Human activity residential exposure

A consensus has developed from the scientists conducting residential exposure assessments screening-level or initial tier exposure estimates need to be obtained from those activities and pesticide applications that maximize human contact potential with the pesticide such as a baby crawling on a treated surface. Assessments which conclude minimal risk to humans from maximum exposures are then used to predict minimal risk at lower exposmes. 

Accurate exposure and biological monitoring data are crucial to the evaluation of residential exposure and risk estimates since the potential health risks associated with a pesticide depend on the amount of exposure to the pesticide, its toxicity and the susceptibility of the exposed population. Prediction of whether adverse health effects will occur in humans can be made by comparing the exposure estimate to the No Observed Adverse Effect Level (NOAEL) derived from the animal toxicity data. Uncertainty arises from the input data used in an assessment, e.g. variability in time-activity patterns, contact with exposure media, bioavailability, exposure duration, frequency of product use and differences in the route of exposure in humans from that in the animal studies (since absorption, distribution, metabolism and elimination kinetics may differ substantially by exposure route). 

Other research activities related to residential exposure assessment currently being sponsored by the USEPA include the National Human Exposure Assessment Survey (NHEXAS) (website http //www.epa.gov/heasd/edrb/nhexas.htm). In addition, the USEPA concluded a Co-operative Agreement, referred to as the Residential Exposure Assessment Project (REAP) with the Society for Risk Analysis (SRA) and the International Society of Exposure Analysis (ISEA) which resulted in a reference textbook (Baker et al, 2001) describing relevant methodologies, data sources and research needs for residential exposure assessment. The REAP and other efforts complement other USEPA initiatives, such as the development of the Series 875 guidelines, and will facilitate a sharing of information and other resources between the USEPA, other Federal and State agencies, industry, academia and other interested parties. 

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). 

Indoor exposure assessments can be more complex than outdoor assessments. The indoor assessments are often complicated by the fact that pesticide application methods and their placement within the indoor environments are very diverse and include, for example, crack and crevice treatment, carpet treatment, room loggers, moth repellents, residual termiticides, disinfectants and pet products. This diversity also means that potential human contact with the residues may range from a low probability (crack and crevice treatment) to a higher probability (indoor broadcast treatment such as an indoor total release logger) because of the nature of the application and the variability in activities that may bring individuals in contact with treated areas. Furthermore, the varied characteristics of the source (e.g. formulation type, application methods, room of application and duration of emission) and the indoor residential environment (e.g. room size, air exchange rates, temperature and types of surfaces, such as carpet, upholstery, vinyl, etc.) significantly influence exposure pofenfial. 

Once there is a measure of the concentration of the pesticide in the exposure medium (air, water, food, etc.) in contact with the body or the actual concentration that comes into contact with the body, a daily dose metric can be calculated (e.g. maximum, average, geometric mean, etc.). This typically involves developing a mathematical equation that expresses dose as a function of pesticide concentration and other important parameters referred to as human exposure factors (USEPA, 1999a). In the context of this discussion, the term human exposure factor refers specifically to (a) human characteristics, such as body weight, surface area, life expectancy, inhalation rates for air and consumption rates for food, drinking water and soil (b) human behaviors, such as activity patterns, occupational and residential mobility and consumer product use, which are used by exposure assessors to calculate potential dose. 

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