YOU ARE NOW CONNECTED TO THE TOXLINE (1981 FORWARD, NON-ROYALTY) FILE. ==SNEEZE DESCRIPTION== 3 AUTHOR Soderholm SC TITLE Size-Selective Sampling Criteria For Inspirable Mass Fraction SOURCE Annals of the American Conference of Governmental Hygienists, Vol. 11, pages 47-52, 7 references, 19841984 ABSTRACT Criteria for size selective sampling of respirable particulate mass are discussed. Airborne material which deposits in the head may be absorbed or swallowed; some deposits may be expelled directly from the body by bulk cleaning mechanisms such as sneezing, spitting, or nose blowing. There are at least three general classes of airborne toxic materials for which a valid hazard evaluation must consider all respirable particles: highly soluble materials which can quickly enter the blood, materials exhibiting toxicity after entering the gastrointestinal tract, and materials which can exhibit toxicity at the deposition site. There may be a significant respirable particle mass concentration in work environments which are close to a source. Aerodynamic diameter is an important parameter in determining whether the particle enters the head. For orientation of 90 to 180 degrees, there seems to be little dependence on wind orientation. Inspiration is sensitive to wind speed when facing the wind, but insensitive to minute volume except when facing a wind with a velocity significantly higher than the inspiration rate. The author recommends that a complete evaluation of an inhalation hazard should include consideration of all airborne particles that can enter the respiratory system. 8 AUTHOR Hinds WC AUTHOR Kuo T-L TITLE A Low Velocity Wind Tunnel to Evaluate Inhalability and Sampler Performance for Large Dust Particles SOURCE Applied Occupational and Environmental Hygiene, Vol. 10, No. 6, Grant Nos. R01-OH-03196 and T42-OH-07214, pages 549-556, 23 references, 1995 ABSTRACT A wind tunnel constructed for use in studies examining inhalable particulate mass was described. The tunnel was designed to simulate typical indoor workplace air velocities, to provide uniform and stable concentrations of test aerosols up to 150 micrometers (microm), to accommodate a full torso mannequin, and be low in cost. The tunnel developed was an 11,000 cubic foot/minute open cycle, closed jet wind tunnel with a cross section of 1.6 by 1.6 meters that was capable of producing wind velocities between less than 0.1 to 2 meters/second. Dust generation was achieved by three gear feed, aspirating dust feeders which delivered narrow distribution aluminum-oxide (1344281) dust to a reciprocating dust distribution manifold. Turbulence in the test section was controlled at intensities between 3% and 14% by a wooden lattice. Testing of the tunnel was performed using a full torso mannequin that simulated human breathing and was modified to collect dust entering the nose and mouth. Air velocity in the tunnel was found to be uniform within 10% and dust concentration was uniform to within 15%. Environmental factors such as humidity, temperature, and noise were discussed. The tunnel met the European Economic Community guidelines for testing indoor inhalable particulate mass samplers and had good performance for particles with aerodynamic diameters ranging between 10 and 145microm. 12 AUTHOR Asgharian B AUTHOR Anjilvel S TITLE A Monte Carlo Calculation of the Deposition Efficiency of Inhaled Particles in Lower Airways SOURCE Journal of Aerosol Science, Vol. 25, No. 4, pages 711-721, 27 references, 1994 ABSTRACT The deposition efficiencies of particles traveling in the lower airways were calculated using a Monte Carlo simulation of particle transport through a straight cylindrical tube and a square cross section of a bifurcating airway. At airflow velocities within the lower airways, particle deposition patterns become a function of diffusion or sedimentation, where sedimentation is the governing force for particles over 2 micrometers and diffusion dictates the deposition of particles smaller that 0.1 micrometer. Performing the simulation with 50,000 particles in both models showed that when diffusion was the dominant loss mechanism, the particles were uniformly distributed and when sedimentation was the governing influence, particle deposition was asymmetrical and related to local flow rate. For particles in the intermediate size range, diffusion and sedimentation compete for particle losses in the airway. To avoid an overestimation of particle loss by simply adding the effects of both particle loss mechanisms, the authors propose an expression for total deposition efficiency that more closely predicted particle loss and considered the simultaneous effect of diffusion and sedimentation. This expression yielded values in good agreement with calculated results. 