Assessment exposure

Exposure assessment is the evaluation of the exposure of an organism, system or (sub) population to an agent (and its derivatives) [74]. An exposure 

Product Stewardship Life Cycle Analysis and the Environment 

The next step is to identify the source(s) of a chemical and the nature of the release(s) of that chemical, including the amount and to what media. The story continues with a description of how the chemical moves through the environment, considering advection and transport between phases, the reactions it undergoes, and the potential to bioaccumulate. Finally, the exposure scenario describes who or what is exposed (i.e., the receptor, ecosystem, or habitat). 

The assessor combines the assumptions stated in the exposure scenario with information about the behavior of the chemical to perform a mass balance that produces an estimated exposure concentration, known as a predicted environmental concentration (PEC), in each of the relevant compartments. 

Exposure assessment is often an iterative process that begins with numerous simplifying assumptions. For example, the assessor might initially assume that no degradation or advective transport occurs, or that all of the substance is bioavailable. Such assumptions produce a worst-case estimate of exposure. If that estimate would not present a significant risk, then no further exposure assessment may need to be done. Alternatively, the assessor may choose to refine his assumptions, perhaps by collecting additional data to quantify more accurately some aspect of the compound s fate and transport, or by incorporating a probability distribution for the values of critical parameters (e.g., Monte Carlo simulation). He may also choose a more sophisticated model to perform the mass balance. 

3 Exposure Assessment. In exposure assessment, the population potentially exposed to hazardous substances and the pathways and routes through which exposure could occur are specified, and the magnitude, duration, and timing of the doses people might receive are quantified. The approach to exposure assessment for hazardous waste disposal can range from very sophisticated and complex e.g., Wilson et al., 1994) to a multiplication of simple factors (e.g., Dornsife, 1995 EG G, 1982 EPA, 1989 Smith et al., 1980). Exposure assessment for waste disposal is itself a multi-step process, and is discussed below. 

Describe the conditions of waste disposal. Wastes in specified physical and chemical forms and having certain compositions or ranges of compositions of hazardous substances are assumed to be emplaced in certain ways in a disposal site having specified characteristics. The disposal site can be a real location or generic with hypothetical characteristics typical of real sites. The exposure assessment usually assumes that disposal operations have been completed and the site is closed, although the 

Describe possible mechanisms by which hazardous substances could be released from a disposal facility. A credible series of processes and events that could result in release of hazardous substances from the disposal site to a portion of the environment that is accessible to humans and the probability that these processes and events would occur, often called a release scenario, is developed. Release scenarios for waste disposal facilities generally should include considerations of inadvertent human intrusion resulting from normal activities, such as excavation or drilling, as well as releases to air and groundwater due to natural processes and events. 

Develop models for scenarios and acquire data. The release and exposure scenarios described above are evaluated through modeling. The models embody the mathematical interrelationships of the possible steps in each scenario. Simplifications and approximations usually are introduced to reflect limitations in knowledge and data or the results of previous risk assessments that show certain scenarios and pathways to be negligible. The result often is a series of models describing (1) degradation of 

Considerations involved in establishing scenarios for release of hazardous substances from waste disposal sites. 

An exposure assessment is required for each of the human populations exposed to the biocidal product during production, use and disposal. These populations could include professional users, non-professional users and humans exposed indirectly via the environment. The exposure assessment should make a qualitative assessment of the concentration of the active substance(s) and substances of concern to which a population may be exposed during the lifetime of the biocidal product. Exposure can be categorized into the following groups  

Secondary (non-users, bystanders, people not aware of exposure) 

For the purposes of the BPD a project was commissioned by DG Environment and conducted by Institutes/ organisations from 6 European Member States, together with representatives from industry. The aims of this project were to develop relevant exposure scenarios of humans to biocidal products and to develop operational predictive models for the purposes of authorisation of biocidal products in each of the 23 product types. The report and proposed models from this project is expected to be finalised in mid-2003. 

The project has identified several approaches in determining the exposure level for each active substance and substance of concern, these include  

The indicative distribution models presume that available occupational exposure is log-normally distributed and determines a matrix with 12 cells containing various exposure studies on different use areas. The 12 cells are made up from 3 categories of width of distribution (GSD) - narrow, medium and wide and 4 categories 

This process is an integral part of the risk assessment process. However this will be introduced only briefly in this chapter, and the reader is encouraged to consult Chapter 28 in this text as well as numerous other texts that describe the process in 

LADD ((- onc- in me(iia) x (Contact rate) x (Contact fraction) x (Exposure duration) 

3 TOXICITY AND RISKS INDUCED BY OCCUPATIONAL EXPOSURE TO CHEMICAL COMPOUNDS 

While occupational hygiene measurements always measure only the concentrations of chemical compounds present in the occupational environment, i.e., the potential dose, the analysis of biological specimens predominantly reflects the body burden. Furthermore, biological monitoring is always limited to assessment of individual exposure. Personal occupational hygiene sampling takes into consideration only some of the individual factors, e.g., working 

FIGURE S.53 Relsttionship between the concentration of toluene in front of a gravure press and the consumption of toluene.  

