INTRODUCTION:

Yerba Mate (Ilex paraguariensis) is a native South American plant, commonly consumed in Argentina, Paraguay, Uruguay and southern Brazil. Both its leaves and branches are marketed; the former can be used for tonic drinks and stimulants made by hot infusion of eaves, such as “chimarrão”, or cold infusions, such as “tererê”. Yerba leaves are also used toasted for the preparation of “mate tea”, as well as pharmaceutical formulations (^{ALBAS et al., 2014}).

This plant has increasingly drawn the attention of the scientific community, since its beneficial effects are also associated with therapeutic effects, such as anti-oxidant, diuretic, stimulant, laxative and anti-rheumatic effects, as well as digestive properties (^{FILIP & FERRARO, 2003}; ^{SAIDELLES et al., 2010}). Conversely, the incidence of esophageal cancer is significant in areas where people consume yerba mate in the form of “chimarrão”.

Some studies suggested that the ingestion of yerba mate infusions at high temperatures, above 60ºC, is the only risk factor; while other support the hypothesis that the risk of cancer is associated with the level of certain substances present in the infusions that exhibit carcinogenic potential or potentiate the action of lesions caused by the frequent consumption of large volumes of “chimarrão”, whose average consumption per capita is 1.265L day^-1 in certain regions, reaching up to 6L day^-1 (^{BARROS et al., 2000}).

The International Agency for Research on Cancer (IARC) assessed the carcinogenic risk of mate and concluded that the yerba mate hot infusions act as a “probable carcinogen” to humans (Group 2A) and that the herb itself is non-classifiable as to its carcinogenicity to humans (Group 3) (^{IARC, 1991}). However, its carcinogenic, chemical and thermal mechanisms should be investigated (^{GOLDENBERG et al., 2003}; ^{ALBAS et al., 2014})

Recent investigations have detected the presence of metals in yerba mate, (^{VULCANO et al., 2008}; ^{SAIDELLES et al., 2010}). due to soil and water contamination by the use of fertilizers, agrochemicals, coal and oil combustion, vehicular emissions, mining, smelting, refining and incineration of urban and industrial waste. Regardless of their origin, metals are accumulated in all plant tissues and are, thus, introduced into the food chain (^{ERNST, 2002}; ^{SAIDELLES, et al., 2013}).

Many of these metals are considered essential for the development of plants, animals and humans, while others are potentially toxic, such as arsenic, cadmium and lead (^{SAIDELLES et al., 2010}). This toxicity depends mainly on the form of the metal and its concentration in the ingested foodstuff, although exposure period and frequency must also be considered.

When absorbed, arsenic is stored in the liver, kidneys, heart, and lungs. A small part remains in muscle and nervous tissues, and its accumulation has been associated with several diseases, such as cancer, diabetes, hepatotoxicity, neurotoxicity and cardiac dysfunction (^{SINGH et al, 2011}). Other symptoms of As intoxication include abdominal pain, vomiting, diarrhea, blood in urine, seizures, coma and death, which can be confused with diseases such as cholera and pneumonia (^{HUGHES, 2011}; ^{TELLEZ-PLAZA, 2012}).

Cadmium is widely absorbed and distributed throughout plants, present in leaves, fruits and seeds (^{MORAIS et al., 2012}). Cadmium intoxication is associated with the prevalence of hepatic, cardiovascular and central nervous system diseases, renal deficiency and breast cancer, hematological and immunological effects, as well as reproductive and embryonic developmental deficiencies (^{TELLEZ-PLAZA et al., 2012}).

Lead is the most common environmental contaminant, distributed throughout the planet in the form of salts, metal alloys and inorganic ions (^{POLETTI et al., 2014}). Food is the main source of exposure to lead, followed by water ingestion (^{MORAIS et al., 2012}). Lead has no biological function and is associated with chronic anemia due to inhibition of the enzyme that catalyzes an essential step in hemoglobin production (^{FRANCO et al., 2011}). Lead poisoning is also associated with nephrotoxicity and neurotoxicity, resulting in reduced central nervous system development, especially in children (^{MORAIS et al., 2012,}).

Recent reports of cadmium and lead contamination in mate have been of great concern to producers and beneficiaries, due to possible losses to the sector. The ANVISA Resolution RDC No. 42 of August 29, 2013, which internalizes the MERCOSUL Technical Regulation on Maximum Limits of Inorganic Contaminants in Food in Brazil, recommends the following maximum limits in teas, herbs and other vegetables used for infusions: Arsenic 0.6mg kg^-1, cadmium 0.4mg kg^-1 and for lead 0.6mg kg^-1.

In view of the growing market for natural products with functional properties and lack of quality standardization for these goods, including mate, studies on possible contamination by metals will contribute to product quality and safety, aiming to add values to the domestic and international markets. In view of this, it is imperative to control the quality of plants used for medicinal and nutritional purposes, such as yerba mate. In this context, the aim of the present study was to determine and compare arsenic, cadmium and lead concentrations in Ilex paraguariensis samples marketed and consumed in the Southern region of Brazil, in the states of Paraná (PR), Santa Catarina and Rio Grande do Sul (RS). In order to evaluate the possible danger of ingestion, infusions prepared with the analyzed samples were also evaluated.

MATERIALS AND METHODS:

Yerba mate samples were collected by the State Sanitary Surveillance Secretaries in commercial establishments located in different cities in the states of Paraná, Santa Catarina and Rio Grande do Sul.

