A soil contaminant is an element (also known as ‘heavy metals’ or inorganic contaminants, e.g. lead) or a chemical (also known as ‘organics’, e.g. diesel oil) present in the soil at a level that poses health risks to plant, animal or human health. Common soil contaminants include PCBs, PAHs, petroleum products, heavy metals and pesticides.
BACKGROUNDER: SOIL TESTING FOR CONTAMINANTS
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On this page:
- Questions people are asking related to soil
- Information on soil contamination
- Activities for understanding your soil
Questions people are asking related to soil
Information on soil contamination
Where does soil contamination come from?
We can be exposed to contaminants through the soil through:
- skin contact: dermal exposure-e.g. pesticides
- inhalation: breathing in dust- e.g. asbestos, lead; and/or contaminants that vaporize from soil-e.g. benzene
- ingestion: eating of dust and soil through hand-to-mouth and to a lesser extent through eating foods grown in contaminated soil as some can uptake heavy metals
With exposure to any contaminant, the likelihood that health effects will occur depends on how harmful or toxic the contaminant is to humans, how much you are exposed to, and for how long and often you are exposed.
Contaminants in soils can come from historical industrial activity, past and present land use, nearness to pollution sources (i.e. a major road, a coal plant) and natural disasters.
Contaminants can end up in your soil through:
- the air (from dust & exhaust)
- water (from rain & groundwater & runoff from a nearby site)
- direct deposition (from on site (e.g. Pesticide application, burning garbage, or nearby polluters).
Why test the soil for contaminants?
People test their soil for contaminants for a range of reasons:
- To see if the soil is safe to grow food in and/or reduce risk of exposure to contaminants through existing or future farms and gardens.
- To see whether contaminants may have been or are being deposited on your site through runoff (water) or air from nearby busy roads or polluting industries.
- To see what the contaminants may have been left behind on the soil after a natural disaster such as flooding or fire, or a chemical spill.
- To see whether remediation efforts are working.
Also see this great overview by Toxics Action Center
Common Soil Contaminants to be aware of:
Heavy metals are those elements which are toxic to humans at certain concentrations, including:
Some of them, like zinc and copper, are necessary or beneficial to living organisms in small concentrations but are toxic above a certain concentration; others, like lead, cadmium and mercury, serve no known biological function and are always toxic. Heavy metals are naturally occurring, found in rocks, soil systems and bedrock, and in some places a certain metal may be naturally present in higher concentrations (such as arsenic in New York State).
The majority of heavy metal contamination arises from human activity– metal mining and smelting, agrochemical fertilizers and pesticides, sewage sludge, oil and gas operations and fossil fuel burning, improper waste disposal, and fill used in residential development. Unlike organic contaminants, heavy metals cannot be broken down, so the they keep building up in soils. But their characteristics may change so that they can be more or less easily taken up by plants or animals.
Organic contaminants are carbon-based, meaning they are derived or manufactured from something that was once alive, for example, oil and gasoline, which is the remains of plant and animal matter that was compressed for millions of years, then pumped out of the earth and processed. Polyaromatic Hydrocarbons (PAH’s) and other petroleum hydrocarbon contaminants, solvents like trichloroethylene (TCE), dioxins, chemical pesticides, and Polychlorinated Biphenyls (PCB’s) are a few organic contaminants of note. They can be present in soils, particularly on or near historical or present-day oil and gas industry, auto and machine repair shops, old or leaky oil tanks, busy roads or highways, landfills and dumps, beneath electrical stations and wires, and places where there were building fires or demolished buildings.
Polycyclic Aromatic Hydrocarbons
PAH’s are a byproduct of incomplete combustion, and are released when fossil fuels are burnt. They are common in soils along busy roads due to vehicle exhaust, and are associated with coal burning power plants, forest fires, and road sealants. Other sources of PAHs include wood burning stoves and oil spills. There are more than 15 different types of PAH’s. Some PAHs are known to be cancer-causing, or carcinogenic. They have also been associated with respiratory illnesses. In soils, PAHs are likely to stick tightly to soil and organic matter particles; though certain PAHs move through soil to contaminate underground water or volatilize into the air.
Poly Chlorinated Bisphenols
Though they were banned in 1979, they are still present in the environment because they are highly persistent (do not readily break down) and can leak from landfills where they have been disposed of and from products that were made before the ban. They were used broadly in the electrical and building industries, and so are common in soils beneath electrical transformers and capacitators, flooded areas, and soils where buildings have been demolished. Since they don’t really break down, and bind to fats, they end up in our water and in our fish and seafood. So it’s especially important to know if they are present in places where people fish!
You can read more about each specific contaminant through the Agency for Toxic Substances and Disease Registry’s 2 page fact sheets, called Tox FAQ’s: [https://www.atsdr.cdc.gov/toxfaqs/index.asp ]
Activities for understanding your soil
Activities should include a materials list, costs and a step-by-step guide to construction with photos. Learn what makes a good activity here.
Several areas for potential development on soil testing and monitoring work include:
- Find and share information on way to biologically test for soil contaminants that's analogous to macro-invertebrate testing for water. Possibly soil microscopic life? Also known as bio-assays. Earthworms are known to be pretty good indicators of toxicity but more info and experimentation is needed so that this could be applied by communities.
- Identifying ways to reduce lab cost for sampling that requires lab testing (for eg., mass spectrometry for validity and reliable data). Partnering with university labs' is one way, or advocating for agriculture extension offices to provide subsidized testing. Do you have other ideas?
- Play with the DIY spectrometer and build up a database to compare with for each toxic metal and organic contaminant at different concentrations. Create a color chart based on the database with many replicates (people trying it out) to compare the colors shown from reaction with each metal and contaminant of concern.
- Figure out which reagents are effective for DIY colorimetric /spectrophotometric tests for soil contamination, and how to produce them.