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the Office of Technology Assessment of the Congress of the

United States (Table 2).

Determining the probability of cancer being caused at

the concentration levels of a substance encountered in the

environment is very difficult. Testing on human beings is

not to be considered; therefore, accidental exposures are an

important source of information, but the actual exposures and

doses are usually poorly documented and existing records

can be misleading. As a result, the use of animals as surro-

gates is the usual alternative, with the size of the doses used

and the difference in response between humans and animals

as serious complicating factors.

Toxicity and Risk Assessment

Three elements must be present for a situation to have toxi-

cological implications:

1. A chemical or physical agent capable of causing a
   response


2. A biological system with which the agent inter-
   acts to produce a response


3. A response that can be considered deleterious to
   the biologic system

The deleterious response—that is, injury to health or the

environment—should be significant. It is counterproductive

to the goal of focusing our available resources on significant

toxicological problems to include substances that cause only

momentary discomfort or quickly reversible physiological

change from the types of exposures that can be reasonably

expected in daily life. There are no harmless substances if

one does not place a limit on the type or extent of exposure.

Nitrogen, oxygen, carbon dioxide, and water can all be harmful

or even deadly under different types of exposures. Therefore,

judgment must be used in making decisions about substances

and the possibility of exposures at levels that can cause harm.

Substances that can cause harm by interfering with or

destroying the functions of organs can be distinguished from

those whose mode of action is attack on cell growth and

reproduction.

Thus, the action of cyanide (which prevents tissues from

using the oxygen provided by the blood) classifies it as dif-

ferent from a carcinogen (which causes the abnormal pro-

liferation of cells), a mutagen (which changes the genetic

material and thus damages new cells), and a teratogen (which

changes the cell framework of an embryo).

Quantification of the risk associated with environmen-

tal exposures is a major activity of environmental control.

Originally, this effort focused on the effects of carcinogens;

noncarcinogens were delegated to minority status. Now

there is an increased level of concern about effects other

than cancer—for example, the impact of synthetic chemi-

cals on the endocrine system that can result in disruptions

of the immune system or behavioral problem. The immu-

notoxicity, neurotoxicity, teratogenicity, and toxicity to spe-

cific body tissues of many compounds have not received

significant attention in comparison to their mutagenicity

and carcinogenicity. There is danger that once a substance’s

carcinogenicity or noncarcinogenicity has been declared, its

other harmful properties will be neglected.

To evaluate the risk from exposure to a specific hazard-

ous material, it is important to obtain as realistic as possible

an estimate of the dose received by a representative individual

via inhalation, ingestion of food or drink, and other possible

ways that substances can be absorbed. In the case of children in

contact with soil and other materials, both indoor and outdoor,

the possibility of hand-to-mouth exposure must be considered.

As an example, an individual living in the vicinity of an oper-

ation that releases dioxin into the atmosphere is affected by

both inhalation and by the amount of food and water ingested

because of possible contamination from fallout. Obtaining the

necessary dose data requires knowledge of emission rates and

patterns, stack heights and local meteorological conditions, and

TABLE 2

Summary of cancer-associated environmental factors

Factor Sites Range of estimates

Diet Digestive tract, breast endometrium, ovary 35 –50%

Tobacco Upper respiratory tract, bladder, esophagus, kidney, pancreas 22–30%

Asbestos Upper respiratory tract, others 3–18%

Occupational Upper respiratory tract, others 4–38%

Alcohol Upper digestive tract, larynx, liver 3–5%

Infection Uterine cervix, prostate, and other sites 1–5%

Sexual development, reproductive patterns, and sexual practices Breast, endometrium, ovary, cervix, testis 1–13%

Pollution Lung, bladder, rectum 5%

Medical drugs and radiation Breast, endometrium, ovary, thyroid, bone, lung, blood 1–4%

Natural radiation Skin, breast, thyroid, lung, bone, blood 1–3%

Consumer products Possibly all sites 1–2%

Unknown—(e.g. new chemicals, dumps, stress) All sites?

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