uptake of chemicals into plants - technical university of ... 1 standard model handout.… ·...
TRANSCRIPT
1
Uptake of Chemicals into Plants
by Stefan Trapp for the course 12906
Plants drive global and local biochemical cycles
(water, oxygen, carbon, nutrients, energy)
> 95% plants, 0.9% fungi, 0.1 % animal (bacteria ? 1-5%?)
The cycle of matter and the origin of our soils
Danish soils have an age
of ca. 12 000 years
How plants function
Roots take up water and solutes
Stems transport water and solutes
Xylem = water pipe
Phloem = sugar pipe
Leaves transpire water
and take up gas
Fruits are sinks for phloem and xylem
Definition “BCF”
BCF is “bioconcentration factor”
Concentration in plants [mg/kg]
BCF = ――――――――――――――――――
Concentration in soil [mg/kg]
Take care! BCF differs for
- dry weight versus wet weight
- with uptake from air
- for roots, leaves, fruits, wood
2
How to determine BCF the right way
Do not just take Cplant/Csoil !
.
y = 0.1744x + 23.845
R2 = 0.982
0
250
500
750
0 1000 2000 3000 4000
C soil
C p
lan
t
slope
CPlant : CSoil = BCF
intercept
= background
from air
Do not just take Cplant/Csoil !
Some measured BCF (organic compounds)
Compound Properties mean BCF Range Plant part
PAH, BaP lipophil 0.001 10-5 to 0.01 roots, leaves
TCE volatile < 10-3 < 10-3 fruits, leaves
Pesticides polar, non-
volatile
1 <1 to 10 roots, leaves,
fruits
Explosives
(TNT, RDX)
polar, non-
volatile
3 0.06 to 29 roots, leaves,
fruits
POPs (DDT,
lindane,
PCB)
lipophil 0.01 0.02 to 0.2 roots, leaves
“dioxins”
TCDD/F
lipophil 10-2 to 10-4 10-5 to 10-3 roots, leaves,
fruits
Sulfolane
(detergent)
Polar, non-
volatile
680 leaves
unit usually dw:dw
Some measured BCF (heavy metals)
Compound mean BCF max BCF
As Arsenic 0.002 0.28
Cd Cadmium 0.1 14
Hg Mercury 0.01 0.09
Ni Nickel 0.01 30
Zn Zinc 0.01 4
Cu Copper 0.01 nd
Pb Lead 0.003 nd
unit dw:dw Regression with log KOW for Conc. vegetation to Conc soil (dry wt.)
588.1log578.0log OWKBCF
BCF: Empirical regression by Travis & Arms
Easy to use
Gives good results
Old (ex-RISK)
Problem: only uptake
from soil; no air
Principles of plant uptake models
Standard Plant Uptake Model DTU
diffusive
equilibrium
flux with water
The Standard model
is a flux based solution:
water flows from soil to leaves
(fruits). Every molecule in the
water is transported –
unless it is adsorbed in soil,
roots, stem
or it is degraded
or it evaporates.
The standard model assumes
purely physical fluxes and
partitioning - no enzymatic
in/exclusion, no active transport
(all can be added on demand).
3
Standard Plant Uptake Model DTU
diffusive
equilibrium
flux with water
The Standard model consists
of four differential equations for
fluxes, partitioning and
exchange with soil and air
several versions
(steady state, dynamic, crop-
specific, coupled soil-plant-air)
The diff eqs remain the same.
find all you need at
http://homepage.env.dtu.dk/stt
Roots
some facts and considerations
Some facts about roots
► We can’t see them, but they are the most important part
of the plant, i.e. most plants can survive when you
remove stem and leaves – but rarely any without roots.
► Roots make up about 50% of the mass of the plant
(in extreme cases, such as desert plants, > 90%).
► The rhizosphere has the highest metabolic capacity of
the earth (roots, bacteria, fungi).
