Emerging organic contaminants (EOCs) in aquatic systems have been connected to various detrimental effects in wildlife. Their diverse entry pathways into bodies of water, along with the current inefficient removal technologies and the fact that such technologies can lead to toxic by-products, means that solving the challenge of effectively removing them from our aquatic systems and protecting our environment is particularly difficult. Researchers at Cranfield University are seeking to develop technologies to mitigate EOCs, better understand removal mechanisms and the way that different organic compounds might react to these mechanisms, while also researching alternative nature-based solutions.
What are the emerging organic contaminants (EOCs)?
Emerging Organic Contaminants (EOCs) can be defined as the organic compounds that occur in the environment due to human activities but with concentrations remaining at trace levels, i.e. up to µg/L. Compounds that fall into this category include:
- Synthetic chemicals such as pharmaceuticals and personal care products.
- Natural compounds such as oestrogens.
EOCs may originate from a wide range of sources - including agriculture, households, traffic networks and industries - and enter water bodies through diverse paths.
The widespread presence of EOCs in aquatic systems is a major concern all across the globe. For example, over 150,000 compounds were registered in the European market and many of them will end up in water systems at some point of their lifecycle. Although they present in trace levels of concentrations, their existence in aquatic systems has been connected to various detrimental effects in organisms such as estrogenicity, mutagenicity and genotoxicity.
Challenges in EOCs remediation: the need for more efficient and cost-effective technology for EOCs mitigation
Most of the EOCs in the contaminated water cannot be effectively removed in conventional wastewater treatment plants (WWTPs). For example, the removal efficiency of tetracycline, the second most widely-used antibiotic, can only achieve up to 30% in WWTPs with an influent concentration up to several µg/L. There is an increasing need for more efficient and cost-effective technology for EOCs mitigation.
Another issue is that current EOCs remediation processes may result in the formation of more toxic by-products. The advanced oxidation processes (AOPs), such as ozonation and UV/H2O2 reactions, have been deemed as useful technologies for EOCs removal. However, the UV/H2O2 treatment of atrazine, the most common pre- and post-emergence herbicide, could lead to the formation of de-alkylated by-products of desisopropyl atrazine (CEAT) and desethyl atrazine (CIAT), which perform much higher acute toxicity than the parent compound.
A major challenge in contaminated water treatment is the need to cope with a large number of EOCs, which are chemically very different, in a broad range of water conditions. Interactions between different compounds could influence the efficiency of the treatment. For example, previous studies have mainly focused on apolar and monopolar compounds, such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). However, the polyfunctional and ionisable pesticides, biocides, and personal care products could undergo numerous interactions with other dissolved or particulate chemical species and materials – and this would have an impact on how efficient the treatment is.
There is still a lack of comprehensive tools and predictive models to assess and speculate the transformation processes during the microbially mediated treatment of EOCs. Due to the specific chemical properties, even compounds exhibiting only minor differences in their structures may react very differently. Moreover, a given organic compound may react by various pathways and/or at different rates under distinct conditions, such as the pH, salinity, and temperature of the water.
Responding to the demands of the EU Water Framework Directive - the Chemical Investigations Programme (CIP) in the UK
The EU Water Framework Directive (WFD) has important implications for the scope and nature of the pollution control measures required to protect surface waters. Environmental Quality Standards have now been set for substances which were previously not subject to detailed monitoring or control. In 2013, the WFD extended the list of contaminants categorised as Priority Substances to 44 contaminants. The majority of the substances on this list are classified as EOCs.
The National Chemical Investigations Programme (CIP) was initiated to meet this legislation, under the coordination of the UK Water Industry Research and in collaboration with the Environment Agency. The first two phases of the programme, spanning 2010-2020, provided an overview of the occurrence, behaviour and management of trace contaminants in wastewater and river catchment.
The current third phase of the CIP (CIP 3) sets out to not only monitor the long-term performance of the emerging chemicals in the sewage, groundwater and sludge, but also investigate the removal mechanisms of the pollutants in the existing and novel treatment processes.
Scientists from Cranfield Water Science Institute are working closely with UK Water Industry Research and contribute to the CIP in all phases. For example, Dr Pablo Campo Moreno and Professor Bruce Jefferson are collaborating with Aqua Enviro and Atkins in the Chem 12, Mechanisms of Removal of EOCs.
