Characterization of Air Contaminants Formed bythe Interaction of Lava and Sea Water

Gregory John Kullman, William Gale Jones, Ronnie James Cornwell, andJohn Eugene ParkerDivision of Respiratory Disease Studies, National Institute for Occupational Safety andHealth, Morgantown WV 26505 USA

Lava flow from the eruption of Hawaii'sKilauea volcano produces large clouds ofmist (lava and sea emissions; LAZE) oninteraction with sea water (Fig. 1). Islandwind patterns (Kona winds) occasionallymove this LAZE toward populated areas inthe adjacent village of Kalapana and intothe Hawaii Volcanos National Park. Thepotential for both occupational and com-munity exposure to this mist led to healthconcerns due to the absence of environ-mental health information on the chemicalcomposition of LAZE. Some local residentsand workers had complained of irritationafter exposures to LAZE. In March 1990,

The National Institute for OccupationalSafety and Health (NIOSH) providedtechnical assistance to the Hawaii StateHealth Department in characterizing theLAZE air contaminants. Environmentalsamples were collected on 13-18 March1990 to quantify air contaminants formedthrough the interaction of lava and seawater. This information was needed toevaluate potential exposure risks and developpublic health policy.

BackgroundThe Hawaiian Archipelago includes eightmajor islands: Niihau, Kauai, Oahu,Molokai, Lanai, Kahoolawe, Maui, andHawaii. These islands are the tops of alarge mountain range built up from theocean floor by numerous volcanic eruptionsand lava flows. Theory suggests that theseislands are formed as the earth's Pacificplate moves across a fixed hot spot (orhole) in the earth's mantle during thenorthwest plate drift (1-3).

Hawaii is the newest island and has themost volcanic activity. The island wasformed by lava flows from five volcanos.Among these, Mauna Loa and Kilauea, thetwo southernmost volcanos, are consideredactive and are among the most active vol-canos in the world. Kilauea, currently themost active Hawaiian volcano, began thelongest sustained eruption of any Hawaiianvolcano in recorded time starting inJanuary 1983 (1,2).

Molten rock from volcanic eruptions isa complex solution of silicates and oxidesassociated with water vapor and possiblyother gases. Lavas can vary in composition.Hawaiian lavas have a lower silica contentand are rich in iron, magnesium, and calcium.Olivine basalt is the most common lavafrom recent eruptions of Kilauea andMauna Loa volcanos (1). Hawaiian lavasare more viscous, with a lower gas content,resulting in milder, less explosive volcaniceruptions. Hawaiian volcanos erupt notonly at their summits but also along riftzones, which are heavily fractured zones ofweakness in the volcano (1-3). Lava flowscan occur on the surface or within lavatubes beneath the surface of lava that hascooled and crusted. The interaction of themolten lava with sea water produces largeclouds of LAZE (1,2). These LAZE cloudsmove in various directions depending on

prevailing wind patterns. Kona conditions,winds moving from the southeast to thenorthwest, can direct the LAZE over landand into the Hawaii Volcanos NationalPark and other populated island areas, cre-ating the potential for both occupationaland community exposure. Park employees,Hawaii civil defense workers, tour guides,geologists, or other scientists studying thevolcano would be at increased risk forLAZE exposure; park visitors and individ-uals living in communities proximate tothe LAZE formation would also be atincreased risk.

MethodsWe conducted environmental sampling tocharacterize the air contaminants formed bythe interaction of lava and sea water. Airsamples were collected for several environ-mental analytes including respirable dust,respirable crystalline silica and other min-erals, fibers, trace metals, inorganic acids,and organic and inorganic gases. Table 1describes the sampling and analyticalmethods used during the survey.

Figure 1. Lava and sea emissions (LAZE), March1990, near Kalapana, Hawaii.

Address correspondence to G.J. Kullman, Divisionof Respiratory Disease Studies, National Institutefor Occupational Safety and Health, 944 ChestnutRidge Road, Morgantown, WV 26505 USA. R.J.Cornwell is now at Martin Marietta EnergySystems, Oak Ridge, TN 37831 USA.We acknowledge the following individuals fortechnical consultation and survey support: JerryClere and John Holtz, NIOSH; Harry Kim,Hawaii Civil Defense; Paul Aki, Hawaii StateHealth Department; Christiana Heliker and BarryStokes, Hawaii Volcano Observatory; andTerrence Gerlach, U.S. Geological Survey.Received 3 December 1993; accepted 25 March1994.

