Calculation of Predicted Environmental Concentrations in Soil - soil
Calculation of Predicted Environmental Concentrations in Soil General assumptions: Uniform distribution of the AS in the upper soil layer - 5 cm depth ( soil,max, soil,act, and soil,twa - 20 cm depth if the AS tends to accumulate in soil ( soil,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 soil following single application soil,max = A (1- f 100 d bd int soil soil,max maximum concentration in soil [mg kg -1 ] A i application rate [g a.s. ha -1 ] f int,i fraction intercepted by plant cover [-] d depth of soil layer (5 cm [cm] bd soil soil bulk density (1.5 g cm -3 [g cm -3 ]
Calculation of the global maximum soil following multiple applications soil,max = n i= 1 Ai (1- f 100 d bd int,i soil e k ( t t n i soil,max maximum concentration in soil after n applications [mg kg -1 ] n number of applications [-] A i application rate at i-th application [g a.s. ha -1 ] f int,i fraction intercepted by plant cover at i-th application [-] d depth of soil layer (5 cm [cm] bd soil soil bulk density (1.5 g cm -3 [g cm -3 ] k degradation rate (= ln (2 / DT 50 [d -1 ] t i time of i-th application [d] t n time of n-th (last application [d]
Calculation of actual concentration for given time points 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 soil, act = soil,max e k t soil,act actual concentration in soil [mg kg -1 ] soil,max initial concentration in soil [mg kg -1 ] k degradation rate (= ln (2 / DT50 [d -1 ] t time after application [d]
Calculation of time-weighted average concentrations 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 soil,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 soil,twa ( t = max 1 m t j + t t= t j soil (t for j = 0,...,200 soil,twa worst-case time-weighted average concentration in soil for time interval t [mg kg -1 ] soil 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 [-]
Results Time * [d] soil,act [mg kg -1 ] AS Crop soil,twa [mg kg -1 ] Global maximum 0 0.384-1 0.377 0.380 Short-term 2 0.370 0.377 4 0.356 0.370 7 0.337 0.360 14 0.295 0.338 Long-term 21 0.227 0.299 28 0.150 0.249 50 0.059 0.173 100 0.000 0.162 *Time: days after maximum concentration ( soil,act or time interval ( soil,twa
Calculation of the soil,accu Considers the use of an AS for many years (10, 20 or 30 Requires the plateau concentration (soil,plateau of the AS at steady state The soil,plateau is defined as the level of residues in soil after the winter regeneration period immediately before the first seasonal application The soil,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
soil,plateau = level of residues in soil after the winter regeneration period
Calculation of soil,plateau soil, plateau = 1 e soil,ini kt e k (t-i soil,,plateau plateau concentration at steady state [mg kg -1 ] soil,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 ]
Calculation of soil,accu The soil,accu represents the highest potential soil concentration considering the multi-year accumulation load as background concentration plus the maximum concentration (soil,max after application in the top soil layer. For this purpose, the soil,plateau and the soil,max in the top soil layer are added = + soil, accu soil,plateau soil,max soil,accu soil,plateau soil,max maximum concentration in soil for the accumulation risk assessment [mg kg -1 ] concentration at steady state (plateau concentration related to the plough layer depth (e.g. 20 cm [mg kg -1 ] maximum concentration with respect to the soil load after one application period related to a soil layer depth of 5 cm [mg kg -1 ]
Results soil,plateau soil,max soil,accu,overall (= soil,plateau + soil,max Crop scenario in 0-20 cm depth in 0-5 cm depth in 0-5 cm depth [mg kg -1 ] [mg kg -1 ] [mg kg -1 ] Crop 0.080 0.154 0.234