 |
|
Photo by David Fallside |
Mercury
Contamination in the Yuba and Bear River Watersheds
A
Report of the
South
Yuba River Citizens League
Fraser
Shilling, Ph.D.
|
|
Photo by David Fallside |
Summary of
the Problem
Historic
hydraulic mining and the use of mercury to remove gold through amalgamation has
left the Bear and Yuba Rivers and watersheds with a legacy of eroding hillsides,
mercury, and excess sediment. The USGS estimates that up to 8,000,000 of the
26,000,000 lbs used in the Sierra Nevada may have been “lost” during gold
recovery. The mercury is present in the bottom (benthos) of rivers and
reservoirs, as well as in pits, sluices, and tunnels remaining in abandoned mine
lands (AMLs) from which it may be mobilized. It is transported by erosion and
runoff as elemental mercury and in ionic form (e.g., Hg2+), in
dissolved form, adsorbed to particles, and as droplets of the metal. The mercury
can be converted by microbial action into methylmercury, which can then be
absorbed by microbes, plants, and animals. As methylmercury makes its way up the
food chain (bioaccumulation) it is concentrated (biomagnification), so that in
larger predatory fish (e.g., trout and bass) concentrations can exceed levels of
concern for human consumption (>0.3 parts per million, ppm). There are very
few areas (primarily within AMLs) where mercury concentrations in surface water
are high enough to warrant concern for public health from consuming the water
itself.
Studies
by scientists at the University of California, Davis in the mid-90s and
follow-up studies by US Geological Survey scientists in 1998-2000 have
demonstrated that there are both “hotspots” of mercury contamination in AMLs
and in downstream aquatic wildlife populations that have levels approaching and
exceeding 1 ppm. Although concentrations of methylmercury in fish, amphibians,
aquatic insects, and water are known for certain sites, the total amount of
mercury (“load”) in the watersheds and rivers is not known and can currently
only be guessed. In addition, it is unknown what populations within the Sierra
Nevada and the Sacramento Valley could be affected and to what extent, due to
consumption of mercury-tainted fish.
Mercury
can cause a variety of health problems in humans, primarily neurological,
including declining motor skills and sensory ability, tremors, inability to
walk, convulsions, and death. The primary pathway for mercury poisoning in
humans (and other animals) is through fish consumption and is a more serious
problem for children due to their lower weight. Although there have been
national surveys of mercury exposure through fish consumption, this information
is not adequate for a local or regional analysis of mercury exposure for humans.
Human Health
Health Impacts from Mercury Exposure
Although elemental and inorganic mercury can cause health problems,
methylmercury in fish is likely to be the primary cause of exposure in the
Sierra Nevada and the Sacramento Valley. Assessing the risk of exposure and
potential health effects depends upon knowledge of the exposed population,
including age groupings, where fish are caught, what species of fish are caught,
the methylmercury load in the fish by species, rate of fish consumption, and the
individual’s body weight (EPA, 1996). Most of our knowledge about mercury
poisoning from fish came from the epidemic of mercury-related health problems in
Minamata Bay and Niigata, Japan in the 1950’s and 60’s. Thousands of people
suffered temporary and permanent impairment of speech, hearing, vision, and
motor coordination. In addition fetuses and infants were especially susceptible
due to their low weight and need for rapid development. Methylmercury readily
crosses the gastrointestinal lining, the blood-brain barrier, and the placental
barrier. Because methylmercury is only slowly de-methylated in the body, it may
accumulate with steady contaminated fish consumption, resulting in increasing
exposure levels.
