1999 Progress Report: Social Impact Assessment of Human Exposure to Mercury Related to Land Use and Physicochemical Settings in the Alabama-Mobile River SystemEPA Grant Number: R827168
Title: Social Impact Assessment of Human Exposure to Mercury Related to Land Use and Physicochemical Settings in the Alabama-Mobile River System
Investigators: Bonzongo, Jean-Claude J. , Lyons, W. Berry , Bryan, Hobson C. , Roden, Eric E. , Ward, Milton G. , Chaubey, Indrajeet
Current Investigators: Bonzongo, Jean-Claude J. , Warner, Kimberly A. , Lyons, W. Berry , Bryan, Hobson C. , Roden, Eric E. , Ward, Milton G. , Chaubey, Indrajeet
Institution: The University of Alabama at Birmingham , Austin College
Current Institution: The University of Alabama at Birmingham , The Ohio State University , University of Arkansas - Little Rock , University of Florida
EPA Project Officer: Chung, Serena
Project Period: December 21, 1998 through December 20, 2001
Project Period Covered by this Report: December 21, 1998 through December 20, 1999
Project Amount: $804,534
RFA: Water and Watersheds (1998) RFA Text | Recipients Lists
Research Category: Water , Watersheds
Objective:The southeastern region of the United States, mainly its Coastal Plain portion, is believed to be particularly vulnerable to mercury contamination in aquatic food chains, due to the coexistence of both natural- and human-imposed conditions, which favor the production/accumulation of methyl-mercury. We have hypothesized that certain urban/suburban activities, as well as some natural physicochemical conditions could favor mercury methylation and its accumulation in food chains. The objectives of this study are to: (1) determine concentrations and mercury species in water, sediments, and fish samples obtained from different aquatic systems in the Mobile Alabama River Basin (MARB); (2) investigate the impact of land use types and that of wetlands within watersheds on microbial processes associated with methyl-mercury production; (3) use GIS to represent spatially arranged data and ultimately to predict mercury levels in fish; and (4) use a participatory approach to environmental decisionmaking to ameliorate conflict, and to conduct a social and economic impact assessment of remedial alternatives as a basis for potential recommendations.
Progress Summary:During the period covered by this report, we have been able to make progress on all aspects of our project. Related achievements are summarized below.
Sampling Sites Selection and Characterization: The following approach was used to select our sampling sites. First, based on expert knowledge of Alabama's resident fishermen, the site selection process was streamlined. Second, information obtained from resident fishermen was then verified using digital land use maps. This approach resulted in the selection of 54 sites. So far, watershed boundaries for major four sub-basins within the MARB have been delineated and land use maps for these basins have been developed.
Mercury Analysis: Meeting the above-stated objectives requires the analysis of a large number of water, sediment, and fish samples. Accordingly, most of the period covered by this report was spent upgrading our mercury analytical facility. Total and methyl-Hg determinations are being conducted presently on fish samples and sediment slurries from laboratory experiments.
Sample Collection and Public Participation: Following both the selection of sites and the upgrade of our mercury laboratory, we started the collection of fish samples. Fish samples were collected through the assistance of different Bass Clubs. Fish caught from our selected sites by Bass Club members were turned in to us at the tournament weigh-in. This sample collection approach of involving experts from the public has had a dual benefit of streamlining the fish tissue collection effort and informing a significant stakeholder, the recreational fisherman. In Year 2, we anticipate using electrofishing boats in addition to the above-mentioned approach to augment fish collection and access remote sites that will not be fished through Bass Clubs. With regard to the public information and participation aspects of our project, we have generated an extensive list of primary stakeholders to approach for issues-identification. Many organizations have been contacted to introduce the research topic and to determine opportunities for informing their membership. Finally, tools for public outreach have been established. The first is a bulletin, the Mercury News, designed to present the project to stakeholder groups. The second is a message-oriented telephone line, the Mercury Project line. Finally, a Web site is currently under construction.
Database Development: We are developing a spatial relational database that will be linked with the GIS coverages of watershed characteristics. Data from this study as well as those obtained from other available sources are being incorporated in this database. We are designing queries using spatial query language (SQL) to obtain information about mercury concentration in fish, water, and sediment as well as land use and other watershed characteristics. The database will have reports to display query results that can be used by researchers and stakeholders.
Experimental Studies of Mercury Biotransformation and Associated Microbial Processes: After review of the cost and difficulty of obtaining radiolabelled 14C-MeHgI and 203Hg(II), we decided to conduct our studies of microbial transformation of mercury in sediment using cold spikes. This approach is based on published methods in which HgX2 and CH3HgX are used in methylation and demethylation assays, respectively. Results from preliminary experiments are given below.
- Experiments with anaerobic slurries of mineral-rich wetland sediments. We conducted a series of preliminary experiments to assess the importance of different electron accepting conditions (iron reducing, sulfate reducing, and methanogenic), relevant to our chosen study sites, on relative rates of mercury transformations. Rates of methylation were found to be similar under methanogenic and sulfate-reducing conditions, while only minor production of methyl-mercury was observed under iron-reducing conditions. In contrast, rates of demethylation of methyl-mercury were similar under all three electron-accepting conditions. Methylation to demethylation ratios, computed from total amounts of methyl-mercury produced or lost in 9 days, were about 5 times lower under iron-reducing conditions. These results suggest that net production of methyl-mercury in riverine systems may be suppressed when underlying sediments contain an iron oxide-rich surface layer.
- Impact of land use types on speciation of ambient sedimentary-mercury. To assess the impact of different land-use types on the speciation of ambient mercury, laboratory experiments using specific additions to sediment slurries were conducted. Sulfate addition for mining, nitrate and phosphate for agriculture and municipal discharges, organic matter for both autochthonous and allochthonous organic matter, silt for damming; and lowering of pH for acid mine waste. No mercury was added to sediment slurries and mercury speciation was determined before and after a dark incubation period of 5 days at 20 C. Results showed that at the end of the incubation period, the fraction present as methyl-mercury increased in all treatments as compared to controls. For example, methyl-mercury levels in the Black Warrior River sediment went from values below our analytical detection limit to concentrations representing up to 3 percent of total mercury concentration. Overall, and to some extent, results from these experiments confirmed our hypotheses, in that certain anthropogenic activities and natural settings could favor the production of methyl-mercury regardless of the amount of inorganic mercury initially present in the sediments.
Future Activities:During Year 2, we will continue our extensive fish sample collection. At the same time, we will continue the identification of stakeholders and informal meetings with stakeholder representatives. These will be "issue-sharing and issue-linking" meetings between scientists and stakeholders to review concerns, clarify positions, and to make connections among different issues and perspectives.
Following completion of our survey of mercury concentrations in fish tissue from our 54 sites, we will select a limited number of sites with contrasting levels of mercury in fish for intensive mercury and sediment biogeochemical studies.
Meanwhile, further laboratory experiments will continue to explore whether the transition to different electron accepting conditions results in changes in relative rates of methyl-mercury production and consumption. We also will examine whether changes in carbon or electron donor availability during transition to various electron-accepting conditions influence rates of mercury transformation.
We will continue to develop GIS-coverages for the watersheds where fish samples are and will be collected. We also will work with the database development and linking the database to the GIS-coverages. Finally, we plan to start working on a spatial GIS-based model that will link land use activities with mercury transport at the watershed scale.