A methylmercury update from the State Water Board

new almaden
Rotary furnace used to extract mercury from cinnabar ore at New Almaden Mine; photo by flickr photographer Daikiki

Mercury contamination is a widespread problem, not just locally but also globally, and its serious effects on health are well known.  It is a particular insidious problem as mercury can be a threat to people and wildlife even in areas that don’t look obviously polluted.  Across the country, forty-two states have issued fish consumption warnings due to mercury, and the reducing global mercury emissions has even been the subject of international talks.

Here in California, many of the state’s streams, rivers, and reservoirs are impaired for mercury, much of it a legacy from the Gold Rush days when mercury was mined in the Coast Range and transported to the Sierras for use in gold mining.  However, atmospheric deposition from power plant emissions, urban and industrial wastewater discharges, and natural sources also contribute mercury to the environment.

Click here for more from the State Water Resources Control Board.

The State Water Resources Control Board along with the regional water boards have been working to address the issue by setting TMDLs for individual water bodies, developing a statewide control program for mercury-impaired reservoirs, and developing fish-tissue objectives to protect human health and wildlife.  At the April 23, 2013 State Water Resources Control Board meeting, staff gave an update on the status of these programs.


Janis Cooke, an environmental scientist with the Central Valley Regional Water Quality Control Board, began the presentation by explaining how mercury in the environment becomes a problem for humans and wildlife.

mercuryupdate0423_Page_03Mercury comes from many sources: it is transported by wind and rain from local and global emission sources, it can be present in urban and industrial wastewater, and it can be naturally occurring in soils and springs, particularly in the Coast Range.  In many areas of California, it is a legacy contaminant from gold rush mining, as abandoned mines are still leaching significant amounts of mercury into the environment.

Most of these sources provide mercury in a non-toxic inorganic form, but when the mercury reaches a wetted environment, such as a wetland or reservoir, it settles to the bottom where bacteria in the sediments convert it to the more toxic, organic form called methylmercury.  The rate of methylmercury production varies by habitat and is affected by water chemistry factors, such as oxygenation and carbon availability.  Some of the methylmercury will be lost through degradation by sunlight or other bacteria, and some of it will move up the food chain.

Methylmercury is bioaccumulative pollutant which concentrates as it moves up the food chain.  mercuryupdate0423_Page_04The single largest increase in methylmercury concentration is in the algae where concentrations can be 100,000 times greater than in the water itself.

Methylmercury continues to increase as it moves up the food chain, from algae to zooplankton to prey fish and the predators that eat them, such as trout and bass. “We are most concerned about toxic levels of methylmercury in fish that birds and people eat,” said Ms. Cooke.

Mercury contamination in California is widespread; while some water bodies have already been addressed by TMDLs, there are many water bodies statewide, including reservoirs, that are impaired and awaiting TMDLs.

Earlier TMDLs focused on controlling sources of inorganic mercury, but controlling inorganic mercury sources often takes decades to actually affect the fish mercury levels.  “So we are trying to add to our toolbox of ways to control the accumulation in fish,” said Ms. Cooke.

Potentially the problem is much larger as we gather more fish mercury data, we find more water bodies that are impaired by mercury,” she said.


mercuryupdate0423_Page_07Ms. Cooke then updated the Board on the status of mercury TMDL programs in the Central Valley region.

Cache Creek contributes 30% of the mercury load to the Delta annually, so the Central Valley water board focused its initial control efforts on the Cache Creek watershed, which includes Clear Lake. The Central Valley water board adopted the mercury TMDL for Clear Lake in 2003, and two years later, completed the TMDL for the Cache Creek watershedA mercury TMDL was adopted for the Delta in 2010. Currently, there are 80 bodies awaiting TMDLs in the Central Valley region.

The implementation plan for the Clear Lake and Cache Creek watersheds focused on controlling the inorganic mercury.  The TMDL identified 15 mine sites in need of remediation to eliminate their discharges to water.  At the Sulphur Bank mine on the shore of Clear Lake, the US EPA is continuing clean up actions.  Elsewhere, two other mines have been remediated.  The mercuryupdate0423_Page_09Central Valley water board is working with the U.S. Bureau of Land Management and private owners to develop remediation plans for the other mines.  Implementation plans for these TMDLs also focused on erosion control because of naturally occurring mercury in the soils of the watershed.

