Choosing the best testing methods for your sample comes down to good lab communication
There are many testing methods which describe how to test for various contaminants in various matrices. Trying to find the best testing method for your specific needs can be complicated. There are a variety of factors to consider.
First and most important, if the testing is intended to meet a regulation, the method that should be used will have to be approved. Secondly, the desired detection level will also play a role in determining the best methods as some instruments are able to detect down to lower levels. Then there are different environmental matrices, including drinking water, groundwater, wastewater, surface water, soil or even hazardous waste, and each can present their own issues when determining what testing methods to use or if additional preparation steps are needed to yield desired results. Finally, the characteristics of the contaminant of concern and how the testing results will be used can help narrow down the best testing option.
Regulations
Regulations can often drive what testing methods are used based upon lab certification. For example, under the Safe Drinking Water Act (SDWA) public water supplies are required to perform certain tests. The SDWA spells out which methods are approved to perform the required testing under these regulations. In addition, laboratory certification and accreditation are based upon the category of potable water, which dictates the types of methods that are approved.
For wastewater, the Clean Water Act spells out the methodology required when testing to meet these requirements. For hazardous waste, the approved methods are included under the Resource Conversation and Recovery Act.
There are also other state, county and township testing requirements which should also spell out the methods that should be used to meet the requirements.
Detection levels
The desired detection level also plays a crucial role in determining testing methods. A great example of this are the methods for running metals analysis. Generally speaking, there are two common methods for running metals in drinking water and wastewater. The first is what is referred to as AA, which stands for atomic absorption. There are some variations like flame or graphite furnace, but essentially both measure atoms being absorbed when heated.
The second method uses an instrument called an ICP-MS, which stands for Inductively Coupled Plasma-Mass Spectrometry. The biggest advantage is that an ICP-MS can get down to much lower detection levels in the parts per billion range as opposed to the AA, which gets into the parts per million range in most cases. With metals that are a significant health concern, such as lead, arsenic and chromium, it is important to have a lower detection level so this ICP-MS may be a more appropriate method.
Matrices and interferences
That is why it’s important when talking to a lab about testing that you describe the matrix. Remember, drinking water would be considered an approved potable water source like a public water supply; whereas a private well that has not been tested on a regular basis would be considered groundwater.
Describing the source of water is very helpful to a lab when trying to help determine the most appropriate testing methods for your project — whether it is a test for a residential homeowner or wastewater that is intended to be recycled.
A good example is water that has high levels of chloride. Whether it’s seawater or brackish water can interfere with other inorganic analysis done by ion chromatography. The high level of chlorides can extend into other analytes’ retention window, making it difficult for analyst to see and quantify potential contaminants.
Additional sample prep and cleanup steps may be necessary for samples with high levels of chloride in order to meet target detection levels. Another very common interference is the clarity of the water. Highly turbid or discolored samples will interfere with methods that depend on color changes.
Contaminants of concern
Contaminants themselves can also present some limitations when testing. Some of these limitations can be controlled by proper sampling procedures. For example, volatile organic compounds (VOCs) have a tendency to go from liquid to air under ambient temperatures so samples are collected in containers that have no headspace or air; therefore,VOCs stay in the water until analysis.
Certain contaminants can break down readily in sunlight so samples are collected in amber colored bottles to help block any light. Chemical contaminants also have half-lives, which is the time it takes for the compound to degrade half of the quantity of the chemical present.
An example is that atrazine, a commonly used pesticide, has a half-life of about 12 weeks, while Polychlorinated Biphenyls (PCBs) have a half-life measured in years. Half-lives play a role in determining holding times for tested contaminants. Other limitations are directly related to the method. A great example of this is the use of Atomic Absorption for elements like vanadium or molybdenum, which does not yield the best results because the maximum temperature reached is inadequate to breakdown these elements, thus making this method less sensitive for these elements. It would be more appropriate to run these via an ICP-MS.
Cost effectiveness
Depending on your needs, you may opt for a less expensive method. My example goes back to running metals analysis. If you are looking to run a group of metals, it would be more cost effective to run samples utilizing an ICP because it can run multiple metals and is more productive than using AA. Whereas if you are looking to run just one metal and do not have a strict detection level requirement, AA may be a cost effective way to go. There is often more than one method for each contaminant and some are more cost effective than others.
Keep in mind that if you need lower detection levels, the cost is usually going to increase.
Intended use of results
How the results are going to be used may be an important factor. If you are splitting samples, collecting two sets of samples and sending them to two different labs, you may want to have both labs run the same methods so the results are more comparable. Some methods are more accurate than others so having two different methods run for the same contaminant may result in drastically different results and further testing may be needed.
Another reason you may want to use a particular method is to confirm a suspicious result. Laboratories may have quality control plans which include verifying an unusually high result, especially for health-based contaminants. Choosing testing methods can be a daunting task, but with the right information your laboratory can assist you in determining the best testing method to meet your particular needs.
When contacting the lab, be prepared to discuss what kind of samples you want tested, whether they are drinking water, wastewater or other. Explain why you are looking to test — to meet a regulation or maybe there is contamination event, construction or drilling activity close to the water supply or a change in the taste, color or odor of the water.
Let the lab know if there are multiple samples — running several samples at once can be cost effective if there are budgetary concerns for your project. Also, be aware of detection levels and how you are using the results. For example, when testing for hexavalent chromium in wastewater, the detection level would be higher than if you are looking for it in drinking water — where we are now looking in the parts per billion range and even lower in some cases.
Detection levels should be meaningful and low enough to show when contaminants are present, even when below health guidelines. Detection levels can be very important when health is at risk because not everyone reacts the same. Typically infants, the elderly and those with compromised immune systems are at a higher risk of becoming ill when exposed to contaminated drinking water.
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Marianne R. Metzger currently works for Certified National Analytics (CNA) Environmental, New Jersey Analytical Labs, Smith Environmental, International Hydronics and TestMyWater.info, providing various testing services for residential, commercial and government regulations. Most of her career has been spent working for laboratories with specialization in water treatment testing. She also worked for Accent Control Systems as a sales engineer. Accent Control Systems is a company that provides equipment for in-line and handheld analyzers, flow meters and chemical feed pumps to be used in water, wastewater and other fluid applications. Sales engineers worked in the field by educating clients about products and helping to diagnose system and sizing requirements.
