Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 5 (2008) / Chapter Skim
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12 Formaldehyde
12 Formaldehyde
Pages 206-249
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, the Agency for Toxic Substances and Disease Registry (ATSDR 1999) , Health Canada (Health Canada 2001)
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Abbreviations: ACGIH, American Conference of Governmental Industrial Hygienists; AEGL1, acute exposure guideline level (nondisabling) ; ATSDR, Agency for Toxic Substances and Disease Registry; CEGL, continuous exposure guidance level; EEGL, emergency exposure guidance level; IDLH, immediately dangerous to life and health; MRL, minimal risk level; NAC, National Advisory Council; NIOSH, National Institute for Occupational Safety and Health; NRC, National Research Council; OSHA, Occupational Safety and Health Administration; PEL, permissible exposure limit; REL, recommended exposure limit; STEL, short-term exposure limit; TWA, time-weighted average.
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• Summarize the approach taken in developing the existing formaldehyde SMACs. • Evaluate whether toxicologic data exist that support development of ACs for end points not evaluated in the original SMAC document.
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pooled indoor air measurements across five different ground-based indoor air studies and found that the average formaldehyde concentration in indoor air was roughly 0.03 ppm. However, concentrations can vary significantly depending on the types of materials used in construction; Hare et al.
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Formaldehyde was identified as a compound of particular concern, as air concentrations increased to 0.2 ppm by Day 15 of the test. At this concentration, one of four crew members experienced eye and upper respiratory tract irritation.
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0.06 0.05 0.04 Service 0.03 Module Lab 0.02 parts per million 0.01 0 1 01 1 1 02 2 02 02 2 2 03 3 3 3 04 4 n -0 g- -0 -0 b- r-0 n- g- -0 -0 b- r-0 -0 -0 b- r-0 Ju ct ec Ap Ju ct ec Ap ct ec Ap Au O D Fe Au O D Fe O D Fe FIGURE 12-1 Formaldehyde concentration measured in the ISS atmosphere. Source: Data from Johnson Space Center Toxicology Laboratory.
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Although the 0.04-ppm long-term SMAC was exceeded for approximately 30 days, crew reported no symptoms in association with these measured formaldehyde concentrations. SUMMARY OF EXISTING FORMALDEHYDE SMACS The existing SMACs for formaldehyde were established in 1994 after review and concurrence by the NRC (Wong 1994)
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. Pertinent occupational exposure limits for formaldehyde and calculated ACs based on this reassessment of formaldehyde are provided later in this document.
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Performance on the digit symbol test was impaired at 1 ppm relative to the lower exposures. There was some uncertainty about the degree to which other variables were properly controlled in establishing the exposure groups.
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Nasal epithelial damage and nasal cancer 3 ppm 22 h/d, 7 Cynomolgus Exposure to 3 ppm resulted in statistically significant amounts of Rusch et al.
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0.4 ppm 2h Human, 9 with skin Increased incidence of transient eye irritation, rhinitis. Change in Pazdrak et sensitive to nasal lavage fluid (increased eosinophil counts and protein levels.
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A direct relationship between concentration and irritant response (mainly eye irritation) was observed at 0.8 ppm and above.
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Odors, sore throat, and eye irritation were reported at this concentration. One volunteer noted severe irritation at 2 ppm, and four others noted moderate irritation; none of them responded during the control period.
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. This was similar to the 7% response rate to clean air.
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Neurotoxicity The 1994 SMAC evaluation does not specifically discuss the potential neurotoxicity of formaldehyde, and evidence generally indicates that eye and upper respiratory tract irritation would be expected to be a more sensitive end point. Woutersen et al.
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in which groups of male rats were exposed to formaldehyde by inhalation for 4 h/d 5 d/wk for 6 mo. The formaldehyde concentrations were 0, 0.1, and 0.2 ppm.
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. Similarly, a population-based case-control study of low-birth-weight newborns in Lithuania evaluated a possible association with formaldehyde exposures and found no statistically significant association between incidences of
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Direct exposure to formaldehyde is clearly irritating to the skin, and allergic contact dermatitis related to formaldehyde exposures is not uncommon (NRC 1981, WHO 2002)
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EVALUATION OF ADDITIONAL DATA AND REFINEMENT OF ACs Sensory Irritation Summary of Previous Approach There are a wealth of data on the sensory irritant effects of exposure to formaldehyde, including animal studies, controlled human exposure studies,
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This study investigated formaldehyde exposures in 65 mobile homes in Wisconsin with airborne formaldehyde concentrations between 0.1 and 0.8 ppm. Approximately half of the individuals exposed to indoor air at formaldehyde concentrations above 0.4 ppm reported mild eye irritation, and this concentration formed the basis for the 1-h AC (Table 12-5)
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(1984) based on incidences of reported eye irritation in a mobile home study.
