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Author: Subject: Carcinogenity of Really Fine Silica Gel
Ioxoi
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[*] posted on 22-5-2009 at 10:48
Carcinogenity of Really Fine Silica Gel


I made some silica gel recently, but in a different manner than the usual sodium silicate / HCl manner.

400 parts 1.42g/mL sodium silicate (from chemsitrystore.com) were diluted with 600 parts water. Separately, 72g (I think) of 93% H2SO4 were diluted to 1000mL volume.
Through trial and error, it was found that 5 parts of silicate solution reacted with 4 parts of acid solution to suddenly jellify, usually within 5 seconds of mixing. I actually had a spoon "freeze" into it once.

The gel was rubbery but brittle, and cleaved like glass. What would happen if it was frozen, I thought? Would the expanding water "shatter" the glass gel into a million glass shards?

About two cups of this "glass rubber" were frozen in a freezer overnight. Thawing gave a clear liquid and a white powder that settled to the bottom. Decanting and rinsing the powder several times, then drying in a toaster oven for half a day (unsure as to exact temperature) gave a fine white powder. The powder appears to contain extremely small particles of silica.

For example, when a small amount of this powder was placed in a glass jar, and the jar capped and shook and let sit, the air above the powder was thick with a white "glass smoke." Additionally, when transferring the powder to the bottle, a large amount of white "smoke" was generated.

This white "smoke" is scaring me. I read that silica gel is not a carcinogen, however, the prospect of inhaling millions of small glass shards is not one I am comfortable with. How careful should I be with my unorthodox "silica gel" powder?


[Edited on 22-5-2009 by Ioxoi]




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woelen
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[*] posted on 22-5-2009 at 12:33


Glass particles indeed are very bad for your lungs. The problem is not their chemical toxicity, but their mechanical properties. They remain there for a LONG time. I think one can better have some toxic soluble chemical in his lungs (not too much of course :P ) than a similar amount of ultrafine glass.

Known risks are silicosis (dust lung) and cancer (due to continuous irritation, the body responds with uncontrolled growth of cells around the irritation).




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[*] posted on 22-5-2009 at 13:32


You made amorphous silica. This is much less dangerous than crystalline silica, ground quartz, which is the real carcinogen.
Of course you really shouldn't inhale it unnecessarily, but that goes for all kinds of insoluble mineralic dusts.
For example, I use ceramic fiber blanket for furnace construction, and this is clearly carcinogenic in the same way asbestos is.

Can you use your product for chromatography or for absorbing water vapor in a desiccator? Did you prepare it for a specific purpose?




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[*] posted on 22-5-2009 at 15:03


Breathing in fibers of fiberglass, that is glass drawn out into thin fibers for building insulation and for making glass reinforced polyester mouldings by embedding in liquid polyester resin, is at least as bad as breathing in fine silica dust (which gives many miners silicosis). See:
http://en.wikipedia.org/wiki/Fiberglass

Even worse is breathing in fibers of blue asbestos (crocidolite or asbestiform riebeckite), also once used as building insulation, and in "fibrolite" or cement-board by embedding in cement, which causes Mesothelioma, a usually fatal form of lung cancer, along with asbestosis (a type of pneumoconiosis); see:
http://www.agius.com/hew/resource/asbestos.htm and
http://en.wikipedia.org/wiki/Asbestos and
http://www.answers.com/topic/asbestos and
http://www.medicinenet.com/asbestos-related_disorders/articl...
Many former insulation workers, and those formerly engaged in making "fibrolite", have died of it, as well as asbestos miners, most often in their late 60s.
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[*] posted on 22-5-2009 at 15:35


I have worked with silica gel for several years and never heard of any carcinogenicity. The glass obtained in the process I used is transparent - which is an indicator of amorphousness.

Ground quartz should in principle not be any more or less carcinogenic than ground glass, which is the same SiO2 with inclusions of 10% or so Na2O, B2O3 etc.

Ceramic tiles also contain SiO2, although it is mostly amorphous. Glass fibres from thermal insulation I use are said to be biodegradable. I have never heard of any cancer cases with insulation layers etc. what one hears of constantly is asbestos, which is a crystaline mass of oxides containing a lot more than silica. So I think carcinogenicity is much more complicated than just the presence of crystal SiO2 and not well understood yet.

This may help cheer you (and me) up
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Although pulmonary granulomatous inflammation and slight to moderate fibrosis of the alveolar septa were observed in three experiments on hamsters that used repeated intratracheal instillation of quartz dusts, no pulmonary tumours were observed (Holland et al., 1983; Renne et al., 1985; Niemeier et al., 1986). In experiments with mice, no statistically significant increase was seen in the incidence of lung tumours in a strain A mouse (i.e., male A/J mice from Jackson Laboratories, Bar Harbor, ME, USA) lung adenoma assay with one sample of quartz (McNeill et al., 1990) or with a sample of quartz in a limited inhalation study of BALB/cBYJ female mice (Wilson et al., 1986). Fibrosis was not observed; however, the lungs of quartz-treated mice did have silicotic granulomas, and lymphoid cuffing was observed around airways (IARC, 1997).

De Klerk & Musk (1998) conducted a cohort study of 2297 surface and underground gold miners in western Australia who participated in surveys of respiratory symptoms, smoking habits, and lung function in 1961, 1974, and 1975. Eighty-nine per cent of the cohort was traced to the end of 1993 for trachea, bronchus, and lung cancer mortality and incidence of compensated silicosis (i.e., compensation awarded by the Pneumoconiosis Medical Board). A nested case-control analysis of the 138 lung cancer deaths found that lung cancer mortality was related to log total cumulative silica dust exposure after adjustment for smoking (cigarette, pipe, or cigar) and for the presence of bronchitis at survey (relative rate = 1.31; 95% CI = 1.01-1.70). However, the effect of total cumulative silica dust exposure on lung cancer mortality was not significant after adjustment for smoking, bronchitis, and compensation for silicosis (relative rate = 1.20; 95% CI = 0.92-1.56). Lung cancer mortality was not significantly related (P > 0.15) to other silica exposure variables (i.e., duration of underground or surface employment, intensity of underground or surface exposure) after adjustment for smoking and bronchitis. Cigarette smoking (relative rate = 32.5; 95% CI = 4.4-241.2 for >25 cigarettes smoked per day), incidence of a compensation award for silicosis after lung cancer diagnosis (relative rate = 1.59; 95% CI = 1.10-2.28), and presence of bronchitis at survey (relative rate = 1.60; 95% CI = 1.09-2.33) were significantly related to lung cancer mortality (de Klerk & Musk, 1998). The results of this study do not support a relationship between lung cancer and silica exposure in the absence of silicosis (i.e., a compensation award for silicosis after lung cancer diagnosis).


[Edited on 23-5-2009 by len1]
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[*] posted on 22-5-2009 at 16:05


I have also worked with silica gel for several years in the past and we preferred to move it around (from container to beaker, and from beaker to chromatography column, for example) in the fumehood whenever possible; other people have worn a simple face mask while dealing with silica gel.

I know of no-one who has become ill from silica gel, but why take risks? Once you have lung disease from silicosis you are in for a slow painful death with no current cure (besides lung transplant which these people never seem to get).

I think you're wise to be concerned, but commercial silica gel can give that "smoke" effect too, so I'd think using it should be fine if you take the proper precautions.




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[*] posted on 22-5-2009 at 16:12


Quote: Originally posted by len1  
Ground quartz, crystalline SiO2, should in principle not be any more or less carcinogenic than ground glass, which is the same SiO2 with inclusions of 10% or so Na2O, B2O3 etc.
If the mechanical properties are only it, then sure. But if the crystal structure of the material is also a co-factor, then it's not clear. Quartz is crystalline SiO2 and glasses are supercooled liquid. The point is that their surfaces should be expected to have different chemical activity.
Quote:
Ceramic tiles also contain SiO2, although that is more amorphous. Glass fibres from thermal insulation I use are said to be biodegradable. I have never heard of any cancer cases with insulation layers etc. [...] So I think carcinogenicity is much more complicated than just the presence of crystal SiO2 and not well understood yet.
Another difference with fiberglass insulation is that the fibers are surface-treated with a bonding agent which, after heat-treatment, bonds them into a mat. So yet again the surface chemistry is going to be different.

As to your final point about "not well understood", I am in full agreement.
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[*] posted on 22-5-2009 at 16:41


Sorry, my mistake above. Transparency in glass is usually an indicatour of amorphousness, which corresponds to lack of (crystal) structure (although crystals which are very large - regular on the scale of 1-1000 microns - are transparent) Glass, silica gel, and fused quartz (of the type used in glass-blowing) are all amorphous and so should have minimal carcinogenicity. Natural quartz and asbestos are crystalline, and so are a different story. Most synthetic glass materials (such as silica gel, glass, the quartz in heater element tubes) are supercooled, and so non-crystaline. Their dust should not be dangerous.

[Edited on 23-5-2009 by len1]
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[*] posted on 23-5-2009 at 09:15


Quote: Originally posted by watson.fawkes  
If the mechanical properties are only it, then sure.

A guy working on SiO2 particles as drug delivery agent told me that amorphous particles in the blood stream are harmless because they dissolve. I don't know if the same is true for larger particles or particles in the lung.
Quote:
Quartz is crystalline SiO2 and glasses are supercooled liquid.

Glasses are amorphous solids. Just because the DFT guys have a hard time computing them does not make them liquids, supercooled or not. :P
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[*] posted on 23-5-2009 at 09:47


Glasses are VERY viscous liquids... my tutor was telling me about how someone had measured the thickness of some really old panes and suprisingly, the glass was thicker at the bottom than at the top (i.e. the glass had flowed over time!) I do hope my quickfit doesnt go like that ;):D
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[*] posted on 23-5-2009 at 10:44


No, they are not. Stop perpetuating that old-wives' tale.
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