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)
A data frame with 18 observations on the following 2 variables.
conca numeric vector of cadmium chloride concentrations (micro g/L)
counta numeric vector of algal counts (10000 x cells /ml)
The data are analysed in Bruce and Versteeg (1992) using a log-normal dose-response model (using the logarithm with base 10).
Bruce, R. D. and Versteeg, D. J. (1992) A statistical procedure for modeling continuous toxicity data, Environ. Toxicol. Chem., 11, 1485–1494.
## 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")
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