Occupational and Environmental Medicine 1995;52:217-224 Cancer incidence and mortality near the Baglan Bay petrochemical works, South Wales Susana Sans, Paul Elliott, Immo Kleinschmidt, Gavin Shaddick, Sam Pattenden, Peter Walls, Christopher Grundy, Helen Dolk Small Area Health Statistics Unit, Environmental Epidemiology Unit, Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, Keppel Street, London S Sans P Elliott I Kleinschmidt G Shaddick S Pattenden P Walls C Grundy H Dolk Correspondence to: Dr P Elliott, Small Area Health Statistics Unit, Environmental Epidemiology Unit, Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT. Accepted 19 January 1995 Abstract Objectives-To study incidence and mor- tality of leukaemias, cancer of the larynx, and other cancers near the petrochemical plant at Baglan Bay, in response to local concerns of an alleged cluster of cancers in the vicinity. Methods-This is a small area study of cancer incidence, 1974-84 and of mortal- ity, 1981-91 based on the national post- coded data held by the Small Area Health Statistics Unit and with population and socioeconomic data from the 1981 cen- sus. The study is centred on BP Chemicals Ltd, Baglan Bay, Port Talbot, West Glamorgan, South Wales and includes a general population sample of 115 721 people (1981 census) living within 7*5 km of the plant. Cancer incidence and mortality for all cancers, leukaemias, and cancer of the larynx were examined within 7*5 km and 3 km of the plant, and tests for decline in risk of these cancers with distance from the plant were carried out. Mortality from several other cancers possibly associated with the petrochemi- cal industry was also studied. Results-There were 5417 incident can- cer cases and 2458 cancer deaths within 7.5 km of the plant during the periods of study. There was an 8% excess incidence of all cancers within 7 5 km, and a 24% excess of cancer of the larynx, consistent with a general excess of these cancers in West Glamorgan, but no apparent decline in incidence with distance from the plant, nor excess mortality. There was also no evidence of decline in leukaemia incidence or mortality with distance, at all ages or in children. Among the other causes included in the mortality study, there was an excess of multiple myeloma within 7-5 km, espe- cially among women, and a significant decline in mortality from non-Hodgkin's lymphomas although there was no excess overall within 7*5 km. Conclusions-The apparent excess inci- dence of all cancers and cancer of the lar- ynx within 7 5 km of the BP Chemical Ltd works was consistent with an excess more generally in West Glamorgan, pos- sibly related, at least to some extent, to cancer registration in Wales. There was no excess mortality from these cancers. The results for multiple myeloma and especially non-Hodgkin's lymphomas may have been chance findings in view of the multiple tests of significance carried out in the study. A study of lymphatic and haematopoietic cancers near oil refiner- ies in Great Britain is to be undertaken that will help put the findings of the pre- sent study in wider context. (Occup Environ Med 1995;52:217-224) Keywords: petrochemical works; small area; environ- mental epidemiology The Small Area Health Statistics Unit is an independent national facility that uses routine data for the investigation of health statistics near industrial installations.1 2 It incorporates a comprehensive national database that includes postcodes of addresses for the analysis of rates of cancer incidence and mortality in small areas located anywhere in Britain. This study was undertaken in response to concerns of a local pressure group based in the Port Talbot area, about an alleged cluster of cancer, especially of the larynx, and leukaemia among children, near the Baglan Bay petro- chemical works (BP Chemicals Ltd) over a period of about six years (1984-9); there was also concern about several deaths among teachers and pupils at the nearby compre- hensive school. The concerns at Baglan Bay received attention in a SKY television programme, and in the Independent Magazine.3 The plant is concerned with petrochemical processing. It first started operation in 1963, and produced alcohols, styrene, olefins, and benzene from the mid-1960s, and vinyl chlo- ride monomer and polyvinyl chloride (PVC) from the early 1970s. Monitoring of environ- mental concentrations of benzene and other compounds in the area has been carried out by the Port Talbot Borough Council4 and by BP Chemicals Ltd.5 A Warren Spring report5 on the sampling carried out by BP Chemicals Ltd concluded that "reported results for ben- zene at community sampling positions (1-5 ppb) are comparable with long term average results . . . at locations ranging from remote rural to non-kerbside town centre." Our report gives an analysis of the inci- dence of all cancers, leukaemias, and cancer of the larynx within 7-5 km of the Baglan Bay petrochemical works, Port Talbot, West Glamorgan (Ordnance Survey grid reference SS 734 923), for the period 1974-84. To con- sider more recent concerns, it also includes an analysis of mortality for the period 1981-91. 217 on September 7, 2020 by guest. Protected by copyright. http://oem.bmj.com/ Occup Environ Med: first published as 10.1136/oem.52.4.217 on 1 April 1995. Downloaded from
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Occupational and Environmental Medicine 1995;52:217-224
Cancer incidence and mortality near the BaglanBay petrochemical works, South Wales
Susana Sans, Paul Elliott, Immo Kleinschmidt, Gavin Shaddick, Sam Pattenden,Peter Walls, Christopher Grundy, Helen Dolk
Small Area HealthStatistics Unit,EnvironmentalEpidemiology Unit,Department ofPublicHealth and Policy,London School ofHygiene and TropicalMedicine, KeppelStreet, LondonS SansP ElliottI KleinschmidtG ShaddickS PattendenP WallsC GrundyH DolkCorrespondence to:Dr P Elliott, Small AreaHealth Statistics Unit,EnvironmentalEpidemiology Unit,Department of PublicHealth and Policy,London School of Hygieneand Tropical Medicine,Keppel Street, LondonWC1E 7HT.
