Page 188 - Soil Degradation, Conservation and Remediation

6.2 Sources of Soil Pollutants 177

Table 6.4 Sources of pollutants in soil
Source Materials Pollutants
Agricultural Phosphate fertilizers As, Cd, Mn, U, V, and Zn
Pig and Poultry manures As, Cu
Pesticides As, Cu, Mn, Pb, Zn, organic pollutants
Oil spillages Hydrocarbons
Electricity generation Fallout, Ash Si, SO x , NO x , heavy metals, coal dust
Gasworks Tars As, Cd, Cu, Pb, S , SO 4 , hydrocar-
=
=
bons, phenols, benzenes, xylene,
naphthalene, PAHs, etc.
Metalliferous mining Dispersed tailings, ore Metals, including heavy metals,
and smelting separates cyanides
Metallurgical Metal wastes, solvents, Metals including heavy metals (As,
industries residues, aerosols Cd, Cr, Cu, Ni, Pb, Mn, etc.)
Chemical industries Particulates, effl uents, Heavy metals (As, Cd, Cr, Cu, Ni, Pb,
scraps, damaged parts Mn, etc.) and organic pollutants,
including PAHs
−
+
Waste disposal Sewage sludge, scrap heaps, NH 4 , PAGHs, PCBs, NO 3 , metals
coal ash, waste incinera- (As, Cd, Cr, Cu, Ni, Pb, Mn, etc.)
tors, landfi lls
Transport Particulates, acid deposits, Pb, Br, Cd, Zn, P, As
solvents, oils

aromatic compounds; polynuclear aromatic hydrocarbons (PAHs); and polychlorinated
biphenyls (PCBs). Monoaromatic hydrocarbons include benzene, toluene, ethyl-
benzene, and xylenes (also collectively known as BTEX). Chlorinated aromatic
compounds include hexachlorobenzene and pentachlorophenol. Among the organic
inputs in soil, some are easily degraded by soil organisms. But there are many
organic pollutants which are very resistant to chemical or biological degradation.
They are called persistent organic pollutants (POPs). They are organic compounds
that, to a varying degree, resist photolytic, biological, and chemical degradation
(Pedro et al. 2006 ). POPs include phthalate esters (PAEs), nonylphenol ethoxylates
(NPEs), PAHs, PCBs, and bisphenol A added to soils with wastewater and sewage
sludge. Dioxins and furans are some toxic organic pollutants that are added to soil
with herbicides and wastes from paper and wood industries. Of all the dioxins
and furans, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8 TCDD). is considered

the most toxic. Crookes and Howe ( 1993 ) reported that the abundance of PCB in
a highly sludge amended soil was about eight times higher than in sludge itself
indicating a buildup of PCBs during many years of heavy sludge amendment at the
site. PCNs (polychlorinated naphthalenes) are newly recognized persistent pollut-
ants. Halogenated hydrocarbons, including dioxins and furans, are by far the most
important group of POPs. A brief account of the major groups of persistent organic
pollutants is given below.
Polycyclic aromatic hydrocarbons (PAHs) are a large group of several 100
compounds which are produced during combustion processes, with a broad range of
physicochemical properties, representative of most other POPs. The International