► Average maximum rooting depth is 2.1 m for cropland,
2.9 m for forest (humid zone), 4.6 m (globe).
► Maximum observed rooting depth is 68 m (Kalahari).
The two big plant empires
Monocotyledone
(seedling with 1 leaf)
grasses, corn, onions, garlic, tulips, lilies
All cereals
Dicotyledone
(seedling with 2 leaves)
herbs, trees, vegetables
All root vegetables
Root structure
Monocotyledone Dicotyledone
Roots start at one point, no
branching; thin, long
Fractal structure, branched roots,
fine roots and thick roots.
thank you dreamstime.com
Root surface
To take up water and
solutes, plants make ”root
hairs” of a few mm length.
These root hairs exist for
only a few hours and
increase the root surface
by factor 100 or more!
The calculated surface of 1 kg roots with 1 mm diameter is 4 m2
at a length of 1.27 km.
The true surface – due to root hairs – is 1000 m2 at a length of 10 000 km of
one single rye plant (!).
It is thus fair to assume local equilibrium between root tips and soil.
4
Root model mass balance
Change of mass in roots =
+uptake with water – transport to shoots
dmR/dt = CWQ – CXyQ
where
m is mass of chemical (mg)
C is concentration [mg/kg, mg/L]
Q is water flow [L/d]
index R is roots, W is water and Xy is xylem
Concentration at inflow root = concentration in soil pore water
From mass to concentration
m is chemicals’ mass (mg)
M is root mass (kg)
C is concentration (mg/kg)
C = m / M
dmR/dt = d(CR MR)/dt
The root grows – integration for C and M required (oh no ...!)
Dilution by exponential growth
Chemical mass: m = constant
Plant mass: M(t) = M(0) x e+kt
m/M = Concentration in plant: C(t) = C(0) x e-kt
0
25
50
75
100
0 24 48 72
Time
Pla
nt
mass,
co
nce
ntr
ati
on
M (kg) m/M (mg/kg)
Root model concentration
Change of concentration in roots =
+ uptake with water
– transport to shoots
– dilution by growth (rate k)
dCR/dt = CWQ/M – CXyQ/M – kCR
where
k is growth rate [d-1]
CXy is concentration in xylem = CR/KRW
CW is concentration in soil pore water
Partition constant Root to Water KRW
= equilibrium root to water
KRW = W + L x KOW
0.77
W ca. 0.85 log Kow
KR
W
Data by Briggs et al.
(1982) for barley
W = water content
L = lipid content
Root model solution
Mass balance: change = flux in – flux out
Set to steady-state and solve for CR
R
RW
RW CkMK
QC
M
QC
0
QCQCdt
dmXyW
Concentration: divide by plant mass M
R
XyW kCM
QC
M
QC
dt
dC
RW
RXy
K
CC
d
SoilW
K
CC
d
soil
RW
RK
C
kMK
Q
MQC
/
5
For high KOW (high KRW): growth dilution.
BCF > factor 100 below equilibrium
Root Model result for roots to soil (Csoil = 1 mg/kg)
0.0001
0.001
0.01
0.1
1
10
0 2 4 6 8
log Kow
C r
oo
t (m
g/k
g w
w)
T&A RCF root model
TCE
BaP
d
soil
RW
RK
C
kMK
Q
QC
0.000
0.001
0.010
0.100
1.000
PCB28
PCB52
PCB10
1
PCB13
8
PCB15
3
PCB18
0
BC
F c
arr
ot
(fre
sh w
eig
ht)
dynamic exp core equilibrium exp peel
Comparison to experimental data
Carrot
model KRW
Slow uptake velocity - factor F
QCQCFdt
dmXyW
W
RW
R C
kMK
Q
MQFC
/
1,
, WaterR
ChemR
P
PF
Mass balance: change = flux in – flux out
but with reduction factor F for slow uptake
solve for CR
7.6loglog , OWChemR KP
Default 2.2x10-9 m/s is used for the permeability water, PR,Water.
