Physiological changes and acetylcholinesterase activity in the cladoceran Moina macrocopa (Straus, 1820) exposed to mercury and sodium dodecyl sulfate

Mercury is one of the most deleterious heavy metals in aquatic systems. Sodium dodecyl sulphate (SDS) is a common surfactant, which may reach relatively high concentrations in aquatic systems. In the present study, water fleas (Moina macrocopa (Straus, 1820)) were exposed to different mercury and SDS concentrations for 24 and 48 h to examine the toxic effect of the two reagents on heart rate, body size and acetylcholinesterase (AChE) activity. The 24 h and 48 h LC50 values were 4.93 and 3.51 μg/l for mercury, and 12.74 and 4.55 mg/l for SDS, respectively. Increased heart rate was observed in water fleas treated with 1.5 and 2.0 μg/l mercury for 24 h and 48 h, suggesting that the animals were stressed. The size of water fleas decreased with increasing mercury concentration. An increase in SDS concentration and exposure time had a negative impact on the heart rate and size of the water fleas. A pronounced inhibition of AChE activity was observed in water fleas exposed to mercury and SDS concurrently. However, the AChE inhibition level was different between mercury and SDS, which may be inferred by different pollutants. Although mercury and SDS have different modes of action, the relation between decrease of physiological parameters and AChE inhibition were relatively close for these two compounds. We conclude that measurements of AChE activity can be used as a biomarker for different aquatic pollutants.