Document g2jgjrRjxdKDoMG13gn3J9Mx3

FILE NAME Talc TALC DATE 0000 DOC TALC054 DOCUMENT DESCRIPTION Unpublished Conference Presentation - NTP Talc Definition Issue Robert Virta of USGS NTP Talc Definition Issue From a geological and mineralogical viewpoint some of the difficulties encountered with the inclusion of talc in the previous Report on Carcinogens were due to a lack of knowledge of exactly what constituted the talcose materials that were tested Talc can be used as both a specific mineralogical term and as a generally applied industrial term A mineralogical term such as talc strictly defines a crystalline chemical compound with distinct chemical and physical characteristics In contrast in commercial or industrial terminology the term tale is more loosely applied to bearing or rich materials To a mineralogist briefly talc is a hydrous magnesium silicate with an ideal formula of Si4O10 and a composition of 63.36 weight % SiO2 31.89 weight % MgO and 4.75 weight % H2O Talc may contain minor amounts of aluminum and titanium replacing silicon minor amounts of fluorine replacing hydroxyl groups and minor to trace amounts of iron calcium chromium manganese nickel potassium sodium and titanium replacing magnesium Talc is a sheet silicate The bonds between the sheets are very weak causing talc to be an extremely soft mineral Talc is used to represent a hardness of 1 softest on the Mohs scale Its color can vary from green to brown to gray to white Additional properties such as cleavage crystal structure optical properties and specific gravity also are used to further identify talc and minerals in general American Chemical Society 1996 Clifton 1984 Deer Howie and Zussman 1976 Evans and Guggenheim 1988 Hurlbut 1971 As a commercial term talc refers to rocks and mineral products that may be composed almost entirely of the mineral talc or rather may be rich but contain other minerals in significant quantities For example soapstone is a form of rich rock that contains 50 to 80 of the mineral talc Hughes 1932 Associated minerals include members of the amphibole carbonate chlorite clay and serpentine mineral groups and such minerals as magnetite muscovite phlogopite and quartz Cosmetics Fragrance and Toiletries Association Inc. 1976 Piniazkiewicz McCarthy and Genco 1994 Van Gosen et al 2004 Amphibole and serpentine minerals may occur in the asbestiform crystal habit in some talc deposits Depending on the particular application the many useful properties of commercial talc are taken into consideration such as its chemical inertness electrical conductivity fragrance retention grease and oil adsorption luster moisture content purity softness thermal conductivity and whiteness these properties can vary considerably amongst mined deposits Clifton 1985 Talc both the mineral and rock is formed during the hydrothermal alteration of magnesium rocks such as some sedimentary rocks typically dolomite rock and ultramafic and mafic igneous or metamorphic rocks such as gabbro dunite and periodotite Chidester Engel and Wright 1964 Piniazkiewicz McCarthy and Genco 1994 The hydrothermal alteration heated silica fluids that caused talc formation may be due to regional or contact metamorphism or a buried magma body nearby When dolomite rock is altered the reaction to form talc is 3 dolomite + 4 quartz + water = talc +3 calcite + 3 CO With the alteration of mafic and ultramafic rocks the usual precursor to talc formation is serpentinite The reaction to form talc from serpentine is 2 serpentine +3 +3 CO = talc +3 +3 magnesite + 3 H DOeer Howie and Zussman 1976 Robert Virta of USGS In many cases there is a deficiency in one of the reacting components on the left side of the equation that can result in incomplete reaction Additionally many of the accessory minerals in the parent rock also will react during the alteration process resulting in a mixture of minerals in the deposit and any mineral products made by milling this rock after the mineralizing process has completed These considerations have given rise to the questions about the mineralogy of the talc samples evaluated in the previous National Toxicology Program NTP review process a As result of our telephone conversation on Monday August 9 it appears that the issue for NTP is not specifically the mineral talc but