Universidade Federal de Santa Maria
Ci. e Nat., Santa Maria v.42, e51, 2020
DOI:10.5902/2179460X22316
ISSN 2179-460X
Received 19/05/20 Accepted: 19/05/20 Published:13/08/20
Chemistry
Chemical parameters of gourmet salts compared withsalt extracted from eichhornia crassipes evaluated by energy-dispersive x-ray spectrometry
Estudo dos parâmetros químicos de sais gourmets quando comparados com sal extraído da Eichhornia crassipes avaliados por espectrometria de raios-X por dispersão em energia
Paulo Afonso RossinoliI
Frederico Fonseca da SilvaII
Wilson Sacchi PeternellaIII
I Biologist, Professor and Researcher at Federal University of Mato Grosso, Brasil. PhD in Health and the Environment. parossi@terra.com.br
II Agricultural Engineer, Professor and Researcher at Federal Institute of Parana, Curitiba Campus, Brasil. PhD in Irrigation and the Environment. prof.frederico.silva@gmail.com
III Chemist, Professor and Researcher at Federal University of Rondonia, Brasil. Department of Chemistry, Porto VelhoCampus. PhD in Nano materials. wpeternella@yahoo.com
ABSTRACT
Salts have been part of human nutrition since 2,000 b.C., having originated in the Zhongba region, in China. Itssubstantial availability in food markets and stores specialized in condiments led us, curiously, to compare its elemental chemical composition with that of salt extracted from a floating aquatic macrophyte, known commonly as “water hyacinth” (Eichhornia crassipes), whose product, after extraction from dry matter, was popularly denominated“indigenous salt”. The objective of the present study was to evaluate the chemical composition of gourmet salts in comparison with indigenous salt using the energy-dispersive X-ray spectrometry (EDX) technique. Eichhornia crassipes exhibited higher concentrations of chloride (35.834%), potassium (62.146%), sulfur (1.095%), calcium (0.450%), bromine (0.177%), silicon (0.124%), copper (0.029%), magnesium (0.123%), and rubidium (0.023%) than the gourmet salts. Our results indicate that this indigenous salt should be consumed under medical guidance due to its high concentration of potassium chloride, a salt whose properties are used for specific human treatment and not daily consumption.
Keywords: Gourmet salts; Eichhornia crassipes; Chemical Composition; EDX
RESUMO
Os sais fazem parte da alimentação humana desde os anos 2.000 a.C., originando-se inicialmente na região de Zhongba, na China. Em função da quantidade e disposição em mercados alimentícios e lojas especializadas em condimentos, levou-se assim, curiosamente, ao estudo de sua composição química elementar em comparação com um sal extraído de uma macrófita aquática flutuante conhecida como “aguapé” (Eichhornia crassipes), cujo produto após extração a partir da matéria seca denominou-se popularmente de “Sal indígena”. O objetivo do presenteestudo foi de avaliar a composição química dos sais gourmets em comparação com este sal indígena utilizando a técnica de espectrometria de raios-X por dispersão em energia (EDX). A Eichhornia crassipes apresentou maiores conteúdos de cloreto (35,834%), potássio (62,146%), enxofre (1,095%), cálcio (0,450%), bromo (0,177%) silício (0,124%), cobre (0,029%), magnésio (0,123%) e rubídio (0,023%) quando comparada ao sal gourmet. Os resultados obtidos indicam queo sal indígena deve ser consumido sob orientação médica em função de sua elevada concentração de cloreto de potássio, um sal com propriedades específicas para tratamento humano e não para consumo diário.
Palavras-chave: Sal gourmet, Eichhornia crassipes, Composição Química, EDX
1INTRODUCTION
Historically, there is evidence of salt production and transport in Asia since at least 2,000 b.C. in the Zhongba region in China, as stated by Zhu (2005).
At the beginning of the 21st century, the dietary norms of several countries recommendedthe daily ingestion of 6.0 grams of salt per individual, an amount that can be easily exceeded without a balanced diet (Dahl, 1958). Meanwhile, the World Health Organization recommends that adults consume less than 2,000 mg of sodium, equivalent to 5.0 grams of salt per day (WHO, 2016).
