Introduction

Clays and health: An introduction

“Clays are thematerials for ceramics production” is thegeneral idea of people about clays. However, clayminerals are not only the “most abundant componentsof the surface mineral world” (Velde, 1995) but are theminerals showing the greatest diversity of reactions.Hundreds of uses reveal the utility of clays in verydifferent fields (Odom, 1984; Jepson, 1984; Murray,1986; Kühnel, 1990; Konta, 1995;Murray, 1999;Murray,2000; Konta, 2000; Murray, 2003; Murray and Kogel,2005; Adams and McCabe, 2006; Harvey and Lagaly,2006; Ruiz-Hitzky and Van Meerbeek, 2006).

During the last decade the properties of claysbeneficial to human health received great interestalthough therapeutic effects of clays were used sinceprehistoric times (Carretero, 2002; Carretero et al.,2006; Gomes and Pereira Silva, 2006). Presently, clayminerals are applied in spa and beauty therapy(pelotherapy), as well as in pharmaceutical and clinicalapplications (Carretero, 2002; Carretero et al., 2006;Droy-Lefaix and Tateo, 2006; Gomes and Pereira Silva,2006). We should not ignore that harmful effects ofsome clay minerals on human health were also knownfor centuries (Carretero et al., 2006).

This special issue is devoted to different aspects ofclays and health. It is opened by a review on thebeneficial and harmful effects of minerals in general andclay minerals by Gomes and Pereira Silva (2007-thisissue): Minerals and clay minerals in medical geology.

In the first section are reported the many applicationsof clay minerals in pharmacy and cosmetics indicatingthe broad variety of these materials as active principles,adsorbents, excipients, for drug delivery and in retardformulations: Use of clays as drug delivery systems:possibilities and limitations by Aguzzi et al. (2007-thisissue), Uses of clay minerals in semisolid health careand therapeutic products by Viseras et al. (2007-thisissue), Compositional, technical and safety specifica-tions of clays to be used as pharmaceutical and cosmetic

products by López-Galindo et al. (2007-this issue).Clay-based formulations for topical applications inbalneotherapy are also described in the review byGomes and Pereira Silva (2007-this issue). The mobilityof chemical elements from healing clays to the humanbody during topical applications and ingestion is dis-cussed by Tateo and Summa (2007-this issue): Elementmobility in clays for healing use. Examples of beneficialclay mineral–organic interactions are reported byBonina et al. (2007-this issue): Adsorption of salicylicacid on bentonite and kaolin and release experimentsand by Damonte et al. (2007-this issue): Some aspects ofglyphosphate adsorption on montmorillonite and itscalcined form. We add the remark that some specialclays are used in shampoos (Mahjoory, 1996). Anexample of the beneficial uses of zeolites is reported byBonferoni et al. (2007-this issue): Zn2+-exchangedclinoptilolite-rich rock as active carrier for antibioticsan anti-acne topical therapy. In-vitro characterizationand preliminary formulation studies.

Another group of layered compounds which providebeneficial effects on human health are the layereddouble hydroxides (LDHs, sometimes called “anionicclays”) (Forano et al., 2006). The review Layereddouble hydroxides and human health, an overview ispresented by del Hoyo (2007-this issue). Choy et al.(2007-this issue) refer to Clay minerals and layereddouble hydroxides for novel biological applications.del Arco et al. (2007-this issue) report on intercalation ofanti-inflammatory agents into LDHs: Intercalation ofmefenamics and meclofenamic acid anions in hydro-talcite-like matrixes.

The section on “Clays in pelotherapy” refers to thetherapeutic effects of clays and clay minerals used aspeloids. The term ‘peloid’ (accepted by the InternationalSociety of Medical Hydrology in 1949) refers todifferent kinds of sediments or deposits which includemainly silicates (clays, micas, feldspars, etc.) but also

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carbonates, sulfates, sulfides, and variable amountsof organic substances. Mixed with different sea or salt-lake mineral waters peloids form pastes or poulticesfor essentially therapeutic uses (Legido et al., 2007-this issue).

The section “Clays in pelotherapy” contains thepapers: Thermal muds: perspectives of innovations byVeniale et al. (2007-this issue), Comparative study ofthe cooling rates of bentonite, sepiolite and commonclays for their use in pelotherapy by Legido et al. (2007-this issue), Comparison of saponite and montmorillonitebehavior during static and stirring maturation withsee water for pelotherapy by Carretero et al. (2007-this issue).

The beneficial effects of clay minerals on humanhealth are not restricted to therapies and uses in pharmacyand cosmetics. Clays and clay minerals became importantmaterials in environmental technology to protect ourenvironment against harmful substances (Nir et al., 2006;Churchman et al., 2006). Contributions considering thisaspect are collected in section IV of this issue. One im-portant process is the removal of organic pollutants fromwater by modified clay minerals, described by Zadakaet al. (2007-this issue): Application of modified silicatemineral adsorbents for removal of organic pollutantsfrom water: Comparison with activated carbon and byRytwo et al. (2007-this issue): Use of CV- and TPP-montmorillonite for the removal of priority pollutantsfrom water. Retention of pollutant gases: Comparisonof clay minerals and their modified products is reportedby Volzone (2007-this issue). An example of verytoxic natural compounds, carcinogens for humans andanimals, are mycotoxins. They are found in grains andother food crops infested by Aspergillus fungi. Studies ofJaynes et al. (2007-this issue) on Aflatoxin B1 adsorptionon clays from water and corn meal reveal the utility ofclayminerals, especiallymontmorillonite and sepiolite, toreduce the risk of aflatoxin intoxination (aflatoxicosis).

Many papers deal with the distribution of toxicelements from geological sources (Selinus et al., 2005;Velde, 1995). The studies of Bertolino et al. (2007-thisissue) on Mineralogy and geochemistry of bottomsediments from water reservoirs in the vicinity ofCórdoba, Argentina: environmental and health con-straints reveal alarming concentrations of trace metals(U, W, As) although the sediments are not preferentialstorage sites for these elements. Water, sediments,and flora from this area should not be used for humanpurposes until contamination sources and the localdrainage systems have been evaluated. This contributionrepresents an example that careful geological studies areessential to avoid problematic ecological situations.

In conclusion, this special issue reports the state of art inusing clays, clay minerals, and layered double hydroxidesin therapy, pharmacy, and cosmetics as well as for en-vironment protection. The contributions may also providea first entry into this unique field of clay science.

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2 Introduction

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Maria Isabel Carretero*Dpto. Cristalografía, Mineralogía y Química Agrícola,

Facultad de Química, Universidad de Sevilla,Apdo. 553, 41071 Sevilla, Spain

E-mail address: carre@us.es.! Corresponding author.

Gerhard LagalyInstitut für Anorganische Chemie,

Christian-Albrechts-Universität zu Kiel,D-24098 Kiel, Germany

E-mail address: lagaly@ac.uni-kiel.de.

3Introduction