Hi everyone,

I'm doing a project at college assessing the 96 hour LC50 value of microplastics upon brine shrimp. If it's okay, I just want some advice about my protocol - I want to know whether I'm doing it right to obtain an LC50 value.

Okay, so I've set up four 200ml vessels (each containing ten organisms); the first is the control, the second has 5g microplastics/ml, the third has 187.5g/ml and the fourth has 500g/ml. My plan is to count the mortality rate for each vessel over the 96 hours. I just have a few questions if that's okay.

Firstly, am I on the right track to obtaining an LC50 value using probit analysis? I plan on using SPSS but I've yet to fully master the statistics side of things yet - it never has been my strong point! All I know is that I can do probit analysis on SPSS (which I have); I just want to know if what I'm doing will give me the correct data to carry out a probit analysis.

Secondly, I'm going to repeat the above procedure, but do I have to use exactly the same concentrations? I seem to think that I can use slightly different concentrations, again counting the mortality rate after the 96 hour test period, and that the probit analysis will decipher the LC50 concentration taking into account the varying concentrations. I would just like to know if that's correct.

Any advice would be much appreciated!

Many thanks,