rather commercial talc products Consequently I have to reverse my original thinking and recommend that the NTP panel use a definition for commercial talc rock or products The definition could be along the lines of Talc is definedfor the purpose of the NTP review as a rich rock or mineral product used in the manufacture ofproducts classified mainly as ceramics cosmetics paint paper plastic roofing and rubber There are other applications such as adhesives flow control agent and insecticide carriers that do notfall into the above broad categories The rock or mineral product contains the mineral talc typically in quantities exceeding 50 but not excluding lesser amounts These rocks and products also may contain numerous associated minerals including amphiboles such as anthophyllite and tremolite carbonates calcite dolomite and magnesite chlorites clays kaolin serpentines antigorite and lizardite and magnetite muscovite quartz sericite and vermiculite Asbestiform amphiboles and chrysotile are present in some talc deposits but not necessarily those mined at present Asbestiform amphiboles also generally are excludedfrom most commercial talc products This definition will avoid having to classify rocks and products as industrial versus cosmetic as it would apply to both Whether it is a cosmetic or industrial probably is irrelevant because the issue appears to be whether or not exposure to talc products results in a site specific form of cancer namely ovarian cancer For your summary of information page you might think about the following Summary of Information Primary uses or exposures Talc occurs in various geological settings around the world Exposure to general population excluding occupational exposure occurs primarily through use of products such as cosmetics particularly in loose powder form Nominated by National Institute for Environmental Health Science Basis for Nomination The NTP deferred consideration of listing talc in the 10th Report on Carcinogens because its 2000 review of talc found that most of the scientific literature did not specify the mineralogy of the talc products that were the subject of the medical studies Given the available evidence on health effects of all exposure routes the NTP only will focus its investigation on the relationship between talc anda site specific cancer namely ovarian cancer Robert Virta of USGS eal I will point out that by using talc as defined above if a causal relationship is discovered the NTP panel still will not know 1 which component of the talc product is the carcinogen 2 if another additive in the talcum powder was the problem or 3 if an accessory mineral has an effect I doubt if many talcum powders are 100 talc References American Chemical Society 1996 Talc Washington DC Chemical Abstract Service Registry Number 14807-96-6 2 p Chidester A.H. Engel A.E.J. and Wright L.A. 1964 Talc resources of the United States U.S. Geological survey Bulletin 1167 61 p Clifton R.A. 1984 What is talc in Definition for asbestos and other related silicates Philadelphia American Society for Testing and Materials Special Technical Publication 834 p 158-174 Clifton R.A. 1985 Talc and pyrophyllite In Mineral Facts and Problems Washington DC U.S. Bureau of Mines Bulletin 675 pp 799-810 Cosmetics Fragrance and Toiletries Association Inc. 1976 Cosmetic talc Washington DC Cosmetics Fragrance and Toiletries Association Inc. Standard 1 p Deer W.A. Howie R.A. and Zussman J. 1976 An introduction to the forming minerals Longman Group Ltd. London 528 p Evans B.W. and Guggenheim S.J. 1988 Talc pyrophyllite and related minerals chap 8 of Bailey S.W. ed Hydrous phyllosilicates exclusive of micas Washington D.C Mineralogical Society of America Reviews in Mineralogy 19 p 225-294 Hughes H. Herbert 1932 Soapstone U.S. Bureau of Mines Information Circular 6563 17 p Hurlbut C.S. 1971 Dana's manual of mineralogy 18th ed John Wiley & Sons Inc. New York 579 p Piniazkiewicz R.J. McCarthy E.F. and Genco N.A. 1994 Talc in Carr D.D. ed Industrial Minerals and Rocks 6th Edition Society for Mining Metallurgy and Explorations Inc. Littleton CO p 1049-1069 Van Gosen B.S. Lowers H.A. Sutley S.J. and Gent C.A. 2004 Using the gologic setting of talc deposits as an indicator of amphibole asbestos content Environmental Geology v 45 no 7 May p 920-939