Chemistry Reference
In-Depth Information
Although cadmium is not strongly mutagenic, it is known that it causes increased oxidative DNA damage and
that it inhibits the DNA repair systems. It has also been found to induce cell death both by necrosis and apoptosis.
Since the latter is extremely calcium dependent, it seems likely that the pro-apoptotic effects of cadmium are due
to its interference with calcium homeostasis.
MERCURY
The toxicity of mercury (
Guzzi La Porta, 2008
)
was highlighted by Minamata disease, first discovered in
Minamata city in Kumamoto prefecture, Japan, in 1956. This is a neurological syndrome caused by severe
mercury poisoning, with symptoms including ataxia, numbness in the hands and feet, general muscle weakness,
narrowing of the field of vision, and damage to hearing and speech. It was caused by the release of methylmercury
in the industrial wastewater from a chemical factory (
Figure 23.3
). This highly toxic chemical is bioaccumulated
FIGURE 23.3
The Chisso factory, responsible for the methylmercury pollution and its wastewater routes. Instead of discharging its waste into
Hyakken Harbour (the source of original contamination), from September 1958 it discharged wastewater directly into Minamata River. The
immediate effect was the death of fish at the mouth of the river, and from that point on new Minamata disease victims began to appear in other
fishing villages up and down the coast of the Shiranui Sea.
in aquatic food chains reaching its highest concentrations in shellfish and fish in Minamata Bay and the Shiranui
Sea, which when eaten by the local population resulted in mercury poisoning. Of the 2265 victims officially
recognised, as of March 2001, 1784 died, and it was only in 2004 that the Chisso Corporation was ordered to clean
up its contamination. Another major outbreak of MeHg intoxication occurred in rural Iraq in 1971
1972 from
seed grain treated with an Hg-based fungicide that was to be used for planting. More than 6500 individuals were
hospitalised and 459 died from consumption of Hg-contaminated bread.
Asia has become the largest contributor of anthropogenic atmospheric mercury (Hg), accounting for over
half of global emissions, with serious Hg pollutions to the local environment influenced principally by the
chemical industry and mercury and gold mining. Studies have shown that in humans and selected Arctic marine
mammals and birds of prey there has been an order of magnitude increase in Hg that began in the mid to late 19th
century and accelerated in the 20th century (
Dietz et al., 2009
)
. The man-made contribution to present-day Hg
concentrations was estimated at 92%.
Hg exists essentially in three forms: organic mercury, primarily methylmercury (MeHg), elemental mercury
(Hg
0
), known as metallic mercury, and inorganic mercury compounds (I-Hg), principally mercuric chloride,
e
