title: Multiple chemical exposures: synergism vs. individual exposure levels.
abstract: Exposure to single chemicals is known to produce congenital malformations in both pregnant animals and humans exposed at sufficiently high intensity. However, real life involves multiple, simultaneous exposures. Using as a database the 43 multiple chemical exposure studies located by Nelson (Teratology 49:33-71; 1994) where synergism was reported, we explored the degree to which such concerns may be realistic from the viewpoint of the current standard developmental toxicity safety evaluation process. Focusing on the assessment of the lowest tested dose of a given agent participating in synergistic activity as compared to its threshold level for eliciting toxicity when administered alone, we found that while the availability of adequate data was limited, all cases, with the possible exception of one, demonstrated synergistic toxic expression only when at least one, and usually both, compounds were used at or above their individual threshold for toxicity. These findings suggest that in animals such phenomena of synergistic chemical interactions are likely to occur only when at least one and more likely both agents are administered at or above their individual threshold for toxicity. To the extent animal studies are predictive of human developmental hazards due to single chemical exposures, available data do not establish multiple chemical exposures as a major human developmental concern.
authors.affiliation: Daniel Baugh Institute, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
authors.forename: N R
authors.initials: NR
authors.lastname: Haghdoost
authors.forename: L M
authors.initials: LM
authors.lastname: Newman
authors.forename: E M
authors.initials: EM
authors.lastname: Johnson
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005314:Embryonic and Fetal Development / Q000187:drug effects*; D005260:Female; D006801:Humans; D011247:Pregnancy; D018675:Toxicity Tests / Q000379:methods