Pergamon
PII: S0003-4878(98)00020-9
Ann occup H\f , Vol 42. No 3, pp 173-189, 1998
© 1998 British Occupational Hygiene Society
Published by Ebevjer Science Ltd. All nghts reserved
Printed in Great Britain
0003-^»878/98 SI9 0 0 + 0 00
Exposures in ttlne Aknmniiinia aimd P r i m a r y AMmrnnimiaDinni
sum Historical Review
GEZA BENKE,* MICHAEL ABRAMSON and MALCOLM SIM
Department of Epidemiology and Preventive Medicine, Monash Medical School, Alfred Hospital,
Prahran, Victoria 3181, Australia
We reviewed specific chemical exposures and exposure assessment methods relating to published
and unpublished epidemiological studies in the alumina and primary aluminium industry. Our
focus was to review limitations in the current literature and make recommendations for future
research.
Although some of the exposures in the smelting of aluminium have been well characterised,
particularly in potrooms, little has been published regarding the exposures in bauxite mining and
alumina refining. Past epidemiological studies in the industry have concentrated on the smelting
of aluminium, with many limitations in the methodology used in their exposure assessment.
We found that in aluminium smelting, exposures to fluorides, coal tar pitch volatiles (CTPV)
and sulfur dioxide (SO2) have tended to decrease in recent years, but insufficient information
exists for the other known exposures. Although excess cancers have been found among workers
in the smelting of aluminium, the exposure assessment methods in future studies need to be
improved to better characterise possible causative agents. The small number of cohort studies has
been a factor in the failure to identify clear exposure-response relationships for respiratory
diseases. A dose-response relationship has been recently described for fluoride exposure and
bronchial hyper-responsiveness, but whether fluorides are the causative agent, co-agent or simply
markers for the causative agent(s) for potroom asthma, remains to be determined.
Published epidemiological studies and quantitative exposure data for bauxite mining and alumina
refining are virtually non-existent Determination of possible exposure-response relationships for
this part of the industry through improved exposure assessment methods should be the focus of
future studies. © 1998 British Occupational Hygiene Society. Published by Elsevier Science Ltd.
INTRODUCTION
The alumina and primary aluminium industry consists
of the mining of bauxite, the refining of the ore to
extract alumina (A12O3) and the electrolytic reduction
of the alumina to produce aluminium. The production
processes in the industry were discovered over 100
years ago and result in a large number of substances
(and mixtures) to which the workforce may be
exposed. The large number of exposures, coupled with
often crude methods used to characterise exposure,
has resulted in most epidemiological studies failing to
establish clear exposure-response relationships
between specific workplace chemicals and morbidity
or mortality. Other contributing factors include the
presence of chemical mixtures in the workplace and
ill-defined health outcomes.
As part of a series of epidemiological studies (Hearthwise) of cancer and respiratory disease in the alumina
Received 23 October 1997; in final form 5 February 1998.
*Author to whom correspondence should be addressed.
and primary aluminium industry, we reviewed the
published and available unpublished literature of
specific chemical exposures in the industry. Our focus
was the exposure methods used in previous epidemiological studies, together with the reported quantitative exposures, with the aim of using these data to
develop improved methods for the Hea/thwise studies.
This review should also benefit hygienists working in
the industry, to familiarise them with past and current
research needs.
There have been a number of reviews which address
the health effects and/or exposures from working in
aluminium smelters (Enterline, 1977; Simonato, 1981;
IARC, 1984; Gilson, 1986; Abramson el al., 1989;
Rjanneberg and Landmark, 1992; Kongerud et al.,
1994). However, recent advances in exposure assessment and recently published epidemiological studies
were not included in these reviews. Conversely, the
mining of bauxite and the refining of alumina have
been the subject of very few epidemiological studies
(Townsend et al., 1985; Townsend et al., 1988), with
no published reviews of this literature. Since a meta173
174
G. Benke el al
analysis of the chemical exposures in the primary
aluminium industry would be limited by the imprecision of the exposure data, highly variable quality
and differing designs of the epidemiological studies, a
semi-systematic review is presented here. This review
has been primarily based upon MEDLINE (National
Library of Medicine, National Institute of Health,
Bethesda, MD) searches and the collation of both
published and unpublished literature assembled by
the authors, some of which were not available in the
English language.
In this review, we have confined ourselves in particular to the exposures of bauxite dust, alumina, caustic mist, fluorides, coal tar pitch volatiles (CTPV),
sulfur dioxide and other dusts. Our aim was to demonstrate the limitations in exposure characterisation
in the current literature and to suggest directions for
future research. The methods used in previous epidemiological studies to assess exposure and quantify
exposure levels were reviewed, to assist with the design
of future studies by epidemiologists, and exposure
assessment by hygienists.
PROCESSES AND CHEMICAL EXPOSURES
Bauxite mining
The first production process in the alumina industry
is the open-cut mining of bauxite ore, which contains
40-60% alumina (A12O3), with iron and titanium
oxides (Fe2O3 and TiO2) and crystalline silica (SiO2).
Bauxite ore deposits are usually located near the earth's surface, and may have a high moisture content,
up to 50% water by volume. Depending upon the
geographical location of the mine, the ore may contain
up to 8% SiO2 (Burgess, 1981). Bauxite dust exposure
can occur with breaking of the crust, dragline stripping and transport of the ore to its eventual crushing.
Dust exposure may also occur to operators if the ore
requires drying and when it is loaded on the trucks,
conveyor belts or ships, for transport to a refinery.
Another chemical exposure commonly encountered
by bauxite mine workers is diesel fumes. However, by
the mid 1980s, most vehicle cabins in bauxite mines
were enclosed and ventilated, considerably reducing
dust and diesel fume exposure.
Bauxite mines are similar to other surface mining
operations in that they involve up to 50% of the
workforce in maintenance activities. The maintenance
work primarily involves the repair of mine vehicles,
crushers and conveyor belt systems. As a result,
exposures similar to mechanical repairers in other
industries can be encountered, eg exposures to oils
and greases, welding fumes, diesel fumes and asbestos.
Alumina refining
The refining of bauxite ore to produce alumina
(A12O3), is undertaken predominantly by the Bayer
refining process. The details of the process are
described elsewhere (Burkin, 1987) and only an overview will be given here. Importantly, the Bayer process
involves constant recycling of energy, with heat
exposure to the workers occurring throughout the
process. There are basically five stages in the refining
process:
o
o
o
o
o
Crushing
Digestion
Clarification
Precipitation
Calcination
With the crushing stage, the bauxite is handled dry
and is crushed in either ball or rod mills. Bauxite dust
is the primary exposure at this stage. In the digestion
stage, a slurry is formed from the ground and blended
bauxite, then caustic soda (NaOH) is added, digesting
the slurry to form the 'green' liquor, containing
sodium aluminate solution. Digestion occurs under
controlled temperatures of 200°C and pressures
greater than 3 atmospheres. The important environmental exposure in this latter stage is the caustic,
which may be present either in liquid form or as a
mist. Bauxite dust is usually no longer of concern in
the latter stages of digestion, as it is a wet process, but
some exposure to sulfuric acid mist may occur during
cleaning of the numerous heat exchange systems in
this area of a refinery.
