We purchase more than we need and most of what we need is packaged and transported in plastic. Poor disposal practice often results in plastic waste ending up in watercourses and, eventually, the sea. Here, recent estimates indicate that this plastic amounts to about 150 million tons. Only one percent of seaborne plastic waste floats on the surface and five percent washes up along shorelines. The remainder is often referred to as "the missing plastic".

The hunt for plastic

Microplastic are plastic fragments less than 5 mm in diameter. Many studies show far higher levels of microplastic on the seafloor compared to the surface. The distribution of plastic across oceans is affected by several factors. Ocean currents and wind patterns transport plastic over great distances.

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Whether or not plastic sinks depends upon its mass density, size and shape. Even plastic floating on the surface may, in time, sink and end up in sediment on the seafloor. As an example, fouling of algae will make plastic heavy enough to cause sinking, as shown in the picture. In addition, plastic consumed by sea creatures may reappear as faeces and sink to the seafloor.

Plastic in the environment will inevitably break down into microplastic. Regardless of size, waste plastic is cause for concern, but microplastic, regrettably, is easily confused with other small particles. When at large in the environment, microplastic is virtually impossible to eradicate.

Furthermore, creatures can easily mistake it for food. This may lead to internal injuries, digestive problems and falsely feeling satiated. In addition, microplastic may contain environmental toxins due to additives in the manufacture of plastic.

Mapping microplastic

To better understand what happens with microplastic in the environment, NGI has developed a method of separation and quantifying microplastic in sediment. The method is made use of in mapping operations carried out in cooperation with DNV GL on assignment from The Norwegian Environment Agency.

Microplastic was discovered in several sediment samples and bristle worms taken from the seafloor in the North Sea and the Barents Sea. (https://www.miljodirektoratet.no/aktuelt/nyheter/2019/februar-2019/mikroplast-funnet-i-flere-prover-pa-norsk-kontinental-sokkel/). This work is carried out by two Master students at NGI, (√ėyvind Lilleeng and Jakob Bonnevie), under the leadership of Prof. Hans Peter Arp and Heidi Knutsen.

Microplastic found in the tested seafloor sediments was consistent with other studies. Furthermore, more microplastic was found in bristle worms than in sediments from the test area. This suggests that microplastic builds up in these organisms.

Work continues to see if there are differences between microplastic levels in the biological material, (the actual bristle worms), and the tubes they build around themselves as protection. Bristle worms are abundant and are found everywhere in the marine environment. Microplastic found in bristle worms may therefore have relevance for large parts of the food chain.

The way forward

NGI's work is ongoing in revealing the extent and sources of microplastic contamination. We must find out how microplastic impacts the environment, how it transports, its toxicity and life cycle and, not least, find the right actions to take.

International cooperation is essential in reducing plastic waste, understanding where all seaborne plastic is to be found and to collectively choose the best way forward. Recycling and a sustainable refuse solution must be the guiding rule in the future.