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OCR for page 3427
Proc. Natl. Acad. Sci. USA
Vol. 96, pp. 3427-3431, March 1999
Colloquium Paper
This paper was presented at the National Academy of Sciences colloquium "Geology, Mineralogy, and Human Welfare,"
held November 8-9, 1998 at the Arnold and Mabel Beckman Center in Irvine, CA.
Health impacts of domestic coal use in China
ROBERT B. FINKELMAN*T, HARVEY E. BELKIN*, AND BAOSHAN ZHENG:L
*U.S. Geological Survey, Mail Stop 956, Reston, VA 20192; and "Institute of Geochemistry, Guiyang, Guizhou Province, People's Republic of China 55002
ABSTRACT Domestic coal combustion has had profound
adverse effects on the health of millions of people worldwide.
In China alone several hundred million people commonly
burn raw coal in unvented stoves that permeate their homes
with high levels of toxic metals and organic compounds. At
least 3,000 people in Guizhou Province in southwest China are
suffering from severe arsenic poisoning. The primary source
of the arsenic appears to be consumption of chili peppers dried
over fires fueled with high-arsenic coal. Coal samples in the
region were found to contain up to 35,000 ppm arsenic. Chili
peppers dried over high arsenic coal fires adsorb 500 ppm
arsenic on average. More than 10 million people in Guizhou
Province and surrounding areas suffer from dental and
skeletal fluorosis. The excess fluorine is caused by eating corn
dried over burning briquettes made from high-fluorine coals
and high-fluorine clay binders. Polycyclic aromatic hydrocar-
bons formed during coal combustion are believed to cause or
contribute to the high incidence of esophageal and lung
cancers in parts of China. Domestic coal combustion also has
caused selenium poisoning and possibly mercury poisoning.
Better knowledge of coal quality parameters may help to
reduce some of these health problems. For example, informa-
tion on concentrations and distributions of potentially toxic
elements in coal may help delineate areas of a coal deposit to
be avoided. Information on the modes of occurrence of these
elements and the textural relations of the minerals and
macerate in coal may help predict the behavior of the poten-
tialb toxic components during coal combustion.
The U.S. Environmental Protection Agency (EPA) recently
issued a report to Congress on the health impacts of 189
potentially hazardous air pollutants (HAPs) emitted from
coal-burning electric utility generators (1~. In this report the
EPA concludes that, with the exception of mercury, there is no
compelling evidence to indicate that trace element emissions
cause human health problems. The absence of detectable
health problems is, in part, caused by the fact that the coals
burned in the U.S. generally contain low to modest concen-
trations of HAP elements and that many coal-burning utilities
use sophisticated pollution control systems that efficiently
reduce the emissions of HAPs (2~.
Such is not the case in many developing countries, especially
in homes where coal is used for heating and cooking. Domestic
use of coal can present serious human health problems because
the coals generally are mined locally with little regard to their
composition, and the coals are commonly burned in poorly
vented or unvented stoves, directly exposing residents to the
. .
emissions.
This paper briefly describes health problems believed to be
caused by, or exacerbated by, trace elements or organic
compounds emitted during domestic combustion of coal.
Although the examples used to illustrate these problems are
taken from China, people in many other developing and
PNAS is available online at www.pnas.org.
undeveloped countries use coal in a similar way and may suffer
from similar health problems.
China is the world's largest coal producer and coal con-
sumer. Coal production has increased steadily during the past
25 years to nearly 1.4 billion metric tons in 1996 (5~. In contrast
to most developed countries, such as the U.S., where domestic
coal use constitutes a small fraction of 1% of coal consump-
tion, a substantial portion of China's coal is used for domestic
energy needs. Smith and Liu (3) estimate that worldwide 330
million people rely on coal for domestic energy needs and as
many as 2.5-3 billion people are using even poorer-quality
biomass fuels. However, Florig (4) estimates that more than
75% of China's primary energy needs are supplied by domestic
coal. Coal stoves and small coal boilers provide more than 50%
of the energy for urban households and 22% of rural house-
holds rely on coal (4~. About 70 percent of the population in
China resides in rural areas, thus Florig's data would indicate
that about 400 million people in China rely on coal for their
domestic energy needs.
Health Problems Caused by Trace Element Emissions
Wood had long been the primary source of energy in southwest
China, but by the early part of this century the forests were
largely denuded and the residents were forced to seek other
sources of fuel. In southwest Guizhou Province (Fig. 1),
surface exposures of coal are plentiful, and coal quickly
became the primary fuel for domestic use. Unfortunately,
some of these coals have undergone mineralization, causing
their enrichment in potentially toxic trace elements such as
arsenic, fluorine, mercury, antimony, and thallium.