Clarification is a four step process and is basically
the purification of the green liquor. Firstly there is the
removal of the coarse fraction, then the liquor is
passed through thickeners, washed and cooled. In the
areas of the refinery where clarification is undertaken,
exposure to caustic mist is the main exposure. The
hydrated alumina is precipitated in the precipitation
area of the refinery. Here the filtered green liquor is
cooled, then passed through aluminium hydrate
seeded precipitation tanks. Caustic mist remains the
main environmental exposure in the precipitation
area. The final step in the Bayer process is calcination,
which involves the removal of the water from the
alumina hydrate. Following horizontal vacuum filtering, the hydrated alumina is heated to 1000°C in
rotary kilns or calciners. Exposure may occur to alumina dust, which appears as a white powder, if effective dust control measures are not in place.
Maintenance workers in refineries may be exposed
to all the environmental contaminants above, as well
as welding fumes, asbestos (depending upon the
location of the refinery, this could be amosite or
chrysotile) and synthetic mineral fibres (SMF). In
refineries predating 1970, asbestos was often extensively used for pipe-lagging and heat insulation. Many
miles of asbestos pipe lagging may have been installed,
with its replacement by SMF slowly occurring in many
refineries in the 1980s and 1990s.
Aluminium smelting
High-quality alumina is transported to the receiving
smelter for extraction of the aluminium metal. The
Hall-Heroult electrolysis process for the reduction of
alumina to the metal has been described in detail else-
Exposures in the alumina and primary aluminium industry
where (Burkin, 1987), and only an overview is presented here. The Hall-Heroult process takes place
in carbon-lined steel vessels called pots, where the
alumina is partially dissolved in an electrolyte of
molten cryolite (Na3AlF6) at approximately 960°C.
Pots have an anode (made of petroleum coke bound
with a coal-tar pitch binder) and a cathode and typically operate at currents of 12 to 200 kA at 4-6 volts.
Pots may be of two types, Saderberg or prebake,
depending upon how the anodes are produced. The
older Soderberg process is cheaper and involves the
baking of the anode paste in situ, using heat produced
in the electrolytic process. Various Saderberg pot
designs have been built, with the two most common
designs being the 'Vertical stud' and 'Horizontal stud'
types. However, due to the difficulties encountered
in the control of environmental factors in Sederberg
smelters, the prebake process is the preferred process
in modern smelters. This involves the production of
the anodes in an area of the smelter, distinct from the
potrooms. In the 'Anodes' or 'Electrodes' area, the
green anode blocks are formed with coke, pitch and
spent (recycled) anode butts. The mixture usually
involves about 15% pitch. They are then sintered at
temperatures over 1000°C in sub-surface baking facilities for a few days then cooled. Finally before transport to the potrooms, the baked anodes are fixed in
the rodding room with a steel stub and conducting
rod made of copper or aluminium.
Since aluminium production is a continuous
process, the crust, which forms above the molten aluminium in the pot, is periodically broken and the
aluminium is tapped off. The hooding configuration
to collect the pollutants is dependent upon the type of
cell, i.e. prebake or Sederberg, and is generally more
efficient in prebake potrooms. However, because the
hoods in the prebake potrooms need to be removed
periodically, there exists a greater likelihood of high
transient peak exposures to dusts and gases. The
molten aluminium is then transported to the casting or
ingot plant where ingots, billets or pigs of aluminium
alloys and high grade aluminium are cast. Many smelters undertake aluminium alloy production, which
requires metal purification by fluxing with chlorine
gas. Intermittent exposures to HC1 gas may occur
during 'dross' skimming. Casting may also involve
exposures to fluorides, ammonia, metal chlorides and
metal oxides. Historically, asbestos was used for lining
and insulation applications in cast houses, but asbestos removal programs in many countries have minimised this exposure in recent years.
A list (which is not exhaustive) of 26 environmental
exposures that may be encountered in aluminium
reduction, has been reported (Walker, 1978). It is
important to realise that chemical exposures to dusts
and fumes in a potroom generally occur as mixtures
and often simultaneously, i.e. pot fume emissions may
contain polycyclic aromatic hydrocarbons (PAHs),
fluoride compounds from the cryolite (in both gaseous
and particulate form), aluminium fluoride, various
175
particulates and gases eg fibrous sodium aluminiumtetrafluoride particles (Gylseth et al., 1984; Hjortsberg
et al., 1986), fluorspar (CaF,), alumina, sulphur dioxide, carbon monoxide, carbon dioxide and trace metals eg vanadium, chromium and nickel. Other ubiquitous exposures in a smelter can include asbestos fibres,
both serpentine and amphibole (Dufresne et al., 1996).
Fig. 1 summarises the possible exposures in bauxite
mines, alumina refineries and aluminium smelters.
REPORTED EXPOSURE LEVELS
There have been many epidemiological studies and
technical reports which have reported on exposure
levels of the various contaminants listed in Fig. 1. In
this review, MEDLINE and the ACGIH (American
Conference of Governmental Industrial Hygienists)
(ACGIH, 1991 and ACGIH, 1996) databases were
first searched for the exposures of interest i.e. bauxite
dust, caustic mist, alumina, fluorides, CTPVs, sulphur
dioxide, trace elements and particulates. The quantitative exposure levels have been cited directly from
the published papers and for each contaminant the
ACGIH Threshold Limit Value (TLV®) has been
stated for comparison purposes. In some cases, conversions from parts per million (ppm) to milligrams
per cubic metre (mg/m3), have been made. Where
possible, relevant exposure data from unpublished
studies have been included, but the following reported
exposure levels are not exhaustive.
Although exposures to dust and chemical agents in
bauxite mines and alumina refineries have not been
extensively published, there exists a substantial
amount of published quantitative exposure data from
smelters. Clearly, the technology and types of process
involved in a particular plant, ie prebake or Soderberg, presence of hooding and type of scrubbing systems etc., are strong determinants of quantitative
levels of exposure. Other factors such as sampling
protocol and equipment, sample analysis methods,
reporting protocols, the unique composition and
source of raw materials (ie bauxite, cryolite, coal tar
pitch, coke etc.), environmental factors during sampling (ie temperature of the working environment,
production volumes and processes, ventilation control
equipment) and work practices, can all influence
reported exposures.
Bauxite dust
Although the ACGIH does not list a TLV* for
bauxite dust, it is usually included under the term
'Paniculate Not Otherwise Classified' (PNOC). These
particulates were formerly known as 'nuisance dusts',
and although not biologically inert, were not on the
TLV* list due to the lack of evidence of specific toxic
effects. The current TLV^-Time Weighted Average
(TWA) for inhalable (total) PNOC is 10 mg/m3, and
the TLV*-TWA for respirable PNOC is 3 mg/m3.
