A pilot study carried out by New Zealand’s National Institute of Water and Atmospheric Research (NIWA) and the University of Auckland has found microplastics in samples collected from the seafloor in the Marlborough Sounds.
A global problem, microplastics have been found across the planet including in alpine soils, Antarctic waters and at the bottom of oceanic trenches, thousands of metres below the sea surface.
Microplastics are defined as pieces of plastic less than 5mm long and are either manufactured to be small, or derived from larger plastics that have broken down into smaller pieces.
Sediment samples collected in waters up to 70m deep
NIWA marine geologist Sally Watson co-led the study with the University of Auckland’s Drs Marta Ribó and Lorna Strachan.
In July 2020, several sediment cores were collected by NIWA research vessel Ikatere from Long Island – Kokomohua Marine Reserve, near the mouth of the Queen Charlotte Sound, 30 kilometres from Picton.
The samples were collected by a corer that extracts sediment up to one metre into the seafloor in waters 30-70 metres deep.
Dr Watson and Dr Ribó processed the samples in a laboratory by mixing them with a chemical solution and filtering them to extract the micro-sized plastic particles.
Microplastic pellets, fragments and fibres detected
Analysis found microplastic pellets, fragments and fibres that coloured blue, black, white, and red in the samples.
“We didn’t expect to see such a range of different microplastics quite far away from an urban area,” Watson said.
Further analysis will be needed to determine where the microplastics may have come from, but Watson says potential sources could include paint chips from boats, mono-filament fishing line and microfibres from clothes.
Recent studies by NIWA and Auckland University found microplastics in the guts and muscle tissue of several species of fish caught in the Hauraki Gulf, a coastal feature off the North Island.
Microplastics known to move up marine food chains
According to Watson, animals that feed on seafloor sediments and microplastics are understood to move up marine food chains. Nanoplastic particles (one thousand times smaller than microplastics) can pass through cell membranes into living tissue, although further research into the impact of nanoplastics is required.
Watson says the next steps for the research will be to determine what items the microplastics are coming from, analysing further sediment cores from the area to determine how widespread the problem is and understanding how deep microplastics are in our seafloor.
The study was commissioned by the Marlborough District Council in partnership with Te Ātiawa iwi Trust.
The Marlborough Sounds are an extensive network of sea-drowned valleys at the northern end of the South Island of New Zealand. They were created by a combination of land subsidence and rising sea levels.