Effect of cadmium on growth of green alga

Green alga (Selenastrum capricornutum) was exposed to cadmium chloride concentrations ranging from 5 to 80 micro g/L in geometric progression in 4-day population growth test.

data(S.capricornutum)

Format

A data frame with 18 observations on the following 2 variables.

conc

a numeric vector of cadmium chloride concentrations (micro g/L)

count

a numeric vector of algal counts (10000 x cells /ml)

Details

The data are analysed in Bruce and Versteeg (1992) using a log-normal dose-response model (using the logarithm with base 10).

Source

Bruce, R. D. and Versteeg, D. J. (1992) A statistical procedure for modeling continuous toxicity data, Environ. Toxicol. Chem., 11, 1485--1494.

Examples

# NOT RUN {
library(drc)

## Fitting 3-parameter log-normal model
s.cap.m1 <- drm(count ~ conc, data = S.capricornutum, fct = LN.3())

## Residual plot
plot(fitted(s.cap.m1), residuals(s.cap.m1))

## Fitting model with transform-both-sides approach
s.cap.m2 <- boxcox(s.cap.m1, method = "anova")
summary(s.cap.m2)

## Residual plot after transformation (looks better)
plot(fitted(s.cap.m2), residuals(s.cap.m2))

## Calculating ED values on log scale
ED(s.cap.m2, c(10, 20, 50), interval="delta")

## Fitting model with ED50 as parameter
## (for comparison)
s.cap.m3 <- drm(count ~ conc, data = S.capricornutum, fct = LN.3(loge=TRUE))
s.cap.m4 <- boxcox(s.cap.m3, method = "anova")
summary(s.cap.m4)
ED(s.cap.m4, c(10, 20, 50), interval = "fls")
# }