Geochemistry of salts and the effect of trace elements on human health: Turkey salt resources

ABSTRACT Salt plays a vital role in many body functions. Humans must consume a well-balanced amount of salt to remain healthy as deficiency or excess of it causes many health problems. The major oxide element’s values are only evaluated while processing for production; however, the type and amount of the trace elements in the salt are also important as they may entail risks for human health. This study concerns the mineralogy and geochemistry of salt samples which are taken from several salt mines and localities in Turkey. In addition, these local samples are compared with well-known samples from Himalayas and Asal Lake (Djibouti Southeast Africa) salt mines. The X-Ray Diffraction (XRD) and Confocal Raman Spectroscopy (CRS) analysis reveal that the most of Turkish salts are mainly composed of halite with minor amounts of thenardite and gypsum as well as the low concentrations of some potentially toxic elements (PTEs) such as As, Cd, Co, Hg, Mn, Ni, Pb and Zn. The samples from Tuz Lake have significant contents of As, Co, Cu, Mn, Ni, U and Zn. The mineralogy and geochemistry of the samples reveal a mixture of residual seawaters with the redissolving of the crystalized salt minerals in the region. Although the quality of the salts is mostly evaluated with the content of NaCl, the significant contents of the PTEs in the salt may be accumulated by time and danger human health.


Introduction
Salt (Halite-NaCl) is a vital nutrition in human life and an indispensable natural mineral for the industry.The pure salt is colourless and transparent, yet, it may go grey, yellow, red, blue, purple and green if naturally mixed with foreign ions and/or other inclusions [1,2].Salts, which are formed as a result of evaporation, are generally in co-existence with anhydride (CaSO 4 ), gypsum (CaSO 4 2H 2 O), thenardite (Na 2 SO 4 ), glauberite (Na 2 Ca(SO 4 ) 2 ), epsomite (MgSO 4 7H 2 O), bloedite (Na 2 Mg(SO 4 ) 2 ).4H 2 O), leuveyite (Na 12 Mg 7 (SO 4 ) 13 15H 2 O), eugesterite (Na 4 Ca(SO 4 ) 3 2(H 2 O), sylvine (KCl), magnesium sulphate (MgSO 4 ), calcium dichloride (CaCl 2 ), magnesium dichloride (MgCl 2 ) minerals and other organic materials causing the impurities of the salt [1][2][3].They also have some inclusions of carbonate Mineralogical and petrographical investigations are very important for determining the impurities of the salts so spectroscopic techniques such as XRD and CRS were used for these purposes [11][12][13].The fluid inclusions in salts reflect the environmental characteristics where salt crystals form and some researchers were used fluid inclusion analyses for understanding the homogenisation temperature of salts, chemical composition of brines or salt lakes and depositional environments [11][12][13][14][15][16][17][18][19].The major and trace element geochemistry of salts has been used in the previous studies from all over the world which have different origin for understanding the main chemical composition of salts [9,11,12,20].Deocampo and Jones [21] studied the geochemistry of saline lakes.Toboła and Kukiałka [13] determined that the high trace element concentrations of Cs, Mn, and Rb performed in the Lotsberg deposit of the Canada suggest extensive ion exchange related to hydrothermal inflow.Risacher and Fritz [22] studied the geochemistry of salts from Bolivia and suggest that Uyuni salts were probably deposited in a playa lake environment and maintained by saline inflows.Velde et al. [20] investigated the trace element geochemistry of American and French salt marshes and indicated that clay minerals are very important carrier in fixing trace elements for historical records as salt marsh sediments.Isotope geochemistry is also very important for understanding the origin of the salts and B, Br, Cl and Li isotopes of salts were used for this purpose [23][24][25][26][27].Some of the researchers investigated the role of salt on food and human health, but they only discussed what kind of health problems will occur with the level of salt consumption [28][29][30].There is very little risk assessment of trace or carcinogenic elements in salts in recent years but there are lots of studies about risk assessment of trace element or heavy metal concentrations in drinking water, soil, the environment around the mines and indoor dust [31][32][33][34][35][36][37][38][39][40][41].
