Things to consider when testing your soil for contaminants- **
**How do you interact with the soil on your site? Who interacts with the soil on your site?**
This will play a role in determining how you and others are exposed to potential contaminants via the soil.
Do you grow a food garden or are you going to grow a veggie garden? Do you harvest fruit, herbs or other plants from the site? Eating fruit, vegetables and herbs grown in contaminated soil may expose you to those contaminants, though if contaminant levels are low there are simple measures you can take to greatly reduce exposure, including washing crops thoroughly before eating and avoiding growing crops known to uptake contaminants. If contaminant levels are high, you can grow in raised beds or remediate the soil prior to gardening there.
Do you have pets that spend time outside on the site? Pets can track soil and dust (with potential contaminants) into your home, increasing exposure.__
Do children play outside on the site? Children, especially under the age of 6, are most likely to being exposed to contaminants via the soil (because of their frequent hand to mouth behavior and likelihood of eating/ingesting soil) and are also most at risk of being harmed through exposure to contaminants in soil (because they are still developing and are physically smaller). Pregnant women are also at a higher risk for lead and other contaminant exposure.
**What kinds of contaminants might be present?**
There are different analytical procedures for measuring each type of contaminant in the soil, so it is important to know what could potentially be present in your soil in order to use the appropriate procedure to measure it. A little detective work is needed to identify which contaminants are likely to be in your soil since it would be very expensive to test the soil for all contaminants.
Step 1: Learn about the site.
Learn about the history of the site and neighboring area and consider what kinds of industry or land use activities may be contributing to soil pollution on your site. You can do this by talking to your neighbors, visiting your town or city hall to look through land use records, and looking through records via the Bureau of Land Management's online record search: https://glorecords.blm.gov/default.aspx
Step 2: Identify likely contaminants.
Once you know about the land use history and have identified possible sources of pollutants, identify which contaminants are likely to be present. Certain contaminants are so common (and known to be toxic) that they are good to test for in most scenarios, such as heavy metals and polycyclic aromatic hydrocarbons (PAH's). Others are associated with proximity to certain industries and past and present land uses.
Cornell Waste Management Institute has a great resource available here with more information about "Sources and Impacts of Contaminants in Soils."
If the answer is "yes" to any of the following questions, you will want to test the soil and take steps to reduce potential exposure:
- Was this house or building built before 1978? If so it is likely lead paint has been used on the outside that may have chipped or peeled off into the soil.
- Was a building demolished on this site? If so, lead, PCB's, asbestos, and a range of contaminants may have been left behind on the soil.
- Are chemical pesticides (and/or insecticides, fungicides, herbicides, rodent poisons) being used on this site or nearby, or have they been in the past? If so, contaminants such as chlordane, arsenic, lead, and other chemicals may persist in the soil. This is also true for certain fertilizers, which can leave metals and dioxins in the soil.
- Is the property near and industrial or commercial site that may be using chemicals or have used them in the past? Or was the site itself formerly an industrial site?
- Is the property near a road or highway with frequent traffic? If so, lead and PAH's are likely present in the soil nearest to the traffic.
- Were decks, swing sets, playscapes or other structures on the property built from pressure treated wood? If so, arsenic and copper may be present in the soil.
- Is there a history of or are there current leaks or spills of fuel oil, gasoline, or other petroleum products on or near the property? This can be from gas stations, fuel tanks, autoshops, or larger oil and gas refineries. These petroleum products, PAH's, as well as solvents like trichloroethylene, and metals including mercury may be present.
- Is the property near a landfill or dump? Was it formerly a landfill or dump? Many different contaminants, including solvents, pesticides, petroleum products, heavy metals and PCB's can leach from landfills.
- Have synthetic materials, buildings, or garbage been burnt on or near the property? Burning can release PAH's and dioxins- a highly toxic and persistent chemical- into the soils.
**Step 3: Make a soil testing plan.**
Things to consider when testing your soil for contaminants:
_How will you use the information? _
If you are going to use the information in a legal case, or for a scientific or professional project, you will want to go with an accredited/professional lab and ensure that you (and the lab) follow EPA guidelines for sampling procedure, chain of custody, and analysis and use suitable methods and take as many samples, over different time periods and depths and locations as possible. See EPA: https://archive.epa.gov/region9/toxic/web/pdf/ee-soilsampling-sop-env-3-13.pdf
Otherwise, if you are using the information to reduce exposure to chemicals and metals for yourself and community, it may be helpful to use cheaper options, such as taking a composite sample (one sample mixed from soils across your site); and you want to explore more accessible methods, such as a community soil lab or DIY soil testing methods. For example, you could test the soil for Total Petroleum Hydrocarbons (TPH's)- which just gives you a sense of whether or not there are significant levels of petroleum contaminants present; which can indicate that you should (or do not need to) do more testing and hone in on which specific petroleum contaminants.
