THOUGHT LEADERSHIP PUBLISHED 4Q 2019 The Fundamental Role of Exposure Science in Human Health Risk Assessment November 26, 2019 Exposure science focuses on characterizing the distribution and determinants of human exposure to chemical, physical, or biological substances potentially affecting health. Exposure distribution is influenced by the intensity, frequency, and duration of exposures; as such, these are typically the parameters that define exposure characterizations. Exposure determinants are factors that influence exposures, either directly or indirectly, such as lifestyle choices, behavioral patterns, and demographic characteristics. Exposure science plays a fundamental role in human including those that may be found in consumer products, health risk assessment because without exposure, “unless the exposure is low enough to pose no significant there is no health risk. Exposures can be characterized risk of cancer or is significantly below levels observed to qualitatively or quantitatively, and the selected approach cause birth defects or other reproductive harm” (OEHHA is often multifactorial with consideration given to available 2019). In other words, exposure to a listed chemical in a methodology, budget constraints, and participant burden, consumer product at a certain level triggers the regulatory among other factors. Depending on the approach, the requirement for a warning, not the mere presence of the exposure characterization may be associated with some listed chemical in the product. level of error, which, in turn, will influence the validity of the health risk assessment. I describe below two examples that demonstrate the critical role of exposure science in evaluating health Exposure science is essential to epidemiologic study risk in epidemiology and in consumer product safety design. Exponent’s exposure scientists understand assessments. the strengths and limitations of exposure assessment methodologies applied in the context of epidemiologic Case Study: Role of Exposure Science in studies. This specialty is particularly useful in critical evaluations of the epidemiologic literature, which requires Epidemiology weighing the body of scientific evidence for a variety Nieuwenhuijsen (2003) appropriately notes, “the of purposes, such as developing environmental and assessment of human exposure … remains the single occupational health policy, establishing regulatory and most important limiting factor in the quality of evidence voluntary exposure limits, and opining in product liability that epidemiology can provide.” This claim is exemplified and toxic tort legal matters, among others. in the evolution of exposure assessment methodologies applied over time in epidemiologic studies exploring In addition to epidemiology studies, exposure science is exposure to extremely-low-frequency magnetic fields fundamental to consumer product safety where exposures (ELF-MFs) and risk of miscarriage, a topic on which I have to chemicals are of interest. For example, in the State of extensively published in the peer-reviewed scientific California, under Proposition 65, also known as the Safe literature. Historically, due to limitations of available Water and Toxic Enforcement Act of 1986, businesses methodology, these studies have relied on surrogate are required to provide warnings for certain listed chemicals, The Fundamental Role of Exposure Science in Human Health Risk Assessment measures of personal exposure, such as wire code Case Study: Role of Exposure Science in classification, self-reported use of electric devices, and spot measurements in residence and workplaces (Lewis Consumer Product Safety Assessment et al. 2016). In recent years, however, investigators have Characterizing chemical exposures during use of consumer benefitted from advancements in exposure measurement products, for Proposition 65 compliance or otherwise, technology such that personal exposure to ELF-MF can can be challenging given the potential variability in product be characterized with greater accuracy than exposure use scenarios. This is especially true when dermal exposure surrogates by means of personal exposure monitors. science methodologies are required, as they are much The main limitation associated with surrogate measures more limited compared to inhalation methodologies, is that humans are not stationary objects; as a result, given the historical emphasis on inhalation exposures in these approaches do not incorporate differences in ELF- environmental health sciences and regulatory efforts. As MF exposures that result from moving between different such, there are great opportunities for innovation in environments. Because personal exposure monitors might dermal exposure science methodology. Exponent’s wealth capture variability