Determination of Chromium Species in Various Medicinal Plants Consumed in Hatay Region in Turkey

Abstract

In this study, 22 species of medicinal plants (anise, centaury, chamomile, fennel, flax, green tea, indian hemp, laurel, licorice, linden, marestail, melissa, nettle, oat, red clover, riesenfenchel, rosehip, rosemary, sage, senna tea, yam, yarrow) were taken from five different local herbalists in Hatay. Chromium concentrations were determined by inductively coupled plasma-atomic emission spectroscopy. The highest chromium concentrations were detected in chamomile (4.21 ± 0.18 mg kg⁻¹), licorice (2.80 ± 0.12 mg kg⁻¹), melissa (2.71 ± 0.10 mg kg⁻¹), marestail (2.66 ± 0.10 mg kg⁻¹), and anise (1.98 ± 0.06 mg kg⁻¹). Minimal concentrations of chromium were found in riesenfenchel (0.33 ± 0.01 mg kg⁻¹), red clover (0.37 ± 0.01 mg kg⁻¹), centaury (0.43 ± 0.01 mg kg⁻¹), senna tea (0.49 ± 0.01 mg kg⁻¹), and linden (0.50 ± 0.01 mg kg⁻¹). Cr(III) and Cr(VI) concentrations in medicinal herbs were found in the range of 0.26–3.12 mg kg⁻¹ and 0.07–1.09 mg kg⁻¹, respectively.

Keywords:

• Medicinal plants
• Chromium
• Speciation
• Spectroscopy
• Hatay

INTRODUCTION

Interest in chemical speciation in the fields of biological and environmental science has increased recently. The assessment of toxic interactions of heavy metals and bioavailability must be based on levels of specific chemical forms, rather than on total element levels.[1] The interest in chromium speciation originates from drastically different chemical properties of Cr(III) and Cr(VI) compounds and their biochemical action. While Cr(III) is a trace element species essential for the proper functioning of living organisms, Cr(VI) has toxic effects on biological systems and has been classified by the International Agency for Research on Cancer as a Group I carcinogen.[2]

A recent survey by the World Health Organization indicated that about 70–80% of the world population relies on herbal sources for their primary healthcare. Especially, chamomile and fennel are extensively used for babies for spasmolytic and antiseptic purposes. However, many medicinal herbs and their mixtures can present a health risk due to the presence of toxic elements, such as Cr, Pb, Cd, Al, and Hg, depending on their oxidation states and presence at high concentrations. For this reason, determination of the amounts of chromium species in medicinal plants is very important.

There are a number of speciation methods, such as solid phase extraction, liquid-liquid extraction, coprecipitation, and ion exchange. In many cases, several manipulation steps, which are time consuming, complex, and labor-intensive, are required. Instead of these methods, in the sampling step, selective extraction of Cr(VI) and Cr(III) from solid samples is a preferable sampling process. The United States Environmental Protection Agency Method 3060 A is an alkaline digestion procedure based on leaching with Na₂CO₃ for hexavalent chromium. This method is used to solubilize both water-insoluble and water-soluble Cr(VI) compounds in soils, sludges, sediments, and plants.[3] The leaching with Na₂CO₃ solution for Cr(VI) speciation is based on transformation of insoluble Cr(VI) compounds into soluble form in an alkaline media forming Na₂CrO₄ while Cr(III) species form insoluble hydroxides or carbonates.[4] The leaching of Cr(VI) with Na₂CO₃ is an effective, reliable, and simple procedure for speciation of chromium accumulated in soil, sediment, and plant samples.[5]

In the literature, there are a number of studies related to chromium speciation in various plants[6–12 12 and determination of trace elements in medicinal herbs.[13–18 18 But, no previous research had focused on chromium speciation in medicinal plants. The objective of this study was to establish the amounts of chromium species in medicinal plants that are widely and habitually consumed for medical purposes in Turkey. The leaching procedure based on use of Na₂CO₃ was used for the speciation analysis of chromium. The chromium concentrations were determined by the inductively coupled plasma-atomic emission spectroscopy (ICP-AES) system.

MATERIALS AND METHODS

Reagents and Standards

SRM 1573 a tomato leaf (from the National Institute of Standards and Technology, Gaithersburg, MD, USA), was used as the standard reference material. All solutions were prepared from high purity analytical reagent grade compounds from Merck (Darmstadt, Germany) and Fluka (Buchs, Switzerland) using ultrapure quality water. High purity water was prepared by passing laboratory-deionized water (reversed osmosis plus ion exchange) through a Millipore Milli-Q Ultrapure water purification system (New Human Power I Model, Seoul, Korea).

Plant Material

Twenty-two species of medicinal plants (anise, centaury, chamomile, fennel, flax, green tea, indian hemp, laurel, licorice, linden, marestail, melissa, nettle, oat, red clover, riesenfenchel, rosehip, rosemary, sage, senna tea, yam, yarrow) were taken from five different local herbalists in Hatay. The most widely accepted and most frequently consumed medicinal plants were selected. Medicinal plants were mixed one by one and placed individually in polyethylene containers. Medicinal plants were washed with distilled water. The samples were dried at room temperature on a sheet of paper. Then, the plants were oven-dried at 80°C and ground in a mortar to pass through a sieve to obtain uniform particle size.