While controlling the discharge of inorganic mercury to the water bodies is effective near the source, it only addresses part of the problem.  “In some water bodies, we have mercury that’s been depositing into our waterways since the mines opened up over 100 years ago; mercury in the creek sediments slowly moves downstream, but it is difficult to contain feasibly,” said Ms. Cooke.

The Central Valley water board adopted a mercury TMDL for the Delta in 2010.  “This TMDL required a different approach because little inorganic mercury is discharged within the Delta,” she said, “but conditions in the wetlands and in the open channels of the Delta are conducive to methylmercury formation.”

mercuryupdate0423_Page_10Therefore, the implementation plan for the Delta addresses both mercury and methylmercury sources.  Dischargers were given specific requirements for inorganic mercury in the project area, and currently merthylmercury control studies are underway to determine how dischargers can meet the objectives effectively.  These studies are being conducted by public and private entities that manage seasonal wetlands, irrigated agriculture, stormwater agencies, wastewater treatment plants, the Department of Fish and Wildlife, the Department of Water Resources, and others.  “The studies will add to our knowledge of potential tools to affect methylmercury production and degradation, and where these tools can be most feasibly applied.”

Recognizing that it’s going to take decades or more to reduce mercury levels in fish, in 2005 the State Water Board directed the San Francisco Bay and Central Valley regional water boards to address the public health impacts by conducting public outreach (or “exposure reduction activities”) to protect people who eat locally caught fish.  These public outreach programs were built into the mercury TMDLs for the SF Bay and the Delta.

mercuryupdate0423_Page_12The goal of the program is to protect fish consumers from the harmful effects of contaminants; while the public outreach programs address mercury, they also address PCBs in fish where they are found.  The program seeks to communicate that there are some fish that are safe to eat as well as those that are not safe to eat; the intention is not to discourage all fishing.

The San Francisco Bay’s exposure reduction program recently completed a 2 ½ year project.  Educational materials were produced in multiple languages, piers signs were posted showing safe and unsafe fish, and four community-based organizations were given funding, training and technical assistance to design their own programs to reach the communities they serve.   Each component of the program was evaluated for its level of outreach, and they are currently planning their next steps.

A similar program for the Delta is being developed with a work plan is due in fall of 2013.  The funding mercuryupdate0423_Page_11for the program is directed by the TMDLs to come from entities responsible for reducing mercury and mercury loads; in the San Francisco Bay region, this was primarily point source dischargers, but in the Delta, it includes everybody from state and federal agencies to private landowners.

Data from the SWAMP program is used to produce the fish consumption advisories.  Support from the Department of Public Health and the Office of Environmental Health Hazards is needed for exposure reduction programs, because educational materials are based on information from advisories and other health information that comes from the Department of Public Health; this can be difficult as the Department of Public Health is lacking in resources and staff.


mercuryupdate0423_Page_15Carrie Austin, an environmental engineer from the San Francisco Bay Regional Water Quality Board updated the Board members on progress made in the region.  The San Francisco Bay water board covers an area that is much smaller than the Central Valley region; it only has 14 water bodies on the 303(d) list and most of these are reservoirs.

Mercury TMDLs have been completed  for the Tomales Bay and its tributary Walker Creek, and for the San Francisco Bay and the Guadalupe River.  Both of these tributaries drain mercury mines into the bays.

Tomales Bay in northwest Marin County was designated as mercury impaired in 1996.  Walker Creek, a tributary to Tomales Bay, drained the Gambonini Mercury Mine, by far the largest source of mercury in the watershed.    In 2000, erosion control best management practices were used to stabilize the mining waste which has already produced results: mercuryupdate0423_Page_16There are measurable reductions in mercury concentrations in the sediment at the Delta at the delta of Walker Creek into Tomales Bay,” said Ms. Austin.  “Unlike most of California, clean up of Gambonini Mine has rapid environmental benefits.”  The relatively short length and the particular geography of Walker Creek are some of the factors that contributed to the rapid success of source control in Tomales Bay.

