Microplastics can transport metal pollutants

There are comparatively many studies on the accumulation and transport of persistent organic pollutants by microplastics. However, data on the accumulation of metals toxic to the environment are very scarce and sometimes scientifically unreliable. A team of scientists from the Helmholtz Centre Geesthacht - Centre for Materials and Coastal Research (HZG), together with colleagues from the Federal Institute of Hydrology and the Christian-Albrechts-University of Kiel (CAU), has now developed a method with which corresponding metals can be reliably detected in microplastics.

Microplastics in the environment is a global problem from two perspectives: firstly, because laboratory tests have shown that the plastic particles can be toxic, and secondly, because the particles can act as a vehicle for transporting pollutants in the environment. The latter is due to the chemical and physical properties of microplastics: some pollutants found in rivers or seawater, for example, can accumulate in the plastic itself; others are already contained in the particles as a result of their production, so that they can carry a whole cocktail of the most diverse substances. The scientists refer to this as the "Trojan horse effect". Up to now there have been hardly any reliable scientific studies on which and how many environmentally toxicologically relevant metals accumulate in plastics. Researchers from the Helmholtz Centre Geesthacht (HZG), the Federal Institute of Hydrology and the Christian-Albrechts-University of Kiel (CAU) have now presented a validated microwave-assisted process in the journal PLOS ONE, with which the most important types of plastics can be examined with regard to the metals they contain.

50 different metals measured in microplastic particles

"The basis for a reliable scientific assessment of the transport of metal pollutants by microplastics are validated laboratory procedures," explains Lars Hildebrandt, first author of the study and doctoral student in the HZG Department of Marine Bioanalytical Chemistry. "With the new method, it is now possible to quantify more than 50 different metals in microplastic particles".

The team led by Lars Hildebrandt used certified plastic reference materials in the microplastic size range of up to five millimetres for the measurements. The researchers know exactly which metals are contained in these materials due to production processes and should therefore be included in the results. The scientists have treated the materials with different combinations of strong acids and heated them with microwave radiation until the respective material has completely dissolved. In this way, they were able to determine a suitable acid mixture with which to reliably dissolve all the materials under investigation. The samples were then examined with a mass spectrometer. This allows to determine which elements are contained in the sample and in what quantities.

Metals from plastic production and the environment detectable

The new method can be used to detect in the microplastic particles both the metals used in plastic production and those that can be bound to the particles from the environment, for example from seawater. For example, the metalloid antimony is often used as a catalyst for the production of PET and is therefore found in the plastic itself. Heavy metals such as cadmium and lead, which are toxic to many organisms, can also be contained by the production process, but can also be bound to the surface of the particles from the environment.

The approach presented in the study was recently used to track metal-labelled nanoplastic particles in a test system.

In a next step, the scientists now plan to apply targeted microplastic samples in the Elbe estuary and at specific points in the river. Containers are to be placed on a rack, which can be imagined in a simplified way as special tea eggs. The sample material is then placed in these containers. "We are interested in which metals from the water bind to the surface of the plastic, scientists refer to this as 'sorption'. We will then take samples at regular intervals in order to measure the concentrations in the plastic with our new method and thus investigate the accumulation over time," Hildebrandt, a chemist, explains as an outlook.

Source: Chemie.de – Mikroplastik transportiert metallische Schadstoffe

Original article: PLOS ONE - A metrologically traceable protocol for the quantification of trace metals in different types of microplastic