|
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 |
