To understand some of the ethical issues in environmental health research with human subjects, it is important to distinguish between different research methods used by investigators as these methods generate different ethical questions and problems. Environmental health research methods involving human subjects can be classified as either observational or experimental.

Observational studies gather information about human subjects in their natural environment. These studies usually only observe subjects being exposed to levels of risk that are no greater than the risks they would likely experience in everyday life. In one type of observational study called a retrospective case-control study, environmental health investigators collect information on the environmental exposures of a group of people with a disease or condition over a period of time and a group of people similar to the exposure group but who do not have the disease or condition in question. In another type of observational study, a prospective cohort study, environmental health researchers follow one group of people (the cohort) who have a particular exposure and also follow a comparison group of people (the control group) who do not have the characteristic. Investigators compare the health outcomes of the two groups over a long period of time.

In contrast, experiments gather information on human subjects under artificially constructed conditions. Experimental research with human subjects includes intentional exposure studies in a particular environment, such as a home, workplace, or school. Intentional exposure studies expose human subjects to an environmental agent, such as ozone, dust, or allergens, under controlled conditions, such as those in a laboratory. Intentional exposure studies help investigators obtain a better understanding of causal pathways from exposure to disease and also limit confounding factors.

One of the important ethical differences between observational and experimental studies in environmental health research is that observational studies usually impose fewer risks on research subjects than experimental ones because observational studies collect data on people in their natural environment. When one compares this to experimental studies which may impose risks on research subjects that are more than minimal, the ethical questions begin to become clear.

Compare the following two studies. The first study seeks to examine the impact of regular contact with highly volatile cleaning products on human health. The study asks janitors at a nearby shopping complex to complete a yearly health survey and provide urine and blood samples. The second study seeks to examine the same thing, but instead, researchers go to a nearby college campus and pay fifty freshmen to participate in weekly “exposure” sessions where the subjects are sprayed with the cleaning products.

The second study, the experimental one, exposes the subjects to much greater risk than what was minimally necessary for college freshmen in that environment, even though individuals are being exposed to the cleaning chemicals in both studies. In observational studies, the exposures of concern would have occurred whether researchers were observing or not. In experimental studies, the exposures would not have occurred at all if it were not for the intentional efforts of the researchers.

The ethical concerns are further exacerbated as some subjects in experimental studies may not be made aware of everything to which they are being exposed. Some environmental health studies may even impose risks on people who are not directly involved in the research. For example, an environmental health intervention in the home may impose risks on people who are not research subjects, such as other occupants of the home. A study on agricultural workers may impose risks on the farmers who employ the workers. Do such ethically suspect practices become justified if the benefit to society is sufficiently great?

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