The subject of this study is the mineralogy and geochemistry of the salts (especially rock salt and saline samples) that have been collected from several salt deposits in Turkey and around the world.Turkey has a wide range of ophiolitic rocks exposure, related igneous and hydrothermal deposition.Potentially toxic elements (PTEs) present in these rocks can be incorporated into the salt formations during evaporation.The toxic (Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn etc.) and mobile (As, Ba, Sr, Th, U etc.) elements depending on the decomposition of these rocks may act in the formation of the salts in their compositions.The mineralogy and geochemistry of Tuz Lake are well studied [3,9,12].Karakaya et al. [12] investigated mineralogy and fluid inclusion geochemistry of salts from Tuz Lake.Ercan et al. [27] tried to clarify the origin of Tuz Lake salts based on B, Br, Cl and Li isotopes and trace elements.The researches only studied on mineralogy, toxic elements and radioactivity characteristics of Çankırı salts [10,39].Previous studies were carried on limited salt deposits and none of these studies focus deeply on the relation ship between the trace or heavy elements and regional geology.However, in this study, the geological and mineralogical effects on the geochemical compositions of the salt and the effects of trace elements on human health were studied using salt samples taken from İzmir (Çamaltı Salt Marsh), Yozgat (Sekili), Ankara (Tuz Lake), Konya (Tersakan ve Meke Lake), Kayseri (Tuzla-Palas Lake), Çorum (İskilip), Çankırı (Çantaş), Kırıkkale and Acıgöl (Çardak Lake) (Denizli) (Figure 1) as well as the Himalaya (Asya) and Asal Lake (Djibouti-Africa).The risk assessment of PTEs for the carcinogenic and non-carcinogenic health risk was calculated for both men and female and the results are evaluated on the effects of the human bodies.

Sampling and analyss
Sixty salt samples were collected from the different salt mines and deposits in the Central Anatolia.The thin sections from each samples were prepared for determining mineralogical and textural characteristics under the microscope.All the petrographical studies of the samples were examined using Zeiss Axio model polarising microscope.The X-Ray Diffractometer (XRD) and Confocal Raman Spectroscopy (CRS) were used for the determination of the detailed mineralogical composition and XRF was used for the determination of geochemical compositions.The XRD equipment is Inel Equinox 1000 model and the measurements were taken in the 30 mA and 30Kv with using cobalt (Co) anode.Confocal Raman Spectroscopy (CRS) analysis was also done to support the XRD studies.The CRS is Thermo Scientific DXR machine and the measurements were carried out by using 633 nm laser, 25 µm slit aperture, 600 lines/mm grating in the range between 150 and 1200 cm −1 .The estimated spot size is 0.7 µm and the estimated resolution is between 2.6 cm to 4.4 cm −1 .Major and trace elements were measured in all salt samples.X-Ray Fluorescence (XRF) Spectroscopy was used to detect the trace element contents because the trace element concentrations are in the range of detection limits of XRF.The details of sample preparation and measurements for Polarised Energy Dispersive XRF Spectroscopy (PEDXRF) is detailed on [42,43].The standard reference materials were used for the calibration and quality assurance of the XRD, CRS and XRF.Y 2 O 3 crystalline sample and polystyrene film were used as the standard reference material for the calibration and quality assurance of the measurements for the XRD and CRS, respectively.Samples were analysed using a method that includes different mineral and rock standards.The quality assurance of the analytical method was also cross-checked by analysing the same samples in other accredited laboratories.All analyses were carried out with the facilities of Earth Sciences Application and Research Centre (YEBIM) of Ankara University.

