Researcher Theresa Schell has defended her Doctoral Thesis entitled: "Microplastics in freshwater ecosystem: Source, Pathways and Risks", under the supervision of Dr. Andreu Rico, associated researcher at IMDEA Water Institute. This Doctoral Thesis is framed within the Doctoral Program in Hydrology and Water Resurce Management, doctor's degree granted by the University of Alcalá and the Rey Juan Carlos University.
This thesis evaluated the contamination by plastics and microplastics (MPs, plastics smaller than 5 mm) in the environment, and their transport and accumulation in the aquatic and terrestrial environment under Mediterranean conditios. In addition, the toxicity of two types of MPs on some freshwater invertebrates was studied and served to provide a broader view on the importance of MPS as vectos of chemical pollutants for aquatic organisms (Trojan horse" effect). A literature review showed that there is little information in the main sources of MP emission, and their environmental fluxes to and between terrestrial and freshwater ecosystems. In order to further research these anpects, an environmental monitoring study was carried out in the Henares River basin, wich pointed out wastewater (treated and untreated) as animportant input pathway of MPs into Mediterranean rivers. In addition, it was that environmental pollution patterns by MPs depend on land use and time of year. In another field study, it was observed that the application of sewage sludge significantly increases MPs concentrations in agricultural soils, while the influence of surface runoff from rainfall events is negligible in the export of MPs to aquatic ecosystems under the climatic and soil conditions studied.
Toxicity studies conducted in laboratory with freshwater invertebrates showed that the uptake and effects of polyester fibers and automobile tire particles depend on the shape and size of the particles, as well as the exposure route and feeding strategy of the organism studied. Although no adverse effects were observed on the survival or reproductive performance of the benthic macroinvertebrates studied, the reproduction and survival of individuals of the Daphnia magna Sp. (pelagic species) to both types of MPs could be affected in the long term when exposed to high concentrations (which are above currently measured levels). Also, it was shown that the presence of PMs does not favor the bioconcentration of hydrophobic organic chemicals ("Trojan horse" effect), and therefore, MP contamination is not expected to aggravate the risks associated with other organic pollutants present in the aquatic environment. Therefore, other exposure pathways (not related to the ingestion of MPs) are considered to be more relevant to the risk of these substances.
This Doctoral Thesis is part of the IMPASSE project: project PCIN-2017-016 funded by MCIN/AEI /10.13039/501100011033 and co-funded by the European Union.