Our results show that increasing toxicity and temperature stressinduced
ameasurable effect on swimming activity and seemto be
a sensitive biological endpoint. The results demonstrate that
K2Cr2O7 can affect the swimming activity of D. magna at both lethal
and sublethal concentrations. Clear effects on swimming activity
were seen at concentrations as low as 0.2 mg l-1 of K2Cr2O7
when tested at 15 °C, but only at higher concentrations when
tested at 20 and 25 °C. At 15 °C, the swimming activity in the 0.2
mg l-1 group was higher compared with the control, whereas at
higher temperatures swimming activity was substantially lower
at all concentrations compared with the control and there was a
significant interaction between temperature and exposure time
at all concentrations. This suggests that the toxicity of K2Cr2O7
on swimming activity is highly temperature dependent. Similar
temperature-dependent responses in swimming activity of D.
magna exposed to cadmium have been found when introducing
a rise of temperature from 20 to 25 °C (Wolf et al., 1998). According
to ISO 6341 (2012), EC50–24 h concentrations for K2Cr2O7 should
range from 0.6 to 2.1 mg l-1. Studies with D. magna have shown
EC50–48 h concentrations ranging from 0.3 (0.2–0.4) mg l-1 to 0.6
(0.6–0.7) mg l-1 when based on percentage immobilization
although test temperatures fluctuated and ranged with up to 4 °
C (Gopi et al., 2012; Reboleira et al., 2013). In the present study,
the EC50–24 h concentrations based on SAM data were 1.7 mg l-1
at 15 °C and 3.2 mg l-1 at 25 °C, whereas the EC50–48 h concentrationswas
0.8mg l-1 at 15 °C and 0.3mg l-1 at 25 °C. These values are
thus comparable to or lower than published EC50 concentrations
of K2Cr2O7