Translocation Upwards
Water transpiration of plants in Central Europe
1 mm = 1 L/m2
Type mm/year mm/d
Broad-leaf trees 500-800 4-5
Needle trees 300-600 2.5-4.5
Corn fields 400-500 up to 10
Pasture, meadows 300-400 3-6
General rule:
About 2/3rd of precipitation (rain, snow, fog) is transpired by plants.
Plants are the most important element of the water budget.
Translocation upwards in the xylem
A ”standard plant” transpires 500 L
water for the production of 1 kg dry
weight biomass!
= approx. 50 L per 1 kg fresh weight
= approx. 1 L/day for 1 kg plant mass
(default value)
6
Definition TSCF
TSCF = ”Transpiration stream concentration factor”
[mg/L : mg/L]
If TSCF is high, good translocation upwards.
Two methods:
1) Regression to log KOW (Briggs et al., Dettenmaier et al.)
2) Calculation from root model
C_water
C_xylem TSCF
Translocation upwards in the Xylem
For translocation upwards, the chemical must cross the root and
come into the xylem.
“TSCF” = transpiration stream concentration factor = CXylem/CWater
2.44
1.78) - K (log-exp0.784 TSCF
2
OW
Briggs et al. (1982) = optimum curve
Method 1: Regression for TSCF by Briggs (1982) Method 2: Regression for TSCF by Dettenmaier (2009)
OWKTSCF
log6.211
11
Dettenmaier et al. = sigmoidal curve
Method 3: Calculation of TSCF with Root Model
RW
RW
RW
W
R
W
XyK
kMK
Q
QK
C
C
C
C//
RW
RXylem
K
CC Model:
Lipophilic chemicals (high log Kow) are
adsorbed in the root and not translocated
Test of TSCF-Methods
Compilation of data from literature Predicted TSCF
0
0.2
0.4
0.6
0.8
1
1.2
-2 0 2 4 6
log Kow
TS
CF
Model TSCF Briggs Dettenmaier
Modern empirical curve and theory in good agreement (for log Kow > -2).
Do not use old Briggs equation any more!
7
0
0.2
0.4
0.6
0.8
1
1.2
-4 -2 0 2 4 6
ca
lc. T
SC
F
log Kow
TSCF
F
RW
RW
RW
W
R
W
XyK
kMK
Q
QFK
C
C
C
C//
TSCF for very polar compounds (with factor F) Sorption to wood
Kwoodlog
KWood = CWood / Cw
log KWood = – 0.27 + 0.632 log KOW
(oak)
log KWood = – 0.28 + 0.668 log KOW
(willow)
Lignin is a good sorbent
for lipophilic chemicals!
Chemicals in the Stem
Chemicals travel upwards with the water in the stem
● loss (volatilization, degradation, growth dilution)
● uptake from air
Iktdz
dC
k: overall loss rate; I: gain from air
)1()0()( // ukzukz ek
IeCzC
Stem is only considered in the Fruit Tree model
Model for uptake into leaves and fruits
+ - exchange with air
+ influx with xylem
- dilution by growth
- metabolism
Mass balance: uptake from soil and air
- phloem
Flux from roots upwards
RRR
RWR
SWS
R
R CkCKM
QCK
M
Q
dt
dC
Outflux roots is influx to (stem) leaves and fruits
R
RWL
L CKM
Q
dt
dC
low log KOW --> low KRW --> high flow upwards
outflow roots
inflow stem / leaves
Leaves – exchange with air
Stomata
Cuticle
8
Equilibrium between leaves and air
Leaves are plant material, like roots. But they do not hang in soil,
and not in water. Leaves hang in air.
