Cognitive DeveLopment in the Urban Environment (The CLUE study)

With increasing population growth and continuing urbanization, air quality and urban noise have emerged as important determinants of the global and European burden of disease, as well as public health within cities. Air pollution concentrations on London's busiest roads continue to exceed UK Air Quality Strategy Objective (AQS) and EU Limit Values, with the Exploration of Health and Lungs in the Environment (EXHALE) demonstrating that approximately 80% of children living in Inner City London boroughs have annual exposures to NO2 in excess of the EU limit value (40 ug/m3), reflecting the high proportion of diesel vehicles. Urban noise also constitutes a problem in densely populated, highly trafficked urban areas. In London, it is predicted that 19% of the population are exposed to residential noise levels, and 100% to night-time noise levels, that exceed WHO guidelines. Recent research suggests that chronic exposure to air pollution and noise may have detrimental effects on cognition, academic performance and behaviour in children, but there is limited scientific evidence and very little is known about possible underlying mechanisms for these effects.

This proposal sets out to investigate the emerging hypothesis that children who were born in and grow up in urban environments display impaired cognitive development due to long-term exposures to air pollution and noise from traffic. The CLUE study, which will be nested within the SCAMP study of 6000 secondary school children in Greater London, will exploit detailed air pollution and noise exposure monitoring (including personal monitoring and indoor and outdoor measurements at homes and schools) to enhance existing models for estimating air pollution and noise exposure in this age group. These enhanced models will then be used to estimate air pollution and noise exposure in all SCAMP children. This enhanced modelling approach, applied to a large longitudinal data set will help overcome many of the limitations of previous research that have attempted to investigate the interrelationships between air pollution, noise, cognition, behaviour and academic attainment. We will also investigate the underlying biological mechanisms by which air pollution and noise may impact on cognitive development using a subset of the children from the SCAMP cohort.

The emerging evidence that traffic-related pollution/noise impacts on neurological development and degeneration raises significant public health and societal issues. To date much of the focus has been on diesel exhaust emissions, but the evidence base is not wholly coherent due to differences in study design, modelling approaches and exposure profiles (i.e. pollutant concentrations and trends, mixture composition and the make-up of the traffic fleet) between studies. A large-scale longitudinal study within London, examining associations between traffic-related air pollution and noise exposures and cognitive development in children therefore provides a unique opportunity to evaluate this association. London has high levels of NO2, largely arising from the high proportion of diesel vehicles and therefore represents an ideal location to test this hypothesis. As a potential association between traffic-related pollution/noise and impaired cognitive development is of significance at both a societal and economic level, this research has the potential to inform policy across a range of sectors to:(a) improve understanding of potential impacts of these environmental stressors on children's developing brains and educational performance;(b) through identifying the major determinants of exposures to inform traffic mitigation schemes and urban planning to identify ways to reduce noise and air pollution exposure among children;(c) by focusing on source informative modelling estimates of exposure and potential adverse mechanistic pathways to identify which components of the urban air pollution mix are most likely to drive adverse cognitive outcomes.

CLUE investigates if exposure to individual air pollutants, pollutant mixtures, and noise, either separately or in synergy, are associated with cognitive impairments in children. We also examine if cognitive deficits are associated with the induction of systemic oxidative stress and neuroinflammtion, and if these adverse responses are related to the pro-oxidant components of the urban airshed (transition metals, and oxidative gases).

The study will make use of data that has been collected as part of the baseline, follow-up and personal monitoring of SCAMP. Personal monitoring involves detailed activity (GPS and activity diaries) and micro-environmental (fixed-site monitoring of noise levels, PM2.5, PM10, NO2, O3, particle number concentrations at home/school, indoors/outdoors) monitoring for 200 children (the investigative cohort) nested within the SCAMP cohort study of 6000 secondary school children in Greater London. These monitoring data will be used to validate, calibrate, and enhance the LHEM air pollution and TRANEX noise models to incorporate indoor environments and address previous exposure misclassification.

We will conduct large scale epidemiological analysis on the SCAMP cohort examining cognitive and behavioural development o in relation to estimates of air pollution and noise at birth and through adolescence.

We aim to advance mechanistic understanding of the link between traffic-related stressors and neurological impacts by relating biomarkers of exposure (metals) and response (oxidative stress, neuronal injury/inflammation) measured in urine and saliva (in samples already collected at 3 time points in the investigative cohort) to: i) measured/modelled air pollution and noise exposures and ii) cognitive performance and behavioural problems measured at baseline and longitudinally. Plausible mechanistic pathways for cognitive deficits identified through the epidemiological analysis will be supported by linked biomarker evidence.

The primary beneficiaries of this research will be children (and their parents) living in Greater London, many of whom are disproportionally exposed to environmental stressors, such as air pollution and noise. This research will strengthen the epidemiological evidence base, and thus our understanding, regarding the relationships between these environmental stressors and cognitive function in adolescents. This will facilitate improved investigation of air pollution, noise and wider health outcomes in a range of population groups by the epidemiological and public health communities. Moreover, this will allow specific identification of activities and environments that may lead to increased risk of harm or impairment, enabling targeted risk reduction strategies by policy makers across a range of sectors, including education, public health, urban planning and environment. Targeted strategies have the potential for much greater impact on behavioural change than simply associating elevated noise and air pollution levels with health or cognitive outcomes. By establishing a more robust evidence base, this research will have a major impact on cost-benefit analyses for local air pollution initiatives aimed at protecting children's long-term health and improving children's behavioural outcomes at an age when children are particularly vulnerable to these environmental insults. This proposal is capable of changing the perception of air quality away from simply meeting national and regional limit values to more extensive exposure reduction, and has the potential to initiate behaviour change through school and education authority-led action. Since exposure to road traffic air pollution and noise is widespread, this research will be beneficial for the 3.9 billion people living in urban areas worldwide.