Parietal Pleural Plaques and Elevated Lung Asbestos Body Content

No serious expert questions the dangers of asbestos exposure to people.  In fact, there is a growing consensus as to how dangerous the Mesothelioma menace has become.  One interesting study is called, "Asbestos bodies in pulmonary hilar lymph nodes." by Roggli VL, Benning TL. - Mod Pathol. 1990 Jul;3(4):513-7.  Here is an excerpt: "Abstract - Asbestos bodies (AB) have long been recognized in light microscopic (LM) sections of pulmonary hilar lymph nodes (LN) from patients with asbestos-related diseases, but the presence of AB on LM has not been correlated with the lung AB burden. The purpose of the present study was to determine whether AB in histologic sections of LN are indicative of heavy lung asbestos burdens. Twenty cases (17 with asbestosis, 15 with carcinoma of the lung, and two with malignant pleural mesothelioma) with at least one AB on a hilar LN section were identified. Bleach digestion of lung tissue in 15 cases demonstrated a median of 24,000 AB/g by LM and 44,000 AB/g by scanning electron microscopy. Digestion of hilar nodes demonstrated 21,800, 15,500, and 3,200 AB/g by LM in three cases which had lung burdens of 22,000, 481,000, and 5470 AB/g, respectively. A fourth LN specimen contained 322,000 AB/g in a case with no lung available to digest. Mean AB lengths in the LN in three cases were 48, 45, and 27 microns. Fourteen control cases of men over 50 without known asbestos exposure or asbestos-related disease had no AB in LN sections even after staining for iron. Among fourteen patients with parietal pleural plaques and an elevated lung asbestos body content, AB were observed in iron-stained LN sections in only two cases. These two patients had 3240 and 610 AB/g lung tissue, respectively (normal range 0 to 20 AB/g). We conclude that the finding of AB on a histologic section of hilar LN is generally indicative of a heavy lung AB burden."

Another interesting study is called, "Asbestos exposure, smoking habits, and cancer incidence among production and maintenance workers in an electrochemical plant" by
Bjørn Hilt MD1, Sverre Langåd MD, MSc, Aage Andersen, and Jan Rosenberg MD - American Journal of Industrial Medicine - Volume 8, Issue 6, pages 565–577, 1985.  Here is an excerpt: "Abstract - The incidence of cancer was studied in a cohort of 287 men who were exposed to asbestos at a nitric acid production plant from 1928 onwards. During the observation period from 1953 through 1980 all cancer cases among the cohort members were identified in The Cancer Registry. For the whole cohort 42 cases of cancer were observed versus 30.6 expected. The figures for cancer of the lungs and pleura combined were 17 observed versus 3.7 expected. The corresponding figures for a heavily exposed subcohort were 11 observed and 1.2 expected. In that group there was also an increased incidence of colon cancer with 3 cases observed against 0.8 cases expected. Within the whole cohort four cases of pleural and one case of peritoneal malignant mesothelioma were found. There was also an increased incidence of malignant melanoma of the skin with 3 cases observed against 0.6 expected. For cancer cases that were registered as of unknown origin there were 7 cases observed and 1.4 expected. There was no increased rate ratio for cancer at any site before 20 years after the first asbestos exposure. The smoking habits of all cohort members were recorded and the relative rates for lung cancer were calculated in relation to smoking habits. In common with previous studies the results indicate a multiplicative model for the interaction between asbestos exposure and smoking in regard to lung cancer risk."

A third study worth examining is called, "Inhalation and injection studies in rats using dust samples from chrysotile asbestos prepared by a wet dispersion process." By
Davis JM, Addison J, Bolton RE, Donaldson K, and Jones AD - Br J Exp Pathol. 1986 Feb;67(1):113-29.  Here is an excerpt: "Abstract - Long term inhalation studies and intraperitoneal injection studies in rats were undertaken with a series of chrysotile asbestos dusts. Three dust samples were generated from chrysotile modified by the wet dispersion process (WDC) and one was from unmodified chrysotile. Following a 1 year inhalation period, all the chrysotile samples proved extremely fibrogenic and carcinogenic and there were no significant differences between the WDC dusts and normal chrysotile. In all experimental groups approximately 25% of animals developed pulmonary carcinomas and in the oldest rats advanced interstitial fibrosis occupied on average 10% of all lung tissue. In the injection studies all the dust samples produced mesotheliomas in over 90% of animals. Very little chrysotile remained in the lungs of the animals that survived longest following dust inhalation and what there was was present as individual chrysotile fibrils. It is suggested that chrysotile is potentially the most harmful variety of asbestos as shown in these and other animal studies but that it is removed from lung tissue quite rapidly. In the long lived human species this may mean that except where exposure levels are very high and of long duration, chrysotile should be less hazardous than other asbestos types."

We all owe a debt of gratitude to these fine researchers for their hard work and dedication.  If you found any of these excerpts interesting, please read the studies in their entirety.