Selmera and Kristiansen (2000) claimed that the majority of the population believes that the salt found in food causes health problems and, thus, tends to reduceits consumption. As a consequence, their demand decreases, not only for salt but also for salt-preserved products.
Currently, the salt sold in Brazil continues to be produced, as established by the National Health Surveillance Agency (ANVISA), under Resolution RDC #23 of 04/24/2013 (BRASIL, 2013). The concentration of iodine is requiredto range between 15 and 45 mg/Kg of the product.
Gourmet salts vary considerably in flavor, chemical composition, and color. There is significant variability in the types of gourmet salts depending on their location of extraction, production, and, consequently, chemical composition.
Considering the vast number of gourmet salts available for consumption, it should be noted that each salt has a unique characteristic, such as sodium content or any other chemical specificity, thus contributing to the well-being of the digestive tract. Therefore, there is a need to chemically evaluate these compounds to complement the data present in the literature.
The aim ofthe presentstudywas to compare the chemical composition of different types of gourmet salts and the salt obtained from the floating aquatic macrophyte Eichhornia crassipes, also known as “water hyacinth”, whose final product is the well-known “indigenous salt”.
2 THEORETICAL REFERENCES
The U.S. Food and Drug Administration (FDA, 2016) classifies salts into: i) table salt; ii) sea salt; iii) kosher salt; and, iv) rock salt, three of which are primarily for human consumption. The agency requires that their composition be of 97.5% NaCl (sodium chloride) and 2.5% other minerals, that is, chemical compounds generated in the production process.
Currently, several types of salts can be found in food markets and storesspecialized in condiment products, including: 1) Table salt or refined salt(400mg of sodium/g of salt) (MOTA, n.d.), which can be iodinated or not, iodine being added in cases of hyperthyroidism or goiter (KNOBEL and MEDEIROS-NETO, 2004); 2) Hypo-sodium or lite salt (197 mg of sodium/g of salt), which, according to Anvisa (ANVISA, 2000), is made from mixtures of salts, whose maximum sodium content is 50%, in the same amount of NaCl. The consumption of this low-sodium salt should be overseen by a doctor or nutritionist; 3) Liquid salt (110 mg of sodium/g of salt), obtained by dissolving high-purity salt without additives in mineral water, is used in all foods, without changing their characteristics (MOLINA et al., 2003); 4) Sea salt (420 mg of sodium/g of salt), which is obtained by the evaporation of evaporation ponds, thus preserving its mineral content (SILVA, 2007); 5) Pink Himalayan salt (230 mg of sodium/g of salt), which contains more than 80 minerals, such as calcium, magnesium, potassium, copper, and iron (ELPAIS, 2018); 6) Black salt (380 mg of sodium/g of salt), also known as “Kala Namak”, which is extracted in central India in natural reserves. In addition to its dark pinkish-gray color, this salt contains sulfuric compounds, iron, and other micronutrients (CARREIRA, 2014); 7) Kosher salt,a coarse salt processed into smaller, non-iodized crystals (BAAS-BECKING, 1931), and 8) Rock salt, a coarse salt that still contains inedible impurities. It is produced in three ways: from underground mining in “salt mines”, solution mining, or solar evaporation (SILVA et al., 2000).
Some indigenous peoples manufacture salt in small quantities from the ashes of the floating aquatic macrophyte[1] Eichhornia crassipes, commonly known as “water hyacinth” (MELATTI, 1993).
According to Reis (2012), who studied the chemical composition of Eichhornia crassipes from the Almada river in Bahia, Brazil, macrophytes have high phenotypic plasticity, with the ability to rapidly increase in biomass as a function of the environment due tothe high levels ofnitrogen and phosphorus, but with adaptations that enable development even in oligotrophic environments[2]. The author analyzed some chemical parameters after harvest in February 2012, and their variations regarding dry matter (DM) were as follows: a) Organic matter (83.30 to 87.70% DM); b) Ashes (12.30 to 16.70% DM); c) Carbon (24.90 to 37.70% DM); d) Nitrogen (0.88 to 2.36% DM); e) Crude protein (5.50 to 14.75% DM), and f) Phosphorus (0.03 to 0.10% DM).