Monitoring Human Health
The primary studies that have been conducted of
mercury exposure through fish consumption have been epidemiological studies to
establish connections among methylmercury and fish consumption rates, body size
and age, and mercury-related disease. The most well-known of these studies have
been the Japanese mercury poisoning epidemics of the 1950’s and 60’s, the
Iraqi epidemics (related to methylmercury contaminated grain) in the 1950’s
and early 1970’s, the more recent and long-term studies of fish-consuming
populations in the Seychelles and Faroe Islands, and smaller studies around the
Great Lakes of the U.S. Although these studies result in reliable “reference
doses” and “dose-response curves” (relationship between amount of mercury
consumed and effect), they lack the precision that would come with site-specific
studies for water bodies containing containing contaminated fish. Children and
pregnant women that may be consuming certain fish species from a limited area
known to be a problem are most in need of individual assessments of risk. This
can often be accomplished by measuring the mercury concentrations in hair, which
has been found to correlate well with actual exposure to mercury. The thresholds
for concern ranges from 25 to 50 mg/gram of hair for the general population to 10 to 20 mg/gram
of hair for pregnant mothers (World Health Organization). The maximum
concentration in the U.S. by 1996 (date of the EPA study) was 15.6 mg/gram of hair for people who consumed
wildlife in the Florida Everglades, a well-known mercury hot-spot.
How Much Methylmercury is “Too Much”
The
new Environmental Protection Agency standard for mercury concentration in fish
is 0.3 ppm. The load considered in 1996 by the EPA to be a “reference dose”
(a methylmercury dose beneath which no adverse health effects were identified)
is 100 nanograms of methylmercury per kilogram body-weight per day (EPA, 1996).
In order to exceed this amount, a 50 kilogram (110 lb) person would have to eat
more than 35 grams (>1 oz) of fish tissue per week from fish with a
methylmercury concentration of 1 ppm, or more than 100 grams (>3 oz) of fish
per week with 0.3 ppm methylmercury. One ppm is equivalent to 1 microgram
methylmercury per gram of fish, the concentration found in some fish from
several Yuba/Bear River reservoirs. As the reference dose is exceeded, risk of
methylmercury-related health effects may increase, however, it depends upon
various factors associated with consumption rate and body size. In addition,
exceeding the reference dose does not necessarily mean that health impacts will
be found. One comparison for the consumers of Yuba/Bear fish is a recommendation
from the World Health Organization that populations that eat more than 100 grams
per day of any commercial fish should be monitored for methylmercury poisoning.
The average methylmercury concentrations for commercial fish and shellfish
ranges from 0.02 ppm for clams to 0.2 ppm for tuna (EPA, 1996). The average fish
consumption rates in the U.S. are 8 – 15 grams/day for the total population
and 20 to 40 grams/day for anglers and Native Americans outside of Alaska.
Mercury and Methylmercury in the Yuba and Bear
Rivers
How Much Methylmercury is in the Yuba/Bear Fish and
other Aquatic Wildlife
The recent report by Charlie Alpers and co-workers (US Geological Survey)
of mercury contamination in fish provided the most detail to date of the extent
of the problem in the Yuba and Bear River water bodies (http://ca.water.usgs.gov/rep/ofr00367/ofr00367.pdf).
Concentrations ranged from barely detectable to over 1 ppm mercury in fish
tissue. Certain reservoirs stood out as having a greater problem, with lower,
warmer reservoirs seeming to predominate. The Environmental Protection Agency
and the Office of Environmental Health Hazard Assessment (OEHHA) standard for
concentrations needing greater attention (“screening value”) currently
stands at 0.3 ppm. Most of the game fish tested and the waterbodies sampled fall
above this threshold, suggesting that although there may be very hot spots, most
of the Yuba and Bear systems should be considered worthy of attention. The Food
and Drug Administration’s (FDA) action level for regulating mercury in
commercial fish is 1.0 mg/kg (1 ppm) wet weight of fish tissue.
