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Asbestiform Fibers: Nonoccupational Health Risks (1984)
Commission on Life Sciences (CLS)

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314
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OCR for page 314
Appendix H COMPARATIVE RISK ASSESSMENT SCORE SHEETS The score sheets on the following pages contain the committee's assessments of the comparative risks posed by various combinations of fiber type, route of exposure, and health effects that were not tractable for quantitative risk assessment. Each assessment is made in comparison with the "prime cell" for chrysotile inhalation leading to lung cancer. lye comparisons are expressed in terms of population risk, which takes into account recent and pro jected exposure patterns for the U. S. population. Individual risks for persons with higher than average exposures could easily be as great or greater than those from moderate exposures to chrysotile. Comparative population risks would change if unanticipated changes in use levels or patterns affected exposure dis~cribut ions . The results are expressed in a +/- system. The O means that the risks (number and severity of effects) are about the same as those for the prime cell, + and + ~ mean that they are greater or substantially greater, - and -- mean that they are less and much less, and so on. A blank means that even comparative risk assessment was untenable given the data available. Thus, the quantitative risk assessment suggested that for lifetime exposures to asbestos in ambient air, mesothelioma risks could easily exceed lung cancer risks by more than a factor of 10, which would result in a comparative risk score for mesothelioma of ++. With respect to the prime cell, all comparative risks have been judged to be either - or --, meaning that they are less or much less important than for the prime cell, even though some of the indicators of risk are positive or more strongly negative. To determine the comparative risks for each cell, the cow ittee combined scores for several factors related to the potential for causing health effecters; each was scores by the same +/- system for comparison with the characteristics of the reference cell. The factors considered fell under three major categories: exposure, biodisposition, and effects. 314

OCR for page 315
315 EXPOSURE l · total production level (metric tons/yr) or surrogate measurement (e.g., level of occurrence in nature) ~ use pattern (e.g., dispersive or contained, matrix-bound or unbound, or accidental exposure of humans) · geographic distribution of sources · numbers of exposed people · trends in production and use (e.g., increasing production o: diversification of use) - BIODISPOSITION · fiber size (e.g., length and diameter) · fiber morphology (e.g., aspect ratio) · fiber chemi s t ry · penetration characteristics (e.g., in lung or other target tissue) · stability in tissue (e.g., solubility, gelling, and fibril formation) EFFECTS · epidemiological observat ions · observations in animals · in vitro observat ions . . · synergism (known or hypothesized) · other considerations (Beg. ~ susceptible populations or theory of ac t ion) The committee' ~ evaluations were based on the following scoring convent ions: 0: Within a factor of about 2 of the corresponding values for the prime cell (in the sense of its effect on the total number and severity of effects); for example , if production were between 0.5 and 2.0 times that of chrysotile, the score would be 0.

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316 + or -: Between 2 and 10 times the corresponding value or between 0.1 and 0.5 times that value, respectively. ++ or --: Between 10 and 100 times the corresponding value or between 0.01 and 0.1 times that value, respectively, and so on. Blank: A blank entry means that there is no basis for judgment; in further considerations, it is assumed to be equivalent to 0. The committee also attempted to provide a sense of the quality of these judgments. The following code was used for this purpose: a: reasonable assurance that comparative risk is in the direction indicated and approximately of the correct magnitude (e.g., if the risk compared with the prime cell was shown as "--", then it is probable , although not assured, that the effects are less than 0.1 times the effec t s for the prime cell) b: comparative risk is probably in the direction indicated, but the level is in great doubt c: comparative risk is highly uncertain due to paucity of information; this does not mean that the committee believes that the cell is very likely to provide as much risk as the prime cell, only that there is little information assuring a lower risk

OCR for page 317
317 COMPARATIVE RISK ASSESSMENT SCORE SHEET / Inge st ion Cell Scored Chrysotile /GI Cancer Fiber Ef feet Route Scores Compared Chrysotile / Lung Cancer / Inhalation with Cell Fiber Effect Route Exposure Score Produc t ion O Use Pattern Geography Populat ion _ O Trend s O Biodisposition Score Fibe r S i ze O Morphology O Chemistry O Penetrat ion Stability O Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment Remarks: Effects Score Human Studies Animal S tud ie s In-Vi~cro Studio s Synergism Other Even though asbestos uses are more likely to result in air pollution than water pollution, Chrysotile enters the water supply from natural as well as human sources (e.g., asbestos-cement water pipe) and the total number of fibers ingested could be greater than the number inhaled. Most is probably excreted rapidly, but the amount that moves into the body is not known. Both epidemiological and animal studies have generally yielded "negative" results, but the epidemiological studies have been too insensitive to detect relatively small effects.

OCR for page 318
318 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Chrysotile / Mesothelioma / Ingestion _ Fiber Effect Route Scores Compared Chrysotile / Mesothelioma J Inhalation with Cell Fiber Effect Route Exposure Score Biodisposition Score Effects Score Production O Fiber Size O Human Studies - Use Pattern O Morphology O Animal Studies O Geography 0 Chemistry O In-Vitro Studies _ Population O Penetration - Synergism Trends O Stability O Other Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment a Remarks: It is not known whether peritoneal mesothelioma results from ingested asbestos, inhaled asbestos, or both. What little epidemiological information exists does not demonstrate an increased mesothelioma risk associated with ingested asbestos. Ingested asbestos is more likely to be excreted rapidly than is inhaled asbestos. ..

