When an incident involving pesticides
occurs, it is important at the outset for those
who think they may have been exposed to record
what they have been exposed to, under what
circumstances, at what levels and with what
adverse effects. This type of information may be
unavailable or very difficult to obtain. The
problems of investigating chemical exposures and
the nature of the current system for generating
and evaluating information about all chemicals
including pesticides has led to a crisis of
public confidence in a number of cases(1). The
process whereby environmental pollution
investigations have been communicated by
professionals to communities has also often been
flawed as with the Camelford case* and many
Finding out about which pesticide has affected you or may affect you in the future, how much and in what form is vital information. It may provide essential evidence for a clinical diagnosis of your problem. It may also be of use to check whether there are long term and possibly chronic effects from an exposure. Studies of these long term effects are called epidemiological studies. Illness (morbidity) and death (mortality) are investigated, where possible, for small or large populations.
Community/lay/worker epidemiology may provide a better way forward for employees and those in communities to investigate the hazards around them either for themselves or in conjunction with sympathetic professionals(2). The approach is proving increasingly effective among employees in workplaces(3). Lay epidemiology has been defined as "the process by which lay persons gather statistics and other information and also direct and marshal the knowledge and resources of experts in order to understand the epidemiology of disease."(4) For example in the US, lay investigations of childhood leukaemia clusters near a chemical plant at Woburn, Massachusetts were carried out. The plant produced pesticides and other chemicals. Professional epidemiologists and lay people involved in the investigations had different views on collecting, interpreting and using data(5). The epidemiologists tended to look only at data they thought 'scientific' and discarded other form of data collected by communities; they used only traditional methods of analysis and discounted less orthodox methods; they relied on 'statistical significance' as the key guide to results and ignored data that was significant but not statistically so.
Lay or community-based occupational and environmental epidemiology should be 'participative, non-expert; subjective; and collective in nature'(6). Epidemiologists should be prepared, in some instances, to work for rather than on communities. Effectively, epidemiologists should help communities do their own epidemiology(7).
This type of approach, sometimes called 'participatory research', involves:
approach is not without problems including
methodological ones, the resistance of
professional scientists to share with the public,
the lack of funds and all the political issues of
the status of professionals and the concerns of
state bodies to control or restrict access to
data. Nevertheless, community or lay epidemiology
is still worth pursuing and has been successful
in Scandinavia and even in parts of the UK as
well as in the US.
The WHO European Charter on Environment and Health provides base line for community and workplace action in the UK
you need to know for lay/community
The sort of information you will n
eed to relate to includes:*
1 What pesticides were being used? Names and data sheets of the pesticide?
2 Who manufactured or formulated them?
3 What solvents and adjuvants were the pesticide active ingredient used with?
4 How were the pesticides applied or released. If applied, with what sort of sprayers, foggers, granules or applicators? What was the condition of the applicators? What amounts were used? If released accidentally, in what form were the pesticides when released? How much was released? Where did the released pesticides initially go (atmosphere, soil or water)?
5 What were the weather conditions at the time of exposure: windy, wet, warm, cold, etc. What was the prevailing direction of wind if drift was likely, or the direction of the stream or current if in lake or sea?
* The Pesticides Trust [now PAN UK] has drawn up an incident form to help ensure all information is covered-available on request
Several years ago, the International Federation of Plantation and Agricultural Workers mooted the idea of a pesticide passport to be held by every agricultural worker listing the type, date, amount and exposure of that worker to pesticides. This has finally been recognised by professional epidemiologists as a useful means to study exposures to pesticides and their effects. Communities should adopt a similar idea with either 'a Community Pollution Passport' or passports for individuals in a community. The sort of information listed above should all be included on such a passport.
with conventional epidemiology for pesticides
Epidemiology explores the occurrence and distribution of diseases and deaths in populations: the populations may be very large or small, and based on small areas. The larger the populations studies, the greater the weight often given to these because of their statistical significance. However, large studies may also dilute the effects of exposures on a small group and fail to show a serious adverse effect on a small group (or cluster) of workers or a small population. Epidemiology shows correlations between various factors. It does not show causes of disease for individuals. This is why in pesticide health and safety, toxicology and occupational hygiene are the key preventative scientific disciplines. Epidemiology checks that the other disciplines are right and working.
There have been enormous problems with epidemiology. This partly relates to the difficulty of getting good data to assess what exposures people may have had to toxic agents and good data on what specific illnesses they have contracted. Sometimes exposure data may not exist and sometimes the medical and scientific professions may not be able diagnose certain effects of exposure to pesticides or may disagree about the effective measures and indicators of exposures.
Sometimes there may be confounding factors in studies which will mean results are not useful: for instance tobacco smoking, gender and age are obvious confounders. Epidemiological studies will attempt to allow for such effects and where necessary adjust figures of diseases and deaths accordingly. There may also be problems with identifying a control group with which to compare the exposed populations. This has happened frequently with epidemiological studies of people exposed to pesticides where finding a control group with no or limited exposure may be difficult. This is because most people almost anywhere in the world will have some exposure through water, food or atmosphere to pesticides. Recent studies of sheep dipping also ran into problems when trying to identify non-exposed rural workers as a control group.
