Abstract
Soil, a natural medium for plant growth, provides the anchorage to the plants and supplies various nutrients required for the plant growth. It is an important ecosystem that not only provides the shelter to various organisms but also participates directly or indirectly in various biogeochemical cycles. However, in recent years, the earth's soil has been stripped away, rendered sterile, and contaminated with toxic chemicals due to various anthropogenic activities. This increasing wide spread pollution has caused vast areas of land to become non-arable and hazardous for both wildlife and human populations. Unlike many other organic pollutants, which are degraded in the soils, some of the hazardous compounds like heavy metals, pesticides, polycyclic aromatic compounds, and phthalates are of special concern as most of these are conserved. The presence of such compounds in soil ecosystem causes severe toxicity and imbalances in the soil ecosystem as a whole. The chapter focuses on various sources of soil pollutants and the effects of hazardous compounds on soil health.
TopSources
There are numbers of factors responsible for release of hazardous chemicals to air, water and soil. The present part of the chapter deals with various sources of hazardous chemicals leading to soil pollution.
Key Terms in this Chapter
Polycyclic Aromatic Hydrocarbons (PAHs): PAHs also Known as polyaromatic hydrocarbons or polynuclear aromatic hydrocarbons are the compounds containing two or more aromatic rings. They only contain carbon and hydrogen and are composed of multiple organic rings in which the electrons are delocalized. The simplest form of PAH is naphthalene which contains only two aromatic rings followed by anthracene and phenanthrene which contain three-ring compounds. Other examples are Phenalene, Tetracene, Chrysene, Triphenylene and pyrene etc. Most of the PAHs have been documented to be potent mutagens and carcinogens.
Dioxins: Dioxins are ubiquitous ecological contaminants that are chemically related to polychlorinated dibenzo-p-dioxins (PCDDs) and are persistent environmental pollutants (POPs). This class of compounds exhibit various toxic effects such as hormonal problems, infertility, cancer, and possibly diabetes. High levels of exposure can even lead to chloracne, a severe skin disease with acne-like lesions mainly on the face and upper body. The most toxic compound of this group is 2,3,7,8-tetrachlorodibenzo-p- dioxin or TCDD. Dioxins are produced during chlorine bleaching of pulp, combustion processes, the synthesis of chlorine gas and various organochlorine chemicals.
Phthalates: Phthalate esters are the esters of phthalic acid and are mainly used as plasticizers (i.e., substances added to plastics to increase their flexibility, transparency, durability, and longevity). They are used primarily to soften polyvinyl chloride (PVC). Studies have shown their potential to induce severe reproductive disorders.
Heavy Metals: Heavy metals are generally defined as metals with density of more than 5 g/cm 3 . These metals have relatively high densities, atomic weights, as well as atomic numbers. In the field of metallurgy, a heavy metal is defined on the basis of density, whereas in physics, the distinguishing criterion is their atomic number and in chemistry, their distinguishing chemical behavior. Some of the examples of heavy metals are copper, chromium, lead, nickel, mercury, and zinc.
Pesticides: Pesticides are substances which are used to control pests and weeds in order to increase the crop yield. The term pesticide includes various forms like herbicide, insecticides, Molluscicdes, Ovicides, weedicides, fungicides nematicides, repellants and defoliage agents.