Importantly, these limits only apply for PNOCs containing no asbestos and < 1 % crystalline silica. Since
G Benke el al
BAUXITE MINING
EXPOSURES
Bauxite dust
Diesel fumes
Oils and greases
Silica dust
Solvents
Welding fumes
ALUMINA REFINING
EXPOSURES
Alumina dust
Asbestos
Bauxite dust
Caustic (NaOH)
Sulfuric acid
Oxalate dust
ALUMINIUM SMELTING
Hydrogen fluoride
Ionising radiation
Nitrogen dioxide
Ozone
Solvents
Welding fumes
EXPOSURES
Alumina dust
Aluminium metal dust
Aluminium fluoride
Ammonia
Asbestos
Beryllium dust
Cadmium dust
Carbon monoxide
Chlorine gas
Chromium
Coal tar pitch volaliles
Coke dust
Copper dust
Vanadium
Hydrogen chloride
Hydrogen fluoride
Magnesium dust/fume
Mercury
Nickel
Fluorides (dust)
Lead
Ozone
Phosgene
Silica
Silica dusl
Sulfur dioxide
Trace elements
(Ni. V. Cr)
Welding fumes
Fig. 1 Chemical exposures in the primary aluminium industry
bauxite can contain up to 8% crystalline silica, the
TLV*-TWA for this dust exposure could be
O.lmg/m 3 , i.e. the same as quartz. No published
reports of bauxite dust exposure levels in mines and
refineries were found in the literature.
Caustic mist
The ACGIH TLV*-Ceiling for caustic mist
(NaOH) is 2mg/m 3 based on ocular and upper respiratory tract irritation. Although no published
reports of health effects from caustic mist exposure in
the primary aluminium industry were found in the
epidemiological literature, case reports of accidental
and suicidal poisoning with ingestion of sodium
hydroxide in the general community have been pub-
lished (Hawkins et al., 1980). The latter reports are
clearly due to acute ingestion of liquid caustic, but
two reports from outside the aluminium industry
(Hervin and Cohen, 1973; NIOSH, 1975), indicate
that chronic exposures to caustic mist among workers
involved in cleaning operations (where levels were
below 2 mg/m3) may cause noticeable nose and throat
irritation.
Alumina
The ACGIH TLV*-TWA inhalable (total) particulate for alumina (A12O3) is 10mg/m3 and is considered a PNOC. A report from Poland (AdamiakZiemba et al., 1977) involved measurements at two
Setderberg plants, Plant A with vertical stud pots and
Exposures in the alumina and primary aluminium industry
Plant B with horizontal stud pots. The geometric mean
alumina dust levels for area or static monitoring were
5.7mg/m3 in Plant A (N = 119) and 1.3mg/m3 in
Plant B (N = 90). Eduard and Lie (1981) reported
levels of 'recovery' alumina (alumina which has been
reacted with the recycled fluoride in the dry scrubbers)
and 'pure' alumina of 7.6mg/m 3 and 5.4mg/m3,
respectively. A later Polish study (Tomaszewski et al.,
1983) described alumina dust level exposures at the
shipping port of Gdynia. The Polish maximum allowable level of 2 mg/m3, was exceeded in four locations
by 7.8, 12.4, 5.1 and 2.1 fold respectively. It was not
stated whether these were area monitoring or personal
177
samples. Tomaszewski et al. (1983) reported that most
of this dust was found to be of respirable size. A
study by Townsend et al. (1985) did not report specific
location dust levels, but only cumulative levels ie
cumulative exposures of less than or greater than
lOOmg-years for more than 20 years.
Fluorides
Exposures to fluorides in aluminium smelters have
been extensively reported and are summarised in
Table 1 and Fig. 2. Caution is advised when comparing levels of exposure for different years since most
reports include exposure measurement levels that were
Table 1. Reported fluoride exposures in the primary aluminium industry (in mg/m3)
Author of report, Year
Gas
Particulate
Total
Agate, 1949
0.9
0.66
1.56
Glomme, 1960
0.75
2 35
3 1
Midttun, 1960
—
—
7-4
36%
50%
50%
—
2 4-3.0
3 0-4.0
4.0-6.0
1.64
0.36
0.5
0.86
0.32
0.5
0.82
Yazaki et al., 1979
Sane et al, 1979b
0.51
0 63
0 15
0.88
0.66
1 51
Clonfero et al, 1981
1 1
—
2.4
Chan-Yeung et al, 1983
0.7
02
0.28
1.3
0.48
EhrneborJa/, 1986
0.31
0.6
091
SanceJa/., 1986
0.56
0.15
071
0.1-1.0
0.2
0 21
0.25
041
0.31
Kongerud et al., 1990
Kongerud and Samuelsen, 1991
—
—
0.63
0.41—0 59
Kongerud and Seyseth, 1991
—
—
0.7
—
—
0.3
0.19
0.18
0.19
0.35
0.38
0.54
0.30-0.94
—
—
0.44
0.24-0.72
Kaltreider el al, 1972
Jahre/a/, 1974
Adammk-Zeimba, 1977
Martinez al., 1986
Chan-Yeung el al., 1989
Ursson et al., 1989
Kongerud and Rambjar, 1991
Seyseth and Kongerud, 1992
Sayseth et a!., 1994
Desjardins et al., 1994
Soyseth et al., 1997
Comments
Mean of 7 static monitoring samples in
furnace room A (prebake anodes) at Fort
William
Median concentration from 27 potroom
workers
'Normal working conditions' described as 1
to 2ppm.
Pot Tender)
Tapper-carbon changer) Prebake potrooms
Craneman )
Mean value (N = 9) of potroom atmosphere
in the Sederberg plant
Geometric means (N = 110) for Soderberg
Plant A
Geometric means (N = 77) for Sederberg
Plant B
Number of samples not given
Mean of personal samples from the
potrooms, N = 9
Mean levels (N = 28) in the potroom of the
Porto Marghera plant
Mean levels (N = 16) in the Fusina plant
Mean TWAs for potroom workers in high
exposure group (N = 157)
Mean of TWA for personal samples
(N = 41).
HF ranged from 0 17 to 1.72mg/m3; and
particulate fluorides ranged from 0.01 to
0.25 mg/m3
TWAs for prebake potroom workers
Mean TWAs for potroom workers (N = 54)
The mean TWA for 8 potroom workers with
the same type of work.
Average exposure in all potroom workers.
Mean exposure levels for total fluorides were
0.59 (1986), 0.47 (1987), 0.40 (1988) and
0.41 mg/m3 (1989).
Mean TWAs for pot operators on Prebake
line.
Mean TWAs for pot operators on
Soderberg line.
Median TWAs for potroom workers
TWAs from routine monitoring in potrooms
TWAs for workers on Prebake line were
0.94 (1986), 0.83 (1987), 0.71(1988) and
0.30 mg/m3 (1989).
TWA in prebake potroom
Median exposure levels were 0.72 (1986),
0.52 (1987), 0.37 (1988), 0.38 (1989), 0.35
(1990), 0.24 (1991) and 0.36 mg/m3 (1992).
1.78
G. Benke el al.
3.5
^^*\d!P^dPs#\dPN#\d^^«p'v
Fig 2 Reported total fluoride exposure levels in the primary aluminium industry (1949-1997)
undertaken many years prior to the publication date
of the epidemiological study or exposure assessment
report The current ACGIH TLV H -TWA for fluorides of 2.5 mg/m3 as total fluoride, is set to prevent
any irritant effects and bone changes. The early
reports (e.g. Agate el al, 1949) of fluoride exposure
were primarily concerned with fluorosis, but with the
introduction and establishment of technical improvements to reduce fluoride levels, more recent reports
have addressed respiratory morbidity. Some studies
only report 'total' fluoride (Kaltreider el al., 1972),
whereas others report both the particulate and gaseous fluoride components (Saric el al., 1979; ChanYeung el al., 1989; Seyseth and Kongerud, 1992:
Seyseth el al., 1994; Sayseth el a!., 1995). Agate el al
(1949) reported air concentrations ranging from 0 I
to 2.6 mg/m3 and Kaltreider el al. (1972) reported
levels ranging from 2.4 to 6.0 mg/m3. Seyseth el al
(1997) reported annual median total fluoride levels on
a yearly basis (1986-1992) in a smelter in Norway.
