7 March 2019

Scientific cruise

UU joins NIOZ in research on ocean micro- and nanoplastics

Ocean modelling engineer Philippe Delandmeter and chemist Ramon Oord from Utrecht University are both interested in very small particles of ocean plastics, however from totally different angles. Delandmeter is modelling trajectories of microplastics through the ocean water and Oord wants to analyze the composition of ocean plastics at the nanoscale. Both boarded the research vessel the Pelagia, of the Netherlands Institute of Sea Research (NIOZ). With UU’s strategic partner, they made a scientific cruise to the South Atlantic Ocean.

The Pelagia (image: NIOZ)

Count particles by hand

In three weeks, the Pelagia cruised from Cape Town at 18° East to the South Atlantic Subtropical Gyre – close to the Mid Atlantic Ridge - at 15.3° West, and back, covering a total of more than 6000 km. Led by NIOZ chief scientist Linda Amaral-Zettler, Delandmeter and Oord took water samples at varying depths, together with the NIOZ crew and other scientists from different disciplines. For the collection of microplastic at the surface, they used so-called manta trawl nets. Delandmeter: “We pulled such a net into the water for half an hour, and then counted the number of plastic particles by hand in our on board lab. In the gyre, there were several hundreds of tiny parts of plastic in a net.”

Platform with 24 bottles

The deeper microplastic samples and the samples of nanoplastics were taken in a different way. Oord: “We used a platform with 24 bottles that could be closed at any depth you want. The platform was fitted with several sensors that – apart from the depth - measured the water temperature, salinity, pressure, density and the amount of chlorophyll. Once drawn in, other scientists filtered the microplastics out and after that, I concentrated the nanoplastic samples from the remaining water for further analysis in our Utrecht University lab.”

Samples from four depths

The numbers provided by the sensors resulted in a clear view on the depths at which the bottles should sample. Oord: “We collected material at four depths: at the surface, at the Deep Chlorophyll Maximum or DCM, at the pycnocline, and at a depth of 500 meters. The DCM is an indication for the amount of organic particles such as algae in the water. Those have the tendency to attach to micro- and nanoplastics, so we expect them to accumulate at the DCM. The pycnocline is the water layer that separates water of different densities. The nanoparticles that I am looking for are so light, they might float on the denser layer. So this could be a second nanoplastic accumulation layer.”

Ramon Oord in his lab on board of the Pelagia.

Molecular buildup of plastics

Ramon Oord works for the Utrecht University hub of ARC CBBC, the institute for sustainable chemistry in the Netherlands. He explains how ARC CBBC hopes to contribute to research on ocean plastics: “In Utrecht, we’ve got a brand new lab, with equipment for advanced spectroscopy, which will provide knowledge into the molecular buildup of these nanoparticles. It enables us to analyze the compositions and types of plastics like PE, PP, or PVC, in such a remote part of the ocean. One of the questions is where all the plastics in the ocean ends up. We can only find one percent of all plastics that goes into the ocean, meaning 99 percent is missing. By analyzing our nanoplastic samples, we hope to answer many questions related to plastics waste in the ocean.”

Philippe Delandmeter (third from the left) and Linda Amaral-Zettler (left) are filtering sea water.

3D map

The Institute for Marine and Atmospheric Research Utrecht (IMAU) is specialized in making models of past, present and future climates. IMAU postdoctoral researcher Philippe Delandmeter studies the anthropogenically-induced problem of ocean plastic from a new angle. “We want to make a model and a 3D map of the three-dimensional dispersion of microplastics in the ocean, as part of our TOPIOS project.” For that, Delandmeter first needs to know more about the way and places ocean water moves from the surface to the bottom and vice versa. “We don’t have insight into the vertical dynamics of those small particles yet. They move up and down through the water column. I want to know where plastic sinks, how it sinks and where it ends up.’