OCR for page 319
319 COMPARATIVE RISK ASSESSMENT SCORE SHEET Ce 11 Scored Croc idolite / Fiber Effect Lund Cancer / Inhalat ion Route Scores Compared Chrysotile / Lung Cancer / Inhalation with Cell Fiber Effect Route Exposure Score Produc t ion Use Pattern _ - Morphology Geography - Chemistry Biodisposition Score Fiber Size O Population O Penetration Trends - Stability Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment Remarks: Effects Score , Human Studies O Animal Studies O In-Vitro Studies O Synergism O Othe r Crocidolite use has been on the dec line and confined to well- contained applications. In the United States, its use is already less than one-tenth that of chrysotile, and its occurrence is also low witch respect to chrysotile. On the other hand, many investigators believe that equal exposures to crocidolite and chrysotile will result in more cancer from the former, possibly from crocidolite' ~ greater ability to penetrate to the lung and its greater stability once there, rather than from a fundamental difference in potency at the since. Anus, the lower risk assessment is due almost entirely to much lower likelihood of significant nonoccupational exposures .

OCR for page 320
320 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored ~ - Fiber Effect Route Scores Compared Chrysotile / Mesothelioma / Inhalation with Cell Fiber Effect Route Exposure Score Biodisposition Score Effects Score Production Use Pattern Geography Population 0 Morphology Chemistry Penetration Trends - Stability Overall risk compared with cell above Overall rick compared with prime cell Quality of comparative risk assessment Remarks: Fiber Size 0 Human Studies + o a Animal Studies 0 In-Vitro Studies O Synergism Other o As with lung cancer, crocidolite appears to be more effective for the same exposures, but current lower exposures and decreasing trends significantly reduce the risk for croc idolite. -

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321 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Other Aabestoa / All / Both Fiber Effect Route Scores Compared Chrysotile t Lung Cancer / Inhalation with Cell Fiber Effect Route Exposure Score- Biodisposition Score Effects Score Product ion Use Pattern O Geography O Population Trends Fiber S ize Morphology Chemistry Penetrat ion Stability Ove rat l ri sk compared wi th ce l l above Overall risk compared with prime cell Quality of comparative risk assessment Remarks: Human Studies ~ Animal Studies O In-Vitro Studies O Synerginm Other Most other forms of asbestos have been shown to cause cancers if introduced into the lung in sufficient quantity. Like crocidolite, most amphiboles appear to penetrate to the lung and remain there more easily than chrysotile. None of the other asbestos fibers are used to a great extent in conduce, so their exposure potential is associated with their natural occurrence or contamination of other produc t ~ such as talc .

OCR for page 322
322 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Fibrous Glass / Lung Cancer / Inhalation Fiber Effect Route Scores Compared Chrysotile / Lung Cancer / Inhalation with Cell Fiber Effect Route Exposure Score Production + Use Pattern Geography Populat ion Trends Biodisposi~cion Score Fiber Size Morphology O Chemistry Penetration Stability - Overal 1 risk compared wi th ce 11 above Overall risk compared with prime cell Quality of comparat ive risk assessment Remarks: Effects Score Human Studies Animal Studies In-Vitro Studies Synergism Other Fibrous glans in produced in large quantities and is used widely, although much of it is in fibers larger than respirable size. Most of the population has opportunities for exposure, and the trends are toward increased production and at least level production of fine fiber. Most of the indicators for biological activity point toward lower risk. Evidence from human studies suggests lower, although not necessarily zero, risk of lung cancer. The latency period may not have fully elapsed, but considerations of fiber size distributions and the gelling of glass in tissue also suggest lower risk. Overall, the population risk appears lower despite higher exposure levels.

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323 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Fibrous Glass / Mesothelioma / Inhalation Fiber Effect Route Scores Compared Chrysotile / Mesothelioma / Inhalation with Cell Fiber Effect Route 1' Exposure Score Biodisposition Score Effects Score Production Use Pattern Geography Fiber S ize Morphology Chemistry o In-Vitro Studies _ . ~ Population ~ Penetration -- Synergism Trends + Stability - Other Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment b Remarks: Human Studies Animal Studies O - Epidemiological studies suggest that the association of a mesothelioma with fibrous glass is weaker than it is for lung cancer, but animal experiments have demonstrated the induction of mesothelioma with implanted material. ..j !

