American Journal of Public Health  [Printer-friendly version]
September 1, 2001


[Rachel's introduction: For more than 100 years the main goal of
public health has been to prevent disease and injury, and to foster
conditions in which people can be healthy. Unfortunately, in 1970,
the U.S. chose to create a new bureaucracy to "protect the
environment" -- thus dividing "environmentalists" from the public
health community. Now environmentalists are adopting the goal of
preventing harm, so perhaps the artificial barrier between
environmental protection and public health can disappear, natural
allies can find each other, and new partnerships can blossom.]

By David Kriebel and Joel Tickner**


The precautionary principle has provoked a spirited debate among
environmentalists worldwide, but it is equally relevant to public
health and shares much with primary prevention. Its central components
are (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.

Precaution is relevant to public health, because it can help to
prevent unintended consequences of well-intentioned public health
interventions by ensuring a more thorough assessment of the problems
and proposed solutions. It can also be a positive force for
change.Three aspects are stressed: promoting the search for safer
technologies, encouraging greater democracy and openness in public
health policy, and stimulating reevaluation of the methods of public
health science.

In March, 1999, the Los Angeles Unified School District, the nation's
largest school district, announced a new policy on use of pesticides
in its school buildings. The district committed to a policy of
integrated pest management, giving priority to nonchemical approaches
to pest control, and set a long-term goal of eliminating all chemical
controls. In establishing this policy, the school district invoked the
precautionary principle, saying:

The Precautionary Principle is the long-term objective of the
District. The principle recognizes that:

1. No pesticide product is free from risk or threat to human health,

2. Industrial producers should be required to prove that their
pesticide products demonstrate an absence of [human health risks]
rather than requiring that the government or the public prove that
human health is being harmed.[1]

By stating a set of basic tenets (all pesticides are potentially
harmful, and nonchemical methods shall be preferred) and a long-term
objective ("to provide for the safest and lowest risk approach to
control pest problems while protecting people, the environment, and
property"), the policy stimulates the search for safer alternatives
without tying the hands of the district when no alternative to a
pesticide can be found. The policy is also significant for what it
does not include: there is no list of banned substances, nor a
stipulation of an "acceptable" level of risk. Whether or not one
agrees with this approach to pesticide management (we do), it seems
clear that the school district's invocation of the precautionary
principle raises important issues for public health scientists and

In this commentary, we briefly describe the key elements of the
precautionary principle, emphasizing several aspects important to
public health. Our perspective is informed by a university-community
collaborative effort to refine the meaning of the precautionary
principle and develop strategies for applying it to environmental
health policy.[2,3] We argue that the precautionary principle is good
for public health because it promotes the search for safer
technologies, encourages greater democracy and openness in public
health policy, and stimulates reevaluation of the methods of public
health science.


The definition of the precautionary principle developed for the Rio
Declaration of 1992 is often cited,[4] and the 1998 Wingspread
Statement contains similar language:

"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."[5]
The statement also lists 4 central components of the 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.

The term "precautionary principle" was introduced into English as a
translation of the German word Vorsorgeprinzip. An alternative
translation might have been "foresight principle," which carries a
connotation of anticipatory action -- a positive, active idea --
rather than precaution, which to many sounds negative. In German
environmental policy, the Vorsorgeprinzip stimulates social planning
for innovation, sustainability, and job creation.[6]

In the United States, the precautionary principle is being promoted by
environmental and public health advocates.[3] To these groups, US
environmental policy often seems to be more reactionary than
precautionary, requiring a high degree of certainty of harm before
preventive action is taken and emphasizing management of risks rather
than prevention. The precautionary principle is viewed as an
opportunity to shift the terms of environmental debates by calling for
preventive action even when there is uncertainty (but with credible
evidence of potentially significant impacts), by shifting the burden
of monitoring and hazard assessment onto those who propose potentially
hazardous policies and by emphasizing alternatives and democracy.[5]

The American Public Health Association recently passed a resolution
reaffirming its support of the principle and urging its application in
the protection of children's health from environmental hazards.[7]
Strong support for precaution is also found in the environmental
policies of the European Union.[8]

The precautionary principle has been advocated for public health
because of the importance of anticipating unintended health
consequences of well-intentioned public health interventions.[9]
Seeking to avoid creating new problems while solving existing ones is
an important aspect of the precautionary principle, but it is not the
only way in which precaution can benefit public health.


