Three of Scorecard's ranking systems generate an "integrated" score that
accounts for risks to both human health and ecosystems. Combined scores
have the advantage of considering multiple attributes that society
desires to safeguard from harm. Chemicals that pose no threat to human
health, for example, will still rank high relative to others if they
pose serious risks to aquatic life or other ecosystem components.
Combined scores require both scientific judgments about to assess a
chemical's potential environmental hazards with available data and
ethical judgments about the relative weight that should be accorded to
human health vs. ecological concerns. Ranking systems with detailed
information requirements (like the UTN Total Hazard Value Scores) cover
fewer chemicals compared to those that rely on screening-level,
surrogate indicators of potential hazard (like the WMPT Overall Risk Screening Score).
The UTN ranks included in Scorecard weigh human health and ecological
concerns equally, while the WMPT ranks put double weight on a chemical's
persistence in the environment. The IRCH system uses a more complicated weighting system, where ecological effects are combined with occupational health effects.
WHY RANK CHEMICALS BASED ON COMBINED HAZARD INDICATORS?
To make sensible decisions regarding toxic chemicals, it is clearly
preferable to have a complete picture of the kinds of environmental
health risks a chemical poses. Society is interested in safeguarding
many potential targets of toxic chemicals, so more comprehensive hazard
ranking systems are desirable if we want to avoid "environmental
surprises" regarding the use or release of toxic chemicals. Such
mistakes have occurred frequently in the past, because decisions have
been based on attempts to minimize just one impact of chemical use.
Chlorofluorocarbons (CFCs), for example, were heavily promoted from
the 1950s for industrial and consumer product uses because they are
generally not very toxic to humans (particularly in contrast to other
chemicals like ammonia, which were then used as refrigerants). The
characteristics of "inertness" and volatility that made CFCs attractive
meant that they were extremely persistent in the atmosphere and could
migrate to the stratosphere, where they had an unanticipated but
devastating effect on the earth's protective ozone layer. Ultimately,
the low human health hazards posed by CFCs was dramatically outweighed
by their global environmental hazard. Such surprises are strong lessons
in favor of precaution and thorough assessment of potential adverse
impacts associated with chemical use or release.
MORE ON ENVIRONMENTAL SURPRISES
Kates, R. and W. Clark. Environmental surprise: Expecting the unexpected.
Environment March: 6-34. 1996.
Prather, M., P. Midgley, F.S. Rowland and R. Stolarski. The ozone layer:
The road not taken. Nature 381: 551-554. 1996.