Page 226 - Materials Chemistry, Second Edition

210 4 Life Cycle Impact Assessment

The same standard specifies in a footnote (*):

The potential environmental impacts’ are relative expressions as they are related
to the fU of a product system.

The most important reasons for this judgement and this designation are:
1. LCA usually has a low temporal and spatial resolution. Only the framework is
designated by system boundaries.
2. The numerical values of the LCI refer to a fU which is freely scalable within
large margins; it is, for example, completely unimportant whether we refer
in a practical example to 1 l, 1 hl or 1000 l (most frequently applied for LCAs
of beverage packaging) or to 1 million litres! The pollutant load per fU and
concentrations derived from the emission data differ proportional to the fU by
many orders of magnitude.
3. For materials bought on the free market (i.e. without supply contract with
a specific supplier), for example commodities, their origin is rarely known
(the same applies to sources of energy), which excludes in principle atight
geographical link to the product tree ‘further above’ – or according to Clift 75)
to the ‘background’. Alternative material procurement by long-term supply
contracts increases the probability of an assignment to the region of origin.
Specific instead of generic data can be used in such cases, the suppliers are
part of the ‘foreground’.
An assignment of the impacts to space and time for an entire life cycle is therefore
usually not possible. Expositions caused by a specific analysed product system
are rarely determinable (see also Section 4.1 – Example 4.1). Nevertheless the
determination of concentration-dependent ‘risks’ is repeatedly demanded in the
impact assessment, which has led to detailed and astute analysis on the limits of the
impact assessment as part of LCA. 76) It is occasionally possible to actually identify
a part of the life cycle (in the ‘foreground’) with sufficient accuracy so that for this
section a risk analysis can be accomplished. In this case, however, assessments
are not based on an arbitrary fU but on real material and substance quantities,
for example,on the basis of the annual production of the examined product.
For example, given the efficiency of the waste water sewage plants, the known
annual consumption of a surfactant in a country can be converted into an average
concentration in surface waters (Predicted Environmental Concentration – PEC). This
value can be compared with impact thresholds or Predicted No Effect Concentrations
(PNECs) to (PEC/PNEC) that corresponds to the common procedure in risk
assessment of chemicals. 77)
Actual impacts are also determinable if the location of the manufacturing plant
of the examined product is known and as well the specific contamination caused
by the specific production of the examined product. In this case a site-specific risk

75) SETAC (1996)
76) White et al. (1995), Owens (1996) and Potting and Hauschild (1997a,b).
77) TGD (1996, 2003); see also ECHA (European Chemical Agency).