SETAC-LCA

(Source:  Hertwich et al., Evaluating the environmental impact of products and production processes: a comparison of six methods. Science of the Total Environment, 1996 Vol. 196, Issue 1, 13-29.)

The life-cycle impact assessment impact assessment method, developed by the Society of Environmental Toxicology and Chemistry, aggregates pollutants with similar impacts to equivalency potentials (measured in kg CO, equivalent. kg benzene equivalent etc.) and uses decision analysis to assign weights to different adverse impacts.

Many impact categories, however, still lack a uniformly accepted aggregation mechanism. Suggestions have been made for human toxicity, aquatic and terrestrial ecosystem toxicity. The photochemical oxidant creation potential has been defined for regulatory purposes, but it depends on the local environmental conditions. Use SETAC LCA to compare the impacts from producing steel and PVC vacuum cleaner tubes. They find significant differences only in the global warming potential, which is higher for steel and the ecotoxicity potential, which is much higher for PVC.

SETAC LCA is a ‘broad’ analysis: pollution streams from every step of production, transport, use, and end-of-life are considered. At the same time, the analysis aims to be ‘deep’: it considers not only pollution streams but also their relative contribution to a specific stress (e.g. acidification) or consequence (e.g. human toxic effect). This consideration, however, is only generic; the method’s ‘equivalency factors’ are not based on a specific situation.

Stress and consequences do not have to be analyzed for each individual situation and are therefore depicted as ‘indirect consideration’. While an explicit quantification of consequences (e.g. number of additional skin cancer deaths from UV radiation) is not included in the three-step scheme, it has been used as part of the valuation step in a proposal that diverges slightly from the SETAC method. 

The equivalency potentials are cardinal measures of environmental impact. Depending on the method of valuation, the final score can be ordinal or cardinal. Traditional methods of decision analysis have been suggested for valuation, such as multi-attribute utility theory and the analytical hierarchy process. These are process-oriented methods which help to clarify the issues and exclude inconsistent preferences. They rely on explicit choices made by subjects in interviews and usually produce ordinal rankings.

LCA practitioners still debate whether to take specific local characteristics of the actual production, use and disposal processes into account, or whether generic processes situated in a generic environment suffice to represent environmental impact. Linked to this debate is the issue of potential versus actual damage: should acidic effluent released into the ocean receive the same weight as if released into a sensitive lake-ecosystem‘?

Location-independent impact analysis and the use of potential damage is not only simpler, it is intended to yield a result that is applicable to a broader range of cases and to avoid the shift of pollution to pristine areas or those with a large tolerance for pollutants. The use of generic analysis is especially favored by European analysts, who warn that a shift of pollution to less sensitive or unpolluted areas through ‘high stacks’ policies might result in surprise environmental problems, as occurred with forest die-back.

In the US, the demand for the consideration of local susceptibility and current pollution levels is tied to the frequent criticism of technology-based environmental regulation, which often requires nationally uniform controls in both pristine and polluted areas. The SETAC LCA is extremely information-intensive and therefore expensive. It requires a host of data relating to resource depletion, human and ecosystem toxicity, substance lifetimes and partition functions, as well as dominant atmospheric reactions.

No accepted procedures exist to deal with data gaps and it is unclear how to use proximate information, such as toxicity estimates derived from structure-activity relationships. The advantage of this method is that it considers a large number of impact categories and thus avoids shifting pollution from investigated endpoints to those not considered. Undesired outcomes could result from poor data quality and not keeping track of uncertainty. There are early efforts to keep track of the quality of input data, but issues of parameter and model uncertainty have not yet been addressed.