Other problems come from what have been termed 'negative epidemiological studies'. 'Negative' epidemiology or rather 'non positive studies' in this context means the presentation of results as evidence that no risks exist from a potential hazard when the studies are not large and not sensitive enough to be more than inconclusive and limited(10). This relates to the problem of studies which are unable to show whether a correlation exists or not, because of methodological problems or small populations or whatever. However, 'negative epidemiological studies' have sometimes been used to argue that pesticides and other environmental hazards are not hazards to the public at all. Yet these studies cannot demonstrate either effects or non-effects and they demonstrate the truism: the absence of evidence is not evidence of absence.
The need to involve workforces in workplace health research has been widely acknowledged(11) but good practice in the field is still lacking. Such an approach would ensure that epidemiology is located in the community and workplace in ways that have rarely happened in the recent past: to the detriment of both community and epidemiology(12). The approach would involve the public or specific communities in an important educational and information process and help them identify serious hazards and risks rather than spurious ones. The very process of involvement would ensure that there was greater public confidence in both studies and results than has hitherto been the case.
to do to start a lay, worker or community epidemiology study
1 Collect as much data as you can about the incident you have been involved in.
2 Speak to any sympathetic professionals you can find who will support in principle the idea of a lay epidemiological study.
Such people may include:
Explain your concerns and refer to the
WHO Charter on Environmental and Health
which states that individuals should be
consulted about those environmental
factors affecting their health.
right of citizens and workers to know about the
hazards they have been or may be exposed to and
the risks following from those hazards should be
fundamental in any democratic society. The right
may create problems relating to doubt and worry
about future health risks but workers should be
informed about hazards affecting her or him(13).
There is also the problem of the extent to which epidemiology has been interpreted negatively on the basis of restricted data. Workplace and environmental health problems have been neglected by some scientists and/or ignored by governments. This approach has been adopted on several occasions by powerful national organisations-commercial, industrial and governmental-in support of policies which may damage or at the least provide no indication of benefit to the public health. The tobacco and the asbestos industries have been notable in the past for selecting, excluding or suppressing epidemiological and toxicological data so that the health hazards attached to their industries or products have been neglected or distorted.
"Any people exposed to a small risk may generate a large total of cases, albeit with no conspicuous risk to any one person or group'(14). The tendency of some epidemiologists and medical practitioners in the past to ignore or minimise low level environmental health risks to large populations from such things as pesticides may be corrected partly by the adoption of lay epidemiology. In the US lay epidemiology has shown greater concern about such low level risks than some professional epidemiologists(15).
The public are often unimpressed by epidemiological analyses which reduce the impact of hazards on individuals to very low statistical risks when perceptions of risk vary so much. Lay epidemiology could therefore have an important role to play in monitoring 'non-positive epidemiological studies', flagging up concerns and worries about hazards which could be investigated at an early stage, possibly to be discounted or put in context as insignificant risks at a later date. This will help to ensure firstly that the possibilities of low level exposures leading to unforeseen ill-health are not forgotten by professionals and secondly that public panics about health fears are reduced when public and professional groups together find them to be unfounded.
1. Watterson, A.E., Chemical Hazards and Public Confidence, Lancet 1993, 342:131-132.
2. Watterson, A.E., Whither lay epidemiology in occupational and environmental health? Journal of Public Health Medicine, 1994, 270-274.
3. Workers Health International Newsletter (1994/5), When it comes to their health, workers always know best, 42:10-11.
4. Brown P.(ed), Perspectives in Medical Sociology. Belmont, California, Wadsworth, 1989.
5. Brown P., Popular Epidemiology and Toxic Waste contamination: lay and professional ways of knowing, Journal of Health and Social Behaviour 1992, 33:267-281.
6. Scott-Samuel A., Building the new public health: a public health alliance and a new epidemiology in Martin, C. and McQueen, D., Readings for a New Public Health, Edinburgh University Press, 1989, 29-44.
8. Loewenson, R., Laurell, C. and Hogstedt, C., Participatory approaches in occupational health research, 1994. National Institute of Occupational Health. Sweden World Health Organisation, European Charter on Environment and Health. Copenhagen, WHO, 1989.
9. World Health Organisation, Environment and Health: The European Charter and Commentary, Copenhagen, WHO, 1994, 1990:68 WHIN.
10. Hernberg S. Introduction to Occupational Epidemiology. Michigan: Lewis Publishers, 1992.
11. Olsen, J., Merletti, F., Snashall, D. and Vuylsteek, K. Searching for the Causes of Work-related Diseases, Oxford University Press, Oxford, 1991.
12. Burrage H. Epidemiology and Community Health: a strained connection. Soc Sci Med 1987, 25:895-903.
13. Beritic T. Workers at Risk: the right to know. Lancet 1993, 341:933-934.
14. Rose G. Environmental health: problems and prospects. Journal Roy Coll Physicians 1991, 25:48-52.
15. Op. cit. 5.
Dr. Andrew Watterson is head of the Department of Health and Continuing Professional Studies and Director of the Centre for Occupational and Environmental Health Policy Research at De Montfort University, Leicester, UK.
* The Camelford case in the South West of England involved a water pollution incident. Many of those exposed found major problems with the conduct of the investigation, the speed with which the incident was officially investigated, the disclosure of information and other matters.
article first appeared in Pesticides News No. 30,
December 1995, pages 8-9]