CHEMICAL PROFILES|Combined Human and Ecological Scores

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.