Occupational and environmental exposures and myelodysplasia: A case-control study

Leukemia Research Vol. 19, No. 2, pp. 127-139, 1995. Copyright 8 1995 Elsevier Science Ud Printed in Great Britain. All rights reserved 0145-2126/95 $9.50 + 0.00

Pergamon 01452126(94)00141-3

OCCUPATIONAL AND ENVIRONMENTAL EXPOSURES MYELODYSPLASIA: A CASE-CONTROL STUDY

AND

R. R. West, D. A. Stafford, A. Farrow and A. Jacob& University of Wales College of Medicine, Cardiff, U.K. (Received 9 April 1994. Revision accepted 16 September 1994) Abstract-A case-control study of newly diagnosed myelodysplastic syndrome patients investigated lifetime exposures through occupation, environment or hobby by questionnaire, structured and semi-structured interview. The exposure histories of 400 individually matched pairs were compared. Increased or possibly increased odds ratios were observed for radiation (2.05, 95% confidence interval 1.163.76), halogenated organics (1.57, 0.97-2.57), metals (1.40, 0.99-2.00), several specific radiation exposures and individual chemicals and for childlessness (1.46, 1.01-2.11). Since myelodysplasia generally carries a poor prognosis, whether or not individuals convert to leukaemia or to other cancer, these findings add to previous reports of exposures implicated in the aetiology of leukaemia and add to the case for minimizing exposures to radiation and halogenated organics. Key words: Myelodysplasia, chemicals, radiation.

case-control

study,

exposure,

occupation,

environment,

leukaemia, there has been little research on the possible occupational and environmental antecedents of preleukaemia or myelodysplasia [l, 14,151. MDS represents a preleukaemic state in which about one-fifth (1530%) develop acute myeloid leukaemia with variable rates of progression. These conditions arise following some mutagenic damage and may be associated with exposure to environmental agents [8,13,16,17]. Our pilot study suggested that petrol and diesel fuels and exhaust gases were risk factors for MDS [14]. Another case-control study investigated exposures to insecticides, pesticides and solvents and, with small numbers, found no statistically significant association [El. Secondary myelodysplasia is well recognised following both chemotherapy and radiotherapy [l, 2,8,14,18]. The aetiology of MDS may be similar to that of leukaemias already studied. The present case-control study investigates the association between occupational and environmental exposures to organic and inorganic chemicals, radiation and other hazards and MDS. The study investigates both duration and intensity of exposure and source of exposure, through occupation, hobbies or environment.

Introduction Myelodysplasia (MDS) or preleukaemia is a clonal haemopoietic disorder, arising as a consequence of haematopoietic stem/progenitor cell damage, which presents at a median age of 65-70 years [l, 21. Many epidemiological studies have been undertaken in leukaemia and many have shown leukaemia to be associated with exposure to aromatic hydrocarbons including benzene and related compounds and to ionizing radiation [3-6]. So far, non-ionizing radiation has not been shown to be associated with leukaemia [7]. Associations have been shown between secondary leukaemia and exposures to alkylating drugs or radiation in medical treatment after a first cancer [3-6,8]. Acute myeloid leukaemia, involving distinct cytogenetic and clinicopathologic features, has been reported after occupational exposure to pesticides and organic solvents [9, lo]. Associations have been found between myeloma and aplastic anaemia and occupational exposure to paints, petroleum products and viruses [ll, 121. Associations have been reported also between leukaemias and non-occupational exposure to chemicals, including pesticides [ 131. While many epidemiological studies have investigated occupational and environmental exposures and

Materials and Methods The study includes all five French-American-British (FAB) Co-operative Group classifications of myelodysplastic syndrome (MDS) [19]. It sought all newly diagnosedpatients over