'Peak' fluoride gas exposures have not been reported
in the epidemiological literature due to the technical
difficulties in their measurement.
Biological monitoring of urinary fluorides has been
a common practice in most aluminium smelters for
many years. Summaries of extensive monitoring have
been reported (Kaltreider el al., 1972; Dinman el al.,
1976; IARC. 1984) and the current ACGIH Biological
Exposure Limit (BEI K ) for fluoride in urine is 3 mg/g
creatinine prior to a work shift and lOmg/g creatinine
end of shift.
Plasma fluorides (Ehrnebo and Ekstrand, 1986)
have only recently been reported and are considered
a more reliable measure of fluoride absorption than
are urinary fluorides. A BEI* for plasma fluorides has
not yet been set by the ACGIH, but fluorides have
been included on the list of substances under study
by the ACGIH, to establish or change the biological
exposure indices. A recent report of controlled HF
exposures in a chamber (Lund el al., 1997) showed a
strong relationship between inhaled HF and concentrations of fluoride in plasma of volunteers.
Coal Tar Pilch Volatile* (CTPV) and fractions
The current ACGIH T L V - T W A for CTPV, as
benzene soluble fraction, is 0.2 mg/m3 (200 /<g/m').
The volatiles contain many lower molecular weight
polycyclic aromatic hydrocarbons (PAHs) which sublime in the carbon bakes and potroom air. Higher
molecular weight PAHs, such as benzo-a-pyrene
(B[a]P), are left in the workers' breathing zone, indicating PAH exposure. Some of the earliest reliable
published data of pitch volatiles in aluminium
reduction facilities was a comparison of quantitative
TWA data for eastern and northwestern facilities in
the USA (Shuler and Bierbaum, 1974). These early
results indicated that the CTPV levels in Saderberg
potrooms (with either vertical pins or horizontal pins)
were significantly elevated compared to the prebake
potrooms, ie up to 18.5 mg/m3 in the horizontal pin
Sederberg potrooms compared to a maximum of
0.5 mg/m3 in the prebake potrooms. This is due to the
pyrolysis of the pitch volatiles that occurs during the
production of the prebake anodes in the anode plant.
Consequently, CTPV exposure in prebake potrooms
Exposures in the alumina and primary aluminium industry
is low but may be relatively high in the anode plant
of the smelter.
Early reports of PAH exposure levels in aluminium
reduction plants in Norway (Bjerseth el al., 1978;
Bjerseth et al., 1981) also indicated that PAH
exposures were significantly less in prebake potrooms
in comparison to Saderberg potrooms. Bjerseth el al.
reported personal sampling results ranging from 37.7
to 2790 /ig/m3 in the Sederberg plant, compared to
0.52 to 2.0/ig/m3 in the prebake plant. Becher et al.
(1984) reported personal exposure levels in a Sederberg plant in Norway ranging from 52 to 268/ig/m3
with an arithmetic mean of 126 /ig/m3. A recent Dutch
study (TjoeNy etal., 1993) undertaken inaSaderberg
plant, reported personal air monitoring results of total
PAH levels for 5 exposure groups ranging from 8.8 to
840 /^g/m3. The location of the plant was not reported
by the authors. Levin el al. (1995) reported levels
ranging from 30 to 400/ig/m3 for Soderberg potroom
workers in a Swedish study.
The PAH levels in Sederberg potrooms also appear
to be higher than the levels in the anode baking area
in prebake plants. Tolos et al. (1990) reported levels
of 9.5 to 94.6/ig/m3, for 18 workers in the bake anode
area. Another Dutch study (Van Schooten el al., 1995)
reported personal TWA air monitoring in a prebake
smelter for total PAHs in the bake oven area of
between 3 and 107/ig/m3. Personal air monitoring
results reported by Petry et al. (1996) in a carbon
179
bake plant of a prebake smelter ranged from 3.99
to 120.6 /ig/m3. These reports all confirm the earlier
findings of reduced exposures in prebake smelters. A
recent Norwegian report on pot-liners (0vreb0 el al.,
1995) which did not state the type of plant, reported
PAH air monitoring levels of 130 /ig/m3. Haugen et
al. (1992) earlier reported a level of 126/ig/m3, from a
Norwegian smelter, where the process was also
unspecified.
Airborne B[a]P monitoring results have been extensively reported in the literature and are summarised
in Table 2. As with fluorides, some caution is advised
when comparing levels because some of the results
reported were based on measurements undertaken
many years before the publication date of the epidemiological study or exposure assessment report. As
with tar and PAH levels, reported B[a]P exposures in
prebake potrooms are lower in magnitude than those
in Soderberg plants. Chan-Yeung el al. (1989) compared levels in 1980 with a follow-up study in 1986
and showed that mean personal monitoring TWAs
decreased from 3.5 to 0.8/ig/m3 (N = 69 and N = 21
respectively). Recent personal 6-hour air-sampling of
Sederberg potroom workers in Germany (Bolt and
Golka, 1993) reported B[a]P exposures up to
292/ig/m3 (range 0.5-292 /ig/m3). In a report from a
Norwegian smelter (Haugen et al., 1992) it was calculated that the average 8-hour workshift exposure
for potroom workers was 33/ig/day (type of anode
Table 2. Reported benzo-a-pyrene exposures in the primary aluminium industry
Cone. B[a]P /ig/m3
Author of report. Year
Process
Kreyberg, 1959
Konstantinov et al, 1971
Soderberg
Sederberg
0 18
17.9-29.4
Shuler etal., 1974
Prebake
Saderberg
Sederberg
0.03-0 1
53.0
1 85 (N = 74)
3 7 (N = 90)
0.8-27 9
.02-0 05
3.4-116 3
3 5 (N = 69)
0.8 (N = 21)
2.2 (N = 10)
Adamiak-Ziemba el al., 1977
Bjarseth et al, 1978
Chan-Yeung et al, 1983
Chan-Yeung et al., 1989
Tjoe Nye/a/., 1993
Anode plant
Prebake
Sederberg
NA
NA
Sederberg
Levin et al., 1995
Sederberg
2.8 (N = 9)
Tremblay el al., 1995
Soderberg
1.04
Prebake
0.0
Van Schooten el al., 1995
Anode plant
Prebake
Petry etal., 1996
Anode plant
1.51 (N = 40)
0.03 (N -= 23)
Comments
From I sample analysed for 7 PAHs
For pot operators during pot processing in
vertical stud Sederberg potroom.
In potroom
For pin setters
Plant A
Plant B
From 3 personal samples
Detected in only 2 of 6 personal samples
From 3 personal samples
Mean TWA for potroom workers
Mean TWA for potroom workers
Although 38 workers were sampled across 5
exposure groups, we report only the results of the
potmen.
Mean of 9 personal samples from workers in
pot-anode (N = 4), cathode (N = 3) and
crane driving (N = 2).
Estimated TWA for potman in the Ssderberg
plant (1985-1989). For 1930-1954 estimated
TWA level was 14.08 /ig/m3.
