Leroy Gardner to Vandiver Brown Enclosing an Outline of His Monograph on Asbestosis (1943)

A two-page letter of February 24, 1943, from Dr. Leroy Gardner of the Saranac Laboratory to Vandiver Brown at Johns-Manville, written for the sponsors of the asbestosis study, with a table of contents and an annotated outline of the monograph Gardner planned (15 pages in all). Gardner wrote that "the question of cancer susceptibility now seems more significant than I had previously imagined," but that because a new study would take two or three years, "it would better be omitted from the present report." The outline reports that "there are now on record 10 cases of lung cancer in asbestos workers," an incidence it calls "excessive," and a lung tumor rate of 81.8% in mice that inhaled long-fiber asbestos for 15 to 24 months.

What it shows

The outline calls the evidence "suggestive but not conclusive that asbestosis may precipitate the development of cancer in susceptible individuals." It also questioned the dust limit then in use: impinger counts were "deceptive" because they collected very few of the fibers, and the tentative standard of 4 or 5 million particles per cubic foot "is probably unreliable" (see Threshold Limit Value (TLV)). A new standard, Gardner wrote, would have to be "correlated with the X-ray findings upon employees." Through Brown, J-M and the other sponsors had both the cancer finding and these doubts about the dust limit in early 1943. Three weeks later Gardner asked the National Cancer Institute to fund a repeat of the mouse experiment (March 15, 1943).

In Johns-Manville's chronology

Johns-Manville's own chronology of what the company knew describes this document as follows:

Letter from Leroy Gardner to Vandiver Brown, 2/24/43. The letter is an apology for the delay in preparing a complete report on the studies underway at Saranac. Gardner reports "the work on methods of dust determination, I consider important enough to include in the study. The question of cancer susceptibility now seems more significant than I had previously imagined. I believe I can obtain support for repeating it from the cancer research group. As it will take 2 or 3 years to complete such a study, I believe that it better be omitted from the present report. If it should become possible to make the study, I hope that I may count on some of your members to supply me with enough long fiber asbestos for the purpose." Gardner included a 15 page summary report on his findings, and noted that there were then on record 10 cases of lung cancer in asbestos workers and that the incidence relative to the total number of autopsies available on asbestosis was excessive. "The evidence is suggestive but not conclusive that asbestosis may precipitate the development of cancer in susceptible individuals."

The summary includes discussion of the appropriate method by which to evaluate atmospheric concentrations. Gardner states that impinger counts are inadequate for sampling fiber levels in an environment. He suggests that sampling with an electrostatic precipitator is a much more efficient means of collecting fibers from airborne suspensions. He concludes that the atmosphere to which the test animals had been exposed contained 32.5% fiber, but that few of those fibers were collected (or counted) in the impinger samples. "The [impinger] sampled largely the inert oracular particles." He continued "as ordinarily employed, precipitator samples are weighed and the results expressed in mg. per cubic foot of air. There is no means of converting such values into numbers of particles particularly when these vary in size, shape and specific gravity. Simultaneous sampling with the precipitator and standard impinger yielded the respective values of 0.65 mg and 60 million particles per cubic foot of air. Theoretically, the best index of hazard would be either the number or weight of fibrous elements in the dust." As to the appropriate TLV, he recommends that a new standard should be developed since the 5 million particle standard "is probably unreliable because it is based upon sampling with a standard impinger which we have shown does not collect most of the fibers that are the source of hazard. We now think that a standard should be based upon samples collected with an electrostatic precipitator if it is feasible to determine readily the relative proportion of fibers in such material. Work is still in progress upon the latter point. To be of value the new standard would have to be correlated with the x-ray findings upon employees exposed to different concentrations of dust."

Gardner's "Outline of Proposed Monograph on Asbestosis," inter alia, raises with J-M and other sponsors the question of possible asbestos-cancer link.

Editor's note: J-M's description calls the enclosure a "15 page summary report"; Gardner's letter describes it as a table of contents and an annotated outline of a proposed monograph, which together take 15 pages. The chronology's quotation "the inert oracular particles" reads "the inert granular particles" on the page.