Determination of Total Cr in Medicinal Plants

Dried samples of 0.25 g of medicinal plants were accurately weighed into a teflon digestion vessel (CEM type) and 5.0 ml of concentrated HNO₃, 3.0 ml of conc. HF, and 1.0 ml of conc. HCl were added. The vessels were capped and the samples were digested at 120 psi for 20 min. After cooling, the cap was removed and the open vessel was heated on a hot plate to evaporate the excess acid; the contents were then diluted with 1% (v/v) nitric acid and filtered through Whatman no. 540 filter paper. Filters with precipitates were washed several times with 1% (v/v) HNO₃. The final volumes of all sample solutions were adjusted to 25.0 ml with deionized water.[19] Concentrations of total Cr in the resulting solutions were measured by direct aspiration into Varian QEC 1401 Model ICP-AES (Sydney, Australia). All analyses were made in triplicate. To monitor the reproducibility and sensitivity of the method, standard reference materials of SRM 1573 a tomato leaf, was used as the control and 99.5% of recuperation was obtained at each run.

Determination of Cr(VI) Amount

Medicinal plant samples of nominal 0.25 g mass were accurately weighed into a glass beaker wherein 25.0 ml of 0.1 M Na₂CO₃ was added and the mixture boiled for 10 min. After cooling, samples were transferred to a plastic tube without filtration. The final volumes of sample solutions were adjusted to 25.0 ml with deionized water. Before analysis, aliquots were filtered through a 0.45-μm filter. These solutions were used for determination of Cr(VI) by an ICP-AES system.[20]

Determination of Cr(III) Water Soluble Fraction of Cr(VI)

The concentration of Cr(III) was calculated as a difference of total Cr concentration and Cr(VI) concentration. First, 0.25 g of dried medicinal plant samples were accurately weighed into a beaker. Then 25 ml of deionized water were added to each tube. The contents of the beakers were boiled for 30 min.[17] After filtration, pH of filtrates was adjusted to 1–2 with 1 M H₂SO₄. Diphenylcarbazone was added to 4 ml of this solution. The absorbance of solutions was measured at 546 nm by Shimadzu 1208 Model UV/vis spectrophotometer (Kyoto, Japan).[21]

Table 1  Total chromium, Cr(VI), and Cr(III) concentrations in medicinal herbs

Sample	Total [Cr], mg kg^−1	[Cr^+6], mg kg^−1	[Cr^+3], mg kg^−1
Anise (Pimpinella anisum)	1.98 ± 0.06	0.43 ± 0.01	1.55 ± 0.06
Centaury (Gentiana lutea)	0.43 ± 0.01	0.08 ± 0.01	0.35 ± 0.01
Chamomile (Matricaria chamomilla)	4.21 ± 0.18	1.09 ± 0.02	3.12 ± 0.18
Fennel (Foeniculum vulgare)	0.75 ± 0.01	0.23 ± 0.01	0.52 ± 0.01
Flax (Linum)	1.47 ± 0.03	0.41 ± 0.01	1.06 ± 0.03
Green tea (Camellia sinensis)	1.22 ± 0.02	0.24 ± 0.01	0.98 ± 0.02
Indian hemp (Cannabis)	1.39 ± 0.02	0.34 ± 0.01	1.05 ± 0.02
Laurel (Laurus nobilis)	1.24 ± 0.02	0.25 ± 0.01	0.99 ± 0.02
Licorice (Glycyrrhiza glabra)	2.80 ± 0.12	0.80 ± 0.01	2.00 ± 0.12
Linden (Tilia)	0.50 ± 0.01	0.12 ± 0.01	0.38 ± 0.01
Marestail (Equisetum arvense)	2.66 ± 0.10	0.40 ± 0.01	2.26 ± 0.10
Melissa (Melissa officinalis)	2.71 ± 0.10	0.28 ± 0.01	2.43 ± 0.10
Nettle (Urtica)	1.92 ± 0.06	0.42 ± 0.06	1.50 ± 0.06
Oat (Avena sativa)	0.97 ± 0.01	0.15 ± 0.01	0.82 ± 0.01
Red clover (Trifolium pratense)	0.37 ± 0.01	0.09 ± 0.01	0.28 ± 0.01
Riesenfenchel (Ferula communis)	0.33 ± 0.01	0.07 ± 0.01	0.26 ± 0.01
Rosehip (Rosa canina)	1.05 ± 0.01	0.25 ± 0.01	0.80 ± 0.01
Rosemary (Rosmarinus officinalis)	1.80 ± 0.05	0.49 ± 0.01	1.31 ± 0.05
Sage (Salvia officinalis)	1.20 ± 0.02	0.33 ± 0.01	0.87 ± 0.01
Senna tea (Cassia)	0.49 ± 0.01	0.13 ± 0.01	0.36 ± 0.01
Yam (Dioscorea alata)	0.58 ± 0.01	0.12 ± 0.01	0.46 ± 0.01
Yarrow (Achillea millefolium)	1.57 ± 0.04	0.26 ± 0.01	1.31 ± 0.04

