Environmental Engineering Reference
In-Depth Information
To analyze the uptake rate we should first consider the base organisms in the food
chain, namely, phytoplankton and detrital organic material. The uptake by organisms
generally depends on the ingestion, sorption, metabolism, and growth. For the base
in the food chain it is only dependent on sorption and desorption processes. If
k
s
(m
3
/d/g dry weight) denotes the rate of sorption from the aqueous phase and
k
d
(d
−
1
)
the desorption rate, the rate of accumulation within the base organisms is
given by
d
d
t
(W
org
[
org
)
w
org
,
A
]
=
k
s
W
org
[
A
]
−
k
d
W
org
[
A
]
(6.266)
org
is the concentration of A in the base organism (mol/kg weight of
organism), [A]
w
is the concentration in the aqueous phase (mol/dm
3
)
,
W
org
is the
weight of the organism (kg),
k
s
is a second-order rate constant (dm
3
/kg d), and
k
d
is
a first-order rate constant (d
−
1
)
. If equilibrium is assumed between the organism and
water, we have
where
[
A
]
org
[
]
A
k
s
k
d
=
=
K
BW
(6.267)
w
[
A
]
as defined in Chapter 4.
In this case the change in
org
with
t
will follow the equation
[
]
A
b
e
−
k
d
t
)
.
[
A
]
org
=
K
BW
[
A
]
w
(
1
−
(6.268)
To p
predator
e.g. human
Level n
Sorption/
desorption
Level i
e.g. Fish
Pollutant
in water
Level 1
e.g. Zooplankton
Ingestion
Excretion
Base of food chain
FIGURE 6.71
Food chain bioaccumulation of a pollutant from water.
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