Understanding environmental impact through the study of sediments

The risk posed to humans, fauna and flora by anthropogenic contaminants in the environment is of growing concern. The impact of pollution on rivers and other waterways is an important area for research, especially in urban settings where the pollution picture often reflects local land use and management policies.

The introduction of waste water from residential areas, hospitals, waste treatment plants, agriculture and/or industrial facilities, alongside less direct pollutants such as those from vehicle use, can create challenging and complex problems. These extend to the soils and sediments of watercourses, which may absorb or bury pollutants and act as contaminant reservoirs. Soils and sediments may become local sources of pollution if later eroded or otherwise disturbed.

Traditionally, technologies such as gas chromatography mass spectrometry (GC/MS) and liquid chromatography mass spectrometry (LC/MS) have been used to detect and quantify contaminants in environmental samples. However, these approaches are limited because they usually only provide information on tens to hundreds of sample components. The mixture of compounds relating to natural organic matter in sediments along with the diverse range of anthropogenic, or human-made, contaminants, can together constitute tens of thousands of molecular components. This means that routine analytical methods can’t unveil the full pollution story locked within environmental samples.

The project

This PhD project, piloted by Rory Downham and project supervisors Dr Mark Barrow of the University of Warwick and BGS’s Christopher Vane, sets out to investigate the range of organic molecules present in urban waterway sediments from different locations around the world, including an urban canal in Hanoi (Vietnam), the Nairobi River (Kenya) and the River Thames (UK). These represent very different samples:

• the Hanoi sediments are from an engineered watercourse under industrial influences
• the Nairobi River sediments are from areas affected by riverside slum dwellings
• the Thames samples were retrieved from a tidal mud island, which represents an archive extending back to medieval times 

Analysis

The sediments were processed and extracted in organic solvent by Chris Vane at BGS Keyworth in July 2020 and subsequently transferred to the University of Warwick. Following a COVID-19 shutdown period, the Millburn House ICR Laboratory at Warwick re-opened and sample analyses began in September 2020.

The non-targeted analytical approach brings state-of-the-art, ultrahigh-resolution mass spectrometry — namely Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) — to the challenge of detecting as many organic sample components in the sediment extracts as possible.

To date, 12 Nairobi, 22 Hanoi, and 18 Thames FTICR MS datasets have been acquired and subjected to data processing. Following molecular classifications and deployment of modern data visualisation tools, they show interesting trends for complex mixtures such as crude oil and natural organic matter. For example, some sediment datasets feature a signature pattern that indicates sulphur-containing thiophenic pollutants, which are highly likely to have a fossil fuel origin. Other datasets reveal sterol biomarker patterns, which highlight the influence of sewage in some of these waterways.

These project datasets have raised additional points of interest, leading to smaller, spin-off investigations to allow for more complete interpretations of the sediments.

Future work

This project is progressing towards analysing sediment samples from the Celtic Sea, from about a hundred meters below sea level. The University of Warwick will extract organic matter from these samples, followed by mass-spectrometric exploration. Using tools for complex mixture analysis and data interpretation, we expect this research to provide insights into organic matter burial processes and carbon storage beneath the waves.

About the author

Rory Downham

I completed my undergraduate degree in chemistry and physical geography at Keele University in 2004 and later joined the Home Office Centre for Applied Science and Technology in support of UK policing. A growing interest in academia and environmental science challenges, and a desire to delve deeper into analytical chemistry, set me on my present PhD journey.