Risk Modeling Tools in the Current and Future Toolkit

Risk Modeling Tools in the Current and Future Toolkit

Wednesday, June 3, 2015, 10:00 AM - 12:00 PM

CS-124-01 Selecting Risk Assessment Tools: Uses, Abuses, and Confusion

B. Beadie, P. Wiescher, T. Ashton, E. Curtis, Maul Foster Alongi, Portland, OR.

Situation/Problem: An equipment manufacturer suspected that the coating on some parts provided by an overseas supplier contained hexavalent chromium. The manufacturer had requested that the supplier disclose the use of hazardous materials, including hexava​​lent chromium, and had been assured that no such hazardous materials were present. The manufacturing company consulted with attorneys to determine an appropriate course of action, which prompted a literature review to help characterize the risks associated with hexavalent-chromium-containing coatings. Unfortunately, no clearly applicable study was discovered during the literature review, so the company had to find a different way to characterize the risk associated with handling coated parts.

Resolution: Reasonable worst-case exposure to coated parts was estimated by reviewing equipment manuals; interviewing people knowledgeable about the operation, maintenance, and handling of coated parts; and observing representative tasks. The presence of hexavalent chromium was qualitatively identified with colorimetric swabs, and wipe sample results provided quantitative data to help characterize potential exposure. An exposure model was developed based on previously published studies. Apparent discrepancies between two different risk screening models were resolved by identifying improper hexavalent chromium exposure assumptions in one of the models. The risk characterization was conducted using established USEPA information as well as the 2010 USEPA draft toxicological review for hexavalent chromium.

Results: Considering the established USEPA toxicological information for hexavalent chromium, the reasonable worst-case hazard index is estimated to be 0.00021, which is much lower than the hazard index criterion of 1. Using the USEPA draft toxicological review for hexavalent chromium, the worst-case hazard index is estimated to be 0.00071 and the worst-case carcinogenic risk is estimated to be 1.1 x 10-7. These results demonstrate that the risk of exposure to hexavalent chromium is not expected to be significant for personnel who operate, maintain, or handle parts associated with the manufacturer’s equipment.

Lessons Learned: Some situations require a scientific approach to characterize risks that may intuitively seem insignificant to many people. Even peer-reviewed published studies may contain errors or faulty assumptions, so it is important to clearly understand the underlying details of the risk assessment to properly characterize the risk. Toxicological information is ever-evolving and a literature review should be conducted as a matter of course to understand the most recent findings and related uncertainties.

SR-124-02 ​Comparison of CHARM and COSHH Essentials for Selected CMR Chemicals

S. Byeon, M. Kim, S. Shin, J. Lee, M. Ham, Korea University, Seoul, Republic of Korea


CS-124-03 A Research Vision for Occupational Based Cumulative Risk Assessment

R. Niemeier, NIOSH, Cincinnati, OH; G. Dotson, Blue Ash, OH

Situation/Problem: Understanding the health risks associated with coexposures to multiple hazards, called cumulative risk assessment (CRA), is an area of increasing interest in environmental health. Awareness of the interaction of these hazards in the occupational setting is important as well. Traditionally, risk assessment in the occupational setting has focused on chemical stressors in the workplace; however, interactions between these chemical stressors and other non-chemical stressors (biological, physical, and psychosocial), inside and outside of the workplace are more representative of exposure scenarios. Also, the interaction of these stressors with personal risk factors (i.e. genetics, personal habits) can affect health outcomes and should be considered in occupational risk assessment. 

Resolution: NIOSH is conducting an exploratory project to investigate methods for incorporating occupational risk factors (ORFs) into already developed CRA techniques. The first phase of the project is to lay the foundation by establishing a research vision that addresses key elements of the CRA project including: 1) identifying problems and the scope for incorporating ORFs into CRA; 2) defining common language for evaluating and communicating key aspects for the advancement of CRA; 3) identifying critical needs and data gaps; and 4) describing critical questions designed to focus and guide relevant research. 

Results: The research vision will be developed in collaboration with subject matter experts (SMEs) from government agencies, private industry, and academia who have expertise on interrelated CRA topics (e.g., risk assessment, toxicology, exposure assessment). These SMEs will be tasked to define key elements and critical questions of the research vision. SMEs will be grouped based on their expertise and personal interests to address specific topics of the research vision. Critical questions will be organized into common themes based on a broadly recognized risk assessment paradigm including hazard characterization, dose-response assessment, exposure assessment, and risk characterization. 

