Periodic Reporting for period 1 - PLANET (understanding PLAstic pollutioN effects on the biogeochemical cycle of ElemenTs)
Berichtszeitraum: 2021-11-01 bis 2023-10-31
Plastic and microplastics (fragments with dimension below 5 mm) are ubiquitous in the environment: 9 to 23 million metric tons of plastics reach the oceans every year. Freshwater environments are observed to be major recipients of plastic pollution. However, some repercussions of plastic pollution on the environment are still yet to be understood. An overlooked implication of plastic pollution is the potential interaction with nutrients and (trace) elements in water. Several experimental setups highlighted the potential of plastic to adsorb metals in laboratory conditions, and the process of plastic alterations in the environment, the so-called aging processes seems to play a pivotal role.
Freshwater environments hold fundamental ecosystem functions for the biogeochemical cycling of elements. If plastic may affect this process, the environmental implications may be worrying.
PLANET project aims at understanding the effects of plastic aging and biofouling in defining its interaction with (trace) elements. This aim will be reached through 4 specific objectives:
1 - Selection and characterization of reference materials and their alteration/ageing, focusing on freshwaters and sediments;
2 - Analysis of adsorption and desorption of different elements;
3 - Modelling the interaction between plastic polymers and elements to quantitatively predict this interaction and projecting implications across ecosystem relevant scales;
4 - Experimental assessment of the relevance of the ions/metals - plastic interaction in microcosms.
Freshwater environments hold fundamental ecosystem functions for the biogeochemical cycling of elements. If plastic may affect this process, the environmental implications may be worrying.
PLANET project aims at understanding the effects of plastic aging and biofouling in defining its interaction with (trace) elements. This aim will be reached through 4 specific objectives:
1 - Selection and characterization of reference materials and their alteration/ageing, focusing on freshwaters and sediments;
2 - Analysis of adsorption and desorption of different elements;
3 - Modelling the interaction between plastic polymers and elements to quantitatively predict this interaction and projecting implications across ecosystem relevant scales;
4 - Experimental assessment of the relevance of the ions/metals - plastic interaction in microcosms.
The work planned for PLANET project aimed at reaching the 4 specific objectives of the project.
To reach the first objective, three plastic polymers were selected (including polyethylene – PE, polypropylene – PP and polylactic acid – PLA) and experiments including the exposure to ultraviolet light (to simulate light exposure) and the incubation with an algal community (to simulate the biofouling process) were performed to create simulated aged plastic.
All these materials were characterized for their chemical properties and these plastics were used to perform adsorption experiments, using two metals (aluminium and copper in solution) to evaluate the factors responsible for their adsorption.
Finally, after the statistical evaluation to assess the factors responsible for the adsorption of elements, a scaling exercise at a more relevant, lab-based scale was performed. This was made through the preparation of a simplified mesocosm at known chemical composition of water and with the presence of a synthetic algal community, created by the inoculation of 5 freshwater species. In these experiments, the control community was disturbed with a known amount of plastic (only PP was selected) with and without biofilm on its surface. The presence of a biofilm community, in fact, was observed to be the key factor in determining the adsorption of elements. This experiment helped in ranking the environmental relevance of plastic biofouling for the biogeochemical partitioning of several nutrients and minor elements in water.
To reach the first objective, three plastic polymers were selected (including polyethylene – PE, polypropylene – PP and polylactic acid – PLA) and experiments including the exposure to ultraviolet light (to simulate light exposure) and the incubation with an algal community (to simulate the biofouling process) were performed to create simulated aged plastic.
All these materials were characterized for their chemical properties and these plastics were used to perform adsorption experiments, using two metals (aluminium and copper in solution) to evaluate the factors responsible for their adsorption.
Finally, after the statistical evaluation to assess the factors responsible for the adsorption of elements, a scaling exercise at a more relevant, lab-based scale was performed. This was made through the preparation of a simplified mesocosm at known chemical composition of water and with the presence of a synthetic algal community, created by the inoculation of 5 freshwater species. In these experiments, the control community was disturbed with a known amount of plastic (only PP was selected) with and without biofilm on its surface. The presence of a biofilm community, in fact, was observed to be the key factor in determining the adsorption of elements. This experiment helped in ranking the environmental relevance of plastic biofouling for the biogeochemical partitioning of several nutrients and minor elements in water.
Results achieved indicated a key role played by plastic biotic ageing concerning the adsorption of (trace) elements. The formation of biofilm on plastic completely changes its properties, regardless of the polymer type and the addition of other aging processes. The results permitted to statistically test the conceptual model of plastic biofilm regulating the surface properties and adsorption rates of trace elements, which was numerically assessed using the adsorption of aluminium and copper. These results are the first to statistically test the importance of biofouling in comparison to other factors in defining the interaction of plastic with dissolved elements in water.
The results also highlighted an important role of plastic as a carrier of specific microbiota. In the experiments performed, in fact, the different properties of different plastic polymers show a marked enrichment of different species in the biofilm community.
The potential implications of this processes may go far beyond the purely governing of adsorption-desorption processes. Preliminary, lab-scale, experiments highlighted in fact that:
1) Plastic selects a specific algal community, which can move again back in the water phase;
2) This specific community can compete with a natural freshwater community for nutrients, leading to changes in water chemistry and in the final assembling of the community.
These results unveiled a new, poorly investigated role of plastic in water ecosystems, which may open a new research branch in the evaluation of environmental impacts induced by plastic pollution.
The results also highlighted an important role of plastic as a carrier of specific microbiota. In the experiments performed, in fact, the different properties of different plastic polymers show a marked enrichment of different species in the biofilm community.
The potential implications of this processes may go far beyond the purely governing of adsorption-desorption processes. Preliminary, lab-scale, experiments highlighted in fact that:
1) Plastic selects a specific algal community, which can move again back in the water phase;
2) This specific community can compete with a natural freshwater community for nutrients, leading to changes in water chemistry and in the final assembling of the community.
These results unveiled a new, poorly investigated role of plastic in water ecosystems, which may open a new research branch in the evaluation of environmental impacts induced by plastic pollution.