Environmental Engineering Reference
In-Depth Information
numerical limit is selected to provide health protection (with an adequate
margin of safety) to both the general population and those who are at special
risk. These health-based standards are based on the assumption that there
is a threshold dose (concentration as a function of time) below which no
adverse effects occur. Standard setting is a difficult activity since the scientific
literature is often insufficiently definitive in supporting both threshold val-
ues and adequate margins of safety. Due to the economic burdens involved,
the regulated community, through due-process procedures involved in rule-
making, usually challenges the validity of studies used in decision making
as well as proposed and promulgated rules and standards. This is often done
through extraregulatory political efforts as well.
The standard-setting process attempts to set acceptable numerical limits
on airborne contaminant concentrations in order to protect public health. It
is based on a review of the scientific literature by regulatory staff and outside
review panels within the context of uncertainties as to what those limits
should be, economic considerations, and the general and detailed criticisms
of the regulated community. In theory, the only consideration in setting
numerical limits should be the protection of public health. In reality, scientific
judgment as well as economic and political considerations play a role. As a
consequence, AQSs may not be sufficiently protective.
In theory, AQSs could be used to regulate air quality in public-access
buildings/environments, and possibly residences. In the early 1980s, Wis-
consin and Minnesota attempted to control HCHO levels in new mobile
homes using indoor air quality (IAQ) standards of 0.40 and 0.50 ppmv,
respectively. These were later rescinded to conform with a federal preemp-
tion in regulating HCHO emissions from wood products used in mobile
home manufacture.
Development and promulgation of AQSs and other regulatory activities
associated with toxic contaminants in the ambient environment is a long
administrative process. Initially, health risks are assessed by regulatory
agency staff.
The risk assessment process includes (1) hazard identification, (2) expo-
sure assessment, (3) assessment of potential dose-response relationships,
and (4) risk characterization. Hazard identification and dose-response
assessment involve determining potential causal relationships between
observed health effects and specific contaminant exposures. Human expo-
sures under real-world conditions are characterized in exposure assessment.
The magnitude and uncertainty of risks associated with an individual con-
taminant are evaluated in risk characterization. Risk assessment for a single
chemical is a long process, easily involving a half a decade or more of
evaluating health risk.
Use of IAQ standards to control human exposures in indoor air would
be subject to the slow timetable common for ambient air pollutants. It would
also be subject to the political and economic considerations which compro-
mise health protection when setting AQSs. A notable example was the
attempt by the Minnesota Department of Health to require a 0.1 ppmv
