Risk assessment dermal contact

SADA provides a full human health risk assessment module and associated databases. The risk models follow the USEPA s Risk Assessment Guidance for Superfund (RAGS) and can be customized to fit site-specific exposure conditions. It calculates risks based on the following exposure pathways ingestion, inhalation, dermal contact, food consumption, and also a combined exposure. 

The bioavailability of contaminants to wildlife and humans is also an area of critical importance, where contaminants can be taken up in pore water and by dermal contact, particle ingestion, or particle inhalation. The dynamics of sorption/desorption are not currently incorporated into exposure and risk assessment models for organic compounds, where availability, in most cases, is assumed to be 100% [224]. Recently, the following have been demonstrated and reported ... 

An exposure assessment is the quantitative or qualitative evaluation of the amount of a substance that humans come into contact with and includes consideration of the intensity, frequency and duration of contact, the route of exposure (e.g., dermal, oral, or respiratory), rates (chemical intake or uptake rates), the resulting amount that actually crosses the boundary (a dose), and the amount absorbed (internal dose). Depending on the purpose of an exposure assessment, the numerical output may be an estimate of the intensity, rate, duration, and frequency of contact exposure or dose (the resulting amount that actually crosses the boundary). For risk assessments of chemical substances based on dose-response relationships, the output usually includes an estimate of dose (WHO/IPCS 1999). 

PTMs-contaminated soils pose a human health risk on the basis of the potential of the contaminant to leave the soil and enter the human bloodstream. In order to assess human health risk, several pathways of transfer of metals from soil to humans have to be taken into account. The most important metal intake takes place via the food chain in which plants or meat of animal play a key role. The direct ingestion of soil can be a major route of exposure for humans to many low mobile soil contaminants, particularly for small children through putting hands into the mouth (Gupta et al., 1996). The contribution from the inhalation of particles smaller than 10 pm and from dermal contact with soil have little meaning compared with oral ingestion and are found to be less than 1% and 0.1% of the total intake, respectively (Paustenbach, 2000). 

The route of exposure is another aspect of exposure in which health-relevance must be considered. In Section One of this book, there is a detailed discussion of exposure assessment methodologies, including the importance of identification of the most prevalent route of exposure (dermal, inhalation or oral) and the necessity of knowing the absorption of the pesticide to allow calculation of the absorbed dose for risk assessment. For epidemiological purposes, exposure-assessment smdies are usually limited to assessing contact exposure levels. Since dermal absorption is not known for many pesticides or complex mixtures, uptake through the dermal route can often not be estimated and contact exposure data are a poor proxy of internal exposure (absorbed dose) (Schneider et al., 1999). 

As important as the hazard identification for a substance is the characterization of exposure to human beings. All known conditions of use have to be compiled to estimate the most realistic exposure of a substance to the environment including an estimate of the intake of a substance via inhalation, dermal contact, oral intake (Table 8). A major result of a risk assessment is the comparison of exposure levels to NOELs. 

Cancer risk assessment for exposure to chemicals in soil involves several unique exposure issues. Volatile chemicals in soil may evaporate off soil particles and thus may result in a potential inhalation hazard, but little or no hazard from dermal or oral exposure. Semi-volatile and nonvolatile chemicals may bind tightly to soil, and thus be less available for absorption. Unlike air, water, and food, soil is not directly consumed (in most cases), but is contacted incidentally while carrying out other activities. Thus exposure scenarios and soil exposure factors are more variable and important for chemicals in soil than in other media. The EPA Exposure Factors Handbook (EPA 1997a) has summarized these principles especially relevant in the handbook are Chapter 4 on soil ingestion. Chapter 6 on dermal exposures, and Chapter 17 on residential exposures. Recently, this has been supplemented with child-specihc exposure guidance (EPA 2008b). 

Ideally, a health risk assessment would characterise the dose-response relationship, i.e. the relationship between the dose of a chemical administered or received and the incidence and/or severity of an adverse health effect in an exposed population. However, estimating the dose-response relationship for many chemicals (particularly environmental agents) is often extremely difficult or, because of the lack of data, unachievable. For example, little is known about dermal uptake rates of soil-bound contaminants or the duration of such contact episodes. Therefore, estimating the dose received from dermal contact with soil can be highly tentative and is usually based upon a number of simplifying assumptions. 

