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MPC Issue Paper No. 1
Cyanide Uncertainties
Observations on the Chemistry, Toxicity, and Analysis of Cyanide in Mining-Related Waters
Robert Moran, Ph.D.
Edited by Susan Brackett
Mineral Policy Center
Protecting Communities and the Environment
1998
CONTENTS
Foreword 1
Introduction 3
Basic Chemistry and Toxicity of Cyanide Compounds 6
Monitoring and Analysis of Cyanide at Mine Sites 11
Case Study: Cyanide Spill in Kyrgyzstan 12
Conclusion 13
Cyanide Uncertainties discusses only select aspects of the chemistry and toxicity of
cyanide in waters associated with hardrock mining—it is not intended to be a
comprehensive review. In this paper, mining-related waters refers to water associated with
mining wastes, such as tailings and heap leach piles, and water that may be impacted by
mining, including rivers, lakes, and groundwater. Cyanide Uncertainties was written for a
general audience with a limited knowledge of chemistry.
Mineral Policy Center (MPC) is the leading national environmental organization working to
prevent environmental degradation caused by hardrock mining. MPC Issue Papers are produced
by MPC on issues related to mining and the environment. Opinions expressed by the authors
do not necessarily reflect those of MPC. All Rights Reserved. Permission to reproduce any
portion of this publication must be obtained from Mineral Policy Center, Suite 808, 1612 K
Street, N.W., Washington, D.C. 20006. Tel: 202-887-1872. Fax: 202-887-1875. Email: mpc@mineralpolicy.org. Visit our homepage at www.mineralpolicy.org. Printed with soy ink on
recycled paper.
FOREWORD
The hardrock mining industry has derived big profits from cyanide. This toxic chemical has
made it possible for mining companies to mine low-grade ore bodies for microscopic flecks
of gold and silver, and still turn a profit.
The use of cyanide in mining, however, is becoming more and more controversial. Mining
such low-grade ore creates vast open pits, and produces huge quantities of waste rock. In
addition, cyanide is a toxic chemical—one teaspoon of two percent cyanide solution
can cause death in humans. And in recent years, a string of cyanide-related mine accidents
has added to community fears and concerns. (See box on page 5.)
The most dramatic mine-related cyanide spill occurred this year in Kyrgyzstan. On May 20,
1998, a truck transporting cyanide to the Kumtor gold mine plunged off a bridge, spilling
almost two tons of sodium cyanide into a local river. In the aftermath, hundreds were
treated at local hospitals, and a Kyrgyz government report documented at least one human
fatality. The mining company, Cameco Corporation, disputes this report.
Nevertheless, the mining industry maintains that cyanide breaks down quickly in the
environment, and that mining companies safely handle large quantities of this chemical.
The Rest of the Story
As this report demonstrates, however, there is much that is unknown and uncertain about
the toxicity of cyanide. The mining industry and regulators claim that cyanide rapidly
breaks down in water into harmless compounds, but this is only part of the cyanide story.
The rest of the story is that cyanide also breaks down into compounds that are potentially
toxic to fish and other aquatic organisms. Many of these compounds are generally less
toxic than the original cyanide, but may persist for long periods of time. And there is
evidence that some of these compounds are stored, or bioaccumulate, in plant and fish
tissue.
In addition, when mine operators test for cyanide, they are not required to test for these
breakdown compounds. In essence, these compounds go unregulated despite the potential
environmental impacts.
There are many legitimate questions about environmental and human health impacts related
to the use of cyanide at mining operations that mine operators, regulators, and health
officials are simply unable to answer at this time. Mineral Policy Center has produced
Cyanide Uncertainties to help industry, government regulators, and local citizens begin
the process of assessing these very real, and very serious uncertainties related to
cyanide.
Stephen D’Esposito
President
Mineral Policy Center
MPC’S RECOMMENDED
STEPS TOWARD ASSESSMENT OF
CYANIDE UNCERTAINTIES
Voluntary industry monitoring of all cyanide-related compounds at mines, with public
release of the information.
Immediate U.S. Environmental Protection Agency investigation to determine standards for
these potentially toxic cyanide-related compounds.
Adoption of stricter environmental standards for all mining operations that use cyanide
and are funded by public institutions. Such projects should be subject to greater public
disclosure.
Appointment of citizen oversight boards at all mines that use cyanide to ensure public
access to information.
Independent environmental audits of all U.S. and international mining operations that use
cyanide.
INTRODUCTION
The use of cyanide compounds by the mining industry, coupled with limitations in current
analysis and monitoring of these compounds, raises serious concerns regarding public
safety and environmental protection at mine sites using cyanide processing.
