Effects of Tributyltin on ephippia production in Daphnia magna

Abstract

Acute toxicity test using of 24-hour- and 8-day-old male and female daphnids, and standard reproduction test (effect on parthenogenesis) using females and sexual reproduction test using maleas and females for bis[tri-n-tributyltin]oxide (TBTO) were conducted in Daphnia magna (Branchiopoda, Cladocera). There was no significant difference between 24-hour-old males and females while 8-day-old males were about 2-fold more sensitive than females in acute toxicity. In standard reproduction test, sublethal effects of low fecundity and a few male released were observed. In sexual reproduction test, there was a marked sex difference between males and females in survival, and male and ephipia production were dose-dependently reduced. LOEC (Lowest Observed Effect Concentration, 0.2 μg/L TBTO) determined from the sexual reproduction test is lower than that (1.0 μg/L TBTO) from standard reproduction test due to the difference in mortality between males and females. The ratio (1.0/0.2 = 5) of these LOECs is not larger than the current uncertainty factor (usually 10) for species, sex or ontogenetic difference on risk assessment. But further investigation is needed for sex and ontogenetic differences and for the sensitivity for asexual and sexual reproduction in Daphnia magna.