Development needs, exposure scenarios

The concept of a hypothetical inadvertent intruder at a nearsurface waste disposal site, including permanent occupants of a site after an assumed loss of institutional control, provides a suitable basis for defining exposure scenarios that would be used to calculate risks that arise from waste disposal and the boundaries between waste classes. For other dispositions of waste, alternative scenarios would need to be developed and evaluated. 

Chief among the knowledge gaps that currently impede progress is a lack of information about cumulative exposure scenarios. Comparatively few studies have measured multiple chemicals in one and the same sample, and consequently, information about how many pollutants co-occur, and at what levels, is patchy. Viable concepts for cumulative exposure assessment strategies need to be developed, and the experiences that have occurred in the areas of bioassay-directed fractionations and with the toxicity identification evaluation (TIE) concepts no doubt provide valuable stimuli. 

Because there are exposure scenarios that are unique to the Navy s work environment, the subcommittee also recommends that the Navy consider developing a research program to meet needs that are not being met by civilian research (e.g., the study of reproductive and developmental toxicity in the context of naval operations). Such a program would allow the Navy to anticipate and rank the agents it would like to use and to study the reproductive and developmental toxicity of those agents before its personnel are exposed. 

Approaches for aggregating exposure for simple scenarios have been proposed in the literature (Shurdut et al., 1998 Zartarian et al., 2000). The USEPA s National Exposure Research Laboratory has developed the Stochastic Human Exposure and Dose Simulation (SHEDS) model for pesticides, which can be characterized as a first-generation aggregation model and the developers conclude that to refine and evaluate the model for use as a regulatory decision-making tool for residential scenarios, more robust data sets are needed for human activity patterns, surface residues for the most relevant snrface types, and cohort-specific exposure factors (Zartarian et al, 2000). The SHEDS framework was used by the USEPA to conduct a probabilistic exposure assessment for the specific exposure scenario of children contacting chromated copper arsenate (CCA)-treated playsets and decks (Zartarian et al, 2003). 

Since a risk assessment for a particular chemical is related to the exposure scenario, toxicity data generated in in vitro systems need to be translated to a dose or a dosage regime for an intact organism. This process, referred to as QIVTVE , includes an interpretation of the chemical s biokinetic behavior. This enables the conversion of an in vitro-derived concentration-effect relationship to a dose-response relationship in vivo. The processes involved in this reverse dosimetry are described in Chap. 24. The development of physiologically based biokinetic (PBBK) models [19] is crucial in this process [13, 20]. 

A MEPAS application uses two sources of data user input and constituent database. The user inputs site and regional data to define the nature of the issue, source term, transport pathway, and exposure scenarios. To help ensure consistency for a large number of applications, a constituent database was developed that contains chemical, physical, environmental, exposure, and toxicity data for each constituent. The constituent database used for the Environmental Survey is documented by Strenge and Peterson (16). This database currently has entries for 397 constituents new constituents are added as needed. 

New methods that we have described are particularly well suited to study both the potential for bacterial contamination during meal preparation and how handwashing interferes with this process. However, additional methods need to be developed that are relevant for other exposure scenarios. When developing meth-... 

Follow the instructions in the SDS and in the exposure scenario (ES), which will be attached to the SDS if the substance is classified as hazardous and >10 tonnes. If your use is not covered by an SDS and an ES, communicate with your supplier to make your use known ( identified use ) and covered in a Chemical Safety Assessment, or you may need to develop your own Chemicals Safety Report (CSR). (More information about SDS and ES is in Chapter 5 How to compile and check SDS.)... 

Many details would need to be considered in developing a new waste classification system based on the framework presented in this Report. Assumptions about generic scenarios for exposure of hypothetical inadvertent intruders at waste disposal sites to be used in classifying waste and the time frames for applying the scenarios would be required. Decisions would need to be made about negligible and acceptable (barely tolerable) doses or risks that would be used in classifying waste as exempt or low-hazard, respectively. 

The dominance of the risk to inadvertent intruders at near-surface waste disposal sites allows the use of this type of scenario to develop a risk-based waste classification system. However, NCRP recognizes that exposures of the public and protection of the environment also are of concern in determining acceptable disposal practices at specific sites. The potential for off-site releases of hazardous substances is the primary reason that classification of waste based on risks to hypothetical inadvertent intruders does not obviate the need for site-specific risk assessments to determine waste acceptance criteria in the form of limits on disposal of particular hazardous substances. 

By brainstorming about potential disaster scenarios and the scope of resources anticipated to be needed under each scenario, the intensity and duration of the mental health response can also be anticipated. The U.S. Department of Health and Human Services (2004) has developed a population exposure model that planners can use to estimate the psychological impact of mass violence and terrorism and, therefore, the resources that might he needed. The model s underlying principle is that individuals who are most personally, physically, and psychologically exposed to trauma and the disaster scene are likely to he affected the most (Figure 5.1). 

One way to demonstrate the potential benefit of consumer antimicrobial products is to develop scenario-specific tests that are more reflective of situations, the activity, and the product use. One remaining question to be answered in order to evaluate products fairly and appropriately is if exposure is accurately represented by mimicking the level of bacteria and type of bacteria encountered or if subjects need to be exposed to the actual source of the bacteria. 

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