54 samples belonging to 23 herbal species (15 individuals and 8 mixtures) were analyzed for their contents of heavy metals in the raw materials and in their water infusions. Trace and toxic elements in these samples were determined by using inductively coupled plasma-atomic emission spectrometry (ICP-OES) following acid digestion. The order of decreasing mean metal concentrations in raw materials (mg/kg) was found to be as follows: Fe (440) > Mn (162) > Zn (45.8) > Cu (12) > Pb (10.4) > Ni (5.4) > Cr (2.9) > Co (0.91) > Cd (0.5). It was found that 21% of the analyzed samples contain both Cd and Pb above their permissible limits. However, the infusions produced from these plants were found to contain fewer amounts of metals than the raw materials. Studied metals had the following mass transfer percentages to the infusion solutions (Fe: 3.5%, Cd: 14%, Cr: 15%, Pb: 20%, Co: 29%, Ni: 31%, Zn: 36%, Cu: 48%, and Mn: 53%). The estimated daily intake calculated for the toxic elements Pb and Cd through the consumption of herbal infusions was far below the tolerable daily intake set by the World Health Organization (WHO).
Medicinal plants and their various products (raw material, mixtures, distillates, extracts, etc.) are well known as herbal medicines; they have been available for many hundreds of years for treatment of human diseases. Nowadays, various species of herbs are widely used as raw materials in the pharmaceutical industries and also extensively consumed as home remedies [
The increasing popularity of herbal products as medications has produced fear about their quality and safety for human consumption. These products may be contaminated with microbial contaminants, chlorinated pesticides, heavy metals, and other chemical toxins [
The growing condition of plant, chemical treatments, type of plant species, processing steps, and storage condition are important factors affecting the levels of different metals in herbal preparations [
All solutions were prepared with analytical reagent grade chemicals. Deionized water with specific resistivity of 18.0 M Ω cm−1 was used. All glassware used in the present study was previously soaked in 10% (v/v) HNO3 solution for 12 h and rinsed with deionized water. Nitric acid (HNO3, 69%) and hydrogen peroxide (H2O2, 30%) were of ultrapure quality (Trace SELECTâ, Fluka). Standard calibration of mixed and individual metal solutions of Fe, Zn, Cu, Cr, Ni, Mn, Co, Pb, and Cd (BDH Spectrosol®, Fluka Chemika®) at concentration of 1000 mg L−1 was appropriately diluted and used to calibrate the ICP-OES before metal determination. A certified reference materials (NIST 1570a), spinach leave, obtained from National Institute of Standards and Technology, USA, was used for method validation.
A total of 54 samples of various commercially available medicinal herbs were randomly purchased from general stores in Irbid city, Jordan. The herbal samples were commercially available in the form of tea bags packaged in boxes with 12–24 pieces of tea bags; each bag contains 1.1–2.7 g of the herbs raw material. The raw herbal material from all tea bags in one box was placed in polyethylene container, mixed, homogenized, and stored at room temperature. Brand codes, contents, and other information are presented in Table
Summary of the medicinal herbal samples, their common and scientific names, and sources and their recommended medicinal uses.
