Modulation of 2,6-dinitrotoluene genotoxicity by alachlor treatment of Fischer 344 rats

Abstract

Due to its widespread use as a preemergent herbicide, alachlor has been detected as a groundwater contaminant. The procarcinogen, 2,6‐dinitrotoluene (DNT), a by‐product of the munitions industry and a precursor to polyurethane production, is found in the manufacturing waste stream. This study explores the effect of alachlor treatment on the bioactivation of DNT by examining urine mutagenicity, intestinal enzymes, and hepatic DNA adducts to detect changes in metabolism. Five‐week‐old male rats were treated daily by gavage with 50 mg/kg of alachlor for up to 5 weeks while control animals received an equal volume of peanut oil. At 1, 3, and 5 weeks following the initial alachlor dose, animals were administered p.o. 75 mg/kg DNT or DMSO. Urine was collected for 24 hr in metabolism cages. Following incubation with sulfatase and β‐glucuronidase, urines were individually concentrated by C‐18 solid phase extraction, dried under N2, and prepared for bioassay in Salmonella typhimurium strain TA98 with and without metabolic activation. Urine from peanut oil‐ and alachlor‐treated rats was not mutagenic. Even though calf thymus DNA–alachlor adducts formed in vitro, no hepatic DNA adducts were detected in vivo in these two treatment groups. Interestingly, a significant increase in excretion of mutagenic urine from DNT‐treated rats was observed following 3 weeks of alachlor treatment in the absence of S9 (690 ± 130 vs. 339 ± 28 revertants/ml) which corresponded to increased DNT‐related hepatic DNA adduct formation (5.90 ± 0.88 adducts/108 nucleotides vs. 10.56 × ±0.59 adducts/108 nucleotides [relative adduct level (RAL)]). Elevation in the production of mutagenic urine from control and treated animals was linked to increases in intestinal nitroreductase and β‐glucuronidase activities; however, the only significant alachlor‐related effects were an increase in small intestinal 1‐week β‐glucuronidase and 5‐week dehydrochlorinase activities. The increased urine mutagenicity and hepatic DNA adduct formation indicates that alachlor has a transient effect on DNT bioactivation that apparently is unrelated to intestinal bioactivation. Environ. Mol. Mutagen. 31:274–281, 1998. © 1998 Wiley‐Liss, Inc.

Toward a molecular equivalent dose: Use of the medaka model in comparative risk assessment

“…The radioactive spots for the high performance liquid chromatography (HPLC) analysis were eluted from the PEI plates with 4.0 M pyridinium formate (pH 4.0) for 18 hours and analyzed according to the method previously described (King et al, 1994). The adduct levels were calculated from the amount of radioactivity (cpm) for each adduct spot on the chromatogram, quantity of DNA, and the specific activity of [γ 32 P]ATP used for labeling (George et al, 1998).…”