Risk assessment
The maximum, minimum and average concentrations were calculated for each element.The PTEs maximum and minimum concentrations were used in the risk assessment calculations.The risk assessment is a method used to determine the probability of occurrence of any given probable amount of the harmful health effects over an average human life [34].The risk level estimation of PTEs was evaluated in terms of carcinogenic and non-carcinogenic health hazards.The following equations were used: ADD (mg/kg-day) is the average daily dose, C (mg/kg) is the concentration, IR (kg/ day) is the daily intake rate, EF (day/year) is the exposure frequency, ED (year) is the exposure duration, BW (kg) is the body weight, AT (day) is the average lifetime.BW and AT were evaluated separately for both men (BW men = 76, AT men = 27,740) and women (BW women = 67, AT women = 29,565) who currently live in Turkey and official data provided by the Turkish Statistical Institute (TUIK).HQ is the hazard quotient for the non-carcinogenic risk, RfD (mg/kg-day) is the oral chronic reference dose, HI is the hazard index for multiple elements, CR is the carcinogenic risk or incremental probability of a human developing any type of cancer over lifetime as a result of 24 hours per day exposure to a given daily amount of a carcinogenic or potentially toxic element for an average lifetime in Turkey according to (TUIK).OSF is the oral slope factor (mg/kg/day) of a carcinogen or potentially toxic element.The input parameters are shown in Supplementary File 1.

Formation of the salt deposits in research areas
Çamaltı Salt Marsh (İzmir), formed the salt from the evaporation of seawater, is one of the biggest salt production areas which supplies 28% of salt production in Turkey.The Tuz Lake in Central Anatolia has the biggest salt formations where the Na-rich solutions with different composition, proportion and origin (seawater or saltwater and groundwater/ freshwater etc.) were effective in the formation of halites formed in the Miocene depositions [3,12,27].The high Br content in the halites points out the marine nature whereas low Br content in the halites is mostly related to the dissolution of pre-precipitated halites and recrystallisation of the evaporite minerals [44][45][46][47][48].The Mg and SO 4 components in the halites increased with the dissolution of preformed gypsum and de-dolomitisation of the unit [3,12,27].The high K content in the fluid inclusions reflects the dissolution of the K rich salts [3,12].The seawater coming to the basin with rising seawater, faults and karst cavity during the Miocene depositional is considered the main cause of the salt formations in Tuz Lake region [3,12,27].The gypsum and other evaporite minerals in the region were formed mainly by the evaporation of the seawater but the dissolution of preprecipitated sulphates and recirculations, decreasing of the bacterial sulphate and arid climatic conditions have also affected the formation [49].About 64% of the salt production in Turkey is supplied byTuz Lake (Ankara), Seyfe Lake (Kırşehir) and Tuzla (Palas) Lake (Kayseri) (Figure 1a).Salt resources in Tersakan and Meke Lake (Konya) were also formed from NaCl rich solutions which derived from the dissolution of the rocks around and deposited in the closed basins (depression areas) as a result of tectonism.Tersakan Lake has formed a residue of the Tuz Lake [50].
Yozgat (Sekili), Çorum (İskilip), Çankırı (Çantaş) and Kırıkkale salt deposits were formed by dried seas or closed inner basins with evaporation in different geological times.Salt deposits of the Central Anatolia which contain the gypsum and clay minerals were formed in the Oligocene-Miocene [7].The Tertiary Çankırı-Çorum basin is the biggest basin which has the evaporitic formations and consists of Pliocene aged halite and glauberite minerals [10].Clay, anhydrite and gypsum minerals are also observed in these depositions.The evaporated minerals in these depositions were formed in the coastal and lake environments.