13 AUTHOR Schneider T TITLE Low-Level Particle Sampling SOURCE Analyst, Vol. 119, No. 1, pages 103-107, 46 references, 1994 ABSTRACT Methods for sampling low levels of particulates were described and discussed. The importance of careful analysis of exposure scenarios was emphasized to allow for the implementation of the most effective and accurate sampling methods. For this purpose the author recommend the use of a scale evaluating the average residence time of an airborne particle. Equations for the calculation of this scale, as well as for the area averaged particle deposition velocity and the unpredictable episodic release of airborne materials were presented. Different aspects of air sampling such as personal versus stationary sampling, sampling interaction with environment and contaminant, and dust fall sampling were discussed. Guidelines for the evaluation of indoor surface contamination were presented and surface sampling methods using adhesive foils, vacuum cleaners, and gelatin foils were described. 39 AUTHOR Baron PA TITLE Calibration and Use of the Aerodynamic Particle Sizer (APS 3300) SOURCE Aerosol Science and Technology, Vol. 5, No.1, pages 55-67, 17 references, 19861986 ABSTRACT Calibrating and using a new aerosol sizing instrument was described. The aerodynamic particle sizer (APS), the first commercial instrument to provide rapid, high resolution aerodynamic sizing of aerosols, was used by NIOSH for more than 2 years, either as a prototype or a commercial version. The APS functioned by accelerating an aerosol through a nozzle and passing it through a laser velocimeter. Eighty percent of the incoming aerosol was filtered and reintroduced as sheath air; the remaining 20 percent was retained for measurement. Aerosol particles were focused into the center of a nozzle and accelerated through the center of two laser beams. Particles in the nozzle lagged behind the air flow and the difference in velocity between the air and particles was related to the aerodynamic diameter of the particles. The APS was originally calibrated with a monodisperse aerosol of di-octyl-phthalate (DOP). Larger particles, 20 to 100 microns in diameter, were observed to flatten into oblate spheroids. The instrument was then calibrated with solid latex particles, and DOP and oleic-acid aerosols were studied to evaluate the effect of droplet flattening. Diameters of DOP and oleic-acid droplets were measured to be 20 percent smaller than the true aerodynamic diameter, for a diameter of 15 microns. The APS was tested with solid monodisperse particles of density 1.15 and 2.15. Shifting the density from 1.15 to 2.15 introduced an 8 percent increase in the measured aerodynamic diameter in the 8 to 14 micron range. When calculations were performed to simulate coincidence, the extent of coincidence observed did not agree with that calculated. The author concludes that the APS is a useful instrument for sizing particles having diameters of 0.8 to 20 microns. The distortion of oil droplets precludes their use as calibration material, unless one is measuring similar liquids. 58 AUTHOR Tufto P~A AUTHOR Willeke K TITLE Dependence of particulate sampling efficiency on inlet orientation and flow velocities SOURCE American Industrial Hygiene Association Journal June 1982, Vol.43, No.6, p.436-443. Illus. 36 ref. ABSTRACT This dependence was studied with a thin-walled inlet tube at wind velocities of 250-1,000cm/s and angles for the inlet orientation relative to wind direction of 0-90 degree(s). Differences in sampling efficiency were found for particles >10:m in diameter when the aerosol was sampled 15 degree(s) upward vs. 15 degree(s) downward from the horizontal. For angles of 30-90 degree(s) sampling efficiency was approximately a function of the Stokes number, with velocity ratio as a parameter. About half or more of the particle deposition in the inlet occurred within the first cm of the 20cm-long inlet tube. 59 AUTHOR Cheremisinoff PN TITLE Air/particulate instrumentation and analysis SOURCE Ann Arbor Science Publishers, 230 Collingwood, PO Box 1425, Ann Arbor, Michigan 48106, USA, 1981. 423p. Illus. 597 ref. ABSTRACT Analytical techniques are presented by experts. The focus is on highly sophisticated methods and equipment. Contents: particle measurement techniques; studies in atmospheric particulate characterisation techniques; imaging and analysis of airborne particulates; stack sampling; bag sequential sampling technique for ambient air analysis; pressure drop measurements across filters; electrostatic precipitator instrumentation and control; measurement of photochemicals in air; analysis of polynuclear aromatic hydrocarbons in the atmosphere; thermal anemometry; fluidic flowmeters; environmental signal processing. 