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Mercury In The Environment

In this section, you will learn about the behavior of mercury in the environment and why, in addition to human health concerns relating to direct exposure, mercury is an important environmental issue. Much of the material in this lesson is from the U.S. Environmental Protection Agency's mercury web site.

Mercury is a silvery, liquid metal at room temperature and is often referred to as one of the "heavy metals." Like water, mercury can evaporate and become airborne. Because it is an element, mercury does not break down into less toxic substances. Once mercury escapes to the environment, it circulates in and out of the atmosphere until it ends up in the bottoms of lakes and oceans. Mercury can be found as the elemental metal or in a wide variety of organic and inorganic compounds. Depending on its chemical form, mercury may travel long distances before it falls to earth with precipitation or dust.

Bacteria and chemical reactions in lakes and wetlands can change the mercury into a much more toxic form known as methylmercury. Fish become contaminated with methylmercury by eating food (plankton and smaller fish), which has absorbed methylmercury.

As long as the fish continue to be exposed to mercury, mercury continually builds up in fish's bodies. Fish that eat other fish become even more highly contaminated. Thus, the largest tend to be the most contaminated.
When people eat the contaminated fish, the methylmercury can remain in their bodies for a long time. If they eat fish containing methylmercury faster than their bodies can get discharge it, the methylmercury accumulates in their bodies and can be toxic. Many states have fish consumption advisories to inform people about how many meals of fish they can safely eat over a period of time.

Where Does Mercury Come From?
Mercury is a naturally occurring element. Mercury ore - cinnabar - is mined in Spain, Algeria, Kyrgyzstan and China. Mercury is also a by-product of gold and zinc mining. Mercury enters the environment from:

  • Natural sources such as volcanoes and the weathering of rocks;
  • Our intentional uses of mercury;
  • Our unintentional releases of mercury from burning fossil fuels and smelting metals.

1994-95 U.S. Mercury Emissions
(in tons)

Mercury Emissions Chart


(Taken from data in the U.S. Environmental Protection Agency's Mercury Study Report to Congress, 1997. )


Mercury's Environmental Effects
Fish are the main source of food for many birds and other animals, and mercury can seriously damage the health of these species. Loons, eagles, panthers, otters, mink, kingfishers and ospreys naturally eat large quantities of fish. Because these predators rely on speed and coordination to obtain food, mercury may be particularly hazardous to these animals.

Recent research in Minnesota indicates that the following environmental effects are occurring:

  • Loons are accumulating so much mercury that it may be affecting their ability to reproduce;
  • Elevated levels of mercury have been found in mink and otters;
  • Walleye reproduction may be impaired by the fish's exposure to mercury.

Similar effects are being documented for other fish and fish-eating species around the United States and Canada. Has there always been mercury contamination, or is this a recent problem? This is a difficult question to answer, in part because of a lack of adequately preserved fish specimens of preindustrial age to compare against contemporary samples. However, several lines of evidence from recent studies on Wisconsin lakes suggest that increased emissions to the atmosphere, and subsequent higher deposition rates to lakes, likely translate into higher mercury levels in fish.

The Mercury Cycle and Bioaccumulation Aquatic Mercury Cycle
There is a constant biogeochemical cycle of mercury. This cycle includes:

  • release of elemental mercury as a gas from the rocks and waters (degassing);
  • long-range transport of the gases in the atmosphere;
  • wet and dry deposition upon land and surface water;
  • absorption onto sediment particles;
  • bioaccumulation (or biomagnification) in terrestrial and aquatic food chains.

Bioaccumulation means an increase in the concentration of a chemical in an organism over time, compared to the chemical's concentration in the environment. Bioaccumulation can be a normal and essential process for the growth of any species, but the accumulation of unnecessary chemicals or toxins, or even the overaccumulation of essential substances can be detrimental. All animals, including humans, daily bioaccumulate many vital nutrients, such as vitamins A, D, and K, trace minerals, essential fats and amino acids, but unfortunately, they can also accumulate many unnecessary substances, such as lead or mercury. What concerns toxicologists is the bioaccumulation of necessary substances to levels in the body that can cause harm. With substances such as lead or mercury, any accumulation at all can be harmful. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted.

Understanding the dynamic process of bioaccumulation is important in protecting humans and other organisms from the adverse effects of chemical exposure, and it has become a critical consideration in the regulation of chemicals.

Bioaccumulation varies among individual organisms as well as among species. Large, fat, long-lived individuals or species with low rates of metabolism or excretion of a chemical will bioaccumulate more than small, thin, short-lived organisms. Thus, an old lake trout may bioaccumulate much more than a young bluegill in the same lake.

