High-volume hydraulic fracturing combined with horizontal drilling has “revolutionized” the United States’ oil and gas industry by allowing extraction of previously inaccessible oil and gas trapped in shale rock . Although the United States has extracted shale gas in different states for several decades, the United Kingdom is in the early stages of developing its domestic shale gas resources, in the hopes of replicating the United States’ commercial success with the technologies [2, 3]. However, the extraction of shale gas using hydraulic fracturing and horizontal drilling poses potential risks to the environment and natural resources, human health, and communities and local livelihoods. Risks include contamination of water resources, air pollution, and induced seismic activity near shale gas operation sites. This paper examines the regulation of potential induced seismic activity in Oklahoma, USA, and Lancashire, UK, and concludes with recommendations for strengthening these protections.
The United Kingdom recently approved the proposal of gas firm Cuadrilla to begin hydraulic fracturing to extract shale gas at the Preston New Road site in Lancashire, Northern England . This marks the first time that a permit for drilling for shale gas has been granted since operations were halted in 2011 following small earth tremors . In discussing the government’s decision to approve Cuadrilla’s request to drill, the current energy minister Claire Perry stated that shale gas has the potential of “further enhancing our energy security and helping us with our continued transition to a lower-carbon economy” . Some commentators assert that using shale gas for electricity can potentially have a lower carbon footprint than combustion of coal [6–8]. This and the argued capacity to deliver economic benefits, including projected job creation, are driving forward plans for commercial extraction of shale gas in the United Kingdom.
In contrast to the United Kingdom, the United States has a longer history with the technique, having employed hydraulic fracturing to stimulate production from horizontal, unconventional oil and gas wells since the 1980s . “Fracking” is now a global issue, because other countries seek energy independence by developing their own unconventional gas reserves. As environmental and public health risks are well documented, it is important to evaluate how best to ensure the protection of individuals and communities [10–12].
AIMS AND METHODOLOGY
Case studies provide a useful mechanism to facilitate learning through reasoning from examples and experiences [13, 14]. To that end, this paper presents two case studies as a way to analyze approaches and challenges to regulation of hydraulic fracturing applied to shale gas development: the American state of Oklahoma and the Lancashire region in the North of England, UK.
The current state of UK regulation is discussed, in the context of the country’s first steps toward shale gas development. Oklahoma was chosen as the second case study due to its longer experience with hydraulic fracturing for shale gas extraction as well as recent experience with induced seismicity. The state’s current—and evolving—regulatory framework governing induced seismic activity is examined. This analysis employs a case study methodology to draw analogs to the emerging shale gas industry in the UK and the potential risks in Lancashire, with emphasis on the regulation of induced seismicity in areas of previously minimal seismic activity. This research, therefore, serves to foster discussion and promote learning through an examination of the two cases.
In both the United States and the United Kingdom, shale gas is currently regulated through the existing regimes for conventional oil and gas extraction . There is thus the potential for gaps in regulation due to the specific potential environmental and health risks from techniques that are used in hydraulic fracturing [16, 17]. Furthermore, ensuring that certain potential impacts that may be new for a region or community, such as the risk for induced seismic activity in an area that has not previously experienced significant seismicity, is crucial. Here, we examine two cases, Lancashire, UK, and Oklahoma, USA, to contrast these jurisdictions’ methods of protecting against the risk of induced seismicity. Although the UK is in the preliminary stages of developing its shale resources, and at the time of writing has only conducted exploratory drilling, Oklahoma has a longer and more developed shale industry.
POTENTIAL SOURCES OF RISK
The United States has been implementing hydraulic fracturing to extract shale gas since 1965, using a mixture of water and sand to fracture the shale rock and liberate trapped gas . However, it was not until the 1980s that the technology of hydraulic fracturing began to be used to stimulate production from horizontal wells .
Data from the USA have shown evidence of risks to the environment and public, including potential impacts on ground and surface water, air quality , and changes in the community and human well-being and livelihoods as nearby communities undergo rapid industrialization [10, 19, 20]. Sources of risk include potential migration of pollutants from fluids used in the extraction process as well as toxic gases, liquids, and solids that exist naturally underground . Studies have shown the potential for environmental and health impacts from contamination and pollution at all stages of the shale gas lifecycle, from site preparation to decommissioning [10, 12, 22–25].