Henry-Silva and Camargo (2006), who evaluatedthe chemical composition of floating aquatic macrophytes used in agricultural effluent treatment, found that the contents were similar to those reported by Reis (2012): a) Mineral matter (17.09%); b) Nitrogen (2.0%); c) Crude protein (12.45%), and d) Phosphorus (0.26%).
The floating aquatic macrophyte Eichhornia crassipes is a monocot that belongs to the family Pontederiaceae, a small family with wide pantropical distribution, including approximately 10 genera and around 30 species. In Brazil, 5 genera and about 20 species have been reported, according to Hoehne (1979) and Souza and Lorenzi (2005).
Currently, the most used techniques in the evaluation of these inorganic chemical compounds includeAtomic Absorption Spectrometry (AAS), Inductively Coupled Plasma – Atomic Emission Spectrometry (ICP-AES), Optical Emission Spectrometry (OES), X-Ray Diffraction (XRD), and X-Ray Fluorescence (XRF). Although thelatter two have the same principle, that is, use an X-ray source, directly affecting the sample, several phenomena occur,leading to the attenuation of the X-ray beam, both by absorption and by scattering (SOUSA, 2011).
Thus, according to Albers et al. (2002), for a more specific chemical evaluation, the XRD technique qualitativelydetermines which crystalline species is present in a given sample, such as Halite (mineral NaCl), for example, using the most intense and characteristic Muller indices of each inorganic chemical species. While the EDX technique provides quantitative information on sample content (X% Na and Y% Cl) by comparison with appropriate standards (PINTO, 2013), the quantification of species by XRD is difficult to obtain due to the height of the peaks, which depend not only on quantity but also the degree of crystallinity of the sample.
Energy-Dispersive X-ray spectrometry (EDX) is the most widely used analytical technique for the elemental characterization of inorganic samples. More specifically, the method is based on the irradiationof a sample by an X-ray beam, in which the atoms present in the sample generate characteristic rays, known as “fluorescent” X-rays, that have specific wavelengths and energy that are unique regarding each chemical element. Qualitative analysis can be done by investigating the X-ray wavelengths, whereas quantitative analysis assesses the number of X-rays exhibiting the specific wavelength of each chemical element, since the intensity of fluorescent X-rays is a function of the chemical concentration of the species in the sample (PARREIRA, 2006).
3 MATERIAL AND METHODS
Samples of gourmet salts were purchasedfrom different commercial establishments, such as supermarkets and stores specialized in condiment products. The sample of indigenous salt was obtained from the floating aquatic macrophyte known as “water hyacinth” (Eichhornia crassipes), which, after harvesting, was washed, dried, and burned. The plant wasidentified and collected in an Aweti village, in Xingu Park, located in northern of state Mato Grosso, Brazil.
After burning, the ashes were dissolved in water and filtered to remove impurities. Following filtration, the residual saline solution was evaporated, producing salt with high KCl content, that is, potassium chloride.
The samples, shown in Table 1, were analyzed by energy-dispersive X-ray spectrometry (EDX), using a Shimadzu 7000 device.
Table 1. List of samples and photos with the respective masses used for quantification
|
Sample number |
Sample name |
Sample photo |
Sample mass (g) |
|
1 |
Indigenous Salt (Brazil) |
|
4.38 |
|
2 |
Black Salt (South Africa) |
|
4.39 |
|
3 |
Himalayan Black Salt (Pakistan) |
|
4.36 |
|
4 |
Himalayan Halite Salt (Pakistan) |
|
4.33 |
|
5 |
Persian Blue Salt (Iran) |
|
4.33 |
|
6 |
White salt (India) |
|
4.36 |
|
7 |
Sicilian white salt (Italy) |
|
4.34 |
|
8 |
HawaiianBlack Salt (United States) |
|
4.33 |
|
9 |
Desert Salt (South Africa) |
|
4.34 |
|
10 |
PinkHimalayan Salt (Pakistan) |
|
4.35 |
|
11 |
Salt Flower (France) |
|
4.34 |
|
12 |
Maldon salt (England) |
|
4.34 |
Source: The authors
In order to determine the chemical species present in the salts, a collimator was used to select a circular region measuring 10mm in diameter. The excitation and detection of the characteristic rays were conductedin an air atmosphere, under low pressure, quantifying the chemical elements in the Al-U range (electrical voltage and current of 50kV and 17µA, respectively) and Na-Sc (15kV of electrical voltage and electric current of 310µA).