Mercury cycle

Above is a schematic drawing of mercury cycling in an aquatic ecosystem. With the exception of isolated cases of known point sources, the source of most mercury to most aquatic ecosystems is deposition from the atmosphere, primarily associated with rainfall.

animalsIn the aquatic environment, mercury can be:

  • dissolved or suspended in the water
  • trapped in the sediments
  • ingested by living things (biota)

Methylmercury is the form of mercury most available and most toxic to biota (including zooplankton, insects, fish, and humans). This form of mercury is easily taken up by biota and bioaccumulates in their tissues. Unlike many other fish contaminants, such as PCBs, dioxin, and DDT, mercury does not concentrate in the fat, but in the muscle tissue. Thus, there is no simple way to remove mercury-contaminated portions from fish that is to be eaten.

Mercury in the Environment

Activity 6 - Mercury in the Food Chain

Purpose
This activity will help the students reinforce their understanding of food webs while gaining a new understanding of bioaccumulation.

Objectives:
Students will:
1) Display a graphic understanding of an aquatic food web for a specific local body of water
2) Demonstrate an understanding of bioaccumulation

Materials:

  • A map of your state showing waterways (a state highway map will usually work), paper and something to draw with
  • Copies of "Example from Florida aquatic food web and mercury cycle" and information provided in Mercury in the Environment section of this curriculum package
  • If you choose the teacher lead option you will need the following materials
    • 10 very small (1-2 oz.) cups (clear containers are the best, but use what you have).
    • 5 small containers (4 -5 oz)
    • 3 medium containers (around 8 oz)
    • 1 clear container (large to hold around 7-8 cups)
    • Glitter (3 colors) or small beads (3 colors) or something similar that is very small and can be found in 3 distinct colors

Procedure:

1. Select a body of water or a number of water systems in your state.
2. Divide the class into study groups. Assign each group a lake, river, bay, coastal area, etc. Each group should then create a food web for their study site. Include as many of the components that they can find (Use the Florida example as an idea sheet)
3. Select either student self-discovery or teacher lead and follow accordingly.
4. Students should share their findings.

Select one of the two options
Two options: (student self-discovery or teacher lead).

Student self-discovery - present each group the following scenario - the water they are in charge of has shown signs of mercury contamination. As scientists they are to demonstrate to the public what "bioaccumulation" is and why we have to be concerned about it.

1. Allow them to use a variety of materials
2. Give each group 5 minutes for their demonstration.
3. If you wish you may want to have a town board set up to judge who did the best job of demonstrating the issue.

Teacher lead:
You will need to gather the following materials: (clear containers are the best, but use what you have).

  • 10 very small (1-2 oz.)
  • 5 small containers (4 -5 oz)
  • 3 medium containers (around 8 oz)
  • 1 clear container (large to hold around 7-8 cups)
  • Glitter (3 colors) or small beads (3 colors) or something similar that is very small and can be found in 3 distinct colors.

1. Fill each container to 1/3 full with water.
2. Now, representing mercury, you will put a pinch of one color of glitter in each of the 10 very small (1-2 oz.), another color in the 5 small containers (4 -5 oz), and the third color in the 3 medium containers (8 oz)

Using one of the food chains the students developed, have the students label the 10 very small ones as the micro-organisms, the 5 small ones as the animal that eats the micro-organisms (small fish, insects, etc.), the medium would be the animal that eats the small ones and the clear container will represent a top predator.

Now have the students help you with the demonstration and put the food chain and bioaccumulation into action. First the 10 very small containers (they are being eaten by the primary consumer) are poured into the small containers. Some of the glitter may stay in the each container as you pour. That is OK, it represents the mercury that is excreted by the animal (not 100% of the mercury accumulates). Now the small containers will be eaten by the medium or secondary consumer. And finally the medium are eaten by the top predator (tertiary consumer).
Discuss what just happened with special emphasis on the glitter. How much of the mercury was accumulated by the top predator.

Regardless of whether you did the student self-discovery or the teacher lead one - Now hand out the: Bioaccumulation in humans chart and discuss what they have learned through the activity.

Example from Florida aquatic food web and mercury cycle

Florida food web

 

Bioaccumulation in humans

Bioaccumulation in humans


Mercury in the Environment

Activity 7 - Atmospheric Mercury

The majority of mercury entering lakes, streams, rivers, and oceans comes from the atmosphere. It is important to understand why mercury is in the atmosphere because once we understand the causes, we can concentrate on controlling the sources. In this activity, students will begin to recognize patterns and make educated guesses based on those patterns.