Mining and regulatory documents often state that cyanide in water rapidly breaks
down—in the presence of sunlight—into largely harmless substances, such as
carbon dioxide and nitrate or ammonia. However, cyanide also tends to react readily with
many other chemical elements, and is known to form, at a minimum, hundreds of different
compounds. (Flynn and Haslem, 1995)
Many of these breakdown compounds, while generally less toxic than the original cyanide,
are known to be toxic to aquatic organisms. In addition, they may persist in the
environment for long periods of time, and there is evidence that some forms of these
compounds can be accumulated in plant (Eisler, 1991) and fish tissues. (Heming, 1989)
Despite the risks posed by these cyanide-related breakdown compounds, regulatory agencies
do not require mine operators to monitor this group of chemicals in mining-related waters.
Therefore, while much of the cyanide used at mining sites does break down fairly readily,
either as a result of natural degradation or the various treatment processes sometimes
employed, significant amounts of the original cyanide form potentially toxic compounds
that remain unaccounted for in the monitoring of mining operations.
Mining with Cyanide
Cyanide compounds are widely used by the mining industry to assist in the extraction of
both precious and non-precious metals from rock. In gold mining, a dilute cyanide solution
is sprayed on crushed ore that is placed in piles, commonly called heaps, or mixed with
ore in enclosed vats. The cyanide attaches to minute particles of gold to form a
water-soluble, gold-cyanide compound from which the gold can later be recovered. Cyanide
is used in a similar manner to extract silver from ores. In the extraction of non-precious
metals, such as copper, nickel, cobalt, and molybdenum, cyanide is used in the milling and
concentration processes to separate the desirable metals from the wastes. Consequently,
cyanide and related compounds often are contained in discarded mine wastes.
While most of the cyanide used by the industry is handled without obvious negative impact,
the unique chemical behavior and toxic nature of these compounds, combined with the risk
of serious mine waste spills, suggest that this topic merits a closer look.
Complex Chemical Behavior
The general term “cyanide” refers to various compounds having the chemical group
CN, that is, one single atom of carbon (C) and one single atom of nitrogen (N). Several
plants, some soil bacteria, and several species of invertebrate organisms produce natural
cyanide and related compounds. Nevertheless, cyanide compounds are seldom present in
uncontaminated waters in measurable concentrations.
Cyanide readily combines with most major and trace metals—a property that makes it
useful in extracting metals from ores. Cyanide also tends to react readily with many other
chemical elements, producing a wide variety of toxic, cyanide-related compounds. And
because cyanide is carbon based—an organic compound—it reacts readily with other
carbon-based matter, including living organisms.
Despite this complexity, regulators generally require that mine operators monitor for only
three categories of cyanide: free cyanide, weak-acid-dissociable (WAD) cyanide, and total
cyanide. Furthermore, the analytical procedures used to determine these categories of
cyanide fail to indicate the presence of many of the other toxic breakdown products of
cyanide. (See page 12 for discussion on analytical procedures.)
For example, routine analyses of cyanide fail to identify cyanates and thiocyanates, two
significant cyanide breakdown products found at mine sites. Water samples from mining
sites where cyanide is used as a process chemical may have WAD and/or total cyanide
concentrations that are quite low or undetected, yet when the same samples are analyzed
specifically for cyanates and thiocyanates, they may show tens of milligrams per liter
(mg/L) or more of these compounds.
Numerous research and regulatory documents describe these categories of cyanide-related
compounds as somewhat toxic, but generally do not state at what concentrations, and regard
their potential presence as unimportant. Since routine analyses do not report these other
compounds, it is often impossible to know if they are present at a mine site, and at what
concentration.
Mine Waste Spills
In recent years, a number of cyanide-related leaks, discharges, and accidents at U.S. and
international mine sites have been reported in the news media. (See box on page 5.) These
accidents raise questions about the current operating practices, monitoring, and
enforcement at cyanide-related mine sites worldwide.
EXAMPLES OF RECENT
CYANIDE-RELATED MINE ACCIDENTS
Colorado, U.S.A.: In Colorado, spills of cyanide and other contaminants from the
Summitville gold mine, owned by Galactic Resources Ltd, contributed to severe
environmental problems on a 17-mile stretch of the Alamosa River. The mine was opened in
1986, and abandoned in 1992. It is now a federal Superfund site.
Montana, U.S.A.: Pegasus Corporation recently closed the Zortman-Landusky gold mine in
Montana. Opened in 1979, it was the first large-scale cyanide heap leach mine in the
United States. The mine experienced repeated leaks and discharges of cyanide solution
throughout its operating life, resulting in wildlife deaths and severe contamination of
streams and groundwater.
