The groundwater ubiquity score GUS is calculated according to the following equation $$GUS = \log_{10} DT50_{soil} (4 - \log_{10} K_{oc})$$


# S3 method for numeric
GUS(DT50, Koc, ...)

# S3 method for chent
  degradation_value = "DT50ref",
  lab_field = "laboratory",
  redox = "aerobic",
  sorption_value = "Kfoc",
  degradation_aggregator = geomean,
  sorption_aggregator = geomean,

# S3 method for GUS_result
print(x, ..., digits = 1)



Included in the generic to allow for further arguments later. Therefore this also had to be added to the specific methods.


Half-life of the chemical in soil. Should be a field half-life according to Gustafson (1989). However, leaching to the sub-soil can not completely be excluded in field dissipation experiments and Gustafson did not refer to any normalisation procedure, but says the field study should be conducted under use conditions.


The sorption constant normalised to organic carbon. Gustafson does not mention the nonlinearity of the sorption constant commonly found and usually described by Freundlich sorption, therefore it is unclear at which reference concentration the Koc should be observed (and if the reference concentration would be in soil or in porewater).


If a chent is given with appropriate information present in its chyaml field, this information is used, with defaults specified below.


Which of the available degradation values should be used?


Should laboratory or field half-lives be used? This defaults to lab in this implementation, in order to avoid double-accounting for mobility. If comparability with the original GUS values given by Gustafson (1989) is desired, non-normalised first-order field half-lives obtained under actual use conditions should be used.


Aerobic or anaerobic degradation data


Which of the available sorption values should be used? Defaults to Kfoc as this is what is generally available from the European pesticide peer review process. These values generally use a reference concentration of 1 mg/L in porewater, that means they would be expected to be Koc values at a concentration of 1 mg/L in the water phase.


Function for aggregating half-lives


Function for aggregation Koc values


An object of class GUS_result to be printed


The number of digits used in the print method


A list with the DT50 and Koc used as well as the resulting score of class GUS_result


Gustafson, David I. (1989) Groundwater ubiquity score: a simple method for assessing pesticide leachability. Environmental toxicology and chemistry 8(4) 339–57.