The equipment was calibrated to quantify the macro elements Cl and Na since they represent more than 80-90% of the samples’ mineral content.
The measurement time was between 3 and 4 minutes, including the live time and dead time (adjusted from 10 to 20%) for each sample.
The EDX spectra was obtained using samples in natura, standardizing the masses to 4.3X, numbered from 1 to 12.
4 RESULTS AND DISCUSSION
The analyzed samples of gourmet salts were quantified in their mineral portions, and the results show the percentage of each chemical element detected. They were divided by region for better visualization and interpretation, that is, in salts of easternorigin (Table 2) and of western origin (Table 3).
Elements that went undetectedin the samples may have been present at quantities below the equipment’s detection limit or may not have been present at all.
The Energy dispersive X-ray fluorescence (EDXRF) quantification of indigenous salt, shown in Figure 1, revealed high levels of chloride (35.834%) and potassium (62.146%), followed by sulfur (1.095%), calcium (0.450%), and other chemical elements in smaller quantities, such as bromine (0.177%), silicon (0.124%), magnesium (0.123%), copper (0.029%), and rubidium (0.023%).
Figure 1. Measurement and quantification conditions of Indigenous Salt (Brazil)by EDX
Source: The authors
Since this evaluation technique is multi-elementary, the chemical elements may have been forming combinations of distinct types of salts from their different negative ions (Cl-, S2-, Br-) and positive ions (K+, Ca2+, Si4+, Cu2+, Mg2+, Rb+), such as a) Potassium Chloride (KCl); b) Calcium Chloride (CaCl2); c) Magnesium chloride (MgCl2), and so on.
Another point that deserves attentionwas the absence of the element Iron (Fe) in the sample, an essential macronutrient inplant development.According to Henry-Silva and Camargo (2006) and Branco (1986), who analyzed the chemical properties of Eichhornia crassipes, the enrichment of waters with nitrogen and phosphorus may cause iron content to become limited.
The absence of iron in the sample can be explaineddue to its possible precipitation during the solubilization process of the ash, rendering the medium basic. In other words, the element (Fe) in alkaline medium precipitates in the form of iron oxide and hydroxide (OLIVEIRA et al., 2013) as hematite, magnetite, and goethite minerals, being removed from the system due to the filtration of the saline solution.
In Table 2, a predominance of Chloride and Sodiumcan be observed. few differences between the eastern salts were found, with the exception of the Black Himalayan Salt (Pakistan), which exhibited high sulfur (S) content, followed by the element potassium (K); and the Persian Blue Salt, which presented greater chloride, sodium, and potassium content than the other chemical groups.