Nevada, U.S.A.: Following the failure of a leach pad structure in 1997, the Gold Quarry
mine in Nevada released about 245,000 gallons of cyanide-laden waste into two local
creeks. In 1989 and 1990, a series of eight cyanide leaks occurred at Echo Bay Company's
McCoy/Cove gold mine in Nevada, releasing a total of almost 900 pounds of cyanide into the
environment.
South Dakota, U.S.A.: On May 29, 1998, six to seven tons of cyanide-laced tailings spilled
from the Homestake Mine into Whitewood Creek in the Black Hills of South Dakota, resulting
in a substantial fish kill. It is likely to be years before the stream fully recovers.
Kyrgyzstan: On May 20,1998, a truck transporting cyanide to the Kumtor mine in Kyrgyzstan
plunged off a bridge, spilling almost two tons of sodium cyanide (1,762 kilograms) into
local surface waters.
Guyana: In 1995, more than 860 million gallons of cyanide-laden tailings were released
into a major river in Guyana when a dam collapsed at Cambior mining company’s Omai
gold mine.
Spain: A dam at the Los Frailes zinc mine in southern Spain ruptured in April 1998,
releasing an estimated 1.3 billion gallons of acid, metal-laden tailings into a major
river and over adjacent farm lands. While news reports of the associated massive fish kill
did not mention cyanide or related compounds in the wastes, their presence seems likely
given the nature of the metals extracted at this site.
BASIC CHEMISTRY AND
TOXICITY OF CYANIDE COMPOUNDS
Most commonly, cyanide used at mining sites is in the form of sodium cyanide, NaCN. This
white solid dissolves readily in water, yielding a sodium ion (Na+) and a cyanide ion
(CN-). Some of the cyanide ion then converts into hydrogen cyanide (HCN) or hydrocyanic
acid.
Free Cyanide and Water pH
The cyanide ion (CN-) and hydrogen cyanide (HCN) are often referred to as free cyanide.
Both free cyanide forms are highly toxic to humans and aquatic life if ingested. The
relative amounts of both forms of free cyanide are largely controlled by water pH—a
scale designed to measure the acidity or alkalinity of materials. Most cyanide in natural
waters, which have a pH ranging between 6.0 and 8.5, is present as HCN. (Streams and
groundwater contaminated with acid mine drainage often have a pH of 4.5 or lower.)
The cyanide ion (CN-) is the predominant stable form of free cyanide above a pH of about
9.2. As the pH drops, increasing amounts of CN- convert to hydrogen cyanide (HCN). The
percentage of HCN continues to increase as the pH drops further, until at a pH of 7.0,
about 99.5 percent of the cyanide exists as HCN. At a pH below 7.0, essentially all
dissolved cyanide is present as HCN. HCN readily forms a gas—the same gas used in
execution chambers—which is released into the air.
Most mining process solutions, such as tailings solutions or leach solutions, are kept at
alkaline pH levels—usually above about 10.0—because metal extraction is more
efficient at these levels. This is accomplished by adding alkaline compounds, such as lime
or sodium hydroxide, to cyanide-containing mining solutions. The elevated solution pH also
prevents the formation of the HCN gas and accidental poisoning of mine workers via
inhalation. (Such high pH mine solutions would be extremely toxic if ingested.)
Free cyanide forms readily react within a few hours to a few days with almost any other
chemicals they contact, producing a wide variety of new compounds. Such compounds are
often categorized as simple cyanide compounds, cyanide complexes, and cyanide-related
compounds. The following sections focus on cyanide breakdown compounds most commonly found
at mine sites.
Simple Cyanide Compounds
Simple cyanide compounds consist of only a single metal ion in combination with CN. Simple
cyanide compounds include sodium cyanide, potassium cyanide, and calcium cyanide—all
of which are readily soluble. Some simple cyanide compounds are insoluble.
Metal-Cyanide Complexes
Cyanide complexes are compounds of cyanide bound together with numerous other organic and
inorganic compounds. Only the metal-cyanide complexes, which are commonly formed in mining
effluents, will be discussed in this section.
When metal-cyanide complexes are formed and released into the near-surface environment,
they begin to decompose at varying rates, some quickly, others quite slowly. This
breakdown releases cyanide into the soil or water, generally at relatively low
concentrations. Those complexes that most readily decompose are referred to as weak
complexes, those most resistant to decomposition are called strong complexes. Examples of
weak cyanide complexes include zinc and cadmium cyanides. Moderately strong complexes
include copper, nickel, and silver cyanides. And strong complexes include iron, cobalt,
and gold cyanides. Some of the strong complexes do not break down in the presence of
strong acids, but will decompose when exposed to various wavelengths of light, releasing
cyanide ions. This is especially true of the iron cyanides, which are often the most
common forms of these complexes found in mining wastes.
