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Vol. 11 No. 4 - October 2005

Toxic Contaminants in Herbal Drugs

By: Vartika Rai And Shanta Mehrotra

Herbal drugs have increasingly been used worldwide during the last few decades as evidenced by rapidly growing global and national markets of herbal drugs. According to WHO estimates, the present demand for medicinal plants is about US $14 billion a year and by the year 2050 it would be about US $ 5 trillion.  Now people rely more on herbal drugs because of high prices and harmful side effects of synthetic drugs, and this trend is growing, not only in developing countries but in developed countries too. Unfortunately, the number of reports of people experiencing negative effects, caused by the use of herbal drugs, has also been increasing. There may be various reasons for such problems, like one of the major causes of adverse effects is directly linked to the poor quality of herbal medicines. Therefore, it has been recognized that insufficient attention was being paid to the quality assurance and control of herbal medicines. Although WHO has developed guidelines for the quality control of herbal drugs which provide a detailed description of the techniques and measures required for the appropriate cultivation and collection of medicinal plants. Despite such guidelines, there is still a lacuna between this available knowledge and implementation, because farmers and other relevant persons like producers, handlers and processors of herbal drugs are not much aware of WHO’s guidelines and they continue their work as before without any quality control measures which results in inferior quality of herbal drugs with lots of contaminants like heavy metals, pesticides and microbes. Therefore, the training for farmers and other relevant persons is an important measure to be taken to ensure good quality of raw herbal drugs.

Several cases of adverse effects of herbal drugs have been reported in developed countries during the last few years, which are allegedly caused by taking herbal products or traditional medicines prescribed by the practitioners of indigenous systems of medicine. These products may be contaminated with excessive banned pesticides, microbial contaminants, heavy metals and chemical toxins which cause various deformities like congenital paralysis, sensori-neural defects, liver and kidney damage etc.  These contaminants may be related to the source of herbal drugs, if these are grown under contaminated environment. Chemical toxins may come from unfavourable post harvest techniques/ wrong storage conditions or chemical treatment during the storage period etc.  Some of these environmental factors may be controlled by implementing good source; good agricultural practices and standard operating procedures (SOP) for producing good quality herbal products.

People believe generally that herbal and natural products are safer than the synthetic or modern medicines but even some indigenous herbal products contain heavy metals as essential ingredients. Thus the expanded use of herbal medicine has led the concerns relating to its safety, quality and effectiveness specially for ‘bhasmas’ as these are usually made of heavy metals like arsenic, mercury, copper, zinc, gold and silver. Therefore, contamination of herbal drugs with heavy metals is of prime concern. The poor quality control of these products causes health hazard as some products may have unusually high concentration of potent and poisonous ingredients that may be fatal if consumed unknowingly. Recently a study conducted by Harvard Medical School on Indian ayurvedic medicines, published in the Journal of American Medical Association (JAMA) reported that ayurvedic medicines bought from 30 South Asian stores in the Boston area had potentially harmful levels of lead, mercury and arsenic. These metals were found in the products like ‘Bal Guti’, ‘Mahayograj Guggulu’, ‘Mahalaxmi vilas Ras’, ‘Safi’, ‘Shilajit’ etc. of some of the leading companies within ayurvedic communities.  Therefore, users of these medicines may be at risk for heavy metal toxicity. Similarly, Koh & Woo (2000) reported excessive toxic heavy metals in Chinese proprietary medicines in Singapore during 1990-1997. Wong et al. (1993) also reported the concentration of nine heavy metals cadmium, cobalt, copper, iron, manganese, nickel, lead, zinc and mercury in 42 Chinese herbal drugs. The concentration range of the metals was comparable to that reported in many of the East Asian vegetables and fruits. Few samples contained relatively higher concentration of toxic metals such as cadmium, lead and mercury. This report suggested that the presence of heavy metals was probably caused by contamination during air drying and preservation.

A study conducted at National Botanical Research Institute also showed the presence of heavy metals like lead, cadmium, chromium, cobalt, manganese, copper and zinc in some crude herbal drugs. Many of the studied samples had these metals beyond WHO permissible limits. The presence of heavy metals in these samples was probably due to the contaminated sites from where these samples were collected. Besides, some ayurvedic formulations were also tested for the presence of heavy metals. The presence of nickel, cadmium, chromium and lead was also confirmed in these samples too.

In general, medicinal plants may be associated with various kinds of microbial contaminants, in which bacterial and fungal infections are regarded as the two dominating groups. According to WHO and European Pharmacopoeia, herbal drugs must meet the modern hygienic standards, which aim at low microbial load or the absence of pathogenic microorganisms. A study conducted at NBRI revealed microbial contamination in some samples of crude herbal drugs and in some cases it was beyond the WHO permissible limits.

Although herbal medicines have been used for thousands of years, basic research programmes need to be focussed on the quality assurance. To overcome contaminations from pesticide residues and heavy metals there should be control measures to implement necessary standard operating procedures (SOP) at source.  Good laboratory practices (GLP) and good manufacturing practices (GMP) are also needed to produce good quality medicinal products. Without all these measures, it is not possible to realize the dream of having a major share of herbal drug industry despite having gold mine of welldocumented and well-practiced knowledge of traditional herbal medicines.


Dr. Vartika Rai is a Project Scientist and ISEB life member, and Dr. S. Mehrotra is an Emeritus Scientist of National Botanical Research Institute, Lucknow


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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