Table 2 - Multi-elemental quantification of the chemical composition of eastern salt samples in comparison withthe indigenous salt
Chemical species (%) |
Indigenous (Brazil) (1)(*) |
HimalayanBlack (Pakistan) (3) (*) |
Himalayan Halite (Pakistan) (4) (*) |
Persian Blue (Iran) (5) (*) |
White (India) (6) (*) |
Pink Himalayan (Pakistan) (10) (*) |
|
Cl |
35.834 |
72.570 |
75.307 |
67.056 |
79.319 |
76.354 |
|
Na |
--- |
19.182 |
22.521 |
16.345 |
18.327 |
18.585 |
|
S |
1.095 |
5.133 |
0.616 |
0.207 |
0.242 |
0.664 |
|
K |
62.146 |
1.066 |
0.452 |
15.128 |
0.377 |
1.562 |
|
Ca |
0.450 |
0.929 |
0.373 |
0.953 |
0.831 |
0.872 |
|
Fe |
--- |
0.374 |
--- |
--- |
0.050 |
0.217 |
|
Br |
0.177 |
--- |
0.021 |
0.195 |
0.086 |
0.021 |
|
Si |
0.124 |
0.071 |
0.033 |
--- |
0.247 |
0.708 |
|
Cu |
0.029 |
0.058 |
0.050 |
0.032 |
0.042 |
0.046 |
|
Sr |
--- |
0.009 |
0.008 |
0.017 |
0.020 |
0.009 |
|
Mn |
--- |
--- |
0.024 |
--- |
--- |
0.040 |
|
P |
--- |
0.300 |
--- |
--- |
--- |
--- |
|
Pm |
--- |
0.162 |
--- |
--- |
--- |
--- |
|
Mg |
0.123 |
--- |
0.595 |
--- |
0.343 |
0.850 |
|
Ti |
--- |
0.047 |
--- |
--- |
--- |
0.034 |
|
Zn |
--- |
0.020 |
--- |
0.010 |
--- |
--- |
|
Ag |
--- |
0.013 |
--- |
--- |
--- |
0.039 |
|
Ir |
--- |
0.034 |
--- |
--- |
--- |
--- |
|
Rb |
0.023 |
0.005 |
--- |
--- |
0.003 |
--- |
|
Br |
--- |
0.026 |
--- |
--- |
--- |
--- |
|
Sc |
--- |
--- |
--- |
0.035 |
--- |
--- |
|
Po |
--- |
--- |
--- |
0.022 |
--- |
--- |
|
Gd |
--- |
--- |
--- |
--- |
0.047 |
--- |
|
Tb |
--- |
--- |
--- |
--- |
0.047 |
--- |
|
Os |
--- |
--- |
--- |
--- |
0.019 |
--- |
Legend: (---) There was not enough excitation of the element for quantification/the element was not present.
(*) These numbers refer to the matrix analysis of the respective salts shown in Table 1.
Source: The authors
Table 3 shows a prevalence of Chloride and Sodium, with little difference between the western salts, with the exception of the South African Black Salt, which exhibitedhigh sulfur content (2.008%), followed by chloride, sodium, and potassium,when compared to the othersalts.
Table 3 - Multi-elemental quantification of the atomic chemical composition of western salt samples in comparison with the indigenous salt.
Chemical species (%) |
Indigenous (Brazil) (1) (**) |
Black(*) (South A.) (2) (**) |
Sicilian white (Italy) (7) (**) |
Hawaiian Black (USA) (8) (**) |
Desert (South Africa) (9) (**) |
Salt Flower (France) (11) (**) |
Maldon (England) (12) (**) |
|
Cl |
35.834 |
75.803 |
79.319 |
81.038 |
76.800 |
79.130 |
81.445 |
|
Na |
--- |
20.035 |
18.327 |
15.514 |
20.045 |
19.798 |
17.325 |
|
S |
1.095 |
2.008 |
0.242 |
0.518 |
0.941 |
0.097 |
0.068 |
|
K |
62.146 |
0.756 |
0.377 |
0.775 |
0.429 |
0.234 |
0.121 |
|
Ca |
0.450 |
0.534 |
0.831 |
0.688 |
0.019 |
0.533 |
0.406 |
|
Fe |
--- |
0.206 |
0.050 |
0.036 |
0.006 |
0.023 |
0.014 |
|
Br |
0.177 |
--- |
0.086 |
0.113 |
--- |
0.054 |
0.040 |
|
Si |
0.124 |
0.078 |
0.247 |
0.023 |
0.038 |
--- |
--- |
|
Cu |
0.029 |
0.031 |
0.042 |
0.047 |
--- |
0.043 |
0.031 |
|
Sr |
--- |
0.010 |
0.020 |
0.008 |
--- |
0.011 |
0.008 |
|
Mn |
--- |
--- |
--- |
--- |
--- |
--- |
0.015 |
|
P |
--- |
0.201 |
--- |
--- |
--- |
--- |