Three factors determine exposure assessment quantity of food consumed, residue concentration in that food, and the marker residue total residue ratio. The food basket adopted by most authorities comprises  

300 g muscle (for flsh, muscle and skin in natural proportions). 

In the EU, for example, the food basket comprises, for mammals, muscle (300 g), liver (100 g), kidney (50 g), and fat (50 g) and, if appropriate, milk, eggs, and honey (for poultry, 10 g kidney and 90 g fat). For poultry and pigs, the MRL for fat relates to fat and skin in natural proportions in the EU, while for fin fish, muscle includes muscle and skin in natural proportions. In general, a numerically greater MRL is allowed for foods likely to be consumed infrequently or in small amounts (e.g., kidney relative to muscle). In addition, residues that occur in food of plant origin or that come from the environment need to be considered when fixing the MRL. 

On the basis of the food basket, the EU authority (EMA/CVMP) then requires applicants for MAs to estimate the theoretical maximum daily intake (TMDI) for persons weighing 60 kg, applying the equation  

Production volume or importation volume is often used as a surrogate for exposure the higher the production volume, the greater the likelihood that humans or the environment may be exposed. More detail can be obtained through the analysis of how the chemical will be manufactured, processed, used, and disposed. Another factor is who is likely to be exposed consumers or industrial workers For the environment, are releases likely to occur to water or to air, and which control measures are used to minimise these releases  

Even under the best of circumstances in which all possible exposure modes are controlled, it would be foolhardy to make a conclusion of zero exposure. Numerous industrial chemical accidents have occurred. One particularly catastrophic incident occurred in Bhopal, India, in 1984 in which the extremely toxic gas methyl isocyanate leaked out of a closed and contained system resulting in the deaths of perhaps tens of thousands of people. The Bhopal incident dramatically demonstrates that zero exposure (and therefore zero risk) can never be concluded, but it is also possible to go too far in the direction of concluding that all toxic chemicals must be banned for all applications, which is sometimes referred to as the precautionary principle . This important nuance is discussed later in this chapter. 

Much of the attention focused on exposure assessment lus come recently. This is because many of the risk assessments done in tlie past used too many consen ative assumptions, wliieli caused an ovcrcstimation of the actual exposure. Without exposures there are no risks. To experience adverse effects, one must first come into contact with the toxic agcnt(s). Exposures to chemicals can be via inlialation of air (breatliing), ingestion of water and food (eating and drinking), or absorption Utfougli the skin. These arc all pathways to the human body. 

Generally, the main pathways of exposure considered in tliis step are atmospheric surface and groundwater uansport, ingestion of toxic materials that luu c passed tluough the aquatic and terrestrial food clunin. and dermal absorption. Onee an exposure assessment determines the quantity of a ehemieal with whieh human populations may come in contact, the information can be combined with toxicity d ita (from the haz ird identification process) to cstiiiKitc potential health risks. The primary purpose of an exposure assessment is to 

As discussed in chapter 3, there are no toxic effects without exposure. This portion of a risk assessment is critical because it defines the conditions under which ex- 

In this portion of a risk assessment, all the ways that chemicals could move in the environment, as well as all types of people that might be located in areas where the chemicals could be present, need to be considered. Even though the leak has occurred in soil below the ground, exposure could occur off-site because chemicals could be in groundwater, which moves over time. This is illustrated in figure 8.2 for the gas station example introduced in the Data Evaluation section. It is beyond the scope of this book to discuss the mechanisms by which chemicals can move in the environment. However, it is important to know that there are predictable factors that can be used to identify the likely ways by which people could come into contact with chemicals from a site. 

There are three basic steps to an exposure assessment  

Not everyone will be exposed to chemicals associated with a site. In this step, the types of people that could be exposed are identified. Using the gas station example, the gas station attendants will represent the people most likely to be exposed to chemicals at the site. People refueling their cars will also be exposed. Small children are unlikely to be exposed to any appreciable degree. Also, if the leak were to be fixed, workers could directly contact the contaminated soil during excavation and removal of the soil. Similarly, if chemicals were present in groundwater at a site used for an office building, we could expect that office workers in the building would be the primary exposed receptors. 

