Manuscript (revised) submitted to Annual Review of Public Health, Vol. 25 (2004)
Implications of the precautionary principle
for primary prevention and research
Philippe Grandjean
Institute of Public Health, University of Southern Denmark, Odense, Denmark; and Department
of Environmental Health, Harvard School of Public Health, Boston, MA, USA
(e-mail: pgrand@hsph.harvard.edu)
Running title: Implications of precaution
Key words: Decision making
Environmental pollution
Research design
Risk assessment
Toxicity
Address for correspondence: Philippe Grandjean, Winslowparken 17, 5000 Odense, Denmark
(phone: +45-6550.3769, fax: +45-6591.1458)
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Contents
Abstract
3
Introduction
4
History of precaution
5
Environmental disease causation
6
Complexities and shortcomings of risk assessment
8
Types of incertitude
10
Defining the Precautionary Principle
11
Critiques of the Precautionary Principle
13
Differences between the United States and Europe
16
The systemic approach to decision-making
17
A precautionary research paradigm
20
Statistical issues of precaution
23
The future of precaution
25
Acknowledgments
27
Literature cited
27
Figure legends
Tables
Figures
Implications of precaution (Grandjean)
Abstract
The Precautionary Principle (PP) is an extension of the public-health presage that prevention is
better than cure. The PP has recently achieved new relevance in regard to serious, but uncertain
threats to human health and the environment, and has now entered national and international
legislation. However, frameworks for its unambiguous application in practice are yet to be
designed. They will depend on legal and cultural circumstances and are likely to involve
pluralities of perspectives and stakeholder participation. The rules for causal reasoning and dosedependence need to be addressed and may be conveniently expressed in accordance with
probability theory. Although the PP will allow action before convincing evidence is secured, it is
not science averse. However, it provides an occasion to review environmental health research
strategies, methodologies, and research reporting traditions. From this perspective, current
research is afflicted by important biases and insufficient focus on major environmental health
problems.
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Introduction
Policy decisions in public health must address some amount of uncertainty when balancing likely
benefits and estimated costs. Although new insight will allow better appreciation of difficult
issues, such as those occurring in environmental and occupational health, an expanded
perspective may also enlarge the list of problems that need to be managed. Ignoring the problems
carries its own costs (as deferring a decision is a decision in itself). With environmental and other
public health problems becoming increasingly complex and international in scope, scientific
documentation alone rarely justifies simple solutions. Unfortunately, important environmental
and occupational hazards often become entangled in legalistic and regulatory combats that block
preventive measures.
As a counter-measure and partial solution to this impasse, the so-called precautionary
principle (PP) has been introduced. It supplements the traditional risk assessment that requires
extensive scientific evidence, because it applies to situations with important threats to human
health or the environment where the evidence is still only suggestive. Additionally, the PP
provides a procedure to obtain a better balance in public-health policy decisions and to
circumvent unrealistic demands for full scientific proof before preventive action is deemed to be
justified. The aim is to be more anticipatory in terms of health and dealing with unknowns. The
PP is now a mandatory consideration according to some national and international legislation.
While precaution is not new in public health, the formal application of the PP offers new
procedural opportunities that affect the ways in which policy decisions are arrived at and carried
out. This growing body of experience in interpreting and applying the PP, especially in legal
settings, is steadily adding to the operational definitions of the PP. As an important and partially
overlooked consequence, application of the PP will also have an impact on the types of scientific
knowledge and documentation that is needed for decision-making. These issues, therefore,
deserve attention by the public health community.
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History of precaution
Precaution is common sense and is crucial in all public health decisions. In general, prudence
would suggest that the benefits of any doubt should befall the patient. While firmly embedded in
common sense and ancient sayings (“in dubio, pro salus”), the most frequently mentioned and
perhaps overrated example from medical history is the removal of the handle on the Broad Street
water pump in London by John Snow (24). The intervention was clearly precautionary: it was
based on incomplete, yet credible evidence, and it prescribed a cost-effective preventive measure,
the success of which could then be monitored. Yet, other examples may be at least as important.
Gockel discovered in the late 17th century that the endemic colic in a wine-producing
district was due to the addition of lead to sweeten the taste of sour wine (22). Based on Gockel’s
recommendation, the Duke of Württemberg then prohibited this practice under the penalty of
death. However, as Gockel had not convincingly ruled out supposed competing causes, and
because lead compounds were thought to be useful as therapeutics, disbelieving scholars rejected
his conclusions.
In extending Gockel’s work, George Baker carried out a series of experiments that
provided further evidence; in this case, examining the Devonshire colic in a district of England
where lead-adulterated apple cider was produced (5). Baker recommended precaution in dealing
with this toxic metal, because ‘abundans cautela non nocet’ (excess safety precautions do not
harm). However, despite Gockel’s and Baker’s efforts, discussions on lead toxicity continued, and
clinical lead poisoning remained prevalent.
Numerous other environmental hazards were identified at a time when prevention would
have been precautionary, but the options were missed (24). Prominent examples were recently
reviewed in a monograph published by the European Environment Agency: asbestos, benzene,
bovine spongiform encephalopathy, diethylstilbestrol, growth promoting antimicrobials,
halocarbons that damage the ozone layer, methyl-tert-butyl ester (MTBE), polychlorinated
biphenyls, sulfur dioxide, and tributyltin (24). Vinyl chloride and alkyllead compounds are also
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considered important examples (48). Thus, the history of prevention clearly documents numerous
credible warnings that were not heeded. Table 1 shows the most important messages gained from
examining early warnings that were missed (24). In contrast, only few examples come to mind
where exaggerated prevention appears to have greatly exceeded the need (24). Among possible
examples are saccharin and acrylamide, but in both cases, corrective action was later introduced.
