How to test soil for OIL & GAS contaminants
Many communities in Texas and throughout the Gulf are facing oil and gas industry related contamination of their neighborhood soils and waterways. Petroleum products have the greatest risk for human health when they are in drinking water. But because many petroleum hydrocarbons are highly mobile, if they are in soil they can be easily transported to water resources.
Several petroleum hydrocarbons like benzene, toluene, ethylbenzene, and xylene can cause cancer. Humans can also be exposed to petroleum hydrocarbons by inhaling the fumes from contaminated soil. Alternatively, humans can ingest contaminated soil, which can be a primary pathway in children. Despite some individual petroleum hydrocarbons being carcinogenic at low levels and continued exposure, even at low levels, creates a risk for health problems for children and adults alike.
Read more about petroleum products in soils here: https://www.soils.org/discover-soils/soils-in-the-city/soil-contaminants/petroleum-products
What are petroleum hydrocarbons?
Petroleum products, such as gasoline, diesel, and heavy fuel oils, originally come from crude oil and consist of complex mixtures of hundreds of compounds, of which petroleum hydrocarbons are one of the main components. Read more about these soil contaminants in the Soil Contamination Wiki (https://publiclab.org/wiki/soil). Because of the widespread use of these products, environmental contamination from petroleum hydrocarbons is common. Alongside busy roads, your driveway or parking area, near any kind of oil or gas storage tank, and generally areas that are near auto-shops, gas stations, refineries, or have been flooded may have petroleum hydrocarbons.
Where to sample for petroleum hydrocarbons
When released to the environment, petroleum products change due to weathering (the breakdown of its components by light, heat, microorganisms), which causes changes in the how they move around and where they end up. Heavily oil contaminated soils have an obvious darker or gray color and a notable petroleum smell. You get to play ecological detective a bit to choose good locations for sampling.
Hydrocarbons with similar physical and chemical properties can be assigned to a specific equivalent carbon range, known as fractions. Some petroleum constituents biodegrade more readily, like the 'BTEX' -- lighter fuels- leaving the relatively non-mobile components (the heavier components like diesel or crude oils) at the original location (ATSDR, 1999). The constituents that biodegrade quickly or volatilize in the vapor phase, though they are of immediate concern after a spill to nearby humans- are less of a concern over the long term than the heavier petroleum products that stick around in the soil and are more likely to impact ecological populations.
_When you are taking soil samples for petroleum hydrocarbons, protect yourself from exposure to harmful chemicals by wearing gloves and possibly a mask. _
**How to analyze soils for Petroleum Hydrocarbons **
Most of the time, people take soil samples to a professional lab for analysis, but this is costly- $200-300 to get one single sample analyzed for PAH's and PCB's, two common petroleum hydrocarbon contaminants in soils. You can also just test for "total petroleum hydrocarbons" (TPH). TPH represents the total level of hydrocarbons rather than the identification of individual components (such as PAH's, toluene, PCB's). This gives you a general sense of whether there are significant levels of petroleum hydrocarbons worthy of investigating more but does not give you specificity. Having one sample analyzed for one or two specific contaminants is not going to give you a good picture of what levels and types of soil contaminants present in your soil, because you are just looking at one spot. The more samples you can do, spread out over your site and at different depths, and the more specificity of what types of petroleum hydrocarbons are present, the better.
If you are sending the samples to a professional lab to be analyzed, because they are organic and some of them can change- volatilize (evaporate in the air) or degrade (break down in light and warmer temperatures)- the samples need to be filled to the very top (no airspace) of glass jars that are ideally dark, kept on ice, and delivered to the lab within 24 hours so that the measurement isn't thrown off.
So for communities wanting to monitor their soil for oil and gas industry related pollution, there's a need to find approaches to doing so that are more affordable and logistically easier, while still giving accurate and reputable results (in case you will use the soil contaminant data to hold an industry accountable). A range of scientific literature related to oil and gas monitoring has been collected on this Public Lab page.
**Field Colorimetry and Reagent-based Approaches to Analyzing Soil Petroleum Hydrocarbons **
There are many commercially available field test kits for soil petroleum hydrocarbon testing that offer an alternative to sending samples to a lab for analysis. These field test kits use chemical reactions to help to identify contaminants, both qualitatively and quantitatively.
A reagent-based approach involves using a solvent to extract contaminants from soils, then a reagent is added which causes a chemical reaction in response to specific compounds. The reaction produces a color which indicates the presence of the target compound, and the intensity of the color produced can be compared with the color of standards of known concentrations.
**_A colorimetric reaction _**measures color or turbidity in response to the presence of the contaminant and the resulting color is compared to a color chart or is measured using a photometer.
Here are some examples of commercially available reagent-based kits:
- The Hanby Field Test Kit - petroleum products and PCBs in soil and water
- The Clor-N-Oil and Clor-N-Soil kits - polychlorinated biphenyls (PCBs) in soil and oil
- The Dexsil L2000DX analyzer - chlorinated organics in soil, water, dielectric fluids, and surface wipes.
- The PetroFLAG(tm)- total petroleum hydrocarbons (TPH) in soil
- SiteLab(r) - aromatic compounds derived from petroleum based fuels in soil, sediment, and water.
- The SDI Quick - total Volatile Organic Halides (VOHs) in soil and water
- AQR Color-Tec(r): total VOHs in soil and water
There are advantages to using test kits in the field, including:
- speed (results in minutes)
- portability (can bring out to various sites)
- low cost per sample ($20-25/sample as compared to $80-200/sample as through a lab)
- the range of contaminants that can be analyzed (PAH's, PCB's, different types of oil, gas and pesticides).
After learning the technique, a beginner can immediately begin to use some of the simpler tests. The challenge with these approaches are that they typically involve the purchase of the field test kit, which can range from $850-1250 USD. This may be within a feasible range for a community group to purchase upfront and use for ongoing soil monitoring at multiple sites.
At the Texas Barnraising, we had a demo from Hanby and got to use their soil petroleum kits to analyze soils. Read about how here: (ADD LINK)
*Although some field test kits are based on EPA methods used for reference and produce equivalent results (such as the Hanby kit), many kits are screening analytical methods, which means that the impact of potentially significant analytical interferences, imprecision, and bias need to be considered when interpreting kit responses, and comparing the results to results from other analytical procedures.
In development are several DIY methods using reagents, colorimetry, and spectrophotometry to detect soil contaminants. Please comment if you have experience with this!
For example, a number of analytical measurement assays have already been developed and documented with the open source colorimeter, including assays for measuring iron, nitrate, potassium and more. However there are still many more analytical measurements that can be carried out using this very simple and cheap measurement device, including a range of heavy metals and hopefully, pesticides. http://colorimeter-wiki.iorodeo.com/