Exposure to butyl alcohol: uptake and distribution in man.

Twelve subjects were exposed to 300 or 600 mg/m3 of butyl alcohol in inspired air during rest and during exercise on a bicycle ergometer. Exposure lasted 2 h. The results were puzzling in view of the high blood/air partition coefficient for butyl alcohol. The arterial blood concentration was low. The concentration in the last part of the expired air, i.e., the ""alveolar'' concentration, was low. The quotient of ""alveolar'' concentration X 100/inspired concentration was low in relation to the low percentage uptake. However the high solubility of butyl alcohol in water may explain the results. Butyl alcohol was probably partially taken up in the water of the dead space mucous membranes during inspiration. It was then partially released from the membranes. Therefore the concentration of butyl alcohol in the last part of expiration was probably not the same as the concentration in the alveolar air.

Butyl alcohol is the name of four aloohols with the same fOI1ffiu!a, C 4 HgOH. Normal butyl alcohol is the most common form and is the alcoh'Ol referred to in this artide. It is used as a s01vent for paint and varnish in automotive and general painting and as a solvent in plastic manufacturin.g. In the textile industry it is used in the plastic coating of v.arious materials. Butyl alcohol 'is also employed as a solvent f,or glue in the plastics and rubber industry. About 4,000 tons are consumed each year in Sweden, and a large number of people aTe exposed to butyl alcohol in their everyday work.
The American 'threshold limit value (TLV) for butyl alcohol in air is 100 ppm or 300 mg/m 3 of air at 25°C and a barometric pressure of 760 mm Hg. One hundred parts per million was selected because irritation of the airways and the eyes is avoided when this v,alue is respeded (8,10). The French TLV is also 100 ppm (9). In 1973, 0.1 mg/m 3 (6,7) was suggested as the Russian va'lue. Such a low v'alue was proposed because it was felt that certain reflexes might be affected by levels around 1-2 mg/m 3 • The -of:fucial Swedish va,lue is 50 ppm (5).
Few studies have been made of the effect of butyl alcohol on the central ner------------. ---' VOll'S system or long-term effects on health (8). Nor has the uptake and distrilbution of butyl alcohol in the body of man been studi€d to any great extent.
Butyl alcohol has been made the subject of the present study beoause of its widespread use in industry and because it is an ,alcohol. As such its properties differ from those of the solvents previously studied (1). Alcohols with a small number of carbon atoms are highly s()luble in water, in contrast to the other substances previously investigated. The soluhiHty of butyl alcohol in water is 7.9 g/100 g of water, i.e., 8 0/0.

SUBJECTS
The subjects consisted of a group of 12 men, 21 to 34 years of age. Their state of health was carefully exaanined, particular atten1tion being devoted to the function of respir,atory and circula'tory organs. The method employed ha,s been described elsewhere (2,3).
All the sulbjects were healthy. None had ever had any illness th1lJt could affect the results in the exposure trials. All the values from the spirometric examination were normal (t1lJble 1). This was also the case fur values obtained in conjunction with exercise a't four different work intensities. AU the subjects had a normal physical work capacity (table 2). No significant ECG changes were recorded.
None of the subjects had been exposed to solvents in their everyday work. Subjects were asked not to consume any form of alcohol for 24 h prior to exposure.

EXPERIMENTAL DESIGN
The experiments were performed generally in the same manner as in the previous studies of solvents (1). Thus catheters were introduced into a brachial artery and a medial cUibilta:1 vein. The subjects were exposed to butyl alcohol through a breathing valve and a m()uthpiece. Each exposure period lasted 30 min, and each subject was e~()sed for iiour periods, i.e., for a total of 2 h. Subjects were exposed to butyl alcohol in inspiratory air in 'a concentration of 100 or 200 ppm, i.e., 300 or 600 mg/m 3 ()f air, during rest and during exercise on a bicycle ergometer. The Swedish TLV for butyl alcohol in air is, as mentioned earlier, TaMe 1. Means and standard errors of the means of the height, weight, and respira.tory data, taken at rest, of the 12 male subjects 21 to 34      The volume of expiratory air was continuously measured thl'loughou:t the entire exposure, i.e., £or 2 h, with Ithe Douglas bag technique. The butyl alcohol content in each bag was analyzed. The volume of inspiratory air was assumed to be the same as the volume of expiratory air « 1 % error), and the amount of butyl alcohol taken up in the body was calculated as the difference between the total quantities in inspira1Jory and expiratory air. The mean value for pulmonary ventilation/min (VE) was calculated for every 30-min period and for each suibject. The mean value for the six subjects in each series was then calculated. The figures describing the results show how the collectionof the volume of expiratory air was fractionated.
The oxygen content of e~piratory air was analyzed and oxygen uptake was calculated for the laltter half of each exposure period during rest and for the last 5-10 min of each period of exercise. The mean value of two determinations for each period and subject was used. Determinations of oxygen uptaJke 'and of lactic acid concentration in blood were performed so that an assessment of exercise intensity in relation to individual work capacity (max V0 2 ) could be made. Alveolar air samples for butyl alcohol assay were extracted from the breathing valve with a glass syringe during exposure and with la glass tube after the condusion ofeXlposure (3). Samples of arterial and venous blood (atbout 0.5 g) were taken straight from the catheters into 15-mf glass bottles for butyl alcohol assay. Details of thi,s sampling procedure have been presented in oprevtous studiies (2,3). A mean value is given for the concentration of butyl a1cohoo. in alveolar ai,r and in the arteri'al and venous blood of each subject and each 30-min period on the basis of the final three measurements.
The concen:trations in alveolar air and in arterial and venous bl'ood were followed for about 1 h after the conclusion of exposure. The -times at which the samples were taken are shown in fig. 2.
ECGs were recorded continuously throughout the entire eXiposure. Heart rotes were determined every other minute from the ECG records, and the mean value of the three final determinations in each exposure period was used.

ANALYTICAL METHODS
The volume of expiratory air, blood lactic acid concentration, and the heart rate were determined accor.ding w methods described elsewhere (2). The oxygen and carbon dioxide content of expiratory air was determined with automatic analyzers (model OM 11 and LB2, respedively, LKB-Beckman Instr. AB, Vallingby, Sweden), and oxygen uptake was calculated. The errors of the methods are described elsewhere (4).
The concentration of butyl aloohol in inspiratory and expiratory air was determined with a gas chromatograph (model F 30, FID, Perkin-Elmer Ltd., Beaconsfield, Buckinghamshire, England) fitted with a stainless steel column (2 m long, 2.2-mm inner diameter) packed with 1 Ofo OS-124 on Chromosorb G, 60-80 mesh. The flow ra-te of the carrier gas (nitrogen) was 30 ml/min, and the column temperature 100°C. One~milMiter samples were injected.
On the balsis of the chromatogram, the butyl alcohol content was determined with the aid of standard air samples with known concentrations of butyl alcohol.    The butyl alcohol level in bLood was determined willi. a "head-space" method. The analysis was pedormed with a gas chromatograph (model F 11, FID, Perkin-Elmer Ltd., Beaconsfield, Buckinghtamshire, England) fitted w~th a stainless steel column (2 m long, 2.2-mm inner diam·eter) packed with 1 010 fraoonitril II on Chrornosorb G, 80-100 mesh. The flow rate of the carrier gas (nitrogen) was 30 rn1/min, and the.column temperature 70°C. The level of bu tyl a·lcohol in the "head-space" was calculated on the basis of individual blood samples with known concentrations of butyl ,aloohol. The samples were prepared as follows: 1 ,ul of an aqueous solution of butyl alcohol containing 0.5,ug of butyl alcohol/,ul of water was injected into a 15-ml glass bottle containing a known quantity of blood, usually 0.5 g, and 100 pJ of ACD2 -solution. On tthe basis of the content in the "head-space" of the standard, the butyl aloohol content of individwal samples was calculated. The error of the method for a single determination was calculated from 10 double determinations made on blood with a butyl alcohol content of 0.81 mg/kg and found to be ± 0.086 mg/kg, i.e., IDA 010. The lowest detectable level of butyl aloohol in blood was 0.08 mg/kg. ! ACD refers to acidum citricum, dextrose.

Pulmonary ventilation and blood circulation
Pulmonary ventilation, oxygen uptake, blood lactic acid concentration, and heart rate displayed ordinary magnitudes during exposure at rest. No signi-ficant differences were recorded at rest between the measurement values during exposure 'bo the two different concentrations (table 3).
During exercise on the bicycle ergometer pulmonary ventilation, oxygen uptake, and heart rate were of the same magnitude at the respective intensities during ex:posure in cnmparison to non-eX'posure (tables 2 and 3), nor were any differences recorded between measurement values in exposure to the two different concentrations during cycling at an intensity of about 50 W (300 kpm/min).
At the intensities of 50, 100, and 150 W the subjeots utilized about 25, 45, and 65 Ofo, respectively, of their physical work capacities. These va'lues, plus the attendant lactic acid concentrations in blood, suggest that 50 W can be regarded as light phy,sical exercise, 100 W as moderate, and 150 W as heavy physical exerdse f.or the subjects tak,ing part in the study. None of the subjects were troubled by the exposure, either at rest or during exercise. No significant ECG changes were recorded at rest or during exercise. Thus no subject disp1ayed an increased incidence of ectopic beats during exposure in comparison with nonexposure.

Uptake in the organism
The amount of butyl aloohol taken up in the organism was measured as the difference between the amounts in inspiratory and expiratory air (table 4). One example from each series of exposure is shown in figs. 3 and 4.
At rest about 80 mg were taken up during a 30~min exposure to 600 mg/m 3 , whereas the absorbed amount was ha'lved when the exposure ooncentration was halved. The amount ta'ken up constituted about 47 Ofo of the amount supplied.
In exercise at an intensity of about 50 W during three consecutive 30-min periods and exposure to 600 mg/m 3 , the absorbed quantities amounted to 160, 155, and 145 mg, respechvely, and corresponded to 39, 38, and 36 Ofo of the amount supphed.
At exercise intensities of about 50, 100, and 150 W during three consecutive 30min periods and exposure to 300 mg/m 3 , the absorbed quantities amounted to about 80, 130, and 195 mg, respectively, and corresponded to 37, 40, and 41 Ofo of the amount suppl'ied.
Thus the percentage uptake declined in the transiUon from rest to work. On the other hand there was no change in uptake during continued exercise irrespective of whether the intensi,ty was maintained or increased. The total uptake during the 2-h exposure amounted to about 535 mg in series I (high exposure -light exercise) and to about 450 mg in series II (low exposure -rising exercise intensity).    tion in inspiratory air. In exercise of rising intensity amounting to 50, 100, and 150 W, the alveolar concentra'tion rose to 87, 80, and 84 mg/m 2 , respectively, and oorresponded to about 30 % of the concentration in inspiratory air (table 3, fig.  6). T,he arterial blood concentration of butyl alcohol after 30 min at rest in series I (high exposure) was about 0.5 mg/kg (table 3). The ooncentraHon rose to 1.1 mg/kg during exercise at 50 W. This con-centra1:ion remained unchanged throughout the three periods of exercise. The arterial concentratiJon in series II (low exposure) amounted to 0.3 mg/kg after 30 min at rest, I.e., about haU of the concentration obtained with twice the level of exposure. The concentrabon amounted to 0.6, 0.9 and 1.3 mg/kg, respectively, during exercise at the three rising intensities.

Alveolar air and arterial blood concen
In principle the venous blood concentration paralleled the arterial blood ooncentration. Earlier investigations (1) pre- sent comments on peripheral venous concentration, arteriovenous difference, and the ca'lculabon of uptake in reference to the cardiac output and the arteriovenous difference in blood.

DISCUSSION
A surpdsing feature of a comparison between the present results and the results obtained in previous experiments was the relationship between a'lveolar air concentration, arterial blood concentration, and the butyl alcohol uptake (1). The substances previously studied were toluene, methy1chloroform, styrene, white spirit, methylene chloride, and trichloI1oethylene. The exposure level of 300 mg/m 3 of air was selected as the lowest level and not 150 mg/m 3 , which corresponds to the TLV, because no butyl a'loohol cnuld be found in the blood with the assay technique described, even after 30 min of exposure at levels around the TLV. Thus the con-centratiJon in arterial blood was low. After 30 min of exposure at rest to. 300 and to 600 mg/m: l of butyl alcohol, the arterial blood concentration was still lnw, i.e., 0.3 and 0.5 mg/kg, respectively. However, the alvenlar concentrations were simultaneously low, corresponding to about 25' 0/0 of the concentration in inspiratory air.
The va'lues are extraordinary in view of the blood/air partition coefficients fOol' the ,substances compared (1). (The term "partition coefficient" refers to the ratio of concentrations of a substance in two immiscible phases at equiIibI1ium and at 37°C). According to the unpublished results of Lindqvist the coefficient for butyl alcohol happens to be about 1,200 but those for the other substances are considerably less, I.e., they range from about 1 to 32 (1). In view of its coefficient, the concentratinn of butyl aloohol in arterial blood should be hig;her than that of the other substances. Even if the ooefficients, determined in vitro, cannot be used for direct calculations of absolute blood concentrations, they stiH provide some idea of the relative leV'els of compared substances (1).
The fact that the butyl aloohol uptake never amounted to more than about 50 0/0 of the quantity supplied was also remarkable, particularly as the blood/air partition coeffident for butyl alcohol, as already mentioned, is very high. The highest percentage uptake recorded hitherto is a figure of about 70 % for styrene and for the aromatic components of white spirit (1). No partition coefficient has been determined for the aromatic components but the .coefficient for styrene is 32 (1). Thus butyl alcohol uptake should have been analogously greater.
Finally the ratio between the alveolar concentration and the concentration in inspiratory air was small in rela·tion to the uptake percentage (1). For all the other substances this relationship, i.e., percentage uptake -air concentrations, could be plotted on a straight line with a small standard devIation, whereas the relationship for butyl alcohol clearly fell outsidẽ that line ( fig. 7). Thus the cited alveolar concentration of butyl alcohol as a percentage of the concentration in inspiratory air was not related to uptake in the same manner as those of the other substances. These divergent results may have been due to the fact that butyl alcohol is readily soluble in water, whereas the other substances studied were insoluble or only slightly soluble in water. As previously mentioned, the blood/air partition coefficient for butyl alcohol is about 1,200, but the water/air coefficient is also about 1,200 (Lindqvist, to be published). Two simple experiments were performed in order to ascertain1fue consequences of s·olubility in water.
A bag was filled with 10 1 of air containing butyl aLcohol at a concentration of 600 mg/m 3 . For about 30 s the air was pressed through a glass tube, packed with water-saturated filter paper, into an empty bag. The concentration of butyl alcohol in this second bag was measured at 210 mg/m 3 • Thus the remainder must have been absorbed in the tube. Pure air from another 10-1 bag was then pressed at the same rate through the tube with butyl alcohol into an initiatlly empty bag. The butyl alcohol concentration in the latter sack was therea,fter found to be 54 mg/m 3 . The experiment shows that butyl alcohol is rapidly dissolved in water but is also released from water to air. A similar experiment was pedormed with one subject. F1011owing a maximal expiration, the subject performed a maximal inspiration of gas containing a concentration of 600 mg/m 3 of butyl alcohol. The subject then expired the same volume of g,as into four different bags. In bag 1, the volume of which was calculated as being equivalent to the volume of the subject's anatomical dead space, the butyl alcohol concentration was measured at 129 mg/m 3 . The concentrations in bags 2, 3, and 4, which should have contained alveolar air, amounted to 87, 51, and 36 • Butanol series I Butanol series n mg/m 3 , respectively. The oxygen content of bag 1 was 20.5 %, i.e., very close to the concentration in inspiratory air, and this value indicates that a very small amount of alveolar air was present. This experiment also showed that butyl alcohol had been dissolved in water, i.e., in the mucous membranes of the dead space. If this were not the case, then the butyl alcohol concentration in bag 1 would have been the same as in the inspimtory air.
In view of the high blood/air partition coefficient, almost all of the butyl alcohol should have been extracted from the air carried to the alveoli, but the air had probably lost a r,elatively large amount of its butyl alcohol before reaching the alveoli. Most of the butyl alcohol absorbed in the water in the mucous membranes during inspiration is probably retained there. Diffusion from water to blood in the mucous membranes probably takes place very slowly. The layer of cells which separates the water from the blood happens to be relatively thick, and the water/blood partition coefficient is relatively small, Le., about 1.0. In the expiratory phase butyl alcohol is released from the mucous membranes of the dead space into the air flowing from the alveoli, since the alveolar air probably contains a very low concentration.
The preceding remarks may explain why the arterial blood concentmtion was relatively low, why the final portion of the expired air had a higher concentration than was expected, and why the uptake was modest, despite a very high blood/air partition coefficient for butyl alcohol.
Thus butyl alcohol is not only taken up in the alveoli, but also in other parts of the respiratory tract. The corresponding phenomenon pmbably failed to occur with the other substaIl:ces examined (1), because they were not absorbed in the water of the muc,ous membranes but were taken up by the blood passing the alveoli.
It should be noted that the concentration in the "alveolar" air, samples of which were taken according to accepted practice, and in the arterial blood were "false" in the sense that they failed to reflect the amounts taken up. Therefore the ratio between percentage uptake and "alveo'lar" air/inspiratory air can only be used for i.e., the relationship does not apply for water-soluble substances.
The carriage of a substance to different organs in the body is pmvided by the blood. As previously mentioned, the concentration of butyl alcohol in brood was low since part of the uptake apparently took plaoe before the gas reached the alveoli. Even if part of the uptake in dead space ultimately diffused into the arterial blood, the concentration there still remained very low. The low blood concentrations must mean that the risk of a large uptake in other organs, such as the central nervous system, is smaller for butyl alcohol than for the other substances studied to da'te. In any event, this is the case for exposure lasting 2 h as in the present study.
One subject in series II (low exposurerising work intensity) differed from the others by displaying an uncommonly small uptake. His total uptake amounted to 190 mg and represented about 19 % of the quantity supplied. All the other subjects had values ranging from 30 to 53 0/0. The subject was in extremely good physical conditton. He had the lowest pulmonary ventilation and oxygen uptake at 100 and 150 Wand probably even the smallest cardiac output at these intensities. On the other hand, he displayed about the same respiratory rate as the other subjects, probably because this rate is governed by the pedaling rate. However, these circumstances do not explain his low uptake. It may have been because this subject's pulmonary ventilation was more even with less variation in flow rate, and therefore the uptake in and rele;ase from the Received for publka,tion: 1976-06-21 mue-ous membranes was larger than for other subjects, i.e., the net uptake was re'latively slight.