The decomposition rates of these complexes also are affected by the water temperature, pH,
total dissolved solids, and complex concentration. Some metal-cyanide complexes degrade
more rapidly when exposed to sunlight, atmospheric carbon dioxide, and air. And some
complexes degrade more rapidly when they percolate through soils, are agitated and mixed
by wind or streams, or are metabolized by bacteria. Cyanide complexes degrade more rapidly
in neutral or low pH environments, but some may be stable for decades. The author has
encountered cyanide-contaminated sediments at a cobalt-nickel mine that contained many
milligrams per kilogram of total CN more than 25 years after all processing had ceased,
indicating the persistence of these complexes—probably iron cyanide and cobalt
cyanide complexes.
Cyanide-Related Compounds
Cyanide in mining solutions can undergo several types of reactions to form various toxic
cyanide-related compounds. The following cyanide-related compounds are considered to be
toxic to aquatic organisms, although generally at concentrations much higher than for the
free cyanide forms.
Cyanate (NCO-) is a cyanide-related compound that is formed when alkaline solutions of
cyanide react with oxidants such as chlorine, hypochlorite, ozone, and hydrogen peroxide.
In fact, the mining industry often uses several of these oxidants to decompose cyanide in
wastes. When hypochlorite is combined with cyanide in alkaline solutions (the process is
referred to as alkaline chlorination), an intermediate toxic compound is formed, cyanogen
chloride (ClCN), which is then converted to cyanate. Various strains of microorganisms
will also convert cyanide into cyanate, and then to carbon dioxide. Alkaline chlorination
may also result in the formation of chloramine (NH2Cl), or similar chlorinated ammonia
compounds. Chloramine is less toxic than CN-, but is likely to be present in much higher
concentrations. Free cyanide also reacts with forms of sulfur in mining effluents,
including thiosulfates, or sulfide ions, to produce thiocyanates (SCN-). Relatively high
concentrations of thiocyanate may persist in the presence of acidic solutions. (Plumlee
and others, 1995) Thiocyanate concentrations in the range of tens of milligrams per liter
have also been reported in copper tailings waters with a pH above 10. Free cyanide will
also form cyanogen (NC-CN) under acid conditions if an oxidant such as oxidized copper
minerals is present. The formation of cyanogen would not be expected where mining
solutions remain alkaline, but might develop if acid mine drainage were to form, or if
acidic solutions were to contact cyanide-bearing solutions.
Nitrate and Ammonia
The chemical breakdown of many of the above-mentioned cyanide and cyanide-related
compounds often results in the formation of high concentrations of nitrate and/or ammonia.
The latter may reach concentrations toxic to aquatic organisms.
While most cyanide forms begin to degrade readily when exposed to air, water, and
sunlight, these same compounds may persist in the environment if released during winter
when lakes or streams may have snow and ice cover, and temperatures are reduced.
Toxicity of Cyanide Compounds
Given the limitations of routine analytical techniques for measuring cyanide, and the
presence of breakdown cyanide forms in mining waste waters, it follows that considerable
uncertainty exists regarding the actual toxicity of various cyanide forms to living
organisms. Much of the uncertainty exists because mining-related waters generally contain
complex mixtures of potentially-toxic metals along with the cyanide and related compounds.
And determining which chemical constituents are actually causing a toxic response can be
very difficult. Instead of specific toxicity data on cyanide compounds, it is more common
to read general statements like the following: “Hydrogen cyanate and cyanate ions are
significantly less toxic than HCN,” and “Thiocyanate is relatively non-toxic,
when compared with cyanide.” (Smith and Mudder, 1993) In this setting, the toxic role
of cyanide breakdown compounds is generally neglected.
There are no established water quality criteria for most forms of cyanide derivatives
found in mining-related waters. The current U.S. Environmental Protection Agency water
quality criterion for cyanide is 5.2 micrograms per liter for freshwater aquatic life, and
1.0 microgram per liter for marine aquatic life and wildlife. (EPA, 1986) Yet no criteria
exist for cyanide-related compounds, including cyanate, thiocyanate, cyanogen chloride and
the metal-cyanide complexes.
Toxicity to Fish
The box on pages 10 and 11 highlights the toxicity of cyanide-related breakdown compounds
that can be found at mine sites. Discussions on toxicity for each of these compounds
focuses on fish, since they are the most sensitive species, and are impacted by relatively
low cyanide concentrations. For example, fish are killed by cyanide concentrations in the
microgram per liter range, whereas bird and mammal deaths generally result from cyanide
concentrations in the milligram per liter range. Acute toxicity is described as those
concentrations of cyanide that lead to the death of more than 50 percent of the test
population within 96 hours. (Ingles and Scott, 1987) Chronic exposure may be described as
exposure to less-than-lethal concentrations of cyanide. Some chronic effects may last for
10 days after an individual spill. In addition, chronic cyanide exposure may affect
reproduction, physiology, and levels of activity of many fish species, and may render the
fishery resource non-viable. Whether the toxic effects of HCN are cumulative is apparently
not known.
