Accumulation of Heavy Metals in Selected Medicinal Plants - Reviews of Environmental Contamination and Toxicology - page 78

Table 2 Comparison of the number of tested species that have Pb, Cd and Hg levels that exceed
the European Pharmacopoeia maximum permissible levels (MPL) and maximum content of the
heavy metals (HMs) reported to exist in the plant species presented in Table 1
European pharmacopoeia MPL Pb (5 mg/g) Cd (0.5 mg/g) Hg (1 mg/g)

No of plant species below MPL 06 02 0

No of plant species above MPL 21 44 10

Data not available 61 44 78

Table 3 Regulatory limit values established by WHO, FDA, and European Pharmacopoeia
(Ph. Eur.) f or metals in herbal drugs daily dietary

FAO/WHO PTWI
(mg kg −1 b wt.)
Al *** *** *** ***
As 10 *** *** 15
Au *** *** *** ***
Br *** *** 1.5-2.5 ***
Cd 0.3 0.5 *** 7
Cl *** *** *** ***
Co *** *** *** ***
Cr *** *** 0.02-0.2 ***
Cu *** *** 1.0-3.0 ***
Fe *** *** 10-18 ***
Hg 1 0.1 *** 5
Mn *** *** 1.0-5.0 ***
Ni *** *** 0.13-0.4 ***
Pb 10 5 *** 25
Se *** *** 0.02-0.2 ***
V *** *** 0.1-0.4 ***
Zn *** *** 15 ***
US RDA recommended daily dietary allowance, PTWI provisional tolerable weekly intake, b wt .
body weight
*** Data not available

WHO/FDA
permissible limit

Ph. Eur. permissible limit
(Gasser et al. 2009 ) Metal RDA (in mg)

(including members of the Asteraceae, Brassicaceae, Caryophyllaceae, Cyperaceae,
Cunouniaceae, Fabaceae, Flacourtiaceae, Lamiaceae, Poaceae, Violaceae, and
Euphobiaceae) (Kramer 2010 ). However, the ecological and biological signiicance
of metal hyperaccumulation is not well understood. Notwithstanding, it has been
irmly established that some medicinal plants do hyperaccumulate heavy metals,
viz., As, Co, Hg, and Pb, and these metals at some levels are highly hazardous and
impinge upon human health, sometimes even at very low concentrations.
The level to which metals accumulate in plants is inluenced by the physico-
chemical properties of the soil in which the plants grow. Such properties include
the bioavailability of the metallic element, characteristics of soil or sediments, pH
level, exposure period, dispersion range, and presence or absence of other elements.
If availability of metallic elements in soil/sediment is high, then some plants