Correspondence to: Dr. R. R. West, University of Wales

College of Medicine, Heath Park, Cardiff CF4 4XN, U.K. 127

128

R. R. West et

15 years of age and resident in three geographic areas centred on Cardiff and Newport in South East Wales, Southampton and Bournemouth in Wessex and Harrogate and Leeds in West Yorkshire. Controls were selected from outpatient clinics and inpatient wards of medicine, ENT, orthopaedics and geriatrics and included a wide variety of diagnoses but excluded malignancy [20,21]. Controls were matched individually with cases for age (+ or - 3 years), sex, area of residence and hospital and year of diagnosis (t or - 2 years). The caseecontrol methodology for estimating exposure to chemical and radiation hazards was based on the approach of Siemiatycki et al. [22], which was designed to develop a hazard-based estimate rather than the more usual ‘job title based’ estimate. The method developed for this study utilized (i) efficient case ascertainment procedure; (ii) searching interviews with cases and controls to obtain details of past occupations, hobbies and medications and exposure to chemicals, radiation and other hazards through work, leisure activities, environment and therapy; (iii) a study of jobs associated with exposure to estimate exposure risk, and (iv) an estimate of lifetime exposure (in both intensity and duration) from patient interview and job study [14]. Patients were first asked to describe all employment of 6 months or more, principal hobbies and whether or not they had lived near a potential environmental hazard. Occupations were grouped according to the Office of Population Censuses and Surveys classification (1980). Patients were then taken through a list of over 70 chemicals, chemical groups or other potential hazards including radiation, and asked to describe any exposure at work, through hobbies or at home. Where exposures were reported, patients were asked to expand in some detail on the nature of the exposure, how the material was used, what protective clothing was worn and whether ventilation was provided. Patients were asked to estimate exposure for each chemical or other hazard as h/day, days/year and years. Intensity of exposure was estimated in three broad classes; low, medium and high; (i) ‘low’ exposure was, for example, being in the same room as the chemical, material or hazard; (ii) ‘medium’ exposure was, for example, working with the chemical; and (iii) ‘high’ exposure was, for example, working with volatile substances within a confined space with poor ventilation and/or poor protection. Estimate decisions were taken after consultations with industrial chemists and occupational hygienists, on, for example, the manner in which a chemical was used in a process, and in the light of published data on, for example, the volatility and toxicity of a chemical.

al.

The estimates took into consideration where or how a hazardous substance may have been handled and whether the substance may have been breathed, swallowed (for example following finger contamination) or absorbed through the skin 1231. While a very low lifetime exposure (possibly only minutes in a working lifetime) may be detectable and may have clinical significance, a minimum practical ‘memorable’ exposure is about 10 h in a lifetime, which might be made up of, for example, lOmin/day, 20days/year and 3 years duration. This has been used as the ‘minimum’ exposure. Classification of exposure (i.e. whether a patient was ‘exposed’ or ‘not exposed’) to an individual chemical or group of chemicals was performed on three ‘sensitivity’ thresholds defined as follows: (i) Low exposure threshold (high sensitivity): 10 h (or more) of lifetime exposure and low (or medium or high) intensity of exposure. (ii) Moderate exposure threshold (medium sensitivity): 50 h (or more) and medium (or high) intensity of exposure (but not low intensity). (iii) High exposure threshold (low sensitivity): 2500 h (or more) and medium (or high) intensity of exposure (but not low intensity). A higher exposure threshold (lower sensitivity), including only exposures at high intensity, was considered but yielded very small numbers of ‘exposures’. Lifetime hours of exposures to each chemical, radiation or other hazard were estimated by multiplying h/day x days/ year x years. An ‘exposure index’ was generated by multiplying the lifetime hours of exposure by 1 or 10 or 100 depending on whether the intensity was estimated as low or medium or high. These ratios (1:lO:lOO) reflect observed decreases in hazard concentration from a source (in parts per million or fibres per cubic metre etc.) and are broadly in line with those recommended for the control of exposures [23]. Since exposures to many chemicals and other potential hazards occurred in only small numbers, chemicals and other hazards were combined into 13 groups, according to generic chemical classification (such as organics or metals) or method of production (such as petroleum products from oil cracking or aliphatics by chemical synthesis) or active (volatile) constituent (e.g. paints, solvents and glues) or use (e.g. agrochemicals). The dusts groups were defined primarily on particle size: dusts were mostly inorganic but included some organics and metals.

Table 1. Age and sex distribution of MDS patients Interviewed Men

15-24 25-34 3544 45-54 55-64 65-74 75-84 85-94 95+

3 2 11 27 72 79 21 0 216

Registered but not interviewed Men

Women

;:; (1) (6) (13) ;:i; (10) (0) (100)

7 4 8 22 50 66 23 3 184

(1) g;

1 0l

(4)

2

I::;

27 l2

E,’

48 19

(2) (100)

1

111

Women

1 1 4 3 6 28 45 33 2 123

129

Occupational and environmental exposures and myelodysplasia

Table 2. Risk estimates of exposure to individual chemicals, hazards or radiation (at low exposure threshold*) Number (per cent) exposed* Cases Controls

