Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 186

Fig. 6 Species sensitivity
distribution for bird species
exposed to chlorpyrifos via
oral gavage exposure

Fig. 7 Hypothetical acute
dose-response curves for
sensitive, median and tolerant
bird species

models tested (Anderson-Darling A 2 = 0.301, p > > 0.1). The model equation for the
two-parameter log-normal cumulative distribution function (CDF) is shown below ( 2 ):

() =+ -

1
2

æ
ç

e f x

m ö

÷

æ
ç

ö
÷

fx 1 ( 2 )

s 2

Where:
x is the LD 50 (log mg ai kg −1 bwt), and the functional response, f ( x ), is the
proportion of species affected. The location and scale parameters, , are the

mean and standard deviation of the dataset, respectively, and erf is the error function
(i.e., the Gauss error function).

μ and σ

Graphical and statistical tests indicated that the homogeneity of variance and
normality assumptions of the parametric regression analysis were met. The fi tted
model parameters were: = 0.391 (Fig. 6 ). The 5th, 50th and 95th cen-

tile LD 50 s from the best-fi t SSD are respectively 7.03, 30.9 and 136 mg ai kg −1 bwt.
These values were combined with the geometric mean probit slope of 3.45 (Table 4 )
to generate the hypothetical dose-response curves for avian species of high (5th
centile), median (50th centile) and low (95th centile) sensitivity (Fig. 7 ).

μ = 1.49 and σ