Esumated TWA for potman in the Prebake
plant (1985-89). For 1930-1954 estimated TWA
level was 0.03 /ig/m3
Geometric mean levels with range 0.1-11.6/ig/m3
Electrolysis workers, geometric mean levels
with reported range < 0.02-0.2/ig/m3.
TWAs for 6 carbon anode workers monitored
on 5 consecutive shifts
180
G. Benke el al.
Table 3. Reported sulfur dioxide exposures in the pnmary aluminium industry (in mg/m3)
Author of report, Year
Process
J a h r e / a / , 1974
Sancer al, 1979b
S0derberg
Prebake
Prebake
Clonfero el al, 1981
Prebake
Chan-Yeunge;a/, 1983
Wergeland el al., 1985
Martin el al., 1986
Saric el al., 1986
Chan-Yeungef a/, 1989
Kongerud and Rambj0r, 1991
Desjardins el al., 1994
Prebake
NA
Swlerberg
Sederberg and
Prebake
Prebake
NA
Sederberg and
Prebake
Prebake
Cone SO^N)
8.3*
3 4'
1.93
5 8(N = 28)
2.3 (N = 16)
2.0* (N = 121)
<2.0
3(N = 13)
3 38
2 1*(N == 53)
0.42
1.0*
Comments
Short term exposure while rinsing burners
Short term exposure while pulling stud
TWA with range of 0 97-3.06 mg/m3, for
potroom workers, with number of samples not
given.
The reported mean levels were for two prebake
Italian plants, with fixed samplers.
TWAs reported in 1989 follow-up study
Only monthly averages were reported
For prebake potroom
TWA levels ranged from 2 26 to 6.32 mg/m3.
TWAs
Median level from a total of 75 samples, which
included fluoride results.
TWA in potroom, number of samples not
reported
• These results were originally reported in parts per million (ppm), but have been converted to mg/m3 for comparison
purposes. Exposures at 25°C and barometnc pressure of 760torr have been assumed
not specified). Petry et al. (1996), reported personal
air monitoring results of six workers in a carbon bake
plant (each worker monitored for 5 shifts) with B[a]P
levels ranging from 0.17 to 4.88 /ig/m3.
Reports of biological monitoring using the urinary
metabolite, 1-hydroxypyrene (1-OHP), for exposure
to PAHsin aluminium smelter workers have appeared
in recent years (Vanrooij el al., 1992, Tjoe Ny el al.,
1993; 0vreb0 el al., 1995; Levin el al., 1995; Van
Schooten et al., 1995; Petry el al., 1996). A tentative
maximum permissible concentration of 2.7/jg/g
creatinine has been proposed (Klaassen, 1996). Jongeneelen (1992) estimates that a unnary concentration
of 1-OHP of 2.3/jmol/mol creatinine after a third
working period corresponds to the ACGIH TLV*
for CTPV of 0.2 mg/m3.
Reports are also appearing of the use of PAHDNA adducts in white blood cells (0vrebe el al., 1990;
'These results were originally reported in parts per million
(ppm), but have been converted to mg/m3 for comparison
purposes. Exposures at 25°C and barometnc pressure of 760
torr have been assumed.
tThese results were onginally reported in parts per million
(ppm), but have been converted to mg/m3 for companson
purposes. Exposures at 25°C and barometnc pressure of 760
torr have been assumed
JThese results were onginally reported in parts per million
(ppm), but have been converted to mg/m3 for companson
purposes. Exposures at 25°C and barometric pressure of 760
torr have been assumed.
§These results were onginally reported in parts per million
(ppm), but have been converted to mg/m3 for comparison
purposes Exposures at 25°C and barometric pressure of 760
torr have been assumed.
"IThese results were onginally reported in parts per million
(ppm). but have been converted to mg/m 3 for companson
purposes. Exposures at 25 C and barometric pressure of 760
torr have been assumed.
Schoket et al., 1991; Haugen et al., 1992; 0vreb0 et
al., 1995; Van Schooten et al., 1995) to monitor carbon
plant and potroom PAH exposure.
Sulphur dioxide
Exposure to gaseous SO2 exists in both Saderberg
and prebake potrooms and in the carbon plants. A
summary of quantitative exposure levels is given in
Table 3. The current ACGIH TLV*-TWA for SO2 is
5.2 mg/m3 with a short term exposure limit (STEL) of
13 mg/m3. Early reports (Saric et a!., 1979) indicated
TWA exposure levels ranging from 0.08 to 4 mg/m3,
with Clonfero et al. (1981) reporting a relatively high
mean TWA level (N = 28) of 5.8 mg/m3 in a prebake
smelter in Porto Marghera Chan-Yeung et al. (1989)
reported a mean TWA of 2.0 mg/m3* (N = 121) for
measurements undertaken in 1980 compared to
2.1 mg/m 3 t (N = 53) for the same smelter in 1986.
However, recently reported personal sampling of
TWA levels from Norway and Canada, appear to
show a decrease in levels to 0.42 mg/m3 (Kongerud
and Rambjar, 1991) and 1.0mg/m3i (Desjardins et
al., 1994).
Although portable monitors capable of measuring
peak SO2 levels have been available for some time,
few peak SO2 levels have been reported. Steinegger
and Schlatter (1992) reported peak values could rise
to 52 mg/m3§ for a few seconds, even though the TWA
was less than 2.6mg/m 3< |.
Trace elements
With the introduction of dry scrubbing in some
smelters in the 1970s, concern was raised about the
likelihood of trace elements such as nickel, vanadium
and chromium being concentrated in the potroom
dust. Dinman (1977) reported that the trace element
Exposures in the alumina and primary aluminium industry
vanadium, present as vanadium pentoxide (V2O5), was
present at levels 15 to 20 fold below the then TLV of
0.5 mg/m3. The TLV has since been revised down to
0.05 mg/m3. In a study of the influence of fluoride
recovery alumina on respiratory symptoms, Eduard
and Lie (1981) reported that exposures to the trace
elements were all far below the hygiene standards.
Unfortunately, no quantitative data were provided.
Although data on alloy composition in casting departments is available, no published measurements of airborne levels in smelters were found.
Particulates
Besides bauxite dust, crystalline silica exposure is
the only dust of significance in bauxite mining, but
quantitative exposure levels were not found in the
literature. In alumina production, particulate
exposures of significance, besides bauxite and alumina
dust, may include asbestos fibres, refactory ceramic
fibres (RCF) or crystalline silica dust. No reported
exposure levels were found in the literature.
Numerous dusts of mixed composition have been
reported in smelters, but reports of the composition
of these dust mixtures are usually lacking. Mixtures
can be dependent upon many factors often unique to
their smelter of origin. Early total dust reports in
potrooms ranged from 0.2 to 135 mg/m3 (Eduard and
Lie, 1981). The TWA levels for total dust in the study
by Eduard and Lie (1981) in a Sederberg potroom
were 7.6 mg/m3 for recovery alumina use and
5.4 mg/m3 for pure alumina use. Casula et al. (1981)
reported total dust concentrations ranging from 2.35
to 6.95 mg/m3 in the potrooms and indicated that the
aerodynamic size distribution of alumina dust in the
potroom influenced the concentration of the dust.
They also reported that the respirable fraction can be
a significant part of the total dust concentrations.