The concentration ratio between air and water is
AW
Water
Air KC
C
LAAWLW
Air
Water
Water
Leaves
Air
Leaves KKKC
C
C
C
C
C /
where KAW is the partition coefficient between air and water
(dim.less Henry's Law constant)
The concentration ratio between leaves and air is then
Because usually KAW < 1 and KLW ≈ KRW >> 1 KLA >> 1
Example calculation: Equilibrium leaf-air for benzo(a)pyrene
leaf density r = 500 kg m-3, log KOW = 6.13, KAW = 1.35 x 10-5
KLW = W + L a KOW b
= 0.8 + 0.02 x 1.22 x 1 348 962 0.95 = 16251 L/L
(to water)
KLA = KLW/KAW = 16251 / 1.35 x 10-5 = 1.2 x 109 (mg/m3 : mg/m3)
KLA/r = 1.2 x 109 (mg/m3 : mg/m3) / 500 kg/m3 = 2.4 x 106 (m3/kg)
(to air)
If CAir = 1 ng m-3 = 10-6 mg m-3
CLeaf = CAir x 2.4 x 106 m3 kg-1 = 2.4 mg kg-1 (in phase equilibrium)
Exchange with air
by
-gaseous deposition
through the cuticle
-gaseous exchange
through the stomata
- dry particulate deposition
- wet particulate deposition
A rough estimate for the exchange
velocity g is 1 mm/s (default value).
- Luckily, the deposition velocity vdep
of fine particles is in the same range.
Conductance versus Permeability
Take care! Typically:
Conductance g is related to gas phase concentration
)(LA
LAir
L
K
CgACgA
dt
dm
)(LW
LAir
AW
L
K
CPAC
K
PA
dt
dm
Permeability P is related to concentration in water
is equivalent, g = P / KAW
Differential equation for concentration in leaves (or fruits)
The change of mass in leaves = + translocation from roots + uptake from
air (gas and/or particles) - loss to air - growth dilution - degradation
from roots from air to air
LL kCI
dt
dCeasy to solve: linear diff. eq. of the type
LLL
LLA
LA
L
LR
RWL
L CkCMK
mLgAC
M
gAC
KM
Q
dt
dC
31000
growth &
degradation
Q: water flow L/d, M: mass kg, A: area m2, g: conductance m/d, k: rate d-1
Take care: Particle deposition and rain can be added on demand
(see script and Standard Model xls-version)
Mass Balance of Fruits
essentially identical to the mass balance in leaves
+ - exchange with air
( + spray application)
+ influx with xylem
and phloem
- dilution by growth
- metabolism
9
Mass balance for Fruits
The change of mass in fruits =
+ flux from xylem and phloem + uptake from air - loss to air
from roots from air to air
kCIdt
dCeasy to solve: linear diff. eq. of the type
FFF
FFA
FA
F
FR
RWF
FF CkCMK
mLgAC
M
gAC
KM
Q
dt
dC
31000
growth &
degradation
Summary: "Standard Model"
LLL
LLA
LA
L
LR
RWL
L CkCMK
mLgAC
M
gAC
KM
Q
dt
dC
31000
FFF
FFA
FA
F
FR
RWF
FF CkCMK
mLgAC
M
gAC
KM
Q
dt
dC
31000
RRWRWR CkMQKCMQCF
dt
dC ///
where index R is root, W is water, L is soil, F is fruit and A is air.
C is concentration (mg/kg), Q is water flux (L/d), M is plant mass (kg), K is
partition coefficient (L/kg or kg/kg), A is area (m2), g is conductance (m d-1)
and k is rate (d-1).
A system of coupled linear differential equations
Standard Plant Uptake Model DTU
diffusive
equilibrium
flux with water
The Standard model consists
of four differential equations for
fluxes, partitioning and
exchange with soil and air
several versions
(steady state, dynamic,
crop-specific, coupled
soil-plant-air)
The diff eqs remain the same.
find all you need at
http://homepage.env.dtu.dk/stt
Summary: "Standard Model"
LLL
LLA
LA
L
LR
RWL
L CkCMK
mLgAC
M
gAC
KM
Q
dt
dC
31000
FFF
FFA
FA
F
FR
RWF
FF CkCMK
mLgAC
M
gAC
KM
Q
dt
dC
31000
RRWRWR CkMQKCMQC
dt
dC ///
where index R is root, W is water, L is soil, F is fruit and A is air.
