See for instance the Handbook of Ecotoxicology:

https://books.google.nl/books?id=qN0I3husm50C&pg=PA30&lpg=PA30&dq=calculation+of+acute+noec+statistics&source=bl&ots=GDP77UltF-&sig=pP_A38pQKFgJmdCijAce-JWMxGY&hl=en&sa=X&ei=eVeQVPTiHIv2UMibgdgM&ved=0CD0Q6AEwBQ#v=onepage&q=calculation%20of%20acute%20noec%20statistics&f=false

t-test or ANOVA statistics are commonly used to determine the lowest test concentration at which an effect is observed (LOEC) or the highest test concentration at which no significant effect is observed (NOEC). Significance should be tested against your unexposed control.

Dear Chigozie,

please note that the use of NOEC/LOEC is controversially discussed since some drawbacks are evident, i.e. determination of NOEC depends on the selection of test concentrations, statistical significance and power largely depend on the number of replicates. Therefore, the concept of dose-response relationships and the use of EC10 as the substitute of NOEC are highly recommended. Have a look into the following papers:

Jager T (2011).

Some Good Reasons to Ban ECx and Related Concepts in Ecotoxicology.

DOI 10.1021/es2030559 Environ Sci Technol 45:8180-81.

Landis WG, Chapman PM (2011).

Well Past Time to Stop Using NOELs and LOELs.

DOI 10.1002/ieam.249 Integrated Environmental Assessment and Management 7(4):vi–viii

Laskowski R (1995).

Some good reasons to ban the use of NOEC, LOEC and related concepts in ecotoxicology.

DOI 10.2307/3545738 Oikos 73(1):140-4.

And have a look into the poster presentation attached I published with colleagues.

Best regards, Thomas

Thank you guys.

@ Thomas, thanks for the poster paper. Actually I read papers criticizing the use of NOEC and LOEC, however, I just want to understand how the calculations are made; the parameters and values involved in them. I would appreciate if you could provide that for me.

Thanks.

Usually the NOEC and LOEC are calculated through ANOVA test with post-hoc Dunnett's Test which will provide the limit values where effects were observed.  

I agree with Thomas' concerns regarding the use of NOECs and LOECs in risk assessment. However, as long as you are aware of these limitations, there shouldn't be anything wrong with calculating them.