1 / 37

A Comprehensive Evaluation of the Potential Health Risks Associated with Occupational and Environmental Exposure to Styr

A Comprehensive Evaluation of the Potential Health Risks Associated with Occupational and Environmental Exposure to Styrene. Joshua Cohen Harvard Center for Risk Analysis Harvard School of Public Health December, 2002. Expert Panel.

feivel
Download Presentation

A Comprehensive Evaluation of the Potential Health Risks Associated with Occupational and Environmental Exposure to Styr

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A Comprehensive Evaluation of the Potential Health Risks Associated with Occupational and Environmental Exposure to Styrene Joshua Cohen Harvard Center for Risk Analysis Harvard School of Public Health December, 2002 Harvard Center for Risk Analysis

  2. Expert Panel • Commissioned by the Styrene Information and Research Center (trade association) in 1999 • Panel members • Gary Carlson -- Purdue University • David Coggon -- University of Southampton (UK) • Elizabeth Delzell -- University of Alabama • Helmut Greim -- GSF-Institute of Toxicology • Daniel Krewski -- University of Ottawa • Michele Medinsky • Richard Monson -- Harvard School of Public Health • Dennis Paustenbach -- Exponent • Barbara Petersen -- Novigen Sciences • Stephen Rappaport -- University of North Carolina • Lorenz Rhomberg -- Gradient Corporation • P. Barry Ryan -- Rollins School of Public Health, Emory University Harvard Center for Risk Analysis

  3. Report Staff • Harvard Center for Risk Analysis • Joshua Cohen • John Graham • Kim Thompson • Health Risk Strategies (Washington, DC) • Gail Charnley Harvard Center for Risk Analysis

  4. Styrene UseTotal Production -- 10 Billion Pounds per Year Harvard Center for Risk Analysis

  5. General Population Exposure:Inhalation Harvard Center for Risk Analysis

  6. General Population Exposure:Food • Naturally occurring styrene in food • e.g., cinnamon, coffee, beer • Total intake (assuming 3 kg food/day) -- 0.6 ug/day • Styrene leached from food packaging and disposable food contact articles -- 9 ug/day • Total -- 10 ug/day, or around 0.2 ug/kg-day for a 70 kg adult Harvard Center for Risk Analysis

  7. General Population Exposure:Water • Minimal -- Styrene does not persist in water due to its biodegradation and volatility Harvard Center for Risk Analysis

  8. Occupational Exposure:Inhalation Harvard Center for Risk Analysis

  9. ToxicologyRats Exposed to Styrene • Gavage studies negative • Inhalation studies • Statistically positive for mammary tumors (Jersey et al., 1978), benign mammary tumors and all mammary tumors (Conti et al., 1988), testicular tumors (Cruzan, 1998) • Dose-response relationships not monotonic and not consistent across studies • Panel concluded relationships were not causal Harvard Center for Risk Analysis

  10. ToxicologyMice Exposed to Styrene • Gavage studies -- some positive for lung tumors, but relationship did not appear to be causal • Inhalation studies • Cruzan et al. (2001) positive for lung tumors • Panel concluded relationship is causal -- tumor incidence statistically elevated at 40, 80, and 160 ppm Harvard Center for Risk Analysis

  11. ToxicologyMice and Rats Exposed to Styrene Oxide • Gavage studies -- positive at site of entry • Dermal studies • Negative Harvard Center for Risk Analysis

  12. Noncancer • Central nervous system depression has been observed in workers at exposure above 100 ppm • Ototoxicity (hearing loss) has observed at 35 ppm and 25 ppm, but those occupational studies were poorly controlled • Styrene does not appear to have endocrine modulating effects • Reproductive and developmental toxicity have been observed in animal studies at high levels of exposure • Panel’s comparison dose – 50 ppm • Subclinical impairment of color vision Harvard Center for Risk Analysis

  13. Reinforced Plastics - Europe Kolstad et al. (1993) Cohort study – 53,731 M and 10,793 W from 552 companies in Denmark Kolstad et al. (1994) Cohort study – Males from Kolstad et al. (1993). N = 53,720. Kolstad et al. (1995) Cohort study – Males from Kolstad et al. (1994) working in 460 companies with “known” exposure status (i.e., excluding 82 companies). N = 50,903 Coggon et al. (1987) Cohort study – 7,949 M and W employed from 1947 to 1984 in 8 British plants Workers from Finland, Italy, Norway, Sweden, and 51 more plants in the UK not included in Coggon et al. (1987) N = 15,863 M and W classified by Kolstad as “highly exposed” Kogevinas et al. (1993, 1994) Cohort study – N = 40, 683 M and W. Harvard Center for Risk Analysis

