Page 186 - Soil Degradation, Conservation and Remediation

6.2 Sources of Soil Pollutants 175

(PCDD/Fs) (Safe 1986 ), are hazardous because of their toxicity and persistence.
POPs have nonpolar molecules and hence can accumulate in adipose tissue and
cause deleterious cellular effects. The potential adverse effects of these compounds
and their environmental mixtures include teratogenicity, carcinogenicity (Muto
et al. 1996 ), and effects on normal physiologic endocrine function of an organism
(Ankley et al. 1998 ). Human fertility has been suggested to be adversely affected by

exposure to pollution from traffic (de Rosa et al. 2003 ). Some studies have demon-
strated in vitro estrogenic as well as antiestrogenic and antiandrogenic effects of

traffic exhaust particulates and road dust (Okamura et al. 2004 ; Misaki et al. 2008 ).

6.2.10 Radionuclides in Soil

Nuclides of any element that have atomic number greater than bismuth-83 are
unstable and therefore radioactive (Igwe et al. 2005 ). They are called heavy nucleons
or radionuclides. Radionuclides disintegrate or change spontaneously with a loss
of energy in the form of ionizing radiation (van der Perk 2006 ). There are more
than 60 radionuclides in nature. They can be placed in three general categories:
primordial, cosmogenic, and anthropogenic. Examples of some naturally occurring
radionuclides are americium-241, cesium-137, cobalt-60, iodine-129 and iodine-131,
plutonium, radium, radon, strontium-90, technetium-99, tritium, thorium, and

uranium. Cesium-137 is produced in nuclear fission, and it has a radioactive half-
life of 30.17 years. Primordial radionuclides are left over from the creation of the
earth. They typically have half-lives of hundreds of millions of years. Examples
include uranium-235, uranium-238, thorium-232, and potassium-40. Primordial
radionuclides end up in soil as part of the rock cycle.

Nuclear fission for atomic weapons testing and nuclear power generation provides
some of the sources of soil contamination with anthropogenic radionuclides. To the
40
87
238
235
14
naturally occurring radionuclides in soil such as K, Rb, C, U, U, and
232
Th, a number of fission products have been added. However, only two of these are

sufficiently long-lived to be of significance in soils: strontium-90 and cesium-137
with half-lives of 29.1 and 30 years, respectively. The average levels of these
−2
−2
nuclides in soil in the USA are about 388 mc km for 90Sr and 620 mc km for

137Cs (Holmgren et al. 1993 ). These levels of the fission radionuclides in soil are
not high enough to be hazardous (Igwe et al. 2005 ). However, artifi cial radioactivity
may be released into the environment during the normal operations of nuclear facilities
and installations such as nuclear ore processing, uranium enrichment, fuel fabrica-

tion, reactor operations, and application of radioisotopes in the fields of nuclear
medicine, research, industry, and agriculture. Soils may receive some radionuclides
from radioactive waste materials that have been buried for disposal (Knox et al.
2000 ). Plutonium, uranium, americium, neptunium, curium, and cesium are among
the elements whose nuclides occur in radioactive wastes. Uranium mining activities
produce large volume of residues for ore processing. These wastes contaminate
adjacent land areas. They release other toxic pollutants as well. The radionuclides