Another dust that has attracted particular interest
is sodium aluminium tetrafluonde (NaAlF 4 ) which
may occur as small respirable fibres (Gylseth et al.,
1984; Hjortsberg el al., 1986). Gylseth et al. (1984)
suggested that short thin fibres of NaAlF< are produced during the recrystallization of fumes from the
electrolyte, they are then collected by the fume extraction system and recycled to the pots along with the
reacted alumina after dry scrubbing. A recent report
by Voisin et al. (1996) of bronchoalveolar lavage fluid
from four primary aluminium workers confirmed the
presence of fibrous aluminium particles. However,
they questioned whether these particles were NaAlF 4 ,
and considered them more likely to be various forms
of aluminium oxides eg alumina trihydroxide A1(OH)3
or either the a or y form of crystallised alumina A12O3.
The importance of dust levels and dust mixtures has
been stressed by several researchers (Saric et al., 1979;
Eduard and Lie, 1981; Saric, 1992) because of the
likelihood of gases such as HF and SO2 adsorbing
onto particles which, depending upon their aerodynamic diameter, may reach areas of the respiratory
tract where these highly soluble irritant gases would
181
not normally gain access. In general, complex mixtures are difficult to address and in the past markers
have been commonly used when the active agent was
unknown.
EXPOSURE ASSESSMENT IN EPIDEMIOLOG1CAL
STUDIES OF THE PRIMARY ALUMINIUM
INDUSTRY
Historically, the presentation of environmental
exposure data in epidemiological studies of the aluminium industry have been dependent upon the health
outcome investigated. In studies investigating cancer,
the exposures of interest have usually been CTPV,
PAHs or BSMs. With respiratory morbidity investigations, the exposures of interest have primarily been
fluorides. However, a recent report (Grandjean et al.,
1993) has suggested that exposure to fluorides could
contribute to an increased cancer risk. Exposure data
in cancer studies has been limited, with only a minority
of studies reporting semi-quantitative data in job
exposure matrix (JEM) form (Tremblay et al., 1995).
Most of the published cancer studies have been retrospective cohort studies which, at best, categorise
exposure by ordinal ranked jobs or duration of
employment in specific areas of the plant. In contrast,
respiratory disease studies have been principally crosssectional or case series study designs. Many of the
respiratory morbidity studies have presented some
quantitative exposure data, which has been possible
because of small numbers and the relevance of recent
monitoring (due to short latent periods) to the health
outcomes of interest such as 'potroom asthma'.
Cancer studies
Table 4 summarises the exposure assessments by
investigators for longitudinal cancer studies in the primary aluminium industry and clearly demonstrates
the lack of adequate exposure data. Even the most
comprehensive studies to date have relied upon major
extrapolations backward in time over many years,
based on limited available quantitative hygiene data
(Armstrong et al., 1994; Tremblay et al., 1995; R0nneberg, 1995). There has also been a heavy reliance upon
retrospective estimations of exposure by company
industrial hygienists where little hygiene monitoring
data are available (Tremblay el al., 1995; Spinelli et
al., 1991). Unfortunately, data on important possible
confounders, such as asbestos, have been missing from
many past cancer studies (Renneberg and Langmark,
1992).
Studies by Armstrong et al. (1994), Tremblay et al.
(1995) and Renneberg and Andersen (1995), constructed job exposure matrices (JEMs) which characterise exposures by agent, job (job code), area and
time. Ranneberg investigated six specific agents compared to only two by Armstrong and Tremblay. The
latter investigators reported continuous quantitative
exposures whereas R0nneberg reported relative categorical exposure groups, ie the most exposed jobs
Table 4. Cohort studies of cancer in the primary aluminium industry
Author, Year
Country
Process
Agents
Gibbsand Horowitz. 1979
Canada
Prebake and Soderberg
'tar'
Milham, 1979
USA
Prebake
Nil
Andersen cl al., 1982
Norway
Prebake and Soderberg
Nil
Rockette and Arena. 1983
USA
Soderberg
Nil
Andersen el ul., 1984
Gibbs, 1985
Mm el ul., 1987
Norway
Canada
France
Prebake and Soderberg
Prebake and Soderberg
Prebake and Soderberg
Nil
'tar
Nil
Rocketteand Arena. 1990
USA
Prebake and Soderberg
Total Particulates. benzene
solubles, B[a]P. F T and SO2
Spinelli elal., 1991
Canada
Soderberg
CTPVand EMF
Armstrong cl til., 1994
Canada
Prebake and Soderberg
BSM and B[a]P
Tremblay el ul., 1995
Ronneberg and Andersen, 1995
Canada
Norway
Prebake and Soderberg
Prebake
BSM and B[a]P
CTPV, AC and DC
electromagnetic fields. Pot
emissions. Heat and
Asbestos
Exposure assessment methods
For each individual the total number of years of exposure to tar. number of
years since first exposed and exposure index in tar-years. Three categones were
used A-no tar exposure; B-some tar exposure (degree 25%) and; C-definite
tar exposure (degree 100%)
Exposure was assessed using job-exposure categories and duration of
employment.
Exposure was assessed by duration of employment and location of worker in
the two categories'—processing department—non-processing department
Exposure was determined by process groups, le horizontal or vertical stud
Soderberg, prebake, remainder. Also by location, le potroom ever or s 5 years,
carbon department ever o r ^ 5 years: and cumulative employment in the
process groups i.e. < 10 years, 10-15 years. 15-20 years and 20-25 years
As in 1982 study (this was the follow-up study)
As in Gibbs and Horowitz, 1979 study
The occupational history of each subject was reconstructed from
administrative records from 11 plants. Exposure assessment by workplace
consisting of 3 categories' electrolysis, maintenance and smelting, and by three
length of employment categories. < 10 years, 10-20 years and >20 years.
Finally, three categories of latency since first exposure were analysed.
Exposure was assessed first by whether the subject worked in a reduction plant
or not, then by "ever' worked in the potroom or carbon department and then
by department which the subject spent the majority of their time The
departments which the subjects spent the majority of their time were a)
nonreduction process, b) potroom dept . c) carbon dept.. d) ingot dept.. c)
mechanical maintenance, 0 electrical maintenance, and g) power Detailed
work histories were not coded and analysed.
Expert panel assessed CTPV and EMF for each job. based on TLV. Four
exposure groups for CTPV were described le (I) no exposure to CTPV, (2) low
exposure (<0.2mg/m ) BSM); (3) medium exposure ( < 0 2-1 0mg/m' BSM);
and high exposure ( > I Omg/m'BSM) Cumulative CTPV (in BSM years) was
tabulated Cumulative exposure to EMF was calculated by summing the
number of years an employee worked in an EM F-exposed job.
A JEM of cumulative exposure to BSM and B[a]P was constructed The B[a]P
was indirectly estimated from the B[a]P.BSM ratio, derived from monitoring
between 1980-1984. Successive 5-year strata from 1950 to 1989 were based on
"several-hundred" personal samples monitored between 1980-1984. Work in
the Soderberg potrooms accounted for 75% of total cumulative BSM exposure
in the sub-cohort.
As in Armstrong el al., 1994 study
A JEM was constructed for 96 defined jobs grouped into 18 categories TWAs
were estimated on a relative scale, with four 'relative" categories for each
exposure Some exposures were based on judgement by 10 former employees
and an industrial hygienist, with others based on results from time studies and
static monitoring taken near the breathing zone during each task.
