Abstract:

We know that 95% of our food is produced directly and indirectly  from soil, which include plant’s food and animals. Here animals depend for their nutrients and food on crops obtained from soil[2]. To increase the crop production, It is necessary to kill insects, rodents, weeds, pests and other bacteria and virus. For this we require insecticides, pesticides, herbicides, medicines to kill virus, medicines to kill bacteria, viruses and fungi[1]. Soils are obtained from weathering of rocks from thousands years. Some rocks have high concentrations of trace elements, thus become toxic for all living beings. Pedogenetic and weathering processes may enhance the trace elements concentrations in soil[2]. Pesticides may include insecticides, herbicides, fungicides, molluscicides, rodenticides, plant growth regulators like-defoliants, preventing premature fall of fruits, desiccants[2]. The soil can be contaminated from point sources such as application of pesticides, insecticides, organic fertilizers ( manure, sewage and sludge) and mineral fertilizers and diffuse sources such as flooding and contaminants deposition[2]. . It is found that DDT levels in Zhongshan park in Beijing exceeded the limit prescribed for soil by Chinese environmental quality standard. DDT level in urban park of Moscow range from 3.78 to 1347 µg/kg soil (where 143.1µg/kg of soil) which is very dangerous for human health [2].  

Key Words: Pesticides, Contaminants, Soil Pollution, Health Care Waste and Accidental Wastes.         

Introduction

The world soil day is celebrated on 5-december each year. This day make aware to the governments, NGOs and public for the growing challenges in soil management. Soil biodiversity and healthy mineral composition of soil is being damaging due to industrial and anthropogenic activities. Our soil provides balanced ecosystem for our healthy development, it is narrated in United Nations Environment Programme (UNEP). Food and Agriculture Organization of United Nations (FAO) published a study on “Soil Pollution: A hidden Reality” state that tree planting, air pollution and water pollution got more attention in public and in government actions but soil pollution is silently damaging our crops quality, fruits quality and health of all humans. Major anthropogenic sources of soil pollution are inorganic (heavy metals, batteries, coal burning and other hazardous salts) and organic (Dyes, drugs, colours, paints, plastic, rubber, paper, power) chemicals and by products of industries, municipal wastes, livestock and household (domestic) wastes [3]. Contaminated sites, Industrial area soil, urban soils, flooded land and agriculture soil are some hotspots for human exposure to soil pollution. There are many contaminated sites in the Europe and in the world which are not monitored, characterized, registered as polluted and remediated. They pose high risk for human health. There are many evidences which show that contaminants accumulate in the soil above threshold pollution level [4]. Anything that contaminate soil and degrade its quality is called soil pollution. Earth’s crust weathering leads to the formation of soil which accumulate over the centuries. The soil is a house of different microscopic and macroscopic organisms. Synthetic fertilizer has become requirement to gain surplus crop production. Above said substances which are necessary to increase crop production and contaminated water actually lead soil pollution. It is very urgent to use these chemicals in limit to avoid more soil pollution [1].

Relationship between soil and human health was studied in 1960. Safety for human health and ecological impact was discovered. Pollutants transporting processes like advection, dispersion and adsorption are considered effective to understand the topic. Surface soil and shallow surface sampling techniques are used to take samples. Site remediation processes are considered as surface water control technology, ground water control, active remediation system, soil vapor extraction and degradation treatment etc [5].

Sources of soil pollution: The origin of contaminants can be anthropogenic and natural activities. Pesticides in agriculture, radionuclides from nuclear power plants,

Trace elements, radionuclides, asbestos occur naturally in soils because of geological processes without any anthropogenic influence (ISO, 2015; Tian et al., 2017). Many elements are essential micronutrients for soil microorganisms, plants and animals, such as Fe, Zn, Mn, Cu, Ni, B, Se and Mo while other elements do not have any metabolic function, such as Hg, Cd, As and Pb. Normally trace elements present in low concentrations in soil.[2].

