer and an assessment is made of weathering, extraction and storage stability under conditions pertaining to the intended use. The characteristics of the tracer allow it to be applied uniformly over the application area. Typically, application monitors are used to verify both the application rate and the uniformity of the application. 

Modeling re-entry exposure estimates techniques and application rates... 

In conclusion it can be stated that the basic assumptions of the re-entry model — a linear relationship between application rate and initial dislodge-able foliar residue and a first-order decay of the DFR — have been confirmed. The relationship between the transfer factor and re-entry time at various DFR levels should be explored further. Including information on foliage surface area or crop density may lead to a refinement of the model however, crop volume estimating methods should be improved before their influence on the exposure processes can be fully evaluated. 

Type Fire Exposure Water Application Rate... 

If, for example, an exposure estimate is scaled down by a factor of 2 (because the application rate per ha is halved), then it is correct to divide arithmetic means and standard deviation by 2, but it is not correct to divide logarithms of mean and standard deviation by 2. 

The Aerial Flagger. The aerial flagger, who had the highest HDE of all workers monitored, is not now commonly used in the aerial applications of pesticides to crops. Still, a flagger is sometimes used in special situations, and was therefore monitored. The flagger was the only worker that had a discernibly different exposure for different application rates. For example, the total HDE for XLR was 606 mg/h for a rate of 2 lb Al/acre and 408 mg/h for a rate of 1 lb Al/acre. 

A relatively accurate estimate can be made of inhalation contact exposure using the information on lung capacity and breathing rates (14). If it is assumed that an applicator occupies a space 2 metres square by 3 metres high, the immediate volume surrounding him would be 6000 litres. The concentration of pesticide that would be contained in this 6000 litres would be that which would impinge on the 2 square metres. For an application rate of 454 g.4047 m 2 the concentration in the 6000 litres would be ... 

It is important that the exposure estimate be realistic yet protective of human health and that it takes into account the frequency and duration of exposure. Uncertainties in the exposure assessment, including the fact that exposure studies are carried out under controlled circumstances, may be compensated for by using conservative assumptions such as maximum application rate, upper bound values and 100 % dermal penetration. These conservatisms can have a negative impact on the regulatory decision and conld be avoided with access to more complete data. 

The general ADD equation described above is applicable when intake rate, exposure duration, exposure frequency, body weight and pesticide concentration remain constant over the time period of interest. If they change over time, then it is necessary to use either a summation or integration approach to calculate potential dose (USEPA, 1992a). 

It is clear that for operators the application rate of the pesticide, relevant meteorological conditions, liquid pressure at the nozzle, geometry of crop and application equipment are very important variables (van Hemmen, 1992a). Furthermore, work methods and hygienic measures taken by the operator (e.g. wearing of protective clothing) also affect exposure. 

Exposures, D(ermal), /(nhalation) and 0(ral) are expressed as mg/person x kg of active substance. The amount handled is calculated from the use rate (application rate) R) in kg of active substance (a.s.)/ha and the area treated (A) per day in ha, leading to the equation for the three relevant routes of uptake, as follows ... 

Table 5.14 Specifications for the PHED, taken from the USEPA surrogate tables (PHED, 1998). Unit exposure values were extrapolated to a comparable scenario (2.5-25 kg a.i. handled, based on an application rate of 0.125-0.5 kg a.i./ha and area to be treated of 20-50 ha) ...

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