General Aspects/Case Studies on Sources and Bioremediation Mechanisms of Metal(loid)s 147
like algae, microbes, yeast and fungi as well as in addition to ecosystems, activities and processes
facilitated by microbes (Giller et al. 2009, Wang et al. 2010, Babich and Stotzky 1985, Baath 1989).
9.2.4 Smelter Contaminated Soils
Smelting and mining of zinc and lead ores have significant negative effects on the environment (Anju
and Banerjee 2011, Dudka and Adriano 1997, Lambert et al. 1994). Health loss, pollution of water
and soil, phytotoxicity, soil deterioration and environmentally harmful effects occur as a result of
contact with Pb, Zn and Cd polluted smelter sites (Adriano et al. 1997, Pierzynski 1997). Instead of
the level of biological contamination, the presence of heavy metals in the soil serves as an indicator
of the level of action needed for soil cleanup or “bioavailability” of heavy metals. However, soil
heavy metal bioavailability is linked to environmental risk. Heavy metals are assimilated by humans
through the following multiple routes from the contaminated soils: (i) Exposure to Cd and Zn via
plant absorption in the food chain, and (ii) accidental consumption of contaminated soil. Hand-to
mouth activity (pica) results in inadvertent consumption of soil. Exposure to metal(loid)s through
incidental soil ingestion represents a significant source of non-dietary exposure to metals (Anju and
Banerjee 2003, Chaney and Ryan 1994, Day et al. 1979, Duggan et al. 1985, Wixson and Davies
1994).
9.2.5 Fertilizer Products
Heavy metal(loid)s input from fertilizers, particularly phosphate (P) fertilizers, is believed to be the
primary source of Cd. However, phosphate fertilizers with low Cd content can be used as fertilizers.
PO₄³⁻ rocks with low Cd contents may therefore be utilized to manufacture fertilizer products. Several
countries have introduced voluntary Cd limits on P fertilizers distributed by fertilizer manufacturers.
By the year 2000, the Cd level of P fertilizer in New Zealand decreased by 280 mg Cd kg–1 P,
compared to 340 milligrams Cd kilogram–1 P in the 1990s. The production of P fertilizers can be
achieved by using PRs that have low Cd content; however, for practical and economic reasons,
many countries continue to use sources with high Cd content (Bolan et al. 2003). Several chemical
approaches have been researched to eliminate Cd from phosphoric acid followed by its conversion
to fertilizers containing P. Two of these are the use of amines to extract wet phosphoric acids and the
use of ion-exchange resins. Phosphate rocks are preheated in a calcination process through a stream
or by a volatilization process to reduce Cd content in phosphate rocks. However, because calcination
is expensive and reduces PRs’ reactivity, it could not be a practical choice in the fertilizer sector;
consequently, they are less suited for immediate usage as a phosphate source (Ando 1987).
9.2.6 Manure and Biosolids
Manure usage is gradually gaining prevalence globally, especially in metal enrichment in soils.
The amount of metal(loid) in soils has multiplied due to frequent and extensive applications.
Animal manure contributes 5247, 1821 and 225 mg of zinc, copper and nickel, correspondingly, to
agricultural areas in England and Wales each year, accounting for 25 to 40% of overall contributions
(Nicholson et al. 1999). Australia contains high Cd and Zn levels in vegetable soils when poultry
manure was applied to agricultural soils Jinadasa et al. (1997). Copper concentrations in cow,
chicken, pig and sheep dung in China were investigated by Xiong et al. (2010), who discovered
the mean Cu concentrations to be higher than the national average in pig, poultry, sheep excrement
and cattle, ranging from 699.6 to 31.8, 81.8 to 66.85 mg kg–1, respectively. A large quantity of
bioavailable cadmium and arsenic are found in poultry feces mixed with soil (Sims and Wolf 1994,
McBride 1995, Haynes et al. 2009). Biosolids are commonly contaminated with heavy metals(loids)
by contamination of Zn, Cu, Ni, Pb, Cd and Cr with industrial wastewater (Haynes et al. 2009).
When heavy metals like Zn, Ni and Pb are transported through sand and sandy loams with
biosolids, Gove et al. (2001) discovered that drying and composting increase groundwater