Page 145 - Soil and water contamination, 2nd edition

132 Soil and Water Contamination

Copper contamination of soils may cause phytotoxicity. The bioavailability of copper
decreases with increasing pH , so the toxicity to plants can be mitigated by liming soils
contaminated with copper, to bring the pH up to 7. In addition, copper is highly toxic to
soil microorganisms. Like zinc , it may affect nitrogen fixation and the mineralisation of plant
litter (Obbard and Jones, 2000). Although sheep are prone to copper deficiency, they are also
most sensitive to copper toxicity (Alloway and Ayres, 1997). When copper is fed in excess
of requirements it tends to accumulate in the sheep’s liver. With minimal stress, the stored
copper can cause cattle or sheep to die within a few hours to a few days. Copper toxicity to
humans is rare, usually occurring after prolonged exposure to copper. Very young children
may be more sensitive to copper, and long-term exposure to high levels of copper in food or
water may cause liver damage and death.
Pollution of soil and water by copper may arise from copper mining and smelting.
Copper is primarily used as the metal or alloy in sheet metal, wires, pipes, and other metal
products. It is widely used for water pipes. Corrosion of these metal products as well as
disposal of their scrap allows the copper to enter the environment either directly or indirectly
via effluent from wastewater treatment plants, sewage sludge , compost, or landfills. Copper
compounds are most commonly used in agriculture to treat plant diseases or for water
treatment and as preservatives for wood, leather, and fabrics. An example of a commonly
used copper-based fungicide is Bordeaux mixture, which contains copper sulphate . It is
widely used in viniculture, where the vines are frequently sprayed after rainfall to prevent
mildew. The copper applied can accumulate to large concentrations in the topsoil. Manure,
especially swine slurry from intensive pig farming, may also contain significant amounts of
-1
Cu, which is added to the livestock’s diet as copper sulphate at up to 250 mg Cu kg to
promote growth.

7.4 LEAD
Lead is present in moderate amounts in igneous and sedimentary rocks , mostly in the form
of lead sulphide (galena; PbS). Nevertheless, its natural mobility is low, because of the low
solubility of lead hydroxide, carbonate , and phosphate . The adsorption of lead on mineral
and organic sediment surfaces and its coprecipitation with manganese oxide also tend
to maintain low concentrations in natural waters. The major dissolved inorganic forms of
2+
lead are the free Pb ion, hydroxide complexes, and, the carbonate and sulphate ion pairs.
Equilibria involving basic lead carbonates maintain the dissolved lead concentration below
-1
-1
-
about 50 μg l in water having 61 mg l HCO and a pH between 7.5 and 8.5. Water
3
having lower alkalinity and pH can contain larger concentrations of dissolved lead (Hem,
1989).
Lead is a non-essential element and it is not as bioavailable as other metals . However, it
is toxic to mammals, including humans. Exposure to high levels of lead can cause damage to
the brain and kidneys and may affect haemoglobin production and male fertility (ATSDR,
2013). Children under the age of seven are particularly sensitive to even small amounts of
lead. Furthermore, lead exposure may increase blood pressure in middle-aged men, but it
is unknown if lead increases blood pressure in women. Lead can enter your body when you
inhale air with lead-containing dust or particles of lead. Almost all of the lead in the lungs
enters the blood and moves to other parts of the body. Most of the lead is stored in bone
and the levels of lead in bone and teeth increase as a person ages. In adults, only a small
part of the lead ingested from food, beverages, water, soil, or dust enters the blood from the
gastrointestinal tract and moves to other parts of the body. However, when children swallow
food or materials containing lead, such as polluted soil found at a hazardous waste site or
chips of lead-containing paint, much more of the lead enters their blood. In the first half of

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