The modern PP has emerged from the German Vorsorgeprinzip that was introduced in a
social context during the 1930s and formally extended to environmental policy about 1970 as a
planning instrument (9). The ‘foresight’ was considered necessary to protect against hazards at an
early time before serious adverse effects occurred. Although not a literal translation, the so-called
precautionary principle was born and included in the first convention on the protection of the
North Sea, held in 1984. This was later to be followed by many other international agreements
(56, 62).
Environmental disease causation
A substantial part of the total burden of disease in industrialized countries has been attributed to
environmental factors, with the bulk of this amount affecting children and vulnerable groups,
such as the poor and women in reproductive age (65). A recent report from the U.S. National
Research Council estimated that a large portion of developmental disorders in children are caused
by environmental factors (53). Lead poisoning appears to be the most important environmental
risk factor in regard to children’s health (47). However, all estimates of this kind are approximate
and based on expert judgment from information on individual hazards, such as lead, that represent
only a small portion of the total exposure burden. Apart from our dependence upon a healthy
global ecology, environmental disease causation is therefore highly important from a public
health standpoint, but its true impact is bound to be seriously underestimated due to the lack of
documentation.
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Scientific information on the health effects of most industrial chemicals has been shown
to be either limited or nonexistent (59): Nearly three out of four (71%) of the sampled highpriority chemicals did not meet the minimum data requirements for health hazard screening set by
the Organisation for Economic Cooperation and Development (OECD) Chemicals Program. Of
the nearly 3,000 high production volume (HPV) chemicals, which are made or imported to the
U.S. at more than 1 million lbs/yr, only seven percent possessed a complete set of publicly
available screening data on their toxicity (71). This review also found that 43% of HPV chemicals
had no testing data on basic toxicity. Among 491 chemicals used by children and families in
consumer products, only 25% had full screening data (71). Furthermore, not all potential adverse
effects are included in the tests required by the authorities. For example, neurotoxicity tests (in
chicken) are normally required only for cholinesterase-inhibiting pesticides (2). Thus, even for
those chemicals that have been tested, limited information exists on how those substances can
influence human health at environmental levels of exposure.
A major reason for this unfortunate situation is the inappropriate allocation of
responsibilities, where regulatory authorities are usually in charge of the assessment instead of the
enterprises which produce, import, or use the substances; information on the use of substances
and exposure potentials is also difficult to access (14).
Important insight also derives from changes in exposure limits. For example, a critical
review of the toxicology data led the Center for Disease Control, in 1960, to decide on an action
level for the blood-lead concentration in children at 600 µg/liter (2.9 µmol/liter). As evidence on
lead toxicity accumulated, the limit was lowered; 30 years later, the action level had been
decreased to 100 µg/liter (0.5 µmol/liter) (13). In hindsight at least, enough information seemed
available much earlier to trigger the stricter actions. On the other hand, had new evidence not
emerged, the high levels acceptable in 1960 might have prevailed. This example suggests that
even exposure limits of today should be regarded as temporary approximations based on currently
available documentation.
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New information is scheduled to be forthcoming more rapidly than in the past. OECD
has coordinated an international effort to screen the HPV chemicals. Among ‘existing’ substances
(i.e., those that were marketed in Europe by September, 1981), about 30,000 are marketed in
volumes above 1 ton per year. The European Commission has now presented draft principles for
obtaining basic toxicological information on those of the chemicals about which little is known
(16). However, US authorities have protested against the proposal and threaten to contest this
requirement within the World Trade Organization (8, 32). Whatever the outcome of this dispute,
additional data will emerge, though only slowly and mainly focusing on limited aspects of socalled priority chemicals. Still, many uncertainties will prevail.
At the same time, anthropogenic changes in the environment are occurring at a greater
pace. Our improved understanding of the world is therefore lagging behind in determining the
risks to human health and the environment, and new knowledge will not eliminate uncertainty as
a permanent concern. If changes in decision-making are not instituted, remaining gaps in critical
knowledge will continue to block or may be used to block the efforts to reduce or eliminate
diseases that might be preventable by better management of environmental hazards.
Complexities and short-comings of risk assessment
During the last 25 years or so, risk assessment has been a successful, evidence-based approach to
management of environmental pollution (52). However, risk assessment, at least as currently
practiced, is most useful when scientific information is virtually complete. Human exposures are
modeled and the dose-response relationship is then used to calculate the risk associated with the
exposure (Fig. 1). Because of high ambitions for systematic priority-setting, with its frequent
links to cost-benefit analyses, risk assessment has become increasingly complicated. Scientific
desires of a full understanding the biology of environmental health have become a stumbling
block, because toxicological mechanisms of action were demanded as a prerequisite for risk
assessment (especially for carcinogens). One recent example is di(2-ethylhexyl)phthalate, where
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intense research has focused on identifying a reason why carcinogenicity in rodents should not
apply to humans (50). In response to this pressure, the International Agency for Research on
Cancer chose to downgrade the classification of this rodent carcinogen from possibly
carcinogenic to not classifiable (39).
Certain default settings have long been used in risk assessment for extrapolation from
laboratory animal studies and high-dose exposure to low doses and vulnerable human
populations. These procedures are now criticized for not being scientific, and have been said to be
‘hallowed’ only by long use and acceptance by a regulatory agency (6). Likewise, the monotone
dose-response curve has come under attack, e.g., because some observations suggested the
possible existence of so-called hormesis at low doses (11). Pragmatic application of linearized
dose-response relationships was challenged, because other models led to widely differing risk
assessments (20). Mathematical modeling, long employed as a useful tool, also appeared to be an
obstacle when the default conditions applied were realized to be of unknown validity (52). These
revelations were then followed by belligerent demands for objectivity in science (31).
While the validity of extrapolation from animal experiments was cast in doubt (10),
epidemiology received the harshest critique (67). Observational studies will always have
weaknesses, since exposures are not determined as a matter of experimental design. However,
sophisticated critiques by recognized experts have been used with the aim of disproving evidence
on environmental hazards, such as man-made mineral fibers (51). An international call for
guidelines on 'Good Epidemiological Practice' was thought by many to serve a useful educational
purpose. However, this ‘sound science’ movement was not an indigenous effort from within the
profession to improve the quality of scientific discourse. It turned out to be part of a sophisticated
public relations strategy controlled by industry executives and lawyers whose aim was to
manipulate the standards of scientific proof to serve the corporate interests of their clients (55).