C is concentration (mg/kg), Q is water flux (L/d), M is plant mass (kg), K is
partition coefficient (L/kg or kg/kg), A is area (m2), g is conductance (m d-1)
and k is rate (d-1).
A system of coupled linear differential equations
Air in/out Growth
, degr.
from roots
soil in roots out Growth, degr.
A ”standard” child eats
100 to 200 mg soil a day (*)
”Pica child: 10 grams (acute effects)
How much soil do you eat?
More than you think ...
* ECETOC: 100 mg/d, MST: 200 mg/d
Direct Soil Uptake
tak for foto, Peter
Transfer to leaves with attached soil
Soil on plant surfaces
(Li et al. 1994)
[g soil/kg plant dw]
Lettuce 260
Wheat 4.8
Cabbage 1.1
Default value: 1% attached soil (wet weight) for leaves
0.1% for fruits and anything else
BCF(leafy vegetables to soil) = BCF model + 0.01 or 0.001
10
Changes on demand
This is an open code, and me and my team modify
as needed. Sometimes we add, or ommit
- factor F for slow uptake
- fraction at particles in air
- wet and dry particulate deposition
- wet deposition (rain)
and more
Doesn't mean that something is false:
There is no "true" standard model, it changes
with the scenario and the compound.
Default Data for Fruits and Leaves
Fruits Leaves Unit
Mass M 1 1 kgww
Area A 1 5 m2
Density r 1000 500 to
1000
kgww m-3
Water stream Q 0.02 to 0.2 1 L d-1
Lipid content L 0.02 0.02 kg kgww-1
Water content W 0.15 0.8 L kg-1
Conductance g 86.4 86.4 m d-1
Deposition velocity
from air
vdep 86.4 86.4 m d-1
Growth rate k 0.035 0.035 d-1
Time to harvest t 60 60 d
Attached soil R 0.001 0.01 kg/kg
Change of result with plant input data Standard Model in excel
http://homepage.env.dtu.dk/stt/
-2 0 2 4 6
1
-3
-7
0.0001
0.001
0.01
0.1
1
10
100
1000
C Leaves
log Kow
log Kaw
1
-1
-3
-5
-7
-9
partitioning
air-water
Accumulation in leaves: polar, non-volatile compounds
(such as pesticides, detergents, pharmaceuticals)
Uptake from soil into leaves
calculated with the Fruit Tree Model
Uptake from soil into fruits
-2 0 2 4 6
1
-3
-7
0.0001
0.001
0.01
0.1
1
10
C Fruit
log Kow
log Kaw
1
-1
-3
-5
-7
-9
Accumulation in fruits: less than in leaves, but same
type (polar and non-volatile) of compounds
11
1 -1 -3 -5 -7 -9
-2
2
6
0.0001
0.001
0.01
0.1
1
10
C Fruits
log Kaw
log Kow
-2
0
2
4
6
Uptake into fruits from air
“the usual candidates”: semivolatile lipophilic organic
compounds such as PCB, DDT, PAH, PCDD/F
Crop specific models
Limitations of the Standard Model
The "Standard Model" is only applicable
● for neutral organic compounds
● for exponentially growing plants
● for steady state
Thus it is difficult to simulate real scenarios.
It is more a "generic" model.
More realistic scenarios can be simulated using the "dynamic
cascade model" (more tomorrow).
Application of the Standard Model
The "Standard Model" is the easiest way to calculate the dynamic
system soil-plant-air in a "correct way". That's why it is rather
popular. It is used by
● EU Chemical risk assessment (TGD, REACH)
● CLEA Contaminated Land Exposure Assessment (UK)
● Csoil (NL)
● RISK (USA)
and also
● Teaching at DTU
● Teaching here and now ☺
Crop specific models
Application of the Standard Model:
Can we do Urban Gardening?