Exposures in the alumina and primary aluminium industry
were assessed as 1.00, with the next category 0.75 or
0.5 depending upon the agent, then 0.25 or 0.1 etc.
Earlier studies (Spinelli el al.. 1991, Rockette and
Arena, 1983; Rockette and Arena, 1990) were not as
detailed in their exposure assessments as Armstrong
et al. (1994), Tremblay et al. (1995) and Renneberg
and Andersen (1995). Spinelli el al. (1991) made use
of a committee to assign values for CTPV and used
these to then develop four categories of exposure
based on the TLV. Rockette and Arena (1990) based
their reported cumulative exposures to BSM, B[a]P,
total fluorides (FT), total paniculate and SO2 on current air monitoring information, collected for each
job location and extrapolated backwards in time.
Respiratory studies
Of the 48 respiratory disease studies reviewed, 29
reported quantitative exposure data to various airborne contaminants (see Table 5). Unfortunately, the
majority of these are case-senes and cross-sectional
studies, which are methodologically weak in design.
The case-series by Midttun (1960), was typical of the
early literature, where only a brief statement of the
possible range of exposures for specific contaminants
was given. It was only in the 1970s that cross-sectional
studies appeared which reported mean TWA
exposures for specific job categories, eg potroom
worker or crane-dnver (Kaltreider el al., 1972; Sane et
al., 1979). Most of the case-series and cross-sectional
studies simply assessed exposure of subjects on the
basis of the subject having worked in a smelter, a
smelting department or by allocating workers to
"exposed" or '"unexposed" categories (Clonfero et al,
1981). Mean urinary fluonde levels for specific job
groups were also popular in case-series and crosssectional studies published in the 1970s and early
1980s, but with the advent of plasma fluorides and
more extensive air-monitoring, there has been a
reduction in the use of urinary fluoride monitonng as
a measure of exposure
A previously published review of the respiratory
health effects due to occupational exposures in smelters (Abramson et al., 1989), identified the lack of
longitudinal studies and sparse environmental
exposure data as significant limitations in the published literature. The lack of longitudinal studies may
be partly due to the inherent difficulties associated
with these studies e.g. recruitment of sufficient subject
numbers, dropouts during the course of the study and
resource requirements. However since the review by
Abramson et al. (1989), longitudinal studies by ChanYeung el al. (1989), Kongerud et al. (1991) and Seyseth et al. (1994), have been published. The methodologically strongest of these studies, by Kongerud
and Samuelsen (1991), measured total fluoride and
total dust exposure by personal samplers. A later
study (Soyseth et al., 1994) demonstrated an association between plasma fluorides and bronchial hyperresponsiveness in 26 subjects where representative personal monitoring of specific job categories was also
183
undertaken. Even the recent methodologically
stronger respiratory studies (Chan-Yeung et al.. 1989:
Kongerud and Samuelsen. 1991: Seyseth et al., 1997)
have relied upon job group or job title mean exposures
to total fluondes and/or dust, and not personal quantified measurements over the follow-up period for each
subject.
DISCUSSION
It is evident that, although the chemical exposures
present in the alumina and primary aluminium industry have been accurately identified, clear exposureresponse relationships are yet to be determined. Significant research addressing the quantification of the
level of exposures (both cumulative and peak) and the
frequency and nature of the physico-chemical mixtures present in the industry (ie interactions between
gases, particulates, heat and EMF) is still required.
The data presented in Tables 1-3 and Fig 2 suggest a
progressive decrease in the quantitative exposure levels for fluorides, B[a]P and SO : over time, but it is hard
to make definitive conclusions due to measurement
errors, differences in analytical techniques and other
factors.
If the TWA chemical exposures are indeed decreasing in potrooms, then epidemiologists and hygienists
will need to consider the implications of this for the
design of future studies. In particular, it could introduce serious exposure misclassification in retrospective cancer cohort studies which often rely upon
recent monitoring results which are extrapolated
backwards in time. The need for improvement in peak
exposure charactensation of irritants will also be critical for any future respiratory morbidity studies.
In this review, we found that the data quality varied
significantly between the various studies and reports
cited. Variability of the exposure levels both within
and between studies and the employment of weak
assessment methods indicated a need to improve
exposure charactensation by future researchers. In
particular, relating exposures to national workplace
exposure standards, MAC (maximal allowable concentration) levels or OELs, was commonly reported
in past studies and has contributed to the imprecision
of the exposure characterisation e.g a statement,
"'exposures were less than the MAC", was encountered
in many pre-1990 studies and reports
Cancer studies
Future cancer studies need to concentrate on
improved exposure characterisation. If possible,
quantitative exposures at the job-title level, or better,
the task level, are required and must be incorporated
into detailed quantitative JEMs. It has been established that excess risk of lung and bladder cancer are
associated with work in Saderberg potrooms (Ranneberg and Langmark, 1992), with CTPV and PAHs
attracting the main attention as carcinogens.
However, it has been suggested (Ronneberg and Lang-
Table 5 Respiratory studies in the pnmary aluminium industry with reported exposures
Author, Year
Study design
Midttun, 1960
Case-senes
Jahrand Wannag, 1972
Kaltreider el al., 1972
Cross-sectional
Cross-sectional
J a h r e / a / , 1974
Cross-sectional
Gispen, 1975
Case-senes
Johannessen, 1977
Case-senes
Van Voorhout, 1977
Cross-sectional
Ministers Committee,
(Coulon, 1978)
Case-series
Sane el al., 1979a
Cross-sectional
Gispen, 1980
Case-senes
Clonfero et al, 1981
Cross-sectional
Eduardand Lie, 1981
Cross-sectional
Maestrellief al., 1981
Cross-sectional
Siemen, 1982
Case-series
Workers
studied
400
(52 cases)
40
338
(37 cases)
218
373-971
(46 cases)
330
(21 cases)
750
(32 cases)
NA
(73 cases)
207
(21 cases)
1,150
(90 cases)
444(117)
163
(54 cases)
200
(5 cases)
650(19)
FT
SO,
/
CO
J
Dusts
Exposure assessment methods
Exposure assessed by duration of working in aluminium industry. Spot
measurements of total fluorides also reported
Urinary fluondes monitored for 40 workers and 40 controls
By assigning mean TWAs for job titles 200 Unnary fluorides and F,
for job-descnptions
Short term personal exposures to fluorides, CO and SO,. Also mean
shift exposures to fluondes, including urinary fluondes. Exposure
assessed by process type, unnary fluonde level and mean air monitoring
levels for some job title.
31 Urinary fluonde measurements with five exposure groups related to
potroom residence time
9 Unnary fluonde measurements
'Gas' and dust in mg/m3
By plant (11 plants in study) and if ever exposed to electrolysis.
Magnetic fields and heat were also measured, but not reported. All
chemical exposures were found to be below the TLVs
Mean exposures of workers with and without respiratory symptoms,
for HF, F p , total fluondes and SO2. Total of 20 measurements
31 Unnary fluondes measurements with five exposure groups related
to potroom residence time
82 static samples across 3 smelters, workers categorised as "exposed"
and 'unexposed'.