Once potential receptors cu e identified, the ways in which they may contact chemicals need to be defined. This is done by identifying complete exposure pathways. There are four components that must all be present for an exposure pathway to be complete  

In general, calculations of industrial emissions rely on default values according to the industrial sector, emission rates, wind velocity and direction, anticipated substance flows through the environment, abatement technologies and wastewater treatment processes (see [114]). Site-specific assessments and local environmental exposure assessments must also account for geographic variability caused by climate, hydrology, geology, and biotic conditions [115]. 

Environmental exposures form the basis for determining indirect exposures to the general public that will usually occur during a lifetime. Direct consumer exposure assessments prove equally challenging, and may vary from acute to chronic exposure scenarios. Ideally the data set for consumer exposure from a substance in a product should include [127]  

Although there is large inter-individual variation in frequency, duration and amount of product used, consumers tend to follow certain routines [128]. The United States (US) National Human Activity Pattern Survey has been gathering important information for determining exposure to environmental pollutants by collecting data on time-activity patterns for various exposure scenarios [129]. In 2005, a similar project began in the EU that focusses on types of product use according to exposure scenario [130]. 

The residues and metabolites of a substance can be measured in an organism or an environmental medium. Alternatively, biological effects known as biomarkers that are known to be the result of exposure to a hazard can be used to determine exposure levels [131]. In some cases, monitoring biomarkers in employees (e.g., metabolites in urine) can prove cheaper than measuring airborne concentrations of a substance in the workplace [132], 

Many models are available for calculating exposure, but the European Union System for the Evaluation of Substances (EUSES) is the most commonly used in the EU. Variations in human populations across Member States are considered in terms of body weight, diet, and activities [133]. Consideration is also given to susceptible individuals such as children and the elderly [133]. More specific models are used in conjunction with EUSES to assess occupational dermal exposure (DERMAL), occupational inhalation (EASE) and consumer exposure (CONSEXPO) (see [134]). 

When the effects of time variations in release rates are included, pulse (or instantaneous) and continuous (plume) emissions are the two most common time-variant inputs in transport models. The classic example of a pulse release is a hazardous waste spill. The steady release of contaminants into groundwater from a subsurface contaminant and the continuous release of volatile solvents from an air-stripping tower are examples of plume emissions. 

Environmental releases of hazardous waste from contaminated sites can result in transport through several media. The most common pathways include (i) transport through the subsurface to groundwater and (ii) atmospheric transport after release into the air. Other less common pathways after release include surface waters, and plant and animal uptake. 

Exposure is the contact of an organism with a toxic substance exposure assessment is the estimation of the magnitude, frequency, duration, and route of exposure (Patton, 1993). The primary tasks of exposure assessments include (i) identifying the populations that may be exposed, 

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James L. Unmack, "A Comparison of Periodic Versus Random Sampling From an Information Theory Point of View," presented at CMA Exposure Assessment Workshop, Washington, D.C., 1986. 

N. C. Hawkins, S. K. Norwood, and J. C. R.oAi, A Strategy for Occupational Exposure Assessment, American Industrial Hygiene Association, Fairfax, Va., 1991. 

National Research Council, "Human exposure assessment for airborne pollutants advances and opportunities," National Academy Press, Washington, DC, 1991. 

Superfund Exposure Assessment Manual," U.S. Environmental Protection Agency, EPA/ 540/1-88/001, OSWER Directive 9285.5-1, April 1988. 

Exposure assessment techniques now attempt to include as many as possible of the locations in which individuals now spend time. The concept involves identification of microenvironments which are important for potential exposure. For example, exposure to CO would include time spent in commuting, parking garages, in residences with gas stoves, as well as time spent outdoors. This approach classifies time spent in these microenvironments and the typical concentrations of CO in these locations. 

Wallace, L. A., et al. (1983) Personal Exposure Assessment Methodology (TEAM) Study Summary and Analysis Vol. I. 

P. J. Lioy, Human Exposure Assessment for Airborne Pollutants, National Academy Press, Washington, D.C.(1991). 

EH 74/2 Respirable crystalline silica exposure assessment document... 

On-line system. Provides support for exposure assessments of toxic substances. Includes chemical properly estimation techniques, siahsiical analysis, multi-media modeling, and graphics display (including models)... 

