Asbestos The TLV Approach

Our plain-English summary of Asbestos The TLV Approach, by W.J. Nicholson (1976).

The study

• Author: W.J. Nicholson
• Published: Annals New York Academy of Sciences (1976)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

In this review, the author asked whether Threshold Limit Values (TLVs) suit control of carcinogens like asbestos. The author traced US limits from 1938 to the 1972 federal standard: an eight-hour average of 5 fibers per milliliter longer than 5 micrometers, with a ceiling of 10. The average was due to fall to 2 in 1976. Citing earlier studies, the author reported that of 689 long-employed workers at an asbestos products factory, 199 died from 1959 through 1971, against about 134 expected. In the same group, 72 cancer deaths were observed, against about 28 expected. In that factory, the share of deaths from asbestosis fell as dustiness fell, but the share from cancer did not. The exception was the dustiest category, the textile mill, where, the author wrote, workers died of asbestosis before reaching the age of highest cancer risk. Among 17,800 US and Canadian insulators, 179 lung cancer deaths occurred in 9,590 men with a cigarette-smoking history and 2 in 2066 without one. Asked about June to December 1972, 171 union insulators reported seeing a dust count and 4956 did not. The author concluded that the TLV approach to carcinogens is of limited effectiveness.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Review and commentary on the use of Threshold Limit Values to control asbestos exposure. It presents data from earlier mortality studies and from a questionnaire survey of insulation workers.
• Who was studied: Data drawn from several groups: 689 production employees of a US asbestos products factory who were working on January 1, 1959 and were first employed before 1939; 17,800 asbestos insulation workers in the United States and Canada, followed from January 1, 1967 to December 31, 1972; New York and New Jersey asbestos insulation workers; and members of the insulation workers' union, asked about the period June 7 to December 6, 1972.
• Exposure: Airborne asbestos dust in asbestos textile mills, asbestos products manufacturing, insulation work and shipyards, discussed against successive exposure limits. The 1972 OSHA standard was an eight-hour time-weighted average of 5 fibers per milliliter longer than 5 micrometers, with a ceiling of 10 fibers per milliliter. The time-weighted average was due to go to 2 fibers per milliliter on July 1, 1976, and the ceiling was to stay at 10.
• Main results:
  • Asbestos products factory cohort, 1959 through 1971: about 134 deaths were expected and 199 occurred (50% more). In this mortality study, about 28 cancer deaths were expected and 72 were observed.
  • In the factory study, the percentage of deaths due to asbestosis fell from more than 40% in the textile mill to less than 5% in the lowest dust category. The percentage of deaths from cancer did not fall as dustiness decreased.
  • The exception was the highest dust category, the textile mill, where the cancer percentage was lower. The author attributed this to textile workers dying of asbestosis before reaching the age of highest cancer risk.
  • Among the 17,800 insulation workers, 179 lung cancer deaths were observed in 9,590 men with a history of cigarette smoking.
  • Among the 17,800 insulation workers, 2 lung cancer deaths were observed in 2066 men with no history of cigarette smoking.
  • The article states that the combination of cigarette smoking and asbestos has a multiplying effect on lung cancer risk.
  • Among New York and New Jersey insulation workers 20 or more years from first exposure, nearly 40% of deaths were attributed to occupational asbestos exposure, taking into account the expected frequency of the various cancers.
  • Survey of insulation union members about the period June 7 to December 6, 1972: for all regions, the table lists 171 workers who had seen a dust count and 4956 who had not. The narrative text gives the denominator as 2956, which conflicts with the table.
  • The author estimated that average asbestos fiber concentrations during past insulation work were 10 to 15 fibers per milliliter.
• The authors' conclusion: The author concluded that controlling carcinogenic exposures with the TLV approach is of limited effectiveness.
• Limitations the authors state:
  • The data were still insufficient to determine accurately the lung cancer risk of nonsmoking asbestos insulators.
  • Average exposure estimates are highly subjective and depend on the work practices and conditions that were sampled.

Topics

Medical terms in this study, explained in our Lexicon: Threshold Limit Value (TLV), Insulator, Lung Cancer.

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