ENVIRONMENTAL LABORATORY 31


Focusing on rapidly increasing chemicals in rivers of the United Kingdom


Dr. Leon Barron has an interest in how chemicals are being used, what happens to them after use, and whether they would pose a risk to our environment. Looking mainly at pharmaceuticals, pesticides, illicit drug, and personal care products, the scope of his team is steadily increasing to include more types of chemical classes including mobile chemicals which also display persistence and toxicity.


Tarun: As the leader of the Emerging Chemical Contaminants (ECC) team within the Environmental Research Group at Imperial College London, which areas of emerging contaminant research do you focus on specifically, and why?


Dr. Leon Barron: ‘Emerging’ chemical compounds have been monitored over the past 20 years and in many cases have been ubiquitously detected in the environment. Advances in knowledge have been largely underpinned by more widespread availability of better analytical technologies, such as high-resolution accurate mass spectrometry. However, often very little is known about their risks. One major focus of ours is whether such contaminants impact low-trophic level aquatic invertebrate behaviour. We are also involved in wastewater-based epidemiology which has been shown to be an excellent way to understand not just lifestyle and activity in a community,5


wastewater monitoring programmes for SARS-CoV-2,6,7 potentially imminent threats to public safety.8


but also health, as evidenced by national and also


Tarun: Could you tell us more about the objectives of the ECC team at Imperial College London with regards to environmental research, and why your work is important for environmental, aquatic animal and human health?


Dr. Leon Barron: The aim of the ECC team is to understand, manage and mitigate chemical contamination in the environment, with a focus on compounds that we know very little about regarding their sources, distribution, fate and effects. Our work sits in several cross-cutting areas including:


a. Analytical methods: We develop new approaches for trace chemical monitoring, usually involving advanced separation science, mass spectrometry and chemometrics for large numbers of compounds (typically >200 for quantitative work, as well as high resolution untargeted analysis and suspect screening for >1000 compounds).


b. Wastewater-based epidemiology (WBE): We identify and monitor exposure, manufacture and/or consumption of chemicals at population scales in near real-time at wastewater treatment plants (WWTPs).


c. Environmental toxicology and risk assessment: The focus here is on occurrence, fate, toxicity and risks of emerging and new chemical contaminants in surface water, soil, sediment and predominantly low trophic-level aquatic and terrestrial invertebrates. This also includes application of ‘omics-based’ approaches such as lipidomics and metabolomics to help understand molecular-level initiating events and effects in these species.


Across these objectives, we are currently pursuing several funded research projects, often in close collaboration with industry, which really strengthens the value and impact of our work including translating it into practice. We are very keen to understand and prioritise wildlife health in our work, not just in terms of monitoring, but also predictively by developing new approaches


to understand and predict which compounds may be an issue now or in the future, as well as management options to potentially minimise exposure.


Tarun: Could you share more about your group’s recent research in screening ‘emerging’ contaminants along the estuarine River Colne in Essex, UK?


Dr. Leon Barron: This work9 followed on from a previous invertebrate monitoring campaign in rural Suffolk, UK, in the summer of 2018, where we detected large numbers of emerging contaminants in a benthic amphipod, Gammarus pulex.10


We wanted to see what the contrast was when


moving to an urban area and to extend this to more species and also to more sample types. We took several samples of river water, sediment and four different invertebrate species including G. pulex, Peringia ulvae (a mollusc), Hediste diversicolor (a polychaete) and Crangon crangon (an amphipod). These invertebrates often play critical roles in river health, by cleaning detritus and acting as a food source for predators. Therefore, any significant disruption to their behaviour or health could potentially be quite an issue.


Following analysis, 33 compounds were detected in the macroinvertebrates sampled, 39 compounds detected in sediment and 59 compounds detected in surface water samples. The most impacted site was next to a wastewater treatment plant discharge point. Over half of the drugs detected in invertebrates were psychoactive substances including pharmaceuticals and illicit drugs. For the latter, cocaine and its metabolite benzoylecgonine were the most frequently detected and highest average concentration compounds which was the same in samples from Suffolk.


