Accumulation of Heavy Metals in Selected Medicinal Plants - Reviews of Environmental Contamination and Toxicology - page 82

metals actually exist in selected medicinal plants. We also evaluate the uses and
effectiveness of medicinal plants in health care, and assess the hazards of medicinal
plant uses, in view of the growing worldwide use of medicinal plants. From our
extensive review of the literature, we discovered that a maximum permissible level
(MPL) of Pb is exceeded in 21 plant medicine species, Cd in 44 species, and Hg in
10 species. Vetiveria zizanioides a potential candidate species for the treatment of
cardiovascular diseases absorb a wide range of heavy metals from metal-contaminated
soils. We believe that this species is the single most impressive example of a poten-
tially hazardous medicinal plant.
Based on our review, we endorse the hypothesis that heavy metal accumulation
by medicinal plants is mainly caused by extraction of soluble metals from contami-
nated soil, sediments and air. One continuing problem in protecting consumers of
plant-based medicines is that permissible levels of all heavy metals in herbal medi-
cine have not yet been standardized by regulating governmental entities. Moreover,
there are few limit tests that exist for heavy metal content of medicinal plants, or
permissible limits for essential dietary minerals, in most medicinal plants. The
dearth of such limits hamstrings development of medicinal plant research and delays
the release of either new or improved versions of medicinal plants or their compo-
nents. In the present review, we emphasize that medicinal plants are often subjected
to heavy metal contamination and that the levels at which these heavy metals some-
times occur exceeds permissible levels for some species. Therefore, collecting
medicinal plants from areas that are, or may be, contaminated should be discour-
aged and banned if possible.
Acknowledgments The authors are grateful to Professor J. Chutia, Director, IASST, Guwahati
for all-round support, and inally this work has been possible through an award of the DBT-RA I
to Hemen Sarma funded by Department of Biotechnology, Govt of India.
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