Furthermore, the growing body of data from the USA shows evidence of induced seismic activity from operations related to shale gas extraction. Seismic activity in nearby areas may be induced or increased throughout the lifecycle of shale gas operations as the fractures created propagate through the shale rock and can cause seismic activity [22, 26]. Larger seismic events, although rarer, are possible in a “prestressed fault” . Different locales vary in how they regulate the potential risk for induced seismicity. However, it is important that regulating bodies have an accurate, up-to-date understanding of the geological processes to develop regulations to protect against induced earthquakes.
HYDRAULIC FRACTURING LIFECYCLE IMPACTS
Although “hydraulic fracturing” (fracking) technically refers to a roughly 2-week period where the shale rock is fractured using a mixture of water, fracking chemicals, and sand pumped underground at high pressure, the term has largely been taken to mean all stages of the shale gas lifecycle . It is important to note that seismicity does not just occur during production itself, but during the end stage, when produced water (wastewater), or flowback, is often disposed of in underground injection pits [22, 23]. This injection has been shown to induce earthquakes . Recent research has shown differences in the level of seismic activity depending on the geology of the areas where produced water is injected  (Figure 1).
The British Geological Survey (BGS) has estimated the volume of shale gas in 11 counties in Northern England, including the Bowland Basin, at 40 trillion cubic meters, yet there is considerable uncertainty about quantity and extraction feasibility . Despite the protests and legal challenges by local communities  and environmental groups concerned about potential environmental and human risks, shale gas company Cuadrilla was authorized by the UK government to begin fracking at Preston New Road site in Lancashire . The formal approval  finalizes a series of evaluations [31–34] by the governmental bodies, including the Health and Safety Executive and the Environment Agency (EA): “After careful consideration and scrutiny of the technical legislative requirements, Energy and Clean Growth Minister Claire Perry has given Hydraulic Fracturing Consent under section 4A of the Petroleum Act 1998 (inserted by section 50 of the Infrastructure Act 2015) to shale gas operator Cuadrilla Bowland Ltd for the horizontal well, number ‘PNR-1z,’ at its Preston New Road site in Lancashire” (UK Government, 24 July, 2018).
The permit, first issued for commercial extraction of shale gas in England, comes at a time of potential policy change and regulatory uncertainty, in light of the UK’s recent populist vote to leave the European Union (EU). Environmental regulations and protections are based on EU Directives (legislative acts). The European Commission has issued a nonbinding Recommendation  that outlines minimum principles for use of high-volume hydraulic fracturing to extract hydrocarbon resources, and establishes that the Member States have the right to determine “conditions for exploiting their energy resources, as long as they respect the need to preserve, protect and improve the quality of the environment,” and acknowledges that “[. . .] hydraulic fracturing technique raises specific challenges, in particular for health and environment.”
REGULATION SPECIFIC TO SEISMIC ACTIVITY
Currently, regulators are required to use a stoplight approach for seismic activity, as illustrated in the infographic in Figure 2. In addition, the BGS voluntarily monitors baseline conditions related to shale gas development, including seismic activity and ground motion such as subsidence and uplift .
SEISMIC ACTIVITY LEADING TO A MORATORIUM IN LANCASHIRE
The first exploratory drilling operations in the UK were carried out by Cuadrilla at Preese Hall, Lancashire, in 2011, and resulted in a 2.3 magnitude earthquake; a few months later a second seismic tremor of 1.5 magnitude occurred [22, 23, 38]. These seismic tremors were well publicized, leading to public scrutiny and increased opposition to fracking . The government of the United Kingdom responded to the seismic events by declaring a moratorium on shale gas activities in November 2011, pending further study . Following the conclusion of the investigation in December 2012, the suspension on drilling was lifted and exploratory drilling was again permitted in England .
Hammond and O’Grady , citing Green et al. , explained that the further studies conducted by the Department of Energy and Climate Change (DECC), as well as the review  jointly conducted by the Royal Society and the Royal Academic of Engineering, showed that there were adequate controls to mitigate the potential for seismicity and also found that the probable cause of seismic activity at Preese Hall was due to the injection of fracking fluids within already stressed faults.
Some earth scientists have questioned whether controls are adequate. For example, Hammond and O’Grady  expressed concern that fault diagnosis was not complete and “proposed the additional use of borehole imaging before injection.” On the other hand, the UK Task Force on Shale Gas (a commercially sponsored body) considered that the limits imposed by the traffic light system were “unfeasibly low” . However, this raises the question of acceptable levels of risk, considering evidence of potential harm from the USA, particularly Oklahoma.