Toxicity to Humans
Stanton and others (1986) states that HCN ingested orally is fatal to humans in doses
ranging from 50 to 200 milligrams, about the size of a grain of rice. Dr. Gerry
Henningsen, a toxicologist with the U.S. Environmental Protection Agency reports that HCN
concentrations above 40 to 200 milligrams per liter are likely to be toxic to mammals,
including humans.
According to numerous industry documents, sodium cyanide has been used for decades in
mining, and no accidental fatality has been recorded associated with its use. However, in
May 1998, at least one death was reported by government officials in Kyrgyzstan to be due
to, or aggravated by, contact with cyanide that spilled while being transported to a mine
in Kyrgyzstan. (See case study analysis on page 14.)
Much of this section is based on the following references: Smith and Mudder, 1993;
Colorado Dept. of Natural Resources, Nov. 1997; Ingles and Scott, 1987; Flynn and Haslem,
1995; Scott and Ingles, 1981; and Stanton and others, 1986. This and other sections
benefited from telephone discussions with Dr. Owen Mathre, consulting chemist and former
research chemist for more than 35 years with E.I. DuPont, one of the main manufacturers of
commercial cyanide. Sections on toxicity are based largely on Ingles and Scott, 1987;
Eisler, 1991; Heming, 1989; and Palmes, 1991.
FACTORS AFFECTING CYANIDE TOXICITY
TO FRESHWATER FISH
Cyanide concentration: Toxicity increases with higher concentrations of cyanide.
Oxygen concentration: Cyanide toxicity increases with any reduction in dissolved oxygen
below 100 percent.
Temperature: Toxicity increases three-fold with a 12 degree celsius decrease in
temperature.
pH: Slight decrease in toxicity at pH above about 8.5 due to conversion to CN-.
Chloride: Greater than about 8.8 parts per thousand of chloride decreases survival time.
Other dissolved constituents: The presence of zinc and ammonia results in a
greater-than-additive increase in toxicity.
Other factors: Toxicity will also depend on the age and health of the fish, the amounts of
water ingested, and the stress level on the animal.
Toxicity of Cyanide and Cyanide-Breakdown
Compounds to Freshwater Fish
Free cyanides: Free cyanides (the cyanide ion and hydrogen cyanide) are well known to be
the forms of cyanide derivatives most toxic to mammals and aquatic life. Acute toxicity to
various fish species ranges from about 20-640 micrograms per liter. (Ingles and Scott,
1987) The more sensitive rainbow and brown trout generally exhibit acute toxicity in the
range of 20-80 micrograms per liter of free cyanide. Chronic toxic effects are reported in
fish in the range of 5-20 micrograms per liter.
Metal-cyanide complexes: Metal-cyanide complexes are generally thought to be less toxic
than free cyanide. However, they are less well understood. These complexes break up to
yield hydrogen cyanide, which is the usual cause of toxicity. Some metal cyanide
complexes, including silver, copper and nickel cyanides, may themselves be toxic. The iron
cyanide complexes are not particularly toxic, but release free cyanide on exposure to
sunlight. Ingles and Scott (1987) report the following toxicity ranges of selected
metal-cyanide complexes: sodium and potassium cyanides 0.02-0.3 mg/L; zinc cyanide
0.02-0.3 mg/L; cadmium cyanide 0.02-0.3 mg/L; copper cyanides 0.4-4.0 mg/L; nickel cyanide
0.4 mg/L (6.5 pH) and 730 mg/L (8.0 pH); and iron cyanides 300 mg/L in darkness and less
than 0.2 mg/L in light. Doudoroff (1976) states that the chronic toxicity of metal-cyanide
complexes needs to be investigated.
Organic-cyanide compounds: These compounds vary greatly in their toxicity; minimal data
has been published relative to fish. Doudoroff (1976) states that malano nitrile, which
has been used to extract gold from ores, is cumulatively toxic at concentrations similar
to those of free cyanide.
Cyanogen chloride: Cyanogen chloride is an intermediate toxic compound that is formed when
hypochlorite is combined with cyanide in alkaline solutions. This compound may be more
toxic to fish than free cyanide (Doudoroff, 1976). Ingles and Scott (1987) state that it
has about the same toxicity as cyanide. It is unclear whether cyanogen chloride persists
in alkaline mining wastes.
Cyanates: Cyanate is the main form of cyanide resulting from most cyanide decomposition
processes employed at mine sites. Cyanate may persist in water for significant, but
undefined periods of time. Ingles and Scott (1987) report cyanates to be toxic to trout at
concentrations ranging from 13 - 82 milligrams per liter cyanate.