Geochemistry of salt
All the salt samples in this research include 23.31-52.43%Na 2 O (with average 46.93%), 10.20-51.04%Cl (with average 41.24%), 0.01-12.90%SO 3 (with average 1.97%), 0.01-9.57%CaO (with average 1.49%), 0.02-1.88%K (with average 0.29%), 0.01-35.93%SiO average 2.283%), 0.03-7.42%Al average 0.50%) and 0.08-12.10%MgO (with average 1.53%) (Figure 4, Supplementary File2).The Na and Cl concentrations of the Tuz Lake salts are lower than those of other studied salt samples whereas the contents of SO CaO, K SiO Al MgO of the salts of Tuz Lake are almost as high as those in the salts from other localities.These salt samples from Tuz Lake were collected from the side of the lake.The wide chemical compositional range of the İskilip (Çorum) and Çantaş (Çankırı) rock salts derived from the presence of the clay minerals in these rock salt samples.

Discussion
The geochemical results of the collected salt samples from various regions of Turkey are compared with the geochemistry of the Himalaya salt (Asya) and Asal Lake salt (Djibouti-Africa) to reveal the quality of use.The major oxide especially NaCl content is the basic way for understanding the purity of the salts.Tuzla and Acigol (Çardak) Lakes contain much higher amounts of SO 3 than other salt samples (Supplementary File2).
According to the experimental studies, the Br content of the salt formed by the evaporation of the brine salt is in the range of 75 and 65 mg/kg [3,52].The Br content of the salt which was formed by the evaporation of the brine must be at least 40 mg/kg but the salts which have the Br content smaller than this concentration formed by dissolution and recrystallisation of the halites [3,46].The mobility of the dissolved halitescause to decreasing the Br content in the mineral [3,46].The salts with high Br contents are a result of continuous evaporation [3,44,46].Halite generally has the Br content ranging from 70 up to 250 mg/kg and the Br contents of the initial crystallised minerals from the evaporation of brine are very low whereas the minerals, which have a Br content lower than 70 mg/kg, may indicate the secondary sea or meteoric water inlet in repeating precipitation [3,45,47].The low Br content may be related to changing with the diagenetic fluids simultaneously with the precipitation or by the redissolution and recrystallisation [3,48].According to this information, the Br contents of all salt samples except five samples from Tuz Lake and one sample from Meke Lake in this research are lower than 70 mg/kg, therefore, it can be said that they were formed by the recrystallisation or the presence of sea or meteoric water inlet during repeating precipitation (Supplementary File3).
To approach the compositional changes of the solution during evaporation, the Br content, which prefers to remain in the solution during the crystallisation process, current brine and evaporation line has been used in variation diagrams [3,[53][54][55].The Br versus Ca element variation diagram reveals that all the samples except the those of Acigol, Tersakan, Meke and Asal Lake show enrichment against the brine evaporation line whereas the salt samples of Tersakan, Meke and Asal Lake show similarity with the brine evaporation line (Figure 6a).The enrichment in Ca element content in the mineral and environment happens due to entrance of the ground and/or surface water [3,55].The enrichment in Ca element in the ground and/or surface water results in the alteration of the surrounding lithologies.The enrichment in Ca element in the salt samples from Tuz Lake (Ankara), Tuzla Lake (Kayseri), Sekili (Yozgat), İskilip (Çorum), Çantaş (Çankırı) and Kırıkkale is related to the carbonate deposition around the area.The salt samples from Sekili (Yozgat), İskilip (Çorum), Çantaş (Çankırı), Kırıkkale, Çamaltı salt marsh (İzmir), Tuzla and Asal Lake with some samples of Himalayan salt and Tuz Lake plotted below the brine evaporation line on the Br versus K diagram (Figure 6b).The other samples of Himalaya and Tuz Lake with the samples of Acigol, Tersakan and Meke Lakes are close to the marine values (Figure 6b).Decreasing the K content in the samples can be associated with the adherence of K entering the composition of the dissolved halite crystals by the clays between the sediments.The Mg contents generally in all the samples plotted above the brine evaporation line (Figure 6c).The samples from Çamaltı salt marsh (İzmir), Asal Lake with the samples except for one sample from Himalaya salt, Meke and Tuz Lake are plotted above the brine evaporation line on the Br versus SO 3 diagram (Figure 6d).Generally, the Mg and SO 3 concentrations of the samples increase with increasing Br content (Figure 6c and 6d).This may be explained with the de-dolomitisation of the minerals [3,56].The Ca and SO 3 concentrations increase with the dissolution of the carbonate rocks and especially evaporitic lithologies around the region.Increasing Ca contents cause calcite formation.Incompatible dolomite dissolution occurs in the solution with the decrease of the bicarbonate ion in the solution, then dolomite replacement with calcite may release Mg from the system [3,56].Mafic and ultramafic rocks around the salt deposition region led to increase of Mg content in the clay minerals in the region (Figure 1b).
