Environmental Engineering Reference
In-Depth Information
For the biotransfer coefficient in milk the relation is as follows:
log B T ,2 =−
8.1
+
log Kow n
=
28, r
=
0.74
(11.46)
with log Kow going from 2.8 to 6.9.
Outside these bounds, the model is not considered to be appropriate. In order to
calculate B T in these cases, use of the value calculated with the minimum or the
maximum value of Kow for which the model is defined is recommended (European
Commission 2008 ).
The user of Eq. ( 11.46 ) should also check that the output rate of contaminant
from milk or eggs calculated with this predicted B T ,2 is less than the intake of
contaminant by the animals.
These relationships are used in different multimedia models (CalTOX, University
of California 1993, California Department of Toxic Substances Control, 2009 ;
HESP, Veerkamp and Ten Berge 1994 ; EUSES, European Commission 2008 ).
However, the validity of these relationships has been questioned in the past years,
for the following reasons (RTI 2005 ):
B T for contaminants with high Kow are overestimated with these relationships
(the predicted amount of contaminants in animal products is greater than the
amount ingested by the animals),
they are not suitable for rapidly metabolising contaminants,
they are based on a mixture of steady-state and non-steady-state data
they are based on a mixture of data from lactating and non lactating animals
Other relationships have been developed, but these are used less often. An
example is the relationships of Dowdy et al. ( 1996 ), based on molecular topol-
ogy (molecular connectivity index) instead of the octanol-water partition coefficient.
However, these kind of relations do not appear to be more realistic.
RTI ( 2005 ) developed a new relationship based on a methodology which aims to
avoid the limits and drawbacks highlighted in the work of Travis and Arms ( 1988 ).
In their analysis, the authors found no significant difference between contaminant
concentrations in milk fat and beef the following equation was derived to predict
contaminant concentration in fat:
(log Kow ) 2
3.56, r 2
log B T ,fat =−
0.099
×
+
1.07
×
log Kow
=
0.83 (11.47)
B T ,meat and B T ,milk are calculated by multiplying B T ,fat by the fat content of meat
and milk, respectively. The authors claimed that this equation is appropriate for
organic contaminants with a log Kow between -0.67 and 8.2. As with the regres-
sion models shown above, for contaminants with log Kow values lying outside this
range, B T, fat has to be calculated with the minimum or maximum value of Kow
for which the model is defined. However, because of the way the relationship was
established, it may overestimate biotransfer coefficient for contaminants that are
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