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---
  layout: post
  title: Cadmium Issues
  author: Joe Schwarcz
  source: McGill Blogs
---
  HYPERLINK "http://blogs.mcgill.ca/oss/2016/03/01/cadmium-issues/" 
Cadmium Issues 

  Shrek the friendly ogre delighted audiences in the 2010 movie hit
“Shrek Forever After.” But for fast food giant McDonald’s, Shrek
turned out to be a nightmare. As a cross promotional feature, the
company introduced a set of glasses decorated with images of Shrek and
other characters from the film. After millions of the glasses had been
sold, a problem cropped up that led to a large scale recall. The yellow
pigment used on the cups turned out to be cadmium sulphide, a substance
toxic even in small amounts. The concern was that the pigment might rub
off on children’s hands and end up being ingested if they then put
their hands into their mouth.

Cadmium was discovered in 1817 by Professor Friedrich Strohmeyer in
Germany while looking into a problem encountered by apothecaries who
were making calamine lotion for skin care. The process involved heating
“calamine,” a natural ore of zinc carbonate, to produce zinc oxide,
which is the active ingredient in calamine lotion. Sometimes the lotion
would end up with a yellow discolouration which Strohmeyer determined
was due to a mineral contaminant that he eventually identified as a
compound of cadmium.

It was the colour of cadmium compounds that led to their first
commercial use. Artists loved the bright yellow of cadmium sulphide and
the reds and oranges resulting from a mixture of cadmium sulphide and
cadmium selenide. Vincent van Gogh used cadmium sulphide to impart the
yellow colour to his flowers in his famous “Flowers in a Blue Vase.”
Unfortunately, with time, cadmium sulphide oxidizes to cadmium sulphate,
which is white, resulting in the original colour of the painting being
slowly altered.   HYPERLINK
"http://www.artnet.com/artists/claude-monet/" \t "_blank"  Claude Monet
‘s famous yellow hues were also achieved with cadmium pigments.

Cadmium paints are still used today, although they are being phased out.
Indeed, Sweden has submitted a report to the European Chemical Agency
claiming that artists rinsing their brushes in the sink are responsible
for spreading cadmium over agricultural land via sewage sludge.

Cadmium is a cumulative toxin and the World Health Organization has
suggested 70 micrograms as the maximum daily safe intake. Ingesting some
cadmium is unavoidable because it shows up in crops. How does it get
there? Sewage sludge and phosphate rock, both used as fertilizer, can
harbour cadmium. As a result, a hamburger can contain about 30
micrograms of cadmium that can be traced to the grass or hay the cow
ate, and ultimately to the soil in which the feed was grown. Coal also
contains cadmium compounds that can end up in the atmosphere from where
they find their way into soil via rain. Other cadmium compounds may also
be released from the nickel-cadmium battery industry, although modern
pollution control methods minimize such losses. Cadmium can be also be
found in significant amounts as a contaminant in zinc ores and some is
released into the environment when the ore is mined as well as when it
is smelted into zinc.

Nobody actually carried out a study to determine how much cadmium
pigment can rub off onto little hands when gripping a Shrek glass, but
it could well be less than what is found in the hamburger those hands
are clutching. Still, eliminating any avoidable source of cadmium is
desirable, especially since there is suspicion that cadmium compounds
may be carcinogenic. Cadmium can also build up in joints and the spine
causing a disease that the Japanese have named “Itai-Itai,” which
translates as “ouch-ouch,” due to the painful sounds made by victims
as cadmium accumulates.

A classic case of environmental cadmium toxicity can be traced back to
the early 1900s, although its cause was not identified until the 1960s.
It was obvious that something was going on in the vicinity of the Jinzu
River and its tributaries in China. People were getting sick, screaming
in pain and dying prematurely. Suspicion fell on the river and the
mining companies that for years and years had been disgorging their
wastes into the water. The mountains upstream were rich in minerals that
contained silver, lead, copper and zinc, and mines had been operating
there for centuries. As demand for these metals increased in the
twentieth century, more and more mining wastes found their way into the
river, including increased amounts of cadmium ores.

River water was used for irrigation of rice fields, and since rice
absorbs cadmium effectively, the metal accumulated in the food supply
and consequently in the bodies of the population. The result was
ouch-ouch disease. Although cadmium was only identified as the cause
around 1965, by the late 1940s it had become obvious that the disease
was linked to the water supply and mining companies began to store their
wastes instead of releasing them into the river. This prevented more
people from contracting cadmium poisoning, but nobody really knows how
many victims the mining operations had since they began to pollute the
Jinzu River back in the sixteenth century.

In 1966 in England a construction worker died and several others were
sickened as a result of inhaling cadmium fumes. The men were using a
welding torch to remove bolts as they were dismantling a construction
tower used in the building of a bridge. It is common practice to
electroplate steel bolts with cadmium, particularly those exposed to
water. This is especially useful when there is contact with sea water
since cadmium reacts with salt to form an impervious layer of cadmium
chloride. In this case the men inhaled the cadmium vapourized by the
heat of the welding torch and suffered an acute reaction.

Shrek glasses are not the only items aimed at children that have caused
a concern about cadmium. With lead being non-grata, cadmium has been
turning up in jewelry aimed at young girls, mostly originating in China.
If pieces are accidentally swallowed, or if the jewelry comes into
frequent contact with the mouth, enough cadmium may enter the
circulation to cause harm. Jewelry made with cadmium should to go the
way of the Shrek glasses.

 

Joe Schwarcz PhD – March 1/2016