A FOLLOW-UP STUDY OF LEAD WORKERS

Brit.J.

industr. Med., 1963,

20, 313.

A FOLLOW-UP STUDY OF LEAD WORKERS

BY

1. DINGWALL-FORDYCE and R. E. LANE

From the Nuffield Department of Occupational Health,UniversityofManchester (RECEIVED FOR PUBLICATION JUNE 12, 1963)

Following the suggestion that lead derivatives might cause cancer in man, the causesof death among workers known to have been exposed to lead were studied. A group ofcompanies made available the records of their pension fund, and an accumulator factory provided details ofmen who had died whilst in their employ. Details of each man's exposure to lead were supplied.

There were 425 pensioners, of whom 184 had died; 153 deaths occurred among an unknown number ofemployed men who had not yet reached pensionable age. Expected deaths were cal- culated from the appropriate rates for all males in England and Wales.

Itwasconcluded that there was no evidence to suggest thatmalignantdisease was relatedtolead absorption. There was, however, evidence that heavy exposure to lead was associated with an increased incidence of deaths from cerebrovascular catastrophies.

Zollinger (1953) described kidney tumours in rats followingtheirlong-term dosing with lead phosphate.

Afewyearslater this observation was confirmed by Mathews and Walpole (personal communication).

Boyland, Dukes, Grover, and Mitchley (1962) fed 20 rats on a diet containing 1

%

lead acetate for one year. Of 16 which survived 320 days, 15 were found tohave either adenomas or adenocarcinomas of the kidney. They suggested that the possibility that lead derivativescause cancerin man should be examined.

Unfortunatelycurrent nationalfigures are of little help in the examination of this problem. The mortality experiences of lead workers become swamped amongst those of men in allied trades which do not involve a lead hazard. Also the actual numbers involved are relatively small; during the five-year period 1949to 1953there were seven deaths attributedtomalignant neoplasms among 1,200 lead burners, a figure which indicated a rather better mortality experience than that which occurred among the general population. Inhisdecennial supplement of 1921 (Registrar-General, 1927) the Registrar- Generalobserved:

"As it has recentlybeen stated that lead confers such complete immunity fromcancerthatleadburnersnever diefrom thiscausetheirrecordhasbeenexaminedonthis pointandfrom suchscantydata(as isavailable) the only certain conclusion tobe drawnis that lead burners can diefrom cancerlikeotherpeople."

A more satisfactory method of approach to the problem appearedto bea retrospective surveyover many years of the fate of a group of workers known to have been exposed to lead. Such information could be obtained froma group of companies who readily made available the records of their pension fund. Alarge accumulatorfactory within the concern alsoprovided details of men who had died whilst in theiremploy.

The companies concerned provided the details necessary to allocate each man to a category accord- ing to the degree ofrecognized lead hazard associ- ated withthe jobs he had held whilst in their employ.

These were defined as follows:-Grade A, no exposure; gradeB, negligible exposure, with lead-in- urine values within the normal range; andgrade C, exposurerepresented for the last 20 years by mean lead-in-urine values between 100 and 250

[tg./l.,

but in the pastthese have notinfrequentlyexceeded 250 ,ug./l. Examples of the types of work in the various categories are shown in Table 1.

TABLE 1

GRADES OF EXPOSURETO LEAD

A B C

General office Casting AssemblyPlatecutting Chem-iist General stores Forming Pastingandmixing Power house Charging Plumbers Lead recovery Stokers IWorksdepartment Packers Tubefilling

office 5 313

4BRITISH JOURNAL OFINDUSTRIAL MEDICINE Pensioners

This population comprised all men who became pensioners between the years 1926 and 1960. In order to beeligible for apensionaman must have reached 65 years of age and have not had less than 25years' service. Arrangements can be made for an earlier retirement but this is very infrequent, and years of service and age must total at least 95.

There were 425pensioners,ofwhom184 had died during the period under review. Detailsofgradeand length of service are shown in Table 2.

TABLE 2

MENBECOMING ELIGIBLE FOR A PENSION, 1926.1960 GradeofExposure

A B C

No. of men 158 80 187

Meanexposure(yr.) - 353 32-3

No.ofdeaths 56 27 101

Causes of death were obtained from the death certificates. Death rates for all males inEnglandand Wales were extracted from the Registrar General's Statistical Reviews (1933, 1938, 1943, 1948, 1953and 1958). Thenumberof"expected"deathsamongthe pensioners was calculated from the populations at risk, assumingthat they had had the same mortality experience,standardizedfor age, asthat of all males.

Deaths whilst in Employment

Anexaminationwasmadeofthe deaths of all men who had died between1946 and 1961 whilst employ- ed by theelectric accumulator company (Table 3).

TABLE 3

MEN DYINGDURING THE PERIOD 1946-1961 WHILST IN EMPLOYMENT

Grade ofExposure

A B C

No. of men 35 40 78

Mean exposure(yr.) - 26-8 21-8

Mean age 57-7 53 4 53 7

There were 153 such

deaths,

the causes of which

weretakenfrom thedeath certificates.

The actual

population

atriskwas notknown for thisgroup.

"Expected"

deathsweretherefore based

on the ratios of numbers from

specific

causes to numbersfromall causesfound amongst all males in

England

and Wales. Thesewerecalculated in five- year age groupsfrom 35 to70 for theyears

1948,1953,

and 1958.

Results

DeathsfromallCauses.-Evidenceofanexcess,or a

deficit,

of deaths from all causes could

only

be

sought

amongthe

pensioners.

