What Does 4 Parts Per Trillion Look Like?

The Environmental Protection Agency has set the maximum contaminant level (MCL) for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) at 4 parts per trillion (ppt). These substances are part of a larger group called per- and polyfluoroalkyl substances (PFAS) and are known as “forever chemicals” because they are highly persistent and can accumulate over time in the environment and the human body. These minuscule concentrations can be difficult to visualize, yet they have significant implications for our health and the environment. Four ppt is an incredibly low concentration and can be challenging to get your head wrapped around. So, let’s compare this to something more tangible.

A single drop of water is about 0.05 milliliters. An Olympic-sized swimming pool holds 2.5 million liters of water, which is equivalent to 50 billion drops of water. If you were to put a single drop of black food coloring in an Olympic pool, it would hardly be noticeable. At 4 ppt, you would need to dilute one drop of PFAS in five Olympic-sized swimming pools to meet the MCL. It’s almost undetectable. This is why it’s crucial for samplers to follow proper procedures to prevent any possible cross-contamination of water samples.

Now, let’s switch gears and talk about distance instead of liquid volume. The moon is approximately 238,900 miles from Earth, which is about 15,136,704,000 inches. This means you would have to make 33 round trips to the moon to travel a trillion inches. Just to give you a sense of scale, if you prepared to make 33 trips to the moon and back, and then stopped just 4 inches into your trip, that would be the equivalent of 4 ppt.

Consider another common analogy of finding a needle in a haystack. A typical haystack might contain around a million pieces of hay. Let’s scale that up to a haystack containing one trillion pieces of hay – this would be roughly equivalent to the height of a 24-story building. Detecting 4 ppt is akin to finding four needles in a 24-story-tall haystack.

Understanding the concept of parts per trillion helps highlight just how miniscule yet significant these measurements are. According to the Center for Disease Control and Prevention, there are 5 micrograms per liter of PFOS in your blood right now. This means your blood has 1,250 times the allowable limit of PFOS in drinking water. So please, be cautious and avoid getting cut if you go swimming!

At Bay West, we offer full-spectrum PFAS solutions, from detection to destruction. Our extensive experience and advanced technologies enable us to tackle the complexities of PFAS contamination, provide solutions, and ensure the safety and health of our clients and the environment.

What Does 4 Parts Per Trillion Look Like?

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Author

John Glabach, PE, PMP

Chief Executive Officer

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