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This publication includes data of Salmonella mutagenicity results on 270 coded chemicals, encompassing 329 tests performed by three laboratories under contract to the National Toxicology Program (NTP). The preincubation modification of the Salmonella/mammalian microsome assay was used to test chemicals in up to five Salmonella strains in the presence and absence of rat and hamster liver S-9. With a few exceptions, inter- and intralaboratory reproducibility was good.

311 chemicals were tested under code, for mutagenicity, in Salmonella typhimurium; 35 of the chemicals were tested more than once in the same or different laboratories. The tests were conducted using a preincubation protocol in the absence of exogenous metabolic activation, and in the presence of liver S-9 from Aroclor-induced male Sprague-Dawley rats and Syrian hamsters. Some of the volatile chemicals were also tested in desiccators. A total of 120 chemicals were mutagenic or weakly mutagenic, 3 were judged questionable, and 172 were non-mutagenic. The remaining 16 chemicals produced different responses in the two or three laboratories in which they were tested. The results and data from these tests are presented.

Three hundred chemicals were tested for mutagenicity, under code, in Salmonella typhimurium, using a preincubation protocol. All tests were performed in the absence of exogenous metabolic activation, and in the presence of liver S-9 from Aroclor-induced male Sprague-Dawley rats and Syrian hamsters. The results and data from these tests are presented.

The results and data from the testing of 255 chemicals for mutagenicity in Salmonella are presented. All chemicals were tested under code using a preincubation modification of the Sulmonellalmicrosome test in the absence of exogenous metabolic activation and in the presence of liver S-9 from Aroclor-induced male Sprague-Dawley rats and Syrian hamsters. Key words: metabolic activation, Ames test, National Toxicology Program INTRODUCTIONA number of in vitro and in vivo test systems are being used in the National Toxicology Program (NTP) to evaluate chemicals for their ability to induce mutations , chromosome damage, and DNA damage. The rationale for testing has been described in detail elsewhere [Zeiger and Drake, 19801. The purpose of this report is to present the results and data from the testing of 255 chemicals for their ability to induce mutations in Salmonella. Because some chemicals were tested in more than one laboratory or at different times within the same laboratory, a total of 291 individual samples were tested. MATERIALS AND METHODS ChemicalsThe chemicals tested, their sources, and purities (where known) are listed in Table I; the chemical structures are presented in Appendix 1. The laboratories were supplied with the chemicals, which were coded by the NTP chemical repository (Radian Corp., Austin, TX), along with information on the physical characteristics of the chemicals, their solubility in different solvents, and safety and decontamination information. Also supplied, but in sealed envelopes, was information on the identity and toxicity of the chemicals. This was to be used in the event of a spill or personnel exposure. All coded chemicals were handled as potential mutagens and carcinogens.A number of chemicals were tested in more than one laboratory or at different times in the same laboratory. When this occurred, the laboratory performing the retest was not informed of the identity of the chemical or that it had been tested previously.The solvent of choice was distilled water, followed by dimethyl sulfoxide, 95% ethanol, and acetone. The individual laboratories made independent assessments of the solvents to be used. Bacterial StrainsAll chemicals were tested in Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537 and/or TA97. The majority of chemicals were tested in TA1537, and a few were tested in TA97. The testing in both strains is the result of an evolution of the protocol described by Haworth et a1 [1983]. In this original protocol, TA1537 was used. In a later protocol, TA97 replaced TA1537, but the option to retest a chemical in TA1537 was retained for chemicals that produced a positive or questionable response in TA97 and negative responses in the other strains.All strains were obtained from Dr. Bruce Ames (University of California, Berkeley) and were stored as recommended [Maron and Ames, 19831. Prior to their use for mutagenicity assays, all cultures were grown overnight with shaking at 37°C in Oxoid broth, and their phenotypes were analyzed, Preparation of Liver S-9 Fraction...

The results and data from the testing of 255 chemicals for mutagenicity in Salmonella are presented. All chemicals were tested under code using a preincubation modification of the Salmonella/microsome test in the absence of exogenous metabolic activation and in the presence of liver S-9 from Aroclor-induced male Sprague-Dawley rats and Syrian hamsters.

Previous studies of the biodegradation of nonpolar nitroaromatic compounds have suggested that microorganisms can reduce the nitro groups but cannot cleave the aromatic ring. We report here the initial steps in a pathway for complete biodegradation of 2,4-dinitrotoluene (DNT) by a Pseudomonas sp. isolated from a four-member consortium enriched with DNT. The Pseudomonas sp. degraded DNT as the sole source of carbon and energy under aerobic conditions with stoichiometric release of nitrite. During induction of the enzymes required for growth on DNT, 4-methyl-5-nitrocatechol (MNC) accumulated transiently in the culture fluid when cells grown on acetate were transferred to medium containing DNT as the sole carbon and energy source. Conversion of DNT to MNC in the presence of 1802 revealed the simultaneous incorporation of two atoms of molecular oxygen, which demonstrated that the reaction was catalyzed by a dioxygenase. Fully induced cells degraded MNC rapidly with stoichiometric release of nitrite. The results indicate an initial dioxygenase attack at the 4,5 position of DNT with the concomitant release of nitrite. Subsequent reactions lead to complete biodegradation and removal of the second nitro group as nitrite.