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not account for the rate of accumulation on the skin. Dermal exposure data are difficult to acquire and interpret. However, methods are avai-
lable for the sampling process, such as the WHO recommended methods developed for occupational exposure assessment WHO IPCS, 1999 and dermal absorption Kielhorn,
Melching-Kollmuss Mangelsdorf, 2006. These methods make use, as in other methods, of a set of gauze pads applied to the skin of different parts of the body; the concentration
measured in the pads is used to calculate the dermal exposure of each part of the body.
Exposure of the hands is often highly significant. Although residential labels of several products recommend gloves as best management practice, homeowners can hardly be
assumed to typically wear protective gloves when applying pesticides in the home. Moreover, poor procedures in putting on and taking off gloves can lead to significant
exposure to the hands, regardless of the barrier properties of the protective glove mate- rial.
Dermal exposure may also result from contacting treated areas. Even where a pesticide has been applied to cracks and crevices, its residues can be detected throughout the house,
and contact may occur through everyday activities. For example, in a case where chlor- pyrifos applications had been made to the cracks and crevices of the homes and along the
perimeters of the walls behind appliances and furniture, surface wipe samples collected from non-targeted surfaces such as play areas, bedrooms and plush toys showed the pre-
sence of chlorpyrifos Hore et al., 2005.
Sampling gloves provide a measure of potential dermal exposure when coming directly into contact with solids, fluids and aerosols; these gloves may over-sample, but they can
reflect actual dermal exposure. Thin cotton sampling gloves worn beneath protective glo- ves demonstrate actual hand exposure but again may overestimate exposure. Sampling
protocols, however, need to recognize that sampling gloves will collect pre-existing conta- mination inside protective gloves. Another technique for assessing hand exposure uses
hand washing with solvent–water solutions and wiping the skin on the hand at the end of use see also Kielhorn, Melching-Kollmuss Mangelsdorf, 2006.
Using surrogate biocide products, further research in progress will indicate the likely percentages and spatial distributions of typical work clothing penetration. Finally, it
should be mentioned that washing contaminated clothing clothing used while applying biocides with everyday laundry might contaminate the household laundry or clothing.
14.6.3. Incidental oral exposure
Unintentional oral exposure is the amount of a biocide entering the mouth. At present, it can only be inferred from biomonitoring or worst case modelling that uses EPA SOPs
EPA, 1997a. Exposure is expressed in mgevent or mgday. Biomonitoring for biocides requires expert advice and appraisal of the results. As biomonitoring measures total expo-
sure, the percentage of the exposure that results from oral unintentional exposure can only be differentiated from other routes of exposure when they are negligible or have
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506
depositedkg AI handled mgkg AI. However, in numerous biocide exposure scenarios, the amount of biocide handled simply cannot be estimated – for example, drilling mud.
Another common metric is the amount of in-use biocide that deposits per unit of time or per task in mgmin and mgcycle, respectively. Practical evidence from field studies
indicates that metrics for potential dermal exposure, such as mgmin or mgcycle, are useful.
Estimated exposure.
In the absence of measured exposure data or representative data on analogous substances, exposure must be estimated using recommended modelling
approaches. To ensure that the predictions are realistic, all relevant exposure-related information on the substance should be used iteratively.
Actual dermal exposure.
This is the amount of compound that actually reaches the skin. It is affected by the efficiency and effectiveness of clothing in acting as a barrier and is
often expressed simply as the weight of biocide product on the skin mg on skin. Another metric of importance is the concentration of a substance AI on the skin mg AIcm
2
of skin, which in turn depends on the amount deposited and the surface of contaminated
skin. By knowing the skin penetration rate of a substance, its concentration on the skin enables the actual intake through the skin to be assessed. It is worth noting that the per-
centage for the skin penetration rate is generally inversely proportional to the concen- tration on the skin, being highest for the low concentration values. Moreover, damages
to skin such as small wounds and fissures, conditions that alter skin permeability such as inflammation and eczema, or the presence of certain solvents may increase the skin
penetration rate.
Although not a major route of exposure, the potential of exposure to the eyes will also need to be considered, particularly when handling irritants or corrosive substances.
Potential dermal exposure normally has to be measured, or estimates may be obtained from database models. Actual dermal exposure, however, arises through:
• direct deposition on exposed skin, such as the face; • permeation through clothing and penetration of clothing around fastenings, openings,
and along seams; • incidental contact with residues on surfaces; and
• putting on and taking off contaminated clothing including protective gloves. It is often impossible to know the actual amount of dermal exposure – that is, the sum
of the total direct and indirect exposures of the skin. Studies that use fluorescent dyes can provide a useful indicator of actual dermal exposure, but there are few data available.
The quantity of a substance deposited on the skin can be expressed in terms of mgcm
2
, with the amount of skin exposed expressed in cm
2
. However, the quantity on the skin is more likely to be simply expressed as a weight mg on skin. Such metrics, however, do
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percentages, can be used to express risk as a function of hazard and exposure. Risk assess- ments usually apply tiered modelling approaches that range from deterministic model-
ling based primarily on conservative assumptions Tier 1 to probabilistic models that use refined assumptions based on real data Tier 3. Pesticide risk assessments apply conser-
vative assumptions that overestimate exposure and hazard, resulting in a quantitative assessment that has a large margin of safety. The conservatism of these approaches is sup-
ported by surrogate data; for example, exposure often can be estimated by using surro- gate data developed previously for other chemicals or an exposure database can be used
for a surrogate estimate of inhalation and dermal exposure for many exposure scenarios.
Relatively few studies in residential environments have examined the exposure of occu- pants to pesticides EPA, 1980. Most risk assessments are based on surrogate data and
conservative assumptions EPA, 1998b, 1999, 2002a. To our knowledge, no study has compared the risk of disease from exposure to urban pests with the risk of pesticide expo-
sure. These risk–risk and risk–benefit analyses would benefit greatly from more expo- sure studies on both of these topics.
14.7.1. Steps of pre-market risk assessment of pesticides
