Page 253 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 239

endpoint characterisation factor. For midpoint characterisation, SF hh is simply
omitted and CF hh is then the midpoint human toxicity (i.e. not human health)
characterisation factor.
The midpoint human toxicity characterisation factor [number of cases/kg emitted ]
expresses the toxic impact on the global human population per mass unit emitted
into the environment and can be interpreted as the increase in population risk of
disease cases due to an emission into a specific environmental compartment. The
endpoint human health characterisation factor [DALY/kg emitted ] quantifies the
impact on human health in the global population in Disability-Adjusted Life Years
(DALY) per mass unit emitted into the environment. DALY is a statistical measure
of population life years lost or affected by disease (or other influences) and is used
among other by the World Health Organisation.
The fate model is, without exception, the same as for ecotoxicity. Logically, the
environment in which a chemical is transported, distributed and transformed is the
same, no matter who will be affected. Therefore, for the sake of consistency, all
LCIA methods that cover human toxicity are using the same fate model as for
ecotoxicity, but of course different exposure and effect models, as this will be
specific for the targeted organism (human or ecosystem species). The fate model is
therefore the same as described in Sect. 10.11.
The exposure model relates the amount of chemical in a given environmental
compartment to the chemical intake by humans (exposure rates). It can be differ-
entiated into direct intake (e.g. by breathing air and drinking water), indirect intake
through bioconcentration processes in animal tissues (e.g. meat, milk and fish) and
intake by dermal contact. An exposure pathway is defined as the course a chemical
takes from the environment to the exposed population, for example through air, meat,
milk, fish, water or vegetables. Exposure pathways can be further aggregated into
exposure routes, such as inhalation of air, ingestion of food including drinking water
and other matter such as soil particles and dermal exposure. The human exposure
model is designed for assessing human exposure to toxic chemical emissions
applying realistic exposure assumptions and being adapted to take spatial variability
into account. In LCIA human exposure is always assessed at the population level.
The intake fraction iF is calculated as the product of fate and exposure factor
(iF = FF * XF hh [kg intake /kg emitted ]) and it can be interpreted as the fraction of an
emission that is taken in by the overall population through all exposure routes, i.e.
as a result of food contamination, inhalation and dermal exposure. A high value,
such as iF = 0.001 for dioxins, reflects that humans will take in 1 part out of 1000
of the mass of a chemical released. Dioxins are very efficient in exposing humans as
reflected by the high intake fraction. For other chemical emissions, intake fraction
−5
values typically lie in the range of 10 −10 to 10 .
The effect model relates the quantity of a chemical taken in by the population via
a given exposure route (inhalation and ingestion, respectively, dermal uptake is not
currently modelled in LCIA) to the toxic effects of the chemical once it has entered
the human organism and can be interpreted as the increase in the number of cases of
a given human health effect (e.g. cancer or non-cancer diseases) in the exposed
population per unit mass taken in. The two general effect classes, cancer and