Objective
1. Students will demonstrate critical thinking skills
2. Students will make educated guesses (scientific inquiry) based on patterns shown in data

Materials

Procedure

  1. This activity is based on critical thinking and the development of the thought process; therefore it is crucial that the different parts are given one at a time, in the prescribed order. The Activity can be done individually, in small groups, or as a large group in a discussion format.
  2. Hand-out the Mercury Sources Factsheet and the Where is Mercury? sheet. Have students review data and complete the assignment.
  3. Once the first assignment is complete, hand out Mercury in the Air. They will need their first assignment to complete the second.
  4. Once the second assignment is complete, hand out the third, Fish Advisories. They will need the first and second to complete the third.

Optional

5. Review and discuss the EPA Fact Sheet (which can be found at the end of this Activity)

 

fact sheet header

Mercury Sources Factsheet

Coal Plants are Largest Mercury Source

The majority of the mercury entering lakes, streams, rivers, and oceans comes from the atmosphere. Air deposition accounts for up to 90% of the mercury entering Lake Superior, and 80% entering the Delaware Bay.

  • 85% of mercury emissions come from smokestacks, primarily power plants and municipal and medical waste incinerators
  • 33% of all mercury emissions come from power plants (coal- and oil-fired), the largest unregulated source, emitting 52 tons per year

How Far does Mercury Travel in the Atmosphere?

EPA estimates 7 to 45% of mercury released from incinerators and power plants is deposited within a 30-mile radius. The stack height at each plant, the chemical species of the mercury, and the amount of rainfall at a given site all affect how much mercury is deposited around the plant. As shown in the table below, power plants with shorter stacks will have more local deposition than those with taller stacks, and more mercury is deposited locally in a humid site compared to an arid site.

The Electric Power Research Institute calculates that up to 10% of the mercury released deposits within 62 miles of a power plant, and the rest is transported regionally and globally.


Activity 7 - Where is Mercury?

Which state(s) do you think have the biggest problem with atmospheric mercury (mercury that travels through the air)?

Keep in mind:

  • Areas of large populations of people using electrical energy
  • General wind patterns travel from west to east

Highlight on map where you think the biggest atmospheric mercury problem would be and explain why.

US Map

 

Activity 7 - Mercury in the Air

National Atmospheric Hg Deposition

How does this map compare to your highlighted map on the previous page? List similarities and differences.


 

How would you explain the pattern shown on this map?
(What are the similarities and differences?)

 

After review of this map would you be more concerned about mercury if you lived in New York, Texas, or California? Does this mean the other two (that you didn't pick) do not have to worry about mercury?

 

 

Activity 7 - Fish Advisories

Total number of fish consumption

How does the National Atmospheric Hg Deposition map relate to this map?
(Are there similarities or patterns between the two?)

 

 

Why would a state like New Mexico (NM), that does not show any atmospheric mercury deposition, have as high or higher amounts of fish advisories than a state that is in the middle of the heavy atmospheric deposition (such as West Virginia, WV)?

 

 

Background information concerning differences in fish advisories and atmospheric deposition in New Mexico and West Virginia

The following information shows that even though West Virginia is in the area of much higher mercury deposition, New Mexico has been able to do more extensive research and is taking a more preventative stand than most states.

Excerpt taken from a release from the West Virginia Bureau for Public Health:

The West Virginia Bureau for Public Health (BPH) encourages anglers and consumers to take notice of advisory notifications issued warning pregnant women, women of child bearing age, nursing mothers and children about the health concerns of consuming fish that may be contaminated with mercury. The warnings were issued by the United States Environmental Protection Agency and the Food and Drug Administration.

This action is being taken based on an assessment by U.S. Environmental Protection Agency (EPA) of data collected nationwide. The agencies in West Virginia that develop fish consumption advisories, the Bureau for Public Health, Division of Natural Resources and Department of Environmental Protection, agree that limited data currently available in West Virginia support this recommendation, however, additional fish sampling is required to determine more specifically the extent, level of contamination and species affected by mercury.


A short summary of New Mexico's efforts:
(taken from New Mexico Environment Department)

Atmospheric deposition of mercury
With the exception of localized mineral deposits and certain industrial settings, the greatest source of mercury to the environment is atmospheric deposition. Even though the concentration in the atmosphere is very low, our watersheds provide large catchments, and mercury is carried by runoff into waterways on fine particles of soil. These particles, easily held in suspension by the force of moving water, are eventually trapped behind dams, where they settle into the poorly oxygenated region at the bottom of the reservoir. In the anoxic sediments and hypolimnetic waters above them, sulfate reducing bacteria combine some of the inorganic mercury with methane, forming the methylmercury that biomagnifies so powerfully as it is concentrated and passed from prey to predator up the food chain.