  14. Conclusions:European Reinforced Plastics • Findings generally negative • Sources of bias towards the null • Inadequate characterization of exposure, with exposures from earlier periods (when they were likely to be higher) only roughly estimated • Inaccurate cancer diagnosis • Where elevated cancer rates were reported, they were inconsistent with findings from other industry segments Harvard Center for Risk Analysis

  15. Reinforced Plastics – North America Wong et al. (1990, 1994). Cohort study – 15,826 (11,958 M and 3,868 F) employed at least 6 mos at 30 plants Okun et al. (1985). Cohort study – 5,021 (4,519 M and 682 F) employed at 2 Washington State boatbuilding facilities. Positive findings for lung cancer Harvard Center for Risk Analysis

  16. Conclusions:American Reinforced Plastics • Wong study findings of elevated lung cancer risk • Findings confined to workers with less cumulative exposure to styrene and shorter duration of employment • Among the cohort as a whole, and especially among short duration workers, other diseases linked to life style elevated (cancer of the cervix, ischemic heart disease, etc.) • No elevation in lung cancer risk in European reinforced plastics industry • Panel concluded elevation reflects confounding • Other elevated rates reported by Wong were not associated with cumulative exposure Harvard Center for Risk Analysis

  17. Styrene Butadiene Industry • Plants built during WWII and the 1950’s in North America • 15 plants built in the U.S. during WWII • 1 plant built in Canada during WWII • 1 plant built in the U.S. during the 1950’ • Plants still operating in 1977: 10, including the Canadian plant and the plant built during the 1950’s Harvard Center for Risk Analysis

  18. Styrene – Butadiene Industry (continued) Matanoski et al. (1990) Cohort study – 8 of the plants still operating in 1977, excluding the 2 studied by Meinhardt et al. (1982). Included with 1+ years of experience workers hired before 1/1/77. Canadian workers restricted to individuals  45 years of age or 10+ years experience. Meinhardt et al. (1982) Cohort study – 2 plants in Texas not included in Matanoski et al. (1990) Delzell et al. (1996) Sathiakumar et al. (1998) Cohort study based on 7 of the 8 plants in Matanoski et al. (1990) and both plants from Meinhardt et al. (1982). Included workers with 1 year work experience by 1/1/92. Santos-Burgoa et al. (1992) Matanoski et al. (1993) Case-control – 59 lymphohematopoietic cancers and 193 controls Matanoski et al. (1997) Case-control – 58 lymphohematopoietic cancers and 1242 controls Macaluso et al. (1996) Cohort study based on all but 2 of the plants in Delzell et al. (1996) Positive findings Harvard Center for Risk Analysis

  19. Epidemiology Findings • Number of expected and observed cancers are small and hence estimates are uncertain • Confounding • Styrene-butadiene industry – Workers exposed to butadiene, which may explain the excess in observed leukemias • Leukemias not elevated consistently in the reinforced plastics industry, where exposure to styrene is much greater Harvard Center for Risk Analysis

  20. Epidemiology Findings(Continued) • Confounding • Styrene-butadiene industry – Workers exposed to butadiene, which may explain the excess in observed leukemias Harvard Center for Risk Analysis

  21. Epidemiology -- Conclusions • Negative study findings are not statistically inconsistent with the risk estimates from the positive Cruzan et al. (2001) study • 95% confidence interval for all neoplasms among highly exposed reinforced plastics workers from both the Wong et al. and Kogevinas et al. studies (average exposure 300 ppm-yrs): 90-109 • Relative risk among these workers predicted using the (adjusted) dose-response relationship from Cruzan et al. (2001) is 1.07 Harvard Center for Risk Analysis

  22. Mode of Action • Styrene exposure leads to adduct formation • Occupational exposure to styrene in the reinforced plastics industry results in persistent O6 adducts • No evidence that these adducts are associated with adverse health effects • Styrene oxide exposure causes DNA strand breaks, but these are quickly repaired. Harvard Center for Risk Analysis

