2.3 Municipal Solid Waste and Industrial Waste Landfills
Millions of tons of municipal solid waste and industrial waste are produced every
year. During this solid waste processing and disposal, huge quantities of toxic metals
are leached into and pollute water bodies. Although a small quantity of HMs is
essential for plant growth, surface and groundwater bodies are said to be contaminated when there is a huge runoff of HMs from agricultural applications and
excessive leaching of HMs. A few reports suggest that this has become a major
issue, especially in the United States and China (Wu et al. 2010; Sarwar et al. 2017).
Even the low concentrations of HMs from contaminated soils and water that are
released into shallow lakes and estuarine and marine waters are very toxic, threatening the lives of fish and other wild animals, and also posing serious problems in
the ecosystem (Shi 2013). This realization necessitated development of eco-friendly
green technologies that improve the ecosystem with positive impacts while
preventing toxic HMs from leaching into the environment, also assisting the efficient
management of HM shortages. Plant-assisted remediation has been so far recognized
to be the better option for positive impacts of HMs as well as ensuring ecosystem and
human health (Song et al. 2003; Tandy et al. 2006).
2.4 Oil Transport, Refining, and Utilization
Oil refineries produce a variety of metal-laden wastes, which cannot be avoided with
current technology. The fossil raw materials formed over the timescale for oils is
reported to be the source of HMs similar to coal. When oil products are used for
energy, pollution problems occur. For example, vehicular exhaust, a hotspot we have
discussed, has brought many environmental problems. Actually, as gasoline is
produced by using crude oil as the raw material, oil probably causes more serious
impacts on soil quality than coal because oil has a higher concentration of HMs than
does coal.
2.5 Agricultural Irrigation
Although pesticides, chemical fertilizers, and mulching film are important agricultural materials that strongly promote the development of agricultural production,
they also lead to soil HM pollution if utilized incorrectly. Most pesticides are organic
compounds; individual varieties contain HM elements such as mercury, arsenic,
copper, and zinc. The HM content in nitrogen fertilizer and potash fertilizer is low
compared with the higher content in phosphate fertilizer. Farmyard manure is
sometimes chosen as the base fertilizer applied to farmland without considering
that heavy metal elements have been added to fodder as original materials at the first
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M. K. Awasthi et al.
Millions of tons of municipal solid waste and industrial waste are produced every
year. During this solid waste processing and disposal, huge quantities of toxic metals
are leached into and pollute water bodies. Although a small quantity of HMs is
essential for plant growth, surface and groundwater bodies are said to be contaminated when there is a huge runoff of HMs from agricultural applications and
excessive leaching of HMs. A few reports suggest that this has become a major
issue, especially in the United States and China (Wu et al. 2010; Sarwar et al. 2017).
Even the low concentrations of HMs from contaminated soils and water that are
released into shallow lakes and estuarine and marine waters are very toxic, threatening the lives of fish and other wild animals, and also posing serious problems in
the ecosystem (Shi 2013). This realization necessitated development of eco-friendly
green technologies that improve the ecosystem with positive impacts while
preventing toxic HMs from leaching into the environment, also assisting the efficient
management of HM shortages. Plant-assisted remediation has been so far recognized
to be the better option for positive impacts of HMs as well as ensuring ecosystem and
human health (Song et al. 2003; Tandy et al. 2006).
2.4 Oil Transport, Refining, and Utilization
Oil refineries produce a variety of metal-laden wastes, which cannot be avoided with
current technology. The fossil raw materials formed over the timescale for oils is
reported to be the source of HMs similar to coal. When oil products are used for
energy, pollution problems occur. For example, vehicular exhaust, a hotspot we have
discussed, has brought many environmental problems. Actually, as gasoline is
produced by using crude oil as the raw material, oil probably causes more serious
impacts on soil quality than coal because oil has a higher concentration of HMs than
does coal.
2.5 Agricultural Irrigation
Although pesticides, chemical fertilizers, and mulching film are important agricultural materials that strongly promote the development of agricultural production,
they also lead to soil HM pollution if utilized incorrectly. Most pesticides are organic
compounds; individual varieties contain HM elements such as mercury, arsenic,
copper, and zinc. The HM content in nitrogen fertilizer and potash fertilizer is low
compared with the higher content in phosphate fertilizer. Farmyard manure is
sometimes chosen as the base fertilizer applied to farmland without considering
that heavy metal elements have been added to fodder as original materials at the first
84
M. K. Awasthi et al.