In this study, both endogenous and exogenous N2-hydroxymethyl-dG adducts in nasal DNA of rats exposed to 0.7, 2, 5.8, 9.1, or 15.2 ppm [ 13CD2] formaldehyde for 6 h were quantified by a highly sensitive nano-UPLC-MS/MS method. Our data clearly demonstrated that exogenous formaldehyde DNA adducts form in a highly nonlinear fashion, with a 21.7-fold increase in exposure causing a 286-fold increase in exogenous adducts. The ratio of exogenous/endogenous DNA adducts demonstrated that endogenous DNA adducts dominated at low exposures, comprising more than 99%. In contrast, exogenous adducts were not detectable in the bone marrow of rats exposed to 15.2 ppm [13CD2] formaldehyde.
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