have been shown to increase the likelihood that mercury will become a problem in
fish. Although scientists from USGS and elsewhere are beginning to unravel the
complex interactions between mercury and the environment, a lack of information
on the sources, behavior, and effects of mercury in the environment has impeded
identification of effective management responses to the nation’s growing mercury
problem (USGS 1995).
3.1.5 Lead
Natural lead occurrence is not common on earth surface. Anthropogenic lead is
introduced through the use of products containing lead additives such as paints,
gasoline, and metal works (Gioia et al. 2006; Boyle et al. 2014). Metallic lead and
lead alloys are extensively used for storage battery plates, sheathing for electrical
cables, small-caliber ammunition, shielding for X-ray apparatus and atomic reactors,
type metal, bearing metal, and solder. Lead is also released as a waste product from
extraction of metals such as silver, platinum, and iron from their respective ores. In car
engines, the burning of fuel in the presence of other impurities (chlorines, bromines,
oxides) produces lead salts (Wang et al. 2010). The lead salts enter the environment
through the exhausts of the cars in particulate form. Lead is also released from
combustion of coal during electric power generation in coal-powered plants. Typical
concentrations of lead released from coal-powered plants have been reported at
7–110 mg/kg with release rates up to 11,200 tons lead/year (UNEP 2010).
The increased non-localized outputs of lead to the environment have generated a
lot of concern mainly due to its toxicity to living organisms. Lead contamination of
water and land is known to produce sub-chronic effects at low concentrations
(Supanopas et al. 2005), acute effects at moderately high concentrations (Papp
et al. 2006), and catastrophic changes to ecosystems at very high concentrations
(Eisler 1988). Lead concentration above 1000 ppm can wipe out almost the entire
ecosystem, whereas, concentrations lower than 10 mg/L can result in endocrine
disrupting activity in sensitive species. In many areas around the United States,
accumulation of lead in aquatic systems has risen to levels detrimental to human
inhabitants (Renner 2010).
3.2 Radioactive Elements
In high temperature gas-cooled reactors (HTGR), also known as fast reactors,
graphite is utilized as the moderator of the nuclear reaction. The graphite is either
used as part of the structural materials for the reactor core vessel or as fuel
containment elements in the form of pebbles. The graphite used from natural sources
contains non-carbon impurities within the carbon matrix. Among these impurities
are oxygen and nitrogen from entrapped air, cobalt, chromium, calcium, iron, and
sulfur (Khripunov et al. 2006).
26
E. M. Nkhalambayausi-Chirwa et al.
fish. Although scientists from USGS and elsewhere are beginning to unravel the
complex interactions between mercury and the environment, a lack of information
on the sources, behavior, and effects of mercury in the environment has impeded
identification of effective management responses to the nation’s growing mercury
problem (USGS 1995).
3.1.5 Lead
Natural lead occurrence is not common on earth surface. Anthropogenic lead is
introduced through the use of products containing lead additives such as paints,
gasoline, and metal works (Gioia et al. 2006; Boyle et al. 2014). Metallic lead and
lead alloys are extensively used for storage battery plates, sheathing for electrical
cables, small-caliber ammunition, shielding for X-ray apparatus and atomic reactors,
type metal, bearing metal, and solder. Lead is also released as a waste product from
extraction of metals such as silver, platinum, and iron from their respective ores. In car
engines, the burning of fuel in the presence of other impurities (chlorines, bromines,
oxides) produces lead salts (Wang et al. 2010). The lead salts enter the environment
through the exhausts of the cars in particulate form. Lead is also released from
combustion of coal during electric power generation in coal-powered plants. Typical
concentrations of lead released from coal-powered plants have been reported at
7–110 mg/kg with release rates up to 11,200 tons lead/year (UNEP 2010).
The increased non-localized outputs of lead to the environment have generated a
lot of concern mainly due to its toxicity to living organisms. Lead contamination of
water and land is known to produce sub-chronic effects at low concentrations
(Supanopas et al. 2005), acute effects at moderately high concentrations (Papp
et al. 2006), and catastrophic changes to ecosystems at very high concentrations
(Eisler 1988). Lead concentration above 1000 ppm can wipe out almost the entire
ecosystem, whereas, concentrations lower than 10 mg/L can result in endocrine
disrupting activity in sensitive species. In many areas around the United States,
accumulation of lead in aquatic systems has risen to levels detrimental to human
inhabitants (Renner 2010).
3.2 Radioactive Elements
In high temperature gas-cooled reactors (HTGR), also known as fast reactors,
graphite is utilized as the moderator of the nuclear reaction. The graphite is either
used as part of the structural materials for the reactor core vessel or as fuel
containment elements in the form of pebbles. The graphite used from natural sources
contains non-carbon impurities within the carbon matrix. Among these impurities
are oxygen and nitrogen from entrapped air, cobalt, chromium, calcium, iron, and
sulfur (Khripunov et al. 2006).
26
E. M. Nkhalambayausi-Chirwa et al.