20 AUTHOR Lundgren DA TITLE A Measurement Technique to Quantitate Fugitive Dust Emission from Handling of Granular Products SOURCE Journal of Aerosol Science, Vol. 17, No. 3, pages 632-634, 19861986 ABSTRACT A dust measurement chamber was developed which provided a quantitative measure of fugitive dust generating potential of granular materials. The major source of dust in handling materials was determined to be the time when transported materials were dropped. Dust generation was determined to be a function of drop height or product impact velocity. A simple vertical flow dust chamber was used to measure the amount of dust generated when a granular product was dropped at a rate of 5 kilograms per minute and allowed to free fall 5 feet onto a cement slab. The cement slab was covered with plastic film to facilitate product recovery. Air flow rate was adjusted so that particles less than 50 microns in aerodynamic diameter (ADD) were drawn up into the vertical wind tunnel and collected on a filter, while particles greater than 50 microns in ADD settled downward. These collection characteristics were in compliance with the United States air quality standard for suspended particulate matter. Several hundred samples of ten different granular products, including granular triple superphosphate fertilizer, dry phosphate rock, and white rock sand, were tested in the dust measurement chamber. The author concludes that the dust measurement chamber provides an efficient method for measuring the fugitive dust generation potential of granular products. YOU ARE NOW CONNECTED TO THE TOXLINE65 (1965 - 80, NON-ROYALTY) FILE. 1 AUTHOR BACHE DH TITLE Particle transport within plant canopies: 1. A framework for analysis. SOURCE ATMOS ENVIRON; 13 (9). 1979. 1257-1262. ABSTRACT HEEP COPYRIGHT: BIOL ABS. The drift of particulate matter is relevant to both assurance of target crop protection and prediction of drift of toxic materials. Analysis is developed to relate the bulk trapping efficiency of airborne particulate matter by a vegetal stand to local trapping within the canopy. Attention is focused on inertial impaction and sedimentation as the principal trapping mechanisms. These are combined to yield a capture probability in terms of the particulate trajectory, an impaction coefficient and parameters relating to foliage structure. Turbulent-diffusion equations are modified to account for particulate absorption defined on a Lagrangian basis, and this provides a fairly flexible framework for estimating particulate transport within plant canopies. A generalized bulk deposition velocity is defined, and shown to approach physically realistic limits when either sedimentation or impaction processes dominate. 9 AUTHOR LUNDGREN DA AUTHOR PAULUS HJ TITLE The mass distribution of large atmospheric particles. SOURCE J AIR POLLUT CONTROL ASSOC; 25 (12). 1975 1227-1231 ABSTRACT HEEP COPYRIGHT: BIOL ABS. The total mass and the mass distribution of atmospheric aerosols, especially that mass associated with particles greater than 10 mum diameter, were determined. What fraction of the total aerosol mass a standard high-volume air sampler collects and what fraction and size interval settle out on a dust fall plate were determined. A special aerosol sampling system was designed to obtain representative samples of large airborne particles. A suburban sampling site was used. Samples were collected under various conditions of wind velocity and direction to obtain measurements on different types of aerosols. Atmospheric particulate matter has a bimodal mass distribution. Mass associated with large particles mainly ranged from 5-100 mum in size; mass associated with small particles ranged from about 0.03-5 mum in size. Combined, these 2 distributuons produced a bimodal mass distribution with a minimum around 5 mum diameter. The high-volume air sampler collected most of the total aerosol mass, not just suspended particulate. Dust fall plates did not provide a good or very useful measure of total aerosol mass. The 2 fundamental processes of aerosol formation, condensation and dispersion, appear to account for the formation of a bimodal mass distribution in natural and anthropogenic aerosols. Particle size distribution measurements frequently are in error because representative samples of large airborne particles are not obtained. Air pollution regulations should specify or be based upon an upper particle size limit. 10 AUTHOR LIDWELL OM TITLE Airborne infection in a fully air-conditioned hospital: III. Transport of gaseous and airborne particulate material along ventilated passageways. SOURCE J HYG; 75 (1). 