Can We Reasonably Predict Chronic Species Sensitivity Distributions from Acute Species Sensitivity Distributions?

Estimation
of species sensitivity distributions (SSDs) is an essential
way to estimate the hazardous concentration for 5% of the species
(HC5) and thus to derive a “safe” concentration. Here,
we examined whether we can reasonably predict SSDs based on chronic
no-observed-effect concentration or level (chronic SSDs) from SSDs
based on acute median effective/lethal concentration (acute SSDs)
by analyzing log-normal SSDs of 150 chemicals. Chronic SSD means were,
on average, 10 times lower than acute SSD means. The standard deviations
(SDs) of acute and chronic SSDs closely overlapped. Our detailed analysis
suggests that the acute SSD SD can be used as an initial estimate
of the chronic SSD SD if the number of tested species is ≥10.
There were no significant differences in the ratios of chronic to
acute SSD means or SDs among three different modes of action. The
HC5 of chronic SSDs was, on average, 10 times lower than the acute
SSD HC5. We suggest that multiplication of the acute HC5 by a factor
of 0.1 is a defensible way to obtain a first approximation of the
chronic HC5, particularly when relative ecological risks of chemicals
are being evaluated. Further study is needed to develop methods for
a more accurate estimation of chronic SSDs.