Week Six: PFAS Makes the EPA Go Round

Hello!

Welcome to week six of my blog. I’m not sure why, but this week felt longer and slower than usual. I guess from the solar eclipse on Monday to me taking Wednesday off and coming in on Friday instead, my normal rhythm was “thrown off.” On a completely unrelated note, I’ve gotten a lot of my coworkers into Hi-Chew candies, and I even traded Hi-Chews with one. I just think it’s funny how that’s become a frequent discussion topic.

I conducted three experiments: a PFOS Water MIP Fabrication and Time Trial Sensing on Monday and Tuesday, a Control Sensing Experiment on Thursday, and another Control on Friday. The PFOS Water MIP and Time Trial Sensing was a repeat of what I did last week. I still combined o-PD with 15 mL of 500 ppm PFOS in water for the MIP; however, the CV I obtained for the Acid MIP Fabrication was the expected current! Last week, I consistently saw “wonky” CVs with currents lower than expected and/or had unexpected spikes, so I was happy to finally obtain the “normal” one (see image below).

(all images: Fiona Xu)

The Time Trial I did this week was also the same procedure as last week’s, but I changed the iteration and wait time to four iterations and 38 minutes, respectively. Thus, I was measuring the current every 40 minutes because the scan takes two minutes. Afterwards, I created a four-data point scatterplot on Excel. There seems to be a slight decay in current over time (~0.5 microamps), but overall, it remained pretty stable.

It was my first time doing the Control Experiment. For this experiment, I was sensing with a bare gold electrode, so there was no molecularly imprinted polymer or electropolymerized o-PD with PFAS molecule imprints on the electrode surface. After I ran the first three characterizations, I let the electrode soak in a water vial for 20 minutes and then characterized again after placing the electrode back in the ferrocene methanol.

I repeated these steps until it soaked for a cumulative time of 120 minutes. The purpose was to have a standard of comparison we can compare the data from the MIP experiments to. We want to confirm that the electron mediator (the ferrocene methanol) is stable so that it doesn’t interfere with the sensor’s PFAS detection. In addition, I was also attempting to replicate one of my coworker’s results of the same experiment. We suspect that one of the potentiostats is not as stable as the others, which is causing there to be extra decay in the current.

My Friday Control Experiment was the same as my Thursday one, but I measured the current after every 40 minutes of letting it soak in water. I don’t have all the data points yet, so I’m not exactly sure what the trend of the graph is; I plan on analyzing the data on Monday.

I think it’s also worth mentioning that this past Wednesday, the EPA set the first ever national, enforceable legal limit of PFAS in drinking water. Most notably, the Maximum Contaminant Level (MCL), which the EPA defines as “the highest level of a contaminant that is allowed in drinking water. MCLs” for PFOS and PFOA is 4.0 ppt. This means that 4.0 ppt is the highest tolerated level, and public water systems are now legally required to act and reduce PFAS levels in water if its current levels exceed the MCL. This new policy is a testament to the growing need for PFAS monitoring and detection methods.

The values or “compounds’ safe level in drinking water” (0.004 ppt for PFOA and 0.02 ppt for PFOS) I referred to in my abstract were not enforceable. I’d also like to make a correction to my abstract because those values are the maximum exposure values to PFOS and PFOA from any source (not just water). Any level of PFOS and PFOA in water is technically “bad.” The MCL goal of PFOS and PFOA in drinking water the EPA set is 0 ppt.

That’s it for now, and next week I will discuss points I found interesting in my source readings.

Fiona

Citations

Environmental Protection Agency. (2024). PFAS National Primary Drinking Water Regulation [Fact sheet]. FACT SHEET (epa.gov)

Environmental Protection Agency. (n.d.). Questions and Answers: Drinking Water Health Advisories for PFOA, PFOS, GenX Chemicals and PFBS. EPA. https://www.epa.gov/sdwa/questions-and-answers-drinking-water-health-advisories-pfoa-pfos-genx-chemicals-and-pfbs#q4