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Frequently Asked Questions: Mercury


What is mercury?
Mercury, also called “quicksilver,” is a naturally occurring metal that is a shiny, silver-white, odorless liquid at room temperature.   If heated, it vaporizes into an odorless gas.  In nature, mercury can also combine with other elements, such as chlorine, sulfur or oxygen and appear as white powder or crystals.  Microscopic organisms in water, sediment and soil also combine mercury with carbon to form organic mercury compounds, the most common of which is methylmercury.  Methylmercury, the form that gets into fish, is far more toxic than inorganic mercury.

What are the health effects of mercury exposure and how does it get into our bodies?
Mercury is of concern because elevated concentrations can be toxic .  High concentrations of mercury can harm the central nervous system, including body coordination, eyesight, and hearing.  Mercury is not quickly eliminated from the body and can be passed from women who are pregnant to fetuses through the umbilical cord.  This is a key concern because early life stages of development appear to be especially sensitive to mercury.

1994-1995 National Mercury Emission Estimates ChartEmissions of mercury to our air (primarily as inorganic mercury) can end up in surface waters like the Delaware River and Bay. Once delivered to the water, the inorganic mercury can get converted to methylmercury, which is then rapidly taken up by fish and other aquatic life.  Consumption of fish is therefore the primary way we get exposed to mercury. Certain fish, like swordfish and tuna, are a particular risk because they are at the top of the aquatic food chain and have therefore accumulated the highest levels of mercury.   By contrast, directly breathing inorganic mercury (“inhalation” route of exposure) is generally regarded as a much lower risk, except in indoor situations where a spill may result in toxic concentrations.

How is mercury used?
Mercury has been and is still used in a variety of consumer products.  Most adults are familiar with mercury thermometers and blood pressure monitors.  Historically, it was used in household batteries and as a paint preservative, but these common consumer uses were discontinued or severely restricted in the 1990s.   Unfortunately, at the same time, some automobile manufacturers began using mercury switches for trunk and hood lights and in some anti-lock braking.  This practice was discontinued in 2003, after mercury switches had been installed in millions of cars.  Mercury switches are also used in household appliances, such as some clothes washers and dryers.  In addition to thermometers, mercury can still be found in fluorescent lamps and some dental fillings, skin lightening creams, and antiseptic creams and ointments. In industry, one of the main uses of mercury is to produce chlorine.  The Occidential Chemical (OxyChem) facility in Delaware City used to produce chlorine using mercury but shut down its chlorine production line in November 2005. 

What are the sources of mercury releases nationally?
It is important to consider mercury from a national and international perspective because sources of mercury are located throughout the world.  Once released, mercury can travel in the atmosphere thousands of miles before being deposited on the land or water.  The top sources of mercury in the US are boilers (predominately coal-fired power plants, other coal-fired boilers and municipal waste combustors) and manufacturing (dominated by chloralkali chlorine production plants and cement kilns).  Area sources include fluorescent lamp breakage and general laboratory use. Source: Office of Air Quality Planning & Standards and Office of Research and Development. December 1997. Mercury Study Report to Congress,  Vol I: Executive Summary. US Environmental Protection Agency.

DE Facilities Mercury Release to Air 2005 TRI Data Chart

What are the sources of mercury releases in Delaware?
Note that with the shutdown of the chlorine product line at Oxychem, DNREC expects to see little to no mercury releases from this facility in the 2006 Toxics Release Inventory Report.   

So what is DNREC doing to reduce mercury releases and exposure in Delaware? Over the past two years, DNREC has taken a variety of steps to reduce mercury releases in Delaware.  These range from education and new regulations to enforcement action.  DNREC’s first significant step was completed in November 2006 with the adoption of new, multi-pollutant air regulations that require power plants to reduce mercury emissions by more than 80%.  Under the regulations, initial reductions are required by May 2009 and full compliance is required by January 2012.