Burning the mineralized coals in unvented stoves volatilizes
the toxic elements and exposes the local population to the toxic
elements in the emissions. The situation is exacerbated by the
practice of drying crops directly over the coal fires. In the
autumn it is commonly cool and damp in the higher elevations
of Guizhou Province. It is common practice for the residents
of this region to dry their corn and chili peppers directly over
the burning coals.
Arsenic. Chronic arsenic poisoning, which affects at least
3,000 people in Guizhou Province, has been described by
Zheng and others (6~. Those affected exhibit typical symptoms
of arsenic poisoning, including hyperpigmentation (flushed
appearance, freckles), hyperkeratosis (scaly lesions on the skin,
generally concentrated on the hands and feet), Bowen's dis-
ease (dark, horny, precancerous lesions of the skin: Fig. 2), and
squamous cell carcinoma.
Zheng and others (6) have shown that chili peppers dried
over open coal-burning stoves may be a principal vector for the
arsenic poisoning. Fresh chili peppers have less than 1 ppm
arsenic. In contrast, chili peppers dried over high-arsenic coal
fires can have more than 500 ppm arsenic. Significant amounts
Abbreviations: SEM, scanning electron microscope; EDS, energy-
dispersive x-ray analyzer.
TTo whom reprint requests should be addressed. e-mail: rbf@usgs.gov.
3427
OCR for page 3428
3428 Colloquium Paper: Finkelman et al.
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Proc. Natl. Acad. Sci. USA 96 (1999J
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Arsenism and Fluorosis
Fluorosis
[mm Respiratory Problems
~ .
ano uorosis
~ Respiratory Problems
* Selenosis
FIG. 1. Map of China indicating provinces in which there are reported health problems caused by domestic coal combustion.
Of arsenic also may come from other tainted foods, ingestion
of dust (samples of kitchen dust contained as much as 3,000
ppm arsenic), and from inhalation of indoor air polluted by
arsenic derived from coal combustion. The arsenic content of
drinking water samples was below the Environmental Protec-
tion Agency's drinking water standard (7) of 50 ppb and does
not appear to be an important factor.
Detailed chemical and mineralogical characterization of the
arsenic-bearing coal samples from this region recently was
conducted by Belkin and coworkers (8-10~. They analyzed
about 25 coal samples that they had collected from several
locations within Guizhou Province. Instrumental neutron ac-
tivation analyses of the coal indicate arsenic concentrations as
high as 35,000 ppm. The magnitude of this concentration can
be seen by comparison with U.S. coals. The mean concentra-
tion for arsenic in nearly 10,000 U.S coal samples is approx-
imately 22 ppm, with a maximum value of about 2,000 ppm
(11~.
Belkin and coworkers (8-10) examined polished blocks of
the coal by using a scanning electron microscope (SEM)
equipped with energy-dispersive x-ray analyzer (EDS) and an
electron microprobe (EMP). They observed a wide variety of
As-bearing mineral phases in the coal samples. Pyrite is the
most common sulfide, occurring as framboids, euhedral crys-
tals, and irregular shapes. The range of As in pyrite determined
by EMP analyses is from the detection limit (~100 ppm) in
unaltered framboids to about 4.5 weight percent in grains
adjacent to arsenopyrite crystals. Arsenopyrite occurs in a
variety of habits, including large 150- to 250-,um crystals,
narrow, 1- to 5-,um veins, and small crystals (Fig. 3A). Sele
nium contents in arsenopyrite are fairly uniform (0.15 to 0.2
weight percent). A third As-bearing sulfide, composed of As,
Pb, and S. is present rarely.
Another group of As-bearing minerals contains arsenic in
the 5 + valence state as arsenate commonly substituting for the
phosphate group. An unidentified As-bearing iron phosphate,
usually associated with banded iron oxide (Fig. 3B), as veins or
masses has a P/As ratio on the order of 4. Jarosite
~K2Fe63+(SO444(OH)~2] was present as an alteration product of
sulfides or as mixtures with iron oxide and commonly con-
tained a few weight percent As. An additional As-rich phase
was observed only as scattered micron-sized grains that con-
tained only Fe and As (+O), as identified by SEM-EDS. The
atomic ratio of Fe/As in this mineral is about 1 and the mineral
may be scorodite, FeAsO4 2H2O.
Some coals display evidence of movement of epigenetic
fluids and show primary phases and their alteration products.
One sample examined by Belkin and coworkers (8-10) showed
a complete range of diagenetic, low-As framboids that
progresses through various stages to framboid pseudomorphs
composed totally of As-bearing iron oxide (SEM-EDS and
reflected light indicates hematite). Veins of jarosite, arsenopy-
rite, and iron oxide are common in some samples.
Three samples from the same location had As concentra-
tions in excess of 3 weight percent and were mineralogically
unusual. Although they contain small grains and veins of
arsenopyrite and As-bearing pyrite, the concentration of these
phases is completely inadequate to account for the As abun-
dance on a whole coal basis. However, in SEM back-scattered
electron images, a distinct banding characterized by differing
OCR for page 3429
Colloquium Paper: Finkelman et al.
