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Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric(More)
We present the application of a nonparametric method to performing functional principal component analysis for functional curve data that consist of measurements of a random trajectory for a sample of subjects. This design typically consists of an irregular grid of time points on which repeated measurements are taken for a number of subjects. We introduce(More)
The tissue distribution and macromolecular binding of benzene was studied over a dose range spanning nine-orders of magnitude to determine the nature of the dose-response and to establish benzene's internal dosimetry at doses encompassing human environmental exposures. [14C]-Benzene was administered to B6C3F1 male mice at doses ranging between 700 pg/kg and(More)
DNA adduction in rodents at doses equivalent to human dietary exposure (10(4)-10(6)-fold lower than laboratory studies) is being studied using accelerator mass spectrometry (AMS). AMS is a nuclear physics technique for detection of cosmogenic isotopes and has been used for specifically selecting and counting 14C. Using AMS, DNA adducts are detectable at(More)
UNLABELLED A new technique was evaluated to identify changes in bone metabolism directly at high sensitivity through isotopic labeling of bone Ca. Six women with low BMD were labeled with 41Ca up to 700 days and treated for 6 mo with risedronate. Effect of treatment on bone could be identified using 41Ca after 4-8 wk in each individual. INTRODUCTION(More)
Metabolites of atrazine were measured in human urine after dermal exposure using HPLC to separate and identify metabolites and accelerator mass spectrometry (AMS) to quantify them. Ring-labeled [14C]atrazine was applied for 24 h with a dermal patch to human volunteers at low (0.167 mg, 6.45 muCi) and high (1.98 mg, 24.7 muCi) doses. Urine was collected for(More)
Long-term physiologic tracing of nutrients, toxins, and drugs in healthy subjects is not possible using traditional decay counting of radioisotopes or stable isotope mass spectrometry due to radiation exposure and limited sensitivity, respectively. A physiologic dose of 14C-labeled folic acid (35 microg, 100 nCi) was ingested by a healthy adult male and(More)
Accelerator mass spectrometry (AMS) is used to determine the amount of carcinogen covalently bound to mouse liver DNA (DNA adduct) following very low-level exposure to a 14C-labeled carcinogen. AMS is a highly sensitive method for counting long-lived but rare cosmogenic isotopes. While AMS is a tool of importance in the earth sciences, it has not been(More)