Lessons Learned: A well designed research vision is a critical initial step to the success of the NIOSH CRA project. After this phase of the project is completed, the project focus will shift to developing a series of risk assessment element case studies and devising a CRA framework which will incorporate ORFs into existing and novel CRA techniques. 

CS-124-04 Cumulative Risk Assessment for Occupational Scenarios: Screening Level Tool for the IH Practitioner

A. Lamba, U.S. Environmental Protection Agency, Vienna, VA


CS-124-05 Modeling Historical Risk to Industrial Building Occupants from Leaking Underground Storage Tank Vapor Intrusion

F. Boelter, J. Persky, S. Song, B. Schnorr, ENVIRON International Corp., Chicago, IL

Situation/Problem: A pair of co-located USTs containing diesel fuel and xylenes were at a facility in a newly industrialized country. The diesel UST was found to be leaking and was ultimately removed. The xylenes UST was also removed but found to be intact. Based on a publically available risk assessment report developed to meet site remediation objectives, an activist precipitated fear by filing a complaint with the local environmental regulatory agency alleging “The contamination continues to be active and what is worse, it goes beyond the property. There are 600 workers exposed to serious risk.” The RA report was found to be flawed.

Resolution: Three scenarios were modeled to evaluate the effect of conservative estimates for worker inhalation exposure from vapor intrusion. Relevant pathways by groundwater migration and vadose zone transport were modeled. The building no longer existed so aerial and site photos were utilized for model input values. The RA model used by others predicted hypothetical indoor air concentrations that were high due to unrealistically conservative assumptions. Correction of the RA models to use realistic parameters demonstrates that theoretical risk does not exceed the risk criteria established by the governing regulatory authority.

Results: The responsible regulatory agency has established a cumulative exposure index of ≤1 as an acceptable criterion for multiple contaminants with non-cancer health effects. A ratio of the conservatively modeled concentration to the OEL facilitated a cross-comparison for each parameter. The summation of all such ratios for all hydrocarbons was presented as a cumulative exposure index. The three models yielded Em values of 0.0035, 0.00023, and 0.0000002 all of which are significantly less than an Em of 1. Actual exposures, if any, would have been even lower.

Lessons Learned: Models have value in characterizing historical exposures, dose, and risk. An improper risk characterization can create outrage making the challenge not about risk management or even risk reduction but rather an unfounded fear of disease both within a workforce and the surrounding community. Attention to detail is required when designing a risk assessment and attention must be given to the characterization of risk. Involvement of relevant stakeholders can be helpful to assure a successful outcome.

SR-124-06 The Need for a Revised, Risk-Based, Occupational Exposure Standard for Asbestos

J. Rasmuson, A. Korchevskiy, E. Rasmuson, Chemistry & Industrial Hygiene, Inc., Wheat Ridge, CO; V. Roggli, Duke University, Durham, NC

Objective: To evaluate the adequacy of the current occupational exposure limit for asbestos and to recommend an alternative general standard or at least a Best Management Practices (BMP) value for amphibole fibers based on separate risk calculations of three separate international government agency methods. 

Methods: Both linear and non-linear characterization of dose-response relationships have been suggested. Different asbestos exposure metrics were considered for the risk assessment. Risk calculations based on the Berman and Crump work in the United States, the non-linear Hodgson and Darnton procedures of the United Kingdom, and the asbestos potency factors determined by the health agency of the government of Netherlands are considered, as well as various case-control studies. 

Results: Current risk assessment procedures demonstrate that risk from amphibole asbestos exposure are up to about an order of magnitude higher than risk calculations performed to justify the current OSHA PEL and the NIOSH REL. Excess risk can be demonstrated for fibrous amphibole exposures above typical cumulative background levels through the results of case-control studies. 

Conclusions: The current EPA and OSHA asbestos risk assessment methodology is believed by some to be adequate because of the precautionary principle, with the understanding that it is precautionary to consider mesothelioma and lung cancer potencies equal for all fiber types. However, that approach tends to average the potency across all asbestos fiber types, and, in so doing, greatly underestimates the risk of amphibole asbestos exposures. Thus, in the name of the precautionary principle, asbestos exposure limits are not precautionary. Although the current United States occupational exposure limit may be adequate for chrysotile, it is woefully inadequate for amphibole asbestos exposure. Moreover, exposure to asbestiform and fibrous amphibole exposure is more common in mining, quarrying, road construction, and soil excavation, than commonly believed. Although excess risk is still present in some circumstances, an occupational exposure limit of PCME 0.01 f/cc for asbestos would significantly reduce risk and likely save many lives. ​