FIG. 2. Extensive scaly lesions (hyperkeratosis) are evident on the
chest of a resident of this region. The dark spot over the left breast was
diagnosed as Bowen's disease.
image brightness is easily observed (Fig. 3C). Some of this
banding forms box-like arrangements, but in all cases the bands
appear to have sharp edges. The bands range from a few ,um
to tens and a few hundreds of ,um in thickness. SEM-EDS
results show that these bright bands are highly enriched in As
{Fin And Thev Alice contain S. Fe, and traces of Al and Si
(,u m-sized clay particles). In fact, there is a relationship
between the EDS count intensity for As and apparent bright-
ness of the SEM image. Semiquantitative analysis by SEM-
EDS demonstrate that the bright bands contain As at levels ~3
weight percent. Fe concentrations in the bands are low but
always present at levels from 0.2 to 0.4 weight percent, S is the
only other major element found. By using an SEM, no discrete
As-bearing phases could be resolved in these bands at 50,000
times magnification. Thin fragments of one sample were
examined by an advanced field-emission transmission electron
microscope. No discrete As-bearing phase could be observed
by using this instrument at magnifications of 1 million times.
Thus, finely dispersed arsenopyrite, As-bearing pyrite, or any
other As-phase can be ruled out as the source of the As.
To define the nature of bonding in the arsenic-bearing
phases, a reconnaissance study of two high-arsenic samples was
conducted by using high-energy x-rays from a synchrotron
source (12~. Collection of diffraction spectrum intensity across
the XANES (x-ray absorption near-edge structure) and
EXAFS (extended x-ray absorption fine structure) regions of
an absorption spectrum can provide three-dimensional infor-
mation on the electronic state and chemical coordination for
~- -D' -- J' ~
PrOC. Natl. ACad. SCi. USA 96 (1999) 3429
each crystallographic site of the chosen element. Results from
this work demonstrate that ~100% of the As in one sample is
As043- and that about 75% of the As in the other sample is
AsO43- with the balance (25%) as sulfide-bound As. Thus, for
the two coals examined, the preponderance of the As is in the
5+ valence state.
An interesting and potentially important relationship exists
between arsenic and gold. Southwest Guizhou Province con-
tains numerous gold mines and deposits that have been
identified as Carlin-type gold deposits (134. Carlin-type de-
posits are characterized by very fine-grained gold (generally
less than 1 Em) and are associated with arsenic, antimony,
mercury, and thallium. In Carlin-type deposits of the Great
Basin region of Nevada, the sedimentary host rock is usually
rich in organic matter. The Guizhou Province deposits also
contain thallium and mercury (14-16~. Ashley and others (13)
concluded that the Chinese and Great Basin deposits formed
from low-salinity fluids at relatively low temperatures. Li and
Peters (17), using fluid inclusion data, indicate that the
Guizhou fluids ranged in temperature from 150°C to 240°C,
comparable to the U.S. occurrences. It is geologically reason-
able to assume that the introduction of arsenic into the coal
strata is related to gold mineralization, although the exact
mechanism is uncertain.
Mineralogical characterization of the coals from Guizhou
Province may help elucidate the geologic process that created
the high-arsenic coals and the relationship of the high-arsenic
coals to the gold. Knowledge of these processes and relation-
ships may help determine the regional distribution of these
environmentally dangerous coals. Information on the arsenic
mineralogy also may help us to anticipate the behavior of
arsenic during coal combustion. Preliminary characterization
of residual ash in coal-burning stoves indicates high retention
of arsenic. Mineralogical characterization in conjunction with
combustion tests may determine whether one or more of the
arsenic-bearing phases is primarily responsible for adsorption
of arsenic on the chili peppers.
Fluorine. The health problems caused by fluorine volatilized
during domestic coal use are far more extensive than those
caused by arsenic (Fig. 1~. More than 10 million people in
Guizhou Province and surrounding areas suffer from various
forms of fluorosis (18, 19), and it also has been reported from
13 other provinces, autonomous regions, and municipalities
in China (20).
Typical symptoms of fluorosis include mottling of tooth
enamel (dental flurosis) and various forms of skeletal fluoro-
sis, including osteosclerosis, limited movement of the joints,
and outward manifestations such as knock knees, bow legs, and
spinal curvature. Fluorosis combined with nutritional deficien-
cies in children can result in severe bone deformation (Fig. 4~.