Sample code | Brand name | Number of samples | Common name | | Product of (source) | Medicinal uses (claimed on the manufacturers’ packaging) |
---|---|---|---|---|---|---|
H1 | Teebah | 4 | Sage | | Jordan | Digestive problems, depression, memory loss, diarrhea, bloating, and overproduction of perspiration |
H2 | Ibn Sina | 2 | Cumin | | Syria | Antiflatulence antispasmodic and diuretic menstruation |
H3 | Al-Bothoor | 2 | Oliban | | Egypt | Chest coughs, nausea, indigestion, and hypertension |
H4 | Al-Khodary | 4 | Chamomile | | Jordan | Anti-inflammatory, sleep aid, treatment for fevers, colds, and stomach ailments |
H5 | Al-Nakhah | 3 | Peppermint | | Jordan | Irritable bowel syndrome and colonic spasms, functional dyspepsia, and enhancement of gastric emptying |
H6 | Al-Rawabi | 2 | Cinnamon | | Jordan | Control of blood sugar levels, powerful anti-bacterial agent, and natural disinfectant |
H7 | Al-Attar | 2 | Anise | | Syria | Remove phlegm and catarrh in the bronchial passageways, relieve asthma symptoms, indigestion and stomach pain, and mouth freshener |
H8 | Bint -Alreef | 2 | fennel flower | | Jordan | Healing for all diseases |
H9 | Al-Nakhah | 2 | Ginger | | Jordan | Inflammation of the colon, asthma symptoms, pain during menstruation, high blood pressure chronic inflammation, and relief of nausea |
H10 | Al-Rawabi | 3 | Thyme | | Jordan | Kidney problems, muscle pain, chronic fatigue, parasites, anxiety, and headache |
H11 | Al-Bothoor | 2 | Roselle | | Egypt | High blood pressure, coughs, and colds |
H12 | Ibn Sina | 2 | Lemon Balm | | Syria | Nervous agitation, urinary spasms, functional gastrointestinal complaints, sleep disorders, and menstrual cramps |
H13 | Bint -Alreef | 2 | Fenugreek | | Jordan | Laxative, digestive aid, remedy for coughs and bronchitis, and increases in breast milk production |
H14 | Teebah | 2 | Cardamom | | Jordan | Digestion problems, common cold, cough, and bronchitis |
H15 | Al-Nakhah | 3 | Roots of shirsh zallouh | | Jordan | Enhance sexual performance |
M1 | Al-Attar | 3 | Herbal tea (zhourat) mixture | Syria | Antimicrobial, antiviral, and inflammation of gastric mucosa | |
M2 | Al-Attar | 2 | Herbal mixture | — | Syria | Sedative of renal colic |
M3 | Al-Attar | 2 | Herbal mixture | — | Syria | Sedative allergic asthma |
M4 | Al-Attar | 2 | Herbal mixture | — | Syria | Coughing |
M5 | Al-Attar | 2 | Herbal mixture | — | Syria | Cold |
M6 | Al-Attar | 2 | Herbal mixture | — | Syria | Inflation and gases |
M7 | Al-Attar | 2 | Herbal mixture | — | Syria | Laxative |
M8 | Ibn Sina | 2 | Mixed Chinese herbs | — | Syria | Slimming |
Aliquots (1-2 g) of the herbal raw material were accurately weighed into a precleaned glass beaker and digested with 15 ml of a mixture of freshly prepared solution of (1 : 1) (v/v) HNO3 (69%)–H2O2 (30%). Each beaker was covered with a watch glass and heated on hot plate at 150–180°C; aliquots of nitric acid were added until the solutions were clear. Solutions were contentiously boiled until the volume for each sample reduced to about 5 ml. The solutions were then allowed to cool, filtered (glass wool), and diluted up to 50 ml with acidified (HNO3) deionized water and then placed in acid washed 60 ml polyethylene bottles.
The herbal infusions were prepared by adding 200 ml of hot (97°C) Milli-Q water to a weighed portion (2 g) of plant material. The suspension was then stirred with a glass-rod stirrer for 1 minute and steeped for a total of 10 min, as recommended by the manufacturers. The 10-minute infusion time was found to be adequate to prepare a good quality tea beverage [
All digested samples and infusions were analyzed, in triplicate, for metal contents using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) (VISTA-MPX instrument). The simultaneous ICP-OES was equipped with axial vision, a radio frequency (RF) source of 30 MHz, a CCD (Charge Coupled Device), a peristaltic pump, and a glass concentric nebulizer.
In order to validate the instrumental methods and analytical procedures for accuracy, all the samples were taken in triplicate and all measurements were run in triplicate for standards and samples. Analytical blank involving all reagents was run (in triplicate) to check for interferences and cross-contamination of every batch of 15 samples. Certified reference material (NIST 1570a) was also analyzed every batch. Accuracy was determined by comparing the measured concentrations with the certified values and was expressed as a percentage recovery (% recov.). The achieved results were in good agreement with certified values. The results are given in Table
Concentrations of selected elements in the NIST1570a certified reference material.
