How to calculate LC50 toxicity value?

[dany612]

Hi,

I have a question and I hope Vgchartz can help me. I am trying to determine and calulate the LC50 value for a sendiment sample. I am using water fleas (Daphnia Magna) as a experimental variable. 

 

Hopefully I will find a source explaining this better but in the meanwhile I thought perhaps I'll check here first.