A possible nature-based solution for EOCs removal
In certain circumstances, constructed wetlands – a nature-based solution of artificially created wetlands designed to filter and treat waterborne pollutants – offer an attractive alternative to conventional wastewater treatment plants, as they are low-cost and easy to maintain.
Previous studies have demonstrated that constructed wetlands could be a promising technology to eliminate a large range of EOCs, including pharmaceuticals and personal care products, and pesticides.
Cranfield researchers are taking a world-leading role in research for constructed wetlands as wastewater treatment. For example, Professor Bruce Jefferson and Dr Gaby Dotro are leading several CWs projects, which are financially supported by GCRF, EPSRC and the water utilities. Dr Gaby Dotro and Dr Tao Lyu are also leading an industry fully funded MSc by Research project, which aims to improve the hydraulic performance of CWs for net zero wastewater treatment.
Recent studies, led by Dr Tao Lyu, have:
- Investigated the responses of the microbial community in constructed wetlands during the treatment of pharmaceuticals  and pesticides .
- Developed the Artificial Neural Network (ANN) model to predict the pesticide removal .
- Optimised the configuration of constructed wetlands to increase the antibiotic mitigation .
- Studied the translocation, transformation and metabolisation mechanisms of biocides in the wetland plants .
Along with other relevant studies, Dr Lyu has also revealed the interactions between the EOCs removal and biogeochemical processes of other nutrients, including N and P, in constructed wetlands. His work has improved the understanding of the removal mechanisms of the EOCs in the cost-effective and efficient constructed wetland system.
These natural wetland systems could also help to reduce both non-point-source pollutants - for example from agricultural run-off –and point-source pollutants, such as from an accidental chemical release. The soil microbial community and wetland plants could contribute to the uptake and bioremediation of the EOCs. This is particularly relevant in the case of EOCs such as polycyclic aromatic hydrocarbons (PAHs) – while these are normally only present at low levels in contaminated soil/sediment, long-term exposure could lead to acutely toxic, genotoxic and carcinogenic effects in humans. Therefore, developing efficient remediation technologies is key.
Furthermore, in some circumstances, PAHs could be released into the environment in high concentrations, such as through an oil spill incident. An example of this occurred on 6 August 2020, when the bulk carrier MV Wakashio leaked more than 1,000t of low-sulphur fuel oil into the Indian Ocean, 2 km off the coast of Mauritius. Cranfield University has significant expertise across the themes of Soil, Water and Environment on the remediation of PAHs from water and soils and currently, they are preparing a NERC Urgency Grant, collaborated with the local NGO and commonwealth secretary. This will monitor the removal and impact of the hydrocarbons, including PAHs, on the microbial communities and plants in the mature Mangrove Wetlands.
It is clear that, when it comes to protecting our wildlife, our environment and human health, research into the most effective methods of removing pollutants from our aquatic systems is key. Find out more about the latest research from the Cranfield Water Science Institute.
 Zhang Y, Lyu T, Zhang L, Button M, Arias C, Weber K, Shi J, Chen Z, Brix H, Carvalho P. (2019) Microbial community metabolic profiles in saturated constructed wetlands treating iohexol and ibuprofen. Science of the Total Environment. 651:1926-1934.
 Lv T, Carvalho P, Zhang L, Zhang Y, Button M, Arias C, Weber K, Brix H. (2017) Functionality of microbial communities in constructed wetlands used for pesticide remediation: influence of system design and sampling strategy. Water Research. 110: 241-251.
 Lyu T, Zhang L, Arias C, Brix H, Carvalho P. (2018) The removal of tebuconazole in unsaturated and saturated constructed wetland mesocosms: dynamics, influencing factors and modelling predictions. Environmental Pollution. 233:71-80.
 Zhang L, Lyu T, Zhang Y, Button M, Arias C, Weber K, Brix H, Carvalho P. (2018) Impacts of design configuration and plants on the microbial community of constructed wetlands treating ibuprofen. Water Research. 131:228-238.
 Lv T, Carvalho P, Casas M, Bollmann U, Arias C, Brix H, Bester K. (2017) Enantioselective uptake, translocation and degradation of the chiral pesticides imazalil and tebuconazole by Phragmites australis. Environmental Pollution. 229:362-370.
Note: The Surname “Lyu” was previously written as “Lv”.