Dr Katsia Pabortsava, National Oceanography Centre, UK
Measuring microplastics in the Southern Ocean
‘So, have you found any microplastics in your samples already?’ This is a question that I, Dr Katsia Pabortsava (NOC, UK), often get asked while I am at sea sampling for microplastics. The answer is usually ‘No, but it doesn’t mean that they are not there – they are just way too tiny to be seen … and they are good at hiding. They are like ninjas…the marine particle ninjas!’.
To get an idea of the size of a microplastic particle, look at how thick a single strand of your hair is – microplastics can be even smaller than that! Microplastics also resemble many natural particles: they can look like a dust particle, or a broken-up antenna of a copepod, or a tiny fish scale. Any plastic item can ultimately become a microplastic. For example, the sun and waves can break down plastic bottles, bags and fishing nets into smaller plastic particles; our acrylic clothing inevitably release fibres when we wear and wash them, ships lose bits of paint from their hull as they sail across the oceans, etc. Furthermore, microplastics are in alliance with marine bacteria, which like to grow on their surfaces and in this way mask microplastics as natural particles. These layers of bacteria, known as biofilms, make microplastics heavier and allow them to sink to the deep ocean. Microplastics also hide within the fluffy marine snow (see previous blog: Marine Snow-Episode 1), which carry them from the ocean surface to the abyss.
Marine organisms are often deceived by the size and appearance of microplastics. Small zooplankton, such as copepods, mistake them for food and eat them. This sets off the passage of microplastics up the food chain, as marine organisms like krill and fish feed on copepods, and then to larger animals, including seals, whales and humans who eat the fish.
Plastics are very versatile in terms of their chemical composition and often contain substances that can be harmful to an organism’s health if they enter the body. However, in order to find out how dangerous microplastics are we need to understand two key factors. First one is exposure: how much microplastics are there in the ocean, what are their composition and size, and where and how long do they stay in the water column? The second factor is harm: does the presence of certain amounts and types of microplastics damage the health of marine organisms, and how long would it take for the negative effects to become noticeable.
The CUSTARD expedition provides a unique opportunity to find out whether microplastics have penetrated the remote Antarctic waters. Here we focus mainly on the exposure aspect of microplastic pollution. We explore how these contaminants are distributed from the surface ocean and throughout the water column all the way down to the seabed. Our deepest samples come from 20 m above the seafloor, which is approximately 5.2 km deep. We also sampled the Antarctic Bottom Waters – a very old water mass that has not been in contact with the atmosphere since before the beginning of the industrial era in the 1850s. The presence or absence of microplastics in these pre-industrial waters will give us new insights on the spread and the transport pathways of microplastics in the ocean.
Over the past 6 weeks, we’ve captured marine microplastics using large volume stand-alone in situ pumps, referred to as SAPs, which are also used to collect marine snow (as discussed in Marine Snow Episode 2). We prepared and processed the SAPs’ sample filters in the particle-free cabinet that is free from any air-born microplastics in the ship’s labs. This allowed us to capture only those microplastics which had already entered the ocean. Once the filters are retrieved, they are kept frozen until they reach our laboratory at National Oceanography Centre in Southampton UK, where we will use an advanced spectroscopic imaging technique to make otherwise invisible marine microplastic ninjas come to light.
CUSTARD Research Expedition Measuring Microplastics in Southern OceanTweet