Natural geogenic sources:

Al (Aluminium), Cu (Copper), F (Fluorine), Ni (Nickel), Pb (Lead), Mn (Manganese), Hg (Mercury) and Zn (Zinc) are major elements of volcanic eruption. Thus, these elements in lava, ash and gases from mantle spread in soil and in atmosphere. Basaltic volcanic rocks of Reunion Island naturally have high concentration of trace elements particularly Hg. Cr, Ni and Zn. Indonesian and Japanese volcanic soils are well known for high concentrations of Cr and Ni [2].

Colourless and odourless Radon is emitted from natural decay of Ra(Radium), Th(thorium) and U(Uranium). The half-life of Rn is 3.8 days and finally it converts into relatively stable 206Pb. Igneous rock like granite, feldspar and illite-rich rock produce soil having high natural Rn.  238U, 40K and 232Th  are natural radioactive elements come from Dolomite and Limestone rocks into soil [2].

Natural Asbestos is consist of fibrous silicate minerals and found in soil which obtained from ultramafic rocks such as serpentine and amphibole .

The asbestos has high physicochemical properties like- heat stability, thermal and electrical insulation, tensile strength, flexibility with high resistance to chemical and biological degradation. Asbestos is found as carcinogenic and cause mesothelioma disease. Its industrial use have been banned in several countries. 

Wild fire is major source of organic and inorganic contaminants such as polycyclic aromatic hydrocarbons (PAHs) come in soil. Above 3800 organo-halogen substances produce from living organisms and abiogenic processes like-forest fire, volcanoes and geothermal activities [2].

Agricultural sources: Soil is contaminated by waste water  for irrigation, plastic materials like-films for mulching, drip irrigation tubes, rural wastes and green house’s plastic sheets.

 Pesticide is also used to treat animals and human diseases. Earlier, pesticides were obtained from inorganic chemicals like-copper, mercury, sulphur and arsenic based substances. But now synthetic organic based pesticides are in use [2].

Soil pollution due to urban activities:

Above 54% of the global population live in urban areas. Houses and industries produce thousands types of chemicals such as waste medicines, personal care products, soaps and detergents, other cleaning agents, paints, petrochemicals, battery works, tanning agents, plastic wastes, pesticides etc. Solid wastes are important to contaminate soil. Lead is very toxic metal and big threat for human health, animal health and plants. Industries related to lead (Pb) contribute major sources to pollute soil. Lead battery sector, lead based paint and transport emissions play major role in polluting soil and environment. Developed countries like America, China and Australia have banned lead based products in the past. Low and middle income countries still allow their industries to use low level of lead in their products. Mercury frequently comes in soil from coal combustion and industrial wastes [2]. 

Phthalic acid esters (PAE) are frequently employed in plasticizers and additives. It raises a serious concern because of its role as endocrine disrupters. Phthalate, di-n-butyl phthalate, and di-iso-nonyl phthalate are important PAEs which have the values 12, 10 and 7 times higher than in agricultural areas. Urban soil has a very toxic chemical Brominated flame retardants (BFR), they are used in electronic circuits, textile and building materials to protect them from fire. Eggs and cow’s milk become contaminated by these chemicals reside in dump sites of urban areas. High impact polystyrene, textile coating, flexible polyurethane foam, wire, cable insulation and electronic & electrical connectors are found to have BFR. Some BFR are polybrominated diphenyl ethers which have similar structure as poly chlorinated biphenyls (PCB) and they bioaccumulate in the body where they considered as endocrine disruptors.

In urban areas, pesticides are widely used to stop weeds and pests which affect vegetation in green areas and DDT is used to kill Anopheles mosquito which spread malaria, thus high level of toxic organic contaminants accumulate in public parks around the world[2].

Accidental Leakage:

Accidental leakage in pipelines, fuel tanks, sewers, landfills and septic tanks  in urban areas contain several toxic contaminants pose big threat to human health. Accidental leakage from electric power transmission equipments may contain PCBs.