The identification of safer alternatives and opportunities for
prevention is central to the precautionary principle. Too frequently,
policymakers ask the question "How much risk does this activity pose,
and is it significant?" or "What level of risk is acceptable?" These
questions, deeply ingrained in the regulatory approaches of many
government agencies, tend to focus on the quantification of potential
hazards rather than the prevention of pollution.[10-12] They often
provoke a sharp debate about whether the risk has been characterized
accurately. When public health advocates and environmentalists enter
into this debate, they may inadvertently be ceding the most powerful
position, that of questioning whether the hazardous substance or
intervention is needed at all.

A different, and potentially more precautionary, way to think about
uncertain risks is to begin from a different set of questions: Is the
proposed activity needed, and if so, how much contamination can be
avoided while still achieving societal goals? and Are there
alternatives to this activity that clearly avoid hazards? For example,
chlorinated solvents fulfill a cleaning function that can often be
accomplished by aqueous solutions. This shift in perspective requires
a set of skills not always found in regulatory agencies -- technology
and product design, full-cost accounting and other management systems.
It also requires the broadest possible perspective on the potential
unintended consequences of policy choices.

A variety of methodologies exist with which to evaluate policy
alternatives and identify potential unintended consequences. Tradeoff
analysis has been proposed as an alternative to traditional cost-
benefit analysis and risk assessment; in trade-off analysis, the full
range of risks and benefits of competing technology options are
assessed without the requirement to translate the potential impacts
into a single quantitative figure.[13] Health impact assessments
provide a means to detect the negative health implications of non-
health-related governmental policies.[14] Work-environment impact
assessments can be used to identify ways in which an intervention in
the work environment may result in unanticipated health risks to
workers,[15] and the Pollution Prevention Options Analysis System
provides a comprehensive semiquantitative approach to comparing and
evaluating the potential adverse effects of technologies designed to
reduce chemical use and waste.[16]

Shifting the questions that frame the problem reorients the focus of
environmental policy from quantification of risks to analysis of
solutions and thus permits a broader examination of all the available
evidence on hazard, exposure, uncertainty, and alternatives. The
precautionary principle is a means of saying yes to innovative,
cleaner technologies (although critics have argued that it will only
lead to stopping new technologies). A thorough alternatives assessment
may identify needs for cleaner technologies, which in turn can inform
the planning of sustainable economic development activity.[11]

Quantitative risk assessment plays a central role in environmental
health policy in the United States. Weighing policy alternatives will
inevitably involve assessing and comparing risks, but the
determination of whether a risk is too big depends in part on whether
there are alternatives to reduce that risk. Availability of a safer
alternative can obviate the need for a costly, contentious, and
potentially misleading quantitative risk assessment.

The decision to ban the use of certain phthalate plasticizers in toys
provides an illustration. The Danish Environment Agency justified this
action with the following reasoning: There is evidence of children's
exposure and evidence of toxicity to animals; children are
particularly susceptible to many toxic substances; alternative
materials exist; and the product serves no necessary function. The
agency concluded that the plasticizers should not be used in toys (L.
Seedorf, MS, Director, Chemicals Division, Danish Environmental
Protection Agency, oral communication, May, 1999). The US Consumer
Product Safety Commission reached a similar decision, but only after a
costly, time-consuming quantitative risk assessment. The commission
concluded that given uncertainties in the size of the risk,
manufacturers should voluntarily remove these substances from
toys.[17] In the end the outcomes were the same, but the decision-
making approach and the costs to the public were quite different.