The values found in the most recent and comprehensive
survey of fish in the Yuba and Bear watershed meet and exceed the EPA/OEHHA and
the FDA levels in some cases and places:
1) Englebright Reservoir: all smallmouth and spotted
bass that were >1 foot and >250 grams (1/2 lb) had levels >0.3 ppm
2) Scotts Flat Reservoir: most largemouth bass >1
foot and 500 grams (1 lb) had levels >0.3 ppm
3) Rollins Reservoir: most channel catfish and most
largemouth bass >1 foot and >400 grams had levels >0.3 ppm
4) Lake Combie: all largemouth bass >1 foot and
>400 grams had levels >0.7 ppm
5) Camp Far West: all spotted and largemouth bass and
channel catfish >1 foot and >300 grams had levels >0.5 ppm, ½ of the
spotted bass exceeded FDA action level of 1.0 ppm
6) Bear R. at Dog Bar Rd. and Little Deer Creek at
Pioneer Park: ½ of brown trout sampled >10 inches and >200 grams had
levels >0.3 ppm
The USGS has also measured the methylmercury
concentrations in aquatic and terrestrial invertebrates, amphibians, and cliff
swallow eggs. This survey was conducted in order to see how well the measured
concentrations correlated with the fish data. It was also intended that this
approach may lead to a rapid and broad assessment technique for prioritizing
mine sites and streams for cleanup and monitoring action based on non-fish data.
The aquatic insects sampled (dragonflies, stoneflies, hellgrammites, diving
beetles, and giant waterbugs) had concentrations of methylmercury ranging from
0.01 ppm to 1.6 ppm for dragonfly larvae in Buckeye Flats (South Greenhorn
Creek). The areas with the highest concentrations found in the different species
were Boston pit and mine tunnel, Buckeye Flats (Greenhorn Creek), and Missouri
Canyon. The foothill yellow-legged frogs, Pacific tree frogs, and bullfrogs had
concentrations ranging from 0.23 ppm to 0.39 ppm, with the areas rating the
highest being Missouri Canyon, Diggins Pond (Malakoff Diggins), and Polar Star
mine tunnels.
The best conclusions to draw from this study are that a comprehensive
understanding of fish consumption by humans and wildlife around these reservoirs
is needed, that there should probably be monitoring of the mercury levels in
people who eat a lot of fish from these waterbodies, and that a continuing
surveying of mercury in fish and other biota is essential, especially in years
where the precipitation and other environmental conditions are different from
1999, the year the samples were taken.
What are the Sources and Distribution of Mercury and
Methylmercury in the Yuba/Bear
Mercury may originate from abandoned mine lands in the watersheds, from
points where it has temporarily collected on its journey to the ocean, and from
the atmosphere. The US Geological Survey and others are conducting measurements
of the mercury and methylmercury in the biota, sediments, and water in
reservoirs and near/within abandoned mine lands of the Yuba/Bear systems. There
do not appear to be direct measurements of the atmospheric deposition of
mercury. There also are few measurements taking place in the waters and
sediments of the upper Bear and Yuba and their tributaries. The extent of
current knowledge is that the mercury is at minimum leaking gradually from
abandoned mine tunnels, sluice boxes, and pits. Dredge tailings are also thought
to be a potential hotspot, as is sediment disturbance during secondary mining
near abandoned mine features, or in contaminated sediments. Mercury is also
assumed to be slowly migrating downstream in the creeks and rivers, temporarily
lodging in the benthic sediments and pockets in the channel bedrock.
There are frequent discussions about the way that mercury assessment and
surveying should be conducted with limited resources. For example, infrequent
sampling at many sites may say where mercury is originating, but not allow a
“load determination”. The ideal appears to be that sampling should be at
well-distributed sites to capture the “where” of mercury contamination and
during and after storm events to capture the when and get a better sense of
load. Monthly or other periodic sampling is important if the mercury is
continuously moving through the system even without storm events. The Sacramento
River Watershed Program has initiated a Mercury Monitoring Program which
includes monitoring mercury at the tributary mouths (e.g., the Yuba River), but
which does not extend far into the Yuba or Bear Rivers.
Gaps in Our Knowledge of the Problem
There
are a huge variety of problem areas for understanding the extent of mercury
contamination in the Sierra Nevada, the distribution of hotspots of
contamination, the exposure rates of humans and fish-eating wildlife, the
potential success for particular sites of available remediation and management
techniques, and the various physical, chemical, and biological factors that
influence the bio-availability of mercury. The following list is not all
inclusive, but identifies some of the major areas where there are big enough
gaps in knowledge to inhibit our understanding of the nature of the problem and
possible ways to address it.