The etiology of fluorosis is similar to that of arsenism in that
the disease is derived from foods dried over coal-burning
stoves. Zheng and Huang (18) have demonstrated that ad-
sorption of fluorine by corn dried over unvented ovens burning
high (>200 ppm) fluorine coal is the probable cause of the
extensive dental and skeletal fluorosis in southwest China. The
mode of occurrence of fluorine in the coal is unknown. The
problem is compounded by the use of clay as a binder for
making briquettes. The clay used is a high-fluorine (mean
value of 903 ppm) residue formed by intense leaching of a
limestone substrate. Ando and others (20) determined fluo-
rine contents of coals from two mines (559 and 802 ppm) and
in the associated soils (592 and 669 ppm). They estimated that
97% of the fluoride exposure came from food consumption
and 2% from direct inhalation. Zhang and Cao (19) report
mean fluorine levels in coals from 11 regions in China to range
from 203 to 1,513 ppm with a maximum value of 3,762 ppm.
Mercury. There is also considerable concern about the
health effects of mercury and the proportion of anthropogenic
mercury in the environment (21~. So far, there is no direct
OCR for page 3430
3430 Colloquium Paper: Finkelman et al.
Proc. Natl. Acad. Sci. USA 96 (1999J
-' ' ~.,.~,~.~ . ., i . .. ~ ~ ,,, . _
_ _
FIG. 3. (A) SEM back-scattered electron image of polished coal showing a pyrite grain (P) and adjacent arsenopyrite crystals (A). (B) SEM
back-scattered electron image of polished coal showing the deposition of a banded complex of iron oxide and As-bearing iron phosphates. (C) SEM
back-scattered electron image of polished block of arsenic-rich coal. Dark areas are coal, bright areas are mainly pyrite, milky area is coal containing
organically bound arsenate. F1UidS moving through the fracture in the coal appears to have removed arsenic from the organic matrix. (D) X-ray
map depicting the distribution of arsenic in the coal. Red areas are high concentrations, and blue areas are low concentrations. Compare distribution
of arsenic to the outline of the milky area in C. A-C originally appeared in ref. 9 and are republished with the permission of the Pittsburgh Coal
Conference.
evidence of health problems caused by mercury released from
coal but there are circumstances where poisoning from mer-
cury released from coal combustion may be occurring. Zhou
and Liu (22) reported on chronic thallium poisoning in
Guizhou Province, China, where the source of the thallium
poisoning appears to be from vegetables grown on a mercury/
thallium-rich mining slag. Most symptoms, such as hair loss,
are typical of thallium poisoning. However, loss of vision in
several patients from this region was considered to be unique
(R. Dart, personal communication). Mineralogical analysis of
the coal being used in the homes of people having visual
impairment revealed abundant mercury minerals. Chemical
analysis of a coal sample being used in Guizhou Province,
China, indicates a mercury concentration of 55 ppm, which is
about 200 times the average mercury concentration in U.S.
coals.
Selenium. Zheng and others (23) report nearly 500 cases of
human selenosis in southwest China that are attributed to the
use of selenium-rich carbonaceous shales known locally as
FIG. 4. Bone deformation caused by nutritional deficiency com-
bined with exposure to high levels of fluorine from domestic coal
combustion.
OCR for page 3431
Colloquium Paper: Finkelman et al.
"stone coal." The stone coals have as much as 8,390 ppm
selenium. This selenosis is attributed to the practice of using
combustion ash as a soil amendment. This process introduced 7
large amounts of selenium into the soil and resulted in
selenium uptake by crops. Symptoms of selenium poisoning
include hair and nail loss.
Organic Compounds. Esophageal cancer is a common fatal
cancer and the fourth-leading cause of cancer death in China.
Parts of Henan Province in north-central China (Fig. 1) have
some of the highest rates of esophageal cancer in the world,
with annual age-adjusted mortality rates of up to 169 per
100,000 and cumulative death rates of over 20% by age 75 for
both sexes (24~. Many studies have been carried out on the high
incidence of esophageal and lung cancers in China, but the
dominant causative agents of the cancer remain unclear.
Polycyclic aromatic hydrocarbons (PAHs) released during
unvented coal combustion in homes in China, have been cited
as the primary cause for the highly elevated incidence of lung
cancer (25~. The PAH levels in homes burning "smoky" coal
are so high that the resulting lung cancer mortality rate is five
times the national average of China (26~. 13.
Conclusions
A better knowledge of coal quality parameters may help to
minimize some of the health problems caused by domestic coal
use. Information on the concentrations and distributions of
potentially toxic elements in coal may assist people dependent
on local coal sources to avoid those areas of a coal deposit
having undesirably high concentrations of toxic compounds.
Information on the modes of occurrence of potentially toxic
elements and the textural relations of the minerals and mac-
erals in which they occur may help us to anticipate the behavior
of the potentially toxic components during coal cleaning,
combustion, weathering, and leaching. Coal characterization
offers geoscientists opportunities to directly contribute im-
proved public health.
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Representative terms from entire chapter:
coal combustion
