Environmental Science (2+1)

Effects of soil pollutants

Effects of soil pollutants

1. Affects soil health and productivity
2. Affects plant and animals
3. Affects soil microbes
4. Ground water contamination through seepage
5. Affects human health
6. Causes biomagnification etc.
7. Soil Remediation process

Phytoremediation

• The process of recovery of hazardous substances from soil or ground water contaminated with municipal or industrial wastes etc. by using plants is called phytoremediation. Among vascular plants, some aquatic weeds such as species of Salvia, Lemna, Azolla, sedges and tree species are known to tolerate and uptake heavy metals. Bamboo can accumulate Zn, Cd, Ni and Pb (lead). Flower crops could be an effective method of remediating soil polluted due to disposal of tannery effluent.

Biological transformation of heavy metals

• Biological transformation of heavy metals is an important detoxification mechanism that can occur in many habitats and can be carried out by a variety of microorganisms especially bacteria and fungi. As a result of biological action, metals undergo changes in valency and or conversion into organometallic compounds.
1. Bioconversions involving changes in valency and resulting in production of volatile or less toxic compounds have been shown in several cases. e.g. oxidation of As (III) to As (V) and mercury ion to metallic mercury.
2. Transformation of metals into organometallic compounds by methylation, e.g. lead, mercury. Although the product of methylation may be more toxic than free metal, they are often volatile and released into atmosphere. Organometallic compounds can also undergo degradation, which may result in the metal being liberated in a volatile form. e.g. mercury.


Recovery of heavy metals

• Green plants such as specific strains of Indian mustard (Brassica juncea) can accumulate heavy metals when grown in chromium-contaminated soils. Modified strains of this plant have been shown to accumulate up to 40% of their biomass as heavy metals, such as lead and chromium. While microorganisms breakdown the organic bonds, the plants themselves take up the metals through their root system and sequester the contaminants in their cells. Useful plants can be found growing on ore outcroppings or contaminated areas. For instance, a variety of tree, Seberia acuminata (Sapotaceae), a native of New Caledonia accumulates an astonishing 20 to 25% of its body dry weight of nickel. The plant bleeds bluish green latex (sap).


• The lead accumulating plants, such as common ragweed (Ambrosia artemisiifolia) and hemp dogbane (Apocynum cannabinum) exhibited shoot concentrations of 400 and 250 mg Pb kg-1 respectively. Efforts are being made to develop more efficient soil remediation methodologies by breeding or bioengineering plants which have the ability to absorb, translocate, and tolerate Pb while producing sufficient biomass.


• Bio stimulation: Stimulation of the native microbes for site remediation
• Bioventing: It is the In-situ method of bio remediation in which air is supplied to an unstaturated soil zone through installation of wells connected to associated pumps and blowers which draw a vacuum on the soil.
• Air spraying: It involves the injection of air into the saturated zone of a contaminated soil