The reproducibility of the three brood Ceriodaphnia test using the reference toxicant sodium lauryl sulfate

The three brood Ceriodaphnia dubia test was carried out three nonconsecutive times, each period being separated by the previous one by three weeks. The toxicant studied was sodium lauryl sulfate (SLS) which bacterially degrades completely by the end of the third day of the test. The mean LC50 based on survival was 41 +/- 3.2 (CV = 7.8%) mg/L for day 3 through day 6. The mean EC50 based on progeny confirmed the LC50 and was 36 +/- 0.49 (CV = 1.4%) mg/L for the ultimate day of the test. The close reproducibility among successive tests is due in part to the use of pure SLS, the use of a mixed algal diet and in part to reducing handling to a minimum. Data failed to indicate any chronic effect exhibited by C. dubia populations since no statistically significant differences were noted between 48 hr (acute) and 144 hr values (chronic). Calculations of brood size for the first four broods clearly indicate a chronic effect of SLS on C. dubia by showing a progressively greater spread between the highest mean brood size and the lowest mean brood size as the brood number increases. It is suggested that calculations of this kind become part of the Ceriodaphnia test methodology so that any chronicity can be better identified.