The Cl/Br and Na/Br ratios are used to determine the nature of the halites in the deposition [3,73,57,58].These element ratios are also used as a guide to determine the effects that cause lowerBr content such as freshwater intake and halite dissolution [3,59].Almost all the samples plotted parallel to the brine evaporation and halite dissolution lines (Figure 7).The salt dissolution may have occurred due to the solutions that may have different composition and origin introduced to the area later [3].The salt samples from Sekili (Yozgat), İskilip (Çorum), Çantaş (Çankırı) and Kırıkkale may be derived from salty water, which is the product of the dissolution (Figure 7).Asal Lake is formed on the rifting basic volcanic rocks in Afar triangle of the Djibouti country.Yemen Sea is the source of this lake through the canal of the Gulf of Aden [60].Yet, the chemical results and the Cl/Br and Na/Br variation diagrams suggest that the source of Asal Lake is also slightly affected by the environmental units (Figure 7).The diagramthat shows the changes in Cl-Br content during the evaporation of seawater was used to determine the chemistry of the solution causing dissolution in the salt samples (Figure 8a).The solution which causes halite dissolution in all of the samples except one sample of Tersakan Lake has high Br content or maybe in the composition such as more diluted saline waters like seawater (Figure 8a) Figure 7. Na/Br versus Cl/Br variation diagram of the İzmir (Çamaltı salt marsh), Yozgat (Sekili), Ankara (Tuz Lake), Konya (Tersakan and Meke Lakes), Kayseri (Tuzla-Palas Lake), Denizli (Acıgöl-Çardak Lake), Çorum (İskilip), Çankırı (Çantaş), Kırıkkale, Himalaya (Asya) and Asal Lake (Djibouti-Africa) salt samples (Evaporation line of seawater and dissolution line of halite were taken from Harvie et al. [56] and seawater was taken from McCaffrey et al. [57].).[3].The lower Br content in the samples may also indicate that the samples interact with the one or more different compositional solutions and then dissolved and recrystallised when the sufficient amount is reached (Figure 8a) [38].
The most of the salt samples plotted parallel to and slightly near the mixture line in the Cl versus Cl/Br variation diagram based on Grandia et al. [61] for making overtures about the mixtures of the solutions with different composition and origin (Figure 8b).This is related to the high Cl and low Br contents of the studied samples.The high Cl content might be caused by the arrival of Cl rich solutions which had a different composition or origin to the environment, the dissolution of the salts with these solutions and the recrystallisation (secondary precipitation) [7,61].The samples except for İskilip (Çorum), Çantaş (Çankırı) and Tuz Lake show the parallel trend to the mixture line.The Cl content increases with the increasing of Cl/Br ratio in the İskilip (Çorum), Çantaş (Çankırı) and Tuz Lake samples and remain constant concerning the Cl/Br content (Figure 8b).This was likely due to mixing of solution of marine composition with Cl-rich solution of different composition and origin [3,61].
