You have choices here. Less than the Limit of Quantification is not the same as zero, so assuming zero concentration would conflict with the principle of being conservative in health risk assessment. To be appropriately conservative, I recommend assuming that the concentration is half the distance between zero and the LOQ (0.5 x LOQ). Another possibility would be to use a different fraction, such as the fraction of samples in which the substance was detected; for example, if detected in 75 percent of samples, assume 0.75 x LOQ for all samples in which the substance was not detected.

I hope this helps. If you have further question, please feel free to contact me.

may be you can add a known amount of arsenic (above the LOQ) in the sample. then, after detected, minus the added known amount of arsenic to get the original value of arsenic in the sample. hope this helps.

Thanks a lot Sir for your cordial suggestion @ Robert Michaels. And I am also thankful to Puganeswary Sukumaran Sir.

Your Suggestions are greatly appreciated.

Dear Sazal, in addition to the previous comments, I would like to share with you an EFSA report that present the methodologies to manage the left-censored data (http://doi.wiley.com/10.2903/j.efsa.2010.1557). Hope that should be useful.

Regards

Many many thanks Sir @ Ricardo Assunção

here is an additional file than may assist - see attached

Bob

Thank you very much Sir. @R.B. Brobst