1. Mercury, Arsenic, Cyanide
TOXICS & MINING
Mercury, Arsenic, Cyanide

2. Mercury (Hg) What is it? How does it get into the environment?
What is at risk?

3. Mercury (Hg)
What is it?
Mercury (Hg) is a naturally occurring element - silvery white liquid; also found as cinnabar (HgS)
Mercury is used in the manufacture of electrical instruments, fungicides, pharmaceuticals, munitions, paper production, extraction of gold in mining

4. Mercury (Hg) How does it get into the environment? Natural sources:
volcanoes
volatilization from oceans
erosion of natural deposits

5. Mercury (Hg) How does it get into the environment? Human Activities:
estimated to be 1/3-2/3 of the total mercury released into the environment.
Sources include:
stack losses from cinnabar roasting
the working and smelting of metals
coal fired power plants
discharges from mines, refineries and factories
combustion of coal and municipal wastes, industrial wastes and boilers
medical waste incinerators
pesticides
runoff from landfills/croplands

6. Mercury (Hg) What is at risk? Persistence: can change form,
cannot be destroyed
Solubility:
Cinnabar (HgS) is insoluble (and resists weathering);
liquid Hg is slightly soluble in water.

7. Mercury (Hg) What is at risk? Bioaccumulation:
Hg methylation forms CH3Hg+ which is easily absorbed by organisms and biomagnifies from the bottom to the top of the food chain
bioaccumulates (concentrates) in muscle and tissue of fish and other wildlife
CH3Hg+ generally increases by a factor of ten or less with each step up the food chain

10. Arsenic (As) What is it? How does it get into the environment?
What is at risk?

11. Arsenic (As)
What is it?
Arsenic rarely occurs in elemental form, but usually is found as a compound or dissolved ion widely distributed in earth’s crust
found in the metal sulfides (e.g. Arsenopyrite FeAsS), and as oxides, and arsenates
Persistence: cannot be destroyed; can only change its form
Bioaccumulation: by fish and shellfish

12. Arsenic (As)
What is it?
the toxicity of inorganic arsenic (As) depends on its valence state (As-3, As+3, or As+5), and also on the physical and chemical properties of the compound in which it occurs
trivalent (As+3) compounds are generally more toxic than pentavalent (As+5) compounds, but As+5 easily converts to As+3 when ingested; thus, this difference in toxicity is no longer considered that important
Organic compounds (i.e., As in compounds combined with carbon and hydrogen) are less toxic than inorganic compounds (i.e., As combined with oxygen, chlorine, and sulfur).

13. Arsenic (As) How does it get into the environment?
Arsenopyrite (FeAsS) is the most common arsenic mineral in ores and is also a byproduct associated with copper, gold, silver, and lead/zinc mining.
Arsenic trioxide (Fe2As3) is present in flue gases from copper ore roasting
coal-fired power plants and incinerators also may release As into atmosphere.
Water: average concentration is 1 ppb, but can be > 1,000 ppb in mining areas; As+5 most prevalent; many compounds dissolve in water

14. Arsenic (As) What is at risk? Arsenic is a human carcinogen
In humans the primary target organs are the skin and vascular system
birds, animals, plants, and freshwater fish can become contaminated
Toxicity in water is determined by water temperature, pH, organic content, phosphate concentration, suspended soils, presence of oxidants, and speciation

16. Cyanide (CN) What is it? How does it get into the environment?
What is at risk?

17. Cyanide (CN)
What is it?
Cyanide (CN) is a highly toxic carbon-nitrogen chemical compound;
may be combined with various organic and inorganic compounds,
hydrogen cyanide (HCN), a colorless, flammable liquid or gas, or
sodium cyanide (NaCN) and potassium cyanide (KCN), both solids

18. Cyanide (CN)
What is it?
Cyanide has been used since the late 1800s for the recovery of gold, replacing the mercury amalgamation process.
Two processes of cyanide leach mining, vat and heap-leaching, now process greater than 90% of US gold ores.
CN is also used in small amounts to depress pyrite in the floatation processes of base metal ores (Cu, Ni, Pb, Zn, Mo)

19. Cyanide (CN) What is it? Usually stored/transported in dry, solid form
Usage:
Hydrogen cyanide is used in the manufacture of other cyanides for nylon, fibers, resins
also used in herbicides, as chemical warfare agents, silver plating, dyes, and specialty products

20. Cyanide (CN) How does it get into the environment?
Can leach from landfills and cyanide-containing road salts as well as to the atmosphere from car exhaust (hydrogen cyanide gas - HCN).
Some foods (almonds and lima beans) contain cyanides naturally
It can be produced by some bacteria, fungi, and algae

21. Cyanide (CN) How does it get into the environment?
Spills: Cyanide and other heavy metal pollutants overflowed a dam at Baia Mare, Romania, contaminating 250 miles of rivers, and killing millions of fish
Most persistent in groundwater & at higher pH

22. Cyanide (CN) What is at risk?
CN- oxidizes in the presence of sunlight and oxygen, forming Cyanate (CNO-), Thiocyanate (SCN-), ammonia (NH3), nitrate (NO3), and other compounds
Cyanate (CNO-) and Thiocyanate (SCN-) compounds are more persistent than CN-, and do have significant toxicity

23. Cyanide (CN) What is at risk?
Oral lethal dose of KCN for an adult is 200 mg
Airborne concentrations of 270 ppm is fatal
Long term exposure to lower levels results in heart pains, breathing difficulties, vomiting, blood changes, headaches and thyroid gland enlargement
CN does not bioaccumulate in fish

24. Cyanide Facility Photos
Cyanide “Isotainer”
Cyanide Mixing Tank Impellor