Periodic Reporting for period 1 - TRAMPAS (Transport, retention, and release of synthesized DNAs through microplastics affected-soils: mimicking bacteria behavior with regards to climate change and global warming)
Reporting period: 2021-10-01 to 2023-09-30
Microplastics can adversely affect soils, but the underlying mechanisms and wider impacts are poorly understood. In TRAMPAS we brought together a wide range of approaches through multidisciplinary studies to explore two challenges of societal importance including microplastic soil pollution and pathogen fate in the environment. Our research primarily concentrated on assessing the influence of microplastics on soil wettability, stability, and structure, alongside their degradation. The TRAMPAS studies aimed to fulfil three key research and training objectives. (i) Measure and determine the hydraulic and hydro-physical properties of soils affected by microplastics under various environmental stresses. This involves understanding the alterations in the structure and stability of polluted soils. (ii) Investigate the transport, retention, and release of bacteria, utilizing tracers and a new generation of synthesized DNA, through microplastic-affected soils. Additionally, assess the fate of microplastic additives. (iii) Characterize the impacts of the plastisphere in agricultural systems to examine microplastics’ degradation in the soil. This helps in comprehending the physicochemical changes occurring in both microplastics and soil. For the first objective, we quantified the impacts using high-energy moisture characteristic curves (HEMC; water retention at matric suctions from 0 to 50 hPa). In the second research, we developed a Silica-DNA tracer to mimic bacteria transport and fate in microplastics-affected soils under extremely dry soil conditions using a comprehensive leaching study that was also extended to focus on the transport and fate of microplastics additives in soil as the third study. Finally, in the third objective was performed through the incubation of microplastics and soil to explore physicochemical changes of microplastics and soils after degradation using ATR-FTIR as well as X-ray photoelectron spectroscopy (XPS) where we proposed a new soil sampling strategy to measure soil plastisphere contact angle.
In the span of this comprehensive research endeavour, our focus on development planning involved establishing clear lab flowcharts through bi-weekly workgroup meetings to gain the main objectives of the TRAMPAS through the defined Workpackages. The achievements include the successful evaluation of microplastics impacts on soil hydraulic properties and aggregate stability, presenting these results at the 22nd World Congress of Soil Science as well as preparation of a manuscript entitled “Microplastics change soil stability and high-energy moisture” which is ready to submit to Environment International. Moving to the second phase, we developed a new generation of bio-tracers (synthesized DNA tracers) that are applied in tracking water contamination. Our leaching tests approved the accuracy and sensitivity of the tracer even to the type of microplastic present in soil, leading to preparation of another manuscript entitled “Impacts of microplastics on bacteria transport and fate as evaluated using silica-DNA microparticles and bromide” to submit in Colloids and Surfaces: Biointerfaces. The third phase involved investigation of microplastics degradation that we studied a pioneering perspective on soil wettability shedding new light on the intricate relationship between microplastics and soil biophysical and chemical properties. Notably, our research demonstrated microplastic exhibit the capacity to significantly influence the contact angle of the bulk soil and the surface elemental compositions of the plastisphere undergo changes contingent on the type of microplastic present in the soil. A manuscript entitled “Physicochemical changes of microplastics in soil” is in preparation and will be submitted to disseminate the findings to PNAS.We did perform an interview with Horizon magazine, highlighting the project’s multifaceted success and broad impacts.
In TRAMPAS we brought together a wide range of approaches through multidisciplinary studies to explore two challenges of societal importance including microplastic soil pollution and pathogen fate in the environment.
First Study. Microplastics, specifically polypropylene (PP) and polyethylene (PE), impact soil aggregate stability, with effects varying based on factors like chemistry, concentration, size, and degradation. Through experiments involving different concentrations, sizes, and incubations of microplastics in soil, we utilized high-energy moisture characteristic curves to assess soil wetting rates and stability. Results showed that higher microplastics concentrations increased drainable pores, especially with larger particles. Both PE and PP microplastics tended to increase modal matric suction, more pronounced in fast wetting. The incorporation of microplastics led to increased soil structural index and stability ratio, indicating significant impacts on soil structure and aggregate stability.
