Metals, their Biological Functions and Harmful Impacts - Mining and the Environment: From Ore to Metal - page 484

chloride (a catalyst in the production of plastics) into the bays of Minemata and Niigata,
Japan in 1953 and 1960 (UNEP 2002). The source of the 'Minamata disease' (later found
to be methylmercury poisoning) was the discharge of untreated efl uent containing methyl
mercury chloride from a polyvinyl chloride plastic plant. Once in the bay's sediments, the
mercury was readily absorbed by marine species, which resulted in the contamination
of the entire ecosystem. Many of the local residents consumed i sh and seafood from the
mercury-contaminated waters as a staple part of their diet. Thirty-nine years later, 2,252
patients had been ofi cially diagnosed with Minamata disease, and over 1,000 had died
( www.ec.gc.ca/MERCURY/EH/EN/eh-hc.cfm ). Since Minemata, mercury has become an
'angst word', although people tend to associate it with mine wastes because of its earlier
use in gold extraction. Mercury does bio-magnify in the food chain with the uppermost
trophic level of marine organisms (sharks, barracuda, etc.) often containing levels of mer-
cury considered too high for safe human consumption.

Mercury does bio-magnify in the
food chain.

Arsenic

With the major market for arsenic being the production of wood preservatives, the
demand for arsenic is closely tied to the home construction market, where timber con-
struction materials containing arsenical preservatives have become ubiquitous.
The name arsenic comes from the Greek word arsenikon , which means orpiment.
Orpiment is a bright yellow mineral composed of arsenic sulphide (As 2 S 3 ), and is the most
highly-visible common arsenic mineral. Historians say that arsenic was identii ed in 1250
by Albertus Magnus, a German monk who spent his life studying and classifying natural
materials. It is believed that he heated soap and orpiment together and isolated elemental
arsenic. Pure arsenic is a grey-colored metal, but is rare in the environment. It is usually
found combined with one or more other elements such as oxygen, chlorine, or sulphur,

With the major market for
arsenic being the production of
wood preservatives, the demand
for arsenic is closely tied to the
home construction market.

CASE 11.1
The Almaden Mine in Spain, Home of One-third of the World's
Known Reserves of Mercury

One of Almaden's most surprising aspects
is its environmental situation. At fi rst, one
would suppose that a region that has been
the world's principal producer of a highly
contaminating substance such as mercury
for more than 2,000 years would be pro-
foundly polluted. Nevertheless mercury has
had negligible environmental effects in the
region, which has no degraded or unproduc-
tive lands as a result of mercury extraction.
Almaden's geological history indicates
that the deposits have been close to the
surface and in direct contact with subter-
ranean aquifers during the last 250 million
years. Although inorganic mercury has a
low solubility, it is surprising that such high

quantities of mercury over a prolonged time
period have caused insignifi cant environmen-
tal effects.
The environmental impacts of mercury
contamination in tropical climates are well
known and generally attributed to the inap-
propriate use of mercury to recover gold
by artisanal miners. Many authors maintain
that under certain physical-chemical cir-
cumstances, metallic mercury can change to
organic compounds with greater solubility
and contaminating capacity (such as methyl
mercury).
The physical-chemical conditions at
Almaden are very different from those of
the tropics. It is important to note

that local people regularly consume fi sh
from local rivers without a single recorded
case of poisoning. This situation suggests
that the mechanisms of methyl mercury
generation and the cause-effect relationships
linking poisoning to small-scale gold mining
are more complex than previously thought.

Source: Excerpt from Girones and Viejobueno
2001: Spain's Almaden Mine: 2000 Years of
Solitude