Thiocyanates: Ingles and Scott (1987) report thiocyanate toxicity for fish to range
between 90 and 200 milligrams per liter. Heming and Thurston (1985) and Heming and others
(1985) report toxicity to be between 24 and 70 milligrams per liter thiocyanate for brook
trout. Heming and Blumhagen (1989) report that thiocyanates cause "sudden death
syndrome" in trout, partly as a response to stress, and because they
accumulate—which is contrary to much previously published literature.
Chloramines: Chloramines are chlorinated ammonia compounds that are less toxic than CN-,
but are likely to be present in much higher concentrations. Chloramines can be formed as a
result of alkaline chlorination. The presence of chloramines is normally determined via
analysis for total residual chlorine. The U.S. EPA criteria document for freshwater
aquatic organisms states that the total residual chlorine concentration should not exceed
11-19 micrograms per liter. (EPA, 1986)
Ammonia: Ammonia is a routinely encountered breakdown product wherever cyanide processing
occurs. It is the only cyanide-related compound discussed in this report that is regulated
by state or federal agencies. It is considered to be about as toxic to fish as cyanide.
U.S. Environmental Protection Agency (1986) reports ammonia to be toxic to fish at
concentrations between 0.083 and 4.6 milligrams per liter. Some data indicate that the
combined effect of ammonia and cyanide is greater than would be assumed on the basis of
their individual toxicities.
MONITORING AND ANALYSIS OF
CYANIDE AT MINE SITES
“Despite its critical importance, the analysis for cyanide in mining-related
solutions remains a source of concern and confusion to both operators and regulators
alike." (Smith and Mudder, 1993)
The great reactivity of cyanide and related compounds makes sample analysis difficult and
the resulting data often subject to significant errors. In addition, water samples from
mining sites are most commonly analyzed for only three forms of cyanide: free cyanide;
weak acid dissociable (WAD) cyanide; and total cyanide.
Cyanide Analytical Methods
The “free cyanide” analytical method reports the sum of both forms of free
cyanide—the cyanide ion (CN-) and hydrogen cyanide (HCN), plus cyanide from the
breakdown of many of the weak complexes (which does not include complexes of nickel, iron,
cobalt, gold, platinum, and palladium).
The "WAD cyanide" method measures the free cyanides plus many of the weak
cyanide complexes that break down in a hot, mildly acid solution—about pH 4.5.
The "total cyanide" analysis measures the free and WAD cyanide forms, plus those
metal complexes that break down in a hot, concentrated acid solution (pH less than 1.0).
This includes most metal cyanide complexes, including most strong complexes. But this
method may not detect many of the organic cyanide compounds. (Although organic-cyanide
compounds are not reported to be found in significant concentrations at mining sites, it
is unclear whether mining samples have been analyzed adequately to determine the presence
of these compounds.)
Both the WAD and the total cyanide methods fail to detect many forms of cyanide or
cyanide-related compounds that are likely to be present at mining sites. The WAD method,
for example, fails to detect cyanates, thiocyanates, cyanogen chloride, chloramines, most
cyanogen, and most organo-cyanide compounds, most gold, platinum, and cobalt complexes,
and most importantly, iron cyanide complexes. The total cyanide method fails to detect
cyanates, thiocyanates, chloramines, most organic-cyanide compounds, and most cobalt and
platinum cyanide complexes. Thus, neither the total or WAD methods measure the total
concentration of cyanide and related forms. If one wishes to determine, for example, the
concentration of cyanates and/or thiocyanates, analyses specific for these parameters must
be requested from the laboratory.
Most mining regulatory agencies require that water samples be analyzed for WAD and/or
total cyanide forms, especially during mine closure. The other cyanide-related forms
discussed in this report, however, are generally neglected.
Because of the previously-mentioned complexities and uncertainties involved in cyanide
analysis, it is usually not reasonable to interpret routine cyanide analytical data more
precisely than ±0.005 mg/L, or even ±0.01mg/L in many cases. Concentrations reported
below these levels are often not meaningful, except under research conditions.
Much of this section has been taken from American Public Health Assoc., 1995, section
4500-CN.; and Smith and Mudder, 1993.
CASE STUDY:
CYANIDE SPILL IN KYRGYZSTAN
On May 20, 1998, a truck transporting cyanide to the Kumtor gold mine in Kyrgyzstan
plunged off a bridge, spilling about 1,762 kilograms (kg) of sodium cyanide into a river
upstream of several villages. (The material that spilled was a concentrated form of
cyanide and not cyanide-bearing tailings or heap leach waters. This incident illustrates
many of the environmental and regulatory problems discussed in this paper.) Within days
after the spill, hundreds of local residents sought treatment at medical clinics.