Oil spills may contain PAHs which is also come in the soil from fuel combustion emissions.

Industries, mining activities, smelter works, transportation, weathering increase trace elements  and organic pollutants in nearby areas [2].

Municipal  Wastes:   People are shifting from rural areas to urban areas for employments and rapid increase in worlds’ populations put immense pressure on urban municipal facilities, thus, more and more municipal wastes high levels of heavy metals and organic pesticides contaminating urban soil. It is estimated that global production of municipal solid wastes (MSW) is 2.01billion tones per year but it may be than estimated.

Municipal waste contain some hazardous chemicals because it contain lead batteries, dyes, paint and its unwashed containers, electronic items having heavy metals, tanning chemicals, PCBs, plastics, colours, pesticides, metals alloys, soap, detergents, waste drugs, oils and hydrocarbons [2].  

Health Care Wastes:

The wastes of health care sector like- hospitals, doctor clinics and pharmaceutical companies mainly contain infectious wastes, pathological wastes (bacteria, viruses and fungi), pharmaceutical wastes, genotoxic wastes (chemotherapeutic and antineoplastic drugs), chemicals waste (rodenticides, insecticides, formaldehydes, halogenated compounds) , wastes with trace elements (battery, thermometers and BP device) and radioactive wastes (99mTc, 131I, 67Ga, 99Mo ) etc.

According to the WHO data, 10% health care waste are infectious waste and  5% wastes are chemicals and radioactive wastes [2].

Electronic wastes: 

All electrical and electronics devices such as mobile phones, geysers, press, TV, computers, solar panel, insulated wires, fridge and welding machines predominantly contain hazardous chemicals and heavy metals which seriously affect human health  negatively. According to a estimate, global e-waste production is found to be 44.7 million metric tons in 2016. It will increase 14% by 2021 [2].

Industrial and transport area:

Mining, Manufacturing, recycling and disposal are the major areas which pollute our soil particularly. Mining activities are important source of trace elements, trace elements also come in soil from mining wastes and emissions in the processing of extracted material like-tailing, smelting operations[2].   

In tailing process is liquid slurries are made of water and fine mineral particles. Fine particles are obtained when ore is crushed, grind and processed. Tailing is collected in sttled ponds and solid are allowed to be dried. The soil pollution take place where tailing dam fail and due to wind erosion. The ores may contain toxic elements like- arsenic, cadmium, copper, zinc and lead. Leaching of trace elements from ores is another way of soils. Mining wastes may contain reduced sulphur mineral like-pyrite when exposed to water and oxygen, the acid mine drainage may be formed. The acid enhance metals solubility from other minerals [2].

Causes of soil pollution: Soil pollution occur due to anthropogenic and natural activities. Some sources of oil pollution are

A-Chlorinated organic substances-These are less persistent to DDT and more biodegradable compounds such as carbamates and organophosphates but they are very toxins for nerves. These substances may the workers to death in fields [1].

B-Pesticides-Nicotine present in tobacco was used as pesticides before world war-II, It was found that DDT was very effective to control malaria infection and pests. After that people started to use it to kill insects, rodents and weeds neglecting its harmful effects. But now it is banned in India and in many parts of world. During this time pests become resistant to DDT. Thus it was necessary to use other pesticides such as Aldrin, Dieldrin. Pesticides are very toxic to humans and live stocks as well. These are mostly insoluble and non-biodegradable thus remain and accumulate in the soil with time. Through food chain they travel in different species of organisms [1].

C-Herbicides- Compounds that kills the weeds is called herbicides. These are sodium arsenite and sodium chlorate which decompose in few months. These may cause birth defects. Research suggest that using herbicides may cause more insect attack and more diseases in plants than manual weeding. There industrial production produce leads more environmental damage [1].

D-Inorganic fertilizers- Excessive use of these fertilizers lead acidification of soil.

E- Industrial waste-Industrial waste disposal of all industries contaminates nearby soil. These include plastic wastes, rubber wastes, heavy metals wastes, toxic chemicals, oil and grease and batteries etc [1].

