Physical and toxicological interactions between anthropogenic pollutants and engineered nanoparticles

Zusammenfassung

The increasing production and widespread use of nanomaterials result in their release into the aquatic environment, thereby constituting a threat to aquatic life. It is, therefore, necessary to evaluate the potential ecotoxicological effects of nanomaterials, considering their possible physical, chemical and biological interactions with aquatic organisms and other pollutants. The overall purpose of this Doctoral Thesis was to evaluate the individual and combined toxicity of representative nanomaterials and chemical pollutants on relevant freshwater organisms, with emphasis on their physical interactions and toxicity mixture effects. The response of aquatic organisms belonging to different trophic levels to different types of nanomaterials was evaluated. Metal oxide nanoparticles formed aggregates in the vicinity of cyanobacteria cells and attached nanoparticles caused damage to the cell membrane. Graphene oxide (GO) induced cell damage due to the formation of reactive oxygen species (ROS) on the unicellular green alga Chlamydomonas reinhardtii. Graphite-diamond nanoparticles and two hyperbranched polymers nanomaterials caused harmful effects to Daphnia magna due mainly to the overproduction of ROS accompanied by the activation of antioxidant defence mechanisms and the uptake into the gastrointestinal tract of D. magna. The pollutants tracked in real effluent from a wastewater treatment plant were polar pharmaceuticals, some of their metabolites and artificial sweeteners with concentrations ranging from tens of ng/L to several µg/L. The adsorption of pollutants from wastewater on different nanomaterials was 5-13 ¿g/g for metal-oxide nanoparticles and 90 ¿g/g for GO. Nano-oxides showed preferential affinity towards the less polar and less hydrophilic compounds such as gemfibrozil, while the adsorption capacity of GO was higher for the more hydrophilic compounds such as ranitidine and hydrochlorothiazide. The toxicological interactions of nanomaterial-pollutant binary mixtures were assessed using the Combination Index -isobologram, Concentration Addition, and Independent Action methods with the aim of elucidating and quantifying non-additive effects for different concentrations, toxicant ratios and affected fractions. Non-internalizing photosynthetic organisms showed important antagonism at low effect levels, which was explained by the reduced bioavailability of pollutants due to sequestration of toxic compounds and the reduction of nanomaterial availability due to the formation of nanoparticle aggregates. Nanomaterial-pollutant mixtures on D. magna resulted synergistic, as consequence of the increased bioavailability due to pollutants adsorption on nanoparticles. In this case nanomaterials served as carriers, facilitating the uptake and accumulation of toxic chemicals inside filter feeding organisms. This Thesis demonstrates that non-additive toxicological interactions between nanomaterials and chemical pollutants are the rule, rather than the exception, and should not be neglected for regulatory frameworks.