What are soil contaminants?
Soil is a complex mixture of minerals, organic material, water, and various life forms. In its original state, soil was an uncontaminated substance covering the earth. But humans have intentionally and accidentally poured harmful products onto it in some areas. The waste can hurt the soil and possibly human, plant, and animal health.
By definition, any substance in the soil that exceeds naturally-occurring levels and poses human health risks is a soil contaminant. As an example, arsenic naturally occurs in some soils. But if a person sprays certain pesticides on their yard, that could cause soil contamination. Lead is also very dangerous but occurs naturally in some soils. It was used in gasoline until 1989 and can still be found contaminating soils today.
The biggest risks for soil contamination are in urban areas and former industrial sites. Common contaminants in urban soils include pesticides, petroleum products, radon, asbestos, lead, chromated copper arsenate and creosote. In urban areas, soil contamination is largely caused by human activities. Some examples are manufacturing, industrial dumping, land development, local waste disposal, and excessive pesticide or fertilizer use. Heavy car and truck traffic can contaminate soil, and so can a single car. When soil is contaminated with these substances, it can hurt the native environment.
Where and how much contamination is added to soils will largely determine how that contamination spreads throughout an area. The type of soil will also play a role in its distribution.
How are people exposed to soil contaminants?
There are several ways humans can be exposed to soil contaminants. The most common are:
- Ingesting soil
Though it might seem odd to eat soil, contaminants can be ingested in a variety of ways. Young children may be particularly susceptible as they play in bare soil. Contaminated soil dust may also affect our food supply. Lavishly washing food products delivered from soil is very important. The biggest risk of ingesting soil happens when the soil is left bare. Covering soil with grass or other plants and mulching well reduces the risk of contamination. If people are eating outdoors near windy soil on a windy day, airborne contaminants may land on food before it is eaten.
- Breathing volatiles and dust
When soils are uncovered, small particles can become airborne with wind for example. Construction or demolition work, mining operations, or poor landscaping efforts can make soil dust. Breathing in contaminated dust may cause physical or chemical damage to humans. For example, asbestos fibers can puncture the lungs. Chemicals such as lead can hurt the nervous system, including the brain.
- Absorbing through skin
Contaminants may also be absorbed through the skin. Creosote is a common material used to preserve wood in the United States. This complex mixture of chemicals can leach out of treated wood and contaminate the soil. If creosote-contaminated soils are touched, then over time the skin may blister, peel or severely redden.
- Eating food grown in contaminated soil
If you grow food in contaminated soil, there is a risk that your food will also be contaminated. Many housing developments and community garden are established in areas that served as industrial or manufacturing areas where contaminants may be present. Many vegetables and herbs can absorb contaminants as they grow. That puts you at risk if you eat them. Also, vegetables and herbs can have soil dust on them. Without proper washing, contaminants remain. Even when gardens or farms may be located on uncontaminated soils, the immediate proximity of contaminated sites, there exist a chance the contamination to be transferred to the food products by the wind.
Sites of special concern
Industrial and manufacturing sites
Industrial and manufacturing sites often have a range of contaminants polluting their soils. The type of contaminant will depend on what the factory was producing. Contamination can occur when chemicals leak out onto the soil. All are dangerous to human safety on their own. When combined, they may react with each other to create even more toxic compounds. Containment and remediation of these areas are costly, technically complex, and logistically challenging.
Landfills, junkyards and waste disposal sites
Landfills, junkyards and waste disposal sites pose high risk of soil contamination, much like industrial sites. These areas often contain a large mix of contaminant types like lead, arsenic, and petroleum products. All are dangerous to human safety on their own. When combined, they may react with each other to create even more toxic compounds. Containment and remediation of these areas are costly, technically complex, and logistically challenging.
Highway corridors, parking lots, areas of heavy traffic
Аreas with high concentrations of vehicles pose a lot of contaminant risks, both from emissions and fluid leaks. For example, presence of lead can be high in areas with heavy traffic emissions, and petroleum or oil leaks on roads or parking lots can be washed onto nearby soils.
Household sites may not be an obvious site for soil contamination. But soils can get contaminated during housing construction. Petroleum products from the construction vehicles can leak and paint may spill. Homeowners may overuse pesticides or herbicides which inadvertently contaminate their soil.
Former farmland with build-up of contaminants
In the United States, many pesticides were composed of lead-arsenate between 1910 and 1950. At the time researchers and farmers didn’t know that lead caused health problems. As a result, lead is found in the soil of remnant farms today. In addition, there has been extensive development and production of herbicides since the 1950s. These chemicals need to be used properly; improper use can harm the soil, plant, and even human health. The use of high-load fertilizer applications may leave contamination in soils, depending on the crop and fertilizer type used.
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