Total dust comparisons between different processes ie recovery alumina
and pure alumina; also PAH and trace elements mentioned
By plant (ie Plant A or B) and if working in potroom HF, F p and SO2
were monitored, but no details are given
Potroom workers were examined, and reported air monitoring levels
were <TLVs
O
Chan-Yeung et al., 1983
Cross-sectional
797
(62 cases)
Tomaszewski et al., 1983
Cross-sectional
Townsend era!., 1985
Cross-sectional
Martin et al., 1986
Cross-sectional
Saric et al., 1986
Cross-sectional
Wergeland et al., 1987
Longitudinal
149
(20 cases)
1,142
(137 cases)
2,144
(211 cases)
227
(7 cases)
105
(35 cases)
Chan-Yeung et al., 1989
Larsson et al., 1989
Longitudinal
Cross-sectional
820
59
Kongerud et al., 1990
Cross-sectional
1,760
Kongerud and Samuelson. 1991
Longitudinal
Loneitudinal
1,301
Saric el al., 1992
Case-series
54
Soyseth et al., 1992
Cross-sectional
370
y
Desjardins et al., 1994
Soyseth et al., 1994
Case-study
Longitudinal
1
26
y
y
Soyseth et al., 1997
Longitudinal
630
y
y
y
y
By three exposure groups: high and medium for potroom workers and
controls (from office and casting departments), job title and location in
plant. Personal sampling was also undertaken for all contaminants and
CO 2 was also monitored
Only aluminadust was measured. Total of 21 measurements at shipping
port
Recent personal samples and estimations by long term employees,
formed two cumulative exposure groups < 100 and ^ 100mg/m3-years
Tar levels for static sampling was also reported All other contaminants
reported were personal samples of TWAs for 7 departments
Only potroom workers examined. All assumed to have same exposure
to the listed contaminants
35 cases examined with time of employment in potrooms, dust. Three
exposure groups, 'exposed case' if working in potrooms, 'unexposed
control' if working outside potrooms and 'exposed control'
FoUow-upof 1983 cross-sectional study
Cumulative exposure to total dust and total fluorides were calculated
for potroom workers (N = 38). Exposure was then assigned to one of
the three groups: Low, Medium or High.
Both static and personal samples were regularly assessed, but only
personal samples were used in the analysis
Following total dust and total fluoride personal monitoring, mean
exposures for a specific job in the potrooms were assigned to 523 study
subjects
Two groups of workers were identified, 24 with respiratory complaints
and working in the potrooms (exposed group) and 30 with increased
bronchial reactivity who had ceased work in the potrooms (unexposed
group).
Two categories were described' High exposure to total dusts and
fluorides was ^0.5 mg/m3 and low exposure was <O.5mg/m 3
One case, with F T = 0 44 mg/m3, SO2 = 0.4 ppm and D T = 2 . 5 mg/m3
Plasma fluorides were obtained from 26 subjects and correlated with
F T . Exposures to total fluorides and total particulates were assigned to
the subjects by the mean of samples taken in their job category.
Work in the potrooms was separated into several job categories. 874
personal measurements were taken, and subjects were assigned their
exposure according to job category mean.
Abbreviations: A1F3, aluminium fluoride; AI2O3. alumina; B[a]P, benzo-alpha-pyrene; CO, carbon monoxide, D R , respirable dust, DT, total dust; F,, gaseous fluorides or hydrogen fluoride; F p ,
paniculate fluorides, F T , total fluorides; F u , urinary fluorides, NA, not available; SO2, sulfur dioxide
E1
1
I
5
•o
186
G Benke el at.
mark, 1992) that more attention should be given to
other exposures such as aromatic amines and nitro
compounds, asbestos, heat stress and magnetic fields
in future studies of cancer in smelter workers. In particular, exposures of some workers to static and alternating magnetic fields are high compared with most
other industries, but published quantitative exposure
data for the primary aluminium industry is minimal
(Moss and Booher, 1994).
Crystalline silica, asbestos and diesel fuel may be
significant exposures which should be assessed in
future cancer studies involving bauxite mines and alumina refineries. The lack of published reports addressing the alumina industry suggests that excess cancers
have been considered unlikely However, cohorts
where smoking habits and asbestos exposure are well
characterised is required to establish the true risk of
cancer in this industry.
The observed reduction in CTPV and B[a]P
exposure is likely to be due to the implementation of
improved technology in recent decades. Although the
exposures to potroom workers should continue to
decline with the increasing predominance of prebake
potrooms, this may not be the case for carbon plant
workers Coupled with the decrease in exposure is
the improved availability and wearing of respiratory
protection by workers in the industry over the past
decade. These factors have important implications for
future cancer epidemiology studies
Respiratory morbidity studies
The exposures which lead to respiratory disease
are as yet unclear. Suspect agents are fluorides, both
paniculate and gaseous, SO2 and trace elements. With
fluorides, the decrease in exposures has already
attracted comment in the literature (Steinegger and
Schlatter, 1992), and a recent study (Seyseth et al.,
1997) has reported a decreasing total fluoride exposure
level on a yearly basis (1986-1992) in a smelter in
Norway. Improved technology and the introduction
of personal respiratory protection have virtually eliminated the nsk of fluorosis in aluminium smelting,
with respiratory morbidity of most concern in recent
studies. Recent studies, particularly those by K.ongerud (1991) and Seyseth et al (1994) suggest a link
between total fluoride exposure and respiratory symptoms or bronchial hyper-responsiveness. However, a
clear link between HF gas exposure and potroom
asthma has not yet been demonstrated. The importance of HF gas exposure "peaks" in causing respiratory morbidity, can only be determined following
the development of new technology in hygiene
monitoring equipment for use in future longitudinal
studies.
Since gaseous SO2 exposure in potrooms may be
closely correlated with fluoride levels (Kongerud,
1992). the finding of decreased SO2 levels is consistent
with decreased fluoride levels. There is still a lack of
published reports on peak SO2 exposure and respiratory morbidity which needs to be addressed.
Ideally peak SO2 and peak HF exposures should be
monitored simultaneously in future respiratory morbidity studies. The documentation of co-exposures
and assessment of chemical exposure mixtures are still
needed in many parts of the industry.
Future research concerned with respiratory morbidity should explore the interaction of mixtures
which may act synergistically. In particular, research
should test the hypothesis that adsorption of fluorides
or SO, onto particulates enables exposure to regions
of the bronchial tree that are normally inaccessible to
these powerful and highly soluble irritants. This may
be achieved with advances in hygiene monitoring and
sample analysis or possibly with the emerging field
of chemometncs (Bye, 1995). Chemometrics involves
multidimensional data analysis, using statistical
methods on large exposure data sets. If combined with
bronchoscopy and examination of bronchoalveolar
lavage fluid, improved statistical analysis may identify
the biologically important exposure variables. Chamber studies have been suggested as an alternative
laboratory approach to this vexing problem and
may ultimately provide the best dose-response data.
Longitudinal designs are preferred for future epidemiological studies, with prospective collection of
exposure data, since there are currently insufficient
data to undertake a quantitative meta-analysis of published respiratory studies.
Acknowledgements—The authors wish to acknowledge Dr
RR Martin and Dr HE Rockette for permission to ate
unpublished work, the International Primary Aluminum
Institute for providing kind permission to cite unpublished
reports and providing papers; Professor G Berry, Professor
H Checkoway, Dr L Fritschi and Professor JJ McNeil for
helpful comments on the manuscript
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