Before the earth tremors, there were no regulatory controls on seismic activity; however, gas operator Cuadrilla agreed to modify the amount of fluid utilized and to implement a warning system for seismic activity . Although a report commissioned by Cuadrilla and the British Government  concluded that potential risk could be managed through a self-regulated monitoring system that would halt fracking operations when seismicity exceeded an established threshold, mandatory impact assessment regimes are arguably needed to fully address these concerns and prevent earthquakes through risk mitigation and regulation . In addition, although DECC has implemented new regulations, the lack of regulation before the demonstration of earthquake tremors highlights the lack of proactive or anticipatory governance of certain aspects unique to hydraulic fracturing [16, 41].
Wilson et al.  explained that shale gas operations have brought about a relatively new source of human-made seismic activity, and although the earthquakes induced by fracking in the UK tend to be of small magnitudes, the UK landscape is “criss-crossed by faults, some of which may be critically stressed” , and fault reactivation can cause larger seismic events. Furthermore, it is possible that not all of the UK’s faults with the potential for reactivation have been documented, and therefore, applying local seismic monitoring could help fill in gaps in the data on baseline levels of fracking seismicity .
PUBLIC OPPOSITION IN THE UK
Whitton et al. , quoting Cotton , argued that public opposition to shale gas in the UK is exacerbated by a complicated planning and regulatory framework. Furthermore, Cotton , as quoted in Whitton et al. , added that navigating the permitting and regulatory framework has been difficult for gas firm Cuadrilla, because in June 2015 Lancashire County Council rejected applications due to potential impacts on the Lancashire local area, citing increased motor traffic and effects on the rural highways, “the visual amenity of local residents,” as well as “an adverse urbanizing effect on the open and rural character of the landscape” and the “industrialization of the countryside” .
Cotton  (quoted by Whitton et al. ) claimed that “competing rationalities and underlying environmental discourses . . . highlight the contested nature of the policy terrain and the lack of consensus on key social and governance issues.”
Research conducted on public perspectives toward shale gas in the UK provides evidence that local residents clearly remember the seismic activity and are concerned about future seismic events. One local resident explained the following: “I remember when we had those earthquakes, and I felt it, I was terrified. I thought, well, for the sake of my daughters, my family, I should—need—to try to find out what it’s all about” (Interview, Lancashire, October 24, 2016) (Figures 3 and 4).
SEISMIC ACTIVITY AND WASTEWATER INJECTION
Seismic activity has also been shown to be linked to the injection of wastewater and other fluid waste after the hydraulic fracturing, or rock breaking stage, in addition to induced seismicity from the actual fracking stage [22, 23, 45]. Once the pressure is released on fracking fluids pumped deep underground, the wastewater flows back to the surface, allowing liberated oil and gas to flow to wells. But the produced water is frequently disposed of by injecting the wastewater deep into underground formations. Wastewater injection—an industrial process similar to fracking and implemented to dispose of fluid wastes from hydraulic fracturing and other activities—has been linked to seismic activity . Wastewater injection in the USA has been connected to induced seismicity at up to magnitude 5 and can generate seismic events at greater distances of up to 35 km from the injection site [22, 47].
However, Hammond and O’Grady , citing Westaway and Younger , explained that the practice of wastewater injection “is unlikely to be carried out in the UK reducing the risk of induced seismicity compared to the USA, as it is understood that the reconstituted Environment Agency (EA) in England would not grant a permit for this method of wastewater disposal under its current interpretation of the European Union (EU) Water Framework Directive.” On the other hand, Hammond and O’Grady  explained that the UK’s Task Force on Shale Gas states in their report that there could “be situations and circumstances – where the geology is suitable – where deep injection is a sensible, cost effective and popular preferred means of waste disposal” (TSFG, 2015).
THE CASE FOR PRECAUTION
The precautionary principle is broadly accepted as defined in the 1992 Rio Declaration: “In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation” [49, 50]. When considering new risks such as increased seismic activity, regulators face the dilemma of not knowing what level of harm we are benchmarking or find acceptable.
Thus, it can be argued that in addition to effective and alternative options for management of wastewater to ensure safe reuse or disposal of fracking wastewaters, a precautionary approach is an optimum response to the potential for seismic activity from the underground injection, particularly in a previously inactive area. Adams  posits that the precautionary principle is particularly relevant in a case where “causal link to effects is unclear” , as is arguably the case with induced seismic activity.