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Area sampling stations were used tomeasure the air contaminants formed bythe lava and sea water. The following sam-pling locations were selected based on con-versation with local health officials (Fig. 2):1) Beach areas. These sampling stationswere positioned in visible clouds of LAZE;samples were collected at distances fromapproximately 10-400 yards from theLAZE source as determined by the terrainand wind direction during sampling. 2)Roadblock. This sampling station waspositioned at the highway 130 roadblockwest of Kalapana, Hawaii; the highway wasclosed at this location from past lava flows.This station was one of the closest pointsof public access to the LAZE formation. 3)Kalapana, Hawaii. Two sampling stationswere positioned in Kalapana at separate vil-lage locations. 4) Hawaii VolcanosNational Park. Two sampling stations werepositioned in the park approximately 2.5and 4.5 miles downwind from the pointsof LAZE origin. 5) Background. This sam-pling station was located in Keaau, Hawaii,approximately 20 miles from the LAZE ori-gin. This station was near the intersectionof highways 130 and 11.

We collected samples during 4 days:13-15 March and 18 March 1990.Difficult terrain, active lava flows, andvarying wind patterns influenced the sam-pling dates, beach sample station position,and the number of samples collected. Bydesign, samples were to be collected duringKona wind conditions when the LAZE wasdirected into Kalapana, Hawaii, and sur-rounding areas. Wind patterns during the

survey did not direct the LAZE towardsampling stations in Kalapana or the high-way 130 roadblock; although, on four ofseven scheduled sampling dates, wind carriedmists directly over land, providing theopportunity to collect samples from theLAZE plume at the beach sampling stationsand at stations positioned downwind in theHawaii Volcanos Park. NIOSH scientistsused respiratory protection and eye protec-tion when sampling in concentrated LAZEplumes at beach sampling stations.

Results and DiscussionEnvironmental measurements show thatthe LAZE is highly acidic. A 6.4 ml sampleof condensate, collected in dense clouds ofLAZE approximately 10-12 yards from itsorigin, had a pH of approximately 1.3.This reading is consistent with pH readingsobtained by placing strips of pH paperdirectly in the LAZE. The condensate sample,analyzed for inorganic acids by ion chro-matography, contained hydrochloric acid(11 mg); hydrofluoric acid (0.25 mg), andsulfate anion (SO4; 0.8 mg). (Analysis ofthis condensate sample by ion chromatog-raphy and ion-pair chromatography failedto give a clear separation of sulfate and per-chlorate anions. Thus, the presence of per-chlorate anion can neither be confirmednor rejected, and a portion of the sulfateanion response may be due to perchlorateanion. Mineralogical results suggest thatthe sulfate ion in this sample may havebeen present as a mineral complex similarto gypsum.) Other anions (bromide,nitrate, and phosphate) were not detected

Figure 2. Sampling locations: Kalapana, Hawaii,and vicinity.

in this sample. These measurements showthat the acidic nature of the LAZE is pri-marily a function of HCI content. Thesefindings are consistent with research datafrom the U.S. Geological Survey indicatingthat HCI can be formed by the steamhydrolysis of magnesium chloride salts pre-cipitated when sea water is evaporated todryness by molten lava (6X7).

Time-weighted average (TWA) airsamples collected to measure inorganicacid concentrations show HCI as the pre-dominant acid in LAZE. We collectedthese samples using several sampling methods(Table 1). The HCI concentration fromthe two types of impinger samples werealso in agreement, ranging from belowdetectable limits (ND = approximately0.004-0.04 depending on impingermethod) to 12 ppm. The HCI concentra-tions measured using the silica-gel sorbenttubes were in also agreement with theimpinger results. HCl concentrations werehighest in the beach sampling stations

Table 1. Environmental sampling methods

Air sampling rateAnalyte Sampler Media (I/min) Sampling time Sample analysesRespirable dust and Respirable cyclone Polyvinyl chloride filter 1.7 2-8 hr 1) Gravimetric, 2) X-ray diffraction,

crystalline silica (37 mm) NIOSH method 7500 (4)Metals/elements Total dust cassette Mixed cellulose ester filter 2.0 2-8 hr 1) Inductively coupled argon plasma,

(37 mm) atomic emission spectroscopy,NIOSH method 7300 (4)

Minerals/fibers Total dust cassette Mixed cellulose ester or 2.0 0.25-2 hr 1) Transmission electron microscopy,polycarbonate filter NIOSH method 7402 (4), 2) polarized

light microscopy (4), 3) scanning electronmicroscopy

Particulate (settled dust) 1) Polarized light microscopy,2) scanning electron microscopy

