Acknowledge – do not hide – uncertainty. Sounding more certain than the data can justify is a sure path to losing trust and credibility. Sources of uncertainty – for example, uncertainties due to generalizing from animal data to humans, gaps in the data, and differences of interpretation – should all be acknowledged up front, not “admitted” belatedly when an opposing interest group points them out. But acknowledging uncertainty is not the same thing as asserting total randomness or declaring ignorance.

Degree of certainty can be represented along a scale or continuum, from “total confidence” in the data to “guesswork” (in science there is never complete certainty, since new evidence can always overturn previous beliefs). When you have total confidence in the data, do not hesitate to say so. Most of the data produced by risk assessments, however, are somewhere in the middle of the scale. Such data are characterized by uncomfortably large margins of error; often they are based on disputable assumptions, models, and extrapolations, such as those from animals to people, from high doses to low doses. Nonetheless, such data are a much better basis for decision and action than guesswork. In these cases, assert frankly that the information is helpful but far from certain. Then explain that risk assessments deal with this uncomfortable level of uncertainty by making assumptions in the direction of overestimating the risk.

Somewhere near the “guesswork” end of the scale are risk assessments based on very inadequate data. When that is the case, say so. State as much as is known and explain (a) what you propose to do to get better risk data, and (b) what you propose to do in the meantime to reduce or protect people against the risk. Projecting this attitude is crucial. Under Title III, communities may begin asking about many possible health and environmental consequences for thousands of different chemicals. In many cases little or no data are available to answer these questions. When you have no evidence one way or the other, such as in the case of data on the relationship between air toxic X and miscarriages, never respond with “There is no evidence to show that air toxic X causes miscarriages.” The statement is technically correct – but profoundly misleading. If similar compounds have been tested and found not to cause miscarriages, say that. If there are theoretical reasons for doubting that air toxic X could interfere with pregnancies, say that. If you have carefully kept track of and monitored female plant employees and found no miscarriage problems, say that. And if the possible connection is still untested and deserves to be studied, say that.

In acknowledging and explaining data uncertainties, talk about how the risk estimate was obtained, and by whom. Demystifying the risk assessment process is a public benefit in its own right and will help your audience understand why you are simultaneously claiming (a) that your risk estimate is uncertain and (b) that your estimate is based on the best available scientific data. Explaining this process will also enable you to make points that are important for the audience to understand. Two points of special relevance and importance for the chemical industry are as follows.

First, the presence of a toxic chemical in the environment, such as an emission from a manufacturing plant, does not necessarily signify a significant health or environmental risk. This point is often extremely difficult to communicate, especially to those worried about long-term, low-dose effects. Even if hundreds or thousands of tons of air toxics are emitted into the air each year, there may be no significant health or environmental risk to people. For a toxic chemical to expose a risk, an exposure must occur. There must be a way for the air toxic to get from where it is (the manufacturing plant) to where people or the things they value are. Routes of exposure are as important in risk assessment as toxicity measurements are.

Second, when a route of exposure exists, the next important question is the concentration of the chemical that may reach people. This concentration amount, typically far lower than the concentration at the source, will often become even lower with the passage of time as the substance breaks down. Risk assessors consider not only whether a toxic substance is in the air or groundwater but also how much is in the air or groundwater.

This distinction becomes more important as measurement equipment becomes better. By means of their ability to measure parts per trillion and parts per quadrillion, scientists are now able to detect “low but measurable” chemical concentrations that were unknown before. Thus the proper question is not “How risky is a toxic substance?” but rather “How risky is the concentration of the toxic substance to which people are being exposed?”

The demand for zero risk may be politically motivated. The demand may be designed to win followers, influence politicians, or attract the interest of journalists. Such political activity is perfectly legitimate in a democracy. Groups opposed to the chemical industry – whether they are staffed by volunteers or paid organizers – are often highly dedicated and committed to their cause. Just as the chemical industry – as an industry – is entitled to build its political case, opponents of the chemical industry are also entitled to build their political case. With occasional exceptions, the strategies used by opponents are legitimate political strategies. For example, an opposing group may appeal to the community’s health concerns, just as the chemical industry may appeal to the community’s economic concerns. An opposing group may recruit and mobilize experts to support its view, just as the chemical industry may recruit and mobilize experts to support its view. Given that such activities are entirely legitimate in a democracy, you will find it unwise to attack the sincerity or legitimacy of opposing groups. A plant manager – or the chemical industry as a whole – has a legitimate right to disagree with the view of an opposing group. Disagreeing, however, is not the same as questioning the integrity of an opposing group or the right of the opposing group to use legitimate political strategies to promote its views.

If the demand for zero risk is politically motivated, you are unlikely to make much headway in meetings held in public settings. One of your main options is to try to arrange a private or semi-private meeting, where frank discussion and negotiation might be possible. In public settings, your best strategy is to clarify your position as best you can, following the advice offered in this manual.