--- |
|
Mg |
0.123 |
--- |
0.343 |
1.228 |
--- |
--- |
--- |
|
Zn |
--- |
--- |
--- |
0.012 |
--- |
0.010 |
0.031 |
|
Ag |
--- |
--- |
--- |
--- |
0.040 |
--- |
0.023 |
|
Rb |
0.023 |
--- |
0.003 |
--- |
--- |
0.002 |
0.002 |
|
Pd |
--- |
0.062 |
--- |
--- |
--- |
--- |
--- |
|
Hf |
--- |
0.058 |
--- |
--- |
--- |
--- |
--- |
|
Cr |
--- |
0.082 |
--- |
--- |
--- |
--- |
0.081 |
|
Hg |
--- |
0.029 |
--- |
--- |
--- |
--- |
--- |
|
Ni |
--- |
0.028 |
--- |
--- |
--- |
--- |
--- |
|
Br |
--- |
0.025 |
--- |
--- |
0.041 |
--- |
--- |
|
Tl |
--- |
0.019 |
--- |
--- |
--- |
--- |
--- |
|
Se |
--- |
0.018 |
--- |
--- |
--- |
--- |
--- |
|
Ga |
--- |
0.014 |
--- |
--- |
--- |
--- |
--- |
|
Pa |
--- |
0.003 |
--- |
--- |
--- |
--- |
--- |
|
Gd |
--- |
--- |
0.047 |
--- |
--- |
--- |
--- |
|
Tb |
--- |
--- |
0.047 |
--- |
--- |
0.037 |
--- |
|
Os |
--- |
--- |
0.019 |
--- |
--- |
--- |
--- |
|
Nd |
--- |
--- |
--- |
--- |
0.626 |
--- |
0.299 |
|
Pr |
--- |
--- |
--- |
--- |
0.598 |
--- |
--- |
|
V |
--- |
--- |
--- |
--- |
0.345 |
--- |
--- |
|
Pt |
--- |
--- |
--- |
--- |
0.045 |
--- |
--- |
|
Au |
--- |
--- |
--- |
--- |
0.014 |
--- |
--- |
|
Th |
--- |
--- |
--- |
--- |
0.007 |
--- |
--- |
|
At |
--- |
--- |
--- |
--- |
0.007 |
--- |
--- |
|
Hf |
--- |
--- |
--- |
--- |
--- |
0.023 |
--- |
|
Co |
--- |
--- |
--- |
--- |
--- |
0.004 |
--- |
|
W |
--- |
--- |
--- |
--- |
--- |
--- |
0.092 |
Legend: (---) There was not enough excitation of the element for quantification/the element was not present.
(*) Including South A.
(**) The numbers refer to the matrix analysis of the respective salts shown in Table 1.
Source: The authors
It can also be noted that most of the salts presented a high degree of purity regarding chloride and sodium, while the indigenous salt was comprised primarily of chloride and potassium.
Regarding the quantified salts, with the exception of the indigenous salt, their elementary matrix was basically composed of Cl and Na.
The mean composition of the 11 samples (except the indigenous salt) of gourmet salts was 76.740% and 18.728% of Cl and Na, respectively, with a standard deviation of 76 ± 4 for Cl and 19 ± 2 for Na. All samples were within this static range, with the exception of the Hawaiian Black Salt (Hawaii) considering the elements Cl and Na, and Maldon Salt (England) regarding the element Cl.
The trace elements highlighted in Tables 2 and 3 were present in most samples, as part of mineral impurities and/or derived from the production process.
There has been a worldwide trend for the reduction of sodium in food (CDC, 2010), especially in industrialized sausages (STROM et al., 2013), due to its relationship with high blood pressure, coronary diseases, and stroke.
In general, several indicationslinking the elevated consumption of NaCl, that is, sodium chloride, to the development of chronic diseases can be found in the literature (HE and MACGREGOR, 2007).
According to the obtained results, it is worth mentioning that this indigenous salt should be consumed under medical guidance due to its high concentration of potassium chloride, a salt with specific properties for human treatment and not daily consumption.
