Calculates average proportion exposed based on log-normal distribution of concentrations.
Examples
if (FALSE) { # \dontrun{
fits <- ssd_fit_dists(ssddata::ccme_boron, dists = "lnorm")
set.seed(10)
ssd_exposure(fits)
ssd_exposure(fits, meanlog = 1)
ssd_exposure(fits, meanlog = 1, sdlog = 1)
} # }