Hydrocarbon vapors Solid sorbet tube Charcoal and silica gel 0.05 2-8 hr 1) Gas chromatography (4)Inorganic acids Solid sorbet tube Silica gel 0.2 2-8 hr 1) Ion chromatography, NIOSH

method 7903 (4)Midget impinger Sodium hydroxide solution 1.0 2-8 hr 1) Ion chromatographyMidget impinger Deionized water 1.0 2-8 hr 1) Ion chromatography, 2) metals

inductively coupled plasma-atomicemission spectroscopy (4)

Glass condenser 2 hr 1) Ion chromatography (4),2) pH measurements

Gases (inorganic) Direct reading 5 min 1) Colormetric-length of stain inindicator tubes sample tube proportional to the air

contaminant concentration-adirect measure (5)

Volume 102, Number 5, May 1994 479

positioned directly in the LAZE. The meanHCl concentration from 10 samples col-lected using impinger methods was 3.5ppm and, with the sorbent tube method,2.9 ppm (Table 2).

These HCI concentrations are based ontotal chloride (Cl) anion per sample. (Ionchromatography analysis cannot distin-guish a chloride anion derived from HClfrom a chloride anion from ocean salts.)Each distilled water impinger sample wasanalyzed for metals commonly bound aschloride salts to estimate the chlorideanion potentially contributed to theimpinger samples by ocean salts. Chlorideanion potentially bound as salts of calcium,magnesium, or sodium may have reducedHCI concentration to an estimated 87% ofthe reported concentration in impingersamples collected in the concentratedLAZE plume near its origin and to 36% ofreported concentration in less dense LAZEplumes approximately 400 yards from origin.

HCI concentrations were the highest inthose sampling stations positioned directlyin the LAZE plume near the point of origin(Fig. 3). The eight TWA samples(impingers and sorbent tubes) collected indense mists within approximately 12 yardsof a tubular LAZE source had a mean con-centration of 7.1 ppm (SD = 2.9). Fourdirect-reading indicator tube samples col-lected at this same location had an averageconcentration of 6.4 ppm. As indicated inFigure 3, HCI concentrations declinedwith distance from the source. At approxi-mately 100 yards, the average TWA HC1concentrations from eight samples was0.69 ppm (SD = 0.51). The nine direct-reading indicator tube samples collected atthis distance had an average concentrationof 0.3 ppm. Four TWA samples collectedat approximately 400 yards from the LAZEsource on March 18 had an average con-centration of 0.39 ppm (SD = 0.11). Thethree indicator tubes collected at this dis-tance had an average concentration of 0.4ppm. Samples collected within the LAZEplume at distances of approximately 2.5and 4.5 miles from the origin were belowquantifiable limits for HCl. HCI concen-

le

E

*

oa

C0

I

4

2

13 12 so 1in 2 5 4m1Yards from source

Figure 3. Effect of distance from source on con-centrations of HCI in air.

tration from all other sampling locationswere outside of the LAZE plume and gen-erally below detectable limits, reflectingambient or background conditions. HClconcentrations measured in the denseLAZE plume within 12 yards of the sourcewere in excess of the permissible exposurelimits (PELs) enforced by OccupationalSafety and Health Administration(OSHA), 5 ppm as a ceiling level. Thesearea HCl concentration also exceededNIOSH recommended exposure limits(RELs) and the American Conference ofGovernmental Industrial Hygienists(ACGIH) threshold limit value (TLV)exposure recommendations (both 5 ppm asa ceiling exposure value) (8-11).

We also analyzed the impinger and silica-gel sorbent tubes for anions of other inor-ganic acids including bromide, fluoride,nitrate, perchloric, phosphate, and sulfate.Of these, fluoride, nitrate, perchloric, andsulfate were identified in some samples col-lected from the sampling stations withinthe plume. Nitric and perchloric acids werebelow quantifiable levels in all samples.Hydrofluoric acid (HF) was detected in 9of 20 samples from the beach sampling sta-tions. Four of these samples had quantifi-able HF concentrations; these samples werecollected from beach areas at distances of10-100 yards from the source. The highestHF concentration, 0.99 ppm, was measuredin a dense LAZE plume approximately 12yards from the source. Fluoride anion wasalso detected at quantifiable levels in foursamples collected from other sampling

Table 2. Hydrochloric acid concentrations by sampling location (ppm in air)aImpinger methods Sorbent tube methods

