By Rick Andrew
A man plummets headfirst from the open, rear hatch of a diving military aircraft, barreling headlong toward the ground as he picks up speed to terminal velocity. He manages to catch up to the villain who leaped out of the craft mere seconds before him with the last parachute and the two begin a desperate mid-air struggle for control of the parachute.
They scream toward the ground as the man manages to snatch away the parachute from the villain just in the nick of time…
It sounds like this man is quite an active agent, perhaps serving one of many possible government spy agencies. Although this may be the case and he may have a very interesting tale to tell, this article is about a significantly different type of active agent. However, as we shall see, other types of active agents can have interesting tales to tell, as well.
Active agents are incorporated into POE/POU systems with the intent to be sacrificially released into the treated water. Although it may not be obvious from reading this definition, most active agents are utilized in POE/POU systems for purposes of reduction/oxidation reactions and/or for microbial control.
What kind of agent are we talking about?
NSF/ANSI 42 defines active agent as “A substance or medium added to or involved in a drinking water treatment process that requires direct or sacrificial release of the agent or its degradation product(s) to reduce specific contaminants in the water.” NSF/ANSI 53 has a very similar definition.
In essence, active agents are incorporated into POE/POU systems with the intent to be sacrificially released into the treated water. Although it may not be obvious from reading this definition, most active agents are utilized in POE/POU systems for purposes of reduction/oxidation reactions and/or microbial control.
Although there is theoretically an unlimited universe of possible active agents, in reality there are three commonly used active agents (see Figure 1).
Why identify active agents?
There is a purpose to defining and identifying active agents within the context of NSF/ANSI 42 and 53. All products conforming to these standards are required to conform to requirements for material safety.
These requirements involve a complete review of the formulation of all materials in contact with drinking water, followed by an extraction test. The extraction test consists of a static exposure of the product to test water under specific conditions, followed by a comprehensive analytical battery to assess the potential for any contaminants to leach from the product at levels of toxicological significance.
Where active agents come into play is that when conducting this test and looking for leaching chemicals, it is nearly certain that any active agents will be detected. After all, they are included in the product with the intent that they will be sacrificially released into the treated water.
With this reality in mind, the Joint Committee on Drinking Water Treatment Units developed alternative criteria to assess the concentration of active agents that are released from products. In other words, active agents in the product water are not addressed during extraction testing, but rather through an alternate procedure.
Evaluation of active agents
Active agent concentrations are evaluated in accordance with the sampling schedule for the verification of a specific contaminant reduction claim. This means that when running one of the contaminant reduction tests to verify claims on the product, the treated water samples are analyzed to ensure that active agents are not being released from the product at concentrations that are too high.
The standards provide guidance on which contaminant reduction test to use for this purpose. It requires that the test that is likely to result in the highest potential extraction of the active agent should be used, considering specifically the chemical composition of the test water used for the contaminant reduction test and the duration of rest periods prior to the specified sample points in the test. The standards also require that at least one sample must be collected immediately after a rest period with a minimum eight hour duration. Two likely tests are suggested, as described in Figure 2.
The standards further note that it may be necessary to run contaminant reduction tests other than those required to verify performance claims specified by the manufacturer for purposes of active agent evaluation. So, although a manufacturer may not claim bacteriostasis on a given product, this test may be conducted for purposes of evaluating the concentration of active agents being released into the product water.
The maximum allowable concentrations of the common active agents are described in Figure 3.
Not like in the movies, but noteworthy nonetheless
The parachute glides to the earth, not smoothly though, because it is bearing the weight of two men. Although our hero has subdued the villain after fighting it out with him for control of the parachute in mid-air, he is uncertain what adventures await him. He has, in fact, landed a good twenty miles inside hostile territory, with rough terrain and several patrol units between himself and friendly forces…
Okay, so POU and POE active agents are not quite as exciting as active agents in the movies. However, they do play several important roles in POU/POE water treatment.
Knowing how to properly evaluate the concentrations of active agents released by these products is critical to understanding NSF/ANSI 42 and 53. This evaluation involves assessment of the concentration of active agents under contaminant reduction test method conditions as opposed to static extraction testing conditions. This knowledge is exciting in its own right, especially for manufacturers of products that incorporate active agents.
About the author
Rick Andrew is the Operations Manager of the NSF Drinking Water Treatment Units Program for certification of POE/POU systems and components. Prior to joining NSF, his previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at 1-800-NSF-MARK or email: Andrew@nsf.org.