Metal | Certified value | Measured value | Recovery % |
---|---|---|---|
Mn | 75.9 | 72 | 94.9 |
Zn | 82 | 84 | 102.4 |
Ni | 2.14 | 2.0 | 93.5 |
Co | 0.39 | 0.36 | 92.3 |
Cu | 12.2 | 11.3 | 92.6 |
Cd | 2.89 | 2.59 | 89.6 |
The concentrations of Fe, Cu, Zn, Mn, Cr, Co, Ni, Cd, and Pb elements in 54 samples of individuals and mixtures of medicinal herbal plants were determined by using ICP-OES. The mean metals concentrations in raw herbal materials are listed in Table
The average contents of heavy metals (mg/kg) in the tested raw medicinal herbal samples.
Sample code | Zn | Fe | Cu | Co | Cr | Mn | Ni | Cd | Pb |
---|---|---|---|---|---|---|---|---|---|
H1 | 54.2 ± 8.6 | 574 ± 260 | 8.6 ± 3.4 | 1.8 ± 1.3 | 2.1 ± 0.9 | 99 ± 136 | 5.9 ± 3.7 | 0.7 ± 0.4 | |
H2 | 51.8 ± 11.4 | 6.60 ± 0.55 | 13.5 ± 1.8 | <0.03 | 2.7 ± 0.7 | 28.7 ± 9.1 | 6.34 ± 2.7 | 0.2 ± 0.04 | 5.5 ± 3.2 |
H3 | 4.9 ± 0.4 | 49.5 ± 3.9 | 7.9 ± 0.7 | <0.03 | 3.7 ± 0.6 | 2.1 ± 0.3 | 1.9 ± 0.9 | 0.5 ± 0.1 | 17.7 ± 4.8 |
H4 | 49.8 ± 3.3 | 824 ± 344 | 12.6 ± 1.3 | <0.03 | 1.52 ± 1.3 | 185 ± 209 | 3.05 ± 2.8 | 0.17 ± 0.34 | 8.01 ± 5.4 |
H5 | 39.6 ± 12 | 1121 ± 308 | 16.9 ± 5.9 | 1.02 ± 1.1 | 3.10 ± 0.6 | 148 ± 41 | 4.45 ± 3.7 | 0.63 ± 0.58 | 16.2 ± 3.1 |
H6 | 24.7 ± 1.9 | 171 ± 14.7 | 7.12 ± 5.3 | 0.04 ± 0.04 | <0.04 | 251 ± 92 | 0.67 ± 0.93 | 0.25 ± 0.36 | 7.90 ± 0.36 |
H7 | 72.3 ± 21.1 | 86.2 ± 111 | 13.9 ± 4.5 | 1.65 ± 0.56 | 2.1 ± 2.7 | 57.7 ± 0.2 | 3.98 ± 4.9 | 0.38 ± 0.15 | 5.33 ± 3.3 |
H8 | 59.4 ± 2.2 | 7.4 ± 0.6 | 16.3 ± 2.2 | 0.77 ± 0.13 | 1.8 ± 0.2 | 20.5 ± 6.2 | 3.91 ± 2.4 | <0.01 | <0.04 |
H9 | 26.3 ± 4.9 | 136 ± 89 | 6.70 ± 1 | <0.03 | 3.2 ± 4.1 | 250 ± 112 | 2.4 ± 1.6 | 0.62 ± 0.06 | 11.0 ± 1.4 |
H10 | 46.5 ± 11.8 | 556 ± 139 | 17. 3 ± 2.4 | 0.29 ± 0.5 | 0.71 ± 0.09 | 324 ± 252 | 2.47 ± 1.7 | 0.92 ± 0.5 | 19.3 ± 10.6 |
H11 | 135 ± 8.5 | 328 ± 30.5 | 14.7 ± 3.1 | 5.19 ± 0.67 | 5.52 ± 0.9 | 660 ± 77 | 12.7 ± 4.3 | 1.01 ± 0.9 | 17.4 ± 10.4 |
