Recent studies have reported the presence of pelagic plastic fragments with diameters <5 mm in the open oceans including polar waters, marginal seas, and coastal waters. Importantly, micro plastics might act as a transport vector of chemical pollutants into the marine ecosystem, due to the absorption of pollutants onto their surfaces.
Methodology
The researchers conducted surveys across the Pacific Ocean from Antarctica to Japan to measure current levels of microplastics (plastic pieces less than 5mm) in different regions. They also developed a numerical model to track the sources, sinks, and transport of microplastics and make future projections.
The surveys measured microplastic concentration at stations along a transect from the Southern Ocean to the North Pacific. The researchers filtered large volumes of surface water through fine nets to capture microplastics. Then, they analyzed the plastic pieces in the lab.
The model simulated the release of microplastics from sources around the Pacific based on estimates of mismanaged plastic waste. It tracked the movements of the particles using ocean currents and waves. A sink term represents processes removing plastics like sinking, breakdown, and washing ashore. The model was calibrated to match observed spatial and temporal gradients of microplastics.
Results
The surveys found microplastic concentrations exponentially increased 10-fold from south to north. The Southern Ocean had 35,000 pieces/km2, while the North Pacific had 160,000 pieces/km2 on average. The East Asian seas were a hotspot with levels an order of magnitude higher.
Abundance of microplastics in the present and future. The panels represent the weight concentrations averaged in February (a) and August (b) in 2016, and February (c) and August (d) in 2066 at the sea surface. The weight concentrations are shown by a red stippling in the line with the scale at the bottom of d. The broken curves denote a weight concentration of 10 mg m–3. The green stippling in e represents surface zooplankton concentrations provided by the Estimated Ocean State for Climate Research dataset (see the bottom of the panel for the scale). The zooplankton data were averaged over the boreal spring and summer seasons (April–September) from 2002 to 2011. Also shown by contours in e are the weight concentrations in d
The model suggested microplastics have an average “lifetime” of 3 years in the upper ocean before sinking or washing ashore. Most accumulate in the North Pacific, with hotspots in the East Asian seas and central North Pacific.
The model predicted that by 2030, microplastic concentrations will double from current levels. By 2060, levels are projected to quadruple. The East Asia seas and central North Pacific hotspots are forecast to exceed 1000 mg/m3 by the 2060s.
Conclusion
The surveys demonstrate an apparent exponential increase in microplastics from south to north Pacific, with an order of magnitude higher levels in East Asia. The modeling forecasts a doubling by 2030 and a quadrupling by 2060 if current trends continue. The projected buildup in the Pacific highlights the need to reduce plastic waste entering the oceans.
Original article : https://www.nature.com/articles/s41467-019-08316-9