Inclusion criterion concerned 106 brands actually and registered in the labor unions of RS, SC and PR. A total of 104 samples representing 73 different brands were sent for analyses: 77 (49 brands) from RS, 11 (8 brands) from SC and 16 (16 brands) from PR. The chemical analyses were carried out in the Inorganic Elements Sector of the Chemistry Department of the National Institute of Quality Control in Health (INCQS), at the Oswaldo Cruz Foundation (FIOCRUZ).

Samples were homogenized, ground in an industrial type crusher and stored in suitable containers. Approximately 0.5g of each sample, in duplicate, were weighed into Teflon tubes and 2mL of deionized water (Millipore, Brazil) were added, along with 2mL of supercritical nitric acid (Merck, Germany) and 2mL of hydrogen peroxide (Merck, Germany). Samples were then digested in a high pressure closed system in a SpeedWave microwave (Berghof, Germany). After cooling, the sample solutions were transferred to 25mL volumetric flasks and completed with ultrapure water.

RESULTS AND DISCUSSION:

Table 2 displays the As, Cd and Pb concentrations in the mate samples obtained from the three southern Brazilian states. Results were analyzed using descriptive statistic techniques (means, standard deviation and median).

The differences in the metal concentrations from the different states may be associated with different soil chemical characteristics of each state, as well as plant genetics and age (^{SAIDELLES et al., 2010}). As concentrations present in the yerba mate samples ranged from 0.015 to 0.114mg kg^-1. Thus, 100% of the samples displayed As levels below the maximum limit allowed by the current Brazilian legislation, of 0.6mg kg^-1.

The lowest Pb concentration was 0.10mg kg^-1, and the highest, 1.20mg kg^-1, with 7% of the samples presenting values above the maximum permitted limit of 0.6mg kg^-1. The highest levels of Pb contamination were observed in samples from RS, five samples, followed by PR, three samples, and SC, in which no samples exhibited Pb concentrations above the maximum permissible limit. A comparative analysis (ANOVA) of the Pb means from the samples originated from the different Brazilian states indicated that SC presented significantly different means from RS and PR. In the study by ^{SAIDELLES et al. (2010}), Pb concentrations in yerba mate were <0.3mg kg^-1, a result comparable to the results reported herein. The mean Pb concentrations in virgin and fertilized soil in the Rio Grande do Sul region have been reported as ranging from 8.23 to 16.38mg kg^-1, respectively, while soil samples from SC and PR showed no variation between soil types and Pb concentrations ranged from 16.38 to 34.20mg kg^-1 (POLLETI et al., 2014). Establishment of a direct relationship between Pb levels in soils reported by POLLETTI et al. (2014) and those reported herein was not possible, and statistical similarities were reported only between RS and PR.

Cd concentrations in the 104 analyzed samples ranged from 0.18 to 1.25mg kg^-1, with 74% of the total samples exhibiting Cd levels above the maximum permissible limit allowed by the Brazilian legislation, of 0.4mg kg^-1. When separated per state, 84% of the Rio Grande Sul samples, 63% of the SC samples and 75% of the PR samples were above this limit. The mean Cd concentrations in the samples from the three studied states were not statistically different by an ANOVA test. ^{SAIDELLES et al. (2010}) observed Cd concentrations in yerba mate ranging from 0.35 to 1.21mg kg^-1, consistent with the results reported herein, while the Cd values reported by POLLETI et al. (2014) in soil samples from RS, SC and PR varied between 1.76 and 3.53mg kg^-1.

The observed Cd concentrations in yerba mate were the same or above the observed Pb concentrations, suggesting that Cd bioavailability in Ilex paraguariensis is much higher than Pb bioavailability in the cultivation conditions where the samples were grown, leading to higher Cd absorption from the soil. This assumption is based on the results reported by POLLETI et al. (2014), in which mean Cd concentrations of in the soil is lower than that of Pb and would result in a plant/soil ratio 20% for Cd and less than 5% for Pb.

The maximum limit recommended by the ANVISA for Cd in yerba mate is four times higher than the limit recommended by the European Pharmacopoeias, of 0.1mg kg^-1 for leaves, fruits and vegetable roots (^{DUGO, et al., 2004}). If the international limit were to be considered, 100% of the 104 samples analyzed in the present study would present unsatisfactory results, resulting in problems regarding product marketing and export.

With regard to the infusions, the mean values of Cd, Pb and As in the supernatants 1 and 2 were not significantly different (P>0.05) after a comparative analysis by an ANOVA test. Comparing total sample decomposition with the infusions, Cd and Pb were extracted at approximately 10% and 5%, respectively. It was not possible to quantify how much As was extracted, since the metal was present in the infusions at concentrations lower than the method limit of quantification.

CONCLUSION:

This study was developed with the aim of providing information and subsidizing discussions on arsenic, cadmium and lead concentrations in different yerba matte samples from southern Brazil. About 80% of the different brands and types of herbs studied were unfit for consumption, due to the high levels of lead and cadmium present, although arsenic concentrations were within the required standards in all samples.

With regard to the metal concentrations in the infusions prepared with the contaminated yerba mate samples, Cd and Pb levels were higher in the first infusion, decreasing in the second and in the following infusions, containing a maximum of 10% of the total metal concentrations reported in the in natura herbs. Thus, this research indicated that the yerba mate used in the form of hot infusions in Southern Brazilian states exhibits low metal concentrations and more studies are needed to elucidate the risk probability related to consumption of this infusions.

In addition, this research can help the competent organs in an evaluation of the maximum permitted value for these products in the yerba mate and the infusion, since the “chimarrão” is a product that possesses innumerable medicinal properties, generates thousands of direct and indirect jobs and is a symbol of the tradition and of country south culture.