REGULATION OF SHALE GAS IN THE UNITED STATES
Fracking, unlike other heavy industrial activities, has been largely exempt from federal regulation in the USA, where regulation is a mix of state and local controls . While Oklahoma currently has state-enacted regulations requiring disclosure of chemicals used in the fracking processes , other significant potential impacts may not be adequately regulated under the states’ existing fracking regulations, including the potential for induced seismic activity, particularly as the state was not previously accustomed to earthquakes or seismic activity.
O’Reilly  explained in the Law of Fracking  that “sufficient geological and seismological evidence has been amassed to establish that the high pressure deep well injection of fracking waste can stimulate natural forces to cause tremors up to the level of significant earthquakes” . In 2014, local authorities in Ohio halted gas operations at Poland Township’s Hilcorp site due to five earthquakes of magnitude 2.1–3.0 occurring close to the well pad .
In the USA, state and local policies have developed as drilling methods have evolved, as have the laws governing zoning. However, there is arguably a lag in the regulations as certain states that previously experienced little or no seismic activity are struggling with developing regulations in response to induced seismicity.
GAPS IN THE REGULATIONS: SOCIAL AND PSYCHOLOGICAL EFFECTS
Studies have shown that there is potential for negative psychological impacts including stress and anxiety, lack of sleep, and feelings of increased fear and betrayal as well as anger, even during the planning stages of fracking—before any actual drilling has begun [57–59]. Hirsch et al. , in a review of the literature on associations between fracking and mental health, found that although those living in communities near fracking sites may experience “minimal, initial benefits such as land lease income or infrastructure development,” they may also experience negative impacts such as “worry, anxiety, and depression about lifestyle, health, safety, and financial security, as well as exposure to neurotoxins and changes to the physical landscape.” Moreover, entire communities may experience “collective trauma” in both anticipation of and after experiencing boom–bust cycles [57, 58]. The issues of mental health impacts are typically not addressed in either governmental  or risk and impact assessments or in company assessments [57, 60], thus leaving a gap in identification and regulation of important negative impacts.
Furthermore, it can be argued that the potential for collective stress and anxiety may be even more severe when it comes to a local community facing new risks for the first time. Casey et al.  conducted a study on the correlation between earthquakes experienced in Oklahoma and anxiety-related Google searches, and show significant associations between the increase in Oklahoma earthquakes and increasing statewide anxiety levels as measured through Google search incidences. They conclude that the recent uptick in Oklahoma’s earthquakes has led to a psychological response with potential implications for public health and regulations . Furthermore, Casey et al.  found that environmental disasters such as large earthquakes induce negative psychological impacts such as anxiety. Moreover, individuals rate human-caused disasters such as induced seismic activity as worse than natural disasters [62–64]. For example, McComas et al.  found in an online survey of 325 individuals in the USA, that induced seismic activity drew more negative feelings from respondents than equivalent naturally occurring earthquakes .
FRACKING IN OKLAHOMA
Fracking has been rapidly growing in the South Central Oklahoma Oil Province (SCOOP) and the Sooner Trend Anadarko Basin Canadian and Kingfisher (STACK) counties shale plays in Oklahoma, in the Anadarko Basin, in what has been touted as the “US’s hottest new area for horizontal development” . The SCOOP and STACK regions have seen a 70% increase of initial production rates since 2013 ; this increase has led to a drastic rise in the number of earthquakes and seismic activity in the area.
NEW RISKS AND UNCHARTED TERRITORY
In 2014, Oklahoma, a state with previously little seismic activity, experienced a fivefold increase in seismicity, recording 585 earthquakes of magnitude 3 or greater; this contrasts with 100 quakes in 2013 . In 2015, there were 903 earthquakes of magnitude 3 or above, compared with only 41 magnitude 3 or greater quakes in 2010 . More recently, in February 2018 a slew of earthquakes triggered from operations related to shale oil and gas activities prompted the states’ oil and gas regulatory body, Oklahoma Corporation Commission (OCC), to develop new laws with hopes of reducing seismic activity . Previously, well regulators were required to take action and halt operations after a magnitude 3 quake, but the new rules place requirements on well operators to act to stop earth tremors from a threshold of magnitude 2.0 or greater  (Figure 5).
