Section 500.86 - Marker residue and target tissue(a) For each edible tissue, the sponsor shall measure the depletion of the residue of carcinogenic concern until its concentration is at or below Sm .(b) In one or more edible tissues, the sponsor shall also measure the depletion of one or more potential marker residues until the concentration of the residue of carcinogenic concern is at or below Sm .(c) From these data, FDA will select a target tissue and a marker residue and designate the concentration of marker residue (Rm ) that the regulatory method must be capable of measuring in the target tissue. FDA will select Rm such that the absence of the marker residue in the target tissue above Rm can be taken as confirmation that the residue of carcinogenic concern does not exceed Sm in each of the edible tissues and, therefore, that the residue of carcinogenic concern in the diet of people does not exceed So .(d) When a compound is to be used in milk- or egg-producing animals, milk or eggs must be the target tissue in addition to the tissue selected to monitor for residues in the edible carcass.Approved by the Office of Management and Budget under control number 0910-0228