Second Study. Silica-DNA microparticles served as surrogates, along with bromide. Microplastics (PP and PE) were mixed with sand particles (0.5% w/w) and tested in packed columns. PE-treated columns exhibited faster breakthrough during the first pulse compared to PP and controls. Similar trends were observed for bromide concentrations. Microplastics type influenced the arrival of bromide during the second pulse. Microplastics-treated columns showed higher bromide mass recovery, with retention of silica-DNA microparticles being lower in contaminated soil. MiP size and chemistry affected retention, demonstrating accelerated bacteria tracer transport in microplastics-affected soils.
Third study. This study investigates the mobility of polyethylene (PE)-derived additives in soil under different heating and leaching conditions. Soil columns were exposed to varying temperatures (no heating, 60°C, 80°C) and leaching methods (continuous and interrupted). Breakthrough curves (BTCs) revealed that previous temperature exposure and leaching conditions affected the retention of additives and Br− transport in soil. Values for PE-derived additives were influenced by temperature and leaching conditions. Additives also altered surface tension and viscosity in water. Overall, the study’s findings have implications for understanding the impact of microplastics-derived additives on water infiltration, plant uptake, and the potential transport of contaminants like heavy metals.
Fourth study. This study investigated microplastics degradation in soil, examining changes in soil and plastisphere interfacial properties. Polypropylene and polyethylene microplastics were mixed with sandy loam at different proportions and incubated for six months. Assessments included contact angle (CA), surface tension, and surface elemental compositions using advanced techniques. Fluorescence microscopy and scanning electron microscopy visualized degradation. Results showed a significant increase in CA values for PE-treated soils over time, indicating enhanced degradation. Plastispheres in both PP and PE-treated soils had higher CA values than the control, suggesting the release of degraded microplastics. In-depth analyses revealed substantial transformations in soil and plastisphere chemistry and surface tension after 180 days. The findings highlight the potential of CA and surface elemental compositions as indicators for monitoring microplastics degradation in soils and plastisphere development.
First Study. Microplastics, specifically polypropylene (PP) and polyethylene (PE), impact soil aggregate stability, with effects varying based on factors like chemistry, concentration, size, and degradation. Through experiments involving different concentrations, sizes, and incubations of microplastics in soil, we utilized high-energy moisture characteristic curves to assess soil wetting rates and stability. Results showed that higher microplastics concentrations increased drainable pores, especially with larger particles. Both PE and PP microplastics tended to increase modal matric suction, more pronounced in fast wetting. The incorporation of microplastics led to increased soil structural index and stability ratio, indicating significant impacts on soil structure and aggregate stability.
Second Study. Silica-DNA microparticles served as surrogates, along with bromide. Microplastics (PP and PE) were mixed with sand particles (0.5% w/w) and tested in packed columns. PE-treated columns exhibited faster breakthrough during the first pulse compared to PP and controls. Similar trends were observed for bromide concentrations. Microplastics type influenced the arrival of bromide during the second pulse. Microplastics-treated columns showed higher bromide mass recovery, with retention of silica-DNA microparticles being lower in contaminated soil. MiP size and chemistry affected retention, demonstrating accelerated bacteria tracer transport in microplastics-affected soils.
Third study. This study investigates the mobility of polyethylene (PE)-derived additives in soil under different heating and leaching conditions. Soil columns were exposed to varying temperatures (no heating, 60°C, 80°C) and leaching methods (continuous and interrupted). Breakthrough curves (BTCs) revealed that previous temperature exposure and leaching conditions affected the retention of additives and Br− transport in soil. Values for PE-derived additives were influenced by temperature and leaching conditions. Additives also altered surface tension and viscosity in water. Overall, the study’s findings have implications for understanding the impact of microplastics-derived additives on water infiltration, plant uptake, and the potential transport of contaminants like heavy metals.
Fourth study. This study investigated microplastics degradation in soil, examining changes in soil and plastisphere interfacial properties. Polypropylene and polyethylene microplastics were mixed with sandy loam at different proportions and incubated for six months. Assessments included contact angle (CA), surface tension, and surface elemental compositions using advanced techniques. Fluorescence microscopy and scanning electron microscopy visualized degradation. Results showed a significant increase in CA values for PE-treated soils over time, indicating enhanced degradation. Plastispheres in both PP and PE-treated soils had higher CA values than the control, suggesting the release of degraded microplastics. In-depth analyses revealed substantial transformations in soil and plastisphere chemistry and surface tension after 180 days. The findings highlight the potential of CA and surface elemental compositions as indicators for monitoring microplastics degradation in soils and plastisphere development.