Page 153 - Soil and water contamination, 2nd edition

140 Soil and Water Contamination

The consequent pyrite oxidation may cause and substantially enhance leaching and runoff of
selenium from mining sites.
The importance of selenium as an environmental contaminant has been recognised
by scientists and, especially in the USA, also by policy makers and the general public.
Nevertheless, there are wide differences in environmental regulations with respect to
selenium between countries across the world (Luoma and Presser, 2009). In Europe,
selenium is not considered an ecological threat. It is not listed as a chemical of concern,
whereas in the USA selenium is ranked 141 in the ATSDR 2011 Priority List of Hazardous
Substances (ATSDR, 2013).

EXERCISES

1. Where can one expect relatively high background concentration s of heavy metals in soil
or water?

2. What are the principal anthropogenic sources of heavy metals
a. in general?
b. in agricultural soils?
c. in urban areas?
d. in forests?
e. in river water?
3. Explain why acid mine drainage often contains high concentrations of heavy metals.

4. a. Name the two most important chemical processes that determine the environmental
mobility of heavy metals.
b. Which other substances are involved in these processes?

5. a. Discuss the mobility of cadmium, zinc, and lead compared to that of iron and
manganese as a function of redox conditions.
b. Under which conditions (pH, redox, aquifer material) are cadmium, zinc, and lead
most mobile in groundwater?
6. Which metal is more mobile under oxidising conditions: zinc or cadmium?

7. Name a specific peculiarity of each of the following elements, which plays a part in their
environmental behaviour.
a. Nickel
b. Chromium
c. Mercury
d. Arsenic
e. Selenium
8. The heavy metal contamination of the river Geul, a tributary of the river Meuse, is
largely due to historic erosion of mine tailings near the zinc and lead mines in Plombières
and Kelmis, Belgium. Near this source the coarse particle size fraction (sand) of the river
sediments is heavily contaminated by heavy metals (zinc, lead, cadmium). The river Geul
flows into the river Meuse just north of Maastricht, the Netherlands. The Geul valley
between Plombières and its confluence with the river Geul is about 35 kilometres long.

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