Assessment of heavy metal content in peloids from some Cuban spas using X-ray fluorescence

Estimación del contenido de metales pesados en peloides provenientes de varios balnearios cubanos mediante Fluorescencia de rayos X                                  

Oscar Díaz Rizo1¹, Margaret Suárez Muñoz¹, Patricia González Hernández², Alina Gelen Rudnikas¹, Katia D´Alessandro Rodríguez¹, Clara M. Melián Rodríguez¹, Alberto Pérez Martín¹, Juan R. Fagundo Castillo², Nadia V. Martínez-Villegas³

¹ Instituto Superior de Tecnologías y Ciencias Aplicadas (InSTEC), Ave. Salvador Allende y Luaces, Habana 10600, Cuba.
² Facultad de Química, Universidad de La Habana, Zanja esq. a G, Habana 10600, Cuba
³ Departamento de Geociencias Aplicadas. Instituto de Investigaciones Científicas y Tecnológicas, San Juan Potosí, México

ABSTRACT

Heavy metal (Co, Ni, Cu, Zn and Pb) content in muds from some Cuban spas (San Diego, Elguea, Santa Lucía and Cajío) have been studied using X-ray fluorescence. The measured metal contents are in the same order of magnitude as those reported for average Earth’s upper crust average shales and muds as well as with worldwide reported peloids. The comparison with sediment quality guidelines (SQGs) shows a different degree of pollution for peloids from each studied spa. Nevertheless, the estimated sum of metal/probable effect level value ratios (0.9 – 2.4) correspond to a low potential acute toxicity of contaminants. Therefore, the heavy metal content present in peloids from the studied Cuban spas is not an obstacle for its use with therapeutic purposes.

Key words: sediment, x-ray fluorescence analysis, heavy metals, Cuba, therapeutic uses.

RESUMEN

Se estudia mediante la técnica de Fluorescencia de rayos X, el contenido de metales pesados (Co, Ni, Cu, Zn y Pb) en lodos terapéuticos provenientes de varios balnearios cubanos (San Diego, Elguea, Santa Lucía y Cajío). Los contenidos de metales pesados determinados en los lodos terapéuticos se encuentran en el mismo orden que los reportados para lodos y esquistos representativos de la corteza terrestre, así como para lodos utilizados en balnearios internacionalmente. La comparación con las Guías de Calidad de sedimentos muestran diferentes grados de polución para los lodos de cada balneario. Independientemente de ello, los valores de las razones suma de metales/nivel de efecto probable (0,9-2,4) corresponden a un bajo potencial agudo de toxicidad por contaminantes. De esta manera, el contenido de metales pesados presentes en los lodos de los balnearios estudiados no representa impedimento alguno para su uso con fines terapéuticos.

Palabras claves: sedimentos, analisis por fluorescencia de rayos x, metales pesados, Cuba, usos terapéuticos.

Introduction

In Cuba, mud application in pelotherapy use started at the end of the 19th century. The reference peloid user in Cuba is the San Diego de los Baños Thermal Center, located in the Western Cuban province of Pinar del Río. The peloid used there is a mud extracted directly from the estuary of San Diego River, and enriched later with inorganic and organic components, as well as with the microbiota of calcic sulfated, fluoric, radionic and sulfurous mesothermal waters (33 ºC) of San Diego de los Baños Thermal Center. These waters, show low oxidation-reduction (Eh) potential values (-226 to -270 mV) and their electric conductivity (EC) values oscillate between 1 480 and 2 200 µS/cm [8]. The maturation process of the sediment is done using a static, open method during 15 days, and under environmental conditions. The gray peloid produced in this way (with high content in clays, and the presence of quartz, and Fe minerals) is classified as a clayed slime by Peláez [9], but according to the organic matter content can be classified as fangi or mud [8]. The peloid is routinely used to palliate inflammatory and dermatological processes, as an analgesic, in male and female infertility treatments, and in cosmetic products. The San Diego raw (non-maturated) mud was recently studied to assess the heavy metal content [10], showing that those are not an obstacle for its use in medical purposes. The rest of the Cuban spas use the so-called “natural” maturated peloids, i.e. muds taken directly from thermal or sulphated water sources.

The peloid used in Elguea is dark gray. Elguea's waters are also hyperthermal (51 ºC), calcic sulfated, magnesic, sulfurous ( 10 mg/L), brominated and radioactive-radonic [11]. This peloid may be classified as fangi or mud, due to strong mineral composition and hydrothermal origin and the predominantly phases are composed by clay, carbonates and halite. The great tradition and experience of Elguea Thermal Center is aimed at using  its waters and peloids in the treatment of different inflammatory and dermatological processes, both as analgesic and as a cosmetic.

In Santa Lucía, the original sediment is extracted directly from El Real salt pond deposit and later enriched with the sodium chlorine hypersaline waters (mineralization of almost 250 g/l) of the salt pond. The obtained dark gray peloid can be classified as sulfurous slime and the predominantly phases are composed by gypsum, carbonates and halite. The main uses of this peloid are related with psoriasis, acne, mycosis, seborrheic dermatitis, degenerative osteoarthritis and rheumatoid arthritis [12].

On the other hand, the Cajío original sediment is extracted directly from the coastal deposit. This gray mud is classified as sulfurous slime and is formed by the waters with mineralization of 39,5 g/l of the Batabano Gulf. These waters show Eh values of approximately 150 mV and their EC value is approximately of 49 700 μSm [13]. The peloid has sandy particles with poor development of clayed phases and high content of organic matter and carbonates. It is used in pathologies of SOMA, arthritis, dermatological diseases (psoriasis), among others.

