Characteristics of Mercury and other Metals Ben Hodges Physical Transport Lynn Katz Surface/Water Chemistry Howard Liljestrand- Air/Water Chemistry The University of Texas at Austin 8 February 2002
Metals in Water Metal Antimony Arsenic Barium Beryllium Cadmium Chromium Copper Lead Mercury Selenium Thallium MCL Health Effects 0.006 Cholesterol, blood glucose 0.05 Skin damage, cancer; 2 Blood pressure (BP) 0.004 Intestinal lesions 0.005 Kidney damage 0.1 Allergic dermatitis primary Texas metal 1.3 problem Gastrointes., liver/kidney 0.015 Development, kidney,bp 0.002 Various 0.05 Circulatory problems 0.002 Blood, kidney/liver/intes.
mercury in watershed Impaired stream and river miles Mercury contamination in Texas watersheds pathogens mercury Impaired lake, estuary and wetland acres 1998 EPA data GIS project by O. Robayo, UT Austin graduate student
fish advisories it s not just a Texas problem USGS http://www.usgs.gov/themes/factsheet/146-00/
Mercury is TOXIC One of the most dangerous substances known Fish are unsafe to eat with only 1/70th of a teaspoon per year in a lake One meal of highly mercury-contaminated fish can cause brain damage to a fetus
Forms of Mercury Elemental mercury (Hg 0 ) Volatile Most common in atmosphere. Inorganic mercury (Hg ++ and Hg + ) Predominates in soils and surface waters Organic mercury Binds with humic substances Methyl and dimethyl mercury are formed through methylation Organic (methyl-mercury) is primary bioaccumulation problem
Routes of Human Exposure % Absorbed into Blood Stream Mercury Species Inhalation Digestion Dermal Contact Elemental >75% negligible <3% Inorganic ~40% ~20% <3% Organic unconfirmed >95% <5% Indoor air problems Eating contaminated fish
Effects of Exposure Elemental Mercury Central nervous system Pulmonary function impairment, kidney damage Inorganic Mercury Central nervous system Possible human carcinogen Severe kidney damage Organic Mercury Central nervous system Possible human carcinogen Blindness, deafness, speech impairment, death Fetal damage
Common Hg Transformations Oxidation Methylation HgCH 3 + Hg 0 Hg +1 Hg +2 Hg(CH 3 ) 2 Reduction Demethylation Elemental Inorganic Organic
cycle Atmospheric Hg USGS: http://www.usgs.gov/themes/factsheet/146-00/
Atmospheric Issues Direct measurements of mercury depositing to U.S. territory are still sparse, and not representative yet of the entire nation. We also do not have any direct data quantitatively linking sources of atmospheric mercury with measured concentrations in soils, waterways, or aquatic species. Leonard Levin 1998 When looking at the atmospheric loading the ability to distinguish global, regional and local scales of air transport and depositions is crucial to formulation of control strategy. Florida Everglades TMDL Pilot Study Report
national pilot National study Pilot Study of Mercury Contamination of Aquatic Ecosystems along Multiple Gradients Brumbaugh et al, 2000, http://co.water.usgs.gov/trace/pubs/setac2000_hg/fig3.gif
Research Needs Multiscale Atmospheric Mercury Models [Seigneur C. et al. JGR 2001] Calculation of Hg deposition fluxes are sensitive to Hg emissions Background ~ 2/3 global Coal combustion emissions are the only well-described Hg Speciation (Hg(0), Hg(II), Hg(particulate)) Background emissions have presumed speciation Atmospheric lifetime and fluxes are strong functions of transformations Aqueous Hg(0) re-dox reactions are incompletely known Re-dox kinetics are uncertain for reactions identifies Oxidants and reductant concentrations are uncertain Fraction of Hg sorbed on particulate matter unknown Dry Deposition Velocities No direct measurements of v d for Hg(0), Hg(II), Hg(particulate) Hg(0) dry flux is nil in regional models but significant in global models Wet Removal Presupposed cloud and rain scavenging rates Extrapolated precipitation fields and collector distributions Source speciation greatly influences local deposition
Hydrology and Physical Transport methylation sites Hg load to aquatic system depends on Terrestrial interception / release of Hg Direct deposition Legacy sources http://www.cwr.uwa.edu.au/~oldham/spec_res_areas.html
Complex Transformation Processes Depend on Environmental Conditions k? k? k? k? k? k? k? k? k? k? k? k? k?
Methylation USGS http://sofia.usgs.gov/sfrsf/rooms/acme_sics/acme Aquatic Cyling of Mercury in the Everglades, 1999, Krabbenhoft,, et al.
Factors Affecting Methylation Rates Dissolved oxygen (DO) Sulfur ph Clay / organic material Low DO (anoxia) required Sulfate-reducing bacteria required Low ph increases rate Binding reduces bioavailability Physical transport affects the spatial and temporal availability of methylation conditions
Research Needs Methylation Processes Quantify Texas methylation sites (mostly wetlands) Site-specific studies laboratory scale factors which affect rates for models mesocosm field scale verification studies Quantify site-specific physical exchange processes (wetlands/stream/lake exchanges) Aquatic Cycling of Mercury in the Everglades (ACME) Project Mesocosm studies http://sofia.usgs.gov/geer/posters/ merc_cycle/images/containersx.jpg
Geographical Information Systems (GIS)
Persistence of Methyl Mercury Mercury concentrations can be relatively low in sediments (pp billion) and water (pp trillion), and yet Bioaccumulates in fish (pp million) Long half-life (t 0.5 ) due to its association w/ lipids
biomagnification http://sofia.usgs.gov/sfrsf/rooms/acme_sics/acme/objective.html, Krabbenhoft, et al. 1999
Research Needs Food Web Uptake and bioaccumulation rates in food web Relation between MeHg production and fish tissue accumulation How do we make the connection between source loadings and fish tissue Hg?
Relating Fish Tissue to Water Column Concentrations EPA suggests possible methods relating fish tissue to water MeHg: Calculate site-specific bioaccumulation factors based on data collected from a specific waterbody; Calculate site-specific bioaccumulation factors based on computer models; Use experimentally-derived bioaccumulation factors that are based on field data published in the literature. This is a difficult approach
mercury vs methyl Aquatic Cyling of Mercury in the Everglades, 1999, Krabbenhoft,, et al.
Legacy Hg Loads Despite our understanding in principle of how mercury enters fish caught for food, measurement data do not reveal the origins of the mercury found in these fish mercury in sediments may have originated decades or centuries earlier, or be due to releases from sources outside of the U.S. - Leonard Levin, 1998
METAALICUS Project http://www.biology.ualberta.ca/ metaalicus/metaalicus.htm
Research Needs Models and Data Models tuned to individual sites linking atmosphere hydrology sediments methylation food web Quantify transfer rates Data for site-specific models development, refinement calibration validation uncertainty, sensitivity Increase scientific understanding to reduce TMDL uncertainty
Simple Models Require Site-specific Data simple processes Hg 0 Quantify the rates Hg 0 transport transport transport transport Quantify the transport
Summary of needs Hg speciation and emission rates for point sources Inventory of methylation sites Quantify methylation rates Quantify bioaccumulation rates from MeHg production Modify and link models for transport processes from sources to fish tissue Collect data for model improvement and refine uncertainty Evaluate model sensitivity for use in calculating safe emission levels