1975 45-56 ABSTRACT HEEP COPYRIGHT: BIOL ABS. A mathematical model is described for the transport of gaseous or airborne particulate material between rooms along ventilated passageways. Experimental observations in 3 hospitals lead to a value of about 0.06 m-2/s for the effective diffusion constant in air with no systematic directional flow. The constant appears to increase if there is any directional flow along the passage, reaching about 0.12 m-2/s at a flow velocity of 0.04 m/s. Together with previously published methods the present formulae enable calculation of the expected average amounts of gaseous or particulate material that will be transported from room to room in ventilated buildings in which the ventilation and exchange airflows can be calculated. The actual amounts transported in occupied buildings, however, vary greatly from time to time. 1 AUTHOR McFarland AR AUTHOR Ortiz CA AUTHOR Bertch RW Jr TITLE Particle Collection Characteristics of a Single-Stage Dichotomous Sampler SOURCE Environmental Science and Technology, Vol. 12, No. 6, pages 679-682, 12 references, 19781978 ABSTRACT The particle collection characteristics of a single stage dichotomous sampler are evaluated. The operational principle of a dichotomous sampler is that an aerosol stream is passed through an acceleration nozzle wherein its velocity is increased such that large particles are collected into a collection nozzle and smaller particles are carried past this collecting zone. The described system provides a cutpoint aerodynamic diameter of 3.6 microns when operated at 14L/min with a large particle transport air ratio, f, of 10 percent. The Stokes number corresponding to this condition for 50 percent efficiency, Stk (0.5) is 0.34. The value of the Stk (0.5) is slightly affected by jet Reynolds number but is a strong function of f. As f is increased from 5 to 15 percent, the value of Stk (0.5) is reduced from 0.56 to 0.19. Wall losses for the system are 7.1 percent at the cutpoint size with 14L/min and f equals 10 percent. These low losses compare favorably with losses of 10.7 percent for the system when operated with two stages. Fractional efficiency curves for both the single and two stage units have steeper slopes than the American Conference of Governmental Industrial Hygienists sampling curve, the reference suggested by the Conference which has a fractional efficiency similar to that of the human lung. 5 AUTHOR Albagli A AUTHOR Oja H AUTHOR Dubois L TITLE Size-Distribution Pattern Of Polycyclic Aromatic Hydrocarbons In Airborne Particulates SOURCE Environmental Letters, Vol. 6, No. 4, pages 241-251, 9 references, 19741974 ABSTRACT Air concentrations of benzo(a)pyrene (50328) (BaP) and benzo(k)fluoranthene (207089) (BkF) associated with various pollutant particle sizes were investigated. Air samples were collected in an eastern Canadian city from September to May. A fractionating sampler with backup filter was used. Particles were aerodynamically separated by inertial impaction into five size ranges. BaP and BkF contents associated with each range were determined by column chromatography followed by fluorescence spectroscopy. Standard geometric deviations (SD) were calculated as the ratio of the diameters at the 84.1 percent and 50 percent concentrations of the cumulative size distribution curve. Sixty percent of the non gaseous atmospheric BaP fell in the range of particles less than 1.1 micron which is the size of particle able to reach the human lung alveoli. An additional 25 percent was less than 7.7 microns, a size capable of being deposited along the respiratory tract. Only 15 percent of BaP was of non respirable size. The same size distribution pattern was observed for BkF. The SD for BaP was calculated as 17.2; the SD for BkF was 10.7. The authors conclude that 85 percent of non gaseous polycyclic aromatic hydrocarbons (PAH) are respirable. Adhesive forces between the PAH molecules and particulates may vary according to the particulate size affecting extraction efficiency and influencing the result. The collection process may also cause coagulation or fractionation of particles. Research on the PAH size distribution pattern of stationary sources is recommended. 6 AUTHOR Landahl HD AUTHOR Herrmann RG TITLE On The Retention Of Air-Borne Particulates In The Human Lung SOURCE Journal of Industrial Hygiene and Toxicology, Vol. 30, No. 3, pages 181-188, 8 references, 19481948 ABSTRACT The retention of airborne particles in the lungs of healthy human volunteers was studied, with attention to particle diameter and the effects of increased air velocity, tidal air, and rate of respiration. The mass median diameter was determined for particles in the air samples introduced. Corn-oil droplets, sodium-bicarbonate (144558) dust, sodium-bicarbonate dispersed from solution, tricalcium-phosphate (7758874) dust, atomized methylene-blue (61734), and glycerol (56815) were introduced at a constant breathing rate of 18 liters a minute, 15 respirations per minute and 450 cubic centimeters tidal air. To study the effect of air velocity, the flow rate of sodium-bicarbonate dust was increased to 60 liters per minute. Respiration rate and tidal volume were altered from a 16 second cycle at 1350 milliliters (ml) tidal air to a 4 second cycle at 450ml tidal air for