Environmental Engineering FOURTH EDITION

Riskhalysis 47

ECOSYSTEM RISK ASSESSMENT

Regulation of toxic or hazardous substances often requires an assessment of hazard

or risk to some living species other than homo sapiens, or assessment of risk to an

entire ecosystem. Methods for ecosystem risk assessment are now being developed by

Suter and others (Suter 1990). Ecosystem risk assessment is done in the same general

way as human health risk assessment, except that identification of the species at risk

and the exposure pathway is a far more complex process than in human health risk

assessment. Assessment endpoints are values of the ecosystem to be protected and

are identified early in the analysis; these endpoints may include numbers of different

species, life-cycle stages for a given species, reproductive patterns, or growth patterns.

Identification of specific endpoints implies choices among potential target species.

Ecosystem risk assessment is as yet in its infancy, and details of its practice are beyond

the scope of this textbook.

CONCLUSION

The best available control for nonthreshold pollutants will still entail a residual risk.
Our industrial society needs accurate quantitative risk assessment to evaluate the pro-
tection afforded by various levels of pollution control. We must also remain aware that
determination of safe levels of pollutants based on risk analysis is a temporary measure
until the mechanism of the damage done by the pollutant is elucidated and understood.
At present, we can only identify apparent associations between most pollutants and a
given health effect. We should note that analysis of epidemiological data and determi-
nation of significance of effects require application of a test of statistical significance.
There are a number of such tests in general use, but their application is not central to
the scope of this text and will not be considered here.
Almost all of our knowledge of adverse health effects comes from occupational
exposure, which is orders of magnitude higher than exposure of the general public.
Doses to the. public are usually so low that excess mortality, and even excess morbidity,
are not identifiable. However, development of pollution control techniques continues
to reduce risk. The philosophy, regulatory approaches, and engineering design of
environmental pollution control compose the remainder of this book.

PROBLEMS

3.1 Using the data given in the chapter, calculate the expected deaths (from all
diseases) for heavy smoking in the United States.
3.2 Calculate the relative risks of smoking and alcoholism in the United States.
Do you think a regulatory effort should be made to limit consumption of alcohol?
3.3 The International Commission on Radiation Protection has determined the
lifetime unit risk for cancer for low-energy ionizing radiation to be 5.4 x per rem
of absorbed radiation. The allowed level of ionizing radiation (the EPA standard) above