How did your background set you on a course toward your current field of study at UVM?

Kate Porterfield: I grew up in Annapolis, MD—right around the Chesapeake Bay, which fostered an early interest in water quality (the Bay has similar issues experienced in the Lake Champlain basin). The Bay has a long history of water quality issues—so, there's a lot of work in the region around that, and while my interests started as far back as high school, the connections between water quality, farming/land use, and our food system became apparent for me in Middlebury where I did my undergraduate work in conservation biology.  While there, I worked a summer on the Middlebury organic farm. I loved it and started conducting my own small, independent research projects. In my readings, I kept coming across a Hawaii-based researcher and decided to reach out to her to ask her for advice on my experiments. Long story short, we developed a relationship, and I was able to get funding from Middlebury to do a summer internship in Hawaii. I guess that is where I really got my official start in this field.

What types of projects did you work on in Hawaii?

Kate Porterfield: I worked on things like soil carbon sequestration in Maui range lands. I also looked at the nitrogen cycle in the context of organic amendments (like fertilizers made from human waste and compost) in a site in Haiti.

Those were both really inspiring projects for me, and I was lucky to be able to go back and work with the same professor again the following summer in California at the University of California Merced where she had taken a position. I did more agricultural-related research that summer. This professor was very influential and ended up remotely advising me for my senior thesis at Middlebury, which involved working with a local cattle farmer to look at soil carbon sequestration in his fields. This work basically involved looking at agricultural practices that take CO2 out of the atmosphere and sequester it in the soil where it builds soil health and keeps the CO2 from contributing to climate change (CO2 is one of the biggest contributors to climate change. When I graduated from Middlebury, I moved to Burlington to work with Dr. Eric Roy, who is doing really interesting things in his Nutrient Cycling and Ecological Design Lab.

One of my first projects at UVM was working with some Vermont dairy farmers to look at recovering phosphorus from dairy manure in order to try and address water quality issues in Lake Champlain.

Then, I worked on a project in the Lake Carmi region where I conducted a nutrient mass balance for the watershed. Specifically, I was looking at how much phosphorus and nitrogen was coming into the watershed and how much leaving. It was sort of an accounting project. I looked at the in/out equation to better understand the source of the extra phosphorus.

The common thread in my research is nutrient cycling. I'm really interested in how elements move through the biosphere and how human activities have altered both their movement and the places they're stored. These alternations are the cause of a lot of our environmental issues. For example, the algae blooms in Lake Champlain are largely a result of phosphorus that is moving through agricultural system and ending up in imbalanced concentrations in the lake.

I understand that your research is "focused on optimizing biogeochemical cycling through agroecosystems to enhance the environmental, social, and economic sustainability of food systems." Could you unpack that a bit for our readers? I'm not exactly sure what biogeochemical cycling is…

Kate Porterfield: Biogeochemistry combines different disciplines to study how elements move through and change the natural environment. Take, for instance, the algae blooms in Lake Champlain. Here, the nutrient cycle has been changed so that the phosphorus is concentrating in one place, causing the blooms.

Another way I sometimes frame my research is that I study resource recovery from waste streams. I take a waste stream and think about how we can use it as a resource rather than something to be disposed of. I am currently focused on food waste. If food waste is allowed to go into a landfill, it will break down and release methane, which is a really potent greenhouse gas. If we capture the methane gas, it can be re-used for something positive rather than contribute to climate change. Another shame about mindlessly disposing of food waste is that all the nutrients and energy that went into creating that food are essentially lost. It is buried in the ground where it's causing harm, and we can't extract value from it anymore. In my research I try to not only look at the potential benefits of a new process, but I also try to be realistic and think ahead to what the challenges are going to be…because there are no silver bullets.

Another emerging issue I'm look at is microplastics in food waste. Vermont has one of the most progressive food diversion programs. A lot of food waste is now being redirected to composting and anaerobic digestion since it is no longer legal to send it to landfills in Vermont. A sub element to this issue is the fact that about 1/3 of food waste in Vermont is still in packaging. This could be yogurts past their sell date or a pallet of ice cream that doesn't meet a manufacturer's specifications. So, there are large quantities of food still in packaging that need to be disposed of. One engineering solution to deal with this is a machine called a "de-packager." Basically, packaged food is put into the de-packager, and the machine hits the packaged food with paddles. Then, the mixture goes through screens that separate (theoretically) the packaging from the food so that the food waste can be sent to composting or anaerobic digestion and the packaging can be recycled or landfilled. There are growing concerns that diverting all this food (including packaged food) to composting and anaerobic digestion could introduce microplastics into agricultural soils. I spent the past year doing a literature review of what is known about microplastics in compost and digestate. Just last week, BioCycle published a short article on our microplastics research with a link to a preprint for the literature review.

The exhaustive look at the currently existing literature has given us a level of expertise on the issue. In fact, my advisor, Eric Roy, was called to testify in front of the Vermont legislative committees that are considering regulating microplastics in compost and digestate. He was able to share some of what we discovered in the literature review. We also wrote a policy brief that summarized our findings and recommendations were for the bills. That's described briefly in the BioCycle article.