12
Urban Gardening in Copenhagen
In most if not all Western cities, people start to grow their own
vegetables and fruits in a wave named "Urban gardening". People do
so for sustainability, fresh and healthy food and for the joy of gardening.
Copenhagen is no exception.
Soil pollution
Most if not all Western city soils are contaminated with pollutants such as
lead (Pb) and more heavy metals (Cd, Cu, Cr, Ni, Zn), arsenic (As), organic
contaminants (tar, oils) and more.
Copenhagen is no exception.
Exercise: Health Risks of Urban Gardening
Question
Which pollutants do you think are of relevance for
Urban Gardening in Copenhagen ?
Example compound
Benzo[a]pyrene very potent carcinogenic (lung cancer)
unit risk (air) 1.2 ng/m3 = 1 cancer in 10 000 persons
Polycyclic aromatic hydrocarbon PAH
log Kow 6.13
KAW (Henry’s law constant) 1.39x10-5 L/L
Emissions from all kind of fires (heating, traffic, industry), tar, oils
Concentrations in air 0.1 ng/m3 to > 10 ng/m3
Copenhagen center (HC Andersen Bvd) 0.34 ng/m3 (average)
Concentrations in soil 0.05 mg/kg to > 3 mg/kg
Copenhagen 0.084 to 2.1 mg/kg
13
Legal standards for BaP water, air, soil and food
Compound (Ground-)
Water
Air Soil Food
Benzo(a)
pyren
10 ng/L 1 ng/m3
0.3 to
3 mg/kg
1 to 10
ug/kg
comment Sum PAH BaP only
quality and
intervention
much
higher than
water…
Legal standards for soil and air were derived without considering
uptake into food from these compartments.
Problem
► few measurements of garden soil, no legal standards
for home-grown food
► uncertainty at authorities + precautionary principle
The City of Copenhagen contacted us and asked whether the people
can do urban gardening
Which advice can we give urban gardeners in
Copenhagen?
Exercise 1
open file
”Standard Plant Uptake model 2015 empty.xls”
and
1) Predict uptake of BaP from soil and air into plant
with Copenhagen data,
2) calculate dietary intake with garden plants and
3) estimate associated health risks
Step 1: Enter substance data for
benzo(a)pyrene in Copenhagen city
► Open file “Standard Plant Uptake Model 2015 empty”
- enter these data for benzo(a)pyrene cells A3 .. C10
Source:
Rippen G., Handbuch
Umweltchemikalien
Air: HC Andersen Boulvd.
soil: clean soil;
water; legal standard
Result: Predicted concentrations in (garden) plant
see cells A21 .. C28 and Figure 1
Result of step 1: Predicted concentrations of
benzo(a)pyrene in plants from Copenhagen City
Now we know the concentrations in air, food, soil ...
but is this dangerous?
It depends on how much of this is eaten.
Who eats what?
Consumption data of average Danish are available for children and adults
14
Average Consumption in Denmark
Data for average Danish women are default in the model
plus Air inhalation: 10.7 and 11.3 m3/d Soil ingestion 0.1 and 0.05 g/d
bodyweight child 35 kg and woman 67 kg
900500
205127 109
7348
12
1
10
100
1000
10000
Wat
er (g
/d)
Milk
(g/d
)
Bre
ad &
Cer
eals
(g/d
)
Tree
frui
ts (g
/d)
Mea
t (g/
d)
Potato
es (g
/d)
Veget
able
s (g
/d)
Fish (g
/d)
g/d
child woman
Step 2: Enter consumption data of an urban
gardener in Copenhagen
Data for average Danish women are default in the model
but how much eats a typical gardener from his own garden in Copenhagen?
I doubt that it’s more than 10% - or? Ingestion of soil I chose 50 mg/d.