Prior to 2006, Oxychem was believed to be the largest emitter of mercury, followed by power plants. According to TRI submissions, Claymont Steel was a relatively minor source of mercury.  Claymont Steel (formerly named “Citisteel”) used calculations instead of actual emission sampling to estimate their releases, which is allowable under TRI).  However, with the shut down of the Oxychem product line and the pending implementation of the power plant regulations, DNREC decided to look more closely at other sources of mercury and consequently ordered mercury stack testing at Claymont Steel. The results of the stack test increased emissions over 10-fold above the calculation method.

Based on the Claymont Steel stack test, DNREC took two significant actions. First, Secretary Hughes issued a Notice of Conciliation and Secretary’s Order to Claymont Steel. This Order requires Claymont Steel to:

  1. Conduct quarterly stack testing.
  2. Undertake a pollution prevention program to reduce the amount of mercury in their scrap steel.
  3. Take actions to reduce mercury emissions to approximately 90% controls or develop an alternative plan by December 31, 2008.

One of the major sources of mercury in Claymont Steel’s scrap comes from mercury switches in salvaged automobiles.  Therefore, DNREC initiated its second action – a mercury switch collection program –to prevent release of mercury from automobiles salvaged in Delaware either during the crushing of the automobile prior to being sent to a steel recycler such as Claymont Steel or from being vaporized in a steel furnace.
On November 28, 2006, DNREC mailed letters to all the automobile salvage yards in the state encouraging their participation in the National Vehicle Mercury Switch Recycling Program.  This program provides automotive recyclers with containers and shipping, plus $1 to $3 for each mercury switch submitted.

DNREC is also undertaking other actions to reduce the potential for releasing mercury into the environment.  The Pollution Prevention Program has undertaken a series of educational initiatives aimed at specific industries that handle hazardous materials such as mercury.  For example, educational workshops were held with the medical community to train them on how to properly dispose of hazardous materials, such as mercury thermometers and blood pressure meters, and non-hazardous alternatives.

Finally, DNREC and the Delaware Department of Health and Social Services’ Division of Public Health have issued fish consumption advisories to warn anglers, their families and friends about mercury and other contaminants in certain locally caught fish from specific Delaware waters (  The goal of those advisories is to reduce human exposure until mercury emissions sources can be brought under control and the concentrations in the fish drop to acceptable levels.  In addition to the warnings issued by the State, the Federal government has also issued warnings concerning mercury in fish.  The Food and Drug Administration (FDA) has issued advice regarding mercury in commercially caught fish (, while the Environmental Protection Agency (EPA) has issued advice for all inland waters of the U.S. not otherwise covered by a State advisory ( Again, the State and Federal advisories are considered to be an important way to reduce exposure while the difficult job of source control is addressed.

What do I do if I have mercury in my home or office?
If you have a mercury thermometer or other item containing mercury that is not broken (in other words, the mercury is not exposed to the air), you can limit your potential exposure to mercury by  taking it to one of the Delaware Solid Waste Authority’s (DSWA) Household Hazardous Waste Collection Days for proper disposal. Information can by found on DSWA’s web site at or by calling their Citizen’s Response Line at 1.800.404.7080.

If you have a broken mercury spill or mercury in anything other than its original container, call DNREC’s Emergency Response line at 1.800.662.8802. One of the Department’s emergency responders will come to your site and either remove the mercury or will advise you on how to have it properly removed. While waiting for a responder, keep people away from mercury liquid to reduce exposure to vapors and to avoid cross contamination by walking in, or through, the liquid. If anyone does come in contact, have them wash with soap and water, remove clothes that have been contaminated and place them in a plastic bag for disposal. Liquid mercury should absolutely not be vacuumed unless using a special mercury vacuum.

For more information please ontact:

Air Pollution Control: 
Ali Mirzakhalili, Director
DNREC Division of Air Quality

Mercury Switch Recycling Program: 
Karen J’Anthony, Program Manager
Hazardous Waste Group

Delaware Air Toxics Assessment Study:
Joseph Martini, Program Manager
Air Surveillance Branch

Toxic Release Inventory: 
Debra Nielsen, TRI Program Coordinator

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