Soil Pollution - An Emerging Threat to Agriculture

Agriculture has always remained backbone of economy and socio-political stability of low and middle income countries, and employs largest work force in India. Maintenance of soil quality has been pointed out as one of the major contributing factors for sustainability of agricultural production. Rising contribution of industry to India's GDP has been speculated to cause adverse impact on the precious land resources; though the issue has received less attention among the policy makers. There is a complex relationship of Indian economy with industry and agriculture, both of which competing for same natural resources with differential impact on land resources. This chapter highlights the need for reviewing different developmental activities having direct or indirect impact on agricultural productivity and the need for accelarating soil research to investigate upon migration of pollutants from source of generation and their impact on soil so as to devise strategies for protection and remediation of precious non-renewable soil resources.

Soil is highly heterogeneous body in the terrestrial ecosystem that has evolved through thousands of years of natural processes and has remained habitat for enormous biodiversity. Due variability in seasonal temperature, rainfall, parent materials and vegetation, different types of soils have been found in India; and each of these soils have distinct mineralogical compositions, physical and chemical properties. Such heterogeneity has resulted wide variations in the response of soils to polluting activities which causes differential location specific impacts. To understand the interaction of pollutants with soil constituents and their impact on agroecosystems, basic knowledge on various aspects of soil resources and its functions are essential. This chapter describes in brief, the major soil types of India and their properties, role of soil constituents on its quality, different soil forming processes, inhabiting organisms and their role in different soil nutrient cycling processes affecting crop productivity.

Impact assessment of pollution is important step towards initiating appropriate remedial measures. However impact of soil pollution may not necessarily be uniform across the agro-ecological regions due to complex relationship among soil types, climate, crop types, nature and level of contamination as well as soil and crop management methodologies adopted. Moreover land resources are habitat of numerous organisms having varying degree of sensitivity towards contaminants. Hence, choosing right approach for assessing impact of pollution becomes important for satisfying various stakeholders affected by soil pollution. This chapter covers different types of impact of pollution on soil quality, economic yield of crop, food quality, biodiversity, fertilizer nutrient use efficiency, economy of the country etc. Pollution has already made adverse impacts on environment including soil in different countries. Widely cited instances of different types of pollution across the world and their impacts on soil and crop has also been discussed in this chapter.

Inorganic pollutants are released into the environment due to activities of mining, industry, transportation and urban activities. Environmental risks associated with inorganic pollutants vary widely due to several complex interactions at both intracellular and extracellular levels. Salts of alkali metals degrade physical and chemical environment of rhizosphere soil affecting water and nutrient uptake as well as reduce rate of several nutrient cycling processes mediated by microbes with overall impact on nutrient use efficiency. Toxic heavy metals and metalloids interact quite strongly with soil constituents as compared to salts of alkali metals, rate of which however, depend on the element and their speciation. Although their mobility in soil is low, these elements disrupt biochemical processes in organisms even at low concentration affecting physiological activities. Toxicity to organisms and transformation reactions for inorganic pollutants with soil constituents and their consequences on transfer to organisms including plants are discussed in this chapter.

Concerns on organic pollutants as threat to environment is increasingly perceived since later half of the previous century. Although initially focus was on some of the pesticides used in controlling insects in agriculture and disease spreading vectors in residential area, concerns on several other types of organic pollutants increased afterwards with activities of chemical and petrochemical industries and use of xenobiotics in many lifestyle products. Threat from organic pollutants arises many a times due to their extreme toxicity at very low level of exposure as well as their high persistency in the soil. Due to advancements in detection capabilities, researchers have generated considerable information on the source, routes of contamination to soil, interactions with soil constituents, degradability by and impact on soil microorganisms, uptake by plants and contamination of food etc. The impacts on agroecosystem are indicated as multidimensional like food contamination, reduced soil enzymes activity leading to disruption in nutrient transformation processes, diminished biodiversity, mutagenicity among microorganisms etc. Most common groups of organic pollutants in soil including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides, dye pollutants, antibiotics are discussed for their sources, fate and impact on the ecosystem.

Risk assessment of polluted land generally involves formulation of site specific remedial strategy, which further depends on history and type of polluting activities, contaminant migration pathways and their visible impact on ecosystem. Methods of soil sample collection and their processing before analysis in the laboratory become highly important for accurate interpretation of results and devising appropriate strategy for remediation of the site. Several statistical and non-statistical methods have been used for identifying sampling locations, each of which has advantages over other. Systematic and judgmental sampling methods are preferred where contaminant migration history is known and polluted area requires more intensive sampling due to high heterogeneity. On the other hand, statistical methods avoid sampling biasness and minimize uncertainty related errors in situations. Processing and storage of samples before analysis of samples depend on the type of contaminants. This chapter also discusses on selection of appropriate instruments for soil sampling, methods of processing and storage as well as precautionary measures for minimizing errors of analysis.

Several heavy metals are toxic to organisms including human and therefore their entry into food chain from polluted agricultural land is required to be controlled. Management and remedial measures of metal contaminated sites depend on the level and distribution of contamination. In view of high heterogeneity of soils in respect of heavy metals concentration, mere analysis of a sample may not confirm contamination due to polluting activities. This chapter describes various approaches for assessing heavy metals contamination of soil and expected degree of threat it may pose to the environment. Importance of baseline concentration in areas with high polluting activity is thoroughly discussed along with statistical significance. Degree of contamination and its threat has also been estimated by researchers through various models. Methods of assessment of risks to organisms due to heavy metals contamination in soil involving critical analysis of their translocation within plants and to human through various routes have also been described. Different countries have adopted regulatory limits to protect the land from contamination based on different approaches which resulted wide variations in their limiting values. Soil testing methods for rapid assessment of contaminated site has also been described in this chapter.