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With the 2-ppm exposures, 32% of the volunteers reported mild eye irritation and 21% reporting moderate eye irritation when the group data were pooled. At 1 ppm, 16% of the volunteers reported mild eye irritation, with one individual still reporting moderate irritation at this concentration.
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. • In evaluating the relevancy of any controlled human exposure study to SMAC development for formaldehyde, the degree of irritation that is appropriate for each exposure time frame should be kept in mind.
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Between 0.3 and 1 ppm, they observed a relationship between concentration and eye irritation. However, for lower exposure concentrations, the association between formaldehyde exposure and irritant effects was more uncertain.
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Above 0.5 ppm, the frequency and intensity of reported irritant symptoms generally increased consistently with the higher formaldehyde exposures. None of the individuals exposed to 0.5 ppm experienced eye irritation, although roughly half of the volunteers discerned odors at this concentration.
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of 0.5 ppm was used as the 24-h AC for formaldehyde. Although none of the individuals reported eye irritation at this concentration during the 3-h exposures, it is reasonable to use this concentration as a 24-h exposure limit, as it likely represents an estimate of the lower limit for eye irritation for most individuals (Kulle et al.
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. It is clear that at these low concentrations, the vast majority of human subjects have difficulty consistently being able to differentiate eye irritation induced by the presence of formaldehyde from clean air (Schuck et al.
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Although this is a general predictive approach, it has merit in the sense that it avoids some of the subjectivity inherent in evaluating individual irritant response at low formaldehyde concentrations. • Supporting evidence from community health studies (e.g., mobile home exposure evaluations)
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Cell proliferation 3.57 0.44 2.3 × 10–2 16 4 0.6 0.1 (power law) Direct airflow extrapolation Tumors 5.58 0.71 1.4 × 10–2 26 6 1 0.2 (Weibull)
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Given the reactivity and water solubility of formaldehyde and available evidence from laboratory animal inhalation exposures, many epidemiologic studies have focused on the incidence of upper respiratory tract cancer. Although many of them were summarized in the 1994 SMAC document, several more recent studies warrant discussion.
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industrial workers and found an association between nasopharyngeal cancers and high peak and cumulative formaldehyde exposures (but not average exposure or exposure duration)
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and 2.4 (95% CI = 1-6) when average formaldehyde exposures were 0.5 to 0.9 and >1 ppm, respectively (they reported larger relative risks when grouping by peak formaldehyde exposure concentrations)
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However, several lifetime inhalation exposure studies in rodents, with formaldehyde exposures in the range of 2 ppm, did not report adverse degenerative effects on the nasal epithelium (Woutersen et al. 1989; Monticello et al.
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The first approach involved using the animal bioassay data in a benchmark dose analysis, where different methodologies were used to extrapolate formaldehyde exposures from rats to humans (see Schlosser et al.
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The use of the cell proliferation end point recognizes its importance in the formaldehyde carcinogenic process and results in slightly more conservative ACs compared with the tumor data. The use of the direct airflow extrapolation approach required fewer assumptions and did not rely on allometric scaling compared with the flux-DPX method and was subject to less mecha
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. Nasal Epithelial Damage It is appropriate to set ACs for the degenerative effects of formaldehyde exposure on the nasal epithelium separate from those for nasal cancer risks.
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2003) Nasal epithelial damage Benchmark dose analysis of cell F344 -- 1b 1a 1 1 -- -- 0.5 0.5 0.5 0.5 proliferation data, rat 95% BMCL01 (3.57 rats ppm)
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In addition, further exposure time corrections are not necessary for the study, as the authors adjusted the 95% BMCL01 concentration for the 24-mo study to reflect continuous exposure conditions. This approach is likely to be conservative, as some have suggested that increased cell proliferation is better related to concentration than to cumulative formaldehyde exposure (McGregor et al.
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2004. Human respiratory tract cancer risks of inhaled formaldehyde: Dose-response predictions derived from biologically-motivated computational modeling of a combined rodent and human dataset.
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1998. Formaldehyde exposure and low birth weight incidence.
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Human Exposure Assessment for Formaldehyde. Health Canada, Health Protection Branch, Priority Substances Section, Ottawa, Ontario.
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1991. Regional increases in rat nasal epithelial cell proliferation following acute and subchronic inhalation of formalde hyde.
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1966. Eye irritation response at low concentrations of irritants.
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Pp. 91-120 in Spacecraft Maximum Allowable Con centrations for Selected Airborne Contaminants, Vol.
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