Biomedical Engineering Reference
In-Depth Information
Proposed framework for ecotoxicity and human toxicity:
To enable
the use of expert judgment in case of lack of quantitative information, it is
important to express the characterization factors as the product of simple
and well-interpretable factors whose order of magnitude can be determined
and checked. The USEtox framework
7, 5 9
constitutes a sound basis to combine
comparative risks approaches and life cycle toxicity approaches, and corre-
sponds to the latest LCIA methods (Figure 11.1). It is extended here to also
include the possibility to account for the fraction of the dose taken up and
its distribution inside the body, linking the external to internal dose with
pharmacokinetics.
The
human toxicity
impact is calculated as the emission source multiplied
by the intake fraction—the fraction of an emission that is taken in by the
population (iF, dimensionless)—and by an effect factor (EF, cases per kg
in
),
generally based on chronic dose-response information (e.g., ED50—effect
dose 50%). The intake fraction is itself the product of the fate factor (FF, d)
multiplied by an exposure factor (XP, 1/d) and needs to be determined both
for indoor and outdoor emissions. The impact
n
, expressed in number of
cancer and noncancer cases per year, is therefore given by
(11.1)
n
=
HCF FiF FXPFF
m
=
m
=
m
where the human characterization factor (HCF) represents the impact per kilo-
gram emitted and is itself equal to the product of the EF multiplied by the iF.
External to internal dose:
Regarding the lack of chronic dose-response
information for different nanoparticle sizes and the recent development in
pharmacokinetic modeling, we propose here an extended framework, open-
ing the possibility to model body burden—the mass or concentration inside
the body (Figure 11.9) in order to be able to extend
in vivo
measurements
obtained for one type of particle to other sizes and surface transformations
using
in silico
models. We therefore have alternatively
HCFECBBiF
=
(11.2)
where
EC
measures the risk associated
to
a given mass or concentration
in the body (
or
in the target organ) and
BB
b
=
f
θ
is the body bur-
den matrix.
BB
is a pharmacokinetic matrix representing the increase in
mass inside the body per unit intake flow and its subsequent distribution
between human organs and tissues. Its diagonal term can be expressed as
the product of the fraction of the intake that is taken up and absorbed inside
the body
(
uptake absorbed
i
i
f
i
intake absorbed
and possibly transferred to the target organ, multi-
plied by the residence time of the substance or the particle in different parts
of the body or target organ (
θ
i
b
).
Ecotoxicological impacts:
The ecological characterization factor
(ECF
freshwater
) link an emission to the temporally and spatially integrated
)