N Mean Range N Mean RangeBeach 10 3.5 0.2-12 10 2.9 LOQ-9.1Roadblock 3 LOQ ND-0.002 4 LOQ ND-LOQHVP 2 LOQ ND-LOQ 4 ND NDKalapana 2 0.03 ND-0.06 4 LOQ ND-LOQKeaau 1 0.02 2 LOQ ND-LOQ

aThe concentrations are based on total chloride anion; interference from chloride salts may havereduced the reported HCI concentrations (see Results and Discussion). HVP, Hawaii Volcanoes Park.ND, below the limit of detection, approximately 0.004-0.04 depending on the impinger method andapproximately 0.08 ppm for the sorbent tube method. LOQ, below the limit of quantification, approximate-ly 0.01-0.04 ppm depending on the impinger method and 0.23 ppm for the sorbent tube method.

locations separate from the beach and out-side of the LAZE plume. The presence offluoride anion in these background, ambientsamples may possibly be attributed to ventgas emissions from Kilauea. None of the areaHF concentrations exceeded the personaloccupational exposure standards/criteria ofOSHA and ACGIH (3 ppm as a TWA) orNIOSH (3 ppm as a TWA and 6 ppm as aSTEL), although HF exposures wouldhave an additive health effect in combina-tion with HCl exposures (10).

Sulfate anion was detected in 14 of 20samples from the beach sampling station,with concentrations rangin3g from belowdetectable limits to 1 mg/m . It is unlikelythat this anion was present as sulfuric acid(H2SO4) because indicator tube samplesfor sulfuric acid, collected in dense LAZE,were below detectable limits. A more prob-able source of the SO4 in these samples is amineral, similar to gypsum (CaSO4e2H20), that was identified in many airbornesamples by transmission electronmicroscopy analysis.

Volatile organic compounds were notdetected in any of the 13 high-volumecharcoal and silica-gel tube samples ana-lyzed qualitatively. Direct-reading indicatortube samples, taken to evaluate potentialpresence of a number of chemical substancesin LAZE, were below detectable levels forammonia, carbon disulfide, carbonmonoxide, chlorine, hydrofluoric acid,hydrogen sulfide, nitrogen dioxide, andsulfuric acid. Carbon dioxide, hydrochloricacid, and sulfur dioxide were measured atdetectable levels with indicator tubes. Thetwo carbon dioxide measurements, 400and 450 ppm, were close to expectedambient levels. Sulfur dioxide was detectedin one of four short-term samples at a con-centration of 1.5 ppm. This sample wasbelow the OSHA PEL (5 ppm as a TWA),ACGIH TLV, and NIOSH REL (both 2ppm as a TWA and 5 ppm as a short-termexposure limit) (8-11).

Respirable dust concentrations rangedfrom below detectable levels (limit ofdetection = approximately 0.01 mg/mi3) to ahigh of 1.3 mg/mi3 (Table 3). The five samplescollected from beach sampling stations,within the LAZE plume, had the highestconcentrations, with an average of 0.5

Table 3. Respirable dust concentrations by sam-pling location (mg/m3 in air)a

N Mean SD RangeBeach 5 0.5 0.49 0.12-1.3Roadblock 2 0.03 0 NoneHVP 2 0.025 0.007 0.02-0.03Kalapana 1 0.01Keaau 1 ND

HVP, Hawaii Volcanoes Park. ND, below the limitof detection, approximately 0.01 mg/m3.

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mg/m3 (SD = 0.49). Respirable dust con-centrations from other sampling stationsout of the plume were <0.03 mg/m3 andreflect ambient or background conditions.Crystalline silica (alpha-quartz, cristobalite,or tridymite) was not detected in any ofthe samples. The limit of detection forcrystalline silica is 0.015 mg/sample orapproximately 0.03 mg/m3 given the averagevolume of air sampled.

Calcium, copper, iron, magnesium,sodium, and zinc were the predominantmetals detected in airborne total dust samplescollected using open-face filter cassettes.Metal concentrations were highest in thebeach sampling stations positioned in theLAZE plume. Sodium and magnesiumwere the most abundant metals. Sodiumwas detected in each sample collected fromthe beach sampling stations at concentrationsranging from 0.03 mg/m3 to 1.0 mg/m3.Magnesium was detected in four of the fivesamples from this area at concentrationsranging from ND (<0.003 mg/m3) to 0.13mg/m3. Sodium and magnesium salts makeup more than 90% of the total ocean salts(by weight), and their presence is consistentwith particulate formed from boiled/evap-orated sea water (12). Exposures to sodium,magnesium, and the other metals identifiedin these samples were below existing occupa-tional exposure standards/criteria ofOSHA, ACGIH, and NIOSH (8-11).