Previous work in our laboratory showed that, despite this, the risk posed by cocaine and benzoylecgonine is likely low in comparison to other psychoactive compounds. In addition to drugs, the banned neonicotinoid pesticide imidacloprid was also found in G. pulex and P. ulvae at 8 ± 3 ng/g and 24 ± 8 ng/g, respectively. Given that no usage was reported around this time, the conclusion was that occurrence was possibly based either on persistence of these compounds in soils which may leach into surface water or veterinary pesticide use, such as flea/tick medication. Interestingly, higher concentrations of emerging contaminants were found in infaunal species than epibenthic organisms showing that the main route of exposure for these organisms was likely through the higher measured concentrations in sediment.


Tarun: How do you think further research in this area could be enhanced?


Dr. Leon Barron: The important thing for us now is to broaden the chemical coverage to include more types of compound, to try to characterise more of the exposome. Aside from ‘omics’ approaches to understand internal biological processes in invertebrates under chemical stress,11.12


Tarun: Are you utilizing the Agilent Measurement Suite (AMS) at Imperial College London to conduct your research? If so, what kind of methods/instrumentation are you using, and how has this impacted your research?


Dr. Leon Barron: We’ve recently engaged with the Agilent Measurement Suite (AMS) and it has been an excellent resource for academic researchers, especially to try out new instrumentation and access the wealth of experience Agilent has in analytical method development and complex data analysis.


We currently have a Biotechnology and Biological Sciences Research Council (BBSRC)-funded project in partnership with Agilent looking at development of 3D-printed passive samplers. We recently engaged with the AMS to perform machine learning- assisted high-


resolution suspect screening on sampler extracts from the River Thames in Central London, which was published on the cover of RSC Analytical Methods.14


Victorian sewers in London have been


coping with a rapidly expanding population and combined sewer overflows occur on a regular basis here making understanding any impacts of chemical pollution from wastewater an important issue. In this work, 65 unique targeted compounds were detected in passive sampler extracts of river water using an Agilent 1290 Infinity II LC system coupled to a 6546 LC/Q-TOF mass spectrometer.


Over the past number of years, we have been working hard to develop retention time prediction models to refine mass spectral suspect shortlists.15,16,17,18


Even with high resolution measurements,


several candidates often exist and the ability to differentiate them often lies in the chromatography. For use in passive sampler extract suspect screening, we developed a machine-learning based tool for retention time prediction for a gradient separation on an Agilent Zorbax Eclipse Plus C18


, 2.1 × 100 mm, 1.8 µm column.


next for us is to develop and apply more efficient suspect screening workflows using high resolution mass spectrometry to detect (bio) transformation products and refining analytical methods to minimise extraction steps.


The new Environmental Research Group facility based at Imperial’s White City Campus


Although challenging to do just yet for semi-solid samples, we are already performing this type of work for wastewater and river water. Advances in instrumental sensitivity now allow us to perform direct quantitative analysis of hundreds of compounds in under five minutes at low ng/L concentration levels, and at scale, with just a few millilitres of sample.13


This enabled in silico tentative identification of 59 additional compounds in the same extracts. In general, we shortlist suspects first based on mass spectral database matching, followed by machine learning-assisted retention time prediction and the latter usually reduces these shortlists by roughly two thirds, which makes things more manageable. This serves therefore as an excellent way to prioritise the identification and confirmation of new and emerging contaminants more rapidly. Whilst we now do this routinely ourselves, the focus now is to make this an integrated application and it is excellent to have the AMS now on our doorstep at the Imperial White City campus to extend our collaborations.


Tarun: How do you think New Approach Methods (NAMs) – such as those involving machine learning – will continue to shape the future of chemical risk assessments in environmental research?


Dr. Leon Barron: There is an increased interest and demand for development and integration of machine learning-type tools within environmental risk assessment (ERA) as a perceived ‘quick-win’ & prioritization mechanism for such a vast array of chemicals, their metabolites and transformation products.19


However, regulatory


bodies such as the European Chemicals Agency have suggested that in silico approaches cannot yet replace classical toxicology, as more underpinning science and assurance is required. I think this is probably a fair appraisal for now given the current lack of skills, research and knowledge of the benefits and pitfalls of machine


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A team led by researchers at the University of Washington Tacoma, UW and Washington State University Puyallup have discovered a chemical that kills coho salmon in urban streams before the fish can spawn. Shown here Zhenyu Tian, a research scientist at the Center for Urban Waters at UW Tacoma, holds a sampling pole, which is used to collect creek water for future tests.


Credit: Mark Stone/University of Washington


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