H12 | 38.9 ± 15.1 | 437 ± 33.6 | 9.79 ± 1.3 | 0.60 ± 0.8 | 1.88 ± 2.2 | 69.3 ± 2.7 | 6.01 ± 3.3 | 0.69 ± 0.9 | 6.56 ± 9.2 |
H13 | 36.4 ± 5.5 | 24.8 ± 4.2 | 9.13 ± 1.7 | <0.03 | <0.04 | 26.5 ± 15.1 | 0.53 ± 0.8 | <0.01 | <0.01 |
H14 | 36.7 ± 6.1 | 311 ± 16.1 | 17.5 ± 3.7 | 0.07 ± 0.4 | 0.21 ± 0.29 | 382 ± 14 | 4.27 ± 1.39 | 0.40 ± 0.16 | 8.26 ± 4.61 |
H15 | 35.3 ± 13.2 | 686 ± 108 | 7.77 ± 1.17 | <0.03 | 6.74 ± 2.47 | 39.7 ± 20 | 8.40 ± 1.8 | 0.66 ± 0.26 | 8.14 ± 4.33 |
M1 | 45.6 ± 5.7 | 519 ± 321 | 14.5 ± 6.2 | 0.18 ± 0.3 | 3.75 ± 3.8 | 353 ± 65 | 7.25 ± 6.17 | 0.44 ± 0.5 | 5.74 ± 9.9 |
M2 | 52.9 ± 7.6 | 693 ± 64 | 6.89 ± 0.9 | <0.03 | 2.40 ± 0.6 | 69.7 ± 17.6 | 8.38 ± 2.1 | <0.01 | 18.20 ± 6.9 |
M3 | 56.6 ± 18.4 | 800 ± 72 | 15.8 ± 3.1 | 3.92 ± 0.14 | 2.00 ± 0.17 | 85.2 ± 10.8 | 11.2 ± 1.3 | 1.27 ± 0.63 | 18.6 ± 8.2 |
M4 | 40.9 ± 7.0 | 570 ± 114 | 10.5 ± 2.3 | 3.59 ± 0.74 | 2.99 ± 0.26 | 76.7 ± 10 | 10.9 ± 0.62 | <0.01 | 6.1 ± 4.0 |
M5 | 41.0 ± 4.5 | 282 ± 63 | 8.5 ± 1.1 | 1.87 ± 0.33 | 8.67 ± 0.61 | 182 ± 31 | 6.2 ± 1.5 | 0.38 ± 0.1 | 9.2 ± 5.3 |
M6 | 37.5 ± 8.4 | 13.1 ± 5.3 | 17.9 ± 4.7 | 0.78 ± 1.1 | 8.27 ± 1.6 | 56.4 ± 9.6 | 7.7 ± 1.0 | 0.15 ± 0.05 | 18.6 ± 26.0 |
M7 | 26.1 ± 3.5 | 62.4 ± 18.3 | 7.3 ± 1.1 | <0.03 | 2.94 ± 0.24 | 24.9 ± 7.4 | 4.6 ± 2.3 | 0.76 ± 0.34 | 4.24 ± 1.3 |
M8 | 37.3 ± 5.9 | 783 ± 59 | 12.3 ± 3.6 | 0.34 ± 0.48 | 1.48 ± 0.34 | 276 ± 59 | 4.2 ± 0.8 | 1.25 ± 0.36 | 28.7 ± 10.5 |
| |||||||||
Statistical values of all 54 samples | |||||||||
Highest | 141 | 1477 | 23.7 | 5.67 | 9.43 | 715 | 15.7 | 1.25 | 28.7 |
Lowest | 4.63 | 6.23 | 3.37 | nd | nd | 1.82 | 0.53 | nd | nd |
Mean | 45.8 | 440 | 12.0 | 0.91 | 2.90 | 162 | 5.44 | 0.5 | 10.4 |
Median | 43.7 | 409 | 11.5 | 0 | 2.29 | 79.9 | 5.40 | 0.4 | 9.25 |
St. dev. | 23.1 | 357 | 4.62 | 1.44 | 2.60 | 172 | 3.82 | 0.45 | 8.44 |
The results for the mean concentrations of studied metals in herbal infusions are presented in Table
Average contents of heavy metals (mg/kg) in the raw samples and water infusions of the medicinal herbs.
