6
Closing Comments1

David Eaton, Ph.D.,

Professor of Environmental Health and Occupational Health Sciences,

School of Public Health and Community Medicine,

University of Washington


The workshop highlighted a number of challenges that scientists, public health officials, and policy makers face in protecting the public against harmful environments and promoting healthy ones (Figure 6-1). Central to the discussion was the inherent tension between science and public health in determining the burden of proof for a toxic chemical. Scientists, as a result of their training, do not exceed the limits of their data, which places chemicals in the “innocent until the data shows otherwise” category. However, those in public health, when faced with uncertainty, would prefer to err on the side of protecting health. While it is relatively easy to show that x can cause y or that there is a mechanism in which x might cause y, it is difficult to demonstrate and accumulate sufficient data to say that x cannot cause y. Thus, there is a conflict about how to establish the burden of proof for toxic substances and how to address this conflict in the regulatory setting.

The general belief is that more science will clarify research gaps. However, science itself may provide uncertainty. One place where this can occur is in the field of toxicology, which relies on the extrapolation of results between species. For example, rats fed aflatoxin at 15 parts per billion (the current tolerance level set by the Food and Drug Administration) develop liver cancer. However, mice fed aflatoxin 150,000 parts per billion do not develop liver cancer. The development of liver cancer is dependent on the expression of a single gene in the rats compared with the mice.

The choice of which species to use to predict human response could lead to vastly different conclusions and, depending on the “truth,” could lead to a false-positive or a false-negative result. In the example of aflatoxin just described, human epidemiological data suggest that the truth is somewhere in between. In

1

This chapter was prepared from the transcript of the summary presentation by Dr. Eaton. The views expressed within this chapter are attributed solely to him.



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6 Closing Comments1 David Eaton, ph.D., professor of Environmental Health and occupational Health Sciences, School of public Health and Community Medicine, University of Washington The workshop highlighted a number of challenges that scientists, public health officials, and policy makers face in protecting the public against harmful environments and promoting healthy ones (Figure 6-1). Central to the discussion was the inherent tension between science and public health in determining the burden of proof for a toxic chemical. Scientists, as a result of their training, do not exceed the limits of their data, which places chemicals in the “innocent until the data shows otherwise” category. However, those in public health, when faced with uncertainty, would prefer to err on the side of protecting health. While it is relatively easy to show that x can cause y or that there is a mechanism in which x might cause y, it is difficult to demonstrate and accumulate sufficient data to say that x cannot cause y. Thus, there is a conflict about how to establish the burden of proof for toxic substances and how to address this conflict in the regulatory setting. The general belief is that more science will clarify research gaps. However, science itself may provide uncertainty. One place where this can occur is in the field of toxicology, which relies on the extrapolation of results between species. For example, rats fed aflatoxin at 15 parts per billion (the current tolerance level set by the Food and Drug Administration) develop liver cancer. However, mice fed aflatoxin 150,000 parts per billion do not develop liver cancer. The develop- ment of liver cancer is dependent on the expression of a single gene in the rats compared with the mice. The choice of which species to use to predict human response could lead to vastly different conclusions and, depending on the “truth,” could lead to a false- positive or a false-negative result. In the example of aflatoxin just described, human epidemiological data suggest that the truth is somewhere in between. In 1This chapter was prepared from the transcript of the summary presentation by Dr. Eaton. The views expressed within this chapter are attributed solely to him. 

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 EnVIRonMEntaL HEaLtH SCIEnCES DECISIon MaKInG Scientific Public Health “Legal” and Other Evidence Advocacy— Vested Toxicology “Precautionary “Interests” Epidemiology Perspective— Principle” Mechanism of Action “Proof of Guilt” FIGURE 6-1 Scientific evidence has many uses that are not often apparent to the sci- entists. Scientific evidence can be used to define research, promote health, and inform the legal process. There is a tension in the use of science when there is uncertainty as to whether policy makers take a precautionary approach or a passive (i.e., “wait until the data 6-1 shows harm”) approach. SOURCE: Eaton, unpublished. many instances, the benefit of human epidemiology is not available to resolve discrepant animal studies. In such circumstances, a false positive can lead to the limitation or ban of a particular useful chemical. However, public health scientists are perhaps more concerned about false negatives, such as the case with arsenic. In this example, animal bioassays for carcinogenicity generally have failed to identify the potent carcinogenic effects of arsenic that are known to occur in humans. Animal toxicology or human epidemiology alone does not address all of the challenges in regulating chemicals, and thus the science behind regulatory decisions requires a multidisciplinary approach. In recent years, tremendous advances have been made in molecular biology to elucidate cellular pathways and mechanisms that contribute to the understand- ing of how chemicals might contribute to human disease, but these advances are not a panacea for regulatory policy. Many cellular and molecular pathways have been highly conserved throughout evolution, and thus fundamental biologi- cal knowledge learned from simple organisms may be quite relevant to human biology. However, the evolutionary processes that dictate how humans respond to their environment select against other pathways, giving rise to large species differences in how organisms respond to their immediate environment, including chemical exposures. This is a challenge in the “omics” technology, in which sci- entists can measure changes in the expression of 10,000–20,000 different genes in response to a chemical exposure, but they are not always able to interpret the significance of such changes in terms of human health. Similar to advances in sci- ence, advances in technology have resulted in the vanishing zero: Environmental health scientists are able to measure chemicals in the body at lower and lower concentrations. However, scientists are not yet at a point at which they can make biological sense of the low-level presence of these chemicals.

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 CLoSInG CoMMEntS In addition to challenges of data interpretation, the workshop also high- lighted many ethical issues. In the real world, perception is reality. It is often difficult for the public to differentiate between perceived bias, significant bias, and conflicts of interest. While many agencies that work at the science-policy interface, such as IARC and the National Academies, have begun to create a good model for conflicts of interest, it does not go far enough to consider conflicts of interest throughout the research enterprise. For example, in the past decade, the perception has been expressed by many people that if a study is funded by an industry, then the results must be biased, and the study is essentially discounted. However, most scientists feel strongly that science should be judged on its merits and not on who funded it. Once the funding source is noted, perception problems begin, as people have biases that will shape their attitudes in response to such knowledge. This is true for all sources of funding and not just for industry. Thus there is a need for the field to address the perception of bias in research and continued discussions as to how biases can be acknowledged and conflicts of interest can be managed. In conclusion, environmental health sciences is sometimes caught between potential overuse of the precautionary principle, which can engender unwarranted fear on the part of the public, and lack of timely decisions of potential public health importance when data are insufficient to make science-based decisions. Continued efforts are needed to improve risk communication of environmental health hazards, as the public is often confused by mixed messages from the scientific community and thus may not understand risk or the scientific process that establishes the burden of proof for regulatory action. While there is clearly overlap, scientists need to address the credibility gap—or at least the public per- ception gap—by involving the public in these processes. There should be more discussions on how to address the needs of the environmental health decision- making process by establishing protocols to ensure that science is judged on its merits, while at the same time acknowledging biases and potential conflicts of interest.

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