The harm caused by cigarette smoking is overwhelmingly due to byproducts of tobacco combustion. Electronic Nicotine Delivery Systems (ENDS) provide nicotine to users without combustion, and may support tobacco harm reduction among cigarette smokers who would not otherwise quit in the near term. Analyses of Wave 5 of the Population Assessment of Tobacco and Health (PATH) Study compared biomarkers of exposure (BOE) levels for nicotine, 3 metals, 2 tobacco-specific nitrosamines and 14 smoking-related volatile organic compounds in 151 exclusive ENDS users, 1341 exclusive cigarette smokers, 115 dual users (cigarettes and ENDS), and 1846 past 30-day nonusers of tobacco, adjusting for demographics. Nicotine exposure in ENDS users and dual users did not significantly differ from smokers. Among ENDS users, 16 of 18 other BOEs were significantly lower than smokers’; 9 BOEs were not significantly different from nonusers. Among dual users smoking < 10 cigarettes/day, 15 of 18 non-nicotine BOEs were significantly lower than smokers’, whereas in dual users smoking ≥ 10 cigarettes per day none of the BOEs significantly differed from smokers’. In this representative sample of US adults, exclusive use of ENDS (vs. cigarette smoking) was associated with much lower exposures to many harmful chemicals associated with smoking-related disease. BOE levels in dual users were directly related to their cigarette consumption. These BOE data provide further evidence that ENDS expose users to substantially lower levels of toxicants than combustible cigarettes, confirming their potential for harm reduction.

The Relative Crowding Coefficient (RCC) is a common measure of interspecific competition in a replacement series experiment. However, the interpretation of RCC depends upon the validity of an assumed functional relationship in total species yield. We develop inference procedures based upon the Relative Yield Total (RY T ), a function of species yields in mixture and monoculture plantings, that may be utilized to assess the plausibility of the species yield functional form under which RCC is a reasonable metric of interspecific competition. The performance of the proposed RYT inference procedures is evaluated on the basis of a simulation study. Using the proposed methodology, we conduct RYT inference in a replacement series experiment of bahiagrass (Paspalum notatum) and smutgrass (Sporobolus indicus).