Impact of Organism Allocations on Potency Estimates from Ceriodaphnia dubia Reproduction Tests

In aquatic toxicology experiments, organisms are randomly assigned to an exposure group that receives a particular concentration level of a toxicant (including a control group with no exposure), and their survival, growth, or reproduction outcomes are recorded. Standard experiments use equal numbers of organisms in each exposure group. In the present study, we explored the potential benefits of modifying the current design of aquatic toxicology experiments when it is of interest to estimate the concentration associated with a specific level of decrease from control reproduction responses. A function of the parameter estimates from fitting a generalized linear regression model used to describe the relationship between individual responses and the toxicant concentration provides an estimate of the potency of the toxicant. After comparing different allocations of organisms to concentration groups, we observed that a reallocation of organisms among these concentration groups could provide more precise estimates of toxicity endpoints than the standard experimental design that uses equal number of organisms in each concentration group; this provides greater precision without the added cost of conducting the experiment. More specifically, assigning more observations to the control zero-concentration condition may result in more precise interval estimates of potency. Environ Toxicol Chem 2023;42:1614-1623. © 2023 SETAC.