Mercury Speciation in Temperate Tree Foliage

Cycling of mercury (Hg) and monomethylmercury (MMHg) in forest ecosystems can affect exposures of terrestrial and aquatic wildlife within the watershed. Litterfall has been posited to be a major source of MMHg and total Hg to the forest floor; however, the origin of MMHg associated with tree foliage is largely unknown. I tested the hypothesis that leaf MMHg would be controlled by root uptake and thereby proportional to levels in soil. Fresh leaves and associated soil samples were sampled from nine tree species (deciduous and coniferous) at 30 locations spanning a 1145 km2 area in southwest Ohio, a region presumed to have relatively homogeneous atmospheric deposition of Hg and MMHg. Concentrations of Hg species in tree leaves were unrelated to those in soil. In contrast, tree genera and trunk diameter were dominant variables influencing Hg levels in tree foliage. The fraction of total Hg as MMHg was relatively constant among all genera and averaged 0.4%. Results of this study suggest that uptake of gaseous Hg0 from the atmosphere is the dominant source of total Hg in foliage and that MMHg is formed by in vivo transformation of Hg(II) in proportion to the concentration accumulated. Via litterfall, it appears that processes associated with tree leaves are a major source of total Hg and MMHg to the forest floor

Testing solar cookers for cooking efficiency

Solar Cookers International (SCI) staff developed and implemented a calculation to measure the cooking efficiency of solar thermal cookers. The calculation complements and enhances SCI's existing performance evaluation process (PEP), which can now be used for determining both the standard cooking power and the cooking efficiency for solar thermal cookers. The standard cooking power value is a single measure of solar cooker performance taken when the temperature of the test water load is specifically 50 °C greater than ambient temperature. Cooking efficiency values extend the perspective of solar cooker performance, as they are applicable to a continuum of load temperature measurements made during a heating cycle. Cooking efficiency is the ratio of energy absorbed by the solar cooking load divided by the input solar energy intercepted by the device during a test interval. Examples of cooking efficiency calculations using water loads during three days of testing for an anonymous group of different types of solar cookers are: solar box oven (18.9 %), reflective-panel solar cooker (28.5 %), parabolic reflector (35.2 %), and evacuated-tube solar cooker (34.6 %)