Page 193 - Soil Degradation, Conservation and Remediation

182 6 Soil Pollution

Such examples are not common in the case of exposure to lower concentrations
derived from the environment and the food chain. Studies on cell cultures in labora-
tory demonstrate that overexposure to certain POPs may be associated with a wide
range of biological effects, including immune dysfunction, neurological defi cits,
reproductive anomalies, behavioral abnormalities, and carcinogenesis. Swedish
investigations have reported that dietary intake of PCBs, dioxins, and furans may be
linked to important reductions in the population of natural killer cells (lymphocytes)
(Svensson et al. 1993 ), while DeWailly et al. ( 1993 ) have reported that children with
high organochlorine dietary intake may experience rates of infection some 10–15
times higher than comparable children with much lower intake levels. The developing
fetus and neonate are particularly vulnerable to POPs exposure, due to transplacental
and lactational transfer of maternal burdens at critical periods. In another report
(DeWailly et al. 1993 ), children in the northern Quebec region of Canada who have

had significant exposure to PCBs, dioxins, and furans through breast milk also had a
higher incidence of middle ear infections than children who had been bottle-fed.
Studies of carcinogenesis associated with occupational exposure to 2,3,7,8, TCDD
also seem to indicate that extremely high-level exposures of human populations
do elevate overall cancer incidence. Some organochlorine chemicals may have carci-
nogenic effects and act as a strong tumor promoter. Some authors suggested a possible
relationship between exposure to persistent organic pollutants and human disease and
reproductive dysfunction. Sharpe and Skakkebaek observed ( 1993 ) that the increasing
incidence of reproductive abnormalities in the human male might be related to
increased estrogen exposure (or estrogenic type compound) and further suggest that a
single maternal exposure during pregnancy of minute amounts of TCDD may increase
the frequency of cryptorchidism in male offspring, with no apparent sign of intoxication
in the mother. Colborn and Clement ( 1992 ) have reported that high concentrations
of various persistent organic pollutants have been associated with reproductive
abnormalities, including changes in the semen quality of adult rats exposed neonatally
to PCBs via their mothers’ milk. Associations have been suggested between human
exposure to certain chlorinated organic contaminants and cancers in human popula-
tions. Preliminary evidence suggests a possible association between breast cancer and
elevated concentrations of DDE, although the role of phytoestrogens and alterations
in lifestyle cannot be dismissed as important risk factors in the increase in estrogen-
dependent breast cancer incidence. Wolff and coworkers ( 1993 ) have reported that
levels of DDE and PCBs were higher for breast cancer case patients.

6.2.11.2 Bioconcentration, Bioaccumulation,

and Biomagnification of Organic Pollutants
Organic pollutants undergo a number of transformations in soils: some can be
degraded biologically, photochemically, and chemically; the low molecular weight
organic pollutants may volatilize, and some may be lost by leaching (Semple et al.
2003 ). Some organic pollutants get adsorbed onto soil minerals and organic matter
(Schwarzenbach et al. 1993 ). A portion of organic pollutants undergoes bioaccumulation
in organisms. Some examples are given below.