Bentonite toxicology and epidemiology – a review

Abstract

Bentonite, a clay with numerous industrial and consumer applications, is mined and processed in many countries of the world. Its many beneficial uses also create the potential for widespread occupational and consumer exposure. The available studies on toxicity and epidemiology indicate that the principal exposure pathway of concern is inhalation of respirable dust by occupationally exposed cohorts. Bentonite itself is probably not more toxic than any other particulate not otherwise regulated and is not classified as a carcinogen by any regulatory or advisory body, but some bentonite may contain variable amounts of respirable crystalline silica, a recognized human carcinogen. Therefore, prudent management and adherence to occupational exposure limits is appropriate. This review summarizes the literature available on production, applications, exposure, toxicity, and epidemiology of bentonite and identifies data gaps and limitations.

• Bentonite
• Fuller’s Earth
• montmorillonite
• mining
• processing
• applications
• toxicity
• epidemiology
• occupational exposure

Declaration of interest

Over the years, the authors have worked for several firms producing industrial minerals. However, this study is based solely on research conducted by the authors and was not sponsored by any bentonite producer.

Notes

¹ Name given to a group of clay minerals that undergo reversible expansion on absorbing water. The smectite group includes several minerals such as aliettite, beidellite, bentonite, hectorite, montmorillonite, nontronite, pimelite, saliotite, saponite, sauconite, stevensite, volkonskoite, yakhontovite, and zincsilite (see, e.g., http://www.mindat.org/min-11119.html, accessed on 29 July 2016).

² The name “montmorillonite” was given to a rose-red, clay-like mineral-forming nests in a brown clay at Montmorillon, France (Hauser & Columbo, 1953).

³ Montmorillonite was discovered in 1847 in Montmorillon in the Vienne prefecture of France (Uddin, 2008).

⁴ Formerly this clay had been referred to as mineral soap or soap clay because of its soap-like characteristics (Hosterman & Patterson, 1992).

⁵ For Algeria, see http://www.eisourcebook.org/cms/January%202016/Algeria%20Minerals%20Yearbook%202013.pdf, for Zambia, see http://nora.nerc.ac.uk/8834/1/Industrial_Mineral_Resources_of_Zambia.pdf.

⁶ Underground bentonite mines were (and still are in some cases) located in parts of China, Croatia, Germany, Japan, and Romania.

⁷ See http://www.wyomingmining.org/minerals/bentonite/ accessed 29 July 2016.

⁸ The “other” category represents an aggregate of categories that the USGS cannot directly report because the data are treated as confidential business information due to the small number of companies using bentonite in the US. In prior years, when the USGS reported disaggregated data, the rank order of applications was slightly different. For example, in 2011, drilling mud was the top use (in thousand metric tons) at 1160 followed by pet waste absorbents (1110), pelletizing (iron ore) (649), foundry sand (592), waterproofing and sealing (181), misc. civil engineering (124), other (93), filler and extender (68), animal feed (36), and adhesives (9). Total US bentonite consumption in 2011 was estimated to be 4 022 000 metric tons (Virta, 2013).

⁹ See http://link.springer.com/article/10.1007%2FBF00748681#page-1, accessed 1 August 2016.

¹⁰ According to USGS, “Accessory minerals are those mineral constituents of a rock that occur in such small amounts that they are disregarded in its classification and definition” (see http://archive.org/stream/glossaryofmining00fayarich/glossaryofmining00fayarich_djvu.txt) accessed 29 July 2016.

¹¹ Some bentonites may contain cristobalite, but more commonly they contain opal-CT, or opal-C, which can be confused with cristobalite. Hillier & Lumsdon (2008) described an analytical technique to differentiate among these materials.

¹² The 30% figure was found in only one SDS for the so-called cement grade bentonite.

¹³ Wendlandt et al. (2007) reported quartz contents ranging from 1.9% to 8.5% weight for western and southern bentonites.

¹⁴ See http://www.nicnas.gov.au/chemical-information/imap-assessments/imap-assessments/tier-i-human-health-assessments, accessed 30 July 2016.

¹⁵ See http://www.health.gov.au/internet/main/publishing.nsf/Content/ocs-arfd-list.htm, accessed 30 July 2016.

¹⁶ See http://www.health.gov.au/internet/main/publishing.nsf/Content/ocs-arfd-list.htm, accessed 30 July 2016.

¹⁷ See https://www.osha.gov/silica/, last accessed 1 August, 2016.

¹⁸ The values in the text come from WHO (2005). IARC (1987) provides a different interpretation stating: “During mining and processing of bentonite in the USSR, mean total dust concentrations in 220 samples were found to vary from 4.6 to 749 mg/m³”.

¹⁹ Arguably some of the studies listed in Table 3 (Dehghan et al., 2009; Huvinen et al., 2002; Petrova, 2010) should also be eliminated using this criterion.

²⁰ We were unable to find published data on occupational or ambient exposures to mining dusts at Milos. There is evidence that occupational exposures to nuisance dusts have decreased over the years in some countries (Creely et al., 2007), but no data for Milos.

²¹ International Classification of Diseases, 9th Revision.

²² However, there are some specific exceptions. For example, the US FDA recently issued a warning for consumers about health risks of using a specific product “Bentonite Me Baby” out of concern that this bentonite product contained elevated lead levels, see http://www.fda.gov/Drugs/DrugSafety/ucm483838.htm accessed 1 August 2016.

²³ A condition in which the concentration of potassium in the blood is low.

²⁴ Both concentrations were higher than the prevailing OEL in China.