Occupational and Environmental Medicine, September 3, 2007


[Rachel's introduction: This is the clearest introduction to the precautionary principle that we have ever seen. It contrasts the precautionary approach with the way decisions are currently made in the U.S. -- the reactionary principle.]

By David Kriebel

Martuzzi's commentary on the precautionary principle is welcome and timely.[1] I will make a few largely supportive comments while perhaps anticipating and addressing some concerns that readers may have.

The 1998 Wingspread consensus statement characterised the precautionary principle this way: "when an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically".[2] The statement went on to list four central components of the precautionary principle:

1. taking preventive action in the face of uncertainty;

2. shifting the burden of proof to the proponents of an activity;

3. exploring a wide range of alternatives to possibly harmful actions; and

4. increasing public participation in decision-making.

A skeptical reader may ask: isn't this just a fancy new name for what any responsible public health scientist has always done?

On the contrary, precaution brings important new insights into occupational and environmental health policy and the science which informs it. To illustrate this, it may be useful to give a name to the policy framework in which occupational and environmental health research currently operates: it is the reactionary principle.[3] Under this system, anyone is free to introduce a new hazard into the environment, and governments must wait until an overwhelming body of evidence is accumulated before intervening. Each new regulatory action is challenged with the objective of slowing down or stopping public oversight of production and distribution of chemicals and technologies. We can see reactionary principle inaction in the unconscionable delays in regulating a long list of hazards whose risks were clear long before effective actions were taken to control them: asbestos, benzene, dioxins and PCBs.[4] While these are "old" hazards, a reactionary approach is evident as well in many current controversies in our field, including the potential health risks from: hexavalent chromium,[5] artificial butter flavouring,[6] and the antimicrobial agent triclosan.[7]

The reactionary principle operates through these key components (referring back to the list for precaution may be useful):

1. requiring incontrovertible evidence of harm for each hazard before taking preventive action;

2. placing the burden on the public (or government agencies) to show that each chemical, material or technology is harmful;

3. not considering potential health and environmental impacts when designing new materials and technologies; and

4. discouraging public participation in decision-making about control of hazards and introduction of new technologies.

Perhaps framing the status quo this way helps the reader to see the kinds of changes in the science/policy interface which Martuzzi and others are advocating.

What can be done to shift from reaction to precaution? One important step would be to reduce the corrupting influence of economic interests on the evidentiary base of environmental health regulation.[8] Recent evidence documents how some corporations seek to impede regulation through the intentional manufacturing of uncertainty about the hazardousness of their products.[9] Clearly, removing conflicts of interest and intentional manipulation of data would make it easier to act in a more precautionary way. But there is more that we can do as responsible public health scientists.[10] I will mention two examples.

Causal inference is a critical step in the recognition and control of hazards, and epidemiologists play an important role. We are taught to distinguish causation from correlation using guidelines like those of Bradford Hill.[11] A precautionary approach would emphasise that this judgement is not purely scientific; our public health responsibility requires that we ask "when do we know enough to act as if something is causal?" This will depend not only on the strength of evidence but also on the availability of alternative ways of achieving the same social good (how essential are artificial butter flavour and antimicrobial socks?), and on the consequences of inaction or acting in error.

When we continue to study the same known hazards while thousands of widely dispersed chemicals remain without basic toxicology, we may inadvertently be promoting inaction by implying that more must be learned before action can be taken. To avoid this, environmental and occupational health scientists can learn from colleagues in climate science. There is now a (nearly) global consensus that human impact on climate is likely to have serious negative consequences.[12] Climate scientists have managed to communicate an important yet complex message: much more needs to be learned about climate AND we know enough that we cannot remain silent about the need for action. These scientists have stepped out of their roles as data gatherers and analysts, and spoken publicly about the need for action.

While striving to do the best science possible, we should be aware of the potential impact of our research and of our social responsibility to do science that protects human health and the environment. The precautionary principle is useful in focusing attention on the need for this balance.


I am grateful to Margaret Quinn and Joel Tickner for comments and suggestions.


Competing interests: None.


1. Martuzzi M. The precautionary principle: in action for public health. Occup Environ Med 2007;64:569-70.

2. Raffensperger C, Tickner J, eds. Protecting public health and the environment: implementing the precautionary principle. Washington, DC: Island Press, 1999.

3. Kriebel D, Tickner J. Reenergizing public health through precaution. Am J Public Health 2001;91:1351-5.

4. European Environment Agency. Late lessons from early warnings: the precautionary principle 1896-2000. Copenhagen: European Environment Agency, 2001.

5. Michaels D, Monforton C, Lurie P. Selected science: an industry campaign to undermine an OSHA hexavalent chromium standard. Environ Health 2006;5:5.

6. Kreiss K, Gomaa A, Kullman G, et al. Clinical bronchiolitis obliterans in workers at a microwave-popcorn plant. N Engl J Med 2002;347:330-8.

7. Adolfsson-Erici M, Pettersson M, Parkkonen J, et al. Triclosan, a commonly used bactericide found in human milk and in the aquatic environment in Sweden. Chemosphere 2002;46:1485-9.

8. Clapp R, Hoppin P, Kriebel D. Erosion of the integrity of public health science in the USA. Occup Environ Med 2006;63:367-68.

9. Michaels D. Doubt is their product, industry groups are fighting government regulation by fomenting scientific uncertainty. Sci Am 2005;29:96-101.

10. Kriebel D, Tickner J, Epstein P, et al. The precautionary principle in environmental science. Environ Health Perspect 2001;109:871-6.

11. Bradford Hill A. The environment and disease: association or causation? Proc R Soc Med 1965;58:295-300.

12. Houghton J T, Ding Y, Griggs D J, et al, eds. Climate change 2001: The scientific basis. Published for the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press, 2001.