According to a report by the Russian Federation Ministry of Defense, at least one human
death was related to the cyanide spill. The mining company and some officials of the
Kyrgyz government, which holds a majority ownership in the mine, have argued that few if
any significant impacts have occurred to any living organisms or the overall environment,
as a result of the spill.
According to Dr. Owen Mathre, a former research chemist for E.I.DuPont, the dissolution of
approximately 1,800 kg (about 2 tons) of solid sodium cyanide under these conditions would
probably require several hours to complete. Since the pre-spill pH of the river was likely
less than 9.0, most of the dissolved cyanide would have formed HCN, a toxic gas that would
have escaped into the air. Within a few hours of the accident, sodium hypochlorite was
applied to areas near the spill site to break down the cyanide. Application of this
chemical, however, would likely result in the formation of cyanate and cyanogen
chloride—cyanide-related compounds that are toxic to aquatic organisms. Cyanogen
chloride is a heavy gas that could have traveled significant distances from the spill, and
has been known to cause throat and eye irritation in mine workers. Therefore this
compound, together with the presence of gaseous ammonia, may have contributed to some of
the medical complaints of the local citizens.
Water samples collected about 20 meters from the spill site (presumably downstream) within
hours of the accident contained up to 79.5 mg/L of free cyanide, which was the only
cyanide form reported. However, since standard cyanide analytical techniques fail to
detect several forms of cyanide and cyanide-related compounds, the concentrations reported
would not include cyanide from many of the stronger metal-cyanide complexes, nor would
they include the toxic cyanide breakdown products in cyanates, thiocyanates, cyanogen, and
cyanogen chloride, or indications of ammonia or chloramine concentrations. All of these
compounds could have formed following the spill, and all are toxic to aquatic organisms.
Furthermore, it is unclear that any of the early samples were collected prior to the
application of the sodium hypochlorite. Thus, available data from the cyanide spill in
Kyrgyzstan provides an incomplete picture of the toxic forms of cyanide potentially
present at the spill site.
CONCLUSION
While much of the cyanide present in mining-related waters breaks down into largely
harmless compounds, significant concentrations of other potentially toxic cyanide
breakdown compounds may persist. These compounds present the most risk to sensitive fresh
water fish species. Such compounds include many metal-cyanide complexes, cyanates,
thiocyanates, cyanogen, cyanogen chloride, chloramines, ammonia, and nitrate.
Gaps in Standards and Analysis
No regulatory standards exist for most of these potentially toxic constituents, with the
exception of ammonia and nitrate. Most state and federal agencies require mining-related
water samples to be analyzed using either the WAD or total cyanide methods only. Neither
method detects the majority of the cyanide-related compounds likely to be present at a
mine site. A tailings or heap leach pad water sample can easily have a WAD cyanide
concentration of less than 0.05 mg/L, and still contain concentrations of cyanate or
thiocyanate that are potentially toxic to fish.
Risks in Developing Countries
Not only are there gaps in U.S. water quality regulations pertaining to cyanide and
related compounds, but even more substantial problems exist in developing countries in
Africa, Asia, and Latin America. Here, mine contaminated rivers may be used as a source of
drinking water. In many developing countries, oversight and enforcement of mining
regulations are often quite lax, and mining operations are often owned, at least partly,
by the government, creating regulatory conflicts of interest. Thus, reasonable enforcement
of cyanide-related regulations becomes even more difficult.
REFERENCES
American Public Health Assoc., 1995, Standard Methods for the Examination of Water and
Wastewater, 19th edit., Amer. Publ. Health Assn., Washington. D. C.
Colorado Dept. of Natural Resources, Nov.1997, Guidelines for the Characterization,
Monitoring, Reclamation and Closure of Cyanide Leaching Projects-" Cyanide Guidelines
for Colorado," Draft, in press: Colo. Div. of Mines and Geology, Denver, CO.
Doudoroff, P. ,1976, Toxicity to fish of Cyanides and Related Compounds: a review. U.S.
EPA, Office of Research and Development, Duluth, Minn., 155p.
Eisler, R., 1991, Cyanide Hazards to Fish, Wildlife, and Invertebrate: A Synoptic Review:
Contaminant Hazard Review report 23, U. S. Dept. Interior, Fish and Wildlife Service,
55pg.
Flynn, C. M. and S. M. Haslem, 1995, Cyanide Chemistry-Precious Metals Processing and
Waste Treatment: U. S. Bureau of Mines Information Circular 9429; 282 pg.
Heming, T., R.V. Thurston, E. L. Meyn, and R. Zajdel, 1985, Acute Toxicity of Thiocyanate
to Trout: Trans. Am. Fish Soc., V.114, p. 895-905.
