Dear Muthukrishnan,

Please read the following text and use the following link for more details:

http://life.bio.sunysb.edu/marinebio/fc.6.toxicity.measures.html

Simple Measures of Toxicity

Some simple measures of toxicity use bioassays to measure death rates in order to quantify the effect of the toxin. Such measures are commonly known as LD50 and LC50. The LD50 is defined as the lethal dose at which 50% of the population if killed in a given period of time; an LC50 is the lethal concentration required to kill 50% of the population. The LC50 is a measure, e.g. in mg/l, of the concentration of the toxin whereas a dose is a more general term (need not be a concentration but may be a specific temperature, etc.). These bioassays involve subjecting several replicate groups of individuals to a range of concentrations (or doses) of a toxic compound and measuring the mortality after a defined time interval, e.g. 24 hours, 1 week, 1 month, etc. The data are then plotted and the LC50 is interpolated from the graph.

Hoping this will be helpful,

Rafik

Bioassays such as LC50's have been criticized on a number of grounds. Such bioassays are not representative for the species as a whole as they are most often performed on a small subset of one population and then extrapolated to the species as a whole. There can be a wide range of tolerance to toxic agents among different populations of a species which should be taken into account. An often ignored component in such studies is the evolution of resistance to the toxic substance. A sudden release of a pollutant at a concentration that is toxic to most organisms is likely to have an immediate and drastic effect on the density and species distribution within an ecosystem. A slow build-up of pollutants in an ecosystem will more likely allow for an increase in resistance over time; changes in taxonomic composition in this case should be less severe.

Dear Professor, Thank you for your valuable answer

Dear muthukrishnan, 

           Please learn probit analysis. this will help to do easily LC,IC,EC and LD50..

with regs,

Bupesh

thank you Dr.Bupesh

As said probit analysis helps you to calculate LC 50. SPSS is of helpful in this kind

http://www.ehabsoft.com/ldpline/DownloadForm.htm

please use this site for calculation LC50, LD50........and so on

best regards