sodium-bicarbonate dust. Values found for the particle diameter in microns corresponding to 50 percent retention for materials in the same breathing pattern were: corn-oil, 3; sodium-bicarbonate dust, 0.9; dispersed sodium-bicarbonate, 0.8; tricalcium-phosphate, 1.5; glycerol, 0.7; methylene-blue, 1.2. The percent retention of larger particles was higher at greater tidal air or lower respiration. Particle diameter for 50 percent retention of sodium-bicarbonate was 0.8 microns at 18 liters per minute and 0.3 microns at 60 liters per minute. The authors conclude that there is a particle diameter giving medium retention for each substance, particles both larger and smaller being retained more readily. Increasing tidal air or decreasing frequency of respiration markedly increases retention. Increasing the inspiratory flow rate causes retention of smaller diameter particles. YOU ARE NOW CONNECTED TO THE MEDLINE (1994 - 97) FILE. 6 AUTHOR Mullan RJ TITLE Health Care Workers, Tuberculosis, and the Human Immunodeficiency Virus Epidemic SOURCE Scandinavian Journal of Work, Environment and Health, Vol. 18, Supplement 2, pages 97-99, 18 references, 1992 ABSTRACT A working group of the Centers for Disease Control was established to address the implications of an epidemic of nosocomial multidrug resistant tuberculosis (TB) transmission. Of eight cases of active multidrug resistant TB reported in health care workers, four were seropositive for the human immunodeficiency virus, and all of these have died from TB. The group concluded that the prevention of TB transmission in health care settings requires that generation of infectious airborne particles be prevented by early identification and treatment of persons with TB infection and active TB; the elimination of the spread of infectious droplet nuclei into general air circulation by applying source control methods; reducing the number of infectious droplet nuclei in air contaminated with them; and surveillance of personnel in health care facilities for TB and TB infection. The use of ultraviolet germicidal irradiation to prevent TB transmission is controversial and its efficacy in clinical settings has not been demonstrated. Appropriate masks may be used to provide additional protection against TB transmission. A TB screening and prevention program for the personnel of health care facilities should be established for protecting both the personnel and the patients. 3 AUTHOR JENNINGS LC AUTHOR DICK EC TITLE Transmission and control of rhinovirus colds. SOURCE EUR J EPIDEMIOL; 3 (4). 1987. 327-335. ABSTRACT BIOSIS COPYRIGHT: BIOL ABS. With the expanding knowledge of rhinovirus transmission and rhinovirus chemistry, the outlook for control of infections with specific agents has brightened considerably. Although rhinoviruses are probably the world's leading cause of respiratory illness, they are surprisingly reluctant transmitters, infecting only about 50% of susceptibles in family-like settings. Current research suggests that rhinoviruses are spread chiefly by aerosol, rather than by formites or personal contact. It has been possible to interrupt rhinovirus transmission completely by careful use of virucidal facial tissues, which, presumably, smothered aerosols generated by coughing, sneezing and nose blowing. Accordingly, it may be feasible to control rhinovirus (and perhaps other virus) dissemination by appropriate air handling and filtration systems in combination with careful nasal sanitation. Anti-rhinovirus drug development is also moving forward. Although there are over 100 rhinovirus serotypes, it has been found that most rhinoviruses attach to a single cell receptor by a single binding site on the virus. Also, the structure of the rhinovirus capsid is now known at the atomic level. These two pieces of knowledge about basic viral architecture appear to open new vistas for reasoned synthesis of antiviral drugs, and some promising compounds are now under investigaztion. Even interferon has been demonstrated useful in a family setting. On several research fronts, there are good grounds for optimism about control of rhinovirus colds. 2 AUTHOR Cole EC TITLE Aerosol Characterization SOURCE Proceedings of the Workshop on Engineering Controls for Preventing Airborne Infections in Workers in Health Care and Related Facilities, July 14-16, 1993, Cincinnati, Ohio, P. J. Bierbaum and M. Lippmann, Editors; NIOSH, US Department -=of Health and Hum, 1994 ABSTRACT Infectious aerosol characterization was reviewed and research needs relative to the application of engineering controls for the prevention of airborne infections in personnel in health care and other related facilities were identified and prioritized. This problem was addressed as a result of the reemergence of tuberculosis (TB) as a public health problem in the United States (US). A total of 26,000 active TB cases