nominal concentrations. Indeed, such characteristics as hydrolysis rate and volatility may make it
impossible. It is important to maintain consistent concentrations during exposure and to confirm
concentrations by chemical measurements. Pre-exposure monitoring will confirm that the diluter
system is operating properly and that fish exposure may begin. Fluctuating exposure
concentrations may indicate an improperly operating diluter system, while slowing rising
concentrations may indicate that system equilibration (e.g., volatility, adsorption to chamber
surfaces, hydrolysis, etc.) has not been achieved.
Once concentrations have stabilized, start exposure. Measure exposure concentrations at
least weekly until the test ends.
Dichotomous data have end points that fall within two categories such as mortality
(alive-dead) and hatch (hatched-not hatched). These data can be analyzed with 2 × 2 contingency
tables, logit, probit, and the chi-square statistic.7
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