Accumulation of Heavy Metals in Selected Medicinal Plants - Reviews of Environmental Contamination and Toxicology - page 79

Table 4 Concentrations of heavy metals that are accumulated in Vetiveria zizanioides roots and
shoots (Truong 1999 )
Heavy metal Soil mg kg −1 Shoot mg kg −1 Root mg kg −1 Shoot/root (%)

As 620 11.2 268 4.2

Cd 1.66 0.31 14.2 2.2

Cu 50 13 68 19

Cr 600 18 1,750 1

Pb 730 78.2 87.8 87

Hg 6.17 0.12 10.8 11

Ni 300 448 1,040 43

Se 74.3 11.3 24.8 46

absorb these metals into the root system and translocate them to aerial plant parts
(Truong 1999 ).
Some grass species, e.g., Vetiveria zizanioides absorb a wide range of heavy met-
als, if such metals are present in soil (Table 4 ), and we believe that this species is the
most impressive example of a potentially hazardous medicinal plant. In general,
grasses are metal-tolerant plants (Rosselli et al. 2003 ), and are high accumulators of
heavy metals (Pichtel and Salt 1998 ); hence, consuming them may be hazardous.
Curiously, V. zizanioides, which is a well-known grass species, is a potential candi-
date for treating cardiovascular diseases (Rajurkar and Damame 1997 ), owing to its
bioactive properties. However, if this plant is collected from metal-contaminated sites,
the metal levels which exist may produce adverse toxic effects on the consumer.
In conclusion, heavy metal contamination may alter the chemical composition of
plants, and thereby seriously affect the quality and eficacy of the plant products pro-
duced by medicinal plant species (Zhu and Cullen 1995 ). If medicinal plant species are
collected from industrial areas, there is a greater risk that the plants will be contami-
nated than if the species are collected from natural (pristine or rural) areas. Moreover,
we urge those who harvest V. zizanioides to ensure that the collected samples are care-
fully analyzed for metallic element before being put to herbal medicinal use.
Some medicinal plants absorb higher amounts of metals selectively from soil
than do others (Table 5 ). Clematis gouriana, used for the treatment of skin diseases,
takes up very high Cd levels. Ingestion of even trace quantities of Cd can inluence
the physiology and health of individual organisms and threaten their distribution,
reproduction and survival (Meena et al. 2010 ).
Woodfordia loribunda has been frequently used in the pharmaceutical industry
for its wide range of bioactive compounds. Unfortunately, this plant also absorbs
Pb. At high levels, human exposure to Pb will damage most organs and organ sys-
tems, including the central nervous system, kidneys, and circulatory system, which
can lead to death (Lansdown and Yule 1986 ; Goldstein 1992 ). Some medicinal
plants contain high proportions of As and Hg, which has resulted in the safety being
questioned of certain mineral and herbomineral medicines that absorb these ele-
ments, e.g., Elsholtzia communis and Ureria picta .
In many African countries, Alchornea cordifolia is commonly used as a medicine
for the treatment of bacterial, fungal, parasitic, and inlammatory disorders (Mangaa