Because mercury has been found in some fish at concentrations which could lead to significant adverse human health effects, specific guidelines have been prepared. These guidelines allow those who fish and their families to make an informed decision as to what fish they can safely eat. While the occasional consumer of fish from these waters is at little risk if they are otherwise in good health, ingestion of mercury at levels found in some fish over a long period of time could result in health problems such as kidney disease and/or eye, respiratory tract, nervous system or brain damage.

How did we first discover the problem?
Some routine spot-checking by the federal government first found the problem. We verified it, and continued testing other lakes in New Mexico.

Have enough fish been tested to be really sure of the level of mercury contamination?
Yes, for the lakes for which we have issued health advisories. Mercury levels are strongly correlated with the length of the fish because longer fish are older and have had more time to accumulate mercury. Thus only four fish of different lengths from each species in a lake need to be tested in order to predict with great accuracy the levels of mercury in all the fish. However, we are testing more fish than this in order to verify our statistical models.

Where is the mercury in the fish coming from?
We don't know for sure, but we have not found any single source for it here in Now Mexico so far. Studies in other areas of the U.S. and the world have found that most of the mercury appears to be coming from the air and then deposits in lakes and on soil. The mercury gets into the air from industrial processes including smelters.
Another possibility is that mercury can be found naturally in different types of soils, and become washed into lakes with soil disturbances such as overgrazing, housing developments, road developments, etc.

Why would some lakes have a problem and others not?
The factors which affect the amount of mercury which gets into the fish are not fully understood. However, some of them appear to be:
1. More acid lakes lead to more conversion of mercury to methylmercury, which is
taken up by the fish more easily.
2. Recently formed lakes, especially those with submerged decaying vegetation such
as trees, are more likely to convert mercury to methylmercury.
3. Smaller lakes may have the mercury more concentrated.
4. Rivers with swiftly moving water will usually have less concentrated mercury.
5. Bigger fish, and species of fish which eat other fish, get larger amounts of mercury.

State/EPA mercury screening survey
In 1995 and 1996, staff of the Surface Water Quality Bureau (SWQB) conducted a screening survey for mercury covering over 2,000 miles of New Mexico's waterways. Analyses were provided, free of charge, by EPA s Environmental Monitoring Systems Laboratory (EMSL) in Cincinnati, Ohio. EMSL was able to provide a minimum detection limit of 0.7 ng/L (0.7 parts per trillion). Using ultra-clean sample handling protocols developed by SWQB staff, over two hundred stations were sampled before the EMSL project lost its funding and was terminated. This study is the most comprehensive evaluation of mercury levels in New Mexico's waters ever conducted. The Surface Water Quality Bureau has been given the use of the analytical equipment used in the State/EMSL mercury screening survey. This equipment now resides at the Scientific Laboratory Division of the New Mexico Department of Health (SLD). Staff of the SLD are currently developing a small clean room to provide a suitable laboratory environment for the analysis of mercury at low parts per trillion levels.

Survey results
The data from that study show that, with some notable exceptions, mercury levels in our rivers and streams are very low. The average concentration of mercury in New Mexico's waters is less than 2.5 ng/L (Range: 0.0 ng/L to 500.0 ng/L). No water sample drawn from any major waterway in New Mexico has been found to contain mercury at a level that could pose any degree of direct risk to humans or wildlife. While much work remains to be done, to date it appears that in all but one instance where mercury was found to exceed the current state chronic criterion of 12 ng/L (parts per trillion) its occurrence can be attributed to either mining activity or storm water runoff from Los Alamos National Laboratories (Up to >3,400 ng/L). The single exception appears to be related to a coal seam in San Juan County.

Fish tissue mercury concentrations
Despite the extremely low concentrations of mercury in the State's waters, levels in the tissues of certain fish, (usually large, predatory species), can still exceed the FDA action limit of 1.0 part per million, an increase over background of six orders of magnitude. It is this tendency of mercury to biomagnify as it is passed up the food chain that generates concern. Fish are about ten times as tolerant of mercury than are humans. This is possible because they have evolved an efficient strategy for sequestering mercury away from vital organs: they store it in muscle tissue - the portion we eat.

EPA Fact Sheet

EPA Factsheet

 
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| Table of Contents |
| Introduction | Focus on Mercury | School Information | Household Information |
| Mercury in the Environment | Mercury in Our World and Community |

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Last revised: August 20, 2004