1)
how mercury is transformed among its different forms in the environments of
concern (creeks, rivers, and reservoirs), including the environmental factors
that influence that transformation;
2)
what the actual distribution and “load” of mercury is for any given
waterbody;
3)
how the mercury is partitioned among “compartments”, such as the benthic
sediment, suspended sediments, biota, and in the water;
4)
how mercury is moved the different compartments in #3;
5)
what the likely impacts are from conducting the various remediation techniques
available (e.g., tunnel closure, pit draining and filling, and local hydrology
diversions);
6)
what the exposure rates are for wildlife and humans consuming contaminated fish.
Fixing the Problem
Planning and Assessment Efforts to Date
Two
overlapping planning groups have met periodically over the last several years to
discuss mercury contamination in the Bear and Yuba (the Bear/Yuba/Trinity
Abandoned Mine Lands group, AML
group) and for all tributaries to the Bay and Delta (the Delta Tributaries
Mercury Council, DTMC). Both groups are multi-agency (county, state, and
federal) and to a limited extent include non-agency people. The Delta
Tributaries Mercury Council went through an exercise in November the product of
which is worth looking at here. The Council spent an hour in break-out groups
strategizing around the basic question of what knowledge is needed (regardless
of how much it might cost) and how to get it for understanding mercury
contamination and remediation. The notes from that meeting are attached to the
end of this report (“DTMC Appendix”). The Sacramento River Watershed Program
also tracks mercury pollution in the Sacramento River and tributaries and has
developed assessment and management models. In terms of the Sierra Nevada,
studies by Darrell Slotton (UC Davis) and co-workers in the mid-90s and Charlie
Alpers (USGS) and co-workers more recently have provided much of the substance
for the discussion groups. The CALFED Bay-Delta program, the State Water
Resources Control Board, and other programs targeting water quality problems
have provided ad hoc leadership and funding for assessing the nature of the
mercury contamination problem. Technical reports from these studies provide
monitoring data for the particular places, species, and time frames chosen.
However, as noted above, there has not been a comprehensive assessment of the
extent, sources, and fates of the mercury for any of these basins.
Mitigation and Clean-up Trials
The
most recent attempt at abandoned mine land treatment was at Polar Star Mine in
the Bear River watershed. The US-EPA spent >$1.5 million to remove mercury
contaminated sediment from abandoned sluice box tunnels on the site. The stated
reason for the clean up action by the EPA was to responsibly remove the mercury
before someone else removed it in a way that threatened human health. Removal of
a potential source of methylmercury was considered a secondary environmental
benefit (Jones, 2001). The EPA chose removal of mercury-contaminated sediment in
the tunnel as preferable to gating the tunnel and routing water through it so
that it did not contact the sediment. The removal action itself required access
road improvements, decontamination of rocks removed from the tunnel, screening
and size separation of removed sediment, leveling of the tunnel floor, and
shipping of mercury-contaminated material to Oklahoma and Idaho.
There
were mixed reports as to the effectiveness of the strategy chosen and EPA has
claimed in meetings to be adapting to lessons learned. The site was successfully
cleaned up as planned at the amount budgeted. The EPA considers the following to
be lessons from the project: 1) site disturbance during clean up should be
minimized so as to not make matters worse; 2) a site reclamation plan should be
prepared prior to project initiation; 3) if gold or mercury recovery is
expected, then advance sampling should take place to determine optimum sediment
processing equipment and the amounts of the metals present; 4) measuring mercury
contamination concentrations will also allow calucaltion of disposal costs; 5)
choice of contractor must be based on a realistic analysis of the permits,
planning, and other actions required; 6) sumps and other mechanisms for
modifying local hydrology must be maintained and designed to withstand 100 year
flood events; 7) post-cleanup monitoring should be conducted to assess the
changes in mercury movement within and from the site. The site cleanup was
complicated by the desire of the landowner for part of the area wanting to log
during the project. The EPA was challenged during this complication to show how
their action was less disturbing than a timber harvest plan. Ultimately, the
project was successful at removing 200 lbs of elemental mecury and 2000 lbs of
highly-contaminated sediment, as well as serving as an example for future
cleanup projects.
