Exercises PhD course 12906 STT 2013
1 Urban Gardening
Open file Standard Plant Uptake model 2013 Empty.xls
Enter data for benzo(a)pyrene in Copenhagen as described in the extra file “Day1Exercise 1
STT.pdf”. Calculate uptake into plants, human exposure and health risk of the chemical
benzo(a)pyrene for gradening down-town Copenhagen.
2 Sensitivity Analysis Urban Gardening
Use same file Standard Plant Uptake model 2013 Empty.xls with data entered in exercise 1.
a) set Csoil to zero to calculate uptake and risk of BaP from air
b) set Csoil to 2.1 mg/kg (7times legal standard) to calculate risk from highly polluted soil.
c) Compare risk from water, air, plants with concentrations at legal standard: set Cair to 1 ng/m3
(1e-6 mg/m3), Csoil to 0.3 mg/kg and Cwater to 10 ng/L (10e-6 mg/L). What are exposure and
risk from the three sources? (note that only 10% of vegetables are consumed from urban
garden).
Classroom exercises without computer
3 Partitioning between air and leaves
The diffusive equilibrium between leaves and air is reached when
CL
 K LA / 
C Air
KLA is the partition coefficient leaves to air (in the unit mg/m3 leaves to mg/m3 air), and  is the density of
the leaves (kg/m3). CL has the unit mg/kg, and CAir has the unit mg/m3.
Furthermore, KLA = K*LW/KAW
The units have to be considered. Similar to the root-water partition coefficient, we can define a partition
coefficient leaves to water [L kg-1]:
KLW = W + L a KOW b
with a = 1.22 L/kg and b = 0.95 for leaves.
However, KAW is in the unit [m3 m-3]. We require a unit correction
K*LW [L L-1 = m3 m-3] = KLW [L kg-1] x L [kg L-1] where L is the density here in the unit kg L-1
a) Calculate the equilibrium leaf-air for benzo(a)pyrene by hand
data leaves:  = 500 kg m-3, W = 0.8 L/kg, L = 0.02 kg/kg
data chemical BaP log KOW = 6.13, KAW = 1.35 x 10-5
Result see script page 37 (Chapter 4)
b) Use the standard model with data BaP from exercise 1 to calculate the partitioning leaves to air
(cells H16, H17). What do you get?
c) Set density of leaves from 500 kg/m3 to 1000 kg/m3. Which values change? What happens to the
calculated concentration in leves, cells H23 to H25?
(script: “as can be seen, the density is there for formal reasons; the value is divided out; only factor 1000
remains, for m3 L; yes, it's confusing. An alternative is to calculate with SI units kg and m3 from the
beginning”).
4 BCF dry weight wet weight
The bioconcentration factor BCF of a chemical in a carrot root be defined as
BCF
C Root
C Soil
where CRoot is the concentration of the chemical in the plant (mg/kg wet weight) and CSoil is the
concentration of the chemical in soil (mg/kg wet weight). If the BCF is 1 kg/kg for wet weight
(both soil and plant), what is it for dry weight (both soil and plant)? (soil data as before, carrot
water content 0.89 L/kg).