Individual chemicals, hazards or radiation A A A A A A A A A A B B B B B C C C C C D D D E E E E E E F F F F F F F F F F F F F F G G G G G H H H I I I I .I .I J J

Ethylene oxide Ethylene glycol Vinyl chlorine Plastic/Resin fumes Butadiene Phenol Nitrobenzene Formaldehyde Naphthylamines Trinitrotoluene Diesels/Petrols Oils/Greases Coal tar DyesKoIourings Inks Anaesthetic gases Dry cleaning fumes Halo carbons Degreasing agents Polychlorinated biphenyls Paints/Varnishes Solvents Glues Insecticides Pesticides Weedkillers Fertilizers Wood preservatives Woodworm treatment Ahrminium compounds Beryllium compounds Chromium compounds Copper compounds Mercury compounds Nickel compounds Steel dust Tin compounds Uranium compounds Welding/Brazing gas Arc welding fumes Molten metal fumes Metal oxide fumes Nickel carbonyl Amine Arsenic compounds Selenium compounds Semi-conductors Thallium compounds Asbestos Stone dust Formica/Plastic dust Exhaust gases Mineral acids Hydrogen peroxide Ammonia fumes Cotton/Jute dust Sisal/Hemp dust Paper dust Cereal dust

6 2: :: ‘Z 2

(2)

ii; ii; ii; ii;

4

(1)

:: 39 9

I:; (10) (2)

‘:

I:;

19 123 123

(5) (31) (31)

‘i 17 122 108

r-:; (4) (31) (27)

ii

g;

%;

ii;

:;

ii;

‘Z

I;;

“i 51 5 127 38 60 51 64 17 39 40

g; (13) (1) (32) (10) (15) (13) (16) (4) (10) (10)

‘: 49 3 135

ii; (12) (1) (34)

:i 45 62

(1’;; (11) (16)

:; 43 15 41 5 16 89 5 53 59

,r:; (11) (4) (10) (1) (4) (22) (1) (13) (15)

‘ii 61

ii; (15)

z: 21

ii; (5)

8

(2)

30 -

(8)

18 96 5 50 68

(5) (24) (1) (13) (17)

‘Z 78 39

g; (20) (10)

:;

g; :

g;

l42 -

it;

‘:

;:;

4 44 66 16 79

(1) (11) (17) (4) (20)

:. 44 65

(1) (11) (16)

3:

{ii

2 27 9

,1’;; (7) (2)

::

ii;

2

I:;

8

(2)

6

(2)

20 39

(5) (10)

Odds ratio 614 = 1.50 21/15 = 1.40 719 = 0.78 25/31 = 0.81 10/8 = 1.25 14110 = 1.40 516 = 0.83 14/12 = 1.17 613 = 2.00 18/16 = 1.13 69/68 = 1.01 66/51 = 1.29 31/29 = 1.07 25130 = 0.83 25/21 = 1.19 1216 = 2.00 26/15 = 1.73 817 = 1.14 41139 = 1.05 513 = 1.67 50/58 = 0.86 35134 = 1.03 47135 = 1.34 37/31 = 1.19 40138 = 1.05 15/20 = 0.75 34137 = 0.92 32135 = 0.91 8115 = 0.53 25136 = 0.69 17/15 = 1.13 76169 = 1.10 515 = 1.00 41144 = 0.93 53144 = 1.20 18/21 = 0.86 61144 = 1.39 31122 = 1.41 30/28 = 1.07 16/20 = 0.80 lo/18 = 0.56 2/l = 2.00 412 = 2.00 35135 = 1.00 35134 = 1.03 15/20 = 0.75 63150 = 1.26 32127 = 1.19 1918 = 2.38 26123 = 1.13 32119 = 1.68 816 = 1.33 25120 = 1.25 39/35 = 1.11

(95% CI)

(0.88-1.89)

(0.883.43)

(0.85-2.13)

(0.93-2.08) (0.79-2.55)

-

(0.86-1.86) (0.99-5.90) (0.93-3.09)

R. R. West et

130

al.

