From 6b4e342b240baaf18150360986d15895fc80a937 Mon Sep 17 00:00:00 2001
From: Johannes Ranke <jranke@uni-bremen.de>
Date: Thu, 15 Oct 2015 14:41:26 +0200
Subject: Add endpoint and GUS functions, roxygenize

---
 pkg/R/GUS.R | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 pkg/R/GUS.R

(limited to 'pkg/R/GUS.R')

diff --git a/pkg/R/GUS.R b/pkg/R/GUS.R
new file mode 100644
index 0000000..2690f50
--- /dev/null
+++ b/pkg/R/GUS.R
@@ -0,0 +1,74 @@
+#' Groundwater ubiquity score based on Gustafson (1989)
+#' 
+#' The groundwater ubiquity score GUS is calculated according to
+#' the following equation
+#' \deqn{GUS = \log_10 DT50_{soil} (4 - \log_10 K_{oc}}{GUS = log10 DT50soil * (4 - log10 Koc)}
+#' 
+#' @references Gustafson, David I. (1989) Groundwater ubiquity score: a simple
+#' method for assessing pesticide leachability. _Environmental
+#' toxicology and chemistry_ *8*(4) 339–57.
+#' @inheritParams endpoint
+#' @param chent If a chent is given with appropriate information present in its
+#'   chyaml field, this information is used, with defaults specified below.
+#' @param DT50 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.
+#' @param Koc 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).
+#' @param lab_field 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.
+#' @param degradation_value Which of the available degradation values should 
+#'   be used?
+#' @param sorption_value 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.
+#' @param degradation_aggregator Function for aggregating half-lives
+#' @param sorption_aggregator Function for aggregation Koc values
+#' @return A list with the DT50 and Koc used as well as the resulting score
+#'   of class GUS_result
+#' @author Johannes Ranke
+#' @export
+GUS <- function(...) UseMethod("GUS")
+
+#' @rdname GUS
+#' @export
+GUS.numeric <- function(DT50, Koc) {
+  score <- log10(DT50) * (4 - log10(Koc))
+  res <- list(DT50 = DT50, Koc = Koc, score = score)
+  class(res) <- "GUS_result"
+  return(res)
+}
+
+#' @rdname GUS
+#' @export
+GUS.chent <- function(chent, lab_field = "laboratory",
+                      aerobic = TRUE,
+                      degradation_value = "DT50ref",
+                      sorption_value = "Kfoc", 
+                      degradation_aggregator = geomean,
+                      sorption_aggregator = geomean,
+                      digits = 1)
+{
+  DT50 = soil_DT50(chent, lab_field = lab_field, redox = aerobic, 
+                   value = degradation_value, 
+                   aggregator = degradation_aggregator, signif = 5)
+  Koc = soil_Kfoc(chent, value = sorption_value, 
+                   aggregator = sorption_aggregator, signif = 5)
+  GUS.numeric(DT50, Koc)
+}
+
+#' @export
+print.GUS_result = function(x, ..., digits = 1) {
+  cat("GUS: ", round(x$score, digits = 1), "\n")
+  cat("calculated from DT50 ", x$DT50, " and Koc ", x$Koc, "\n")
+}
-- 
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