TOXICS & MINING

Mercury, Arsenic, Cyanide

Mercury (Hg)

• What is it?

• How does it get into the environment?

• What is at risk?

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

Mercury (Hg)

• How does it get into the environment?– Natural sources:

• volcanoes• volatilization from oceans• erosion of natural deposits

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

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.

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

Arsenic (As)

• What is it?

• How does it get into the environment?

• What is at risk?

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

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).

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

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

Cyanide (CN)

• What is it?

• How does it get into the environment?

• What is at risk?

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

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)

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

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

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

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

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

Cyanide Facility Photos

Cyanide Mixing Tank Impellor

Cyanide “Isotainer”