The aim of the present study is to determine heavy metal contents (Co, Ni, Cu, Zn and Pb) in maturated peloids used in different Cuban spas, to assess the potential pollution and radiological risks for the users of peloid therapeutic practices.

Materials and methods

Five replicas were collected in each of the four main peloid-users spas in Cuba, located in four different Cuban provinces (see Figure 1). Samples for non-natural maturated peloids were taken from the San Diego spa, while those of natural maturated peloids were taken from spas in Elguea, Santa Lucía and Cajío. Every sample used in this study was dried at 60 oC. Large rock debris, mollusk skeletons and organic debris were removed before sieving. The fraction, smaller than 1 mm, was ground into a fine powder (<63 mm) in an agate mortar. The pulverized samples were newly dried at 60 ºC until obtaining a constant weight.

Heavy metal concentrations were determined by external standard method of X-Ray Fluorescence Analysis (XRF) using the Certified Reference Materials (CRM) IAEA-SL-1 “Lake Sediment”, IAEA-Soil-5, IAEA Soil-7, BCR-2 “Basalt Columbia River” and BCSS-1 “Marine sediment” as standards. All samples and CRM were mixed with cellulose (analytical quality) in proportion 4:1 and pressed at 15 tons into the pellets of 25 mm diameter and 4 - 5 mm height. Pellets were studied using Canberra Si(Li) detector (150 eV energy resolution at 5,9 keV, Be window thickness = 12,0 mm) coupled to a multi channel analyzer. A (1,1 GBq) excitation source with ring geometry was used. All spectra were processed with WinAxil code [14]. Detection Limits were determined according to Padilla et al. [15] (in concentration units) as LD = 3/mt, where m is the sensibility in per concentration unit,   is the standard deviation of the area of the background windows (peak window at 1,17 times the FWHM) and t is the measuring time (4 hours).

The accuracy was evaluated using the SR criterion, proposed by McFarrell et al. [16]:

where is the experimentally determined concentration value, is the certified concentration value and s is the standard deviation of . On the basis of this criterion the similarity between the certified value and the analytical data obtained by proposed methods is divided into three categories: SR 25 % = excellent; 25 < SR 50 % = acceptable, SR > 50 % = unacceptable. The analysis of five replica of the CRM IAEA-356 “Polluted Marine Sediment” [17] is presented in Table 1. All heavy metals determined by XRF analysis, using the external standard method [17], qualify as “excellent” (SR 25 %) and the obtained results show a very good correlation (R = 0.999) between the certified and measured values.

Numerical sediment quality guidelines (SQGs) have been used worldwide for both freshwater and marine ecosystems, and to identify contaminants of concern in aquatic ecosystems as well [19]. SQGs have been developed for many potentially toxic substances (i.e., trace elements, chlorinated organics, and polynuclear aromatic hydrocarbons). SQGs were applied to this study for the assessment of the ecotoxicological sense of metal concentrations in peloids with the threshold effect level (TEL) and probable effect level (PEL) values.

Results and discussion

The average concentrations of heavy metals determined by XRF analysis in peloid samples from the studied Cuban spas are shown in Table 2, along with the concentrations of the elements under consideration in representative shales and muds [20]. The metal content ratios determined for peloid and raw healing mud [10] from San Diego spa were 0,4 for Co, 0,7 Ni, 0,6 for Cu, 1,0 for Zn and 0,7 for Pb, confirming that peloid maturation processes do not change the heavy metal content present in the raw mud, as it was also shown by Tateo and Summa [5].

The levels of the toxic metals examined in the Cuban spas peloids are, in general, in the same order of magnitude as those previously reported for average shales, Argillaceous sediments and muds [20, 21]. From a geochemical standpoint, the level of individual elements in shales and muds can be considered as a good approximation to the specific element in Earth’s upper crust. In terms of potential toxicity of the Cuban spas peloids, it is important to note that none of the values of toxic element levels documented in the studied peloids are significantly higher than the terrestrial background values [20]. The only exception is the Cu content in Santa Lucía peloid, since the geochemical values are exceeded by 1,8 – 3,6 folds. On the other hand, except for Ni content in Elguea spa, the metal contents in the studied peloids are in the range of the concentration limits established by the U.S. Pharmacopeia [29] and the European Medicines Agency EMEA [30] for pharmaceutical formulations and cosmetics (see Table 2). The mentioned regulations were proposed by Quintela et al [28] for peloid chemical composition, considering that both pharmaceutical products and cosmetics have similarities with peloids. On the other hand, the comparison with metal contents reported worldwide for peloids (natural and commercial) used for different medical purposes, show that heavy metal concentrations in Cuban peloids are also in the same concentration ranges.

The comparison with SQGs values (Table 2), show that Ni contents in peloids from San Diego and Elguea are above Ni PEL value, while Cu content on peloids from Santa Lucía is above the Cu TEL value. Furthermore, the potential acute toxicity of contaminants in peloid samples could be estimated as the sum of the toxic units (ΣTUs), which is defined as the ratio of the determined concentration to PEL value [31]. A ΣTUs value larger than the number of studied metals, indicate the potential toxicity by metal content in the peloid sample. The estimated ΣTUs values (Figure 2), based on concentrations of Ni, Cu, Zn and Pb, are lower than 4 for all of the sampling spas, with the highest value obtained for peloids from Elguea spa (ΣTUs = 2,4) and the lowest (ΣTUs = 0,9) for Cajío’s.

Cuban regulations do not specify a maximum allowable limit for heavy metal content in peloids. However, according to the obtained results in the present study and its comparison with existing and in force international regulations, we can conclude that the heavy metal content determined in peloids from studied Cuban spas is not an obstacle for its use with therapeutic purposes.

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Recibido: 17 de octubre de 2016
Aceptado: 31 de enero de 2017