Thus, strict interpretation of epidemiological rules had the purpose of dismissing
epidemiological findings that, for some reason, were unwelcome. This effort first targeted
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evidence on environmental tobacco smoke, but also dealt with other environmental contaminants.
As a result, the Chemical Manufacturers Association (later renamed American Chemical Council)
co-funded these efforts along with the Philip Morris Company (55). In this atmosphere, scientific
rigor became misunderstood as the unrealistic need to conduct controlled experiments with
statistically robust conclusions. Inconclusive studies were labeled “negative” and were thought to
represent “no risk” rather than “no information”.
Risk assessment also became a battling ground in regard to access to information.
Because evidence is the basis upon which the evaluation of risks must rely, suppression of
information occurred, as did withholding of evidence, lambasting of whistle-blowers, and
releasing of half-truths or untruths (45). For example, in determining occupational exposure
limits, and often maintaining them at inappropriately high levels, corporate representatives acted
as expert consultants to committees thought to be neutral (12).
The ongoing contentious scientific debates on minute scientific details, the incomplete
access to toxicology information, the associated challenges in the legal system, and the resulting
defensive reaction from regulatory authorities has led to “paralysis by analysis” (24, 66). Risk
assessment has therefore become part of the problem and not part of the solution.
Types of incertitude
The major problem in the standard risk assessment approach is uncertainty (37). “Incertitude”, as
a general term for all types of uncertainty, is a given in public health, as well as a key
characteristic of environmental health problems. Examples from past experiences show that
incertitude was not appropriately interpreted, with the result of unnecessary human suffering and
environmental degradation (24). Lack of scientific data is of course not the same as proof of harm
or the opposite, but this ignorance means that any conclusion about safety is unfounded. One
could question why 70% of chemicals marketed after 1981 (and about which adequate toxicology
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information is required before marketing) are considered hazardous, while only a few percent of
previously marketed chemicals are similarly labeled from available toxicity data.
Different heuristic taxonomies have been used to categorize the types of incertitude
involved. The simplest dimension of incertitude is so-called “risk”, which encompasses
variability due to factors such as imprecision and sampling error in the data base. Uncertainty (in
the narrow sense of the word) involves incomplete knowledge on the type of adverse effect, the
particular aspect of the exposure that may be harmful, the dose-response model, the impact of
combined exposures, and similar considerations that cannot be settled from current information.
Ignorance is considered when even less information is available, but may still be potentially
remedied by further research. The final aspect is indeterminacy, where the problem shows
dependence on multiple variables or chaotic properties that defy attempts to predict the outcome
(66).
Some forms of incertitude may be dealt with in risk assessment by including so-called
“uncertainty factors” (formerly called “safety factors”) (40). While a greater incertitude also leads
to the use of larger uncertainty factors, the incertitude in regard to the uncertainty factors also
increases. Therefore, this approach has important practical limitations and the PP appears like a
useful approach when knowledge is lacking (e.g., on the type of outcomes and also their
probabilities) (66).
Defining the precautionary principle
Given this complex background, it is hardly to be expected that a simple statement of a logical
principle will provide a key to resolving the conundrums of decision-making in environmental
health. Nonetheless, to counterbalance the imperfect solutions provided by traditional risk
assessment, statements have been phrased that indicate how precaution should be exerted.
Probably the most widely known definition is the one provided in the Rio declaration:
“Where there are threats of serious or irreversible damage, scientific uncertainty shall not be used
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to postpone cost-effective measures to prevent environmental degradation” (70). Other definitions
include stronger wordings, e.g., by leaving out that actions must be cost-effective, or by including
a reverse burden of proof. Thus, a group of experts formulated the Wingspread definition (73):
“When an activity raises threats of harm to the environment or human health, precautionary
measures should be taken even if some cause and effect relationships are not fully established
scientifically.” Also, in regard to the onus of proof, the statement reads: “In this context the
proponent of an activity, rather than the public, should bear the burden of proof.”
In the European Union, the PP is considered “a general rule of public policy action to be
used in situations of potentially serious or irreversible threats to health or to the environment,
where there is a need to act to reduce potential hazards before there is strong proof of harm,
taking into account the likely costs and benefits of action and inaction” (24). Table 2 summarizes
the most important aspects of the PP as used in Europe (i.e., that the application must be
proportional, non-discriminatory, comparable, cost-efficient, and subject to revision) (17).
As many as 19 different definitions have been put forward on various occasions (62).
They generally include four dimensions (3, 62): 1) the existence of a threat, 2) uncertainty about
its implications, 3) anticipatory action, and 4) a command to act. Fig. 2 shows how the PP may
lead to action against serious threats where uncertainty would not justify proper risk assessment.
Given that the PP is a culturally framed concept, the words “sometimes”, “if necessary”, and
“may” suggest space for negotiation for which procedural rules need to be established. In regard
to causal associations, similar distinctions are also important (e.g., between “beyond reasonable
doubt”, “preponderance of evidence”, “weight of the evidence”, “more likely than not”, and “a
definite possibility”). Still, differences between the definitions have been taken as an alleged
weakness of the PP and a sign of disagreement on the interpretation of the PP (61).
An exact definition of the PP must depend on the legal and cultural circumstances (25).
From a legal viewpoint, the PP is considered a guide to utilizing scientific evidence in decisionmaking contexts (19). Although such guides need specification and refinement before they can be
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used in a predictable way, the PP does not differ in this regard from other approaches to using
factual information such as in the law (19). Employing the PP may involve, for example,
alternatives assessment, full-cost assessment, and a participatory decision process. It may be
coupled with the right-to-know aspect, empowering the citizen to take action, and these aspects of
information access are probably most consequential in regard to legal ramifications (61). The
wording of the PP must also carefully consider the serious problem of state authority in the face
of scientific incertitude. The PP should be considered a policy tool to deal with scientific
uncertainty and ignorance, with the aim of deciding upon actions involving more research, a
preventive intervention, or both.