At
meetings of the Abandoned Mine Lands group, Buckeye Flats (which is on private
and USFS lands), near Greenhorn Creek in the Bear River watershed appears to be
next up for this treatment.
Nevada
County has also joined with SWRCB and the USFS in requesting that county
residents bring mercury they may have to a central location on special
collection days. Over two hundred pounds of mercury was recovered in this
fashion on two separate days at a cost of over $1,000. Because this approach
will eventually reach the end of casually-available mercury (e.g., from
peoples’ garages), it has limited impact on the problem. Similar outreach is
being attempted to recreational dredge miners in order to encourage them to
collect mercury they observe or recover incidental to their operations. This
method has slightly greater potential to recover mercury from the rivers and
streams where it is, presumably, continuously being re-supplied from surrounding
AML lands and tunnels.
Immediate and Medium-Term Research and Management
Needs
Staffing
One obvious feature of the policy landscape is that all of the concerned
parties are undergoing a rapid education process and are developing management
and other strategies in a somewhat ad hoc fashion. There is an immediate
need for decision-support for both the research and monitoring funding and for
clean-up and management strategies. Dedicated staff for this role are needed who
are not also the researchers or regulatory agents. The county could play this
role, or some state or federal body that is charged with technical support for
pollution control. Another role for such staff would be public education and
outreach to assist in public health surveys, mercury reclamation/collection,
education about health impacts of mercury, and identification of populations in
need of additional attention (e.g., subsistence fishers).
Research needs
Discussions
with key scientists in mercury research and management (both casually and at
meetings of the Yuba/Bear/Trinity AML group and the DTMC) and reading of
available technical reports suggest the following are funding needs for research
to support long-term mitigation and restoration decision-making: 1) better
understanding of the process of methylation and de-methylation of mercury under
various realistic biological, chemical, and physical regimes; 2) measurements of
river and reservoirs mercury loads in order to understand the distribution of
mercury contamination of sediments and water; 3) measurements of the association
of mercury and methylmercury with particular features of river and reservoir
water/sediment (e.g., suspended particles); 4) determination of potential
contributions of land-use/development and atmospheric deposition to river loads;
and 5) monitoring of pilot clean-up and mitigation efforts in order to
understand their beneficial and harmful impacts.
1)
Methylation and de-methylation Although
the possible pathways of the chemical conversion of mercury are well-known for
certain environments, the actual pathways in situ (e.g., in the
reservoir) are unknown for many of the Yuba/Bear system’s waterbodies and
sediments. For example, sulfate-reducing bacteria are known to methylate
mercury, but they are not the only mediators of this reaction and are dependent
on certain environmental conditions in order to thrive and survive. Knowing the
actual pathways for mercury (de)methylation and the rates of reaction under
ambient environmental conditions is critical in evaluating the transformation of
mercury in the river and reservoir system and modeling the likely impacts of
restoration and management actions.
2)
Mercury load in the watershed There
have been several assessments of mercury contamination “hotspots” in the
Yuba and Bear, primarily in or near abandoned mine lands. There have also been
spot measurements (as opposed to long-term monitoring) of mercury in aquatic
invertebrates, fish, and amphibians in creeks and reservoirs in the system.
There has not been a survey of the mercury “load” in the entire system,
composed of measurements of mercury and methylmercury in the water, sediments,
and biotic components. We therefore cannot say what the total mercury is in the
watershed at any given time. Nor do we know how it is moving and being stored
throughout the watershed. Understanding the total amount of mercury in its
various states and its bulk movement through the hydraulic system is critical to
prioritizing actions and areas to focus limited resources. Methylmercury
contamination in insects and fish serve as a surrogate for methylmercury
availability within the life span of these organisms, but may not indicate the
actual loads in reservoir sediments, for example.
