Page 286 - Materials Chemistry, Second Edition

270 4 Life Cycle Impact Assessment

and too little is known on the causal and quantitative relations with the chemical
or other noxes that are part of the inventory.
This multitude of impact mechanisms can be ordered into groups but show
a large diversity concerning dose-response relationships. For many substances,
toxicological impact thresholds, which are the basis of limit or indicative value
calculation, can be identified. Of these only those effect thresholds investigated
and measured by experiments can be considered. The level of scientific knowledge
of possible impacts is a prerequisite for an experimental examination. Further-
more, for the specification of effect thresholds the metrological conditions for
the quantification of a defined impact is essential. Ideally the basis for a limit or
indicative value is the highest dose where no (adverse) effect has been observed
(NO(A)EL 277) ). However, below this dose impacts which have not (yet) been targeted
in experiments or can neither be measured nor quantified are possible. The regu-
latory toxicology is concerned with possibilities and limitations to derive safe limit
or indicative values. 278) Important points of discussion are combination effects,
chronic impacts in the low dose range, a definition of what can be considered as
adverse effect as well as the handling of safety factors. This discussion targeted risk
assessment considering defined exposure conditions are not regarded here.
The derivation of indicative values for carcinogenic or mutagenic substances
without effect threshold may refer to an acceptable upper-bound excess lifetime
cancer risk (e.g. US EPA: unit risk method).
Many approaches to the treatment of the impact category human toxicity are based
on limit or indicative values which have been derived within diverse explanation
contexts.
4.5.3.2.2 Simple Weighting Using Occupational Exposure Limit or Indicative Values
For a weighting of toxic emissions into the air documented in the inventory a highly
detailed chart with limit or indicative values deduced scientifically by a uniform
method would be useful. The absolute amount of these values is not decisive for a
relative ordering system in the impact assessment as the substances are arranged
by their risk potential alone (see Sections 4.1 and 4.4.3.2).
In Germany, for example, for hazardous working materials and chemical sub-
stances toxicologically substantiated limit values of a maximum working site
concentration (MAK 279) ) are derived on behalf of the German research founda-
tion. 280),281) These values are the German occupational exposure limits (OELs) and
serve as example here. The limits are published by the German Federal Institute
for Occupational Safety and Health in Technical Rules for Hazardous Substances
(TRGS 900 282) ) and are updated every year. The DFG list is rather long and both

277) No observed (adverse) effect level: the highest level of a dose where no (adverse) effect has been
observed.
278) Reichl and Schwenk (2004).
279) Maximale Arbeitsplatzkonzentration.
280) DFG (2007).
281) For an overview on occupational exposure limits in other countries see: http://www.ilo.org
(International Labour Organization)
282) German: Technische Regeln f¨ ur Gefahrstoffe 900: Occupational exposure limits.