The PP can also be looked upon as an extension of risk assessment and, in accordance
with, for example, the “de minimis” approach used in regard to the so-called threshold of
toxicological concern (44). It represents a “negligible” cut-off point below which a hazard is
ignored (also a matter that is open to interpretation). As a precautionary decision, an Executive
Order from the US President required special emphasis on children’s environmental health, and
the subsequent Food Quality Protection Act allows the use of a 10-fold factor to secure that
children are not exposed to toxic amounts of pesticides and other pollutants (21). A similar
blanket approach has been used in the EU, where water contaminant concentrations must be
below a limit of 0.1µg/liter (the detection limit at the time) (1).
Critiques of the precautionary principle
It has been claimed that the PP results in huge expenses invested into risks that don’t exist,
because “...it is plainly irrational to fear risks the existence of which is conjectural...” (31). The
assertion is that the PP will result in unjustified costs that would be far better deployed improving
social welfare elsewhere.
On the same note, the concern is that the grandmotherly maxim of' “better safe than
sorry” will stop all innovation in society. The consequences of such exaggerated concerns with
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risks were examined in a “survey of 40 scientists”. Had the precautionary principle been allowed
to prevail in the past, the response was reportedly: no heart surgery or antibiotics, and hardly any
drugs at all; no airplanes, bicycles or high-voltage power grids; no pasteurization, pesticides or
biotechnology; no quantum mechanics; no wheel; no discovery of America. In short, their
message was: no risk, no gain (69).
However, as indicated above, the lack of information currently offers automatic rewards
to the producers who do not provide toxicological data. Furthermore, the PP may be a “speed
bump” in some cases, but is not an inevitable prediction that leads to an obstruction or a ban of
new technology or human enterprises in general. While science-based conjecture is not flawless,
at least the application of the PP aims at offering a better balance. The risk to human health and
the environment may otherwise be too great. One only has to think of the US chemist Thomas
Midgley, who first invented tetraethyllead as an octane-boosting gasoline additive and later on
invented chlorofluorocarbons. Midgley has been said to have had a greater impact on the
atmosphere than any other single organism in Earth history (49, p.111).
The harsh criticism of the EC communication claims that it is ill-defined, lacks checks
and balances, and omits evidentiary criteria for precaution (32). Given the dependence upon legal
circumstances and tradition, the weak or vague points must deserve careful scrutiny. While the PP
clearly prescribes a value judgment (which may be subjective), the same is true for risk
assessment (18, 52). It therefore seems that the PP is no more ambiguous than other decision rules
(62). Open and transparent procedures are necessary to prevent biased decisions, with regard to
the perceived level of evidence required for proof of causality. The specific procedures for
applying the PP must then be carefully worked out as appropriate for the legal and cultural setting
(19). Thus, the weaknesses in instrumental aspects should be considered temporary in regard to a
newly introduced legal principle. EC Court rulings are already providing assistance in this
development.
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A related but more general issue is whether the precautionary principle is at all legitimate
in a democratic society. Because the PP prescribes action in the face of incertitude, it may lead to
exercising arbitrary power unchecked by democratic processes; thereby, potentially leading to
capricious discrimination and/or trade protectionism. Again, this concern is relevant and must be
confronted (62), but current disagreements between the US and the EU seem to have kindled
controversies on this issue beyond proportion. In fact, the participatory aspects of PP-based
decision-making seem more legitimate in a modern democracy than technocratic solutions based
on traditional risk assessment.
Application of the PP should not lead to piecemeal solutions, like those sometimes
attributed to misdirected risk management. Countervailing risks must be kept in mind (32). Thus,
the risk balance was not considered when providing clean drinking-water from wells that leached
toxic substances from soil minerals. In Bangladesh, arsenic contamination is now causing severe
health effects (29), while parallel problems in India are mainly due to fluoride. Similarly, octaneboosting gasoline additives like MTBE were not sufficiently evaluated before introduced as
substitutes (24, 29). Therefore, application of the PP will lead to problems of comparisons
between risks that are exchangeable and, at the same time, subject to precautionary reduction
(Table 1).
Finally, the PP has also been criticized for being hostile to science. Accordingly, if a
decision may be reached on the basis of incomplete information, then the incentive for further
research could be less (30). However, application of the PP may itself require new research and
monitoring. Goldstein (30) proposed that the public agency that made the initial hazard claim
should also invest in independent research to establish the validity of it. Likewise, as discussed
below, the use of the PP is likely to change the way that scientific information is applied and
probably also the way it is planned and reported.
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Differences between the United States and Europe
In discussing potentials for trade wars and clashes between legal systems, the differences between
US and EU approaches become highly apparent (e.g., in regard to genetically-modified foods and
hormone-treated beef) (72). While the precautionary principle is now part of the treaty that forms
the legal basis of the European Union, U.S. legislation, in various ways, also reflects
precautionary approaches, although in a diluted or compromised form (3). The now rescinded
Delaney Clause was a prime example of this concept, but the superceding Food Quality
Protection Act allows consideration of uncertainty by mandating the use of uncertainty factors.
Another US approach has been to impose maximal allowable control technology to regulate air
pollution. Although such requirement may be advantageous in current perspective, it may not
necessarily provide sufficient protection in the longer term as new insight into health risks
emerge. In addition, it may freeze pollution abatement at the level that is achievable now (3, 29).
However, the current overzealous practice of evidence-based risk assessment and the
“hard look” reviews by the courts have diminished precautionary approaches (3). In an important
decision in 1980, the US Supreme Court held that OSHA cannot regulate benzene exposure on
the basis of mere conjecture about uncertain risk and that OSHA must demonstrate ‘significant
risk’ before regulating. This decision constituted a significant motivation for adoption of risk
assessment as a basis for risk regulation in the US (72).
