When you want to test your soil, there are a few different options. Regardless of which type of lab you choose, you will need to start by taking a soil sample.
Soil is tested professionally at independent laboratories. To find a lab, you can ask your local Lead Prevention program for a referral, research labs on the internet, or see if your state or local Public Health department has a list of "certified" environmental labs. For example, the California Department of Public Health has a list of labs that are certified to conduct certain lab tests for government agencies. If you decide to contact an independent lab, you should ask them if they use tests (called methods) approved by the U.S. EPA and if they are certified or accredited. You can then research the methods on the U.S. EPA website to see if they are the ones current recommended to use. In California, a test known as CAM17 looks at the 17 metals that the State of California considers of most concern. Costs will vary, with labs charging $100 to $200 per sample for testing for one or more metals.
Labs that uses less expensive
methods will likely not be as accurate as a labs that are certified or accredited for metals testing. However, it is better to get your soil tested then not get it tested at all because you cannot afford using a certified lab. Many non-certified labs, such as the University of Massachusetts, Amherst Soil Lab (UMass) are commonly used by gardeners and agricultural groups to get a ballpark estimate of the health of their soil. The UMass lab offers a "Standard Soil Test" for $10 per sample (not including shipping the soil), and tests for lead, cadmium, nickel, chromium, pH, and nutrients like potassium and nitrogen. Make sure that you look at the actual amount (ppm or parts per million) of each metal and compare it to the table of safe levels. Relying on the lab's interpretation of of your results may be misleading if they simply tell you if the levels are low or high.
Lastly, you may want to contact your local agricultural extension office. They may provide soil testing for residents in their county at a lower cost than you might find elsewhere. Be sure to ask what methods will be used and what will be tested for (i.e., pH, certain metals and nutrients, etc.).
Your test results, also called an Analysis Report, should lists each metal followed by its concentration in the soil in parts per million (ppm). 1ppm literally means one in a million. For example, 80ppm of lead means that you have 80 parts of lead in a soil sample made up of 1,000,000 equal parts. Concentrations that were too small to measure may say "undetectable" or have a “less than” symbol (<) before a number. That number is referred to as the minimum detection limit, and is the lowest concentration that the lab can detect with the methods they use.
It is not possible to compare results you get from labs that use different testing methods in that different methods will test for different things. For example, certified labs can often provide a fairly accurate value for total lead in your soil, where as non-certified labs, such as UMass, may only provide an estimated value for the total amount of lead in your soil.
If your test results come back higher than you would like, you may want to do more testing (test specific areas or use a certified lab for more accurate results) and consider ways to manage the metals in your garden.