Page 287 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 271

organic and inorganic compounds and chemically badly characterised airborne
substances like dust are listed.
As a relative ordering system of substances concerning human toxicological
impact, OEL-values are basically suited as mid-point characterisation factors: They
are available for many substances without the necessity of a breakdown into
individual damage impacts (illness patterns, endpoints), which would imply more
subcategories. They are deduced by a uniform method with consideration of
scientific literature.
The characterisation according to this method results in a human toxicity
potential (HTP) 283) of type ‘c.V. human toxicity’ (Equation 4.24), which is acceptable
here because only the environmental problem field ‘human toxicity’ is discussed.
The ecotoxicological impacts and other impact categories contrary to being jointly
addressed in the BUWAL method 284) are handled separately.
( m )
−1
HTP = ∑ i (m fU ) (4.24)
3
MAK
i i
HTP = human toxicological potential. m = mass of the substance i released into
i
theair,for whichaMAK value was deduced per fU:
i
−1
−3
3
The unit (m fU ) results for a load (mg per fU) and a MAK value (mg m ).
The HTP can also be normalised to a reference substance (e.g. 1,4-dichlorobenzene
(DCB)) Guin´ ee et al., which is arbitrarily assigned to a HTP of one; this could,
however, lead to the impression of a uniform impact indicator, which in this
category would be even less adequate than for those already discussed.
The HTP defined in Equation 4.24 only maps the risk potential of emissions
weighted according to the MAK-values assessed in the inventory. The quantifica-
tion according to Equation 4.24 therefore provides an aggregation by weighting
according to MAK-values which have been uniformly deduced by a DFG expert
team. These values have the exclusive function of a relative toxicity scale and are
not to be applied for a weighting of an actual exposure to hazard at the working
site, the more since the working site at the centre of the technosphere is out of the
scope of an LCA. 285)
The experts of MAK-commission in DFG also proposed the ranking of carcino-
genic or suspected carcinogenic chemicals into groups of varying carcinogenic
impact probability for humans that are also applicable for a relative weighting. 286)
An objection against MAK-values or OELs of other countries as starting point
for weighting is based on the fact that the numbers of limit and indicative values
vary by nation within a certain range. Here a scope for a discretion margin can
be perceived on the part of those boards deducing these values. In view of the
geographical system boundary, German MAK-values could be used for studies in

283) Heijungs et al. (1992).
284) BUWAL (1990).
285) This is controversially discussed, particularly by colleagues from the Scandinavian countries
Poulsen et al. (2004); in our opinion hazards at the working site is part of a ‘product related social
assessment (Societal LCA, SLCA)’ as part of a sustainability valuation of products. See Kl¨ opffer
and Renner (2007) and Kl¨ opffer (2008, Section 6.3.3).
286) See also unit risk concept of US-EPA.