[Code of Federal Regulations]
[Title 21, Volume 3]
[Revised as of April 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 21CFR170.18]

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                        TITLE 21--FOOD AND DRUGS
 
CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN 
                          SERVICES (CONTINUED)
 
PART 170_FOOD ADDITIVES--Table of Contents
 
                      Subpart A_General Provisions
 
Sec. 170.18  Tolerances for related food additives.

    (a) Food additives that cause similar or related pharmacological 
effects will be regarded as a class, and in the absence of evidence to 
the contrary, as having additive toxic effects and will be considered as 
related food additives.
    (b) Tolerances established for such related food additives may limit 
the amount of a common component that may be present, or may limit the 
amount of biological activity (such as cholinesterase inhibition) that 
may be present or may limit the total amount of related food additives 
that may be present.
    (c) Where food additives from two or more chemicals in the same 
class are present in or on a food, the tolerance

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for the total of such additives shall be the same as that for the 
additive having the lowest numerical tolerance in this class, unless 
there are available methods that permit quantitative determination of 
the amount of each food additive present or unless it is shown that a 
higher tolerance is reasonably required for the combined additives to 
accomplish the physical or technical effect for which such combined 
additives are intended and that the higher tolerance will be safe.
    (d) Where residues from two or more additives in the same class are 
present in or on a food and there are available methods that permit 
quantitative determination of each residue, the quantity of combined 
residues that are within the tolerance may be determined as follows:
    (1) Determine the quantity of each residue present.
    (2) Divide the quantity of each residue by the tolerance that would 
apply if it occurred alone, and multiply by 100 to determine the 
percentage of the permitted amount of residue present.
    (3) Add the percentages so obtained for all residues present.
    (4) The sum of the percentage shall not exceed 100 percent.