The Queen Charlotte Sound-Tōtaranui case study
Plastics can enter the sea in many ways, including through sewage and wastewater systems, riverine inputs, aquaculture and fishing activities. Large plastic debris can break down into small pieces, micro-sized particles (< 5mm), which are not readily visible to the naked eye.
Once in the ocean, these micro-sized plastics can have negative impact on marine animals, such as mussels, as they eat filtering particles from the water and they can ingest the plastic particles, which can then be transferred along the food chain with potential risk for human health. Ultimately, the microplastic particles end up accumulating into the seafloor sediments.
In mid-July 2020, a team of scientists including Drs Marta Ribó, Sally Watson and Lorna Strachan embarked upon a 3-day marine geology voyage to the Queen Charlotte Sound-Tōtaranui. The team collected marine sediment samples to investigate the amount of plastic accumulating in the bottom of the ocean.
Back in the laboratory, the sediment samples were processed for plastic analyses.
To accomplish this, separation of the plastic particles was performed using the method of density separation: lighter plastic particles are separated from the heavier sediment grains by mixing a sediment sample with a saturated chemical solution. After that, the solution is filtered to isolate the plastic particles.
The team have found different types of plastic particles throughout the sediment cores, such as fibres, fragments and pellets of plastic in several colours (i.e., blue, red, white, black…). It has also been observed that these plastic particles have been accumulating for very long time, since microplastics were detected as deep as ~45 cm.
This research is funded by an MBIE Envirolink Grant (2140-MLDC160) in partnership with Marlborough District Council, Te Ātiawa Manawhenua Ki Te Tau Ihu Trust, The University of Auckland and NIWA.