Environmental Engineering Reference
In-Depth Information
bladder, and kidney cancer as well as pigmentation changes, skin thick-
ening (hyperkeratosis) neurological disorders, muscular weakness, loss of
appetite, and nausea. h is dif ers from acute poisoning, which typically
causes vomiting, esophageal and abdominal pain, and bloody “rice water”
diarrhea [14]. Arsenic in natural waters is a worldwide problem. Arsenic
pollution has been reported recently in the USA, China, Chile, Bangladesh,
Taiwan, Mexico, Argentina, Poland, Canada, Hungary, New Zealand,
Japan and India. h e largest population at risk among the 21 countries with
known groundwater arsenic contamination is in Bangladesh, followed by
West Bengal in India.
h e toxic ef ects of mercury depend on its chemical form and the route
of exposure. Methylmercury (CH
3
Hg) is the most toxic form. It af ects the
immune system, alters genetic and enzyme systems, and damages the ner-
vous system, including coordination and the senses of touch, taste, and
sight [42]. It is particularly damaging to developing embryos, which are
i ve to ten times more sensitive than adults. Exposure to CH
3
Hg is usually
by ingestion, and it is absorbed more readily and excreted more slowly than
other forms of mercury. Elemental mercury (Hg
0
), the form released from
broken thermometers, causes tremors, gingivitis, and excitability when
vapors are inhaled over a long period of time. Although it is less toxic than
CH
3
Hg, Hg
0
may be found in higher concentrations in environments such
as gold mine sites, where it has been used to extract gold. If Hg
0
is ingested,
it is absorbed relatively slowly and may pass through the digestive system
without causing damage. Ingestion of other common forms of mercury,
such as the salt HgCl
2
, which damages the gastrointestinal tract and causes
kidney failure, is unlikely from environmental sources.
Cadmium is a relatively rare element that is a minor nutrient for aquatic
organisms at low concentrations, but is toxic to aquatic biota at only
slightly higher concentrations. In aquatic environments, organisms are
exposed to cadmium in dissolved and particulate-bound forms. Cadmium
can be taken up by bacteria, phytoplankton, zooplankton and i sh directly
or through the food chain as a potentially toxic metal, which can enter the
organism's body via waterborne and dietary pathways, although regula-
tory assessments of metal toxicity to aquatic organisms assume that toxic
ef ects are caused by dissolved metals. In recent years, concern has been
expressed about the possible ef ects on aquatic organisms from exposure
to cadmium.
h e toxicity of a chromium compound depends on the valence state
of the chromium atom and the nature of its ligands. h ere are several
routes to human chromium exposure which include inhalation, inges-
tion, dermal contact and respiratory tract, etc. h e ingestion of Cr(VI)
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