Joshua Marquez

University of San Diego Department of Chemistry and Biochemistry

Abstract:

Perfluoroalkyl (PFAs) compounds are in a lot of manufacture goods. Even though PFAs are used for important comodaties, they are harmful to the enviroment. Not only are they toxic to your body, but they also are very strong molecules. Since they are strong, PFAs build up in dirt becasue they cannot be broken. This brings the questions of how do these compounds accumulate. In my expirment, three dirt samples were collected from three different locations. The locations were strategically picked to assess how PFAs travel. With rivers connecting contaminated places in San Diego, the data shows that bigger PFAs travel less far, while smaller PFAs travel father.   

Introduction:

PFAs compounds are heavily produced industrial products that have become known as “forever chemicals” in recent years. The strong carbon-fluorine bonds of these compounds make it difficult to break down PFAs. Because PFAs are persistent, they accumulate in the environment including water and dirt. This can be a concern due to their level of toxicity. Some health effects from PFAs that are known can be found here :https://www.atsdr.cdc.gov/pfas/health-effects/index.html . The Health effects include an increased risk of kidney or testicular cancer, changes in liver enzymes, decrease in infant birth weight, and pre-eclampsia in pregnant women. These health effects are not good considering PFAs build up in dirt and when the dirt is overpopulated with PFAs, they can be very moble in water. This mobility allows PFAs to travel great distances from the orginial source. That is why we are testing concnetrations in local waterways to see the movement of PFAs.

Hypothesis:

There are two classes of PFAs, Perfluorinated carboxylic acids (PFCAs) and perfluoroalkyl sulfonate (PFAS). The difference between them are two things, first, PFCAs have a corboxilic acids on the end and PFAs have sulfonate on the end. Second, the two classes have different carbon lengths in order to be considered short chain or long chain. Short chain PFAs for PFCAs are 7 and fewer carbons, while PFBS are 6 and fewer carbons. For long chains it is anything above those numbers for the two classes. We hypothesize that short chain PFAs, due to their high mobility in water, will be widely distributed to the surrounding areas and Long chain PFAs are slowly secreted into the immediate area of the landfill due to its higher binding affinity to sediment.

Experimental Design:

Three different samples were taken at three different locations. The locations were picked due to there positioning of a landfill nearby that could be a source of PFAs. 

The landfill site is in Teal, Mission Bay in blue, Rose Creek in red, and purple for Tecolote Canyon. Each site is farther away from the landfill in order to see how far the PFAs travel and what chain length is present in that location. At each site, we collected about 10 grams of dirt. We preped the samples in order to get the PFAs out of them using ASTM procedure D7968-14: https://www.astm.org/DATABASE.CART/HISTORICAL/D7968-14.htm

After extracting the PFAs, a 1 mL samples was to put through a mass spectrometer (MS). To compare our samples, we created a standard with common PFAs which will give us starting point in analizing the MS data. To interpret the MS data, we used Xcalibur. By integrating the data, we can find the concnetrations of our samples through a calibration curve. Evey molecular weight scanned for had a calibration cure based off our standard.

From these calibration curves, we could take the integrations from the MS analysis to find the concnetration of our samples.

Results:

The average concnetrations calculated from the calibration curves are provided below.

The highest PFAs contamination was in Mission Bay Tecolote exit. The average concnetration was 2.1 ppb with high amounts of short chain PFAS. Tecolote Canyon had the next most overall PFAs contamination with the highest amount being short chain PFCAs. Mission bay rose creek exit was the third most contaminated site with the highest amount being short chain PFCAs, but also high amounts of short chain PFAS. Lastly, Rose Canyon has the lowest amount of PFAs with the highest amount being long chain PFCAs. 

Disscusion: 

We hypothesize that short chain PFAs will be widely distributed to the surrounding areas and Long chain PFAs are slowly secreted into the immediate area. Based off the data our hypthesis is correct. Rose caynon was the closest to the contamination site. That is why it has mostly long chain PFAs. To further prove this, the Mission Bay Rose Creek exit contains way more short chain PFAs. This shows the mobility of the Short chain PFAs. You could also look at the Tecalote Creek and Mission Bay Tecalote exit data. There was more short chain PFAs found farther down the river in the Mission Bay Tecalote exit data. Also, there is more long chain found in Tecalote Creek. A comparison of this data further proves our hypothesis. 

Conclusion:

It is once again important to limit PFAs in the enviroment. They are bad for human health and do not break down. Once more studies come out on PFAs, hopfully we can figure out how to get them out of the enviroment. One way of doing this is to stop production of PFAs, and find other molecules to replace it with lower toxicity. That is the next research question, how can society switch or not use goods produced with PFAs.