146

Bioremediation for Sustainable Environmental Cleanup

natural phenomenon that uses fungi, bacteria and higher plants. It reduces the toxicity of soil by

changing the soil environment through bioaugmentation and biostimulation processes. The organic

amendments, higher plants and microorganisms include biological agents in the bioremediation of

contaminated soil with metal(loids). These organisms can render metal(loid)s harmless by lowering

their bioavailability and using chemical contaminants as a source of energy (Alexander 2000,

Zhuang et al. 2007).

9.2 Sources of Environmental Contamination by Heavy Metals(loid)s

The quantity of metals contained in the parent material from which the soil evolved and chemical

contributions from human activities make up the heavy metal(loids) total concentration in soil

(contamination sources). Heavy metals(loids) are found in the atmosphere in raindrops, aerosol

particles (< 30 mm diameter), agriculture fertilizers, agrichemicals, organic manure, livestock

sludge and compost. Metal(loids) are present in the soil as parent material, anthropogenic material,

ashes, mine wastes and demolition rubble. Metal(oids) leach into the soil profile by water and

winds (Alloway 2013). These metal(loids) in higher concentrations cause a loss in agriculture yield

(Alloway 2013).

9.2.1 Sulfidic Mine

The Earth’s crust contains a number of sulfur-containing minerals. There is a significant proportion

of rocks that are composed of sulfides. Various deposited metal sulfides ores are copper, lead, zinc,

gold, nickel, iron, uranium, PO4

–3 ores, oil shales, coal seams and mineral sands. Sulfides eventually

get exposed to oxygen during mining and give rise to acidic mine drainage. Tailing dams, waste rock

dumps, open pit floors, open-pit faces, haul roads, quarries and other rock mines are all common

places to expose sulfide minerals. In the presence of oxygenated groundwater or the atmosphere,

the sulfides are oxidized to produce acidic water rich in sulfate, metalloids and heavy metals (Anju

and Banerjee 2010). There are a few types of sulfide minerals that are relatively common, including

pyrite (FeS2). At mine sites, acidic water containing sulfate and metal(loids) is released mostly as a

result of the weathering of these minerals. Consequently, acid mine drainage has emerged as a main

environmental issue that has an impact on the mining sector as a whole (Bernd 2007).

9.2.2 Acidic Mine Waste

The formation of low pH waters is attributed to the oxidation of sulfur-bearing minerals. Mining

activities tend to cause this type of event, affected by Acid Mine Drainage (AMD) from open-pit

mined areas or after mine abandonment, the formation of Acidic Mining Lakes (AML) in surface

depressions (İlay et al. 2019). Hazardous substances and metals and metalloids, Al, Cr, As, Mn, Ni,

Cd and Zn are a few examples, have higher concentrations at low pH. Aquatic life downstream can

be destroyed by AML drainage water. The dissolution of carbonate minerals in soil caused by acidic

mining lakes causes landslides along with degraded water quality (Geller et al. 1998, Schultze and

Geller 1996).

Acid mine drainage has an impact on aquatic species that live in water bodies. Acid mine

drainage lowers the diversity of the environment, abundance and aquatic macroinvertebrates in

streams. Polluted waters also affect many fish species (Letterman and Mitsch 1978). Pollution levels

can alter the abundance of specific macroinvertebrates, as some species range widely, while others

are confined to a limited area (Rasmussen and Lindegaard 1988).

9.2.3 Bauxite and Magnesite Mine

Mining has generated mine waste for several centuries. In mining tailings, metal concentrations

range from 1 to 50 g kg^–1, depending on the metal (Monica et al. 2008). In the environment, metals

are a significant source of toxicity for biota. The effects of these elements are felt by organisms