MESOCHEM Chemical Atmospheric and Hazard Assessment System Impell Corporation Becky Cropper 300 Tristate Internat l Suite 400 Lincolnshire, IL 60069 (312) 940-2090 Software for atmospheric dispersion and chemical exposure assessment. A plume dispersion model. 

HAZWOPER applies only where exposure to hazardous substanees or to health and safety hazards resulting from a hazardous waste operation is likely (see Eigure 2-1). This ean be determined by analysis of exposure monitoring data, hazard eharaeterization, hazard analysis, or exposure assessment [1]. Some of the speeifle examples of work aetivi-ties and situations will be eovered later. 

Integrate hazard analyses to identify worker hazards and to provide a basis for speeifieation of job and task hazard eontrols. (The upeoming seetion eovering hazard eharaeterization and exposure assessment will provide some suggestions on effeetive ways of eondueting hazard analyses using the HAZWOPER job, task, and hazard analysis approaeh [1].)... 

Wlien utility work is located in an exclusion zone, are workers who enter the area exposed to hazardous materials Hazard characterization and exposure assessment performed by a competent person may show that the area surrounding the equipment and an access corridor leading to the equipment can be cleaned so that the utility workers can work in the... 

An exposure assessment uses air-monitoring data to determine possible worker exposures. This data is used to identify eontrols for worker proteetion and provide monitoring results to physieians for proper medieal assessment, treatment, and follow-up eare. 

Work zones are designed to control access to actual and anticipated hazards. Work zone positioning is based on hazard characterization and exposure assessment. Anticipated work activity, potential releases, and the amount of contaminant dispersion are important for delineating these zones [3]. 

FIGURE 7-1. Hazard Characterization Exposure Assessment Strategy... 

Condueting a hazard eharaeterization and exposure assessment to identify ... 

EPA, 1996, is the third edition of EML/DVIES on CD-ROM for distributing exposure models, documentation, and the IMES about many computer models used for exposure assessment and other fate and transport studies as developed by the EPA s Office of Research and Development (ORD). 

IMES was developed to assist in the selection and evaluation of exposure assessment models and to provide model validation and uncertainty information on various models and their applications. IMES is composed of 3 elements 1) Selection - a query system for selecting models in various environmental media, 2) Validation - a database containing validation and other information on applications of models, and 3) Uncertainty - a database demonstrating apfhieatum nl a mode uncertainty protocol. 

Data files on the THERdbASE CD are 1990 Bureau of Census Population Information, California Adult Activity Pattern Study (1987-88), AT T-sponsored National Activity Pattern Study (1985), Chemical Agents from Sources, Chemical Agent Properties, Air Exchange Rates, Information from EPA s TEAM (Total Exposure Assessment Methodology) Studies, Information from EPA s NOPES (NonOccupational Pesticides Exposure Study) Studies, Information from EPA s AIRS (Aerometric Information Retrieval System), and Human Physiological Parameters. 

The models in the THERdbASE CD are Chemical Source Release, Instantaneous Emission, Chemical Source Release, Timed Application, Indoor Air (2-Zone), Indoor Air (N-Zone), Exposure Patterns for Chemical Agents, Benzene Exposure Assessment Model (BEAM), Source Ba.sed Exposure Scenario (Inhalation + Dermal), and Film Thickness Based Dermal Dose. 

The benefit of a prospective cohort study is the possibility for accurate exposure assessment. However, these are not common, because many occupational diseases (including cancers which are being intensely investigated currently) require long exposure times to develop. It is not practical or ethical to wait for decades before one obtains the result. 

Exposure assessment to reveal the exposure of different groups of people, and to compare their exposure levels to the doses that cause harmful effects in humans as shown in epidemiological studies, or to doses that cause toxic effects in experimental animals... 

In densely populated areas, traffic is responsible for massive exhausts of nitrous oxides, soot, polyaromatic hydrocarbons, and carbon monoxide. Traffic emissions also markedly contribute to the formation of ozone in the lower parts of the atmosphere. In large cities, fine particle exposure causes excess mortality which varies between one and five percent in the general population. Contamination of the ground water reservoirs with organic solvents has caused concern in many countries due to the persistent nature of the pollution. A total exposure assessment that takes into consideration all exposures via all routes is a relatively new concept, the significance of which is rapidly increasing. 

Exposure assessment, step three, allows a risk assessor to estimate the significance of the effects induced by high doses of a chemical in experimental animals in a human situation. Exposure assessment is, in fact, a prerequisite for quantitative risk assessment because it allows a comparison between effects induced by high dose with those induced by low doses, and also allows... 

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