Element | Zn | Fe | Cu | Co | Cr | Mn | Ni | Cd | Pb |
---|---|---|---|---|---|---|---|---|---|
Dried herbs (mg/kg) | 45.8 ± 5.1 | 440 ± 77 | 12 ± 1.0 | 0.91 ± 0.3 | 2.9 ± 0.6 | 162 ± 38 | 5.4 ± 0.8 | 0.5 ± 0.1 | 10.4 ± 1.8 |
Infusions (mg/kg) | 16.5 ± 3.7 | 15.6 ± 4.3 | 5.8 ± 0.8 | 0.26 ± 0.1 | 0.4 ± 0.1 | 86 ± 9 | 1.7 ± 0.5 | 0.07 ± 0.1 | 2.1 ± 0.8 |
Extraction efficiency (%) | 36 ± 4 | 3.5 ± 4 | 48 ± 5 | 29 ± 5 | 15 ± 7 | 53 ± 6 | 31 ± 7 | 14 ± 6 | 20 ± 5 |
Relationship between Cu, Ni, Pb, Cd, Cr, and Co content of the dried herbal samples and the extracted metal contents of the labile fractions in the infusions.
Relationship between Fe, Mn, and Zn contents of the dried herbal samples and the extracted metal contents of the labile fractions in the infusions.
The extraction efficiency of metals from the herbal raw material to the water infusion was found to be influenced by the kind of herbal species, while Fe extraction efficiency was below 10% in most cases, it reaches more than 25% for ginger, cumin, and fennel flower. The extraction efficiencies for Zn, Cd, and Pb were high for roselle and exceed 60%. Thyme infusion was found to contain 50% of the initial chromium amount.
The average iron content of the medicinal herbs was in the range of 6.2 mg/kg to 1477 mg/kg with the lowest value in cumin and highest value in peppermint. Samples of chamomile, roots of shirsh zallouh, thyme, and sage had high iron concentrations of 824 mg/kg, 686 mg/kg, 556 mg/kg, and 547 mg/kg, respectively. The mean iron content of all the analyzed samples was 440 mg/kg. In another related work, chamomile and sage had comparable iron contents of 502.7 mg/kg and 297.4 mg/kg, respectively [
Manganese mean concentration was 162 mg/kg with a range of 1.8 mg/kg (oliban) to 715 mg/kg (roselle). In addition to roselle; the thyme, cinnamon, ginger, and chamomile samples were found to contain significant amounts of manganese as 324 mg/kg, 251 mg/kg, 250 mg/kg, and 185 mg/kg, respectively. Similar concentration range of manganese (<6 mg/kg to 450.7 mg/kg) was reported for some medicinal plants [
Zinc and cooper were high in roselle (141 mg/kg) and peppermint (23.7 mg/kg), respectively. The mean zinc and copper concentrations in all of the analyzed herbal samples were 45.8 mg/kg and 12.0 mg/kg, respectively. Zinc concentrations varied from 4.6 mg/kg to 141 mg/kg and copper concentrations ranged from 3.37 mg/kg to 23.7 mg/kg. In a related work, similar concentrations ranges of zinc and copper were reported as 3.75–88 mg/kg and 3.32–30.2 mg/kg, respectively [
Lead and cadmium are toxic elements for human; they perform no beneficial biological roles and can be very dangerous even at low concentrations. The highest mean concentration of lead in individual herbs was detected in thyme (19.3 mg/kg) followed by oliban (17.7 mg/kg), roselle (17.4 mg/kg), and peppermint (16.2 mg/kg). Among the mixtures of herbs, the Chinese herbal mixture for slimming was found to contain a high mean concentration of lead (28.7 mg/kg). The lowest mean concentration of lead was observed in fennel flower (black seed) and fenugreek where it was below the detection limit (0.06 mg/kg). The mean concentration of lead in all of the analyzed samples was 10.4 mg/kg. Comparable result for the lead concentration range has recently been reported as from below detection limit to 33.8 mg/kg [
The content of cadmium in the analyzed herbs varied between <0.04 mg/kg and 1.27 mg/kg with an average value of 0.5 mg/kg. The highest cadmium content was found in allergic asthma mixture (mix 3) as 1.27 mg/kg and Chinese herbal mixture (mix 8) as 1.25 mg/kg. In the individual herbs, cadmium was detected at high concentrations in roselle (1.01 mg/kg), thyme (0.92 mg/kg), lemon balm (0.69 mg/kg), and sage (0.65 mg/kg). Comparing the results obtained in this research with results found in the literature, the cadmium concentration range is similar to that reported by Onwordil et al. for various types of herbal medicines (0.48–3.08 mg/kg) [