Table 2. cont. Individual chemicals, hazards or radiation Wood dust Bird products Live/Dead stock Cooking oils Soap powders Detergents

Cytotoxic drugs M M M M M

High voltage Radio transmission Microwaves/Radar Ionizing radiation Radiochemicals

Number (per cent) exposed* Cases Controls 43 34 35 16 7 16

6

33

18 18

(11) (9) (9) (4) (2) (4)

37 32 3.5 17

6

24 4 28 9 11

(2)

(8) (5) (5)

(9) (8) (9) (4)

(2)

(6) (1) (7) (2) (3)

(95% CI)

Odds ratio 37/31 = 1.19 31/29 = 1.07 30130 = 1.00 16/17 = 0.94 7/6 = 1.17 12/20 = 0.60 614 = 1.50 31/26 = 1.19 1718 = 2.13 18/11 = 1.64 1517 = 2.14 512 = 2.50

(0.87-5.36) (0X2-5.79)

* Low threshold; 10 h and low intensity of exposure.

Non-occupational exposures that may contribute to a risk of disease were also estimated: these included ionizing radiation (for example, in diagnosis or treatment or living near a nuclear power station), non-ionizing radiation (for example, by living near high voltage electric power cables) and chemicals in a hobby (such as photography or gardening), or environmentally (such as by living near a polluting industry or farm) or in transport (such as self-service of petrol). Cigarette smoking history was also sought. Since secondary myelodysplasia has been reported by several investigators, patients’ past medical history, including radiotherapy or chemotherapy for cancer, was summarized. This was done late in the interview to reduce the risk of unblinding the interviewer to case or control status. The reported work histories of samples of both cases and controls were validated with regard to years worked and nature of job by correspondence with the relevant employers and close agreements of both duration of employment and job histories were obtained. A small samnle of cases were reinterviewed and close correlation of exposures obtained. All

N ” nl

b s r

data were stored on the university computer and analysed by matched pairs analysis using SPSS programmes and results are presented as odd ratios, with 95% confidence intervals.

Results Six hundred and thirty five patients diagnosed with myelodysplasia (MDS) were reported to the study by participating haematologists. Although patients were notified to the study within 1 year of diagnosis to be eligible for inclusion, 163 (28%) died before interview, 21 (3%) were deemed too ill (by consultant or general practitioner), 12 (2%) had moved away from the area and 34 (5%) refused. Thus, 400 MDS patients were interviewed with regard to their lifetime exposure histories.

300(

250

f7l

P 0

1.0 1.5 Odds ratio (log scale)

Fig. 1. Odds ratio for 71 chemicals, radiation and other potential hazards. *Cases (and controls) may be exposed to several hazards.

131

Occupational and environmental exposuresand myelodysplasia

Table 3. Risk estimatesof exposure to individual chemicals, hazardsor radiation at low threshold* Chemical, hazard or radiation group A B C D E F G

H I .I K L M

Number (per cent) exposed* Cases Controls

Organic chemicals Petroleum products Halogenatedorganics Paints/Solvents/Glues Agrochemicals Metals Semi-metals Inorganic dusts Inorganic gases/Fumes Plants (and products)

99 203 83

(25) (51) (21)

84 196 70

(21) (49) (18)

157 122 185 21 103 124 121

(39) (31) (46) (5) (26) (31) (30)

161 121 190 26 103 105 108

(40) (30) (48) (7) (26) (26) (27)

Animals (and products)

59 37 78

(15) (9) (20)

56 42 54

(14) (11) (14)

Aliphatics Radiation

Odds ratio

(95% CI)

70/55 = 1.27 85178 = 1.09 64/51 = 1.25 66170 = 0.94 67166 = 1.02 93198 = 0.95

(0.88-1.84)

16/21 = 0.76 53/53 = 1.00 91172= 1.26 85172 = 1.18 48145 = 1.07 32/37 = 0.86 69145 = 1.53

(0.86-1.84)

(0.92-1.74) (0.85-1.64) (1.04-2.27)

*Low threshold; 10 hours and low intensity of exposure.

The age and sex distribution of MDS patients included in the study is given in Table 1. Similar numbers of men and women were notified to the study, but rather more elderly women were lost to interview. The table shows clearly the extent to which MDS is a disease of the elderly. 79% of interviewed men and 77% of interviewed women were aged over 65 years, (85 and 88%, respectively, of those registered and not interviewed were aged over 65 years). Exposures to 71 individual chemicals or chemical groups, radiations or other potential hazards, defined on the low threshold (high sensitivity) of 10 h and low intensity of exposure, are summarized in Table 2. Odds ratios (OR) were estimated as the ratios of discordant pairs for matched case-control study and for clarity the 95% confidence intervals (CI) are entered only for those chemicals with the lower 95% CI >0.80. No individual chemical was statistically significantly associated with myelodysplasia at ; < 0.05, although hydrogen peroxide was of borderline significance (OR = 2.38, 95% CI = 0.994.27). The overall pattern of association between exposure and myelodysplasia is summarized in Fig. 1, which shows the point estimates of odds ratios of all exposures listed in Table 2. The distribution centres on an odds ratio of 1.2, (with standard deviation 0.4). This is significantly greater than 1.0 (evens) at p < 0.01 and would suggest that overall, patients with MDS were more likely than controls to have experienced exposures. Table 3 summarizes the risk estimates of chemicals, hazards or radiations grouped into 13 generic groups. Radiation was significantly associated with myelodysplasia (at p < 0.05) and the association between inorganic gases and fumes and myelodysplasia was of borderline significance. There were also suggestions of

