R: Effect of cadmium on growth of green alga

S.capricornutum {drc} | R Documentation

## Effect of cadmium on growth of green alga

### Description

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.

### Usage

    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

    ## 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")

[Package drc version 3.0-1 Index]