Understanding the effects of plastic pollution on the biogeochemical cycle of elements: introducing PLANET project

The interaction of plastics with (trace) elements has recently attracted research interest. Plastic particles, in fact, are contaminating water environments and can possibly act as sinks or vector of (trace) elements affecting their environmental fate and bioavailability.

The details of the mechanisms driving the interaction of plastic particles and (trace) elements are unclear. It has been argued that the degradation processes of polymers and the colonization by micro-organisms can enhance adsorption of (trace) elements. Moreover, the chemistry of water solution is a determinant of the interaction equilibria.

The PLANET project (understanding PLAstic pollutioN effects on the biogeochemical cycle of ElemenTs) aims at elucidating the mechanisms behind plastic - (trace) element interactions and at investigating the implications for the biogeochemical cycle of (trace) elements in water bodies. This aim will be reached through 4 main pillars, consisting in: i) experiments with artificially aged plastics and biofouling experiments, including the characterization of surface physicochemical properties in aged plastics, ii) sorption and desorption tests with ions and metals in batch experiments under varying physicochemical conditions to measure the energy of the interaction; iii) construction of predictive mathematical frames describing this interaction and its impication for (trace) elements’ cycling; iv) assessment of model predictions through microcosms experiments.

The project was launched in November 2021 and currently the first pillar is under development. Tested materials included both polyolefins (PE and PP) and biodegradable materials (PLA and PBAT). Controlled artificial ageing is achieved through UV radiation in water at varying salinity and pH and through inoculation of bacteria and algae consortia into specially designed microcosms. Plastic materials are analyzed through Fourier transform-Infrared spectroscopy to measure changes in surface functional groups, and through scanning electron microscopy to analyze surface morphology. Preliminary results show that biofouling processes take place rapidly under these experimental conditions on different types of polymer (with attachment of first algae in few days). Biofouling has a strong influence on functional groups changes on the polymers: the presence of polysaccharides from bacteria is observable in most of the biofouled plastics. These evidences highlight that a main role in adsorption-desoprtion processes in plastic particles is mediated by the colonizing microorganisms, which can cover an abundant portion of the plastic surface in waters.