The study by Lawson (1981), conducted with special patients, confirms the concomitant presence of hypokalemia[3], reinforcing the strict need for its monitoring and the replenishment of potassium, when necessary.
5 CONCLUSIONS
The energy-dispersive X-ray spectrometry technique proved to be an adequate tool in the elementary evaluation of different salts used by the human population.
Regarding the quantified salts, with the exception of the indigenous salt, their elementary matrix is basically composed of chloride and sodium. Unlike the other samples, the elementary matrix of indigenous salt is comprised of chloride and potassium.
More than 40 trace elements were detected and quantified in reduced quantities in the samples, with considerable variability in quantity and diversity.
In most samples, the trace elements detected pertained to mineral impurities and/or were derivedfrom the production process.
The indigenous salt should be used under medical guidance, except in traditional indigenous populations that produce and consume the salt, thus preserving the culture and its traditions.
REFERENCES
ALBERS, A.P.F.; MELCHIADES, F.G.; MACHADO, R.; BALDO, J.B.; BOSCHI, A.O. A simple method for the characterization of clay minerals by X-ray diffraction. Cerâmica 48 (305) Jan./Feb./Mar. 2002.
ANVISA - National Health Surveillance Agency, Resolution RDC nº 28, March 28th, 2000, that provides for the basic procedures of Good Manufacturing Practices in establishments that process salt intended for human consumption and the health inspection script in industries that process salt, 2000.
BAAS-BECKING, L. G. M. Historical notes on salt and salt-manufacture. Scient. Mon., N.Y., vol.32, p. 434-446, 1931.
BRANCO, S.M. Hydrobiology applied to sanitary engineering. São Paulo, CETESB / ASCETESB, 1986.
BRASIL. Health Ministry. Resolution RDC Nº 23, April 24, 2013. Available at: http://bvsms.saude.gov.br/bvs/saudelegis/anvisa/2013/res0023_23_04_2013.html, Accessed on Apr.10, 2020.
CARREIRA, C.M. Know it. Folha de Londrina, 2014. Available at: https://www.folhadelondrina.com.br/folha-da-sexta/conheca-881100.html. Accessed on Apr. 18, 2020.
CDC - Centers for Disease Control and Prevention. CDC 24/7. Most Americans Should Consume Less Sodium. 2010. Available at: https://web.archive.org/web/20131019175037/http://www.cdc.gov/salt/. Accessed on Apr. 18, 2020.
DAHL, L.K. Salt Intake and Salt Need. New England Journal of Medicine 258: 1152-7. 1958.
EL PAÍS.The lies of the fashionable pink salt: it is neither so beneficial nor comes from the Himalayas.2018. Available at: https://brasil.elpais.com/brasil/2018/12/19/ciencia/1545208054_174787.html. Accessed on Apr. 20, 2020.
EPA - Environmental Protection Agency.Wetlands Monitoring and Assessment. Macrophytes as Indicators of freshwater marshes in Florida. 2020. Available at: https://www.epa.gov/wetlands/wetlands-monitoring-and-assessment. Accessed on 26/04/2020.
FDA - U.S. Food and Drug Administration. Scientific Report of the 2015 Dietary Guidelines Advisory Committee (PDF). US Department of Agriculture. 2015. p. 7. Archived (PDF) from the original on 18 April 2016.
HENRY-SILVA, G.G.; CAMARGO, A.F.M. Chemical composition of floating aquatic macrophytes used in the treatment of aquaculture effluents, Plantas daninhas, Viçosa-Mg, Vol. 24, N.1, p. 21-28, 2006.
HE, F.J.; MACGREGOR, G.A. Dietary salt, high blood pressure and other harmful effects on health. In: KILCAST, D.; ANGUS, F. Reducing Salt in Foods. Boca Raton: CRC Press LLC, 2007. part 1, p. 18-46.
HOEHNE, F.C. Aquatic plants. Publishing Institute of Botany. São Paulo, 1979.
KNOBEL, M.; MEDEIROS-NETO, G. Disorders associated to chronic iodine deficiency. Arq. Bras. Endocrinol. Metab, vol.48, no.1, São Paulo, Feb. 2004.