Foresight should involve setting long-term goals, a practice that is
fairly common in public health. Examples are the smallpox eradication
campaign, the US Public Health Service Healthy People 2010 priorities,
and national nutrition goals. Goal setting focuses not on what future
events are likely to happen but rather on how desirable future
outcomes can be obtained.[18] Once established, goals help to focus
attention on the development of policies and measures to achieve goals
while minimizing social disruption and unintended consequences.

With regard to hazardous substances, goals could include reducing
exposures to such substances, reducing production of hazards (e.g.,
phasing out the most hazardous chemicals), and reducing the incidence
of environmentally related diseases. Another suggested goal is to
reduce general population body burdens of broad classes of potentially
toxic substances by 5% to 10%.[19] Such an effort is likely per year.
to have a positive health impact, even though it may never be possible
to understand all of the ways in which mixtures of low concentrations
of chemicals may affect health.


Participation and transparency are essential components of a more
precautionary approach to public health decision making. Fiorino has
identified several reasons for democratizing environmental decision
making. First, because nonexperts think more broadly and are not bound
by disciplinary constraints, they see problems, issues, and solutions
that experts miss. Second, lay judgments reflect a sensitivity to
social and political values and common sense that experts' models do
not acknowledge. Third, the lay public may be better than experts at
accommodating uncertainty and correcting errors.[20] Openness brings
different perspectives, which may reduce the danger of an unintended
consequence. Also, the weighing of alternative policies should include
many points of view, because the benefits and costs of public health
and environmental policy choices may accrue to different groups.

When there is much uncertainty about alternative courses of action, it
is risky for experts to decide without input from affected
communities. The usual strategy is to attempt to present the options
as clear and the science as convincing. However, a long series of
public health and environmental crises that were apparently unforeseen
by scientists have undermined public confidence, making it more
difficult for simple reassurances to be effective. The list includes
the Three Mile Island and Chernobyl nuclear accidents, Love Canal, the
destruction of the ozone layer, and global warming. An increasingly
educated citizenry has begun to challenge the apparent confidence of
the experts. Add to this the successful campaigns of AIDS activists
and breast cancer survivors to participate in the planning of health
research, and it appears to be time to fundamentally change the way
that the public participates in the use of public health science.

Broader public participation processes may increase the quality,
legitimacy, and accountability of complex decisions. Given the public
nature of environmental decisions (which involve highly uncertain,
contested values), more effective processes for involving affected
communities could increase trust in government. Such processes must be
both fair and competent, meaning that they allow all those who want to
participate to have substantive access to the decision-making process
from the beginning and that they provide financial and technical
resources so citizens can participate on equal terms with experts.21
In addition, there must be clearly defined mechanisms by which citizen
input is fed into the policymaking process.

A long-term educational strategy to increase the public's
understanding of the strengths and limits of scientific evidence is
needed as part of increasing public participation. The Danish Board of
Technology has been experimenting for several years with innovative
forms of decision making on broad technology policy decisions. These
"consensus conferences" involve lay panels trained in the science and
other aspects of a contemporary concern, resulting in a focused
dialogue between the general public and experts. To date, more than 20
such conferences have been held in Denmark, informing government
policy on topics including genetically modified foods, the human
genome project, and air pollution.[22]


Environmental scientists study highly complex, poorly understood
systems, in which causal links between exposures and disease are
difficult to quantify. In this uncertain terrain, what are the
appropriate standards of evidence for science to inform public health
policy? The answer must be tailored to the task. We believe that there
are ways in which the methods of scientific inquiry often implicitly
impede precautionary action, making it more difficult for policymakers
to take action in the face of uncertainty.[2] Often, scientific
research focuses on narrowly defined quantifiable aspects of a problem
while the reality is more complex, requiring systems-level thinking
and interdisciplinary research methods.

