#' Estimation of the transpiration stream concentration factor
#'
#' The FOCUS groundwater guidance (FOCUS 2014, p. 41) states that a reliable measured
#' log Kow for neutral pH must be available in order to apply the Briggs
#' equation. It is not clarified when it can be regarded reliable, but the
#' equation is stated to be produced for non-ionic compounds, suggesting that
#' the compound should not be ionogenic (weak acid/base)
#' or ionic.
#'
#' The Dettenmaier equation is given to show that other views on the subject exist.
#' @references FOCUS (2014) Generic Guidance for Tier 1 FOCUS Ground Water Assessments.
#'  Version 2.2, May 2014
#' Dettenmaier EM, Doucette WJ and Bugbee B (2009) Chemical hydrophobicity and uptake
#' by plant roots. Environ. Sci. Technol 43, 324 - 329
#' @param log_Kow The decadic logarithm of the octanol-water partition constant
#' @param method Short name of the estimation method.
#' @export
#' @examples
#' plot(TSCF, -1, 5, xlab = "log Kow", ylab = "TSCF", ylim = c(0, 1.1))
#' TSCF_2 <- function(x) TSCF(x, method = "dettenmaier09")
#' curve(TSCF_2, -1, 5, add = TRUE, lty = 2)
#' legend("topright", lty = 1:2, bty = "n",
#'   legend = c("Briggs et al. (1982)", "Dettenmaier et al. (2009)"))
TSCF <- function(log_Kow, method = c("briggs82", "dettenmaier09")) {
  method <- match.arg(method)
  TSCF <- switch(method,
    briggs82 = 0.784 * exp(- (log_Kow - 1.78)^2 / 2.44),
    dettenmaier09 = 11 /( 11 + 2.6^log_Kow)
  )
  return(TSCF)
}