3)
Association of mercury with other elements/features in the water
Mercury in its various chemical forms may associate preferentially with
fine particles suspended in the water or in benthic sediments. This association
has ramifications for bacterial activity and bulk movement of mercury through a
river system. Bacteria often adhere to particles and anything associate with
fine particles will move according to the flow regime over the benthic
sediments. It is important to know what proportion of mercury and methylmercury
is associated with various sediment size classes, as well as how much these
sediments are disturbed by actual and potential flow regimes in the Yuba/Bear
systems. This information will aid in determining the fine-scale distribution
and potential movement of mercury.
4)
Contributing factors to mercury contamination
Atmospheric deposition of mercury can be a significant source of mercury
in certain regions. There have been measurements of mercury deposition downwind
of the Bay Area showing deposition rates higher than other areas in Northern
California. Urban centers are a potentially significant source of mercury due to
incinerators, automobiles, and poor emission controls. This mercury could be
considered the background level, however, its actual contribution to current
mercury contamination is unknown and may be worth measuring. Land-use near
abandoned mine lands and within the affected watersheds (Yuba/Bear) can impact
the distribution of mercury, its chemical transformation, and growth of mercury-methylating
bacteria. Most human land-use results in impacts on hydrology, nutrient cycles,
or sediment contributions to streams and rivers. Because these processes all
influence mercury distribution and transformation, assessing their potential or
actual impacts is an important part of managing and cleaning up
mercury-contaminated landscapes and river systems. This could be accomplished
through a GIS that included potential and actual land-use/development maps,
topography and hydrology, and other natural resource information.
5)
Monitoring clean-up/restoration actions
Abandoned mine lands are currently being targeted for pilot restoration
projects aimed at removing mercury and mercury-contaminated sediments and
modifying local hydrology to reduce flow of mercury into local creeks. The value
of the actions is unknown without careful assessment of the condition before
action, monitoring during water and ground disturbance, and long-term follow-up
monitoring of soils, biota, and water. Without this monitoring the action loses
its values as a local clean-up effort as well serving as an experiment to
increase understanding of how to conduct these actions.
County programs
Additional
funding should be sought to meet county needs for mitigation and management of
mercury contamination, as well as decision-support for land-use/development in
areas that are known to be contaminated. The California Department of
Conservation has entered into an agreement with Nevada County to provide such
support through a DOC staff person tasked with supporting the county’s
approach to mercury contamination in land, water, and biota. Nevada County has
partnered with state and federal agencies in collecting mercury from residents
on Hazardous Waste pick up days and at relatively central drop-off points.
Programs that support receiving newly-collected or recycled mercury by affected
counties should be encouraged and specifically funded. Recreational and
small-scale gold-miners have been identified by the AML group as a community
that could both assist in collecting mercury from stream and river bed gravels
and be a target of regulatory action if they are disturbing or returning mercury
to the river through their operations. Continuing education of river miners
through mailings attached to California Department of Fish and Game permits and
other devices could aid in collecting mercury directly from the river and stream
bed gravels.
Monitoring human health
One common theme in the mercury literature and in discussions within the
Delta Tributaries Mercury Council and the AML group is the need for testing of
methylmercury and mercury levels in human populations that are likely to be
exposed to these toxicants, primarily through fish consumption. This could be
approached through a combined public education and hair testing programs.
Rigorous design of the sampling regime and parallel analysis of fish consumption
rates could make this a region-specific epidemiological study. Alternatively,
mercury testing in hair could be carried out as a voluntary program where a
public health agency is funded to take hair samples and submit them for analysis
during routine health exams. This would allow follow-up with individuals found
to be at risk of exposure and mercury-related disease. An important component of
this would an interview/questionnaire process that addressed fish consumption.