Public health scientists may be able to assist in the cause of
precaution by choosing research methods, well within the bounds of
good practice, that would be more helpful to policymakers faced with
high-stakes decisions and scientific uncertainty. For example, more
and better investigation and communication of uncertainties (what we
know, what we do not know, and what we cannot know) in study results
will assist a more open decision-making process. Public health
scientists could also use qualitative methods more effectively to
characterize the complexities of the populations, communities, and
ecosystems from which quantitative results are drawn.

Finally, the precautionary principle should challenge scientists to
explore new areas of research -- interactions, cumulative effects, and
effects on different levels of systems (individuals, families,
communities, nations) -- and new collaborations between disciplines
and scientists and the lay public. Multidisciplinary teams will be
more likely to develop hypotheses that lead to insights not possible
from narrow disciplinary viewpoints, as well as to identify data that
may not be accessible to one particular group. The development of the
environmental endocrine disruption hypothesis provides one

The precautionary principle represents a call to reevaluate the ways
in which science informs policy, and in particular the ways in which
scientific uncertainty should be handled. Scientific research plays an
essential role in evaluating the costs, risks, and benefits of
proposed public health policies, but the scientific data are often
limited by large areas of uncertainty. In these gray areas, activities
that potentially threaten public health are often allowed to continue
because the norms of traditional science demand high confidence to
reject null hypotheses and so detect harmful effects. This scientific
conservatism is often interpreted as favoring the promoters of a
potentially harmful technology or activity when the science does not
produce overwhelming evidence of harm. Being "conservative" in science
is not the same as being precautionary.

When there is substantial scientific uncertainty about the risks and
benefits of a proposed activity, policy decisions should be made in a
way that errs on the side of caution with respect to the environment
and the health of the public.[2]


The precautionary principle has been criticized for being overly
vague.[24,25] To some extent the critics are correct, but much work is
now under way to define what precaution means in practice and how it
can improve decision making regarding uncertain, complex
hazards.[2,26,27] This is an opportunity for the public health
community to affect the ways in which precaution is defined in
practice. At the same time, there is a risk that proponents of the
principle will be held to an unrealistically high standard -- an
assumption that all public health problems should somehow be resolved
through the application of precaution. Where science and politics
collide, there will always be ambiguity and contention, and it seems
unreasonable to expect any single new idea to sweep these away
entirely. We should be careful not to overuse the precautionary
principle, particularly when there is clear evidence that damage has
been done or there is no reasonable evidence to suspect a risk to
public health.

If the precautionary principle represents a desirable goal in public
health, one may ask, What is the "not sufficiently precautionary
principle" on which policies are currently based? Too often, we
believe, public health and environmental policies are based on a
principle of reaction rather than precaution. Government regulatory
agencies are often put in the position of having to wait until
evidence of harm is established beyond all reasonable doubt before
they can act to prevent harm. A shift from reaction to precaution is
entirely consistent with the core values of public health practice. We
believe that public health officials, researchers, and advocates
should embrace the precautionary principle as an opportunity to
reinvigorate the great preventive tradition of public health action in
the face of uncertainty.

About the Authors

The authors are with the Lowell Center for Sustainable Production,
Department of Work Environment, University of Massachusetts, Lowell.

Requests for reprints should be sent to David Kriebel, ScD, Department
of Work Environment, University of Massachusetts Lowel, 1 University
Ave, Lowell, MA 01854 (e-mail:

This commentary was accepted March 29, 2001.


This work was supported in part by grants from the John Merck Fund,
the Jessie B. Cox Charitable Trust, the New York Community Trust, the
V. Kann Rasmussen Foundation, and the Mitchell Kapor Foundation.

The Science and Precaution Working Group participated in discussions
that helped to define and clarify our understanding of the
precautionary principle. We thank Dr. Margaret Quinn for many helpful
comments. Dr. Carlos Eduardo Siqueira suggested that it might be
useful to define reaction as the status quo principle impeding


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