where:
C = the % concentration of constituent A, B ... Z in the mixture;
T = the oral LD50 values of constituent A, B ... Z;
TM = the oral LD50 value of the mixture.
Note to formula in paragraph (c)(3): This formula also may be used for dermal toxicities provided that this information is available on the same species for all constituents. The use of this formula does not take into account any potentiation or protective phenomena.
49 C.F.R. §173.132