Monitoring Wildife and Fish Health
One idea that tends to get left out of discussions about mercury
contamination in fish is the potential impact on fish-eating animals, primarily
hawks and eagles. Exposure of wildlife to mercury in fish can be a much more
serious event because certain animals may rely primarily on fish as a source of
food, as opposed to humans who consume a much lower proportion of their total
diet as fish. Wildlife will suffer
neurological damage from mercury exposure, with the relevant dose likely being
size and species-dependent. Discussions at the Delta Tributaries Mercury Council
and the EPA report (1996) lead to the recommendation that there needs to be a
comprehensive study of mercury exposure for hawks and eagles, and mammals such
as otters. This could require fairly specialized sampling techniques (trapping
the animals), unless there are surrogate measures (e.g., use of feathers or
hairs) that would allow sampling. The fish consumption rates could be estimated
from published literature, but the concentrations in particular areas for
particular fish sizes would have to be known. Thus, by running such a study in
parallel with ongoing or proposed measurements of mercury in fish for human
consumption concerns, the same fish data could be used to estimate both human
and wildlife exposure rates.
Bibliography and Online Resources
Mercury contamination from hydraulic placer-gold mining in the Dutch Flat Mining
District, California (M.P. Hunerlach, J.J. Rytuba, C.N. Alpers, report from USGS
Toxic Substances Hydrology Program, 1999).
Mercury sources in the Sacramento River watershed (technical report to the
Sacramento River Watershed Program, 1/2000).
The historic use of mercury for gold mining in the Yuba River watershed (H.
Meals, unpublished report).
Mercury Bioaccumulation in Fish in a Region Affected by Historic Gold
Mining: The South Yuba River, Deer Creek, and Bear River Watersheds, California
(JT. May, R.L. Hothem, C.N. Alpers, and M.A. Law, 1999) USGS Open-File Report
00-367. http://ca.water.usgs.gov/rep/ofr00367/
http://www.ice.ucdavis.edu/Hg/default.htm (Delta Tributaries Mercury Council)
http://www.epa.gov/ncea/methmerc.htm
(EPA reference dose for Methylmercury, 10/00)
http://www.epa.gov/waterscience/criteria/methylmercury/
(EPA Water quality criteria for methylmercury, 12/00)
http://www.epa.gov/ost/fishadvice/
(EPA Fact sheet on mercury in fish consumption advisory for women and children,
1/01)
http://www.epa.gov/mercury/fish.htm
(EPA Fish Advisories, 12/00)
http://books.nap.edu/books/0309071402/html/R1.html#pagetop
(National Academy of Sciences, “Toxicological Effects of Methylmercury”,
2000)
http://ens.lycos.com/ens/sep99/1999l%2D09%2D08%2D07.html
(Mercury crosses blood-brain barrier news piece, 12/99)
http://minerals.usgs.gov/mercury/index.html
(links to USGS and other mercury studies and research)
http://www.epa.gov/oar/mercury.html
(EPA, Mercury Study Report to Congress, 12/97)
http://www.epa.gov/oar/merwhite.html
(EPA, Mercury White Paper, 1997)
http://www.epa.gov/ncea/pdfs/mercstra.pdf
(EPA, Mercury Research Strategy, 11/99)
http://www.epa.gov/opptintr/pbt/mercury.htm
(EPA Persistent Bioaccumulative and Toxic (PBT) Chemical Initiative, Mercury
Fact Sheet and Action Plan, 1998)
http://elib.cs.berkeley.edu/cgi-bin/display_page?page=1&format=gif&elib_id=1479
(SNEP Report, 1996: Geology and Minerals chapter, hydraulic mining discussed)
Mercury in automobiles:
http://www.cleancarcampaign.org/pdfs/toxicsinvehicles_mercury.pdf
http://www.cleancarcampaign.org/pdfs/ToxicbyDesign.PDF
Mercury Policy Project:
http://www.mercurypolicy.org/
http://www.mercurypolicy.org/emissions/
Some terms and explanations
“Load” refers to the total amount of something in
the river or reservoir. For example, the sediment load would include the bed
sediment and suspended sediment (unless the term “bed load” was used in
reference only to bed sediment). Determining load is a critical feature in
understanding the benefits of potential clean-up and mitigation actions, as well
as understanding the impacts of actions where the load may be disturbed.
