Calculate predicted environmental concentrations in soil

This is a basic calculation of a contaminant concentration in bulk soil based on complete, instantaneous mixing. If an interval is given, an attempt is made at calculating a long term maximum concentration using the concepts layed out for example in the PPR panel opinion (EFSA 2012).

PEC_soil(rate, rate_units = "g/ha", interception = 0, mixing_depth = 5,
  PEC_units = "mg/kg", PEC_pw_units = "mg/L", interval = NA,
  n_periods = Inf, tillage_depth = 20, chent = NA, DT50 = NA,
  Koc = NA, Kom = Koc/1.724, t_avg = 0, scenarios = c("default",
  "EFSA_2015"), porewater = FALSE)

Arguments

rate: Application rate in units specified below
rate_units: Defaults to g/ha
interception: The fraction of the application rate that does not reach the soil
mixing_depth: Mixing depth in cm
PEC_units: Requested units for the calculated PEC. Only mg/kg currently supported
PEC_pw_units: Only mg/L currently supported
interval: Period of the deeper mixing, defaults to 365, which is a year if rate units are in days
n_periods: Number of periods to be considered for long term PEC calculations
tillage_depth: Periodic (see interval) deeper mixing in cm
chent: An optional chent object holding substance specific information. Can also be a name for the substance as a character string
DT50: If specified, overrides soil DT50 endpoints from a chent object If DT50 is not specified here and not available from the chent object, zero degradation is assumed
Koc: If specified, overrides Koc endpoints from a chent object
Kom: Calculated from Koc by default, but can explicitly be specified as Kom here
t_avg: Averaging times for time weighted average concentrations
scenarios: If this is 'default', the DT50 will be used without correction and soil properties as specified in the REACH guidance (R.16, Table R.16-9) are used for porewater PEC calculations. If this is "EFSA_2015", the DT50 is taken to be a modelling half-life at 20°C and pF2 (for when 'chents' is specified, the DegT50 with destination 'PECgw' will be used), and corrected using an Arrhenius activation energy of 65.4 kJ/mol. Also model and scenario adjustment factors from the EFSA guidance are used.
porewater: Should equilibrium porewater concentrations be estimated based on Kom and the organic carbon fraction of the soil instead of total soil concentrations? Based on equation (7) given in the PPR panel opinion (EFSA 2012, p. 24) and the scenarios specified in the EFSA guidance (2015, p. 13).

Value

The predicted concentration in soil

Details

This assumes that the complete load to soil during the time specified by 'interval' (typically 365 days) is dosed at once. As in the PPR panel opinion cited below (PPR panel 2012), only temperature correction using the Arrhenius equation is performed.

Total soil and porewater PEC values for the scenarios as defined in the EFSA guidance (2015, p. 13) can easily be calculated.

Note

If temperature information is available in the selected scenarios, as e.g. in the EFSA scenarios, the DT50 for groundwater modelling (destination 'PECgw') is taken from the chent object, otherwise the DT50 with destination 'PECsoil'.

References

EFSA Panel on Plant Protection Products and their Residues (2012) Scientific Opinion on the science behind the guidance for scenario selection and scenario parameterisation for predicting environmental concentrations of plant protection products in soil. EFSA Journal 10(2) 2562, doi:10.2903/j.efsa.2012.2562

EFSA (European Food Safety Authority) (2015) EFSA guidance document for predicting environmental concentrations of active substances of plant protection products and transformation products of these active substances in soil. EFSA Journal 13(4) 4093 doi:10.2903/j.efsa.2015.4093

Examples

PEC_soil(100, interception = 0.25)
#>      scenario
#> t_avg default
#>     0     0.1

# This is example 1 starting at p. 79 of the EFSA guidance (2015)
PEC_soil(1000, interval = 365, DT50 = 250, t_avg = c(0, 21),
               scenarios = "EFSA_2015")
#>      scenario
#> t_avg      CTN      CTC      CTS
#>    0  21.96827 11.53750 9.145259
#>    21 21.78517 11.40701 9.017370
PEC_soil(1000, interval = 365, DT50 = 250, t_av = c(0, 21),
               Kom = 1000, scenarios = "EFSA_2015", porewater = TRUE)
#>      scenario
#> t_avg       CLN       CLC       CLS
#>    0  0.7589401 0.6674322 0.9147861
#>    21 0.7506036 0.6590345 0.8987279

# The following is from example 4 starting at p. 85 of the EFSA guidance (2015)
# Metabolite M2
# Calculate total and porewater soil concentrations for tier 1 scenarios
# Relative molar mass is 100/300, formation fraction is 0.7 * 1
results_pfm <- PEC_soil(100/300 * 0.7 * 1 * 1000, interval = 365, DT50 = 250, t_avg = c(0, 21),
                        scenarios = "EFSA_2015")
results_pfm_pw <- PEC_soil(100/300 * 0.7 * 1000, interval = 365, DT50 = 250, t_av = c(0, 21),
                           Kom = 100, scenarios = "EFSA_2015", porewater = TRUE)