Wrong Tests, Wrong Conclusions

To the Editor.—  The article in the Archives by Black et al,¹ "The Mutagenicity of Dinitrochlorobenzene [DNCB]," presents an inaccurate, straw-man version of our position. Black et al stated that we "conclude that highly purified DNCB might still be safe for clinical use." We presented this only as a possibility in the context of an article that broadly argued against the use of all current commercially available sources of DNCB. Furthermore, their experimental design has managed to miss testing any important hypothesis.In the two studies cited by Black et al,^2,3 we (and our coauthors) hypothesized that DNCB contaminated with mononitrochlorobenzene is mutagenic, at least in part, because of this contaminant. Black et al argued that DNCB is inherently mutagenic and that contaminants have no role in this activity. Unfortunately, they chose to test—except for controls—only dichloronitrobenzenes (2,3-DCNB; 2,4-DCNB; 2,5-DCNB; and 3,4-DCNB) rather than mononitrochlorobenzenes (l-chloro-2-nitrobenzene and 1-chloro-4-nitrobenzene), which we had postulated to be the major offenders. Thus, Black et al have failed to refute our contention that mononitrochlorobenzenes add to the potential hazard of the use of DNCB in humans.