occurred in the US in 1991, representing a 2.3% increase over 1990 and an 18.4% increase over 1985. The sharp increase occurred primarily among the homeless, drug abusers, and those infected with the human immunodeficiency virus. All new cases of TB infection today are contracted by the aerosol route from infected patients who disperse infective droplet nuclei into the air when coughing. Health care and other related workers exposed to confined and TB prevalent populations have a high risk of infection, and are also at risk of contracting other infectious airborne diseases such as influenza, measles, chicken pox, psittacosis, Legionnaire's disease, and aspergillosis. Factors to consider when characterizing bioaerosols include source of generation, particle size, aerodynamic properties of the particles, infectivity and virulence, and viability as it relates to temperature and relative humidity. Most respiratory infections are transmitted through the air from human sources and result from inhalation of droplet nuclei. Infective bioaerosols can also be produced from environmental sources. Legionnaire's disease originating from exposure to aerosols generated from contaminated cooling towers was cited as an example of an opportunistic infection arising from an environmental source. The area of deposition within the respiratory tract is an important factor in determining the response to an inhaled infective bioaerosol. Deposition is also influenced by hygroscopicity. Inhaled aerosol particles increase in size as they move through the airways due to their taking up water. Environmental sampling and analysis of bioaerosols were considered. 30 AUTHOR Handley BA AUTHOR Webster AJ TITLE Some factors affecting the airborne survival of bacteria outdoors. SOURCE J Appl Bacteriol 1995 Oct;79(4):368-78 ABSTRACT Airborne survival of two pseudomonads and a reference strain of Escherichia coli (strain MRE 162) was studied outdoors using a modified microthread technique. When cells of E. coli were suspended as clusters, survival was much greater than single cells, particularly outdoors. Culture age had a highly significant effect on survival of Pseudomonas maltophila with survival of 24 h cultures being more than 100-fold higher than 48 h cultures. Survival of Pseudomonas fluorescens was variable and depended also upon the method of culture. Survival of E. coli and Ps. maltophila was studied at three locations differing in air quality and was found to be significantly reduced outdoors, particularly when held in direct daylight. Outdoor survival was not significantly different at the three locations but was reduced at increasing temperatures. There was no apparent effect of wind direction or air quality. Results are discussed with reference to the release of genetically-modified micro-organisms. 6 AUTHOR Copeland TL AUTHOR Holbrow AM AUTHOR Otani JM AUTHOR Connor KT AUTHOR Paustenbach DJ TITLE Use of probabilistic methods to understand the conservatism in California's approach to assessing health risks posed by air contaminants. SOURCE Air Waste 1994 Dec;44(12):1399-413 ABSTRACT Many state and federal agencies have prepared risk assessment guidelines, which describe methods for quantifying health risks associated with exposure to vapors and particulates emitted from point and area sources (e.g., California Air Pollution Control Officers Association [CAPCOA] under the Air Toxics "Hot Spots" Act [Assembly Bill 2588] and the U.S. Environmental Protection Agency [EPA] under the Clean Air Act). In general, these guidelines recommend or require the use of upperbound "point" estimates for numerous exposure parameters. This methodology yields a single risk estimate, which is intended not to underestimate the true risk and may significantly overstate it. This paper describes a risk assessment of a facility's airborne emissions using a probabilistic approach, which presents a range and distribution of risk estimates rather than a single point estimate. The health risks to residents living near a food processing facility, as estimated using techniques recommended by California AB2588, are compared to the results of a probabilistic analysis. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were identified as the emitted chemicals of concern. The point estimate method recommended by CAPCOA resulted in estimates that were greater than the 99.99th percentile risk predicted by the probabilistic analysis. As shown in other assessments of persistent airborne chemicals, secondary or indirect exposure pathways (i.e., ingestion of beef, ingestion of cow's milk, and ingestion of mother's milk) rather than inhalation, were the greatest contributors to risk. In this analysis, the probability distributions for the cancer potency factor and ingestion of cow's milk had the largest impact on the results of the 33 exposure factors considered.