LAWSON, A.A.H. (1981). Potassium replacement: When is it necessary? Drugs; 21:354-61.
MELATTI, J.C. Indians of Brazil. 7th edition, Sao Paulo: HUCITEC, 1993.
MOLINA, M.D.C.B.; CUNHA, R.S.; HERKENHOFF, L.F.; MILL, J.G. Hypertension and salt intake in an urban population. Rev Saúde Pública 37(6):743-50 743, 2003.
MOTA, T.M. Know the Types of Salt. AEC Nutrition. Available at: http://www.anchietaba.com.br/nutricao/dicas/55-ConhecaostiposdeSal.pdf. Accessed on Apr. 20, 2020. n.d.
OLIVEIRA, L.C.A.; FABRIS, J.D.; PEREIRA, M.C. Iron oxides and their applications in catalytic processes: a review. Quím. Nova, Vol.36, no.1, São Paulo, 2013.
PARREIRA, P.S. EDXRF methodology and application with a portable system, Technical publication of the Laboratory of Applied Nuclear Physics- UEL, Vol.10, Nº1, 2006.
PINTO, H.P.F. Three strategies for quantitative or qualitative analysis by X-ray Fluorescence Spectroscopy by Dispersive Energy. Masters dissertation. USP. Chemistry Department. 139 p. 2013.
REIS, R.B.B. Chemical composition of Eichhomia crassipes, in Almada river, Bahia, p. 53, 2012 (Dissertation - UESC).
SELMERA, R.M.; KRISTIANSEN, I.S. Cost and health consequences of reducing the population intake of salt, J Epidemiol Community Health, 2000; 54:697-702.
SILVA, M.B. The terminology of salt in RN: A socio-terminological approach. Masters dissertation. Federal University of Ceará. 211 p. 2007.
SILVA, M.A.M.; SCHREIBER, B.C.; SANTOS, C.L. Evaporites as mineral resources. Brazilian Journal ofGeophysics, Vol. 18(3), 2000.
SOAR, J.; PERKINS, G.D.; ABBAS, G.; ALFONZO, A.; BARELLI, A.; BIERENS, J.J.; BRUGGER, H.; DEAKIN, C.D.; DUNNING, J.; GEORGIOU, M.; HANDLEY, A.J.; LOCKEY, D.J.; PAAL, P.; SANDRONI, C.; THIES, K.C.; ZIDEMAN, D.A.; NOLAN, J.P. European Resuscitation Council Guidelines for Resuscitation, 2010, Section 8. Cardiac arrest in special circumstances: Electrolyte abnormalities, poisoning, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution". Resuscitation. 81 (10):1400-33. doi:10.1016/j.resuscitation.2010.08.015. PMID 20956045
SOUSA, A.L. Method study aiming at the direct analysis of alumina, cement and quartz in ICP OES. Department of fundamental chemistry. Chemistry Institute. USP. Doctoral thesis.147 p. 2011.
SOUZA, V.C.; LORENZI, H. Systematic botany: illustrated guide for the identification of Angiosperm families in the Brazilian flora, based on APG II. Nova Odessa: Plantarum Institute, 2005. 640p.
STROM, B.L.; YAKTINE, A.L.; ORIA, M. (2013).Sodium intake in populations: assessment of evidence. Committee on the Consequences of Sodium Reduction in Populations; Food Nutrition, Board; Board on Population Health Public Health Practice; Institute of Medicine of the National Academies. doi:10.17226/18311. ISBN 978-0-309-28295-6. PMID 24851297. Archived from the original on Oct. 19, 2013.
WHO – World Health Organization. WHO issues new guidance on dietary salt and potassium". 2016. Available at: https://www.who.int/mediacentre/news/notes/2013/salt_potassium_20130131/en/. Accessed onMar. 24, 2020.
ZHU, R.F.J. Archaeologicalandchemicalevidence for earlysaltproduction in China, PNAS, 12618-12622, 30/08/2005, vol. 102, nº. 35.