Minnesota Aquatic Plastic Pollution Study
Welcome to the joint University of Minnesota Duluth and Minnesota Department of Natural Resources plastic pollution study.
This study focuses on determing the amount, chemical composition, and morphology of microplastics found in the water column, sediment, and fishes of four Minnesota DNR Sentinel Lakes.
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Plastics and Fish: FAQ's
Fibers seem to be the major problem in relation to plastics and lakes. What do you know about where these fibers come from and what human use products produce these?
One of the most obvious sources is probably clothes and doing laundry. A lot of clothes are made out of plastics. Fibers can easily break off of clothing, especially when doing laundry. Most washing machines do not have filters, but filters can be added to some machines.
Additionally, fibers can break off of plastic rope, plastic fishing nets, and other items that have synthetic fiber components.
We also see a fairly wide distribution of synthetic fibers, which indicate fibers can also become airborne, so dryer vents may be another source. There is also some evidence that when plastics in other morphologies, like films that are used to make plastic bags, are exposed to moving water, they degrade and turn into fiber material. The original plastic may not be fibrous, but they can become fibrous over time.
Are there any ways that we can manage or reduce the amount of fibers that are coming into our environment through those sources you just identified?
There are a couple of things you can do with your washing machine. There are some aftermarket filters, depending on the configuration of your machine. There are also bags, like lingerie bags, that you can put your fiber-shedding clothes into, and then you can wash them in the bag. There are also bags that are specifically sold now to reduce fiber loads that get into the water.
Do restrictions on single use plastics, such as single use grocery bags and water bottles, help reduce the amount of plastic in the environment?
Restrictions may help because there's so much plastic present, and it gets reworked and degraded into microplastics in the environment through wind and wave action. Ultraviolet radiation also degrades plastic, breaking larger pieces into smaller and smaller pieces until they are microplastics (less than 5 mm in size).
Additionally, restrictions that result in plastic reduction decreases the number of animals that become entangled in plastic.
There are many efforts underway to limit the use of plastic. Here are five steps you can take to limit the amount of microplastics in the environment.*
Reduce - Limit your own plastic waste.
Reuse - Bring your own shopping bags.
Refuse - Say, “No thank you,” when offered a plastic straw.
Remove - Pick up trash from your neighborhood.
Recycle - Recycle plastics you no longer need.
*These steps were adopted from the Earth Day Network.
Can we document the ways that restrictions could help and communicate this to decision makers?
We know that not throwing as much plastic into the environment or into landfills does reduce the amount of plastic that's present. If we could find a better way to make recycling economically viable, that would be a big help in ensuring we have more options for the plastic than landfill. For example, pyrolysis (high temperature combustion without oxygen) converts plastic waste into energy. Japan does this. Additionally, there are countries that have much higher recycling rates than we do. At this point in time for us economically, in the United States, it's so much cheaper to use new plastic than to recycle plastic. We have got to figure out how to make that better.
At this point, the science of documenting the impact of plastic reduction is still very young, so understanding exactly what the impacts are is difficult. Those sorts of epidemiology studies aren't present. The studies of what really happens in terms of whole ecosystems aren't present. So it's really hard to say what exactly specific actions will do.
It seems that Ten Mile and White Iron have the same rate of development. Do you expect that the amount of plastics will be comparable?
As we move farther along with the project, comparing those two lakes will be the most interesting. In terms of surface area, they are very similar, but in terms of watershed area are very, very different. White Iron Lake only has 1% development, but it has the largest watershed of any lake in the study by tenfold. As a result of watershed size, White Iron has a much higher inflow and outflow than Ten Mile, but Ten Mile has more development. Ten Mile is also a very deep lake that doesn't necessarily have as much inflow and outflow, so it's possible that we will see evidence of higher retention time within Ten Mile for plastics. In White Iron, it may be that plastics are flowing in, but because of the higher outflow, they stay suspended and flow out of the lake. Alternatively, we may see that because of the large watershed, there's just way more space for plastics to be coming from in its watershed and White Iron may show a lot higher concentration than Ten Mile. It is hard to say which lake will have more plastic right now. However, once the results are in, Ten Mile and White Iron may indicate what drives microplastic concentrations in northern Minnesota lakes - watershed size or population density.
When lakes are being selected for study, is there any consideration given to where they are located in the watershed?
This is the first small lake study that's existed, and so we tried to survey a few different types of lakes. We actually had in mind when we first proposed this idea to survey more lakes, but practical limitations required us to be more selective. We hope to do more research in the future on more lakes.
Since you are collecting plastics from the surface, can we conclude that the vast majority of plastics float on the surface?
Collecting plastics from the surface of the water is a common and relatively easy technique, and it allows us to compare our results to many other studies in the literature. But, that doesn't necessarily mean the majority of plastics are there. More study is necessary to determine depth fractionation of plastic particles, and we are planning to sample Lake Superior at the beginning of August at multiple depths in the water column. For the small, inland lakes, we also use surface sediments so that we can get an idea of what's floating and what's sinking with the idea that the fish might tell us about what's in between the two. as nice collectors of the mid-water column, at least with the fish that we chose, which are bluegills and cisco.
For Lake Superior. We actually are going to do in situ pumping, so pumping water right out of the lake, which is not for the faint hearted. Pumps are large and unwieldy and somewhat cranky to work with, but we're going to try and see if we can get samples at different depths and at multiple sources or in multiple places in the lake to get an idea of what's sinking and what's not. If you look at plastic densities, plastic densities relative to water are both floating like Polypropylene and polyethylene and sinking like, PVC. However, we don't find that the native density of the plastic affects whether we find it in the sediments, or on the surface. It appears that these plastics get involved with other particles that might either float or sink because of the other things within the aggregate, so we find things that should float in the sediments, and we find PVC hanging out at the surface, so it's complicated.
Can people skim the surface of the lake to reduce plastic, or would this be more damaging to the ecosystem than helpful?
I imagine this would be more damaging to the ecosystem, because the surface layer has a lot of stuff in it, rather than just plastic. If you look at waters, there tends to be a lipid layer that occurs right at the surface. A bunch of fats hang out right at the surface, and those fats do amazing things. They affect gas exchange across the air-water interface. They act as a nice rich layer food for certain things that live in the water, and they also interact with the light. I think you might want to let the natural surface layer be a natural surface layer, rather than try to skim. Unless you have really visible active high loadings of plastic. In that case, you might want to pull it out. The plastic levels that we're seeing at the present time are not very high relative to the natural particles that are present within the water, so you'd be pulling a lot of other stuff out along with the plastic.
What is the extent of pollution in the lakes in northern Minnesota compared to other systems?
We're doing much better than very highly populated lakes in Italy. We're doing about similar to some of the lakes in Switzerland. We're doing less well than Lake Huron. We're doing better than the North Atlantic and the South Pacific, except for Peltier which might not be doing as well as the North Atlantic and South Pacific. We're in an intermediate range in terms of the plastic that we're seeing. This is interesting because in terms of population pressure, I would guess that we’re on the lower end of some of the population pressures of these other systems.