Environmental Engineering Reference
In-Depth Information
Keywords
Heavy metals ﾷ Phytoextraction ﾷ Phytoremediation ﾷ Phytostabilization ﾷ
Rhizofiltration
minerals are associated with exposure to lead,
mercury, chromium, cadmium, copper, arsenic
and aluminium. These enter the human system
mainly through contaminated water, food and air,
leading to various health complications. Global
environmental agencies such as United Nations
Environment Programme (UNEP), European
Environment Agency (EEA), World Nature Or-
ganization (WNO) and in India Ministry of En-
vironment (MoE), Government of India, work
for finding preventive and remedial solutions for
management. Existing options involve expensive
technology and recurring investments, thus mak-
ing them difficult to be affordable to most of the
developing countries like India. Therefore, con-
sidering developing countries' economic status,
increasing population and malnutrition, appropri-
ate intervention in terms of indigenous research
towards mitigation and remediation needs to be
pondered and designed for effective and efficient
application.
In general, heavy metal toxicity can cause
chronic degenerative diseases, with the symp-
toms of mental disorders, pain in muscles and
joints, gastrointestinal disorders, vision prob-
lems, chronic fatigue and susceptibility to fungal
infections. Sometimes the symptoms are vague
and difficult to diagnose at early stages and lead
to genotoxicity and cancers. Industrial workers
and populations living near the polluting indus-
tries are more susceptible and need to be moni-
tored regularly. Malnourished people and preg-
nant women are vulnerable. Crippling effects
of fluoride and arsenic toxicity due to nonavail-
ability of safe water for drinking and farming has
become a major public health problem and needs
to be addressed. Management strategies are being
prioritized to mitigate such problems. Consider-
ing the fact that the metal once out of the rock
is destined to mix in the environment, different
physicochemical and bioremediation strategies
are being implemented to reduce the environment
load, preferably at the site of generation. How-
ever, large industries should be forced to set up
their own effluent treatment plants, and smaller
industries should use common effluent treatment
facilities. Industries as sources of heavy metals
are summarized in Table
5.1
.
Although heavy metals and minerals (fluoride
arsenic salts) are reported to be hazardous be-
yond safe limits, smaller quantities of Fe, Zn, Cu,
Co, Cr, Mn and Ni are required for proper human
metabolism. However, Pb, Hg, Cd, and As have
no beneficial role and are absolutely toxic. Small
amounts of fluoride help to prevent dental cavi-
ties, but excess is harmful. In the environment,
these elements have a tendency to get stabilized
in the form of organic salts and complexes and
are bioaccumulative. Consequently, deriving
their safe limits is very difficult. The toxicity of
metals also depend on their chemical form and
oxidation state which further complicate the
toxicity assessment. Toxicity studies therefore
required the consideration of metal speciation in
terms of valency and oxidation state e.g. CrIII
(non-toxic) and CrVI (toxic).
To alleviate these microbial hazards, bioreme-
diation strategy has been emphasized, and exten-
sive funding has been provided to research and
development (R&D). Bioremediation is using mi-
croorganisms to degrade pollutants in situ. Since
heavy metals and radionuclide wastes cannot be
chemically degraded, application of microbial
bioremediation is limited to the immobilization
of heavy metals by precipitation or reduction or
conversion of toxic to nontoxic forms in situ.
The use of plants for cleaning the environ-
ment has been implemented from ancient times
and considered as indigenous knowledge. The
physiological exploration of plants revealed ion
exchange pumps and transporters that can extract
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