Toward a risk-based assessment of microplastic pollution in marine ecosystems

We now know that there are plastics everywhere in the oceans. Plastics have been found in the intestinal system of virtually all marine organisms studied to date, but less is known of internal concentrations. Until recently, the focus has been on particles that can be identified using a microscope - down to 0.001 mm - mainly due to the methods available. There is however concern that smaller particles, i.e. below the sizes visible in a normal microscope - may have environmental impacts since they can be taken up into organisms. This project is part of the EU JPI-Oceans project RESPONSE, with objectives to clarify questions relating to how micro- and nanoparticles behave in marine ecosystems, whether they are taken up in pelagic or benthic organisms, how they may affect marine organisms and, finally, to establish a model to evaluate their potential risk in different marine habitats. RESPONSE had 14 partner institutions and was organised in different work packages (WP). UiO contributed to three WPs and led the WP on cellular mechanisms of toxicity. A wide range of organisms will be studied, including jellyfish, copepods, different bivalve species, polychaetes, shore crab, cod, whiting and goby. The most important contributions from UiO in RESPONSE has been the quantification of microplastics (down to 10 micrometer) i the Glomma estuary and in Skagerrak, particularly since we then were able to sample water from a larger depth than most other studies (down to 430 m), the evaluation of leaching of an organic contaminant from microplastics in stomach and intestine of cod and whiting, and finally, whether sediment-dwelling organisms would accumulate microplastics and the plastics would affect sediment biodiversity. To enable a plastic-free water sampling, an all-metal water sampler was designed by the workshop at UiO that could be connected directly to an all-metal filter unit borrowed from the University of Ålborg (commonly referred to as "UFO"). This equipment was deployed to collect and filter one cubic meter of seawater from the Glomma estuary and from 430 m depth near Torbjørnskjær in Skagerrak. Nearly all (97%) of the plastic retained in the samples were in the size range 10 to 300 mikrometer (only a few percent larger). There were microplastics in all samples and the concentration in the deep water was at a similar level as that found in the estuary (100-200 particles/square meter). The sample from 430 m depth contained predominantly polyester, polyethylene and polypropylene. A method was developed to quantify whether pyrene would leach from plastic particles under environmentally relevant conditions. Stomach and intestinal content from cod and whiting was incubated with polystyrene particles coated with the contaminant for 24 hrs, then pyrene analysed for after separation. The concentration of pyrene in all samples was below the detection limit for the method. Even though we expect that the majority of plastics in the oceans eventually will end up in sediments there is limited knowledge about the extent to which microplastics will be taken up in organisms. There is also limited knowledge of whether plastics in sediments will affect biodiversity. To clarify such questions we used sediment mesocosms. We added 1 and 6 micrometer fluorescent polystyrene particles to sediment as well as two concentrations of ground-up beach plastic (100-200 micrometer; 33 and 5 g/square meter, respectively). The mesocosms were maintained under semi-natural conditions for two months before termination. Macrofauna was sieved from sediment, comprehensively rinsed, then each individual counted for fluorescent particles. Wherever needed, the organisms were dissected to facilitate counting. Close to all organisms had taken up particles in the mesocosms with added flourescent particles, including meiofauna such as foraminifera. Crustaceans and some tubedwelling polychaetes had somewhat lower concentrations. The presence of ground beach plastic did not appear to affect accumulation. Bioinformatics analyses does not indicate that the biodiversity of bacteria or meiofauna differed between treatments. In sum, results from UiOs contribution to RESPONSE show that there are similar concentrations of microplastics in deep water of Skagerrak (430 m) as in estuarine waters. It is generally assumed that micro- and nanoplastics will end up on the seafloor. Particles with a size range around 1 micrometer appear to be taken up by just about all sediment-living species. The treatments described, with addition of up to 33 g/square meter ground beach plastic, did not appear to affect the diversity of bacteria or meiofauna.

RESPONSE have performed extensive Europe-wide field studies using state-of-the-art sampling and filtering equipment. The results are published or under publication and shows very variable concentrations of MPs in coastal marine and brackish waters. In addition, comprehensive effect and accumulation studies with both pelagic and benthic organisms and ecosystems were performed, the results of which were used to develop and test a weight-of-evidence model providing a holistic assessment of the environmental risk of microplastics in marine habitats. RESPONSE has had close contact with stakeholders during the project, both directly and through wider meetings organised by the project or JPI-Oceans. A specific activity in the project focused on the understanding of the environmental consequences of MPs by researchers and managers, reported through the RESPONSE website.

RESPONSE integrates expertise on oceanography, environmental chemistry, ecotoxicology, experimental ecology and modelling to answer key research questions on fate and biological effects of microplastics (MPs) and nanoplastics (NPs) in marine ecosystems. Hydrological transport dynamics will identify possible accumulation zones in European coastal ecosystems, while characterisation of vertical distribution of MPs and NPs in the water column and sediments will optimise practical monitoring and sampling efforts. Links between oceanographic conditions, environmental distribution of MPs and NPs, trophic transfer and impact to pelagic food webs and benthic communities will be addressed by analysing their abundance and typologies in representative marine species, as well as relevant ecosystem functions and services. Innovative mesocosm and laboratory studies will validate weighting factors and toxicological thresholds for MPs and NPs. The approach will assess the role of size, shape and other polymer characteristics in modulating biological effects of particles, both alone and in combination with other environmental stressors. A technological Smart Hub, combining complementary instrumental facilities and expertise of some partners and external companies, will support analytical needs of the consortium and further methodological developments. The overall aim of RESPONSE is to develop a quantitative Weight Of Evidence (WOE) model for MPs and NPs in the marine environment. The model will be designed to integrate and weigh data from different lines of evidence, including (1) the presence of MPs and NPs in water column and sediments, (2) their bioavailability and bioaccumulation in key indicator species from benthic and planktonic communities (3) sublethal effects measured via biomarkers, (3) the onset of chronic adverse effects at the organism level, and (4) ecological functioning. The results will provide support for development of MSFD monitoring strategies.