Accumulation of Heavy Metals in Selected Medicinal Plants - Reviews of Environmental Contamination and Toxicology - page 67

health care, although perhaps preferentially in developing countries. Medicinal
plants are in demand both because of their natural origins and lower costs com-
pared to synthetic drugs. In India, where 74% of the population resides in its seven
million villages, the use of medicinal plants in health care may also be welcomed
as a strategy for assisting in the development of the hitherto underdeveloped
countryside.
Currently, nutraceuticals from plants have gained popularity with consumers,
who are increasingly careful in choosing components of their diet; such people
are interested in incorporating high nutrient levels into their standard diet, prefer-
ably sourced naturally from plants (Bhat and Sridhar 2008 ; Bhat et al. 2010 ).
There are at least 50 elements that are vital for the well-being of humans (Tolonen
1990 ). Dietary elements required in amounts greater than 100 mg/day are called
“minerals,” and those that are required in amounts less than 100 mg/day are called
“trace elements.” Trace elements are necessary for human health and include the
following: iron, copper, manganese, zinc, selenium, chromium, etc. (Hendler and
Sheldon 1990 ). Minerals include calcium, magnesium, phosphorus, sodium,
potassium, sulfur, and chlorine. It is well established that a majority of trace ele-
ments act as key components of essential enzyme systems or other proteins, e.g.,
the hemoprotein or hemoglobin, which perform vital biochemical functions
(Obiajunwa et al. 2002 ). Many medicinal plants contain elements of vital impor-
tance, which are needed for growth and development, for prevention and healing
of diseases, and the plants that provide such beneit have long been heavily used
in Asia and Africa.
Both deiciencies and excesses of dietary metals may result in several human
disorders. Some toxic metals are capable of damaging vital organs even at extremely
low concentrations, e.g., Pb causes both acute and chronic poisoning and also poses
adverse effects on the kidney, and liver, and on the vascular and immune systems
(Heyes 1997 ). Heavy metals are the main cause of excessive free radical activity,
which can also cause damage to healthy tissues of the body and can deplete the
body's immune system (Cranton and Frackelton 1998 ).
The uptake of heavy metals by plants may be duration-dependent, and once
absorbed by plants, they may accumulate in certain plant parts (Khan et al. 2007 ).
In some plant species, prolonged exposure to metals may result in levels that,
when consumed, are hazardous to humans. The international agency for research
on cancer (IARC) identiied the following metals as being potentially carcino-
genic to humans: arsenic, antimony, beryllium, cadmium, chromium, cobalt, lead,
nickel, and vanadium. Moreover, some of these toxic heavy metals can cause DNA
damage; hence, the carcinogenic effects they produce in animals and humans may
result from mutagenic activity. It is because of the potential intake by humans of
potentially toxic amounts of heavy metals that researchers have emphasized the
importance of monitoring for the presence of such carcinogenic metals in medici-
nal plants, to hopefully prevent excessive human exposures (Liang et al. 2004 ;
Arceusz et al. 2010 ). Moreover, medicinal plants are used in folk medicine, and
knowledge of the metal content, is important for this reason (Chuparina and
Aisueva 2011 ).