The K content of the analysed salt samples is generally higher than 440 mg/kg (Supplementary File 4a).The K contents of the Çamaltı salt marsh (İzmir), İskilip (Çorum), Çantaş (Çankırı), Tuzla Lake, Meke Lake and Himalaya salt (white coloured) sample are low compared with K contents (440 mg/kg) in the salts which formed during the Cenozoic (Supplementary File 4a) [3,46].This may be related to the clay minerals found in the salts while K is preferentially adsorbed by clay minerals [3].Excess K content of the samples of especially Tuz Lake may be related to the granitic units (Ağaçören Intrusive Suite-AIS) in the basement rocks (Figure 1b).Similarly, the high K and low Ca contents of the Himalaya salts may be connected with granitoid rocks in the region.The Ca contents of the analysed salt samples are higher than Ca content of the Eocene seawater (384 mg/kg) and current seawater level(264 mg/kg)  [3,53,54,74], (b) Cl versus Cl/Br (molar) variation diagram the İzmir (Çamaltı salt marsh), Yozgat (Sekili), Ankara (Tuz Lake), Konya (Tersakan and Meke Lakes), Kayseri (Tuzla-Palas Lake), Denizli (Acıgöl-Çardak Lake), Çorum (İskilip), Çankırı (Çantaş), Kırıkkale, Himalaya (Asya) and Asal Lake (Djibouti-Africa) salt samples (modified from Grandia et al. [61]).
(Supplementary File2, Supplementary File 4b) [27,58].The Ca contents of the analysed salt samples change in direct proportion to the SO 3 content (Supplementary File 4b).This may be related to the de-dolomitisation during the deposition [3].The Ca and SO 3 contents of the solutions increase with the de-dolomitisation and dissolution of the sulphate minerals.The Mg contents of most of the investigated salt samples (except Çamaltı salt marsh, Tuz Lake, Tersakan Lake, Sekili and Çankırı salt samples) are higher than those of the Eocene seawater (874 mg/kg) and current seawater (1136 mg/kg) level(Supplementary File2, Figure 8c) [46].The high Mg content is associated with de-dolomitisation whereas the low Mg content is related to the environments with a limited active hydraulic cycle [3].The SO 3 contents of some of the salts from Çamaltı salt marsh (İzmir), Sekili (Yozgat), İskilip (Çorum), Çantaş (Çankırı), Himalaya (white coloured), Tersakan, Salt and Asal Lakes are very low (Supplementary File2, Figure 8d) This could be associated with the presence of impermeable clayey parts in the region.The As, Cl and Na contents are generally constant with increasing SO 3 content (Figure 8d-f).The Ba and La contents do not change with increasing SO 3 content in some samples but they decrease in some samples (some samples of Sekili and Tersakan Lakes) (Supplementary File 4 g-h).The Sr and Fe show a similar relationship with Ca and Mg (Supplementary File 4ı-j).
The crystal morphology of halites can be effective in removing metal ions in the solutions [5].The enrichment of Hf is generally observed in the primary halite formations [5].The metal ions usually accumulate on the outer surfaces of the salt crystals and metal ions from dissolved salt enter the environment as a result of human activity [5].The Bi, Hf, La, Te and U contents of the investigated salt samples are very high (Supplementary File 5, Supplementary File3).The Pb and Th contents of some samples are higher than those of other samples (Supplementary File 5, Supplementary File3).The presence of transitional metals such as Co, Cr, Ni, and V indicates that the magmatic minerals formed in the first phase did not contain these elements or these elements transported to the nearby basin by surface water or groundwater due to the decomposition and weathering of these minerals.These elements have the potential to be toxic due to their relation with Fe element.Some of these trace elements may not prefer the solid (mineral) phase in the formation of the rocks and they may have been enriched in the remaining solutions (residual melts) and moved to the environment or they may have occurred due to the environmental (external or human-induced) factors.The high contents of Co, Cr, Ni and Ti especially in the samples from Tuz Lake are associated with the ophiolitic units of Inner Tauride belt at the side of the lake (Figure 1b).The high U and Th contents of Tuz Lake and Himalaya samples are related to the granitic units of the basement in the region whereas the very high concentrations of these elements in the Çankırı salts may be related to their interaction with spring water resources in the region (Figure 1b).
