Re: Will detergent have an effect on the heartrates of Daphnia and Why?

Hello Laura,

This sounds like an interesting experiment.  I have had a search and cannot 
find any suggestion of detergents being tested on Daphnia before.  

I would think that any effect that the detergent has on the Daphnia would 
be due to toxicity rather that an effect on the heart muscle and nerves 
directly although without a thorough investigation this could not be ruled 
out, but I think there could be a more general explanation for any effect 
that you see.

You mention that the detergent may interfere with the phospholipid 
membranes.  It is certainly true that some detergents do interfere with 
phospholipid membranes and this is often used experimentally and has the 
effect that is termed skinning.  Treatment of tissue with detergents puts 
pores in the membranes, which allows molecules to diffuse easily into and 
out of cells.  If this were to happen in a living creature it would 
certainly result in rapid death since it would be unable to sustain life 
under such circumstances, as this would have a drastic effect on the 
controlled transport of ions and molecules into and out of cells.  It would 
certainly be impossible to maintain a beating heart if the cells were 
porous in this manner.

However I am not sure if detergents used to make washing up liquid would be 
that strong and therefore this effect may not be apparent, especially at 
lower concentrations

If the detergent has toxic effects on the daphnia you may be able to find a 
concentration where the daphnia exhibit signs of stress without being 
permanently harmed.  An increase in heart rate may be an indication of a 
response to a stressful stimulus being applied to the daphnia as one may 
find with a detergent.  Daphnia are often used to test the toxicity of 
different substances and of water effluent in this way.

I certainly recommend that you use a range of concentrations of your 
detergent trying to find the lowest concentration required to give and 
effect.  It is also important that the pH of all your solutions is the same 
and the detergent does not change the pH as this will also have an effect 
on the daphnia in addition to the detergent itself.  Daphnia enjoy a pH of 
around 7.2 to 8.5 and outside this range they will not survive so chose a 
pH in the middle of this range and ensure all your solutions are at the 
same pH.  You can adjust the pH of your solutions by the addition of a 
small amount of acid or alkali to ensure that they are in the correct 
range.

Good luck with your experiment and I hope that you find the result 
interesting.

Dave Burton