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324 COMPARATIVE RISK ASSESSMENT SCORE SHEET Ce 11 Scored Attapulgite ~Lung Cancer / Inhalation Fiber Effect Route Scores Compared Chrysotile / witch Cell Exposure Score Produc t ion + Use Pattern Geography Population Trend s Lung Cancer / Inhalat ion Fiber Ef feet Route Biodisposition Score Fiber S ize Morphology _ O Chemistry Penetration + Stability Overall risk compared with eel 1 above Overall risk compared with prime ce 11 Quality of comparative risk assessment Remarke: _f feet s Score Human Studies Amimal Studies In-Vitro Studies Synergism Other Except for its extremely localized occurrence, attapulgite is more likely to lead to exposures than is chrysotile asbestos. The short, fine fibers are also likely to reach the lung but are cleared rapidly. Evidence is being collected on attapulgite miners, but no positive results have been obtained to date. Positive animal evidence suggesting biological activity is sparse. Overall, the risk is probably less than for chry~otile, but the support for that statement is weak.

OCR for page 325
325 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Mineral Wool / Lung Cancer / Inhalation Fiber Ef fee t Route Scores Compared Chrysotile / with Cell Fiber Effect Exposure Score Produc t ion Use Pattern Lung Cancer / Inhalat ion Route B iodispos it ion Score Fiber Size Morphology O Effects Score Human Studies O Animal Studies Geography O Chemistry In-Vitro Studi._ Population O Penetration - Synergic Trends Stability Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment b Remarks: Other Mineral wools--both slag wool and rock wool--are not produced in as high a volume as asbestos, but neither is the ir product ion on the decline. They are used somewhat less widely than asbestos, but probably in forms that are more easily obtainable. Average f iber size is somewhat thicker. Scanty results from studies in occupational cohorts and animals suggest that mineral wool is no more potent than asbestos ~ and probably less ~

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326 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Chrysotile Scores Compared with Cell Fiber Minera ect Route Mesothelioma / Inhalation Effect Route Exposure Score Biodisposition Score Effects Score Production - Fiber Size - Human Studies O Use Pattern - Morphology O Animal Studies O Geography O Chemistry In-Vitro Studies _ Population O Penetration - Synergism Trends + Stability Other Overall risk compared with cell above Overall risk compared with prime eel 1 Quality of comparative risk assessment Remarks: See remarks for lung cancer on previous page. ) ..

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327 COME ARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Attapulgite / Mesothelioma / Inhalation Fiber Effect Route Scores Compared Chrysotile / Mesothelioma / Inhalation with Cell Fiber Effect Route Exposure Score Biodisposition Score Effects Score Geography Popuiat ion Trends Chemistry Penetration Stability Production _ + Fiber Size -- Human Studies_ Use Pattern + Morphology O Animal StudiesO Overall risk compared with cell above Overall risk compared with prime eel 1 Quality of comparative risk assessment c Remarks: . See remarks for lung cance r on previous page . In-Vitro Studies Synergism Other -

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328 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Ceramic Fiber / Lung Cancer / Inhalation ~ ect Route Scores Compared Chrysotile / Lung Cancer / Inhalation with Cell FiberEffect Route Exposure Score BiodispositionScore Effects Score Production -- Fiber Size O Human Studies Use Pattern -- Morphology O Animal Studies Geography - Chemistry In-Vitro Studies Population - Penetration _ O Synergism Trends ++ Stability Other Overall risk compared with cell above Overall rink compared with prime cell Quality of comparative risk assessment b Remarks: - Most of the assessment is based on curr~nt production and very limited bees. Fibers are respirable in size but are often well contained, and only a few major sources are likely to provide Significant exposures. Little information is available on biological effects. .,

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329 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Ceramic Fiber / Mesothelioma / Inhalation Fiber Effect Route Scores Compared Chrysotile / Mesothelioma / Inhalation with Cell Fiber Effect Route Exposure Score Biodiaposition Score Effects Score Production Use Pattern Fiber Size O Human Studie __ Geography Population - Penetration O Synergism Trends ~ + Stability Other Morphology Chemistry Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment c Remarks: See remarks on previous page. - SO Animal Studies O In-Vitro Studies .

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330 COMPARATIVE RISK ASSESSMENT SCORE SHEET Cell Scored Carbon Fiber / Lung Cancer / Inhalation - Fiber Effect Route Scores Compared Chrysotile / Lung Cancer / Inhalation with Cell Fiber Effect Route Exposure Score Biodisposition Score Effects Score Production Use Pattern Geography Population Fiber S ize O Human Stud ie s Morphology O Animal Studies Chemi s t ry In-Vi ~ ro Stud ie s Penetration O Synergism Trends +++ Stability _ Other Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment c Remarks: l Assessment is based almost entirely on consideration of the currently low exposure levels r

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331 COMPARATIVE RISK ASSESSMENT SCORE SHEET Ce 11 Scored Carbon Fib Fiber Effect Route Scores Compared ChrYsotile / Mesothelioma / Inhalation with Cell Fiber Effect Route Exposure Score Biodisposition Score Effects Score Produc t ion Use Pattern Fiber Size ~Human Studies ___ Geography Population - Penetration O Synergism Trends +++ Stability Other Morphology O Semis try Overall risk compared with cell above Overall risk compared with prime cell Quality of comparative risk assessment c Remarks: Animal Studies In-Vitro Studies See remarks for lung cancer on previous page.

Representative terms from entire chapter:

fiber effect