The concentrations of the elements such as Li and B, which dissolve from the units in the environment and can reach the sedimentation basin by being moved by surface waters, are also very important.The Li contents are between 318 to 325 mg/kg for Tuz Lake, 28 to 34 mg/kg for Tersakan Lake, 18-52 mg/kg for Tuzla Lake and 30-33 mg/kg for Acigol (Çardak) [62,63].The B content of Tuzla (Palas) Lake and Tuz Lake is in the range from 20 to 378 mg/kg and 5 to 43 mg/kg, respectively [64].
According to the study of the World Health Organization (WHO), the elements are classified as essential for human health, possibly necessary and potentially toxic [65].The essential elements are the Cr, Cu, Fe, I, Mo, Se and Zn [65].Probably necessary elements are B, Mn, Ni, Si and V [65].Potentially toxic elements (PTEs) are for example, As, Al, Cd, F, Fe, Hg, Li and Sn [65].Salt is very important for human life and its deficiency and excess intakes can cause serious health problems [28][29][30].The salt is not only taken from table salt but also is found in many foods consumed daily [28,29,65].Some of the elements which were taken into the human body together with the salt cannot be excreted from the human body and accumulate in the body [65].This can cause diseases after reaching a certain concentration [65,66].Therefore, risk assessment of PTEs in salts in Turkey and some of the locations of the world is needed to assess non-carcinogenic and carcinogenic health risks for the human who is exposed to PTEs in edible salts.The risk assessment calculation results were given in Supplementary File 6.The As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sn, V and Zn were used in the calculations.The value of HQ, which is calculated from the minimum and maximum concentration for each element, is smaller than 1 in all studied salts (Supplementary File 6).The HQ values are at an acceptable level [67].The HI values, which are used for the risk assessment of a multiple elements, are <1 and this means an acceptable level of risk according to ECETOC [68].The CR values were calculated for the As, Cd, Cr and Pb whose OSF value is available in the Risk Assessment Information System and previous studies.If the CR values range from 1 × 10 −4 -1x10 −6 , the CR is acceptable.If the CR values are below 1 × 10 −6 the element is considered to be significantly safe [69].The CR of As, Cd, Cr and Pb is in the safety range in all salt samples.Therefore, continuous and long-term use of the salts causes likely no harmful effects on the human health.

Conclusions
This study evaluates the human health risk of PTEs in the salts collected from nine locations from Turkey and two salt samples (Asal Lake and Himalaya salts) around the world.The analysed salts are derived from the solutions formed by the mixture of seawater with the different compositional solutions and dissolution-recrystallisation of reprecipitated marine salts with the waters which have a different composition and high Cl content.The rock salts reflect directly the precipitation source but they are also affected by the surrounding lithologies.Accordingly, the mineralogical and chemical compositions of rock salts are easily affected by the easily soluble rocks around them during their formation.The high Al and Si contents in the rock salts originated from the clay minerals which occurred as inclusions in the salts.The risk assessment calculations suggest acceptable non-cancer health risk levels for the salt samples.Unrefined rock salts are not suitable for use as a natural mineral source in the nutrition of human because of their different mineral and variable chemical composition.The salts from Central Anatolia region should not be used without detailed analysis because these salts are affected from different sources with different proportions.Asal Lake (Djibouti-Africa) composed only of halite does not contain harmful elements because of feeding directly from the Yemen Sea.The results of this study should be used by respected departments of the government related with food and health and also salt producers and the local people should be informed who generally use unrefined rock salts.

Figure 1 .
Figure 1.(a) The map of Miocene marine and non-marine basins of Turkey modified from [49,70], (b) The simplified igneous and ophiolitic rocks map of the study areas and Turkey (modified from [71]).

Figure 5 .
Figure 5.The trace element diagrams showing the element concentrations of the studied salt samples.