Interview: "Satellite technology helps to describe the problem, but not to solve it"
Dr. Jörg Lefèvre is involved with the topic of environment-friendly and health-friendly processes and products within the German Federal Environmental Foundation (DBU), works in the government commission of the State Government of Lower Saxony, and is a member of management boards and committees of various organisations. In these various functions, he also deals with the problems surrounding microplastic emissions and their avoidance, for example in the development and design of car tyres and textiles. In this connection, he has also become involved with the topic of data recording via satellite technology. Against this background, we asked him to appraise the process presented in this newsletter from the University of Michigan, with which movements and concentrations of plastics particles in the sea are calculated from satellite data.
Dr. Lefèvre, in our newsletter we report on a project to determine the global distribution of microplastic particles with the help of data obtained via satellites. You have also been involved with satellite technology for acquiring data. What are your experiences with this technology? Were you able to obtain usable results?
The DBU also works intensively with satellite data in the field of geoinformation systems – in brief: GIS – to describe and map above all nature conservation habitats. In the field of agriculture, we deploy multispectral satellite sensor data, for example for the measurement of soil moisture and the nutrient situation at a soil depth down to 90 cm. For this reason, it was fairly obvious that satellites, equipped with the relevant sensors, would be suitable for supplying more detailed monitoring data on marine litter, at least close to the water’s surface.
Where do you see the strengths of satellite technology, and where are its weaknesses?
Its strength is certainly in the field of monitoring. The spreading of floating plastic litter on the ocean surface is subject to complex physical parameters, depending on whether it floats on the surface driven by the wind and waves like an empty bottle, or whether it follows more the sea currents like a plastic bag being driven just below the surface. Here, satellite technology can supply useful information. On the other hand, it contributes more to describing the problem than to solving it. Floating bottles and bags are only the "visible" part of the waste emissions into the seas. Once they have been broken down mechanically, this problem becomes similarly invisible as, for example, tyre abrasion from road traffic, abrasion from paints and other surface coatings, and fibre fractions that are emitted via the wastewater from our synthetic fibre textiles. Also many of the so-called biodegradable plastics belong more to the problem side than to the problem-solving side: It often happens that they are not degraded back into their ubiquitously occurring, natural constituents.
How do you appraise the procedure and the results obtained by the research team at the University of Michigan? With their newly developed procedure, they chart the presence of microplastic on the basis of data that gives information on how agitated the ocean surface is. The team of authors is working on the assumption that divergences between wind speed and roughness of the sea indicate the presence of microplastic.
The charm of this method lies in the presence of the satellites and the availability of the measuring data. From this it is possible, with a reasonable amount of time and effort, to learn a lot about the distribution pathways and the average "travel time" of the plastic litter. Other approaches focus, for example, on the direct spectral or optical recognition of the litter or they measure the turbidity of the water. That is highly promising when the density of the "garbage patches" is lower – and it potentially also provides data for identifying the substances. This task is challenging above all because, on the one hand, we have enormous quantities of plastic litter and, on the other, giant sea areas affected by the turbulence – 5 kg per square kilometre is regarded, for example, as a high value in the Great Pacific Garbage Patch – that would correspond to 5 mg of plastic litter per square metre. The measuring task here has many similarities with the search for the proverbial needle in the haystack, but I am nevertheless of the opinion that it can be solved. But does it also help to solve the problem?
Do you see further potential in the satellite technology for example for preventing discharges of microplastic?
In my view, satellite-supported monitoring is important for being able to better estimate the size of the problem and potential consequences. What is basically decisive, however, is avoiding the uncontrolled emission of plastic waste. This begins with the separation of plastic fibres back in the washing machine at home, and then continues with the need to achieve a finer separation in the context of the fourth cleaning stage in wastewater treatment plants. It also requires tyre and paint recipes with environmentally compatible degradable end-products, more suitable products and materials in regions with a poorer waste-oriented infrastructure, and the adoption of suitable measures for large rivers – especially those with highly fluctuating volumes of water in densely populated regions.
For me, the major challenges lie in tackling the problem as regards the quantity and harmfulness of the emissions and – in cases where the prevention measures are not effective enough – in waste separation close to the emission source. Several funding projects from the German Federal Environmental Foundation have also been dedicated to tackling these challenges.
Once the litter has entered the sea – and then only really becomes visible on the surface even though it accumulates at an average depth of four kilometres at the bottom of the sea, where it has been less researched – we are left, according to my understanding, with no other possibility in the short and medium term but damage limitation. It is precisely here that satellite-supported monitoring can be seen as a helpful instrument for measuring the interactions.