However, other TMDLs are more complicated and require a multi-pronged approach.  The San Francisco Bay TMDL is an inorganic mercury TMDL with methylmercury investigations; the  permit strategy uses both watershed and regional approaches to address mine drainage and contaminated sediments in the Bay.  The largest source of inorganic mercury is legacy mercury from mines.

In 2007, the first watershed NPDES permit for wastewater dischargers was issued; however, these dischargers have significantly controlled mercury in their mercuryupdate0423_Page_18wastewater discharges well in advance of the 20-year implementation timeline for the TMDL, and so the permit was revised in 2012 to account for the fact that the average annual wastewater mercury load is below the final TMDL limit.

Some of the actions that have led to success in reducing mercury discharges include installation of dental amalgam separators in more than 85% of the dental offices in the San Francisco Bay region, coordinated efforts between wastewater and stormwater agencies to increase household hazardous waste collection programs and fluorescent tube recycling, and requirements that municipal urban stormwater permits initiate pilot projects to evaluate the full spectrum of best management practices for both mercury and PCBs.

A regional monitoring program and a mercury strategy have been developed, and studies have been done to reduce key uncertainties.  The studies so far have shown that dominant source of mercury is from mining; the studies have also determined that the amount of methylmercury production in the bay is 100 times greater than what is coming in from the tributaries.  “This is further confirmation that controlling both mercury sources and methylmercury production are key factors in TMDLs,” said Ms. Austin.

mercuryupdate0423_Page_20The New Almaden Mine began operations in 1846 in the hills above south San Francisco and was one of North America’s most productive mines, producing over 1 million flasks during its span of operations.  The mine drains to the Guadalupe River, and so the Guadalupe River TMDL starts with erosion control requirements for the mine site.

However, given the scale of pollution from mercury and gold mining, source control, while important, is not a short-term solution, so innovative techniques are being tested.

The Santa Clara Valley Water District began studies of reservoir water chemistry management to reduce methylmercury production by installing a solar-powered water circulator to mix the water to increase the amount of dissolved oxygen.  Although this has been used to control algae or drinking water taste and odor problems, this is the first time it has been used to reduce mercury.  “This has reduced methylmercury in the water column by 95% and it does hold promise for reducing methylmercury in fish,” she said, noting that the Santa Clara Valley Water District will be continuing its studies voluntarily.


Ms. Austin then discussed the control program for mercury impaired reservoirs, which is part of the Statewide Mercury Program for Inland Surface Waters and Closed Basin Estuaries that is currently in development.  Reservoirs are being addressed first because many reservoirs are statewide are impaired for water bodies, and because they are already highly managed water bodies.

mercuryupdate0423_Page_23Reservoirs are most often created by damming a creek or river, or by damming a natural lake to increase its volume.  This can affect water chemistry, such as temperature and oxygen.  Prior to building the dam, the creek is a fast-flowing water body, it is cold and well shaded, and its waters are usually turbulent and well oxygenated.  After the dam is built and the reservoir created, however, there is now a broad water surface as the water slows down and spreads out.  There are fewer trees and more fish; the reservoir is usually stocked with fish, oftentimes nonnative predatory fish.  “All of these changes contribute to increased rates of methylation and higher mercury levels in fish,” said Ms. Austin, noting that dams also have many benefits, such as water for agriculture, drinking water, hydropower, recreation, and flood control.

Ms. Austin said that they have reviewed scientific literature to identify factors and then evaluated these factors for California, identifying the linkage from sources of methylation to bioaccumulation and into fish.  “Theoretically each of these sources is controllable factors, but some reservoirs do not have controllable sources or it will take many decades or even centuries to see benefits of source control,” she said, “but we have multiple tools now at our disposal for reservoirs that we would like to employ.

Mercury contamination in reservoirs is widespread; mercuryupdate0423_Page_05the current project lists 74 reservoirs, with approximately another 75 reservoirs that will likely soon be listed for mercury.  As more data is gathered, even more reservoirs will be listed.  State Water Board staff estimates that of the 1000 to 1400 reservoirs in California, about half of these reservoirs are impaired, so the scope of project is large and involves many hundreds of reservoirs.

