Detective Work: Coastal Researchers on the Hunt for Microplastics

Plastic waste is a serious problem for our oceans. There are already more than 5.25 trillion plastic particles swimming in the world’s oceans. According to estimates, approximately fourteen per cent of the plastic floating in the water’s upper layers consists of microplastic particles. Using new measurement instruments and improved analytics, Hereon coastal researchers are working on a standardisable method for measuring these microplastics. The new methodology aims to determine precisely and far more quickly and effectively how many small particles and which types of plastic are present. After all, not enough is known yet about the dangers of fine particulate plastic waste to the environment and humans.

Photo: Hereon/ Lars Hildebrandt

Microplastic particles are no larger than a half centimetre and can be as small as a micrometre, fifty to eighty times smaller than the diameter of a human hair. They are created in part from the disintegration of larger plastic pieces in the sea or wind up via the wastewater in the rivers and subsequently in the oceans. Scientists have detected the alarmingly ecological ubiquity and longevity of plastic particles worldwide. The results of many studies, however, are only comparable to a limited extent so that the current overall situation can hardly be estimated reliably.

“Hopefully new analytical guidelines and legal measures will be provided in the future, at the European level, to determine the proportion of microplastics in the global oceans and to estimate how hazardous the substances are,” explains Hereon doctoral candidate Lars Hildebrandt. “More precise, time-efficient and robust analytical methods as well as technology for measuring the microplastics are desperately needed to generate more comparable data since currently too many different methods are used.” Natural particles, such as grains of sand, are often visually identified as plastic particles. Erroneous results also arise from unsuitable methods for sampling and sample processing in the laboratory, which presents another huge problem.

To measure the occurring plastic in the environment in a reliable, valid and time-saving manner, Hildebrandt together with his colleagues in the Marine Bioanalytical Chemistry department are developing automatable methods for sampling and particle measurement. The first step was to develop a device for obtaining the particles from the sea.

The researchers are using the “Geesthacht Inert Microplastic Fractionator” (GIMPF) for the first time, carrying out sampling on board the SONNE research vessel in the Indian Ocean and on the LUDWIG PRANDTL in the Elbe estuary. The devices use two stainless steel cartridge filters to separate particles of two size classes from the seawater. Particles larger than 300 micrometres and between 10 to 300 micrometres can thus be enriched from large volumes of water. After the sampling the particles are subsequently analysed in the laboratory.

Microplastics are so ubiquitous, that containers, devices and even gloves, dust in the air and clothing can act as particle sources. “To ensure that only the microplastics from the sample are measured, the microplastic analysts prepared the laboratories and instruments accordingly. They also, for example, created the GIMPF entirely out of stainless steel and aluminium,” explains master’s student Fadi El Gareb, who carried out sampling on board the SONNE in 2019 with Prof Kay-Christian Emeis, coastal research institute director. To minimise contamination, all work was done in small, mobile clean benches, equipped with special filters so that the incoming air was continuously filtered of particles. Glass containers were rinsed beforehand with filtered alcohol, seals were coated with Teflon and the filters and all other equipment were thoroughly rinsed after each sampling.

The work continues on land: here the particles are studied using optical methods, but beforehand the unwanted natural organic and inorganic components must be removed from the sample using an enzymatic-chemical treatment as well as a physical separation method.

For the subsequent detective work, the scientists used another new technique: they further developed a spectroscopic method with which the varying types of plastics can be more securely and quickly identified. Hildebrandt says, “We studied the samples using a new quantum cascade laser. The laser lights up the samples with infrared light and analyses the light absorption through the particles. The different particles reflect with different intensities at varying wavelengths depending on their chemical composition. This is how we determine a type of molecular fingerprint for individual particles.“ What is new about this method is that, on the one hand, the very fast infrared source takes one second to produce a spectrum, whereas with standard instruments it takes more than thirty seconds. On the other, the spectral assessment is carried out in an automated process so that the researchers no longer need to compare the spectra manually with a substance database as they did before.

“The new method is much quicker and more powerful than traditional infrared spectroscopy and can therefore analyse a far greater number of particle samples in the same amount of time,” explains Hildebrandt. The fully automated analysis of eight hundred particles and comparison of the produced spectra with the database takes approximately one hour. In comparison, the standard assessment methods used so far can take days and the error rate is higher, as the subjective spectra classification depends on the respective scientist.

The Hereon scientists still need a bit of time for analysis until their final results are available. In December, an additional large research campaign has been carried out with the GIMPF in the Atlantic Ocean.

After all, it is still unclear what damage microplastics can do to the environment and to human beings. The question as to the amount of microplastics in the environment also cannot be answered. Data and standardised evaluation criteria are missing on how much microplastic the environment can tolerate or what possible biological effects develop. The new methods utilised by the Geesthacht microplastic detectives could help to provide answers.