Soil Pollutants and Their Effects Notes

What is Soil Pollution?

Soil pollution, also known as contaminated land, occurs when soil is chemically altered in its natural environment.
There are several types and causes of soil pollution, each posing environmental and health hazards.

Soil pollution is commonly caused by industrialization, agricultural chemicals, and wastes.
It results from intentional or accidental activities and can be worsened by natural events disturbing contaminated land.
Poor sanitation and dumping of sewage lead to biological pollutants like bacteria, fungi, viruses, and allergens.
Other sources include:
- Oil spills
- Acid rain
- Corrosion of metallic wastes underground
- Mining
- Waste disposal of sewage
- Dumping
- Coal ash
- Electronic wastes

In developed countries, industrialization has historically been a major source of soil pollution.
Developed countries now have regulations to reduce the environmental impact of industry.
In developing countries, industrial activities are often unregulated.
Factories in industrialized nations require large amounts of energy and produce lots of waste.
Coal is a major energy source, burned for heat in:
- Ore smelting (metal production)
- Cement production
- Chemical production
- Electricity generation
Burning coal concentrates heavy metals (lead, zinc) and polycyclic aromatic hydrocarbons (PAH's) in its ash.
- PAH's are known to cause cancer.
Improperly disposed coal ash contaminates the soil.

Polychlorinated biphenyls (PCBs) are large organic compounds once used as:
- Electrical insulators
- Coolants in electrical apparatuses (e.g., transformers)
- To make plastics more flexible
- Added to paint to make it dry softer and less brittle
- Coatings on bridges, water tanks, and other large infrastructure
PCBs were desired for their stability, low-flammability, and insulation properties.
Prior to the 1960s, 1.2 million tons of PCBs were produced globally.
Manufacturing has been banned due to their toxic effects but they are still in use today.
PCBs are now present in soil in many countries all over the world.

Thousands of accidental spills of oil, gas, and other chemicals occur yearly during transportation or processing.
Chernobyl nuclear power plant meltdown (Ukraine, 1986):
- 30 people died
- Radioactive material released into the soil
- Area uninhabitable by humans, though animals have returned.
Bhopal disaster (India, 1984):
- Gas leak exposed 500,000 people to methyl isocyanate (MIC), a highly-toxic gas.
- At least 3,787 people died, possibly over 16,000.
- Soil and water polluted with toxic levels of heavy metals and pesticides.

Common agricultural chemicals include:
- Herbicides (kills weeds)
- Pesticides (kills pests)
- Fungicides (kills fungus)
- Insecticides (kills insects)
These chemicals kill organisms that compete with humans for food.
High concentrations can cause short and long-term health effects.
When these chemicals are in water and soil, they become part of the food chain and affect animals and the ecosystem.

Soil pollution has many health and environmental effects, some immediate and some with long-term consequences.
Some contaminated sites are not a concern due to low contaminant levels.
Other areas are more concerning due to high contamination levels and the ability of contaminants to persist and/or move through the environment.
Contaminated soils can leach toxic chemicals into groundwater, lakes, and streams.
These chemicals can be taken up by plants or animals, contaminate drinking water, and vaporize to be breathed in.

Biomagnification refers to the increasing concentration of a toxin within the tissues of organisms as it moves through the food chain.
Toxins enter the food chain through small organisms that take them in from contaminated soil or water.
These toxins are slowly metabolized or broken down in the organisms.
When smaller organisms are consumed by larger ones, the toxin is consumed and concentrated in the larger organisms.
Examples of toxins that biomagnify include:
- Dichlorodiphenyltrichloroethane (DDT)
  - Starts as 0.04 ppm in algae and rises to over 13 ppm in humans.
- PCBs
- Heavy metals (e.g., mercury)

Human health is affected through direct exposure to soil contaminants, inhalation of vaporized contaminants, or consumption of contaminated groundwater.
Human health is affected indirectly by biomagnification of toxins in the food chain.
Exposure to high concentrations of DDT can cause vomiting, tremors, and seizures.
- Animal studies have shown that DDT is a carcinogen (causes cancer).
Chronic exposure to heavy metals (e.g., lead) may cause cancer.
- Lead poisoning is especially a concern for children because it has severe effects on mental and physical development.
- High exposure to lead can be fatal.
Chronic exposure to agricultural chemicals (herbicides, pesticides) are also known to be carcinogenic (animal studies).
- They may also cause liver and kidney damage and have effects on reproduction.