Source control, such as mine remediation or controlling air emissions, is important, but it is not expected to be effective in the near-term, said Ms. Austin.   Therefore the Board is hoping to foster innovation by reservoir owners and fishery managers to conduct coordinated studies and pilot tests on innovative techniques, such as trying different ways to add oxygen to reservoirs or changing the balance of fish stocking to fish that are less predatory and bioaccumulate less.  These projects would be eventually expanded to more reservoirs before full-scale implementation.


Amanda Palumbo, environmental scientist for the State Water Board, then discussed the development of fish tissue standards, a program that could potentially affect the rest of the water bodies in the state.

mercuryupdate0423_Page_29In 2001, the EPA issued a new guidance for human health by setting the criterion in fish tissue rather than as a water column value, because consumption of contaminated fish is the primary route of human exposure to methylmercury, she explained. This has not been adopted in a statewide form, although it has been used in determining TMDLs.

US FWS evaluated California’s toxic rule criteria and found them not to be protective of several endangered and threatened species, so there is a need for a new water quality objective for California in terms of both human health and wildlife,” said Ms. Palumbo.  Therefore, a team is working at the State Water Board to develop a methylmercury fish tissue objective to align California with the EPA’s guidance as well as to fill a long-standing gap in protection for wildlife.

The objective will be specifically for methylmercury and, like the San Francisco Bay TMDL, will be based on one fish meal per week.  A fish tissue objective based on one fish meal per week should provide protections for most of the threatened and endangered species that the US FWS was concerned about, except for one, the California least tern, explained Ms. Palumbo.

mercuryupdate0423_Page_30The California least tern is an endangered bird species that is small and eats a lot of fish.  The work team is developing a second fish tissue objective that would apply to the very small fish that these birds eat.  One option might be to apply the second fish tissue objective only in areas that this bird lives, which is the coastal areas from Southern California to the Bay Area, she said.

The State Water Board is also developing an implementation plan to achieve these objectives. The geographic scope could be inland waters, enclosed bays, and estuaries, except for where TMDLs have already been adopted.

We are working with the reservoir team as we go through options for our implementation plan,” said Ms. Palumbo.  “We’re looking at mostly relying on existing water board programs, such as the non point source policies, permit programs, and 401 certifications,” adding that this would be a baseline level of implementation plan; the reservoir plan was looking at more innovative measures.

The proposal for the statewide fish tissue objective would be based on one fish meal per week, but Ms. Palumbo said that there are other groups, such as tribes and subsistence fishers, that likely eat more fish than that. “So we’re working on a proposal to have beneficial use definitions for Native American culture and subsistence fishing that will be defined statewide,” said Ms. Palumbo, noting that the proposal would be to define the beneficial use, but not the designation for the actual water body; that is something that would be left to regional board’s discretion.

Ms. Palumbo said that the State Water Board has contracted with UC Davis to do a tribal fish consumption study to gather information on how much fish, which fish and from which water bodies the tribes are eating, including both current and historical fishing.  There are 20 tribes interested in participating and the survey methods are currently being developed.  However, she said that the results likely won’t be completed by the time the proposal is ready for consideration by the State Water Board.  mercuryupdate0423_Page_34The thinking is to reopen the plan to review the information when it is finalized and at that time, the Board could decide whether additional objectives are necessary to protect these uses, said Ms. Palumbo.


The control program for mercury-impaired reservoirs and the fish tissue objectives project are still in the development phases, with public review scheduled for next year and possible adoption by the board in 2015.


From the water boards:

  • For information on the State Water Board’s statewide program for mercury, click here.
  • To visit the Central Valley water board online, click here.
  • To visit the San Francisco Bay region water board online, click here.

More information on mercury:

  • For a fact sheet from the USGS on mercury contamination from gold mining in California, click here.
  • To read the report, Mining’s Toxic Legacy: An initiative to address mining toxins in the Sierra Nevada, click here.
  • For a list of fact sheets available from the USGS on mercury contamination, click here.  More resources on mercury from the USGS by clicking here.
  • For a list of fish consumption warnings for the state of California, click here.
  • For a global perspective on mercury, click here for the EPA’s webpage on mercury.



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