Microbial mixture means any combination of microorganisms or microorganisms and other chemical substances, if the combination does not occur in nature and is not an article.
40 CFR § 725.3
Definitions in section 3 of the Act (15 U.S.C. 2602), as well as definitions contained in 704.3, 720.3, and 721.3 of this chapter, apply to this part unless otherwise specified in this section. In addition, the following definitions apply to this part: