Environmental Engineering Reference
In-Depth Information
[
n
1
]
10
α
1
+
[
n
2
]
10
α
2
+
...
[
n
n
]
10
α
n
[
n
]
10
α
n
and: TP
CAj
=
1
HU
j
=
.
+
=
e
−
log(HU
j
)
·
β
−
1
1
+
j
n
with: HU
j
is the Hazard Units of the group of toxicants for which the CA
model is valid. [n
1
], [n
2
], et cetera are concentrations of toxicants 1, 2,
.
(e.g. in mg/kg
dw
; after correction for a standard soil and background concen-
trations; see Swartjes (2010)).
...
α
n
is a log-transformed value for toxicity (e.g.
a logHC50).
β
j
is a slope parameter of the SSD (these
α
n
and
β
j
constants can
for instance be found in Rutgers et al.
2008b
).
In the next step the TP of the complete mixture of toxicants is calculated
using the RA model:
TP
MM
=
1
−
(1
−
TP
CA1
)
·
(1
−
TP
CA2
)......(1
−
TP
CAn
)
=
1
−
(1
−
TP
CAn
)
The Toxic Pressure obtained from the mixed model (TP
MM
)isexpressed
as a multi substance Potentially Affected Fraction (msPAF) value and ranges
from 0 (no effects) to 1 (theoretical maximum effect value).
Toxicity Characterization with Bioassays
The scaling of results from bioassays is usually straightforward, when test
performance in control and reference samples is known. Sometimes, it is nec-
essary to define a theoretical value for the full effect (1
=
100%). The final
result can then be expressed as a fraction, ranging from 0 to 1. Examples
of using and scaling results from bioassays can be found in e.g. Jensen and
Mesman (
2006
) and Semenzin et al. (
2008
). The basic principles can be
illustrated with earthworm tests. Data from the survival or reproduction of
earthworms in contaminated and reference samples are straightforwardly fed
into the ERA (ISO 16387:2004, ISO 11268-2:1998). The reference is set to 0;
no survival is set to 1. The percentage of survival compared to the reference
can be directly used as an effect value. The results from the chronic reproduc-
tion test can also follow this scheme, although arguments to use a different
scale can be put forward. It becomes a bit more difficult with, for instance, the
earthworm avoidance test (ISO 17512-1:2008). Typically, the distribution of
worms between control and contaminated soil can be used on an effect scale
(Amorim et al.
2005
):
C
)
−
1
Effect
=
(
R
−
C
)
·
(
R
+
with:
R
is the number of worms in the reference or control soil;
C
is the num-
ber of worms in the contaminated soil. A negative outcome indicates attraction
to the contaminated soil, which should be set to zero. Also with the avoidance
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