Heming, T. and R.V. Thurston,1985, Physiological and Toxic Effects of Cyanides to Fishes:
a Review and Recent Advances, in Cyanide and the Environment, Proc. of a Conf., D. Van Zyl
(ed.), Dec. 1984,Colo. State Univ., Ft. Collins.CO, Geotechn. Engineering Program, Dept.
Civil Engineering, v. 1, p 85-104.
Heming, T. A. and K. A. Blumhagen, 1989, Factors Influencing Thiocyanate Toxicity in
Rainbow Trout Salmo gairdneri: Bull. Environ. Contam. Toxicol. V. 43, p. 363-369.
Ingles, J. and J. S. Scott, 1987, State-of -the-Art Processes for the Treatment of Gold
Mill effluents: Industrial Programs Branch, Environment Canada, Ottawa,ON.
Palmes, John, 1991, Cyanide: A Review of Literature on the Toxicity of Cyanide to Fish and
Wildlife Related to Its Use in Mining: Alaska Dept. of Fish and Game, unpublished internal
document, available at: Alaska Dept. of Fish and Game, Habitat Div., P.O. Box 25526,
Juneau, AK 99802 , p.47-57.
Plumlee, G. S., K. Smith, E. Mosier, W. Ficklin, M. Montour, P. Briggs, and A. Meier,
1995, Geochemical Processes Controlling Acid-Drainage Generation and Cyanide Degradation
at Summitville: in Proc., Summitville Forum, Colo. Geological Survey Special Publication
38, p. 23-34.
Scott, J. S. and J. Ingles, 1981, Removal of Cyanide From Gold Mill Effluents: Proc.,
Canadian Mineral Processors Thirteenth Ann. Mtg., Jan. 1981, Ottawa, ON.
Smith, A. and T. Mudder, 1993, The Environmental Geochemistry of Cyanide: in Reviews in
Economic Geology, V. 6, Soc. of Economic Geologists, G. S. Plumlee and M. H. Logsdon
(eds.).
Stanton M. D.; T. A. Colbert; and R. B. Trenholme, 1986, Environmental Handbook for
Cyanide Leaching Projects: U.S. National Park Service, 57 pg.
U. S. Environmental Protection Agency, 1986, Quality Criteria for Water 1986: U.S.EPA,
Office of Water Regulations and Standards, Washington, D.C.
ACKNOWLEDGEMENTS
Mineral Policy Center and Dr. Moran would like to thank the following individuals who
reviewed various drafts of this report: Glenn Miller, Ph.D., University of Nevada at Reno,
Reno, Nevada; David Chambers, Ph.D., Executive Director of Center for Science in Public
Participation, Bozeman, Montana; Tom Hemming, Ph.D., Associate Professor, Marine
Biomedical Institute, Galveston, Texas; and Carolyn Harper, Ph.D., Agency for Toxic
Substances and Disease Registry, Atlanta, Georgia.
ABOUT THE AUTHOR
Robert Moran, Ph.D., is a geochemical and hydrogeological consultant with more than 26
years of domestic and international experience in conducting and managing projects for
private investors, industrial clients, tribal and citizens’ groups, non-governmental
organizations, law firms, and governmental agencies. Much of his technical expertise
involves the water quality and geochemistry of natural and contaminated waters and
sediments as related to mining, nuclear fuel cycle sites, industrial development,
geothermal resources, hazardous wastes, and water supply development. In addition, Dr.
Moran has significant experience in the application of remote sensing to natural resource
issues, development of resource policy, and litigation support. He has been employed by
the U.S. Geological Survey, Water Resources Division, several consulting firms, and as a
private consultant. He has worked in Senegal, Guinea, Gambia, Oman, Pakistan, Mexico,
Peru, Chile, Canada, and the United States. Dr. Moran received his doctorate from the
University of Texas, Austin. He can be reached via the internet at remoran@aol.com.
MINERAL POLICY CENTER
Mineral Policy Center (MPC) is a non-profit environmental organization dedicated to
protecting communities and the environment from the impacts of irresponsible mining. The
Center’s programs and activities include mining-related research and public outreach;
advocacy of regulatory and legislative reform of mining laws; and technical assistance and
community organizing. MPC’s work is supported by our membership, private donations,
and foundation grants. Join MPC, and help protect our land, water, wildlife, and natural
resources for future generations. Donations are tax deductible. Mineral Policy
Center’s main office is located at 1612 K Street, N.W., Suite 808, Washington, D.C.
20006. Tel: 202-887-1872; Fax: 202-887-1875; E-mail: mpc@mineralpolicy.org. Visit our homepage at www.mineralpolicy.org. The Center has regional
offices in Durango, Colorado, and Bozeman, Montana.
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