Effects of temperature and nutritional state on the acute toxicity of acridine to the calanoid copepod, Diaptomus clavipes schacht

Acute toxicity tests were performed on adult males and females of a freshwater calanoid copepod, Diaptomus clavipes Schacht, using the azaarene acridine as the test compound. Tests were performed at three temperatures (16, 21 and 26°C) and over a range of nutritional states (fed, starved and stock). Observations on mortality were made at 24-h intervals for 96 h. Analysis of the data was based on comparisons (using different treatment combinations) of the parameters in a logistic survival function used to describe the mortality data. Median lethal concentrations (using 96-h LC50 values) were estimated from the logistic survival function as well as from the probit function, for comparative purposes. The LC50 values ranged from 1.64 to 6.70 mg/L, depending on temperature, nutritional state of the animals and sex. The LC50 values were highest for animals (fed before testing) at 16°C. As food availability decreased and temperature increased, toxicity of acridine increased up to fourfold. No significant differences in LC50 values were found between the sexes except in starved animals at 26°C, when males were more sensitive than females. This difference in toxicity between the sexes at 26°C may be due to differences in nutritional stress between the sexes (at this temperature), since control mortality at this temperature was also higher in males than in females.