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Calculation of Predicted Environmental Concentrations in Soil
PECsoilPECsoil
General assumptions:
� Uniform distribution of the AS in the upper soil layer
- 5 cm depth (PECsoil,max, PECsoil,act, andPECsoil,twa)
- 20 cm depth if the AS tends to accumulate in soil (PECsoil,accu)
� DT50 > 100 d and/or DT90 > 365 d
� Dry bulk density: 1.5 g/cm³
� Degradation kinetics: SFO
Use specific informations:
� Crop specific application rate
� Application timing (BBCH growth stage)
- Crops specific interception at time point of application (acc. to FOCUSgw)
- Amount of AS that reaches the soil surface
Calculation of the global maximum PECsoil following singleapplication
PECsoilPECsoil
soil
intmaxsoil,
bdd100
)f-(1APEC
⋅⋅
⋅=
PECsoil,max maximum concentration in soil [mg kg-1]
Ai application rate [g a.s. ha-1]
fint,i fraction intercepted by plant cover [-]
d depth of soil layer (5 cm) [cm]
bdsoil soil bulk density (1.5 g cm-3) [g cm-3]
Calculation of the global maximum PECsoil following multipleapplications
PECsoilPECsoil
( )∑=
−⋅−
⋅
⋅⋅
⋅=
n
1i
ttk
soil
iint,imaxsoil,
inebdd100
)f-(1APEC
PECsoil,max maximum concentration in soil after n applications [mg kg-1]
n number of applications [-]
Ai application rate at i-th application [g a.s. ha-1]
fint,i fraction intercepted by plant cover at i-th application [-]
d depth of soil layer (5 cm) [cm]
bdsoil soil bulk density (1.5 g cm-3) [g cm-3]
k degradation rate (= ln (2) / DT50) [d-1]
ti time of i-th application [d]
tn time of n-th (last) application [d]
Calculation of actual concentration for given time points
PECsoilPECsoil
tkmaxsoil,actsoil, ePECPEC ⋅−
⋅=
PECsoil,act actual concentration in soil [mg kg-1]
PECsoil,max initial concentration in soil [mg kg-1]
k degradation rate (= ln (2) / DT50) [d-1]
t time after application [d]
� Actual concentrations in soil should be calculated for different time points after the
maximum concentration in soil (t = 1, 2, 4, 7, 21, 28, 50 and 100 days)
Calculation of time-weighted average concentrations
PECsoilPECsoil
� Time-weighted average concentrations should be calculated for exposure periods
(∆t) of 1, 2, 4, 7,14, 21, 28, 50 and 100 days
� TWA concentrations could be derived from time series of PECsoil,act values ranging
from the day of the first application up to 200 DAT (days after first treatment) using a
moving time-frame Excel spreadsheet
� For a given exposure period ∆t, the spreadsheet calculates the respective set of time-weighted average concentrations from the time series first (moving time-frame)
and scans for the highest value in the set afterwards
Calculation of time-weighted average concentrations
PECsoilPECsoil
0,...,200jfor(t)PECm
1maxt)(PEC
∆tt
ttsoiltwasoil,
j
j
=
=∆ ∑
+
=
PECsoil,twa worst-case time-weighted average concentration
in soil for time interval ∆t [mg kg-1]PECsoil concentration in soil at time t [mg kg-1]
t time [d]
tj start time point for integration [d]
∆t time interval [d]j running variable for time step [-]
m number of time steps in time interval ∆t [-]
PECsoilPECsoil
*Time: days after maximum concentration (PECsoil,act) or time interval (PECsoil,twa)
0.1620.000100
0.1730.05950
0.2490.15028
0.2990.22721
0.3380.29514
0.3600.3377
Long-term
0.3700.3564
0.3770.3702
0.3800.3771
Short-term
-0.3840Global maximum
PECsoil,twa [mg kg-1]PECsoil,act [mg kg-1]
Crop
AS
Time *[d]
Results
PECsoilPECsoil
Calculation of the PECsoil,accu
� Considers the use of an AS for many years (10, 20 or 30)
� Requires the plateau concentration (PECsoil,plateau) of the AS at steady state
� The PECsoil,plateau is defined as the level of residues in soil after the winter
regeneration period immediately before the first seasonal application
� The PECsoil,plateau refers soil layer depth of 20 cm (arable crops) or 10 cm
(permanent crops) as a result of substance distribution in the top soil after soil
cultivation over many years
PECsoilPECsoil
PECsoil,,plateau plateau concentration at steady state [mg kg-1]
PECsoil,ini initial soil concentration following last application
considering a mixing depth of 20 cm [mg kg-1]
t interval between application seasons (365 days) [d]
i interval between first application and last application in
the cropping season [d]
k degradation rate (= ln(2) / DT50) [d-1]
i)-(tk
kt
inisoil,
plateausoil,e
e1
PECPEC ⋅−
−⋅
−=
Calculation of PECsoil,plateau
PECsoilPECsoil
PECsoil,accu maximum concentration in soil
for the accumulation risk assessment [mg kg-1]
PECsoil,plateau concentration at steady state (plateau concentration)
related to the plough layer depth (e.g. 20 cm) [mg kg-1]
PECsoil,max maximum concentration with respect to the soil load after one
application period related to a soil layer depth of 5 cm [mg kg-1]
Calculation of PECsoil,accu
maxsoil,plateausoil,accusoil, PECPECPEC +=
� The PECsoil,accu represents the highest potential soil concentration considering
the multi-year accumulation load as background concentration plus the maximum
concentration (PECsoil,max) after application in the top soil layer.
� For this purpose, the PECsoil,plateau and the PECsoil,max in the top soil layer
are added