  23. Mode of Action – ContinuedCytogenetic Activity • In vitro studies • Positive for both styrene and styrene oxide • Results are sensitive to the simulated metabolic environment • Implications for human health unclear • Animal studies • Styrene and styrene oxide are genotoxic only at very high exposure levels • In humans • Chromosomal abnormalities – Evidence compelling at occupational exposure levels, with dose responses both within and across studies • Sister chromatid exchanges –most studies negative • Micronuclei -- No association with styrene exposure Harvard Center for Risk Analysis

  24. Mutagenic Effects • Styrene oxide causes mutations in the Ames Salmonella assay, but results in animals and humans are less clear cut Harvard Center for Risk Analysis

  25. Key QuestionAre Humans Like Rats or Mice • Panel concluded that only one styrene exposure study was positive • Cruzan et al. (1998) -- Lung tumors elevated at 40 ppm • Same methodology applied to rats (Cruzan et al., 2001) • Results negative at 1,000 ppm ! Harvard Center for Risk Analysis

  26. Cruzan et al. (2001) - Male Mice Harvard Center for Risk Analysis

  27. Cruzan et al. (2001) - Female Mice Harvard Center for Risk Analysis

  28. Rats -- Cruzan et al. 1998Pulmonary Adenomas Harvard Center for Risk Analysis

  29. The Metabolism of Styrene Styrene Cytochrome P-450 Epoxide Hydrolase Styrene Oxide + glutathione (GSH) Phenylethylene Glycol x-Phenyl- 2-hydroxy- ethylmercapturic acid Further metabolism and excretion Harvard Center for Risk Analysis

  30. Factors That May Predispose Mice to the Development of Tumors Harvard Center for Risk Analysis

  31. Factors That May Predispose Mice to the Development of Tumors Harvard Center for Risk Analysis

  32. In Terms of Pharmacokinetics, Humans are more like Rats • SO levels in the blood of humans are “5 - 20 times lower than the corresponding values in rodents” (IARC, 1994, p. 274). • The ratio of R-SO to S-SO production (Carlson et al., 2000): • Lungs -- 1.15 • Liver -- 0.72 • Note -- Human measurements are relatively sparse and hence not as reliable as measurements in rodents • Does pharmacokinetics explain why mice are more susceptible to the development of lung tumors than rats following styrene exposure? Harvard Center for Risk Analysis

  33. Findings • Calibration of model to Cruzan et al. (1998) and Cruzan et al. (submitted): • Mouse pulmonary SO < rat pulmonary SO • Reverse of what is expected! • Calibration of model to Kessler et al. (in prep), Morgan et al, (1993b), and Kessler et al., 1992: • Mouse pulmonary SO 5X greater than rat pulmonary SO at styrene concentrations up to 300 ppm • Mouse pulmonary SO 25X greater than rat pulmonary SO at styrene concentrations above 300 ppm Harvard Center for Risk Analysis

  34. Findings(Continued) Panel Model Predictions – Concentration of Styrene Oxide in the Lungs of Rats and Mice: Exposure Six Hours per Day, Five Days per Week Harvard Center for Risk Analysis

  35. Findings(Continued) • Glutathione depletion in the lungs of mice notably exceeds glutathione depletion in the lungs of rats, but it is notable only at concentrations greater than those at which mice first develop tumors • R-SO concentrations in the lungs of mice are not substantially greater than corresponding concentrations in mice Harvard Center for Risk Analysis

  36. Post Script • Sarangapani et al. developed a model that can be used to estimate SO concentrations on a finer scale (i.e. inside and near the cells that produce SO in the lung) • They found a greater difference in delivered dose between mice and rats than we found Harvard Center for Risk Analysis

  37. Post Script • Mice exposed to 20 ppm styrene had a 21% increase in lung tumor incidence above controls (not significant). Rats exposed to 1000 ppm had no increase in lung tumors above controls. • Delivered dose in mice exposed to 20 ppm increase was only 2x higher than in rats exposed to 1000 ppm • Substantial uncertainty - Many other sets of assumptions would produce higher delivered dose values for rats than mice at those exposures • Although pharmacokinetics play a role in sensitivity of mice to styrene, other factors must also be at play Harvard Center for Risk Analysis

More Related