PECsoilPECsoil

Calculation of

Predicted Environmental Concentrations in Soil

-

PECsoil

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 = level of residues in soil after the winter regeneration period

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

PECsoilPECsoil

Results

0.2340.1540.080Crop

[mg kg-1][mg kg-1][mg kg-1]

in 0 - 5 cm depthin 0 - 5 cm

depthin 0 - 20 cm

depth

PECsoil,accu,overall

(= PECsoil,plateau + PECsoil,max)PECsoil,maxPECsoil,plateau

Crop scenario