Introduction

Qualitative risk assessment has its roots in the beginning of human history. For example, people observed that human exposure to particular plants, such as hemlock, led to adverse health effects. In addition, they noted that some beneficial materials, such as wine, had adverse effects when taken in excess. As a result, they recognized both qualitatively and quantitatively that some products of the environment posed risks. In the main, the effects they noted were those that occurred almost immediately. Long-term effects were difficult to discern, especially when life spans were short and other health problems, particularly infectious diseases, were more prevalent.

Although the situation changed somewhat over the centuries, it was not until the present century that humans learned how to control infectious diseases. As a result, people have been living longer and have experienced an increased incidence of chronic health problems. Coincidentally, modern society has learned to synthesize a large variety of chemicals and to extract and manipulate naturally occurring chemicals. Some of the resulting chemical exposures have contributed to an increase of chronic diseases, especially cancer.

To protect the public from long-term adverse health effects from chemical exposures, a large number of environmental and occupational statutes have been enacted since 1970. Most of these laws and associated rules require that the risk from chemicals be assessed, whether the chemicals are in the workplace, the ambient air, water, soil, or food supply. The results of the risk assessments are used to set limits on environmental or workplace levels of these chemicals.

As a result of the regulatory needs for consistent rules, a number of risk assessment approaches were codified in policy years ago. Unfortunately, they reflect the state of science as it was decades ago and do not incorporate current understanding of the different ways chemicals cause toxicity. Thus, there is an increasing gap between the scientist's best judgment about the risk of chemicals and the official risk assessment numbers that are most commonly released to the press and public by government agencies.

The purpose of this primer is to give the reporter an understanding of how risk assessment is currently practiced and publicized. It is intended to enable the journalist to sort through the numbers and scientific terminology to detect whether they are getting the whole story and to identify the strengths and weaknesses of a study. The ultimate goal is to improve public understanding and decision-making regarding environmental risks.

In this handbook, risk assessment refers to the process of estimating the type and magnitude of risk to human health posed by exposure to chemical substances. The handbook does not cover chemical risks to wildlife or other types of risk. Many of the principles of risk assessment described, however, also apply to measuring other forms of risk.

This handbook distills the basics of risk assessment. It is designed to give the reader an overview of the process, what it can achieve, its limitations, and problems to watch for. It will not make the reader an expert on risk assessment, but it should provide an elementary knowledge of basic concepts and enable reporters to approach risk stories with more confidence and knowledge.