Theresultswereexamined

according

to

grades

and date of death. There wasfound tobe a

significant

excessin

grade

C

(p

< 0

01).

Detailsareshown in Table4.

Deaths from

Malignant

Neoplasms, All

Sites.-

Deaths from malignant neoplasms were examined according tograde and date of death. In gradeB therewasanincrease inobserveddeathsamongboth

pensioners

and

employed

men

(Table 5).

Thediffer-

ences,

although

not

significant

in eithergroup

alone,

werepossibly significantwhencombined(p < 0

05,

n =

2,

x2 =

7f5).

However,

in

grade C,

the most

heavily exposed grade,

therewas noevidence ofanyexcessofdeaths

amongeither

pensioners

oremployedmen.

Thus theexcessofdeaths from all causes could

not beattributedtomalignantneoplasms.

Deaths from Cerebral Haemorrhage,

Cerebral Thrombosis,

and Cerebral Arteriosclerosis.-There appeared to have been arelatively largenumber of deaths attributed to vascular lesions affecting the central nervous system. Deaths from cerebral catastrophieswerethereforeexamined(Table6)and

were found to be in excess to a highly

significant

extent

(p

< 0001)amonggradeC

pensioners.

Althoughthenumbers involvedaresmall,itmay be noted that the ratio of observed to

expected

deathsincreasedwithexposurein bothgroups;also

TABLE 4

EXPECTED AND OBSERVED DEATHS FROMALL CAUSESINPENSIONERS, 1926-1961 Grade of Exposure

Yearof Death A B C

Expected Observed Expected Observed Expected Observed

1926-1940 6-0 4 04 1 3-6 5

1941-1950 9-6 14 2-3 6 11-2 16

1951-1961 51-2 38 22-6 20 60-2 80* xs=65

1926-1961 66-8 56 25-3 27 750 101* x'=9 0

*p <0-01

314

A FOLLO W- UP STUD Y

OF

LEA D WORKERS

TABLE 5

EXPECTED AND OBSERVED DEATHS FROM MALIGNANT NEOPLASMS IN PENSIONERS, 1926-1961,AND IN EMPLOYED MEN, 1946-1961

Grade ofExposure

A B C

Year of Death

Expected Observed Expected Observed Expected Observed

Pensioners 1926-1940 0 9 2 0 1 0 0-6 0

1941-1950 1-7 3 0 5 0 1 9 1

1951-1961 8-7 9 41 10 10-0 9

1926-1961 11-3 14 4-7 10 12 5 10

Employed 1946-1961 8-8 10 9 5 15 18-5 17

TABLE 6

EXPECTED AND OBSERVED DEATHS FROM CEREBRAL HAEMORRHAGE, CEREBRALTHROMBOSIS, AND CEREBRAL ARTERIOSCLEROSIS INPENSIONERS, 1926-1961, AND INEMPLOYED MEN, 1946-1961

theincrease was most marked amongst the earliest deaths. This indication of a possible correlation between thesedeathsand the degree of lead hazard is in complete contrast to the pattern shown by deaths duetomalignant neoplasms.

In 1921 cerebral haemorrhage was the cause of a significant excess of deaths amongst plumbers, painters, and decorators (Registrar-General, 1927).

Amongst the small numbers of lead burners there were during 1930-1932 three such deaths to one

"expected", and during 1949-1953 four deaths to two "expected"

(Registrar-General,

1938 and 1957).

Discussion and Conclusions

There was found to be a significant excess of deaths from all causes amongst those pensioners who had been exposed to the greatest lead hazard. This excesscouldnotbeattributed to malignant neoplasms asthe number ofdeaths from this cause was found to be slightly less than expected among these heavily exposedmen.

Although there was an excess of deaths from malignant neoplasms among the men with slight lead exposure, the increase was only apparent in the lastdecade.

Thus the incidence of malignant disease is least among the men engaged on the most hazardous processesandhas become greater as the exposure to lead has become less following improvements in factory conditions. It is concluded therefore that malignant disease is not related to lead absorption.

The pattern of deaths from vascular lesions of the central nervous system ismarkedly different. Deaths from these causes are very significantly inexcess in thegroups mostheavilyexposedtolead.Analysishas shown, moreover, that, as exposure has decreased with improved working conditions, the excess of central nervous systemvascularlesions has diminish- ed. It appears therefore thatmenwhowereexposed to a lead hazard during the first quarter of this century mayhave had their livesshortened. Cerebral haemorrhage in later life has been shown to occur more frequently amongst them than in the general population. There are, however, indications which suggest that the danger may by now have been reduced.

We wish to thank the Chloride Electric Storage Company for allowing access to their records and for financial assistance; Dr.D.Malcolm forproviding details of those whodied inservice; and thosemembers of the staff of the various associated companies who provided detailed information regardinglead exposure.

REFERENCES

Boyland, E., Dukes,C.E., Grover, P. L., andMitchley, B.C. Y.

(1962).Brit. J.Cancer,16,283.

TheRegistrar-General (1927). DecennialSupplement, Englandand Wales. 1921.

TheRegistrar-General (1938). DecennialSupplement,Englandand Wales. 1931.

TheRegistrar-General(1957). DecennialSupplement, Englandand Wales. 1951.

TheRegistrarGeneral'sStatistical ReviewofEnglandandWales,Part 1.1933, 1938, 1943,1948, 1953,1958.

Zollinger, H.U.(1953). VirchowsArch.path.Anat.,323,694.

315