Gaseous elemental mercury (GEM), the primary form of mercury (Hg) in the atmosphere, can undergo bidirectional exchange with the Earth's surface, with uptake in growing vegetation constituting the dominant atmospheric deposition process. Whereas direction and magnitude of this exchange can be determined using micrometeorological and chamber techniques, these approaches are complex, costly and labor‐intensive, and often only yield fluxes over relatively short time‐scales at few sites. We demonstrate that an inexpensive and easy‐to‐use passive air sampler can identify and quantify vertical GEM concentration gradients on scales ranging from centimeters to tens of meters over long time periods (up to 1.5 years) and with coarse temporal resolution (monthly to seasonally). Samplers were deployed above clean and contaminated soil and through a deciduous forest canopy at two sites in Southern Ontario. Significant and seasonally variable gradients of GEM concentrations, both increasing and decreasing with height above ground, were observed and can be explained through the influence of factors such as soil contamination, canopy growth, temperature, solar irradiance, and snow cover. At a minimum, the sampler can identify the GEM flux direction, but, when combined with the Modified Bowen Ratio method, can also be used to estimate the evaporative GEM flux from mercury‐contaminated soil. We further demonstrate the application of the approach to contaminated site assessment, using a field in Brescia, Italy, known to contain elevated levels of Hg in soil. By allowing for cost‐effective measurements at multiple sites and over extended time periods, passive sampling complements existing techniques for studying atmosphere‐surface exchange of GEM.

<p>The specific properties of gaseous elemental mercury (GEM) allow it to undergo bidirectional exchange between the atmosphere and the Earth’s surface. Determining the direction and the magnitude of GEM’s atmosphere-surface flux is possible and has been accomplished using micrometeorological and chamber techniques, but (i) is complex and labor-intensive, and (ii) often only yields fluxes over relatively short time scales. A recently developed passive air sampler for GEM has the precision required for identifying and quantifying vertical concentration gradients above the Earth’s surface. The feasibility and performance of this approach is currently being tested in a number of field studies aimed at the: (i) measurement of GEM concentration gradients above both mercury-contaminated and background forest soils, (ii) quantification of vertical concentration gradients on a tower through a temperate deciduous forest canopy, and (iii) measurement of mercury concentration gradients over stable and thawing permafrost to determine the effect of permafrost degradation on GEM evasion. Contrasting with earlier flux studies, these investigations cover long time periods (up to 1.5 years) and have coarse temporal resolution (monthly to seasonally). Significant gradients of GEM air concentrations, both increasing and decreasing with height above ground, were observed, implying that at a minimum, the method is able to identify the flux direction of GEM. Under the right circumstances, this method can also be used to estimate the approximate magnitude of the GEM air-surface exchange flux. The measured gradients also reveal the impact of factors such as temperature, solar irradiance, and snow cover on air-surface exchange. The method holds promise for establishing the direction and size of exchange fluxes at long time scales of months to a year, especially in study areas where access, effort and cost are prohibitive to longer duration studies with existing approaches.</p>

Aim: To evaluate and compare the viability of periodontal ligament cells of avulsed teeth in five different storage media followed by simulated avulsion injury. Settings and Design: Seventy-five premolars extracted for orthodontic therapeutic purposes were randomly and equally ivided into five groups based on storage media used [A: HBSS (control), B: Milk (experimental), C: Aloe Vera (experimental), D: Egg white (experimental), E: Coconut water (experimental)].Methods and Material: Following extractions, the teeth were placed in one of the five different storage media for 60 minutes, following which the scrapings of the PDL were collected in Falcon tubes which already contained collagenase enzyme in 2.5 mL of Phosphate buffered saline. The tubes were subsequently incubated and centrifuged. Then acquired PDL cells were stained with Trypan Blue dye and were counted under an optical microscope. Statistical Analysis Used: Results were subjected to statistical analysis using ANOVA test and Post Hoc Tukey test. p-value < 0.05 is considered to be significant. Results: HBSS showed the highest percentage of viable cells (80.14%), followed by Egg white (74.01%) and Aloe Vera (73.68%). Milk and Coconut water showed the least percent of viable cells 63.20%, 63.58% respectively.