Introduction to Unit 7: GIS and Diseases of Exposure

This is the seventh unit in the module ‘GIS for the Analysis of Health’. This unit describes the application of GIS for assessing environmental exposures. One of the strengths of GIS lies in its ability to integrate data from different sources and it is in this role that GIS is used here. In assessing exposure, environmental data about ambient pollution levels are combined with health or population data. Exposure assessment has a wide range of policy applications: in setting environmental protection regulations for factories and mines, in assessing the risks from an industrial accident by exploring possible future scenarios, and in finding the most cost-effective ways of reducing ill health. Environmental exposures are also frequently the subject of both media and public concern, so much so that some authors now speak of ‘virtual’ exposures, in which people have had contact with information about an environmental hazard rather than the hazard itself. Some of the key concepts in this unit are introduced in the illustrations below.
 

 

Environmental exposure:
‘An event that occurs when there is contact at a boundary between a human and the environment with a contaminant of a specific concentration for an interval of time’

(National Academy of Science, 1991)

 

There are 8 subsections in this unit:

1. Methods in environmental epidemiology
2. Environmental hazards
3. Indicator-based methods and dispersion models
4. Ambient pollution monitoring
5. Linking populations and environmental risk
6. Time-activity data and personal monitoring
7. Assessing causality
8. Assignment

 

This subsection sets out the structure for the remaining materials.

‘Methods in environmental epidemiology’ provides an overview of the methods used to quantify the risks associated with different environmental exposures and how GIS can be used with these methods. ‘Environmental hazards’ considers the different sources of hazardous materials in the environment and how these are monitored. The third and fourth subsections consider methods for representing environmental hazards within a GIS. The third part of the unit looks at indicator-based methods, which are indirect ways of representing risk. For example, the distance to a nuclear processing plant would be an indicator-based risk measure. This part of the unit also introduces dispersion models, which are mathematical predictions of how a pollutant will be distributed from a source into the surrounding environment. Unlike indicator-based methods, dispersion models take into account meteorological or hydrological conditions in estimating risk. The fourth subsection, ‘ambient pollution modelling’, assesses how environmental risks may be represented spatially when there is a network of monitoring sites measuring levels of a given pollutant.

The next 2 parts of the unit focus on the population at risk. The fifth subsection considers how population data may be integrated with environmental risk data. More specifically, this part of the unit introduces statistical methods for testing whether a disease cluster is focused on a particular source. The sixth subsection, ‘time-activity data’, investigates methods by which populations may be represented geographically in terms of their daily movements, rather than by residential address only. This is important since most people spend large parts of the day outside their homes and so environmental hazard levels at their residential addresses may not reflect their true levels of exposure. This part of the unit also explores ‘personal monitoring’ – the idea that exposure monitoring systems should be closely linked to individuals at risk rather than at static points in the environment.

‘Assessing causality’ considers some of the methodological problems in establishing causal relationships between environmental hazards and health effects in this strand of GIS work.

The final part of the unit involves GIS practical work, investigating the health risks from exposure to uranium in groundwater. This activity forms the assignment for this unit and should be undertaken after completing all of the earlier objects. Deadlines and further information are provided in the syllabus and your calendar. Expect to spend about 2 weeks working through these materials. These activities can be carried out in any order but the Assignment question should be left as the final activity.

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