Microplastics (plastics < 5mm) and pharmaceuticals are both classed as emerging contaminants of environmental concern. These contaminants are increasingly detected in our natural environment, for example in rivers, lakes, soils, and sediments. Microplastics and pharmaceuticals are routinely discharged into our aquatic systems via the release of effluent following wastewater treatment whilst the use of organic soil amendments, such as sludge application, can inadvertently introduce these contaminants to our soils systems. Microplastics and pharmaceuticals are omnipresent in our environment and their presence has been shown to elicit effects in non-target organisms.
Research has so far identified that pharmaceutical exposure in aquatic systems can result in both lethal and sub-lethal effects in non-target organisms, including effects on reproduction and behaviour (Brodin et al., 2014). Pharmaceuticals are also known to cause toxic effects in soil organisms such as acute toxicity in earthworms and affect the soil microbial community (Pino et al., 2015). Similarly, recent research has also identified that microplastics present in the environment can result in toxic effects in aquatic organisms, such as fish and daphnia. Microplastic contamination has been shown to disturb vital relationships between soil and water, as well as having consequences for soil structure and microbial function (de Souza Machado et al., 2018) with recent research also demonstrating negative affects of microplastics on crop growth and development.
However to date, these studies have largely focussed on the exposure of non-target organisms to contaminants within the same class (i.e. pharmaceuticals or microplastics) and research has so far neglected to account for the fact these contaminants are typically present in the environment together. The presence of multiple contaminants in the environment poses a very different risk to individual contaminant exposure. Pharmaceuticals, for example, may become bound to the microplastics thereby making them less bioavailable for uptake. Studies will evaluate whether pharmaceuticals in combination with microplastics will result in effects that are the same as the sum of the individual effects (additivity) or produce a combined effect greater than the sum individual effects (synergism) using non-target invertebrates such as earthworms, daphnia and gammarus.
It is also important that we establish how the fate of these contaminants is affected when present in the form of multiple contaminant mixtures. The persistence of pharmaceuticals in the environment can vary greatly from a few days to years. Comparatively microplastic fibres are known to be very persistent in the environment, with detections reported in agricultural fields up to 15 years after sludge was incorporated into the soil (Zubris and Richards, 2005). Studies will therefore seek to determine if the persistence of these contaminants can be affected by the presence of another contaminant using controlled laboratory studies and field experiments.
Fig 1. Controlled laboratory experiments to understand the fate of pharmaceuticals in soil columns
Ultimately, the fate of these contaminants in the form of a mixture and subsequent effects on non-target organisms is something which we know very little about. A significant knowledge gap remains surrounding the interplay of these contaminants and whether the presence of these contaminants in combination can exacerbate or reduce the effects previously identified in a single exposure. This raises a number of concerns pertaining to current environmental risk assessment and urgently warrants further investigation given the increasing use of wastewater by-products and routine detection of these contaminants in the environment. Given the lack of current data on this topic there is a wide scope to carry out cutting-edge scientific research as part of this PhD.
Aim and objectives
The overall aim of this project is to better understand the fate and effects of mixtures of microplastics and pharmaceuticals in a suite of aquatic and terrestrial systems. This will be achieved using a combination of an experimental approach in the laboratory and field trials utilising facilities available at the University of Leeds farm. The specific objectives are to:
• Undertake controlled experiments to understand how the presence of both pharmaceuticals and microplastics affects the fate of these contaminants (i.e. persistence and degradation) using field and laboratory experiments
• Investigate the toxicity of combinations of microplastics and pharmaceuticals in controlled laboratory studies
Fit to NERC Science
This project is aligned to both the NERC ‘Pollution waste and resources’ research area and the ‘Terrestrial and freshwater environments’ research area. Specifically the project aligns to the following NERC research area: (1) Pollution – by considering interaction and effects of substances which are present at concentrations above those normally expected in a clean environment and understanding the long-term availability and fate of pollutants and waste materials.
The student will work under the supervision of Dr Laura Carter and Dr Paul Kay within the River Basin Processes and Management research cluster in the School of Geography, University of Leeds. The successful candidate will develop a range of research skills, including experimental design, field sampling, chemical analysis, statistical analysis and data interpretation, academic writing skills and giving presentations. The successful candidate will benefit from inter-disciplinary training in analytical techniques and chemical fate and effects, as well as wider water management skills. Training will be provided in field/laboratory health and safety procedures and the use of field and analytical equipment. In addition the candidate will develop their understanding of (i) environmental pollution, in particular the impact of microplastics and pharmaceuticals, (ii) toxicity characterisation and multiple end-point measurements, and (iii) soil and aquatic organism growth and development.
Supervision will involve regular meetings between all supervisors. Students present results and receive constructive wider feedback from peers in a Research Support Group and at the University postgraduate research days. The successful applicant will, under guidance of the supervisory team, contribute to all aspects of the research including designing the experiments, laboratory analysis and data collection. The student will be encouraged to write and submit papers for publication during the project and to attend national and international conferences to present results and gain feedback from the wider academic community.
The student should have a keen interest in environmental pollution with a strong background in a physical geography, earth sciences, soil chemistry, environmental sciences or related discipline. Strong analytical/statistical/fieldwork skills are desirable but not essential, as full training will be provided during the PhD.
Brodin, T., Piovano, S., Fick, J., Klaminder, J., Heynen, M., Jonsson, M. 2014. Ecological effects of pharmaceuticals in aquatic systems – impacts through behavioural alterations. Phil. Trans. B. http://doi. Org/10.1098/rstb.2013.0580
Pino.R. Val, J., Mainar, A. M.., Zuriaga, E. 2015 Acute toxicological effects on the earthworm Eisenia fetida of 18 common pharmaceuticals in artificial soil. Sci. Tot. Environ. DOI: 10.1016/j.scitotenv.2015.02.080
Foley, C. J., Feiner, Z. S., Malnich, T. D., Hook, T. O. 2018 A meta-analysis of the effects of exposure to microplastics on fish and aquatic invertebrates. Sci. Total Environ. 631-632, pages 550-559. DOI:10.1016/jscitotenv.2018.03.046
de Souza Machado, A.A., Lau, C.W., Till, J., Kloas, W., Lehmann, A., Becker, R., Rillig, M.C., 2018. Impacts of Microplastics on the Soil Biophysical Environment. Environ. Sci. Technol. 52, 9656–9665. https://doi.org/10.1021/acs.est.8b02212
Zubris, K.A. V., Richards, B.K., 2005. Synthetic fibers as an indicator of land application of sludge. Environ. Pollut. 138, 201–211. https://doi.org/10.1016/j.envpol.2005.04.013