associations with organic chemicals, halogenated organics, and plants and plant products. These findings are altered little when analysis is restricted to men only. The exposure threshold used to calculate the odds ratios in Tables 2 and 3 was low and exposures according to this definition may have been overcounted, particularly for several common exposures (such as diesel, petroleum, oils/greases or paints/ solvents/glues). Accordingly, odds ratios were reestimated at medium threshold exposure (>50 h and amedium intensity) and high threshold exposure (>2500 h and amedium intensity) for the 72 chemical or hazard groups: these are presented in Table 4. Most individual chemicals, hazards or radiation, that showed possibly elevated odds ratios at the low threshold (Table 2), showed possibly elevated odds ratios also at the higher exposure thresholds (Table 4). While for some the apparent risks were not maintained (e.g. ethylene glycol), for rather more the estimated relative risks were stronger. Copper, arc welding fumes and hydrogen peroxide were significantly associated with MDS and degreasing agents, nickel, exhaust gases and radio transmissions were close to being significantly associated at (one of) the higher thresholds. The individual chemicals or hazards were grouped as before and risk estimates at the two higher thresholds are summarized in Table 5. The associations between several chemical or ‘hazard groups suggested an increasing trend with increasing threshold. For example, the estimated risk associated with radiation at low threshold was 1.53 (Table 3), at medium threshold was 2.05 and at high threshold was 2.25 (test for trend, p < 0.01). These trends, apparent in several groups (e.g. halogenated organics, metals and inorganic gases/ fumes) are suggestive of a dose response.

R. R. West et

132

al.

Table 4. Risk estimates of exposure to individual chemicals, hazards or radiation at medium and high threshold* >SOh and > medium intensity* Odds ratio (95% CI) A A A A A A A A A A B B B B B C C C C C D D D E E E E E E F F F F F F F F F F F F F F G G G G G H H H I I I I J J J J

Ethylene oxide Ethylene gIyco1 Vinyl chloride Plastic/Resin fumes Butadiene Phenol Nitrobenzene Formaldehyde Naphthylamines Trinitrotoluene Diesels/Petrols Oils/Greases Coal tar Dyes/Colourings Inks Anaesthetic gases Dry cleaning fumes Halo-carbons Degreasing agents Polychlorinated biphenyls Paints/Varnishes Solvents Glues Insecticides Pesticides Weedkillers Fertilizers Wood preservatives Woodworm treatment Aluminium compounds Beryllium compounds Chromium compounds Copper compounds Mercury compounds Nickel compounds Steel dust Tin compounds Uranium compounds Welding/Brazing gases Arc welding fumes Molten metal fumes Metal oxide fumes Nickel carbonyl Amine Arsenic compounds Selenium compounds Semi-conductors Thallium compounds Asbestos Stone dust Formica/Plastic dust Exhaust gases Mineral acids Hydrogen peroxide Ammonia fumes Cotton/Jute dust Sisal/Hemp dust Paper dust Cereal dust

l/2 = 0.50 516 = 0.83 514 = 1.25 17/21 = 0.81 615 = 1.20 814 = 2.00 314 = 0.75 713 = 2.33 l/2 = 0.50 1219 = 1.33 48147 = 1.02 46150 = 0.92 16/16 = 1.00 13/18 = 0.72 12/10 = 1.20 612 = 3.00 1618 = 2.00 714 = 1.75 33123 = 1.43 l/2 = 0.50 39143 = 0.91 17/19 = 0.89 27126 = 1.04 14/13 = 1.08 10/19 = 0.53 619 = 0.66 9113 = 0.69 12/15 = 0.80 317 = 0.43 10/14 = 0.71 714 = 1.75 40123 = 1.74 21/11 = 1.91 34129 = 1.17 11/7 = 1.57 34125 = 1.36 1615 = 3.20 22113 = 1.69 10/6 = 1.67 9/15 = 0.60 3/l = 3.00 22115 = 1.47 26128 = 0.93 10/7 = 1.43 31/18 = 1.72 13/12 = 1.08 1312 = 6.50 11/18 = 0.61 19/10 = 1.90 3/l = 3.00 1017 = 1.43 20/18 = 1.11

