22 - Mercury

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What is mercury (Hg)?

A heavy metal and antrual crsutal element found at 70-80ppb in soil and rock

Typical mercury concentration in water?

0.01-10ppb — drinking water limit is 1ppb

Why is mercury dangerous?

some forms, especially methylmercury, are highly toxic

What is elemental mercury (Hg⁰)

a metallic liquid or vapor, rare in nature

What is cinnabar (HgS)?

The most common natrual form, found in volcanic regions

what is methylmercury (MeHg)?

An organimercury compound, the most toxic form

what are natrual soruces of mercury?

volcanic activity and weathering of rocks

What are major antrhopogenic sources of mercury?

• Industrial catalysts & electrodes

• Agricultural pesticides/biocides

• Gold mining

• Fossil fuel burning

• Instruments (thermometers), dentistry, preservatives

How does human input compare to natural input?

Antrhopogenic mercury is ~20x higher than natural sources

How does atmospheric deposition contribute to lakes?

Mercruy falls onto watersheds and accumulates in sediemtns (e.g., ELA lake 375)

why is mercury significant for bacteria?

It is toxic, but bacteria can detoxify it

What reaction creates methylmercury?

Methylation by sulfate-reducing bacteira:

Hg2+ —> MeHg

Where does methylation occur?

Anoxic environments with active microbial communities

where is MeHg production enhanced?

• Dytrophic waters

• wetlands

• acidic waters

• Newly flooded resevoirs

Why do new resivoirs produce mercury problems?

Flooded soils become anoxic, releasing mercury and increasing bacterial methylation

What is bioconcentration?

uptake of mercury directly from water

What is bioaccumulation?

Mercury increases in an organism becuase it accumulates faster than it is eliminated

What is biomagnification?

Increase in mercury concentration higher up the food chain

How concentrated can mercury become in fish?

Up to 3,000x concentrations in water

Where does mercury accumulate in fish?

Muscle tissue — it cannot be cooked out

How does methymercury enter humans?

Through contaminated food, especially fish

Why is MeHg dangerous?

• Lipophillic (absorbed quickly )

• Strong protien binding

• Enzyme inhibition

What systems does mercury damage?

• Brain and nervous system

• Immune system

• Genetic integrity and enzymes

• Fetal development (birth defects)

What was Minamata disease?

Severe Hg poisoning from industrial effleuent (Japan, 1950s-60s)

sysmptoms inclueded neurological damage, also affected wildlife (dancing cats)

What casued grassy narrows mercury contamination?

A papaer mill (1962) used Hg-based bleaching and dumped 20 tons of untreated mercury

what were the consequences of Grassy Narrows?

• Entire watershed contamintaed

• Unsafe drinking water

• Fish unsafe to eat

• Long term health effects still ongoing

What did researchers do at ELA 658?

Added different Hg isotopes to lake, wetland, upland to track movement

What happened in the lake?

Rapid MeHg production (within 2 weeks) and MeHg appeared in fish within months

What happened in wetlands?

Some Hg emitted back to atmosphere

Slow movement to lake (months)

What happened in uplands?

Mercury stayed bound to soils with little movement

what happens when mercury loading is reduced?

Mercury decreases at all trophic levels

Why is recovery slower at higher trophic levels?

Longer lifespan and slower tissue turnover