In the so-called Daubert Decision, the US Supreme Court instructed federal judges to
allow only expert testimony that was both reliable and relevant. The court also stated that
evidence should be based on a testable peer-reviewed theory with a known error rate and be
widely accepted by the scientific community. The implications of this decision could make PPbased decisions difficult to defend in these courts.
Generic regulation has been accepted in the US based on extrapolations from detailed
knowledge on single chemicals, but only in restricted situations, such as benzidine-related dyes.
Because occupational exposures are often mixed, the IARC (International Agency for Research
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on Cancer) has grouped these exposures together, and this classification has been heeded.
However, in other circumstances, no such extrapolation is accepted (19), and court decisions
have reversed some agency decisions to apply generic regulations (3). In Europe, generic
regulation is used (e.g., in regard to the above mentioned drinking-water contaminants) (1).
In some regards, the EU therefore may be more precautionary than the US; while the
opposite appears to be the case in others. Blood donations provide an interesting example, where
the FDA requires rejection of blood from a donor who has spent three months or more in the UK,
or five years or more in Europe, since 1980. This decision is meant to decrease the risk of transfer
of the BSE agent via blood. Clearly, this decision is precautionary, but of course it can in no way
be matched by the EU. Meanwhile, the EU’s strong stand on GMO (genetically modified) corn
and hormone residues in meat is being challenged by the US in the World Trade Organization
(72).
The systemic approach to decision-making
Current risk assessment in regard to human health and the environment suffers from reductionism
(24, 38). The requirement that decisions must be based on solid evidence and scientific proof
results in a reification of environmental health and piecemeal solutions. Although important
achievements have been made, the problems of complex chemical exposures and ecological
intricacies require a different approach. Instead, what is needed is a decision that is approximately
right and timely, rather than one that is precisely correct but too late. Because of the failure of risk
assessment to appropriately address incertitude and to provide guidance in large-scale and
complex environmental health problems, it needs to be supplemented by a systemic paradigm that
includes shared decisions within a broader context. For purposes, such as this, de Rosnay (60) has
recommended the use of a systemic approach that he calls the macroscope (Table 3).
The PP is relevant in this regard, because it is not a rule that is only to be applied when
faced with a concrete threat. The PP is also an overarching principle that is applicable throughout
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the whole process of policy formulation. Tickner (68) proposes a framework that he calls
precautionary assessment. It starts with problem scoping, stakeholder identification, and
allocation of responsibilities. Then, it follows the environment and health impact analysis that
includes an uncertainty analysis. Analysis of alternatives is included before the final precautionary
action analysis. Such systemic perspectives provide a necessary alternative to technology-based
environmental management. Fig. 3 shows, graphically, how precautionary actions lead to better
insight that may eventually allow formal risk assessment.
Costs and benefits include non-economic considerations (17). For this reason, the
European Commission has affirmed that requirements linked to protection of public health should
‘undoubtedly’ be given a greater weight than economic considerations. Thereby the singularity of
strictly financial cost-benefit analysis is challenged as a decision-making tool.
The role of science in PP-based decision-making must therefore be to allow pluralities of
perspectives instead of hiding a single view under the veil of scientific truth. Because of the
substantial degrees of incertitude, decisions in environmental health are no more a matter of
applied science or even professional consultancy based on extrapolation and inference. They
become “post-normal science” (27); where, in plain words, we need to promote gardening rather
than botany. This need then calls for a passage from a substantive rationality to a procedural
rationality, where the quality of the process becomes paramount (27).
In designing consistent and accountable procedures, a major problem is to establish the
detailed rules of evidence, including the hierarchy of knowledge, evidence, documentation,
individual results, and permissible extrapolations. Although when to act is not a new question, the
challenge is to define the threshold under more complex circumstances, while applying consistent
criteria (32, 57). Different levels of proof may be needed for different purposes, depending on the
severity of the problem (Fig. 2). False positives and unfounded vetos must be avoided, because
the blocking of useful innovations could unreasonably hamper social and economic development,
while, at the same time, cast doubt upon the validity of the process (57). Additional attributes are
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goal-setting for the long term; for instance, establishing desirable futures rather than crisis
management and aiming at clean production coupled with monitoring to secure high quality (24).
The PP-based decision process must address public concerns, which may be more
directed at ensuring that a potential problem is not ignored, in contrast to scientists who are often
reluctant to give credibility to unproven possibilities. The decision-making framework should
provide a process where different positions can be reconciled. It must become more participatory,
substituting technocratic or authoritarian leadership styles with widening acceptance of qualitative
criteria for judging the environment (e.g., human rights, ethical values, animal welfare, quality of
life issues, socioeconomic considerations, and sustainability) (15). The European Commission
requires that minority views be considered in this process, provided that the credibility and
reputation are recognized (17). In this participatory process, the consumer will be empowered to
take informed precautionary action so as to exercise choices of risks (61). Although polarized
opinions will undoubtedly remain, this process allows consideration of all aspects and, therefore,
also a better chance of resolution of opposing views.
A variety of methodological approaches have been proposed, including trade-off analysis
(4) and multicriteria mapping (66). Using maximin criteria, one gives priority to actions aimed at
improving the condition of those who are worst-off, thereby avoiding the policy with the worst
possible consequences. Implications of the maximin approach are likely to agree with decisions
based on the PP; although potentially in conflict with a utilitarian strategy (54). Quantitative
Bayesian evaluation is possible and attractive (54), but these methods also possess some inherent
difficulties (58). The California Department of Health Services has sponsored an admirable
program to explore the possible health effects of electric and magnetic fields (EMF) from power
lines (54). Using transparent democratic foresight strategies, it examined the advantages and
disadvantages of different actions. The lessons learned from this experience will be highly
appropriate for the procedures used for future decision-making on similar environmental health
Implications of precaution (Grandjean)
20
problems. Indeed, EMF serves as a useful example of the significance of incertitude in regard to a
potentially serious hazard (28, 74).