The nature of the particulate formedby the interaction of lava and sea water wasevaluated in several ways. By visual inspectionof the LAZE plumes, particulate fall-outcould be observed on occasion. These par-ticles, thin sheets or flakes measuring up toapproximately 10 cm in diameter, havebeen recently described as Limu'o Pele orPele's seaweed. They are composed largelyof amorphous silicon dioxide. This material,as well as fibrous glass particles, could beobserved in the crevices of hardened lavaflows near the ocean (Fig. 4). Theaerosolization of this amorphous glassresults from the explosive interaction oflava and sea water.

Microscopic analysis of air samples col-lected on filter media or by suspending amicroscope slide directly in the LAZEplume showed a predominance of cubiccrystals (Fig. 4). Further observation ofthese particles by polarized light mi-croscopy indicated that they were isotrop-ic, which suggests NaCl. Confirmation wasobtained by scanning electron microscopywith X-ray analysis.

Airborne fibers were also detected insamples collected from the LAZE plumeusing transmission electron microscopy.Only one of the five LAZE plume sampleshad a quantifiable fiber concentration,0.16 fibers/cm3. Energy dispersive X-rayanalysis suggests a large portion of these

Figure 4. Digital images of (A) air sample collected in plume showing cubic crystals (differential interfer-ence contrast illumination); (B) settled dust sample showing glass fibers (Rheinberg illumination); (C) set-tled dust sample showing glass fragments (brightfield illumination); and (D) air sample collected in aplume showing a glass fiber (differential interference contrast illumination).

fibers was composed of a hydrated calciumsulfate with a morphology characteristic ofgypsum, although the calcium-to-sulfurratios were variable, and exact fiber identity(as gypsum) could not be verified in allinstances. Some of the airborne fibersappeared to be composed largely of calcium.Glass fibers were also detected on some ofthe air samples. Figure 4 shows a digitalimage of an air sample observed under themicroscope, showing one of these isotropicglass fibers. Exposures to gypsum andfibrous glass particles could cause irritationto the eyes, skin, and upper respiratorytract (13,14). There are no occupationalexposure standards specifically for gypsumfibers, although the OSHA standard fortotal gypsum dust is 15 mg/mr as a TWA.NIOSH and ACGIH recommend occupa-tional exposure to total gypsum dusts bemaintained below 10 mg/m3 and respirablegypsum dusts below 5 mg/mr3 as a TWA.Concentrations of gypsum dusts (includinggypsum fibers) were well below these occu-pational exposure standards. Airborne fiberconcentrations were also low by comparisonto existing occupational exposure standards/criteria for fibrous glass. NIOSH recom-mends a TWA exposure limit of 3 fibers/cm3(for glass fibers <3.5 plm in diameter and.10 pm in length) and 5 mg/mr3 as totalfibrous glass. ACGIH recommends a TLVlimit of 10 mg/mr3 for fibrous glass as aTWA exposure. Concentrations of air-borne fibers (including fibrous glass) werebelow these occupational criteria (8-11).

Conclusions

The interaction of lava and sea water gen-

erated quantifiable concentrations of HCland HF; HCI was predominant. Con-densate samples of LAZE were highlyacidic, with a pH of 1.3. The potential forexposure to inorganic acids (HCl and HF)presents the most significant health riskfrom LAZE. HCI and HF concentrationswere highest in dense plumes of LAZEwithin approximately 12 yards of the sea.

The HCl concentrations measured at thosesampling locations exceeded the 5 ppm

ceiling standard and presented an occupa-

tional health hazard according to occupa-

tional exposure criteria of OSHA, ACGIH,and NIOSH (8-11). HF concentrationswere below existing occupational exposure

standards, although HF would produceadditive exposure effects in combinationwith HCI (9,15,16). HCI and HF concen-

trations decreased with distance from thesource. At distances of approximately 400yards or greater, HCl concentrations, mea-

sured directly in the diluted plume, were

less than 1 ppm.The exposure criteria referenced in this

report are derived from occupationalhealth research settings and are not an

appropriate a tool for evaluating communityhealth risks. Community exposures to HClshould not exceed the 5 ppm ceiling standardused for occupational settings; a lower expo-

sure limit may be appropriate to protect thepublic.

