Science Gazette

Deep in the water, scientists discover’missing’ plastics

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A recent research reveals the presence of plastics throughout the water column of an offshore plastic accumulation zone in the southern Atlantic Ocean, implicating the ocean interior as a key source of’missing’ plastics. The findings reveal that microscopic microplastics are important, understudied, and essential components of the marine plastic inventory. Furthermore, weak ocean current systems lead to the creation of microscopic microplastics hotspots at deep, implying a greater encounter rate for subsurface particle feeders such as zooplankton.

Around 51 trillion microplastics float on the surface waters of the world’s seas. These small pieces (less than 5 millimeters in length) come from many forms of plastics and damage natural habitats. Hundreds of research have looked at plastic trash on the ocean’s surface or near-surface. These studies, on the other hand, just “scratch the surface” and do not offer a comprehensive picture of what’s lying under the surface.

The first research to reveal the frequency of plastics throughout the whole water column of an offshore plastic accumulation zone in the southern Atlantic Ocean, undertaken by Florida Atlantic University, implicates the ocean interior as a critical source of’missing’ plastics.

The findings, which were published in the journal Global Change Biology, show that tiny microplastics are important, understudied, and essential components of the marine plastic inventory. Furthermore, weak ocean current systems lead to the creation of microscopic microplastics hotspots at deep, implying a greater encounter rate for subsurface particle feeders such as zooplankton.

“Our study emphasizes the importance of further quantification of deep-ocean microplastics, particularly the smaller size fraction, in order to better understand ecosystem exposure and predict the fate and impacts of these microplastics,” said Tracy Mincer, Ph.D., senior author and assistant professor of biology at FAU Harbor Branch Oceanographic Institute and FAU Harriet L. Wilkes Honors College.

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The researchers used in-situ high-volume filtration, Manta net and MultiNet sampling, and micro-Fourier-transform-infrared imaging to sample plastic particles in the South Atlantic Subtropical Gyre to gain a better mechanistic understanding of how plastics sink from the ocean surface beyond the mixed layer and eventually to abyssal depths of the ocean.

Due to the numerous and intricate redistribution mechanisms engaging with distinct plastic particles, they discovered that the abundances and distribution patterns of tiny microplastics differed regionally and vertically. They also noticed significant horizontal and vertical differences in the abundances of microscopic microplastics, with some showing inverted vertical trends. The abundances of small microplastics in pump samples were more than two orders of magnitude greater than the abundances of big microplastics obtained simultaneously in MultiNet samples.

“Small microplastics differ from large microplastics in terms of abundance, chemical nature, transport behavior, weathering stages, interactions with ambient environments, bioavailability, and plastic additive release efficiency,” said Shiye Zhao, Ph.D., first author and post-doctoral fellow at FAU Harbor Branch. “Their environmental destiny and potential consequences on marine ecosystems are influenced by these different traits.”

More than 65 percent of the total pump sample count in the research was made up of higher density polymers such alkyd resins, which are used in most commercial oil-based coatings like ship hull paints, and polyamide, which is extensively used in textiles like apparel, ropes, and fishing nets. This discovery emphasizes a disparity between polymer compositions from prior ocean surface-based studies, which are generally dominated by buoyant polymers like polyethylene used in packaging film and shopping bags and polypropylene used in plastic containers and reusable water bottles.

Small microplastics particles are more highly oxidized and appear to have a longer lifetime in the water column than net-collected large microplastics, implying increased marine ecosystem health risks due to possible bio-uptake of plastic particles and associated chemicals, as well as potential impacts on global biogeochemical cycles.

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“As plastic particles break into smaller size fractions, they may become toxic in a variety of unanticipated ways,” Mincer said. “These micron-sized microplastics have the ability to migrate past the gut epithelium, get stuck in biomass, and transmit across marine food webs, providing an unknown ecological danger and biogeochemical consequence.”

The researchers add that studies concentrating on smaller microplastics intake are urgently required to estimate the level of plastic contamination in biomass as commercial fishing activities scale up to catch marine animals for human consumption.

Mincer, Zhao, and collaborators from the Royal Netherlands Institute for Sea Research and the Woods Hole Oceanographic Institute used a combined analysis procedure to get a more comprehensive picture of the distribution, abundance, dimensions, and chemical nature of plastic particles in the interior of an ocean gyre.

Erik R. Zettler, Ph.D., a microbial ecologist at the Royal Netherlands Institute for Sea Research; Ryan P. Bos, M.S., a Ph.D. student at FAU Harbor Branch; Peigen Lin, Ph.D., a research associate at Woods Hole Oceanographic Institute; and Linda A. Amaral-Zettler, Ph.D., a marine microbiologist and professor at the Royal Netherlands Institute for Sea Research are study

The trip was funded in part by start-up money from the Royal Netherlands Institute for Sea Research. The American Chemistry Council, the FAU World Class Faculty and Scholar Program, a NOAA marine debris grant (NA17NOS9990024) issued to Amaral-Zettler and Mincer, and the American Chemistry Council awarded to Amaral-Zettler, Zettler, and Mincer provided funding for this work.

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