F-Household wastes-household wastes include every thing that may be used in our house and become useless after a definite time period. These all wastes like toilet waste, toilet cleaner, plastic waste, rubber waste, metal pieces, damage batteries, colours, paints, synthetic clothes, soap, detergents, phenyle and floor cleaner etc. Leaking of sewerage system also degrade lead soil quality [1].

Type of soil pollution:

1-Heavy metal pollution- Heavy metals (Hg, Pb, Cr, Cu, Cd, As) above the prescribed limit become very toxic pollutants. They store in different parts of plants and enter in humans and live stocks through foods. 

2-Polycyclic aromatic hydrocarbons (PAH) pollution-Polycyclic aromatic hydrocarbons (PAH) are organic compounds of hydrogen and carbon. These are very toxic. Automobile emissions, cigarette, oil refinery, coke production, shale oil production and thermal power plants are major sources of PAH and other organic pollutants.

3-Industrial wastes dumping-Industrial wastes dumping leads soil contamination.

4-medicine pollution- pesticides, insecticides, herbicides and other medicines cause this type of pollutions. (1)

Effects of soil pollution: It is global problem. Contamination of soil lead downgrade agricultural products, poor quality of vegetable and fruits, less crop production and less income. These toxic chemicals and microorganisms become major cause of severe critical diseases in humans and livestock. Playing in contaminated soil may lead respiratory problem and skin infections[1], Organochlorine pesticides (OCP), POP, PCB, PCDD, PAH, heavy metals and PBDE are found in urban gardens and parks, these toxic chemicals bioaccumulate in human and animal bodies like-chickens and cattle. Children are very vulnerable of these chemicals. In southern Sweden, elevated concentrations of heavy metals are found in lettuce and potatoes because that area was heavily polluted due to former glass manufacturing industry, thus Cadmium Cd exceeds WHO maximum tolerance value[2]. In similar case, Cadmium and lead accumulation in lettuce found above tolerance limit in the garden of France. Exposure to contaminated soil and intake of contaminated food with elevated trace elements produce cumulative adverse health effect. High concentration of lead, arsenic, chromium and cadmium are found in the soil of private garden of New York city, which present high risk to human and animal health. When soils contaminate with oil, it seriously affects metabolism and growth of the plants with low photosynthesis rate in legumes [2]. 

The data collected in 2012 indicates that nearly 23% of global deaths {12.6 billion deaths} were assigned to environmental factors [2].

Conclusion: When soil contain organic and inorganic contaminants more than their prescribed limits set by CPCB, WHO and FAO-UN, the soil become contaminated and toxic for plants, humans and all other living organisms. Soil pollution is obtained from a number of sources and these sources are needed to be controlled for the benefit of future generations. All governments, NGOs and  public collectively are necessary to accept the changes in our social system, industrial setup and agricultural system  needed to reduce soil as well as environment pollution.

References:

1-Topper. Soil pollution, Environment chemistry.

https://www.toppr.com/guides/chemistry/environmental-chemistry/soil-pollution/.

2-Chapter 3:sources of soil pollution. Lead authors: Natalia Rodríguez Eugenio (FAO-GSP) and Marilena Ronzan (FAO-GSP).

https://www.fao.org/3/cb4894en/online/src/html/chapter-03-3.html.

3-1-UN environment programme. Soil pollution a risk to our health and food security. 04 dec 2020.

https://www.unep.org/news-and-stories/story/soil-pollution-risk-our-health-and-food-security.

4-European environment agency. Soil pollution and health. Last modified on 08 dec 2022.

https://www.eea.europa.eu/publications/zero-pollution/health/soil-pollution.

5-M.N. Rao, Razia Sultana, Sri Harsha Kota. Chpter-7 Soil remediation technologies., Book: Solid and hazardous waste management, science and engineering, 2017, pages: 243-260. ScienceDirect.