The rise in number of earthquakes in recent years in Oklahoma is unprecedented, as the state has experienced a roughly 900-fold rise in annual rates of seismic activity since 2009, an increase that had made the state go from one of the least to the most seismically active region in the USA’s contiguous states [11, 70]. We contend that the increase in Oklahoma’s seismicity is largely due to wastewater injection.
Hincks et al.  reported in their recent study that disposal of wastewater could lead to seismic activity at several miles away from the site. Hincks et al.  referencing Chen et al.  found that induced seismicity is influenced by local hydrogeological conditions in addition to the scale and locations of stressed faults, and thus underscores the importance of “local-scale” assessments in addition to existing seismic controls. The study crucially sought out how to develop a better comprehensive understanding of the various factors controlling induced seismicity and enable enhanced forecasting and improve decision-making under geological uncertainty .
OKLAHOMA’S UPDATED REGULATIONS
In Oklahoma, the Oklahoma Corporation Commission (OCC) is responsible for regulation and safety of shale gas, where shale gas operators work with OCC inspectors to ensure compliance with state regulations governing the oil and natural gas production process . In addition, well operators must comply with federal requirements including those from the Occupational Safety and Health Administration; the Toxic Substances Control Act (SUPERFUND); and the Environmental Response, Compensation and Liability Act .
In March 2015, the OCC introduced a directive covering 300 disposal wells that inject into the state’s Arbuckle formation, and are considered “areas of interest,” due to increased seismic activity . However, additional induced seismicity forced the Oklahoma Oil and Gas Conservation Division (OGCD) to expand the areas of concern in July 2015 and take action on an additional 211 disposal wells  to reduce the amount of oil and gas wastewater injected underground. Yet the magnitude or energy of the earthquakes experienced in the state did not drop as much as expected, but rather, some of the states’ largest earthquakes, including one of magnitude 5.8 near Pawnee, occurred after the new wastewater injection regulations were implemented .
In December 2016, the OCC introduced new industry seismicity protocols for detection of earthquakes . In light of recent and increasing seismic activity, the OCC has begun implementing amended directives for the disposal of wastewater, based on the potential of injection-disposal of wastewater into bedrock to trigger seismic activity . In 2018, updates to the OCC’s regulations mandated that all gas firms within certain areas use a seismic array, which detects underground shaking and gives information in real-time . These directive amendments also reduce the minimum earthquake threshold for when operators must reduce shale activity from magnitude 2.5 to magnitude 2; after tremors of magnitude 2.5 or greater, well operators and drillers must cease all activity for at least 6 h .
However, although current wastewater injection regulations in Oklahoma require operators to either reduce the amount of waste injection or decrease the depth of the injection site, the regulations often do not specify by how much . Therefore, increasing the depths of injection wells further above the basement rocks in areas of risk “could significantly reduce the annual energy released by earthquakes, in turn making larger earthquakes less likely”  (Box 1).
“All operators in the defined area will be required to have access to a seismic array that will give real-time seismicity readings.
The minimum level at which the operator must take action has been lowered from a 2.5 magnitude (ML) to 2.0 ML. Generally, the minimum level at which earthquakes can be felt is about 2.5 ML.
Some operators will have to pause operations for 6 h at 2.5 ML. Under the previous protocol, the minimum level requiring a pause was 3.0 ML.” 
SPATIAL DISTRIBUTION OF INDUCED EARTHQUAKES
A recent study by Goebel and Brodsky  showed that injection wells could cause seismic activity at distances of over 10 km and that these larger-reaching effects could increase the magnitudes and seismic risks beyond the expected distances. The study identified two types of earthquakes: one type was formed close to the injection sites but abruptly stopped within a kilometer from the site; and the other type could appear far from the well, resulting from “poroelasticity,” or deformation of sedimentary rocks. Thus, although sedimentary would appear to be a better choice for disposal of wastewater due to its sponge-like permeability, meaning greater space to hold wastewater, the study shows that injection of wastes into these rock types (instead of rigid bedrock) could lead to seismic effects at greater spatial distribution, as the newly filled sedimentary rocks swell and push on faults at farther distances from the injection sites . Therefore, further research is required to better understand the mechanisms leading to seismic activity at greater distances and to determine the safest and most appropriate geology for wastewater disposal.
