ABSTRACT
This study investigated the relationship between 18O and 2H isotopes in samples of Mexican hair and drinking water. The purpose of this study was twofold: to quantify the relationship between isotopes in Mexican hair and tap water, in order to understand the impact of water stress and differing socioeconomic status on accurate predictions of drinking water; and to determine whether currently existing semimechanistic models can accurately represent the relationship between hair and tap water. This study used a subset of paired samples of human hair (n = 62) and tap water (n = 76). Isotope values in tap water ranged from -11.4 to -4.3 and -79.1 to -22.5, and in hair from +9.5 to +16.1 and -90.8 to -53.7, for δ18O and δ2H, respectively. The most depleted δ18O and δ2H hair values came from individuals in the state of Morelos. For modern Mexican populations, positive correlations between isotopes in hair and water were not significant, with correlation coefficients r = 0.61 (p = 0.05) and r = 0.60 (p = 0.06) for 18O and 2H, respectively. Error-in-variables regression yielded linear fits that were somewhat better for 2H relative to 18O: δ18Oh = 0.183 [±0.132] δ18Otw + 15.7 [±0.9] (r2 = 0.23); δ2Hh = 0.181 [±0.076] δ2Htw - 64.0 [±3.0] (r2 = 0.34). In short, data from this Mexican population did not exhibit the strong relationships between isotope values of 18O and 2H in tap water and hair that have been characteristic of other populations studied to date. Given the economic stratification of this region and the poor correlation between hair and water samples, the authors considered the possibility that l, the fraction of the diet derived from local sources, and fs, the fraction of nonexchangeable H in keratin that was fixed in vivo, are local rather than global parameters for this population. The authors estimated different values of l and fs for each location. Given the anticipated importance of the nonlocal dietary contribution, they treated the isotopic content of nonlocal food and the offset parameters for predicting isotopes in locally derived food as tuning parameters and compared the results with parameters based on the American supermarket diet. They found that, although O and H isotopes in water and hair maintained similar geographic distributions, O and H isotopes in tap water explained only a small part of the variation observed in hair samples. Compared to the standard American supermarket diet, the Mexican estimates for nonlocal diet and local diet offsets predicted regional distributions of l and fs that cleanly segregated urban areas from rural towns.
ABSTRACT
OBJECTIVES: We examined factors influencing physician practice decisions that may increase primary care supply in underserved areas. METHODS: We conducted in-depth interviews with 42 primary care physicians from Los Angeles County, California, stratified by race/ethnicity (African American, Latino, and non-Latino White) and practice location (underserved vs nonunderserved area). We reviewed transcriptions and coded them into themes by using standard qualitative methods. RESULTS: Three major themes emerged in relation to selecting geographic- and population-based practice decisions: (1) personal motivators, (2) career motivators, and (3) clinic support. We found that subthemes describing personal motivators (e.g., personal mission and self-identity) for choosing a practice were more common in responses among physicians who worked in underserved areas than among those who did not. By contrast, physicians in nonunderserved areas were more likely to cite work hours and lifestyle as reasons for selecting their current practice location or for leaving an underserved area. CONCLUSIONS: Medical schools and shortage-area clinical practices may enhance strategies for recruiting primary care physicians to underserved areas by identifying key personal motivators and may promote long-term retention through work-life balance.
