Asbestos Abatement >> Chrysotile

Abstract This review provides a basis for substantiating both kinetically and pathologically the differences between chrysotile and amphibole asbestos. 
Chrysotile, which is rapidly attacked by the acid environment of the macrophage, falls apart in the lung into short fibers and particles, Chrysotile while the amphibole asbestos persist creating a response to the fibrous structure of this mineral. 

Inhalation toxicity studies of chrysotile at non-lung overload conditions demonstrate that the long (>20 µm) fibers are rapidly cleared from the lung, Chrysotile are not translocated to the pleural cavity and do not initiate fibrogenic response. 

In contrast, long amphibole asbestos fibers persist, Chrysotile are quickly (within 7 d) translocated to the pleural cavity and result in interstitial fibrosis and pleural inflammation. 

Quantitative reviews of epidemiological studies of mineral fibers have Chrysotile determined the potency of chrysotile and amphibole asbestos for causing lung cancer and mesothelioma in relation to fiber type and have also differentiated between these two minerals. These studies have been reviewed in light of the frequent use of amphibole asbestos. 

As with other respirable particulates, there is evidence that heavy and Chrysotile prolonged exposure to chrysotile can produce lung cancer. The importance of the present and other similar reviews is that the studies they report show that low exposures to chrysotile do not present a detectable risk to health. 

Since total dose over time decides the likelihood of disease occurrence and Chrysotile progression, they also suggest that the risk of an adverse outcome may be low with even high exposures experienced over a short duration. Numerous investigators have suggested that there is likely to be a cumulative chrysotile exposure below which there is negligible risk of asbestos-related diseases. 

However, to date, little research has been conducted to identify an actual "no-effect" exposure level for chrysotile-related lung cancer and Chrysotile mesothelioma. The purpose of this analysis is to summarize and present all of the cumulative exposure-response data reported for predominantly chrysotile-exposed cohorts in the published literature. 

Criteria for consideration in this analysis included stratification of relative risk or mortality ratio estimates by cumulative chrysotile exposure. Over 350 studies were initially evaluated and subsequently excluded from the analysis due primarily to lack of cumulative exposure information, Chrysotile lack of information on fiber type, and/or evidence of significant exposures to amphiboles. 

Fourteen studies meeting the inclusion criteria were found where lung cancer risk was stratified by cumulative chrysotile exposure; Chrysotile four such studies were found for mesothelioma. All of the studies involved cohorts exposed to high levels of chrysotile in mining or manufacturing settings. 

The preponderance of the cumulative "no-effects" exposure levels for lung cancer and mesothelioma fall in a range of approximately 25-1,000 fibers per cubic centimeter per year (f/cc-yr) and 15-500 f/cc-yr, respectively, and Chrysotile a majority of the studies did not report an increased risk at the highest estimated exposure. 

Sources of uncertainty in these values include errors in the cumulative exposure estimates, conversion of dust counts to fiber data, and Chrysotile use of national age-adjusted mortality rates. Numerous potential biases also exist. 

For example, smoking was rarely controlled for and amphibole exposure did in fact occur in a majority of the studies, Chrysotile which would bias many of the reported "no-effect" exposure levels towards lower values. 

However, many of the studies likely lack sufficient power (e.g., due to small cohort size) to assess whether there could have been a significant increase in risk at the reported no-observed-adverse-effects level (NOAEL); Chrysotile additional statistical analyses are required to address this source of bias and the attendant influence on these values. 

The chrysotile NOAELs appear to be consistent with exposure-response information for certain cohorts with well-established industrial hygiene and Chrysotile epidemiology data. 

Specifically, the range of chrysotile NOAELs were found to be consistently higher than upper-bound cumulative chrysotile exposure estimates that have been published for pre-1980s automobile mechanics (e.g., 95th percentile of 2.0 f/ cc-yr), Chrysotile an occupation that historically worked with chrysotile-containing friction products yet has been shown to have no increased risk of asbestos-related diseases. 

While the debate regarding chrysotile as a risk factor for mesothelioma will likely continue for some time, future research into nonlinear, Chrysotile vermiculite is mined at three U.S. facilities and in other countries which have lower levels of asbestos contamination in the finished material. threshold cancer risk models for chrysotile-related respiratory diseases appears to be warranted.

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