**What is your budget?**
Soil testing can be expensive if done through a professional lab. For example, to test one soil sample for PAH's, key heavy metals and PCB's can cost between $200-300 USD, and one soil test for dioxins is $450. Options to keep prices down include:
- taking composite samples (where you mix soils from different depths and locations across your site into one sample for analysis)
- seeing if your local community or university soil lab has the equipment (XRF, IC-PMS, or Hanby or other colorimetric approaches to testing for petroleum hydrocarbons) and ability to perform the tests you need (ie- Soil Kitchens, free or subsidized soil contaminant tests through extension offices or environmental justice programs) * if this doesn't exist where you live and there is need, maybe you could start it- either build a relationship with a university who has the equipment, or fundraise (or seek donations) to get soil contaminant testing tools (like a hand-held XRF and Hanby kit) available for community use.
- explore DIY methods for getting a sense of levels of soil contaminants (DIY colorimetry, spectrophotometry, etc)
What is your sampling strategy?
This should be based on how the contaminants you expect may be distributed in the soil, how you interact with the site and what your goals and uses are for the site (and the soil testing).
How many samples? What sample depth? Where will you sample? Will you do individual samples or composite (mixed) ones?
If you are you trying to get baseline data about the soil contaminant levels, a good strategy would be to take individual samples from various locations on site, taken from various depths. If you are wanting to grow food in the soil and want to check for lead and other contaminant levels, you'd want to take samples from 2-14 inches deep, because that is the depth of the roots of most vegetables you would grow.
**Options for testing the soil for contaminants **
The most common way that people find out if their soil has contaminants present is to take soil samples and pay for them to be analyzed at a professional lab. That is fairly easy to do and gives reliable results, but the downside is that it can be expensive. There are other options, such as connecting with a university who can offer the soil analysis for cheaper; connecting with a 'soil kitchen' or community soil group who can offer XRF soil testing for heavy metals for cheap; and/or exploring DIY soil testing versions of colorimetry or spectrophotometry.
If you do go the route of sending soil samples to an accredited lab for analysis, here are a few good resources on how to take the samples to send to the lab:
See Citizen Science Community Resources, Inc https://csresources.org/own-a-soil-sampling-toolkit
See Cornell Waste Management Institute Guide to Soil Testing and Interpreting Results.
To find a lab to analyze your soil for contaminants, you can do a google search or try the NCAT Alternative Soil Testing Lab Locator to help locate a soil testing laboratory. We have worked with Test America for soil contaminant analysis, and they have labs across the US.
Your County's UC Cooperative Extension office and County Environmental Health Department may have more information regarding soil testing or be able to offer it. However, most extension offices offer soil analysis for nutrients, pH, and other qualities related to agriculture, few offer soil contaminant testing beyond lead testing.
good job on this article, very thorough. One other resource that can be helpful is EPA's TRI https://www.epa.gov/toxics-release-inventory-tri-program
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here's a visualization of research findings about lead contamination (soil or water-borne) concentrations in different plant parts. Original research from Finster, M. E., Gray, K. A. & Binns, H. J. (2004) Lead levels of edibles grown in contaminated residential soils: a field survey. Science of The Total Environment, 320, 245-257. Drawing below is from Soleri, D., Cleveland, D. A. & Smith, S. E. (2019) Food Gardens for a Changing World: A resource for growing food for healthy people, communities, and ecosystems, CABI (Centre for Agriculture and Biosciences International), Wallingford, Oxfordshire, UK, a book with PL pole photo on the cover!
Also, b/c contaminants often associated with zinc, some researchers suggest using cheap soil tests for minerals to assess zinc levels, and if those are high, then try to get lead and other heavy metals tested for. That's from Mitchell, R. G., Spliethoff, H. M., Ribaudo, L. N., Lopp, D. M., Shayler, H. A., Marquez-Bravo, L. G., Lambert, V. T., Ferenz, G. S., Russell-Anelli, J. M., Stone, E. B., et al. (2014) Lead (Pb) and other metals in New York City community garden soils: factors influencing contaminant distributions. Environmental Pollution, 187, 162-169
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This is really interesting information. a few questions: 1- love the schematic of the lead concentrations in various food crops. What levels are considered "safe" ? I realize it depends on bioavailability too. 2- where do you get these zinc test kits? I understand , good for heavy metals, but potentially there are so many other toxins in soil.. depends on application- as you have stated in your article.
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