Microplastic 'hotspots' identified in Long Island Sound

Forensic and environmental experts have teamed up to develop a new scientific method to pinpoint microplastic pollution 'hotspots' in open waters.

A study by Staffordshire University, The Rozalia Project for a Clean Ocean and Central Wyoming College trialled the technique in New York's Long Island Sound.

Professor Claire Gwinnett from Staffordshire University explained: "Long Island Sound was a location of interest because it has lots of factors that can cause pollution.

"It is an estuary that has high populations of wildlife, it is a busy transport route frequented by cargo ships and is a popular fishing area. Located adjacent to New York City, it is also highly populated and a major tourist destination."

Funded, in part, by the National Geographic Society, the study saw samples collected from the deck of the 60′ oceanographic sailing research vessel, American Promise. The team took 1 litre 'grab samples' of surface water every 3 miles from the East River along the middle of Long Island Sound to The Race, where it meets Rhode Island Sound.

Grab sampling allows analysis of specific locations, with the researchers applying a statistical approach to identify hotspots where microplastics were most in evidence.

"People often use the term 'hotspot' but it is not scientifically defined. Previous studies have used largely subjective methods, without the use of any rules or thresholds that differentiate hotspots from non-hotspots," Professor Gwinnett commented.

"Our study proposed a simple yet objective method for determining hotspots using standard deviation values. This is the first time that this has been done."

Two primary and two secondary hotspots were observed, near either end of the sampling area. There is potentially a "bottleneck" effect in the narrower zones or, conversely, a dilution effect in the wider section of Long Island Sound. Similarly, hotspots were observed as being close to or in line with a river mouth, specifically the Thames and Connecticut Rivers.

Overlaying heat maps of various types of shipping and vessel traffic with the microparticle heat map from this study shows potential similarities. In particular, between areas of high recreational and passenger vessel traffic and higher microplastic concentration.

Professor Gwinnett said: "We need to consider factors that might influence these results, such as population, geography and human use. The identified hotspots, however, were found in both densely populated areas and adjacent to some of the least densely populated land areas surrounding Long Island Sound.

"The first step in combatting this type of pollution is by characterizing microparticle samples so that we can begin to understand where they might have come from."

97% of samples contained human-made particulates. Microparticles were classified as 76.14% fibres and 23.86% fragments. 47.76% of the fibres were synthetic and 52.24% were non-synthetic.

Forensic science approaches developed by Staffordshire University were used to analyse the microparticles -- including type, colour, shape, material, presence of delusterant and width -- which identified 30 unique categories of potential sources of pollution.

Rachael Miller, Expedition lead and Rozalia Project Founder, explained: "Unlike larger fragments of plastic, which may exhibit clear features that easily identify its original source, such as bottle cap ridges or a partial logo, this is generally very difficult for microparticles unless an analysis approach which fully characterizes the particle is used.

"Identifying a specific type of item from which a microparticle came from e.g. pair of jeans, carpet, tyre or personal hygiene product increases the likelihood of discovering the mechanism for transport to the environment. That, in turn, increases opportunities to prevent a subset of microplastic pollution."

The authors are now calling for reference databases of potential pollutants of waterways. PhD researcher Amy Osbourne specialises in forensic fibre analysis at Staffordshire University after progressing from the undergraduate degree in Forensic Investigation.

She said: "We cannot confidently identify the sources of pollution without being able to cross reference samples against large, easily searched known provenance databases. Such databases are already used in forensic science when identifying sources of evidence found at crime scenes.

"For example, we might begin with a database of all the different types of fishing nets or tarpaulins that we know are commonly used in areas like Long Island Sound."

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Genetically modified bacteria break down plastics in saltwater

Researchers have genetically engineered a marine microorganism to break down plastic in salt water. Specifically, the modified organism can break down polyethylene terephthalate (PET), a plastic used in everything from water bottles to clothing that is a significant contributor to microplastic pollution in oceans.

"This is exciting because we need to address plastic pollution in marine environments," says Nathan Crook, corresponding author of a paper on the work and an assistant professor of chemical and biomolecular engineering at North Carolina State University.

"One option is to pull the plastic out of the water and put it in a landfill, but that poses challenges of its own. It would be better if we could break these plastics down into products that can be re-used. For that to work, you need an inexpensive way to break the plastic down. Our work here is a big step in that direction."

To address this challenge, the researchers worked with two species of bacteria. The first bacterium, Vibrio natriegens, thrives in saltwater and is remarkable -- in part -- because it reproduces very quickly. The second bacterium, Ideonella sakaiensis, is remarkable because it produces enzymes that allow it to break down PET and eat it.

The researchers took the DNA from I. sakaiensis that is responsible for producing the enzymes that break down plastic, and incorporated that genetic sequence into a plasmid. Plasmids are genetic sequences that can replicate in a cell, independent of the cell's own chromosome. In other words, you can sneak a plasmid into a foreign cell, and that cell will carry out the instructions in the plasmid's DNA. And that's exactly what the researchers did here.

By introducing the plasmid containing the I. sakaiensis genes into V. natriegens bacteria, the researchers were able to get V. natriegens to produce the desired enzymes on the surface of their cells. The researchers then demonstrated that V. natriegens was able to break down PET in a saltwater environment at room temperature.

"This is scientifically exciting because this is the first time anyone has reported successfully getting V. natriegens to express foreign enzymes on the surface of its cells," Crook says.

"From a practical standpoint, this is also the first genetically engineered organism that we know of that is capable of breaking down PET microplastics in saltwater," says Tianyu Li, first author of the paper and a Ph.D. student at NC State. "That's important, because it is not economically feasible to remove plastics from the ocean and rinse high concentration salts off before beginning any processes related to breaking the plastic down."

"However, while this is an important first step, there are still three significant hurdles," Crook says. "First, we'd like to incorporate the DNA from I. sakaiensis directly into the genome of V. natriegens, which would make the production of plastic-degrading enzymes a more stable feature of the modified organisms. Second, we need to further modify V. natriegens so that it is capable of feeding on the byproducts it produces when it breaks down the PET. Lastly, we need to modify the V. natriegens to produce a desirable end product from the PET -- such as a molecule that is a useful feedstock for the chemical industry.

"Honestly, that third challenge is the easiest of the three," says Crook. "Breaking down the PET in saltwater was the most challenging part.

"We are also open to talking with industry groups to learn more about which molecules would be most desirable for us to engineer the V. natriegens into producing," Crook says. "Given the range of molecules we can induce the bacteria to produce, and the potentially vast scale of production, which molecules could industry provide a market for?"

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