Volume 102, Number 5, May 1994 481

Al ZML lSulfur dioxide was detected in one of

four short-term detector tube samples at aconcentration of approximately 1.5 ppm,demonstrating the potential for intermit-tent S02 exposure near areas of volcanicactivity and active lava flow. Airborne par-ticles in the LAZE plume were composedlargely of sodium chloride crystals.Crystalline silica concentrations in TWAair samples were all below detectable limits(less than approximately 0.03 mg/mi3).This is consistent with the basaltic natureof Hawaiian lavas (1-3). Airborne fibers,composed largely of hydrated calcium sul-fate similar to gypsum, were detected atquantifiable concentrations in one of fivesamples collected from the beach samplingstations. Glass fibers were also detected insome samples collected from beach samplingstations. These fiber concentrations didnot exceed the occupational exposure stan-dards/criteria ofOSHA, ACGIH, or NIOSHfor gypsum or fibrous glass (8-1 1).

Our findings indicate that individualsshould avoid exposure to the concentratedLAZE near its origin to prevent overexpo-sure to acid gases, specifically HCL. Elderlypersons, young children, and individualswith cardiopulmonary problems may be atincreased risk and should avoid all expo-sure to this mist (15,16). Appropriate per-sonal protective gear (including a chemicalcartridge respirator for acid gases and eye

goggles or a full facepiece chemical car-tridge respirator) is recommended, as partof a formal respiratory protection program,in those occupational settings when exposureto the LAZE, near its origin, is unavoid-able (17).

REFERENCES

1. McDonald GA, Hubbard, DH. Volcanos ofthe national parks in Hawaii. Honolulu:HawaiiHistory Association and National Park Service,1989.

2. Heliker C, Weisel D. Kilauea, the newest landon earth. Honolulu:Bishop Museum Press,1990.

3. Bullard FM. Volcanos of the earth. Austin:University of Texas Press, 1980.

4. NIOSH. Manual of analytical Methods, 3rded. DHHS Publication No. (NIOSH) 84-100.Cincinnati, Ohio:National Institute forOccupational Safety and Health, 1984.

5. Leichnitz K. Detector tube handbook, 6th ed.Lubeck, Germany:Draegerwerk AG Lubeck,1985.

6. DOE. Acid rain from vaporization of seawaterby molten lava: a new volcanic hazard.Albuquerque, NM:Department of Energy,1989.

7. Gerlach TM, Krumhansi JL, Fournier RO, andKjargaard J. Acid rain from the heating andevaporation of seawater by molten lava: a newvolcanic hazard. EOS 70:1421-1422(1989).

8. Occupational Safety and Health Administra-tion. Occupational safety and health standards.Code of federal regulations 29, part1910.1000. Washington, DC:U.S. Govern-

ment Printing Office, 1990.9. ACGIH. Threshold limit values for chemical

substances and physical agents in the workenvironment with intended changes for1990-1991. Cincinnati, Ohio:American Con-ference of Governmental Industrial Hygienists,1990.

10. NIOSH. NIOSH/OSHA occupational healthguidelines for chemical hazards. DHHS(NIOSH) Publication No. 81-123. Cincinnati,Ohio:National Institute For OccupationalSafety and Health, 1981.

11. NIOSH. NIOSH recommendations for occu-pational safety and health. DHHS (NIOSH)Publication No. 92-100. Cincinnati, Ohio:National Institute for Occupational Safety andHealth, 1992.

12. Allison IS, Dalmer DF. Geology. NewYork:McGraw-Hill, 1980.

13. NIOSH. Occupational Respiratory Diseases.DHHS (NIOSH) Publication No. 86-102.Washington, DC:U.S. Government PrintingOffice, 1986.

14. Oakes D, Douglas R, Knight K, Wusteman M,McDonald JC. Respiratory effects of prolongedexposure to gypsum dust. Ann Occup Hyg26:833-839(1982).

15. Rom WN, Barkman H. Respiratory irritants.In:Environmental and occupational medicine(Rom WN, ed). Boston:Little, Brown andCompany, 1983;273-283.

16. LaDou J. Acid rain and acid fog. In: Occ-upational medicine (LaDou J, ed). Norwalk,CT:Appleton and Lange, 1990;521-522.

17. NIOSH. Guide to industrial respiratory pro-tection. DHHS (NIOSH) Publication No. 87-116. Cincinnati, OH:National Institute forOccupational Safety and Health, 1987.

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482 Environmental Health Perspectives