The PP-based decision may be a request for further research to allow an improved basis
for future decisions, but all decisions should be considered provisional and dynamic. Measures
based on the PP may assign responsibility for providing the supplementary information required
(17). At present, the principle of prior approval (‘positive list’) has shifted the responsibility for
producing scientific evidence for drugs, pesticides, food additives. Likewise, monitoring may be
needed to track environmental health factors to allow linkage of increased prevalence ranging
from chronic diseases to causative pollution factors (23). In such cases, the decision process will
involve a dynamic relationship with research, where new information is taken into account while
reconsidering the previous decision.
A precautionary research paradigm
Due to the fact that decisions under the PP may be taken on the basis of incomplete evidence,
precautionary science is likely to emphasize association rather than proof (i.e., at a lower
scientific validity) (43). The PP has been interpreted as research averse, since no new research
would be needed once a decision has been made. However, all decisions are provisional, and
some decisions may mandate additional research and monitoring, perhaps as the only action until
new information allows reconsideration. As expressed by the European Commission,
uncertainties should stimulate research (17). Indeed, targeted toxicology and intervention studies
would likely serve both scientific purposes and policy means.
Several authors have discussed whether there is such term as “precautionary science” (7,
30, 43, 68). Although some general ideas have been presented, it is clear that science should not
change drastically due to the application of the PP. However, PP-based thinking has elucidated
some weaknesses in the current approaches in environmental health research. Several important
Implications of precaution (Grandjean)
21
aspects are indicated in Table 4. Mending these problems and redirecting research efforts could
constitute an important shift in paradigm.
First of all, the PP may provide a welcome occasion to critically consider the overall
strategies for environmental health research (43). Although replication is necessary in science
where a single observation may represent an accident or an exception, replication can also be
carried too far. A review of major environmental health journals will reveal that the vast majority
of published papers deal with a few hundred well-studied environmental toxicants. Some of this
information may still be useful for paradigms of PP-based decisions on, say, groups of persistent
or bioaccumulative chemicals (including compounds not yet studied). However, the failure of
environmental health research to target unstudied or understudied pollutants is a major
embarrassment.
The PP suggests that attention be shifted to new issues, instead of narrow and narrowing
research topics that elicit repetition to reduce already limited uncertainties. New research should
focus more on larger-scale patterns, trends, early indicators, and other ‘red flag’ parameters that
may be of more general importance. Rather than attempting to provide complete documentation
for the purpose of sophisticated risk assessment, research should be directed toward expanding
perspectives and covering new ground. This shift does not mean that efforts to support evidencebased risk assessment should be halted, but they do need to be complemented.
PP-based decisions are also likely to mandate follow-up monitoring; this type of effort
then effectively becomes an intervention study, where changes are documented as a result of a
ban or other action. Far too much scientific literature is descriptive rather than analytic, and thus
provides even more limited guidance for primary prevention.
Some authors (7) have recommended a shift from “mechanistic” science to precautionary
science. This change is parallel to the shifts from analytic to systemic approaches in Table 1 and
is thought to affect the design of research, the scale of the issues confronted, and how error,
validity, and uncertainty are addressed. Clearly, the hubristic language and thinking about
Implications of precaution (Grandjean)
22
uncertainties in regard to risk assessment should be discarded (66). Instead of systematically
neglecting unknowns and poorly understood issues, these problems should now become an object
of research. They should become the center of attention rather than an annoying interference with
good science. Related statistical issues are considered separately below.
Among priority issues to tackle are interactions between different toxic exposures (43,
64) and the significance of individual vulnerability within groups at risk (33, 46). For example,
subtle adverse effects may decrease the physiological reserve capacity and thereby the
susceptibility toward some other exposure or adverse incident (35). This issue deserves to be
further explored, as it could have wider implications for our understanding of low-dose toxicity
and the long-term effects as well as interactions. On the whole, much research is based on
biochemical effects on a molecular scale, but effects on populations and ecosystems need to be
incorporated, as do the potential effects on future generations. This may appear like a tall order.
However, large numbers of physicists are capable of collaborating on huge projects to seek new
complex knowledge. Environmental health research should also become a joint enterprise that
tackles some of the above scientific problems that have already been apparent for too long.
One final issue that deserves to be mentioned is openness, which relates to research as
much as to decision-making. Transparency and accountability are crucial for research to provide
credible guidance for PP-based decisions as described above. Just as laboratory accreditation
requires traceability of all procedures, researchers should retain records to document the methods
as well as the choices that inevitably must be made. Stakeholder participation should be
considered both in the planning phases of the study and in communicating progress and
outcomes. Research publication may now benefit from rapid publication on the internet, and some
scientific journals allow or even solicit publicly accessible storage of data materials and protocols.
Implications of precaution (Grandjean)
23
Statistical issues of precaution
Conceptually, scientists will normally support a positive association (i.e., the risk is real) if the
probability that the observed risk has arisen by chance is below 5%. A type I error means that an
innocuous factor is mistakenly identified as a risk, but this should then happen only in one out of
20 studies. Scientists are often willing to ‘miss’ a real association (i.e., conclude the risk does not
exist, when it actually does) with a probability of 20%. This is referred to as a type II error, which
is then bound to happen in one out of five studies. However, there is an implicit bias in being
more cautious about falsely detecting something than about failing to detect something (43).
Table 4 lists this imbalance along with other tendencies that cause a bias in evaluating potential
environmental causes of disease.
The caveats expressed by Hill (36) in regard to the aspects of causal thinking are often
overlooked: “All scientific work is incomplete. (...) All scientific work is liable to be upset or
modified by advancing knowledge. That does not confer upon us the freedom to ignore the
knowledge we already have, or to postpone the action that it appears to demand at a given time.”