The concentration ranges of nickel and chromium are similar; they were measured as from 0.53 mg/kg to 15.7 mg/kg and from <0.03 to 9.43, respectively. The mean nickel and chromium concentrations in all of the analyzed herbal samples were 5.44 mg/kg and 2.9 mg/kg, respectively. In related work, a concentration range of 0.72 mg/kg–13.1 mg/kg with an average of 3.62 mg/kg and a concentration range 0.44 to 8.71 with an average of 2.5 have been reported for nickel and chromium, respectively [
Cobalt is the least detected element in the analyzed herbs; it was quantified in 54% of the samples in the range of <0.03 mg/kg to 5.67 mg/kg with mean value of 0.91 mg/kg. High mean concentrations of cobalt were detected in roselle (5.19 mg/kg), sage (1.83 mg/kg), anise (1.6 mg/kg), and peppermint (1.02 mg/kg). In the herbal mixture, high cobalt concentrations were found in allergic asthma mixture (mix 3) (3.92 mg/kg) and coughing mixture (mix 3) (3.59 mg/kg). Comparable results for the cobalt concentration ranges in herbal medicines have been reported as 0.05–2.35 mg/kg [
The extraction efficiencies of various metals from raw material to the water infusions were found to be variable; this was also observed by other related studies. For instance, Queralt et al. [
Because of the toxic properties of lead and cadmium, it is important to evaluate the safety of the herbal preparation. In this work the two toxic elements lead and cadmium were quantified in the raw materials of herbal remedies with average values close to or slightly above their permissible limits of 10 mg/kg and 0.3 mg/kg, respectively. It was found that 40% of the analyzed samples contain more than 10 mg/kg of lead and 60% of the analyzed samples contain more than 0.3 mg/kg of cadmium, while 30% of the samples contain the two elements above their permissible limits. Indeed, the determination of total concentration of the toxic elements in the herbal raw materials gives indication of the toxicity of the herbal preparation, but this step is not sufficient in assessing the safety of these products because the consumers take these remedies as recommended by the producers as their infusion in hot water. In fact, all infusions were found to contain fewer amounts of metals than the raw materials, and so it is important to evaluate the infusions for their safety. By assuming the consumption of 200 ml infusion prepared from 2-scahets (2 g) two times a day, as recommended by the manufacturer, and by using the mean value of the % extraction efficiency for Pb and Cd, the estimated daily intake was calculated as 8.32
Quantification of nine metal elements (Fe, Mn, Zn, Cu, Cr, Co, Ni, Pb, and Cd) in the raw materials and water infusions of selected herbal remedies and comparison with the values in the literature revealed that the heavy metal contents of these commercially available products vary and are affected by the plant species. In the raw materials, Fe had the highest mean content (440 mg/kg) and Cd had the lowest mean content (0.5 mg/kg). Mn and Cu demonstrated relatively high extraction efficiencies to the infusions while Fe had the lowest extraction efficiency. Some raw herbal materials had lead and cadmium contents above the permissible limits. However, the water infusions of these medicinal preparations contain lower levels of lead and cadmium and consumption of the tested beverages poses no risk to human health.
The author declares no conflicts of interest.
The author acknowledges Al-Hussein bin Talal University for the sabbatical leave.