> 2500 h and > medium intensity* Odds ratio (95% CI) l/l = 1.00 513 = 1.67 10/13 = 0.77 413 = 1.33 312 = 1.50 212 = 1.00 412 = 2.00 l/l = 1.00 514 = 1.25 36133 = 1.09 44136 = 1.22 718 = 0.88 216 = 0.33 812 = 4.00 2/l = 2.00 913 = 3.00 312 = 1.50 20/10 = 2.00 l/l = 1.00 17126 = 0.65 11/9 = 1.22 12/16 = 0.75 212 = 1.00 l/7 = 0.14 l/l = 1.00 10/9 = 1.11 213 = 0.67 33114 = 2.36 1417 = 2.00 27119 = 1.42 917 = 1.29 17/12 = 1.42 1013 = 3.33 15/10 = 1.50 814 = 2.00 317 = 0.43 lO/lO = 1.00 22126 = 0.85 5/5 = 1.00 22114 = 1.57 615 = 1.2 419 = 0.44 13/11 = 1.18 2/l = 2.00 5/5 = 1.00 8110 = 0.80 -

(0.81-5.09) (0.82-2.52)

(1.01-3.00) (0.88-4.22)

(0.79-2.35) (1.10-9.97) (0.82-3.55)

(0.93-3.20) (1.40-41.67) (0.84438)

(0.79-27.23)

(0.89-4.57)

(1.22-4.62) (0.76-5.46) (0.76-2.66) (0.64-3.15) (0.85-15.23)

(0.77-3.23)

Occupational and environmental exposuresand myelodysplasia

133

Table 4. corrf. >50b and > medium intensity* Odds ratio (95% CI) Wood dust Bird products Live/Dead stock Cooking oils Soap powders Detergents Cytotoxic drugs High voltage radiation Radio transmission Microwaves/Radar Ionizing radiation Radiochemicals

22124 = 0.92 17119 = 0.89 17120 = 0.85 6110 = 0.60 l/2 = 0.50 317 = 0.43 l/l = 1.00 1618 = 2.00 1113 = 3.67 915 = 1.80 413 = 1.33 l/l = 1.00

>25OOh and > medium intensity* Odds ratio (95% CI) 13117 = 0.76 7113 = 0.54 12/11 = 1.09 217 = 0.29 l/3 = 0.33

(0.81-5.09) (0.95-16.52)

;5/8 = 1.88 913 = 3.00 4/l = 4.00 l/l = 1.00 -

(0.75-4.82) (0.75-13.94)

* See text.

Non-occupational exposures are summarized in Table 6. A significant association with MDS was observed for exposure to dental X-rays (OR = 1.85, 95% CI 1.25-2.76) and a possible association was observed for diagnostic X-rays of bones. Weak associations for those living near factories ( medium Odds ratio 48140 = 1.20 71176 = 0.93 47/30 = 1.57 63158 = 1.09 33140 = 0.83 80/57 = 1.40 12116 = 0.75 41/35 = 1.17 53/41 = 1.29 50/43 = 1.16 27130 = 0.90 lo/18 = 0.56 39/19 = 2.05

exposure and intensity (95% CI)

(0.97-2.54) (0.99-2.00) (0.84-1.98)

(1.15-3.68)

High exposure > 2500 h and > medium intensity Odds ratio (95% CI) 28124 = 1.17 66/53 = 1.25 26/12 = 2.17 32138 = 0.84 3/11 = 0.27 66/37 = 1.78 417 = 0.57 27134 = 0.79 33125 = 1.32 31132 = 0.97 16/20 = 0.80 4110 = 0.40 27/12 = 2.25

(0.85-1.82) (1.05-4.54) (1.17-2.72) (0.76-2.29)

(l.lw.70)

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R. R. West et al.

Table 6. Risk estimatesof non-occupational exposure Exposure Diagnostic X-rays Chest X-rays Bone X-rays Barium enema/h4eal IVP-Angiogram Dental X-rays Other X-rays Domicile (26 months) near Factory (< 100m) High voltage cable (< 200m) Nuclear power station (