Potential total dermal dose

The potential total dermal dose (PTDD) for workers is a summation of the skin exposure data, the hand wash data, and the head patch data for each individual worker. 

The calculation of potential total dermal exposure of mixer-loaders and re-entry workers using dosimetry data and calculation of the internal dose using biological monitoring data is complex but will be discussed briefly. 

Doses of chlorpyrifos in human volunteers were also estimated using physical measurements. Air sampling was conducted in order to estimate the inhalation dose to each volunteer. Dislodgeable residues were also measured throughout the study to estimate the dermal contribution to total dose. Finally, hand rinses were conducted on each volunteer immediately following the 4-hr activity period to assess the potential contribution to total dose from hand exposure and to estimate an oral dose to a crawling child. 

The relative contributions of the exposure routes and sources are as follows. For persons exposed to isophorone in the workplace, total doses will probably be substantially higher than those exposed only to ambient air and drinking water, and their inhalation and dermal exposures for the occupationally exposed can be assumed to result exclusively from the workplace exposures. Inhalation and dermal exposure for persons not exposed to isophorone in the workplace will most likely result from showering or bathing, but only in locations that receive their drinking water from contaminated surface water sources. These exposures are expected to be very small. In locations that do not have the potential for isophorone in the drinking water, any ingestion, inhalation, or dermal exposure is unlikely. 

Measurement of pesticide metabolites in nrine holds the potential for developing a more accurate estimate of internal dose, and is particnlarly nsefnl when exposnre is from multiple routes, oral, as well as respiratory and dermal, as is almost always the case for pesticide-exposed workers. If the total nrinary ontput is collected, until either there are no detectable residues or background levels are reached (usually 48-96 h), the levels can be used to estimate the internal dose. Stndies carried out in animals and humans for several pesticides have shown a good correlation between the amount of pesticide applied to the skin and the urinary output (Franklin et al., 1983, 1986 Popendorf and Eranklin, 1987). However, there are limitations to using this approach. The pharmacokinetics of the pesticide must be known in humans, while those pesticides that are highly volatile are extensively metabolized to numerous minor metabolites or seqnestered and are... 

The challenge in determining the dermal absorption values most relevant to factor into a risk assessment process for environmental contaminants is to define the most relevant parameter (i.e., flux, permeability coefficient, percentage absorption, or total systemic load). For example, when using in vitro techniques to determine potential dermal absorption of a contaminant in water (in which it will probably be present at low concentrations), the most common model would use an infinite dose aqueous application. This will allow the determination of flux and the calculation of a permeability coefficient. However, from such an experiment, the percentage absorption value will be practically meaningless. The total systemic load will be dependent on many other factors, such as concentration and solubility of contaminant within the medium, pH of the medium (and thus the degree of ionization of the contaminant). 

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