Stable isotope food-web analysis and mercury biomagnification in polar bears ( Ursus maritimus )

Mercury (Hg) biomagnification occurs in many ecosystems, resulting in a greater potential for toxicological effects in higher-level trophic feeders. However, Hg transport pathways through different food-web channels are not well known, particularly in high-latitude systems affected by the atmospheric Hg deposition associated with snow and ice. Here, we report on stable carbon and nitrogen isotope ratios, and Hg concentrations, determined for 26, late 19th and early 20th century, polar bear ( Ursus maritimus ) hair specimens, collected from catalogued museum collections. These data elucidate relationships between the high-latitude marine food-web structure and Hg concentrations in polar bears. The carbon isotope compositions of polar bear hairs suggest that polar bears derive nutrition from coupled food-web channels, based in pelagic and sympagic primary producers, whereas the nitrogen isotope compositions indicate that polar bears occupy > fourth-level trophic positions. Our results show a positive correlation between polar bear hair Hg concentrations and δ 15 N. Interpretation of the stable isotope data in combination with Hg concentrations tentatively suggests that polar bears participating in predominantly pelagic food webs exhibit higher mercury concentrations than polar bears participating in predominantly sympagic food webs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73930/1/j.1751-8369.2009.00114.x.pd

Maternal activity and birth weight: a prospective, population-based study

To determine the association between maternal activity and pregnancy outcome, the authors investigated the separate influences of time, physical effort, and posture at work, both at a job and in the home, on birth weight. Study subjects were 1,507 of 1,889 women appearing consecutively for antenatal care at a district general hospital in inner London, England, in 1982-1984. Data were collected prospectively by interview and examination at several stages of pregnancy. Multivariable linear regression was used to distinguish associations with physical activity from confounding by other factors. The mean birth weight of infants born to women in full-time employment was 49 g less than that for births to women not in paid work (95 percent confidence interval (Cl) 1-97 g). However, the difference was due to confounding, and after adjustment, full-time employment was associated with a 12-g increase in birth weight (95 percent Cl -39 to 63 g). There was little difference in birth weight related to gestational stage at leaving work. Duration, physical effort required, and energy expenditure in paid work and in work at home had no discernible association with birth weight. A small increase in birth weight was associated with increased hours of sleep. These data allow estimates of associations with birth weight as precise as 80 g. Within the range of activities performed by pregnant women in the population studied, birth weight is unlikely to be associated with maternal physical activity