Accumulation of Heavy Metals in Selected Medicinal Plants - Reviews of Environmental Contamination and Toxicology - page 69

4 Safe Limits vs. Actual Levels of Heavy Metals

in Medicinal Plants

Among the 88 medicinal species tested for metal contamination, the number of spe-
cies in which safe levels were exceeded was as follows: Pb in 21 species, Cd in 44
species, and Hg in 10 species (Table 2 ). This is extremely disquieting and explains
why metal contamination of marketed medicinal plants is often criticized. The
chronic accumulation of heavy metals in certain vital human organs from prolonged
ingestion of these plants has been well established (Sharma et al. 2009 ; WHO 2005 ).
Hence, the importance to consumer protection of having good quality control
practices for screening of herbal medicines, particularly for heavy metals, is
underscored.
Although permissible levels of heavy metal contaminants in herbal medicine are
not yet standardized, the European Pharmacopoeia (Ph. Eur.) has drafted limits for
Cd, Pb, and Hg (Table 3 ). Furthermore, the European Commission established lim-
its in March 2001 for lead, cadmium, and mercury in food supplements (Commission
Regulation 2001 ). The WHO and the Food and Agriculture Organization (FAO)
have also jointly proposed acceptable levels of toxic substances that can be ingested
on a weekly basis - the Provisional Tolerable Weekly Intake (PTWI) for As, Cd,
Hg, and Pb (International Program on Chemical Safety 2009 ). In addition, the
United States has standardized recommended daily dietary allowance (RDA) for
essential dietary metals, but not for toxic ones.
However, there are few established safe limits for the content of heavy metals in,
or permissible limits for minerals in medicinal plants (Wang et al. 1985 ). This dearth
invariably hamstrings development of medicinal plant research. The governmental
agencies responsible for establishing such safe limits for essential metallic minerals
or for metal content in medicinal plants must address appropriate standard-setting
with the urgency it deserves. WHO, which is one of the monitoring bodies, should
intervene to help identify what limits are necessary and to establish and standardize
such limits.

5 Hazardous Medicinal Plants

Having heavy metal analytical results available on medicinal plants is the critical
step in knowing if such plants have potentially toxic levels of metals that could be
dangerous to living organisms. Moreover, having data on hyperaccumulator plants
is even more critical. Such plants accumulate high concentrations of metallic ele-
ments and pose special risks to consumers, because they can absorb 50-100 times
the amount of metals than do normal plants (Chaney et al. 1997 ). The phenomenon
of hyperaccumulation is intensiied if the environment has high concentrations of
heavy metals. To date, about 500 plant species are recognized to be hyperaccumula-
tors; this number represents approximately 0.2% of all angiosperm species