Due to rapid growth in industry and service sectors, urbanization has seen phenomenon increase in many countries across the world with consequent rise in solid and liquid wastes. Per capita generation and nature of such urban wastes has been found highly related to level of economic activities of a country. Due to insufficient treatment facilities for these wastes, urbanization has been found polluting agricultural land considerably, particularly in lower and middle income countries. Unscientific processing of solid wastes as well as release of sewage effluents in environment and their use for benefit to crop production have been found an important route for contamination of agricultural land with toxic trace metals and organic pollutants. Safe and beneficial recycling of municipal solid wastes in agricultural land after appropriate processing and treatment is facing obstacles due to lack of appropriate quality and hazardousness of the end products. Widely prevalent marginal quality sewage water use for irrigation in agriculture in urban and peri-urban areas in developing countries like India has also been discussed in details through different perspectives like carbon sequestration, crop productivity, plant nutrient supply as well as risks from various pollutants and pathogens.

Industrial profile of a city indicate nature of pollution that surrounding environment is facing or is likely to encounter. Though investigation on land resources for changes in soil quality due their activity has not been made adequately in India, an assessment of mining & industrial activities may indicate the potential threat to surrounding agroecosystem. The country has considerable environmentally destructive mining activities in about 57 million ha land area in several states altering the land morphology and existing land use and releasing heavy metals in the environment. About 595 metallic mines along with associated smelters, 145 thermal power plants, quite a large number of large & small scale metallurgical, chlor-alkali industry and tannery industry are likely to have adverse impact on land and water bodies through release of metals. More than 70,000 chemical and petrochemical industries in the country have the potential to contaminate land and water resources with toxic organic pollutants affecting various life forms. Considerable number of high volume effluent generating industries like textile, distillery, tannery, paper mill etc. may increase salinity of soil and groundwater. This chapter describes extent, distribution and possible impacts of polluting industries in India indicating potential threat faced by the environment including agroecosystem.

Soil fertility is highly important for countries where economy is dependent considerably on agriculture and animal husbandry. With the ambition of boosting economic growth many countries like India tap their vast mineral and human resources and expand industrial sector which also have considerable impact on soil fertility and agriculture. In order to have sustainable economy of a country, a harmony between industry and agriculture is highly essential. Though the cost involving protective and remedial measures appears to cut away the profit of industrial sector, these are extremely essential for shielding non-renewable soil resources which anchor the food producing agriculture sector. In order to formulate effective policies on protective and remedial measures, knowledge on the impact of different industries is required. This chapter reviews the research carried out worldwide to study the impact of major industries on soil quality and its consequences on quality of life including human. While some of the industries like thermal power plants, mining and associated ore beneficiation processes have direct impact on soil resources, other industries like textiles, paper & pulp, chemical & petrochemical, distillery etc. affect soil quality via polluted water used for irrigation.

Industrial sector in India is witnessing rapid growth since the last decade of twentieth century with reforms in economic laws and with establishment of special economic zones (SEZ). Such rapid industrial growth has also increased threat to the environment. In spite of great difficulty in its remediation in comparison with polluted air and water, soil pollution as a threat to human life is by and large ignored at national level in India due to lack of comprehensive information on the subject. Though coordinated effort on assessment of soil pollution is absent at national level, sporadic information has been generated by several researchers on various aspects of pollution affecting soil quality. This chapter analyses these information and attempts to assess the quantum of threat being faced by agroecosystem in the country. It indicates that soil resources are facing threats from deliberate use of contaminated organics, amendment materials and irrigation water or from atmospheric depositions, spillage of effluents etc. Nature pollutants varies from salts, toxic metals, metalloids, persistent organics with varying degree of toxicity and may be of both industrial and geogenic origins.

Soils perform several important ecosystem functions and therefore polluted land requires remediation and appropriate management for restoration of its life sustaining functions. Several technologies have been developed for their remediation based on clean-up, detoxification and risk minimization approaches. All of these technologies have both advantages and disadvantages in respect of the extent of applicability, side-effects on other components of environment, cost & ease of adoption, speed & effectiveness of remediation etc. While removal of contaminants and the risk minimization are the major approaches for heavy metal polluted soil, degradation to non toxic or less toxic compounds is the most common approach for soils polluted with organic pollutants. Plants, microorganisms, nanotechnology have also been used for remediation of polluted sites with varying degree of success. Waste products from agriculture, industries, city etc. have also exhibited their potential in minimizing risk from pollutants. Growers may minimize risks from polluted land through modification of soil, crop and nutrient managements. This chapter also discusses examples of a remediation approaches followed in case of different polluted sites worldwide.

Since independence, agriculture and food security has received considerable importance in policy documents of Planning Commission of Indian government. Although issue of land protection has been raised and addressed in the Five Yearly Plan documents, focus remained mainly on rational use of land by different sectors of economic activity and on prevention of soil erosion from agricultural land. Protection of land from chemicals & radionuclides pollution and prevention of toxic contaminants entry into soil have received less reference in environmental acts and rules as compared to that received by air and water pollution. Therefore, the need for soil protection policy has been felt by environmentalists that can regulate anthropogenic activities responsible for land pollution and put forward guidelines on remedial measures of already contaminated land. This chapter identifies key considerations for soil protection policy after analyzing basic functions of soil and types of threats perceived from human activities.