Ocean Plastics May Pose Greater Threat Than Can Be Seen



Scientists have this week released what is to date perhaps the most accurate description of plastics in the ocean, demonstrating that the man-made pollutant may pose a greater threat than what can be seen from the surface. The research, which was conducted by a nine member team and entailed 24 expeditions in more than 1500 field locations across six global regions, found that the worlds oceans are carrying more than 5 trillion individual pieces of plastic equating to over 260,000 tons of dangerous debris. However, the team indicated that the volume of debris found was far less than expected given the world’s current rate of plastic production and consumption, and cautions that these numbers may be just the tip of the plastic iceberg.

Despite the enormous amount of plastic pollutants examined, the results of the seven year study, which also compared the sizes of plastic fragments, found less than expected microplastics floating on the sea’s surface. The result was incongruent with previously estimated quantities. Though far from assuming the reduction was due to proactive human intervention, the team suggested the small pieces, which measured less than 5mm, may simply have been redistributed and are still posing a threat to the marine ecological system.

One theory was that much of the smaller debris is being ingested by sea life, and is subsequently excreted in fecal pellets which then sink to the sea bed. This indicates support for previously published research suggesting the existence of microbial communities, which may assist in the breakdown of ocean plastics. This earlier study published in 2013, indicated that some of the “human-generated debris” may also be sinking to the bottom due to the weight of “biofilm formation and colonization by invertebrates.” Although researchers have not yet established the exact effect of the sinking ocean plastics, indications are that the threat runs greater and deeper than can be seen at the surface.

Plastic litter may be carried across the seas for several years before accumulating in gyres found in the north and south Atlantic and Pacific Oceans, and the Indian Ocean. Yet the research team was surprised to find the volumes of plastic debris in the southern regions were of similar quantities to the northern regions; an unexpected result as “…[southern hemisphere]coastal population density is much lower than in the northern hemisphere,” their report said.

Despite learning more about the degree of plastic pollution in the oceans, scientists are still mystified regarding its exact process of degradation. One possible reason for this is that plastic has been in mass production since the 1940s, but its behavior as ocean garbage has only become a subject of research in the last 10-20 years.

Marine ecologist Andres Cozar Cabañas told National Geographic that large quantities of plastic ocean debris are unaccounted for. “…We don’t know what this plastic is doing,” Cabañas wrote. He added that the increasing amount of plastic likely to be found on the ocean floor is potentially modifying the marine ecosystem “…before we can really know it.”

Although the effects of ocean plastics on larger sea life such as fish, turtles and corals has already been demonstrated, researchers fear these pollutants have the potential to pose an even greater threat to the marine environment than is currently visible. Therefore, until scientists are able to solve the mystery of the missing fragments, there is no sure knowledge as to the extent of the ocean’s plastic problem.

By Monica Grant

Environmental Science and Technology
National Geographic

Photo by Kent K. Barnes/kentkb – Flickr Page