Epidemiologists and environmental health researchers have a joint responsibility to acquire scientific knowledge that matters to public health and to apply the knowledge gained in public health practice. We examine the nature and source of these social responsibilities, discuss a debate in the epidemiological literature on roles and responsibilities, and cite approaches to environmental justice as reflective of them. At one level, responsibility refers to accountability, as in being responsible for actions taken. A deeper meaning of responsibility corresponds to commitment to the pursuit and achievement of a valued end

Public health ethics is on the map. In the past year, bioethicists and public health practitioners have begun to focus their critical attention on this complex and understudied topic. Much remains to be done. Childress et al. (2002), for example, describe their account of public health ethics as a rough conceptual map of a terrain with undefined boundaries.

Our focus will be on the responsibilities of epidemiologists, a choice made for several compelling reasons. Epidemiology sits at the center of the science and practice of environmental health, and more generally, at the center of public health. Although it is often referred to as a basic science of public health, epidemiology connects the acquisition of scientific knowledge with its application in preventive interventions, programs, and policies. This connection suggests a fundamental question: What are our responsibilities as epidemiologists? Do we, for example, have a joint responsibility to participate in science and to apply the knowledge gained? This is a key concern for us as researchers, health professionals, and as teachers.

The social responsibility of public health professionals is but one of many concerns in the broader picture of public health ethics. It is nevertheless a central concern. As Ogletree (1996) reminds us, responsibility is a concept particularly well suited to flame many key aspects of the ethics of professions faced with making decisions and taking actions in complex situations. These decisions often involve advanced technologies, high levels of specialization, and overlapping areas of expertise and concern among decision makers from diverse educational, political, and social backgrounds, precisely the situation in contemporary epidemiology and public health. In sum, responsibility organizes many (although not all) of public health's ethical issues in terms appropriate for professional practitioners.

Responsibility has a deeper meaning as well, corresponding to commitment. To be responsible means to be committed to someone or to some thing. Being responsible in this deeper sense involves a commitment to positive action, to the pursuit and achievement of something of value, such as a social good (Jonas 1984). We will return to the notion of social goods in public health. For now, we want to emphasize that responsibility focuses attention on professional commitments

Finally, our inquiry is intended to assist all public health researchers who seek to define their social responsibilities. For those who are involved primarily in environmental health research, we can think of at least two connected and current topics--environmental justice and community-based participatory research.