Health Problem Identification
Health problem identification is the most easily recognized of the actions of regulatory agencies. It is defined as the process of determining whether human exposure to an agent could cause an increase in the incidence of a health condition (cancer, birth defect, etc.) or whether exposure by a nonhuman receptor, e.g., fish, birds, or other wildlife, might adversely be affected. It involves characterizing the nature and strength of the evidence of causation. Although the question of whether a substance causes cancer or other adverse health effects in humans is theoretically a yes-no question, there are few chemicals or physical agents on which the human data are definitive. Therefore, the question is often restated in terms of effects in laboratory animals or other test systems: “Does the agent induce cancer in test animals?” Positive answers to such questions are typically taken as evidence that an agent may pose a cancer risk for any exposed human. Information for short-term in vitro tests and structural similarity to known chemical hazards may, in certain circumstances, also be considered as adequate information for identifying a health problem .
A health problem identification for a chemical plant or industrial application can include information about:
- 1. Chemical identities.
- 2. The location of facilities that use, produce, process, or store hazardous materials.
- 3. The type and design of chemical containers or vessels.
- 4. The quantity of material that could be involved in the airborne release.
- 5. The nature of the hazard (e.g., airborne toxic vapors or mist, fire, explosion, large quantities stored or processed, and handling conditions) most likely to accompany hazardous materials spills or releases .
An important aspect of identification is a description of the pervasiveness of the problem. For example, most environmental assessments require knowledge of the concentration of the material in the environment, weighted in some way to account for the geographical magnitude of the site affected; that is, a 1-acre or 300-acre site, a 1000-1,000,000 gal/min stream. All too often, environmental incidents regarding chemical emission have been described by statements like “concentrations as high as 150 ppm” of a chemical were measured at a 1000-acre waste site. However, following closer examination, one may find that only 1 of 200 samples collected on a 20-acre portion of a 1000-acre site showed this concentration and that 2 ppm was the geometric mean level of contamination in the 200 samples.
An appropriate sampling program is critical in the conduct of a health risk assessment. This topic could arguably be part of the exposure assessment, but it has been placed within health problem identification because, if the degree of contamination is small, no further work may be necessary. Not only is it essential that samples be collected in a random or representative manner, but the number of samples must be sufficient to conduct a statistically valid analysis. The number needed to ensure statistical validity will be dictated by the variability between the results. The larger the variance, the higher the number of samples needed to define the problem .
As noted in the previous chapter, the reader should once again note that toxicologists commonly refer to two general types of health risks. These are classified as:
- 1. Acute. Exposures that occur for relatively short periods of time, generally from minutes to 1 or 2 days. Concentrations of (toxic) air contaminants are usually high relative to their protection criteria. In addition to inhalation, airborne substances might directly contact the skin, or liquids and sludges may be splashed onto the skin or into the eyes, leading to adverse effects. This subject area falls, in a general sense, in the domain of hazard risk assessment (HZRA), a topic treated in the next chapter.
- 2. Chronic. Continuous exposure occurring over long periods of time, usually several months to years. Concentrations of inhaled (toxic) contaminants are usually relatively low. This subject area falls in the general domain of health risk assessment, (HR A), and it is this subject that is addressed in this section. Thus, in contrast to the acute (short-term) exposures that predominate in hazard risk assessment, chronic (long-term) exposures are the major concern in health risk assessments.
The means of identifying health problems are complicated. Different methods are used to collect and evaluate toxic properties (those properties that indicate the potential to cause biological injury, disease, or death under certain exposure conditions). One method is the use of epidemiological studies that deal with the incidence of disease among groups of people. Epidemiological studies attempt to correlate the incidence of cancer from an emission by an evaluation of people with a particular disease and people without the disease. Long-term animal bioassays are the most common method of hazard determination. (A bioassay as referred to here is an evaluation of disease in a laboratory animal.) Increased tumor incidence in laboratory animals is the primary health effect considered in animal bioassays. Exposure testing for a major portion of an animal’s lifetime (2-3 years for rats and mice) provides information on disease and susceptibility, primarily for carcinogenicity (the development of cancer).
The understanding of how a substance is handled in the body, transported, changed, and excreted, and of the response of both animals and humans, has advanced remarkably. There are many questions concerning these animal tests as to what information they provide, which kinds of studies are the best, and how the animal data compares with human data. In an attempt to answer these questions, epidemiological studies and animal bioassays are compared to each other to determine if a particular chemical is likely to pose a health problem to humans. Many assumptions are made in health risk assessments. For example, it is assumed that the chemical administered in a bioassay is in a form similar to that present in the environment. Another assumption is that animal carcinogens are also human carcinogens. An example is that there is a similarity between animal and human metabolisms, and so on. With these and other assumptions, and by analyzing identification procedures, lists of problematic chemicals have been developed .