Table 2  Water soluble fraction of Cr(VI) in medicinal herbs

Sample	[Cr^+6], mg kg^−1	Water soluble fraction of [Cr^+6], mg kg^−1	Percentage of water soluble [Cr^+6]
Anise (Pimpinella anisum)	0.43 ± 0.01	0.407 ± 0.01	94.65
Centaury (Gentiana lutea)	0.08 ± 0.01	0.076 ± 0.01	95.00
Chamomile (Matricaria chamomilla)	1.09 ± 0.02	1.026 ± 0.02	94.13
Fennel (Foeniculum vulgare)	0.23 ± 0.01	0.214 ± 0.01	93.04
Flax (Linum)	0.41 ± 0.01	0.382 ± 0.01	93.17
Green tea (Camellia sinensis)	0.24 ± 0.01	0.223 ± 0.01	92.92
Indian hemp (Cannabis)	0.34 ± 0.01	0.332 ± 0.01	97.65
Laurel (Laurus nobilis)	0.25 ± 0.01	0.233 ± 0.01	93.20
Licorice (Glycyrrhiza glabra)	0.80 ± 0.01	0.759 ± 0.01	94.87
Linden (Tilia)	0.12 ± 0.01	0.112 ± 0.01	93.33
Marestail (Equisetum arvense)	0.40 ± 0.01	0.380 ± 0.01	95.00
Melissa (Melissa officinalis)	0.28 ± 0.01	0.268 ± 0.01	95.71
Nettle (Urtica)	0.42 ± 0.06	0.398 ± 0.06	94.76
Oat (Avena sativa)	0.15 ± 0.01	0.141 ± 0.01	94.00
Red clover (Trifolium pratense)	0.09 ± 0.01	0.085 ± 0.01	94.44
Riesenfenchel (Ferula communis)	0.07 ± 0.01	0.066 ± 0.01	94.28
Rosehip (Rosa canina)	0.25 ± 0.01	0.235 ± 0.01	94.00
Rosemary (Rosmarinus officinalis)	0.49 ± 0.01	0.468 ± 0.01	95.51
Sage (Salvia officinalis)	0.33 ± 0.01	0.317 ± 0.01	96.06
Senna tea (Cassia)	0.13 ± 0.01	0.123 ± 0.01	94.61
Yam (Dioscorea alata)	0.12 ± 0.01	0.114 ± 0.01	95.00
Yarrow (Achillea millefolium)	0.26 ± 0.01	0.248 ± 0.01	95.38

RESULTS AND DISCUSSION

The standard reference material used (SRM 1573 a tomato leaf, indicates if this is from the NIST) has a certified chromium concentration value of 1.99 ± 0.06 mg kg⁻¹. The value found by us after the analysis of chromium level in SRM 1573 a tomato leaf was 1.98 ± 0.02 mg kg⁻¹. This result showed excellent agreement with the certified value.

Medicinal plants may be contaminated easily during growing and processing. It is important to have a good quality control for herbal medicines in order to protect consumers from contamination. The speciation and determination of chromium in various medicinal plants was successfully performed in the present study. Used procedure was useful for routine control analyses of medicinal plants because of its rapidity, sensitivity, and economy. The total chromium, Cr(VI), and Cr(III) concentrations are represented in Table 1. The highest chromium concentrations were detected in chamomile (4.21 ± 0.18 mg kg⁻¹), licorice (2.80 ± 0.12 mg kg⁻¹), melissa (2.71 ± 0.10 mg kg⁻¹), marestail (2.66 ± 0.10 mg kg⁻¹), and anise (1.98 ± 0.06 mg kg⁻¹). Minimal concentrations of chromium were found in riesenfenchel (0.33 ± 0.01 mg kg⁻¹), red clover (0.37 ± 0.01 mg kg⁻¹), centaury (0.43 ± 0.01 mg kg⁻¹), senna tea (0.49 ± 0.01 mg kg⁻¹), and linden (0.50 ± 0.01 mg kg⁻¹). Cr(III) and Cr(VI) concentrations in medicinal herbs were found in the range of 0.26–3.12 mg kg⁻¹ and 0.07–1.09 mg kg⁻¹, respectively.

Medicinal plants are generally consumed as herbal tea. For this reason, water soluble fractions of Cr(VI) in medicinal plants are investigated. Obtained results are represented in Table 2. As it can be seen from this table, 95% of Cr(VI) in medicinal herbs were dissolved in water. Medicinal herbs are generally in tea bags containing an average 2 g of herb leaves. This means that only 10 g of herb is to be consumed if herbal tea is drank 5 times in a day and, therefore, ADDI (average daily dietary intake) (0.05–0.2 mg/day for Cr) is never reached and there is no danger mainly for toxic Cr(VI) originating from herbal teas.

CONCLUSION

The biggest advantage of this study was being the first study in the literature for the determination of chromium species in medicinal plants. Furthermore, the results obtained from this study show that chromium concentrations in medicinal herbs were not thought to create a risk factor for human health. This study will be an example for studies related to speciation of other heavy metals in medicinal plants.