Because the exigencies of public health problems demand action, causal inferences must be made
despite imperfect knowledge. In addition, the public is more concerned that any potential risk is
not overlooked, irrespective of statistics. Public policy, as well as the application of the PP, must
then avoid anti-precautionary tendencies.
The potential biases (Table 4) need to be considered when evaluating causal evidence
and dose-response relationships, and one needs to take into account what can be known, given the
methods and study opportunities available. Nonetheless, Pharisaic efforts to discount evidence of
causal associations prevail, as already indicated in regard to the “good science” strategy.
Sometimes, review documents mistake the validity of the conclusions for meticulousness
in identifying presumed violations of causal criteria. Uncertainty of information is then confused
with the quality of the information (43). For example, in evaluating the possible decline in semen
quality as an effect of exposure to endocrine disrupting chemicals, an expert committee used
Implications of precaution (Grandjean)
24
Hill’s criteria in reaching the following conclusion (41): “For outcome, the evidence is judged to
be weak. A global trend for declining semen quality is not supported by current data. (...) There is
no evidence relating to the strength of the hypothesis because of the lack of exposure data. There
are no human data to support an EDC-related mechanism. However, the biological plausibility of
the hypothesis remains strong, based on information from clinical experience and experimental
systems.” A similar conclusion was reached in regard to breast cancer and endocrine disruptors,
although the experts at the same time admitted that few studies had provided exposure
assessments that related to the time of greatest relevance. While in accordance with good science,
these conclusions do not reflect PP-based conjectures.
Although a normal reporting practice, standard probability values are of little interest in
regard to PP-based thinking, because they only indicate the likelihood of the data, or some that
are more extreme, given that the null hypothesis is true. However, a frequent issue is that the null
hypothesis is not true and these p values are therefore not helpful. Given the PP-related concerns
with potentially large threats, confidence limits (e.g., with a 95% coverage) would be much more
appropriate to ascertain the possible upper range of a hazard.
In standard analyses of epidemiological data, the exposure as independent variable is
considered to be without error, which is almost always wrong. A non-differential imprecision,
which would be typical of biomarker analyses, generally causes a bias toward the null hypothesis,
thereby resulting in an underestimation of the true effect of the exposure. Epidemiological studies
rarely take into regard the error function of the exposure estimate or consider only the laboratory
imprecision. The full extent of the misclassification, which includes biological and other
preanalytical sources of variation, may be considerable larger than the laboratory error alone.
Accordingly, the underestimation of the toxic potential of the exposure may be far greater than
normally assumed (34).
Although exposure imprecision can be modeled in sensitivity analyses, they require that
the degree of imprecision be known (which is rarely the case). From a precautionary viewpoint,
Implications of precaution (Grandjean)
25
sensitivity analyses should include appropriate magnitudes of exposure errors to explore the
reasonable extent of possible underestimation of the dose-effect relationship.
One approach to estimation of safe exposure levels is the benchmark dose, which takes
into account some aspects of statistical power, so that smaller studies will result in a lower
benchmark dose. However, when applied to epidemiological data, where exposure
misclassification is a common problem, benchmark doses have now been found to be
overestimated due to imprecision of the exposure parameter (42). These impacts of exposure
misclassification show that a critique of risk assessment for being overly conservative (6) should
acknowledge that some aspects, such as benchmark dose calculations, may not be conservative
after all. Moreover, unadjusted benchmark dose levels are often misconstrued by regulatory
agencies to represent approximate thresholds, even when adverse effects are documented below
this level. Such interpretations of statistical data may indeed be non-conservative and antiprecautionary (42).
In addition to errors of type I and type II mentioned above, researchers sometimes refer
to type III errors (i.e., when the research has answered the wrong question) (63). As indicated by
some commentators on precautionary science (7), good science may well commit type III errors
when judged from a precautionary viewpoint. The highest scientific quality may be a poor publichealth effort.
The future of precaution
Threats to human health and the environment must be identified and managed to every extent
possible, but the links between research and public health action are insufficient. The
precautionary principle offers a possible solution to escape from the impasse created by
reductionist approaches to risk assessment and piecemeal prevention. The idea expressed by the
PP is not new, but perhaps the time has now come for this worthy approach to be applied in
larger-scale environmental health issues.
Implications of precaution (Grandjean)
26
At this point, the PP, as it is expressed in primary legislation and case law, does not yet
provide the necessary framework to link uncertain facts to causation and the dose-dependency of
effects (19). The primary legislation needs to include more detailed guidance on handling large
uncertainties for the sake of agency-based rule-making. If possible, a threshold of scientific
evidence needs to be defined that, when crossed, commands a branch of government to provide
protection against a hazard deemed potentially serious (32). This threshold must aim at reducing
legal ambiguity. Unless the PP is formalized and operationally defined, it will remain susceptible
to the critique that it is haphazard and uncertain itself.
A first step could be to identify the threshold that justifies a shift of the onus of scientific
proof. For example, countries like Denmark and Sweden have used objective criteria to draw up
lists of “undesirable” chemicals that are persistent or bioaccumulative. Where new restrictions
apply, unless countered by new test data, a chemical will be taken off the list.
The European Commission has already expressed that decision-making should
incorporate issues such as inequity and injustice, psychological stress and discomfort, and animal
welfare (15). Such aspects are not encompassed by the current framework of risk assessment, but
would seem to be appropriate for risk management and for the types of decisions that may follow
PP-based considerations. These prospects highlight the need for new procedural rules to achieve
the necessary multidisciplinary collaboration, stakeholder participation, and transparency.
In decision theory, aspects of causal conjectures may be defined in accordance with the
calculus of probability theory. Thus, the uncertain elements that form the basis of a PP-based
decision may be expressed as a matter of probabilities that can be updated by new empirical
information. Several techniques are available and need to be critically evaluated. A constructive
framework should aim at utilizing modern statistical methods of causal analysis that will allow
choices that are both reproducible and efficient (58).
