|Iranian Journal of Pharmaceutical Research
(2009), 8 (2): 95-99
Received: October 2007
Accepted: September 2008
Copyright ? 2009 by School of Pharmacy
A Quantitative investigation on some toxic and non-toxic
metals in popular medicinal herbs in Iranian market
Fazel Shamsaa*, Shamsali Reza Zadehb, Hashim Shamsaa and Khosro Abdia
aDepartment of Pharmaceutical Chemistry, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Islamic Republic of Iran. bMedicinal Herbs Research Center, Jihad Institute, Tehran, IR Iran.
This study was performed to explore the presence of heavy metals in some popular herbal medicines of the Iranian market. Primarily, this study was planned to do the task by the USP method. In the second step, those plants which contained more than 10 ppm of total heavy metals were analyzed by atomic absorption method. In this study, 43 popular herbal medicines were investigated according to the limit test procedure in the USP. It was found that 27 of these plants contained less than 10 ppm heavy metals compared to a standard lead solution, while 16 contained more than 10 ppm. The presence of Pb (<2.5), Cd (<0.25), Co (<1) and Ni (<1.5) could be considered safe.
During recent decades, there has been an increasing attention using herbal products for combating diseases. One of the reasons that people prefer herbal medicines over modern chemicals is their low price, while another reason is their safety compared to the chemical drugs, ignoring the fact that there are chemical materials in plants as their active ingredients. Because the plants are directly in contact with air, water and soil, the constituents of these sources might contaminate the plants. In addition to toxic elements such as mercury, arsenic, lead, nickel and cadmium which might be present in some plants and threaten the consumer health, especially the children and elderly, useful elements such as calcium, magnesium, zinc, manganese and iron are also usually present in plants, which helps the good health. Many countries have already evaluated their popular herbal medicines with regard to toxic heavy metals (1-5).
Therefore, a study was undertaken to evaluate the herbal medicines in Iranian market with regard to the toxic and nontoxic metals, according to USP, by using atomic absorption spectrometry.
The popular plants used in this study were purchased from herbal medicines stores in Tehran and were diagnosed by a botanist.
Sulfuric acid, nitric acid, hydrogen peroxide, thioacetamide, glycerin, acetic acid, ammonium acetate, and lead nitrate were bought from the Iranian agent of Merck Co.
Acetate buffer (pH=3.5), thioacetamide TS, thioacetamide-basic glycerin TS, and glycerin basic were prepared according to USP.
Standard lead solution
Lead nitrate (160 mg) was dissolved in double distilled water (ddW) and nitric acid (6N, 1 ml) and was made to volume (100 ml). One ml of this solution was diluted to 100 ml with ddW to contain 10 ?g/ml of Pb.
General screening method
The 3rd method of USP was applied for monitoring the total heavy metal content in herbal medicines under study. In this method, three different solutions should be prepared, i.e., a standard, a monitor and herbal sample solutions.
A mixture of sulfuric acid (8 ml) and nitric acid (10 ml) was transferred to a Kjeldal flask (100 ml). The mixture was heated until the appearance of white vapors. Double distilled water (10 ml) was added cautiously and boiled until a white vapor appeared. After cooling, ddW (5 ml) was added to reach a volume of 2-3 ml, mixed and boiled. After cooling, ddW (5 ml) and lead standard solution (2 ml, 20 ?g Pb2+) were added and mixed. For color comparison the mixture was transferred to a 50 ml test tube (TT), the flask is washed, transferred to the TT and the volume is made to 25 ml.
Preparation of the herbal product under study for heavy metal limit test
Herbal sample (2.0 g) was transferred to a dry Kjeldal flask, moistened by a mixture of sulfuric and nitric acids (8:10 v/v) and heated gently until the reaction started. This process was repeated until 18 ml of the acid mixture was consumed. The solution was boiled gently until the appearance of a deep color, and then cooled. Nitric acid (2 ml) was added, and re-heated until the solution became deeply colored. Heating and adding nitric acid were repeated until the solution was no more deeply colored. After cooling, ddW (5 ml) was added and boiled until the appearance of white vapors. The volume was reduced to 2-3 ml and then cooled. If the solution was colored yellow, it should have been decolorized using hydrogen peroxide. The solution was transferred to a 3rd TT, the flask was rinsed by ddW and transferred to the same TT and the volume was made to 25 ml.
The solution was prepared and processed similar to the preparation method of the herbal product under study and was then cooled and diluted with ddW. Then, the standard lead solution (2 ml, 20 ?g) was added and mixed. The mixture was transferred to the 2nd comparison TT, the flask was washed and transferred to the same TT, and made to 25 ml by ddW.
Heavy metal levels of the herbal products under study
The pH values of the monitor, standard and herbal solutions were adjusted to 3-4 using dilute ammonia solution. The volumes were made to 40 ml by ddW, acetate buffer (2 ml, pH=3.5) and thioacetamide glycerin base TS solution (2 ml) were added, to each TT, the volumes were made to 50 ml by ddW, and left for 2 min. By watching of comparing the solutions against a white surface, the test solution color intensity should not exceed that of the standard and monitor solutions.
Sample preparation evaluation of toxic and non-toxic metals in herbal products
The herbal products under study (2-5 g) was moistened with 30 ml of ddW and boiled for 20 min. After filtration, the extraction was repeated twice, and the extracts were combined and concentrated 10 ml. The solution was transferred to a crucible and dried by gentle heating. The crucible was left for 2 h at 400-500?C in a furnace. After weighing the ash (Table 3), it was dissolved in hydrochloric acid 20 ml, transferred to a 50-ml volumetric flask and made to volume by ddW. Individual metal content of this solution were analyzed by atomic absorption spectrometry.
Results and Discussion
For total heavy metal content in Iranian herbal medicines, the third USP method was successfully applied. Due to the presence of significant quantities of calcium, magnesium, sodium, and potassium, in the last step and before the addition of thioacetamide solution, the solutions should be filtered to make them transparent and clear. To these clear solutions, thioacetamide-glycerin basic TS solution was added and the turbidities of the solutions were compared. Those solutions with less turbidities than the standard and monitor solutions, were to contain less than 10 ppm of total heavy metals and (Table 1). Consumption of such products is considered safe. On the other hand, some of the herbal products showed more turbidities than the standard solution; therefore, they were considered to contain more than 10 ppm of total heavy metals (table 2). These products were ignited, dissolved in hydrochloric acid, and analyzed by atomic absorption spectrometry. The results of this analysis are shown in Table 4. From this table, the followings could be concluded:
1. Toxic heavy metals including lead, cadmium, cobalt, and nickel are present in insignificant quantities.
2. Flixweed seeds contain the highest amounts of iron and zinc (Fe=318, Zn=39.6 ppm).
3. Calcium and magnesium are present in significant quantities in different herbal products. For example, Staechus contains 75 mg/g and 4 mg/g, Flixweed seeds contains 24 mg/g and 1.85 mg/g, Celery seeds contains 32 mg/g and 2.5 mg/g, Savory seeds contains 78.5 mg/g and 14.9 mg/g of Ca and Mg, respectively.
4. Copper contents were low and acceptable, while savory seeds and small
caltrops contain the highest Cu contents, i.e. 3 and 2 ppm, respectively.
5. Some of the therapeutic activities of herbal products could be attributed to the presence of some metals such as iron (6), zinc (7), nickel (8, 9), manganese (10) and magnesium (11).
This study was supported by a grant from the Research Council of Tehran University of Medical Sciences, which is gratefully acknowledged.
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