Tuesday, July 26, 2005

Philosophy of Asbestos Science

BrooklynDodger here mixes theoretical or philosophical concerns for authority in risk assessment with the actual case of asbestos.

The Dodger perviously commented that original research generates the aggregate which requires the cement of a paradigm to be concrete knowledge. Those who mine the aggregate may not have the temperment to extend and apply the paradigm, or see the paradigms' weaknesses. The full text of the abstract is presented here to show how little the "little picture" might be to risk managers, who are lawyers and congress people [congress people are also usually lawyers, unless they are physicians like Frist and Coburn, who are really reactionary.]

Now to the risk policy point. The big debate in asbestos risk assessment is ABC [anything but chrysotile] and OAB [only amphoboles are bad]. The same Houdini risk assessment types who denigrate epidemiology in relation to fine particles inflate epidemiology in relation to potency of various mineral types.

Biological plausibility for this contrast would be found in animal toxicity experiments, then moved to the biochemical level.

One theory for why chrysotile [the main type used, clean white asbestos from the Great White North] is less toxic [which it isn't] is the mineral content of the surface. The iron metaphor for oxidative stress [will be discussed later]. This study shows, BrooklynDodger thinks, that treating chrysotile to put more iron on the surface, like the amphiboles, makes it less toxic, not more toxic.

Toxicology and Applied Pharmacology Volume 206, Issue 3 , 15 August 2005, Pages 356-364

Different cellular responses evoked by natural and stoichiometric synthetic chrysotile asbestos

Elena Gazzanoa, b, Elisabetta Forestic, Isidoro Giorgio Lescic, Maura Tomatisb, d, Chiara Rigantia, b, Bice Fubinib, d, Norberto Roveric and Dario Ghigoa, b, , aDipartimento di Genetica, Biologia e Biochimica-Sezione di Biochimica, Università di Torino, Via Santena 5/bis-10126 Torino, ItalybCentro Interdipartimentale “G. Scansetti”, Università di Torino, ItalycDipartimento di Chimica “G. Ciamician”, Università di Bologna, Via Selmi 2, ItalydDipartimento di Chimica IFM, Università di Torino, via P. Giuria 7, Italy

The carcinogenic potency of asbestos, including chrysotile, is well established. Several physico-chemical features of the fibers appear implied, such as fibrous habit, size, crystallinity, morphology, and surface active metal ions, where free radical generation may take place. In contrast to other asbestos forms, iron is not a stoichiometric component of chrysotile, but is only present together with other extraneous ions as a magnesium- and silicon-replacing contaminant. To determine the role played by contaminating ions and morphological features of the fibers, a stoichiometric chrysotile with constant structure and morphology was synthesized in hydrothermal conditions. Free radical generation and the effects of these fibers on human lung epithelial A549 cells have been compared to that elicited by a well known toxic natural chrysotile (UICC A, from Rhodesia). After a 24-h incubation, the natural, but not the synthetic, form exerted a cytotoxic effect, detected as leakage of lactate dehydrogenase. Homolytic rupture of a CH bond and lipoperoxidation in A549 cells took place in the presence of the natural, but not of the synthetic, chrysotile. Antioxidant systems were also affected differently. The pentose phosphate pathway and its regulatory enzyme glucose 6-phosphate dehydrogenase were markedly inhibited only by the natural specimen, which also caused a depletion of intracellular reduced glutathione in A549 cells. These results suggest that metal ions, fiber size and state of the surface play a crucial role in the oxidative stress caused by chrysotile asbestos. Stoichiometric synthetic fibers may thus be proposed as a reference standard (negative control) for toxicological studies.

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