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Determining the Spatial and Temporal Distribution of Macro- and Micro-plastics in Soil and Their Impact on Soil Function

Project Description

Current global production of plastics has reached over 300 million metric tons and is predicted to reach 1200 million metric tons by 2050. Plastics are used widely as they are durable and stable, but these properties have caused an environmental crisis. Plastic islands (the largest is three times the size of France) have developed in oceans due to prevailing currents. Plastics have been found in the deepest ocean trench and in pristine Arctic environments. Marine wildlife has suffered due to accidental ingestion of, or entanglement in, plastic debris. Larger plastic items degrade to form microplastics (particles <5 mm), which accumulate in the food chain (they have been documented in fish, salt, sugar and beer), and so has implications for public health; recently microplastics were found in the human gut. Relatively little attention has been paid to plastic pollution in soil despite it being 4-23 times higher in soil compared to within marine waters. Inputs of plastics to soil can come from organic wastes used as fertilisers; alarmingly, composts were shown to contain up to 1200 mg/kg plastics, whilst sewage sludge contain up to 24,000 plastic items per kg. Breakdown products from plastics can be toxic for plants and animals, e.g. phthalates and bisphenol A that leach from plastics disrupt hormone systems of vertebrates. Moreover, plastics adhere to emerging contaminants including PAH, PCB, pharmaceuticals and personal care products. Soils supply ecosystem services including plant growth, biogeochemical cycling, clean water, clean air and cultural provision; without their effective functioning much of life on earth will suffer. The combination of plastics, their breakdown products and emerging contaminants is likely to impair soil function and have detrimental effects on ecosystem services that we rely on.

It is extremely timely and important to understand the extent of macro- and microplastic (MP) pollution in Scotland, their mobility (and that of their breakdown products and adsorbed emerging contaminants) and their impact on soil function.

The Hutton curates the National Soils Inventory for Scotland, which is a unique resource for exploring the extent of MP pollution on a national scale. This will allow visualisation of any hot-spots of MPs in Scotland and to correlate abundance with associated background data including land use, soil type, environmental parameters and biological factors (bacterial, fungal and nematode community compositions). In addition, we hold soil samples collected from 2013-2018 from long term sewage sludge treated soils. Together, these soil archives will allow us to elucidate MP prevalence over time and space. This project will use a novel fluorescence-based assay being developed in-house to quantify MPs, thereby validating the technology and improving efficiency, enabling more widespread use. Soil microcosms spiked with MPs in the presence and absence of other pollutants will be used to investigate mobility and leaching through a soil column (important for quantifying contamination of ground and surface water) and their impact on biological processes that affect ecosystem services. Understanding plastic pollution in soils will inform future mitigation and remediation strategies for the protection of one of Scotland’s most valuable natural assets.

Aim: To determine the extent of macro- and microplastics (MP) in soils and evaluate the impact of MPs on soil function and ecosystem services. We will address the following research questions:
1. What is the spatial distribution and abundance of MPs in Scottish soils covering a wide range of soil types and locations; are there ‘hot-spots’ of MPs and is this influenced by land use, soil physico-chemical properties, environmental and biological factors?
2. What is the behaviour and fate of MPs and their breakdown products in soil; is mobilisation dependent on plastic type and soil properties?
3. What impact do MPs, their breakdown products and MPs carrying emerging contaminants have on soil function and ecosystem services?

1. Measure MPs in soils archived in the National Soils Inventory for Scotland to determine the prevalence of MPs on a national spatial scale using two methods for quantifying MPs (visual inspection and a novel fluorescence-based assay ).
2. Measure MPs in soil archives (2013-2018) collected from sewage sludge treated land to investigate their fate over time.
3. Investigate factors that influence MP distribution (land use, soil type, environmental and biological factors) using multivariate statistics, and map MP distribution and/or likelihood of occurrence.
4. Track the behaviour and fate of different MPs (+/- emerging contaminants) and their breakdown products through the soil column over time and measure soil function using soil microcosms and measuring microbial respiration (MicroResp), biomass (plant/microbial/algal growth) and metabolic pathways (functional genes analysis).

Funding Notes

The studentship is fully funded by the Macaulay Development Trust and will be registered at the Robert Gordon University in Aberdeen. Applicants should have a first-class honours degree in a relevant subject or a 2.1 honours degree plus Masters (or equivalent).Funding is available for European applications, but Worldwide applicants who possess suitable self-funding are also invited to apply.

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