Soil contamination presents further complexities in dermal risk assessment (see Chapter 11, this volume). Briefly, additional factors involved in the estimation of risk include soil type (and particle size) and loading rate skin-soil adherence (Holmes etal., 1999), which can vary according to body site area of exposure (fraction of body area exposed is limited by clothing) and climate. The equation used to determine the dermally absorbed dose from soil contact is the same as that... 

Exposure pathways for adult amphibians include soils (dermal contact, liquid water uptake), water (dermal contact with surface water), air (cutaneous and lung absorption), and diet (adults are carnivores). All routes of exposure are affected by various physical, chemical, and other factors. Dietary exposure in adults, for example, is related to season of year, activity rates, food availability, consumption rate, and assimilation rates. Knowledge of these modifiers is necessary for adequate risk assessment of mercury as a possible factor in declining amphibian populations worldwide. 

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. 

Dermal Absorption and Dermal Dose-Resnonse. These data are needed in the risk assessment of field workers, mixers/loaders, applicators, and flaggers they may also be used in the development of reentry intervale. The data gathered informs CDFA of how much of the chemical actually enters the body once it comes into contact with the skin. Guides for these types of studies in test animals are available through, and were conducted by, the CDFA. At times, data from human volunteer studies are available when available, this type of information usually takes precedence over animal test data. 

Dermal Exposure Opportunity In assessing dose and risk for PCB s and PCDD s/PCDF s, a critical variable is the opportunity for dermal exposure. In determining dermal exposure opportunity it is customary to differentiate between areas within a given space that are readily assessable for high level contact such as exterior vertical and horizontal surfaces vs. areas less directly accessible. In these areas the person with potential exposure was high probability of dermal contact. This is in contrast to areas inside mechanical systems or in areas that because of height or inaccessibility allow for less opportunity for dermal exposure. 

Exposure to PAHs mainly occurs from atmospheric pollution through inhalation, ingestion and dermal contact. PAHs half-lives in humans are in fact in the range of days/hours, and metabolism is responsible of the formation of carcinogenic metabolites. Risk assessments and potency assessments of various individual and complex mixtures of PAHs... 

Exposure to PAHs mainly occurs from atmospheric pollution through inhalation, ingestion and dermal contact. PAHs half-lives in humans are in fact in the range of days/hours, and metabolism is responsible of the formation of carcinogenic metabolites. Risk assessments and potency assessments of various individual and complex mixtures of PAHs have been attempted. BaP is the only PAH for which a database is available, allowing a quantitative risk assessment. PAH potencies are used to determine quantitative health risks posed by PAH exposure. The risks posed by a mixture of PAHs are based on an assumption of additively of the individual risks posed by the PAHs. 

Generally, the main pathways of exposure considered in tliis step are atmospheric surface and groundwater transport, ingestion of toxic materials that luu c passed tlu-ough the aquatic and tcncstrial food chain, and dermal absorption. Once an exposure assessment determines the quantity of a chemical with which human populations nniy come in contact, the information can be combined with toxicity data (from the hazard identification process) to estimate potential health risks." The primary purpose of an exposure assessment is to... 

Any possible risk to users while spraying plant-protection products must be evaluated before its authorization. When it is necessary for workers to reenter crops shortly after their treatment, they may be exposed to the plant-protection product through contact with the spray deposit therefore, this possible means of exposure must be evaluated when a plant-protection product is to be used. This chapter discusses the procedure for and some examples of the assessment of re-entry exposure and provides instructions for placing protective measures on product labels if dermal and inhalative exposure is relevant. 

Exposure should normally be understood as external exposure, which can be defined as the amount of substance ingested, the total amount in contact with the skin (which can be calculated from exposure estimates expressed as mg/cm or mg/cm ), or either the amount inhaled or the concentration of the substance in the atmosphere, as appropriate. In cases where a comparison needs to be made with systemic effects data (e.g., when inhalation or dermal toxicity values are lacking or when exposures due to more than one exposure route need to be combined) the total body burden has to be estimated. Since the assessment of the amount that is absorbed after ingestion, by inhalation or by the skin is usually done in the effects assessment (section on toxicokinetics), this calculation of the total body burden is often placed in the section on risk characterization. 

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