Although erroneously criticized for being science averse, the PP is an important impetus
to review current research strategies, methodologies, and research reporting traditions. Traditional
Implications of precaution (Grandjean)
27
risk assessment must continue to be supported by research, but it should be supplemented by
research that more directly targets the perspectives that require application of the PP. In this
regard, the research must facilitate PP-based decisions by exploring the potential extent of
uncertain threats to human health and the environment. By addressing these important issues,
environmental health research can help reestablish the link between science and public health.
Acknowledgments
The author’s research is supported by the US National Institute of Environmental Health Sciences
(ES09797 and ES11681), and the Danish Medical Research Council. The contents of this paper
are solely the responsibility of the author and do not represent the official views of the NIEHS,
NIH, or any other funding agency.
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Figure legends
Fig. 1. Risk assessment is based on exposure assessment and dose-response relationships. Each
parameter and model is associated with some uncertainty, but can be included in statistical
models. In this way, risk assessment can approach the types of analysis that would be appropriate
for precautionary analysis. Redrawn from Covello & Merkhofer (18).
Fig. 2. While risk assessment may address hazards at all levels of severity, when sufficient
evidence is available, the precautionary principle fills in the empty space where uncertainty
prevails, although the hazard may be serious.
Fig. 3. When an environmental health issue is poorly known, it may first become the object of
precautionary analysis, and the information will gradually increase as stakeholders become
involved and precautionary actions are instigated, including subsequent monitoring and research.
These efforts may eventually provide the basis for a formal risk assessment.
Implications of precaution (Grandjean)
36
Table 1. Lessons learned from early warnings about environmental hazards and the delayed
responses. From European Environment Agency (24).
1. Acknowledge and respond to ignorance, as well as uncertainty and risk, in technology appraisal
and public policymaking.
2. Provide adequate long-term environmental and health monitoring and research into early
warnings.
3. Identify and work to reduce “blind spots” and gaps in scientific knowledge.
4. Identify and reduce interdisciplinary obstacles to learning.
5. Ensure that real world conditions are adequately accounted for in regulatory
appraisal.
6. Systematically scrutinize the claimed justifications and benefits alongside the potential risks.
7. Evaluate a range of alternative options for meeting needs alongside the option under appraisal,
and promote more robust, diverse and adaptable technologies so as to minimize the costs of
surprises and maximize the benefits of innovation.
8. Ensure use of “lay” and local knowledge, as well as relevant specialist expertise in the
appraisal.
9. Take full account of the assumptions and values of different social groups.
10. Maintain the regulatory independence of interested parties while retaining an inclusive
approach to information and opinion gathering.
11. Identify and reduce institutional obstacles to learning and action.
12. Avoid “paralysis by analysis” by acting to reduce potential harm when there are reasonable
grounds for concern.
Implications of precaution (Grandjean)
37
Table 2. Elements of the precautionary principle, according to the European Commission (17,26).
Proportionality
"Measures...must not be disproportionate to the desired level of
protection and must not aim at zero risk"
Nondiscrimination
"comparable situations should not be treated differently and...
different situations should not be treated in the same way, unless
there are objective grounds for doing so."
Consistency
"measures...should be comparable in nature and scope with measures
already taken in equivalent areas in which all the scientific data are
available."
Examination of the
"This examination should include an economic cost/benefit analysis
benefits and costs of
when this is appropriate and feasible. However, other analysis
action or lack of action
methods...may also be relevant"
Examination of scientific
"The measures must be of a provisional nature pending the
developments
availability of more reliable scientific data"... "scientific research
shall be continued with a view to obtaining more complete data."
Implications of precaution (Grandjean)
38
Table 3. Two approaches to environmental health represented by the reductionist view of
traditional risk assessment and the systemic approach associated with the precautionary principle.
Revised from de Rosnay (60) and Holling (38).
Attribute
Philosophy
Causation
Analytic
Systemic
Risk assessment
Precautionary principle
Narrow and targeted
Broad and exploratory
Disproof by experiment
Multiple lines of converging evidence
Parsimony the rule
Requisite simplicity the goal
Single and separable
Multiple, interactions, only partially
separable
Hypotheses
Incertitude
Single and null hypotheses
Multiple, competing hypotheses
Rejection of false
Separation among competingq
hypotheses
hypotheses
Eliminate uncertainty
Incorporate and learn from incertitude
and aim at high precision
Models
Discipline-oriented
Multidisciplinary
Precise and validated, used to Imprecise and tentative, developed
account for observations
in response to observations
Statistics
Concern with Type I error
Concern with Type II error
Evaluation goal
Peer assessment to reach
Peer assessment and judgment to
ultimate unanimous agreement facilitate consensus-building
The danger
Exactly right answer for
Exactly right question but useless
the wrong question
answer
Implications of precaution (Grandjean)
39
Table 4. Potential bias in environmental research using standard methodological approaches.*
Type of scientific study
Experimental study
Observational studies
Both
Methodological feature
Main direction of error:
High doses
Limited range of doses
Low genetic variability
Exposure to single
substances only
Chronic rather than
fetal-lifetime exposure
Standard effect measures
Social confounders
Concomitant exposures
Inappropriate controls
Exposure misclassification
Inadequate follow-up
Lost cases
Ignoring complexity in data analysis
Publication bias
toward positive findings
Post hoc hypothesis
Scientific and social
pressure to avoid false alarm
Low statistical power
(e.g., small studies)
Use of 5 % probability level to
minimize chances of false positives
Use of 20% probability level to
minimize chances of false negatives
False positive
False negatives
False negative
False negative
False negative
False negative
False positive
False positive
False positive/negative
False negative
False negative
False negative
False positive/negative
False positive
False positive
False negative
False negative
False negative
False negative
*Based on discussions at the Collegium Ramazzini Conference on The Precautionary Principle:
Implications for Research and Prevention, Bologna, 23-24 October, 2002; revised from Gee (28).