According to one definition, the heavy metals are a group of elements between copper and lead on the periodic table of the elements—having atomic weights between 63.546 and 200.590 and specific gravities greater than 4.0. Living organisms require trace amounts of some heavy metals, including cobalt, copper, manganese, molybdenum, vanadium, strontium, and zinc, but excessive levels can be detrimental to the organism. Other heavy metals such as mercury, lead and cadmium have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of mammals can cause serious illness.

A stricter definition restricts the term to those metals heavier than the rare earth metals, at the bottom of the periodic table. None of these are essential elements in biological systems; all of the more well-known elements with the exception of bismuth and gold are horribly toxic. Thorium and uranium are sometimes included as well, but they are more often called simply "radioactive metals".

In medical usage, the definition is considerably looser, and "heavy metal poisoning" can include excessive amounts of iron, manganese, aluminium, or beryllium (the second-lightest metal) as well as the true heavy metals.

Also, often the elements beyond mercury, e.g., the actinides such as uranium and plutonium, are not excluded from the heavy metals. In the context of nuclear power plants, tHM means tons of heavy metal.

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Medicinal herbs: a potential source of toxic metal exposure for man and animals in India
From Archives of Environmental Health, 5/1/02 by Shailendra K. Dwivedi

USE OF MEDICINAL HERBS for amelioration of toxic effects of different chemicals and heavy metal pollutants in man and animals is receiving attention worldwide. The magnitude of their uses during recent years for the cure of various ailments is obvious from a report by the World Health Organization, (1) which indicated that many people in developing countries still rely on herbal medicine for treatment of various ailments. In ancient India, most of the herbs were collected from hills, forests, and areas least inhabited by humans. Ironically, medicinal plants today are cultivated commercially in polluted environments, where soil, (2) water, (3) and air (4) contain rather high levels of pollutants. Therefore, the environment required for growth and synthesis of these plants is affected drastically, and the possibility that toxic pollutants are deposited in the plants cannot be disregarded. Little is known about the status of toxic metals in these medicinal plants grown in polluted environments. The possibility that toxic pollutants can be translocated to humans and animals through the use of herbs grown in polluted zones has concerned scientists who promote use of herbal medicines. We decided, therefore, to assess the levels of toxic metals (i.e., lead and cadmium) in 28 commonly used medicinal plants in India.

Method

A total of 28 commonly used medicinal plants were obtained from different sources, including collection centers of commercial herbal medicine manufacturers. Each medicinal plant was procured in 3 batches obtained during the summer, rainy season, and winter, respectively. The plants were identified and authenticated at the Department of Botany at Rohilkhand University prior to toxic metal analysis. The plants were washed thoroughly with deionized distilled water, dried in a shed, and compressed into a powder with the help of a manual grinder. One gram of each powdered sample was wet digested, (5) and lead and cadmium content was estimated with an atomic absorption spectrophotometer (6) (Model 4120, Electronic Corporation of India, Ltd. [Hyderabad, India]). Air acetylene was used as the combustion gas. The detection limits for lead and cadmium in the spectrophotometer were 0.02 ppm and 0.001 ppm, respectively. The analytical quality was maintained by repeated analysis of reference standards obtained from Sigma Chemical (St. Louis, Missouri). Eight freshly prepared working standards were run with each sample series. Quality control criteria were strictly enforced. (7) In this study, we expressed mean lead and cadmium values in ppm. (8)

Results and Discussion

Concentrations of lead and cadmium in the medicinal herbs studied are presented in Table 1. Mean lead concentration ranged between 2.624 ppm (standard deviation [SD] = 0.426) and 32.757 ppm (SD = 0.124), whereas mean cadmium concentrations ranged between 0.056 ppm (SD = 0.002) and 0.419 ppm (SD = 0.006). There was no positive correlation between lead and cadmium levels within the same plant part. However, leaf portions contained higher concentrations of toxic metals than stem bark or roots. With the exception of the fallout of atmospheric pollutants through rain and accumulation of pollution in leaves, it is highly probable that these metals were translocated through air and water. Furthermore, low concentrations of lead and cadmium recorded in seeds confirm this conclusion. There were no available published reports on lead and cadmium levels in medicinal plants from India; therefore, we were unable to compare the results of our study with any others. However, in several recent studies, investigators have reported that herbal drugs used in the Indian subcontinent and China contain higher concentrations of heavy metals than in other areas, and that their continuous use might be toxic. (9-12) Unfortunately, in India, most of the population believes that herbal medicines are safe and nontoxic, unlike modern chemotherapeutic agents, and they are unaware of the toxic potential of these medicinal plants.

Individuals generally use herbal medicines for prolonged periods to achieve a desirable effect. Prolonged consumption of such herbal medicine might induce chronic or subtle health hazards. Our findings indicated that toxic metals can be translocated through inorganically grown medicinal herbs. Strict quality-control mechanisms must be instituted so that use in humans and animals is safe.

The authors thank Dr. S. R. Sharma for his help in collecting the medicinal herbs, and Mr. Brijesh Tyagi for his technical assistance during the estimation of toxic metals in this study.

Submitted for publication November 13, 2000; accepted for publication December 29, 2000.

Requests for reprints should be sent to Dr. Shailendra K. Dwivedi, Director, National Research Centre on Equines, Sirsa Road, Hisar 125001, India.

References

(1.) World Health Organization (WHO) report on Regulatory Situation of Herbal Medicines: A Worldwide Review. Geneva, Switzerland: WHO, 1998; TRM-98.1.

(2.) Sahu KC, Warrier R. Lead, cadmium and copper concentration of soil and vegetation along Powai road in North Bombay. Indian J Earth Sci 1987; 12:50-57.

(3.) Chandra SV. Toxic Metals in the Environment R&D Bulletin. Lucknow, India: Industrial Toxicological Research Centre, 1980; pp 62.

(4.) Sadasivam S, Negi BS, Mishra UC. Atmospheric lead in some cities in India. Indian J Environ Health 1987; 27:280-86.

(5.) Association of Official Analytical Chemists. Official Methods of Analysis, 14th ed. Arlington, VA: AOAC International, pp 444-76.

(6.) Hessel DW. A simple and rapid quantitative determination of lead in blood. Atomic Absorp News 1968; 7:55-56.

(7.) Claeys F, Ducoffre G, Sartor F, et al. Analytical quality control of cadmium and lead in blood and cadmium in urine. In: Nordberg G, Herber R, Alessio L (Eds). Cadmium in the Human Environment: Toxicity and Carcinogenicity. Lyon, France: International Agency for Research on Cancer, 1992; publication no. 118.

(8.) Snedecor GW, Cochran WG. Statistical Methods. Ames, IA: Iowa State University Press, 1989; pp 217-72.

(9.) Dunbabin DW, Tallies GA, Popplewell PY, et al. Lead poisoning from Indian herbal medicine. Med J Aust 1992; 157:835-36.

(10.) Chan TYK, Chan JCN, Tomlinson B, et al. Poisoning by Chinese herbal medicine in Hong Kong: a hospital base study. Vet Human Toxicol 1994; 86:546-47.

(11.) Chan TYK, Chan AYW, Critehley JAJH. Hospital admissions due to adverse reactions to Chinese herbal medicine. J Trop Med 1993; 96:62-63.

(12.) Keen RW, Deacon AC, Delves HT, et al. Indian herbal remedies for diabetes as a cause of lead poisoning. Postgrad Med J 1994; 70:764.

SHAILENDRA K. DWIVEDI SAHADEB DEY Division of Medicine Indian Veterinary Research Institute Izatnagar, U.P., India

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