Over the past year I've also been measuring microplastics myself. Specifically, microplastics in de-packaged food waste and in anaerobic digestate. I think everyone is pretty familiar with the composting, a relatively dry process that involves the aerobic decomposition of organic material.  Anaerobic digestion, on the other hand, is usually a wet process, and it happens without oxygen. Anaerobic digestion allows the released biogas to be captured and used to make electricity. Not everything in the anaerobic digester can be converted to biogas, however. There is always some liquid leftover (digestate), but the digestate is very high in nutrients and can be used as an organic soil amendment like compost. I'm working on methods to measure microplastics in both the food waste and digestate.

Common sense tells me that that letting microplastics get into things that will eventually be eaten by humans or animals is not good, but what is the main concern exactly from your perspective?

Kate Porterfield: The presence of microplastics in the oceans and waterways has received a lot of attention over the past few decades, but there has been scant research about the effects of plastics in the soil. This fact was part of the reason we did the literature review. There are still a lot of unknowns and a lot of debates in the scientific community about what the risks are from microplastics is in soil.

Of course, there are a lot of potential risks, but there just isn't much data yet on proven risks. Research is in the very early stages. That's why I've been spending a lot of time with the microscope lately—identifying microplastics. We're trying to come up with a faster and easier method to measure microplastics. If microplastics are going to be regulated state-wide, we have to be able to measure them quickly and easily. Another major finding of our literature review was that the realization that there aren't currently standard methods of measuring microplastics, which is a huge problem. Some studies are producing data in one unit and other studies are producing data in other units—so, essentially, you can't compare different studies, which makes it really challenging to figure out if everyone is finding the same thing. So, one of our first suggestions in the literature review was to establish standard methods for measuring microplastics. Another thing we found in our literature review was that microplastics aren't just an issue in one particular part of the process. They're not just an issue for digestate or de-packaging machines, for example. They're an issue across the board in organics recycling.

Do you think it is important/realistic to move to compostable plastics like some that are made from corn?

Kate Porterfield: That's a really good question. Intuitively, that seems like the direction that we need to go, but a lot of composable or biodegradable plastics on the market right now actually only degrade under very specific conditions. So, people have found "compostable" plastics in finished compost and digestate. Also, in our literature review, we found some indications that biodegradable plastics could be harmful to the soil biota in much the same ways that conventional plastics are. So, biodegradable plastics are not a clear-cut solution. I think innovations in compostable plastics will eventually lead to something better.

Do you have any new projects in the works?

Kate Porterfield: I have just begun working on a project that will be the last chapter of my dissertation. I'm going to do a life cycle analysis of food waste management options in the state of Vermont. A life cycle analysis is a way to compare processes or products across multiple environmental impact categories. So, I'll give each process a score for things like global warming, ecotoxicity, human toxicity, etc. I'll be doing a life cycle analysis for a variety of food waste management scenarios in the state of Vermont, and I'm going to pick a food waste stream that is difficult to deal with (e.g., food waste streams where there's a high level of anonymity—so, people don't feel as accountable and aren't careful about properly sorting things). I'll be talking to the stakeholders across the food waste management spectrum in order to get different perspectives on the issue of microplastics. I am interested in hearing what the all the stakeholders think in order to determine which elements should be included as parameters.

Is there one thing that the everyday consumer could do that would have a big impact? Is mis-sorting the biggest issue? For example, is it better to put something into the landfill bin when you're not sure if it is compostable/recyclable, or is it better to put it into the recycling and hope it gets sorted out if need along the way?

Kate Porterfield: You know, we need to better understand these issues. It is necessary to go further upstream and make things simpler and clearer because the way we dispose of food has to be compatible with lifestyle realities, and the packaging needs to reflect that too. Part of what we're doing is using infrared spectroscopy to figure out what types of plastics we're finding in the in the compost and digestate. This will allow us to know what types of plastics are most prevalent. With this information, we can prioritize changes in order to have the biggest impact.

We want to figure out how we can better design a food waste system.  If we're going to move towards a system where food waste is not going into the landfill and it's being eventually returned to the soil, then we have to redesign our packaging so that it's compatible with returning the food waste to the soil. Unfortunately, even if we could somehow magically eliminate all food packaging tomorrow, there would still be microplastics going into agricultural soils because there are other pathways for microplastics to get into the soil. For example, they can travel in the air or via irrigation channels and be deposited that way. Tire abrasion on the roads also create microplastics that run off. A lot of agricultural operations use black plastic around plants, which puts plastics in the soil too. So, we need to find out how significant the microplastics problem is in food waste in order to determine if it is a major contributor to microplastics in soils…

Kate Porterfield, M.S., is a Gund Graduate Fellow in the Department of Civil and Environmental Engineering. Kate is part of Dr. Eric Roy's Nutrient Cycling and Ecological Design Lab, and her research is focused on optimizing biogeochemical cycling through agroecosystems to enhance the environmental, social, and economic sustainability of food systems.