“Concentration” refers to the load per unit
volume, for example, 1 microgram of mercury per liter of water. Thus if you know
the concentration of something and the continuously or periodically measured
river volume per unit time (cubic feet per second) you could calculate the load
per unit time of the something in the river. Concentration is also expressed per
unit mass in organisms, as in “parts per million” (ppm). One ppm of mercury
in fish tissue would be equivalent to one microgram of mercury per gram of fish
tissue.
Mercury can occur in a variety of forms in river
systems. Uncharged or elemental mercury can be dissolved, adsorbed to particles,
or in the characteristic silvery droplets of “quicksilver”. Charged mercury,
Hg2+, can occur in
compounds such as mercury chloride or hydroxide, which are relatively reactive.
“Inert” mercury, such as cinnabar, refers to mercury involved in compounds
that are relatively un-reactive. Methylmercury chloride and mercury chloride are
the most available for uptake by microbial life, such as phytoplankton. Chloride
concentration, pH, sulfate/sulfide concentration, redox conditions, suspended
solid concentration, and the presence of sulfate-reducing bacteria are all
important in determining what form(s) of mercury will be present as well as the
opportunities for methylation of mercury. Suspended particles are a particularly
good site for bacterial conversion of mercury to methylmercury.
“Atmospheric deposition” of mercury occurs
constantly throughout the world, with varying amounts deposited depending on
weather, proximity to sources of airborne mercury, and other factors. The
technical report “Mercury Sources in the Sacramento River Watershed” cited
above includes the estimate of 720 kg/yr of mercury deposited in that watershed.
It is unknown how much actually is deposited and what the fate of the mercury is
(i.e., whether it ends up in the river or not). This may be an issue for
watersheds downwind of the Bay Area, which has the highest airborne mercury
concentrations in Northern/Central California.
It is not a trivial task to determine the rates of
and conditions for mercury methylation and the interaction of mercury and
methylmercury with naturally-occurring features of rivers and reservoirs (water,
biota, and sediment). Without this knowledge, it will be difficult to determine
prioritization of clean-up or potential impacts of management actions. There is
probably sufficient knowledge to proceed with tunnel and sluicebox cleanup
activities, but benthic sediments in reservoirs and sediment-borne and dissolved
mercury in rivers will need more study before clean-up action should be
considered.
DTMC Appendix
DTMC
STRATEGIC PLANNING
In
response to the strategic planning discussion at the last DTMC meeting the group
planned to dedicate a major portion of the meeting to strategic planning.
The primary goal was to establish a plan for mercury management that
would guide the group and help to establish priorities. The plan and resulting
priorities would not be tied directly to any one project or budget, but would be
integrated with all that were relevant. For
example, the results of the planning would help to shape feedback to the SRWP on
their next phase of planning and budgeting. After a detailed discussion of the
direction, the group agreed to use its existing objectives as the framework for
its planning. They agreed to break
into two subgroups to flush out the details of four of the objectives:
Group
one
1.
Develop Goals and Targets
2.
Develop Models
Group
Two
3.
Identify Sources Fate and Impact
4.
Identify Control Measures
The
results from the breakout groups are outlined as tasks for each objective as
follows:
1)
Problem
definition (DTMC responsibility)
Historical knowledge of solutions/successes
Identify data gaps
Identify exposure population
Monitor humans, fish
2)
Educating public/private parties (DTMC responsibility)
more public health personnel/education
3)
Develop programs and identify
sources/players and answers (DTMC responsibility)
i.e. agriculture, BLM, Forest Service, environmental
groups, gravel operators, suction dredgers, OEHHA, planners
4)
Fund
5)
Risk appraisal
1)
Link tools to reach goals (GIS) land, stream bed use, alteration
2)
Test strategic controls plan, alternatives, success of goals.
3)
Identify critical paths and how to interfere successfully.
(DTMC responsibility)
4)
Everyday exposure (included in model), air, industry, ambient occurrence.
(DTMC responsibility)
5)
Data collection and input
validate data
synthesis
data gap identification
6)
bring model/chart/graphic/poster to every meeting to record where we have
gone and where we are going. (DTMC
responsibility)
7)
build model
Human
Health:
Wildlife: