Ethylene oxide doses in ethene-exposed fruit store workers

Ethylene oxide doses in ethene-exposed fruit store workers. Scand J Work Environ Health 1989;15:436-438. Blood samples from 10 ethene-exposed fruit store workers and 10 referents were analyzed for the level of hydroxyethyl adducts to N-terminal valine in hemoglobin (H b). A statistically significant difference was obtained between the nonsmoking workers (N = 7) and the nonsmoking referents (N = 6). This find ing demonstrates that ethene is metabolized to ethylene oxide in man. According to this preliminary study, ethene exposure at 0.3 (uncertainty range 0.1-1) ppm during workhours increases the adduct level by 23 pmo llg Hb . This figure is compati ble with a metabolic conversion of 3 010 (1-10 070) of the inhaled ethene to ethylene oxide.

The determination of adducts in hemoglobin (Hb) is a useful approach for mon itoring tissue doses of ultimate carcinogens (1, 2), and it pro vides a basis for risk estimat ion (3).
The measurement of hydroxyethyl adducts to Nterminal valine in hemoglobin (4) by gas chro matography-mass spectrometry has been used as dosimetry for ethylene oxide in smokers and non smokers (5, 6). The adduct level in smokers [an increment of about 85 pmol/g Hb and 10 cigarettes/d (7») ind icat es that the ethene in tob acco smoke may be the source. This hypothesis is based on the assumption that human s and experimental anim als metabolize inhaled ethene to ethylene oxide (8)(9)(10) and detoxify ethylene oxide (see references II and 12) at approximat ely equal rat es or that the ratio of the rates of bioa ctivat ion and epoxide detox ification is approximatel y the same for man and rodents, with the same epoxide dose per milligram of inhaled ethene as a consequence (5).
However, this quantitative agreement between found and expected adduct levels cannot be considered proof that ethen e in tobacco smoke is the source of the adduct s. Natural metabol ites may give rise to hydro xyethyl adducts, ethene may be formed endogenously (5, 13), and it cannot be excluded that such processes are affected by smoking in a way that results in increased 2-hydroxyethyl addu ct levels. Unequi vocal proof that ethene is metabolized to ethylene oxide in humans I Department of Radiob iology, Unive rsity of Stockholm, Stockhol m, Sweden. , Foretagshalsovardscentralen, Skar AB, Go tebo rg, Sweden.
Reprint requests to: Dr MA Tornq vist, Departm ent of Radiobiology, University of Stoc kholm, S-106 91, Stockholm, Sweden . 436 could be gained in studi es of the adduct level in persons with a specific expo sure to ethene. For this purpose employees in a compa ny using ethene for controlling the ripening of ban anas were examin ed with regard to the N-(2-hydroxyethyl)valine (HOEtV al) level in their hemoglobin.

Subj ects and methods
Blood samples were obtained from 10 stoc kroom workers and 10 referent s. Dat a were recorded on exposure to tobacco smoke, urb an air pollution , and oth er cond ition s that might influence the results. Personal and stationary monitoring of ethene in the workplace was carried out for 2 d in conn ection with the blood sampling. The anal ysis was based on the enrichment of ethene on a solid sorben t (13X, Union Carbide) and subsequent thermal desorption for gas chromatographic analysis. The blood samples were collected in heparinized tubes with gamma-sterilized cannulae. The red cells were recovered by centri fugation and were carefully washed with an 0.9 % sodium chloride solution. Th e cells were stored at -70°C. Globin was precipitat ed according to the method described by Mowrer et al (14). The samples were anal yzed by gas chromatography-mass spectrometr y with respect to HOEtVal in hemo globin by an updated version (10) of the N-alkyl Edman method (4). For practical reasons, the samples from the referents were collected one month later than the sample s from the exposed persons, but replicate blood sampl es from two of the exposed persons were collected at the same time as the reference samples. This repeat ed sampling was considered necessar y as a check that the storage of samples, through arte fact formation of HOEtVal , had no influence on the results (15). nation ale Research Maatschappij BV, and the National Swedi sh En vironment Protection Board.

Acknowledgments
We are grateful to Professor L Ehrenberg fo r his valuable viewpoi nts. The st udy was su ppo rted fina ncially by the Swedish Work En vironment Fund, Shell Inter-

Results and discussion
The results from the analyses of the HOEtVallevels in hem oglobin and th e data on smo king habits are pre sented in table I. A statistically significa nt difference (P < O.OI) was o bta ined bet ween the nonsmoking fru it sto re workers a nd th e nonsmoking referents with respect to the level o f HOEtVal in hemoglobin. This result is important since it suppo rts qualitatively the assumption, ba sed on animal experiments and studies on smokers-no nsmo kers, th at et hene is metabolized to ethylene oxide a lso in man. Personal and statio na ry monitoring o f ethen e in th e workplace show ed a ir co ncent ra tio ns in the range o f 0.02-3 .35 ppm, the a vera ge co nce ntr ation being estimated as 0.3 (uncertainty range 0.1-1 ) ppm . A cco rding to thi s preliminary study, ethene expo su re at a level of 0.3 ppm during wor khours would thus incre ase the HOEtVallevel by 23 pmollg Hb.
With the use of a probable valu e of the rate of clearance of ethylene oxide in man [approximately 3 h-I (II)], a ventilation rate of 0.2 I · kg -I . min -I , absor ptio n of 80 % of the inhaled a mo unt (16), and a rate constant of k = 0.45 . 10-4 I . (g Hb)-I . h -I (17) for the reaction of ethylene oxide with N-t erminal valine in hemoglobin , the steady-state level of HOEtVal esta blished during long-term expos ur e at , eg, I ppm of ethylene oxid e during workho u rs is estima ted to be 2.2 nmol (g Hb) -t . This estimate agrees with determination s of adduct levels in wo rkers well chara cterized wit h respect to eth ylene oxid e exposure [2.4 nmol HOEtVallg Hb , corresponding to exp osure at I ppm for 40 h/week (12)].
Accordingly I ppm of ethene in a mbient air wo uld give rise to the sa me adduct level as 0.03 (ra nge 0.01-0.1) ppm of eth ylene ox ide and wo uld correspond to a co nversio n rat e of 3 0/0. Cigarette smo kers ha ve been estima ted to convert about 6 % o f the inhaled ethene to ethylene oxid e (5, 7). This value fall s within the interval found in the present study. For att aining a more accurate value for the conversion rate -useful for the hygienic surveillance of work en vironments and for risk assessment -studies with a better cha ra cterization of exposure doses are required . A comparison of exposed and unexposed smokers indica tes that the former exhibit a larger adduct level increment per cigarette and gram of hemoglobin (15. 7 pmol) th an the latter (9.3 pmol) , and , in fact, a t-test show ed th is difference to be wea kly significa nt (P = 0.02). A difference of this kind wo uld a pply if the system bioa ctivatin g ethene is induced in smo kers. This po ssibili ty, of importance to risk assess me nt , will be su bjected to fu rther studies.