in exposure over space and time, these of experience in developing methodologies to fill exposure provide a more valid estimate of personal exposure. science data gaps for purposes of consumer product safety, coupled with access to both laboratory testing Nevertheless, unless carefully considered in the study facilities and experts from other relevant disciplines, design phase, the mere use of ELF-MF personal exposure such as human factors and polymer science and materials monitors in epidemiologic studies of miscarriage does not chemistry, positions us well to address such needs. completely minimize all potential bias in the exposure characterization. For example, some miscarriage studies Skin contact area is among the most important factors employing personal exposure monitors have collected needed to quantify dermal exposure to chemicals in hand- data for only a single 24-hour period, which may not be applied liquid cleaning products. Due to the limitations of sufficient given that the period over which exposure available methodology, estimates of this exposure factor data were collected was very narrow relative to the time remain an important source of uncertainty in dermal window of risk for miscarriage, which is upwards of exposure assessments involving this type of product use 20 weeks. This may be especially true for peak exposure scenario. Recently, my colleagues and I demonstrated the metrics, such as the maximum and other upper percentiles, feasibility of a novel simulation approach involving cotton which have been hypothesized to be the biologically rags wetted with pigmented cleaning solutions, volunteers relevant exposure metrics, due to their likelihood of high wearing white cotton gloves during hand cleaning with day-to-day variability in pregnant women (see Figure 1). those cotton rags, and digital imaging of those gloves In other words, if there is interest in peak ELF-MF exposure post-simulation, to quantify the area of the hand contacted metrics, more than one day of measurement is needed by the cleaning solution during use (Bogen et al. 2019, over the window of disease (or adverse health event) Lewis et al. 2018, Singhal et al. 2017; see Figure 2). Overall, susceptibility to minimize measurement error. use of this method could reduce uncertainty in assessing dermal exposure to chemicals associated with hand- applied cleaning and perhaps related activities involving liquids, thereby leading to improved assessments of human health risk. Given this, the accessibility of required materials, and the relative ease of implementation, this novel method has potential for broad application. Figure 1. Day-to-day variation in daily personal ELF-MF exposure metrics over 1 week for the same 10 pregnant Figure 2. Image of cotton glove obtained after simulated women. Each color represents a different woman. cleaning with pigmented denatured alcohol: original Note: TWA = time-weighted average; %tile = percentile; photo (left panel), same photo after image processing mG = milligauss. Figure from Lewis et al. (2015). (right panel). Figure from Bogen et al. (2019). The Fundamental Role of Exposure Science in Human Health Risk Assessment Exponent’s Expertise Organizations often turn to Exponent to improve their understanding of human health risks in the context of complex human exposure scenarios. Exponent’s multi- disciplinary team of scientists and engineers leverage expertise in exposure science and related disciplines, such as industrial hygiene, toxicology, epidemiology, medicine, modeling, and human factors, to characterize exposures and critically-evaluate exposure science methodology. References Bogen KT, Lewis RC, Singhal A, Sheehan PJ. Development Nieuwenhuijsen, MJ. Foreword. In: Exposure Assessment of a novel method for estimating dermal contact with in Occupational and Environmental Epidemiology (M.J. hand-applied cleaning solutions. Environmental Nieuwenhuijsen ed.). New York: Oxford University Press, Monitoring and Assessment. Inc. 2003. pp. v–vi. Lewis RC, Evenson KR, Savitz DA, Meeker JD. Temporal OEHHA. 2019. “About Proposition 65.” California Office of variability of daily personal magnetic field exposure Environmental Health Hazard Risk Assessment. https:// metrics in pregnant women. Journal of Exposure Science oehha.ca.gov/proposition-65/about-proposition-65. and Environmental Epidemiology 2015;25(1):58–64. Singhal A, Bogen KT, Lewis RC, Gauthier A, Winegar Lewis RC, Hauser R, Maynard AD, Neitzel RL, Wang E, Sheehan P. A novel approach to estimating dermal L, Kavet R, Meeker JD. Exposure to power-frequency contact with hand-applied cleaning solutions: a magnetic fields and the risk of infertility and adverse simulation study involving denatured alcohol. Poster pregnancy outcomes: Update