Grantee Research Project Results

1997 Progress Report: Light Induced Mercury Volatilization from Substrate Mechanism(s) Responsible and In situ Occurrence

EPA Grant Number: R825249
Title: Light Induced Mercury Volatilization from Substrate Mechanism(s) Responsible and In situ Occurrence
Investigators: Gustin, Mae Sexauer
Institution: University of Nevada - Reno
EPA Project Officer: Chung, Serena
Project Period: December 15, 1996 through December 14, 1999 (Extended to December 14, 2000)
Project Period Covered by this Report: December 15, 1996 through December 14, 1997
Project Amount: $288,645
RFA: Exploratory Research - Air Chemistry & Physics (1996) RFA Text | Recipients Lists
Research Category: Air , Safer Chemicals

Objective:

The objectives of this project are to determine the mechanisms responsible for the light enhanced mercury volatilization from substrate using controlled laboratory experiments and investigate the effect of ambient light conditions on mercury flux in the field.

Progress Summary:

A sequential extraction method for mercury has been developed. This is a modified version of that developed by Wallschlager et al. (in press, Journal of Env. Quality). This method uses selective extractions methods for distinguishing mercury species. During the summer of 1997, a comparison of two mercury speciation methods was carried out, one being a selective extraction method (Lechler et al., 1995) and the second a pyrolytic technique (Biester and Scholz, 1997). The intercomparison yielded similar determinations of the predominant mercury species in the samples but disagreement regarding the species present in small amounts. Based on this first intercomparison we chose to develop a method modified from that of Wallschlager et al. (in press). Currently our laboratory, P. Lechler (Nevada Bureau of Mines) and H. Biester ( Institute of Geochemistry, Heidelberg) are collaborating on an intercomparison of mercury speciation results obtained using two sequential selective extraction procedures and a pyrolytic method, respectively. All groups will analyze mercury speciation in splits of 12 samples, six samples from different representative field sites and six of standards containing specific mercury species. Splits of these samples are to be used in laboratory light studies.

During 1997 the relative influence of light on soils amended with specific mercury species, Hg^o, HgS, and HgCl₂ was investigated.

Field work was initiated on the effects of light on mercury flux. Collaborative work with nine teams of researchers in September 1997 brought seven field flux chambers and four micrometeorological methods to the Steamboat Springs Geothermal Area, Reno, Nevada to intercompare methods used for measurement of mercury flux in situ. Experiments were carried out that measured the effect of light on mercury flux by shading field flux chambers and measuring the change in flux as the transition from darkness to light occurred. Based on the data obtained during this intercomparison, the micrometeorological methods to be applied in year two will be developed.

Discussions are currently underway with a Ph.D. student currently working with Jerry Keeler at U of Michigan to work as a post doctoral and continue to accelerate the work on this project. Field sites have been chosen to continue in situ light experiments, developed speciation methods are being applied and laboratory experiments using the gas exchange chamber are underway.

Accomplishments and Research Results:

We have established there is a significant enhancement in elemental mercury flux from substrate amended with elemental mercury and mercury chloride of at least an order of magnitude which is significantly greater that occurring with mercury sulfide. Light effects have also been demonstrated to vary temporally, as a function of host material and wavelength. The data suggest microorganisms may not be an important factor in controlling light enhanced flux.

Controlled in situ field flux chamber experiments demonstrated a two-fold increase in mercury flux after exposure to light versus that in the dark. Mercury fluxes measured during the night-to-day transition show an increase with light exposure. Data collected during this study do not demonstrate the magnitude of the light influence relative to that of other environmental factors during the night- to-day transition. Experiments done at night with a halogen light showed no increase in flux. Results of these light experiments will be published as part of a special section of Journal of Geophysics-- Atmospheres.

Future Activities:

In this next year we will carry out the mercury speciation intercomparison and develop a peer-reviewed manuscript summarizing the results. The effects of various wavelengths of light on mercury flux from soils amended with different individual and combinations of mercury species will be quantified and the influence of substrate characteristics and microbial communities evaluated and documented.

The equipment necessary for the micrometeorological field studies will be purchased. This equipment along with a field flux chamber will be used to constrain light effects on mercury flux at the Carson River and Clear Lake Superfund Sites.

Data from some of these studies will be submitted in (a) paper (s) for the upcoming 1999 Mercury as a Global Pollutant International meeting in Rio De Janeiro and compiled for at least one to two papers to be submitted to peer reviewed journals.

Journal Articles:

No journal articles submitted with this report: View all 10 publications for this project

Supplemental Keywords:

Scientific Discipline, Air, Water, Mercury, Environmental Chemistry, air toxics, Ecology and Ecosystems, geochemical cycling, in situ occurance, light induced mercury volatilization, air-water interface, anthropogenic disturbances, chemical flux, photoreactive, contaminated sites, volatile organic species, lake ecosystems, mercury cycling, Superfund sites

Relevant Websites:

Synthesis Report of Research from EPA’s Science to Achieve Results (STAR) Grant Program: Mercury Transport and Fate Through a Watershed (PDF) (42 pp, 760 K)

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.