These case studies illustrate the wide-ranging potential impacts of induced seismic activity related to shale gas drilling operations and fracking wastewater disposal. The shale gas lifecycle has the potential for risks to the environment and public health, as well as to infrastructure and property due to the threat of induced seismic activity. Furthermore, research has shown that there is a potential for psychological and mental impacts, such as stress and anxiety, even before drilling has actually begun. Recent research from Oklahoma showed a correlation between increased seismic activity and anxiety levels, as demonstrated from rates of anxiety-related Google searches. It is, therefore, crucial for additional research to focus on all potential impacts of shale gas operations, from direct environmental, health, and seismic effects as well as more indirect social and psychological impacts. Further research is needed to develop a better understanding of geologic and seismic processes to minimize induced seismicity, and a more comprehensive understanding of wastewater injection risks and research into the development of alternative waste disposal methods is crucial to ensure safety and reduce seismicity from underground injection.
RECOMMENDATIONS FOR THE UK
There is a clear and well-documented link between unconventional oil and gas operations and induced seismic activity, and until all of the complex processes are better understood, regulators should take a more precautionary approach to avoid increasing numbers of earthquakes, such as by lowering the threshold for halting seismic activity. Environmental and regulatory assessments should seek to gather data and protect against both direct and indirect impacts, and particularly negative psychological impacts, in addition to physical impacts.
Application of the precautionary principle is arguably the most appropriate strategy to deal with the potential for induced seismic activity from the underground injection, especially in a previously inactive area. Due to evidence of induced seismic activity—at greater distances and magnitude than previously thought possible—from injection of wastes underground, until there is evidence that this does not post the same risk in the UK, fracking wastes should not be disposed of through injection underground.
There is a need to develop alternative methods of managing waste fluids generated in shale gas operations. Further research into techniques for reuse and recycling of produced water, as well as research into safer methods for disposal of flowback in the event that reuse is not possible, is necessary.
There is an important role for citizen science and educational initiatives to advance public understanding of potential risks, particularly induced seismicity. For example, schools and public institutions can be equipped with low-cost seismic monitors to both educate and engage children and the wider public, as well as grow the database on seismic activity, fill gaps in seismic monitoring coverage, and improve baseline data.2
There is a crucial need for enhanced baseline data to demonstrate levels of seismic activity before fracking, to better understand the complex geological mechanisms at play. There is thus a need to ensure, before the development of shale gas resources in the UK, that there are no gaps in monitoring of seismic activity as well as in the available environmental and seismic baseline data.
LEARNING OUTCOMES AND DISCUSSION QUESTIONS
Based on the above case studies (Lancashire and Oklahoma), can we conclude with certainty that fracking causes seismic activity?
Do you think the answer to question 1, above, will vary, depending on your “political” view of fracking or how you frame the issue, say as a local resident or as a fracking company director? If so, how would you balance your view?
Noting question 1, above, what might we need to do to establish for certain whether fracking causes or does not cause seismic activity? Can the public play a role here and if so, how?
If we cannot ascertain for certain, in the short term, that fracking causes seismic activity, what policy and regulatory approaches, might we employ? Further, what pragmatic safeguards might we employ “on the ground”?
Is fracking in the “public interest” of the “majority” in terms of energy security, employment, and economic growth, versus the adverse impacts for the “minority” of homeowners and locals?
Why might fracking-related seismic activity be more disconcerting for home-owners and the public in Lancashire/UK as opposed to Oklahoma, USA?
Who ought to be in charge of regulating fracking? Local communities, central government, fracking companies, or other? Give reasons for your response.
Do we need a specific regime for the regulation of fracking, rather than regulating hydraulic fracking under conventional oil, gas, minerals, and energy regulations?
Do you think that energy from fracking is a step toward energy independence and security? What about renewable energy? Is there a bigger climate-related issue at stake, here, in this discussion?
All persons who meet authorship criteria are listed as authors, and all authors certify that they have participated sufficiently in the work to take public responsibility for the content, including participation in the concept, design, analysis, writing, or revision of the manuscript.
This research was generously supported by the Imperial College London President’s Ph.D. Scholarship. The authors express their gratitude to the residents of Lancashire, UK, and Oklahoma, USA, and to Debra Aczel and Antoinette Moon.
Imperial College London President’s Ph.D. Scholarship.
The authors have declared that no competing interests exist.
For our purpose, the Environment Agency of England and Wales: https://www.gov.uk/government/organisations/environment-agency (accessed 27/11/17).