Divide numbers for roots, leaves and fruits by factor 10 (cells B33 to B35)
Consumption data
Water 1.4 L/d
Air 11.3 m3/d
Soil 5.00E-05 kg/d
Roots 0.043 kg/d
Leaves 0.019 kg/d
Fruits (corn) 0.137 kg/d
Bodyweight 67 kg
Consumption data
Water 1.4 L/d
Air 11.3 m3/d
Soil 5.00E-05 kg/d
Roots 0.0043 kg/d
Leaves 0.0019 kg/d
Fruits (corn) 0.0137 kg/d
Bodyweight 67 kg
Before: all diet (default) After: diet from urban garden (10%)
Dosis facit venum
“All substances are
poisons:
there is none which is not
a poison. Only the right
dose differentiates a
poison from a remedy.”
Paracelsus (1493-1541)
German physician and father of
modern toxicology.
“The amount makes the toxicity”
How toxic are PAH and benzo(a)pyrene?
0
25
50
75
100
0 2 4 6 8 10 12
Concentration
Eff
ec
t
Effect (threshold) (linear)
Dose-response relationships - Unit Risk
toxic without
threshold
linear
toxic with
threshold
sigmoid
Levels below the threshold are non-toxic sigmoid dose-effect curve.
Some effects (cancer, gentoxicity) do not have a threshold
– the risk of effect decreases linearly and we use Unit Risk
Common measures of health risk
ADI: Acceptable daily intake – no effect below the ADI
“Unit risk”: Linear slope, victims per million per lifetime.
for stochastic risks (e.g. cancer).
Target: not more than 1 victim per 1 000 000
inhabitants per lifetime for each chemical
is "virtually safe".
Effect ≈ exposure x toxicity
Complication BaP is never alone:
other PAH --> risk x 10
naphthalene
pyrene
dibenz[a,h]anthracene
benzo(a)pyrene
fluoranthene
anthracene
Often, only benzo(a)pyrene is measured as substitute for all:
The oral unit risk of PAH is 0.06 (to 0.5) ng BaP/kg bw/d
(BaP is used to calculate the risk from all PAH)
15
Health risks due to uptake of PAH
Unit risk for oral ingestion: BaP as marker for all PAH
1 cancer case per million for 0.06 to 0.5 ng per kg bodyweight and day
for lifelong exposure = 6 x 10-8 mg/kg bw/d
or 67.3 kg x 0.06 ng/kg bw/d = 4 ng/day for 1 cancer/million
Unit risk for inhalation of PAH (BaP):
87 x 10-6 per ng/m3 (read: 87 cases per million at 1 ng/m3)
= 1.2 x 10-8 mg/m3 for 1 cancer case (lifelong)
Enter these data cell B19, B20
Source: SCENHIR EU expert group, unit risk of PAH (sum of all),
”virtually safe dose”.
Step 3: Enter Unit Risk of benzo(a)pyrene
► Into “Standard Plant Uptake Model 2013 empty” -
enter these data (cells B19 and B20):
Unit Risk
oral 6.00E-08 mg/kg bw/d
inhalation 1.20E-08 mg/m3
Result step 3: health risks from gardening in
Copenhagen (benzo(a)pyrene only)
Predicted disease in the unit per million for lifelong exposure
See cells B50 to B52
Inhalation of BaP via air leads to 28 diseases per million
inhabitants (lifetime). Gardening is 6.4.
Conclusion: Better gardening than jogging ?
Check your results (and find mistakes)
by use of the file
”Standard Plant Uptake model BaP
Copenhagen 2015.xls“
Exercise Result
What shall we recommend to the City and People of Copenhagen,
which are so wonderful?
1 Can they do urban gardening in containers with clean soil (uptake
mainly from air, exercise 1a)?
2 Do we recommend urban gardening for soil above legal standard
(0.3 mg/kg BaP)?
3 Do we recommend to measure also heavy metals (i.e. do you wish
to hear these results, too?)
4 Do we recommend to do gardening, instead of jogging?