Waste management and public health: the state of the evidence

Appendix 1: The literature search

A1.1           Scoping exercise

An initial scoping exercise was carried out to discover what has been written on the subject of waste and health. Searches were conducted of online databases and references in published papers (Appendix 2).  The search revealed thousands of documents about the many health hazards and health impacts associated with waste and about a number of different types of waste management. It raised questions about the focus of the topic under consideration. At this stage, any reference about waste and health was kept. As a result of the scoping exercise, decisions were needed about how to focus the search to what was considered relevant for this project.

A1.2          Decisions

Decision 1: to focus on review papers

Since the project brief was to carry out a systematic literature review, the first decision was to find out what reviews had been published. To avoid unnecessary duplication of effort, the CRD protocol recommends a thorough search for review papers before searching for primary studies. The project management team made the decision to narrow the search to reviews and not to systematically search for all the primary studies carried out. 

Decision 2: to define health broadly

The decision was taken not to define health too narrowly but to use the WHO definition of health as a ‘state of complete physical, mental and social well-being and not merely the absence of disease and infirmity’.

Decision 3: to focus on health impacts instead of health hazards

A health hazard is anything that can potentially cause harm . (For examples see Table 5, Factors Affecting Health.)

A health impact is any change in health risk that is reasonably attributable to a project, programme or policy. (Definitions from BMA 1998, p53.)

The decision was made to search for documents about the health impacts associated with waste disposal and not to systematically search for documents about the health hazards. This decision was made in order to focus the project on those research studies that provide the strongest evidence of a link between the waste disposal method and human health.

Decision 4: to focus on particular waste disposal methods

The initial brief was to focus primarily on the health impacts of landfill, incineration, sewage treatment, and soil amendments such as sewage sludge. The advisory group suggested that composting and recycling be included. Disposal of radioactive waste was not included although a few papers discovered during searching were retrieved and added to the database.

Decision 5: to focus on studies of direct relevance to waste disposal

The decision was made to prioritise papers directly relevant to waste disposal methods, rather than to papers that are only indirectly related. The hazards identified are not unique to waste disposal methods. They also originate from other sources such as industrial processes, power generation and natural sources.

 

Examples:

•   Tetrachloroethylene may contaminate drinking water when it leaches from a landfill site or when it leaches from the vinyl lining of drinking-water distribution pipes. 

•        The source of dioxins is any combustion process in which chlorinated organic chemicals are burned.

•        Metals processing is the major source of lead emissions to the atmosphere.

•        Volcanic activity and soil degassing during natural fires are important contributors to global emissions of mercury (National Research Council 2000).

 

A study demonstrating an association between a health impact and a hazard arising from a non-waste source is an important indication of the harmful nature of that hazard. However, the focus of this report is on waste disposal.

Decision 6: to focus on recent papers

The decision was made not to search thoroughly for papers written before 1982 partly because of the difficulties in obtaining papers from before this time but mainly because of changes in waste management practices over the years. Only reviews written since 1992 were included.

Decision 7: to focus on developed countries

No consistent decision was made about including references from other countries. Priority was given to papers about the South West of England and the UK. However, studies from other developed countries in temperate zones were included as there are likely to be many similarities with the UK in waste production and management. There was a bias towards continental Europe, the United States, Australia and New Zealand.  Papers about the health impacts of waste disposal in tropical, developing countries were generally not included.

A1.3             Search strategies

The literature search involved the following methods.

 

1.       Search of online databases – Biosis, CAB Abstracts, Cochrane Controlled Trials Register, Compendex*Plus, Index to Theses, Ingenta, Medline, Mental Health Collection, PsycINFO, ScienceDirect, The Science Citation Index Expanded.

 

2.       Search for published and unpublished documents that would not be found on online databases – Composting Association, County Councils and Unitary Authorities in the South West of England, Department for Environment, Food and Rural Affairs, Dyfed Powys Health Authority, Entrust, Environment Agency, Friends of the Earth, Greenpeace Research Laboratories, University of Exeter, London Hazards Centre, WARMER Bulletin Library, Wastewatch.

 

No search strategy that relies only on online databases will retrieve all of the relevant papers. Some discussion papers and primary studies are published in journals which are not covered by any of the online databases.

The search consisted of myriad permutations of relevant keywords – air pollutants, bathing beaches, birth defects, cancer, community health, composting, congenital, dental waste, disposal, gastroenteritis, hazardous waste, health, human, incineration, Incinerator, infection, land fill, landfill, medical waste, occupational, occupational health, public health, recreation, recycling, refuse disposal, sanitary engineering, sea, sea bathing, seawater, sewage, waste, waste disposal, fluid, waste management, waste treatment, water pollution.

In any search of an online database, it is easy to miss relevant papers because of the way the papers are indexed. There are many ways to index each type of waste disposal method and there are many health impacts associated with waste. For example, many of the US papers about hazardous waste sites did not include the subject heading ‘landfill’ while some papers about waste incinerators did not have the subject heading ‘incineration’. ‘Health’ and ‘health impact’ are not useful search terms on Medline. No search strategy could be found that could easily differentiate between studies about health hazards and health impacts. Although laborious, the most reliable way to find most of the papers on any of the online databases was by checking the titles of the thousands of papers retrieved on a general search for waste or hazardous waste.

The most comprehensive way of finding relevant documents is by hand searching particular journals, by checking the reference sections of review papers, and by contacting agencies and researchers who collect this material.

A1.4  The database

References were added to a Procite database and categorised according to a rough classification scheme developed for this project. All were coded by type of waste disposal method and by type of document, i.e. primary study, discussion paper or review. Reviews summarise a number of primary studies and draw conclusions. Discussion papers summarise or discuss the topic and put it into perspective but do not analyse primary studies. Primary studies were coded according to whether it was a study of a health hazard or of a health impact. Details of the classification scheme and keywords used to construct the database are available from L Saffron, or the SWPHO.

 

A1.5  A summary of the number and types of records

The number and types of records are shown in Table A below. This table does not include the following:

 

•        Types of document – reviews, discussion papers and primary studies on health hazards

•        Types of waste – radioactive waste, hazardous waste, clinical waste, agricultural waste, mining waste, etc

•        Specific hazards – dioxins, arsenic, PCBs, etc

•        Issues in waste management – waste disposal, waste collection, risk perception, risk communication, planning,  waste local plans, etc.

 

Table A: Number and types of studies identified (correct as of May 2002)