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The environmental fate and effects of microplastics in freshwater ecosystems

Periodic Reporting for period 1 - FreshwaterMPs (The environmental fate and effects of microplastics in freshwater ecosystems)

Reporting period: 2015-04-01 to 2017-03-31

EU member states are currently working towards the realisation of environmental goals specified in the Water Framework Directive, which aims to protect both human and ecosystem health. Microplastics (MPs) are pollutants of emerging concern and are formed primarily when plastic waste degrades in the environment. The impacts of MPs on freshwater biota are not known, however, they may present a potentially persistent and ecotoxicological stressors.

Accordingly, the goal of this project is to assess the environmental degradation of plastics and the arising risk of MPs in freshwater habitats. To achieve this, a detailed investigation of MP environmental persistence will be carried out. This will provide environmental degradation characteristics for different polymers. This will be combined with laboratory studies to assess relevant sub-lethal endpoints such as reproduction, fitness, inflammation, and oxidative stress. As MPs are known to accumulate co-occurring organic pollutants, the toxicity of virgin MPs will be compared to MPs conditioned with relevant freshwater pollutants. This work will build towards a sophisticated state-of-the-art mesocosm study that will evaluate both MP fate and impacts in model ecosystems. An environmental risk assessment of MPs will inform our ability to achieve conservation objectives taking into account MPs as emerging pollutants.

The merit of this project is that protection goals may be better accommodated in policy and management through the generation of so far unavailable data on MP persistence and environmental toxicity. Taken together, the freshwaterMPs will generate so far unavailable data sets to assess for the first time the environmental impacts of freshwater MPs. Thus, the outcomes will highly relevant for academia, politics, stakeholders, and society.
We performed extensive degradation experiments in the laboratory to characterise the ageing of various polymers and the formations of MPs. This work for the first time demonstrated that the immediate step in polymer degradation involves surface erosion, which generates a considerable amount of nanoscale fragments that we coined nanoplastics. We also observed the formation of MPs, however to a lower extend. Based on these results, we performed degradation experiments in outdoor microcosms to cover a more realistic scenario.

To understand their biological impacts, we performed a range of long-term experiments with the key freshwater invertebrate Daphnia magna. In contrast to previous research, we focused on irregular MPs and population-level effects. Our results on three different polymers and one natural particle as reference demonstrate that the impacts of MPs on daphnid populations are subtle and occur at high concentration only. We further investigated the migration of toxic chemicals from virgin MPs and MPs conditioned with wastewater. Using various in vitro bioassays, we confirmed the leaching of estrogen-like chemicals from all investigated polymers.

In the third part of freshwaterMPs, we conducted a large-scale, long-term mesocosm study to investigate the fate and ecological impacts in semi-controlled model ecosystems. We spiked 1 500 L outdoor ponds with three different MP types (virgin and conditioned) and analysed their behaviour in the water column and sediment, their degradation and their effects on zooplankton and macroinvertebrate communities. We show that all MPs, even buoyant ones that, rapidly sink to the sediment and undergo surface degradation. Similar to our laboratory studies, the impact on biota was limited, if detectable at all.

Finally, data from the literature was then used alongside the project data to begin developing a framework for the environmental risk assessment of MPs. We identified two key issues hampering a risk assessment: First, critical data on the occurrence and toxicity of MPs in a freshwater context are still missing. The project contributed towards filling these gaps. Second, MPs are extremely heterogeneous in terms of their physicochemical properties and, thus, cannot be treated as one stressor. In theoretical exercises, we propose and performed two different risk assessment approaches based on chemical composition and particle properties. Results imply that the risk assessment is very sensitive to data gaps and to how the input parameters are defined. Accordingly, we propose strategies to move forward.
From a scientific perspective, the project has successfully contributed towards advancing our knowledge on the fate, degradation, ecotoxicity and ecological effects of freshwater MPs. This work resulted in the publication of six peer-reviewed papers and one book as well one more paper under review and four papers in preparation. The impact of these papers on the scientific community is highlighted by high citation rates and the results have been presented in four contributions to international conferences.

In terms of education and career development, three Bachelor and Master thesis were supervised and successfully awarded within the project. In addition, the project contributed to an international summer school in 2016 and 2017 with practical courses and seminars on the plastics issue for Master students from Goethe University’s global partner institutions.

The impact on European society is on the intermediate scale. Our project demonstrated for the first time than nanoscopic particles are generated from degrading plastics. This opens up a new area of research into the occurrence and impacts of nanoplastics, which are not considered in European policies so far. Further, we demonstrate that MPs rapidly sink to sediments under natural conditions although some polymers are considered buoyant. This highlights that freshwater sediments are the sinks of MPs in the short and the long term. Accordingly, European monitoring efforts need to cover sediments, which are so far neglected.

With regard to the biological and ecological effects of MPs, we demonstrate that these are subtle and only detectable at exposure levels unlikely to occur in aquatic ecosystems. Likewise, certain material properties (e.g. MP size, shape) and biological traits (e.g. filtration as feeding strategy) may be ecologically more relevant than others. Based on these insights, we are now in a much better position to formulate and advise on future research and risk management priorities.

In terms of an environmental risk assessment, we have provided the ground by summarising the current state of the science in our book on freshwater MPs. In addition, we have proposed two approaches for a risk assessment framework. These activities prepare the ground for further advancing risk assessment activities on a European level. For instance, the issue will be discussed with stakeholders from government agencies and industry on a special workshop to be held in autumn 2017.

Finally, the communication and dissemination efforts of freshwaterMPs resulted in an article in a public journal that is distributed Europe-wide. Furthermore, the project was presented to the public during two open day events at Goethe University’s Science Garden. With about >200 visitors each, this was considered successful. In addition, the wider implications of the project and plastics pollution in general were discussed with students from different local schools. We also performed a range of practical exercises to familiarise them with the actual laboratory work on microplastics.
Mesocosm ponds: Science Garden open day
Daphnia magna population study
Multisizer instrument used for particle counting in the lab at Frankurt
Students measuring environmental parameters in one of our mesocosm ponds
NanoSight instrument