Accepted 19 January 1995
AbstractObjectives-To study incidence and mor-tality ofleukaemias, cancer of the larynx,and other cancers near the petrochemicalplant at Baglan Bay, in response to localconcerns of an alleged cluster of cancersin the vicinity.Methods-This is a small area study ofcancer incidence, 1974-84 and of mortal-ity, 1981-91 based on the national post-coded data held by the Small Area HealthStatistics Unit and with population andsocioeconomic data from the 1981 cen-sus. The study is centred on BPChemicals Ltd, Baglan Bay, Port Talbot,West Glamorgan, South Wales andincludes a general population sample of115 721 people (1981 census) living within7*5 km ofthe plant. Cancer incidence andmortality for all cancers, leukaemias, andcancer of the larynx were examinedwithin 7*5 km and 3 km of the plant, andtests for decline in risk of these cancerswith distance from the plant were carriedout. Mortality from several other cancerspossibly associated with the petrochemi-cal industry was also studied.Results-There were 5417 incident can-cer cases and 2458 cancer deaths within7.5 km of the plant during the periods ofstudy. There was an 8% excess incidenceof all cancers within 7 5 km, and a 24%excess of cancer of the larynx, consistentwith a general excess of these cancers inWest Glamorgan, but no apparentdecline in incidence with distance fromthe plant, nor excess mortality. Therewas also no evidence of decline inleukaemia incidence or mortality withdistance, at all ages or in children.Among the other causes included in themortality study, there was an excess ofmultiple myeloma within 7-5 km, espe-cially among women, and a significantdecline in mortality from non-Hodgkin'slymphomas although there was no excessoverall within 7*5 km.Conclusions-The apparent excess inci-dence of all cancers and cancer ofthe lar-ynx within 7 5 km of the BP ChemicalLtd works was consistent with an excessmore generally in West Glamorgan, pos-sibly related, at least to some extent, tocancer registration in Wales. There wasno excess mortality from these cancers.The results for multiple myeloma andespecially non-Hodgkin's lymphomasmay have been chance findings in view of
the multiple tests of significance carriedout in the study. A study oflymphatic andhaematopoietic cancers near oil refiner-ies in Great Britain is to be undertakenthat will help put the findings of the pre-sent study in wider context.
(Occup Environ Med 1995;52:217-224)
Keywords: petrochemical works; small area; environ-mental epidemiology
The Small Area Health Statistics Unit is anindependent national facility that uses routinedata for the investigation of health statisticsnear industrial installations.1 2 It incorporatesa comprehensive national database thatincludes postcodes of addresses for the analysisof rates of cancer incidence and mortality insmall areas located anywhere in Britain. Thisstudy was undertaken in response to concernsof a local pressure group based in the PortTalbot area, about an alleged cluster ofcancer, especially of the larynx, and leukaemiaamong children, near the Baglan Bay petro-chemical works (BP Chemicals Ltd) over aperiod of about six years (1984-9); there wasalso concern about several deaths amongteachers and pupils at the nearby compre-hensive school. The concerns at Baglan Bayreceived attention in a SKY televisionprogramme, and in the IndependentMagazine.3The plant is concerned with petrochemical
processing. It first started operation in 1963,and produced alcohols, styrene, olefins, andbenzene from the mid-1960s, and vinyl chlo-ride monomer and polyvinyl chloride (PVC)from the early 1970s. Monitoring of environ-mental concentrations of benzene and othercompounds in the area has been carried outby the Port Talbot Borough Council4 and byBP Chemicals Ltd.5 A Warren Spring report5on the sampling carried out by BP ChemicalsLtd concluded that "reported results for ben-zene at community sampling positions (1-5ppb) are comparable with long term averageresults . . . at locations ranging from remoterural to non-kerbside town centre."Our report gives an analysis of the inci-
dence of all cancers, leukaemias, and cancerof the larynx within 7-5 km of the Baglan Baypetrochemical works, Port Talbot, WestGlamorgan (Ordnance Survey grid referenceSS 734 923), for the period 1974-84. To con-sider more recent concerns, it also includes ananalysis of mortality for the period 1981-91.
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Sans, Elliott, Keinschmidt, Shaddick, Pattenden, Walls, et al
Population and methodsThe study area was defined by a circle of 7-5km radius centred on the petrochemical works(fig 1); this was considered large enough toinclude any likely health effects related to theplant. At the time of study, postcoded data oncancer incidence were held for 1974-86(England), 1974-84 (Wales), and 1975-87(Scotland), and postcoded mortality data for1981-1991 (England and Wales); thus at least10 years had elapsed between first operationof the plant in 1963 and first registration ofcancers in the study. Standard incidence rateswere based on postcoded cancer registrationsfor Great Britain. For mortality, rates forEngland and Wales were used as data forScotland were unavailable beyond 1986.Deaths over the age of 74 were excludedbecause of known inaccuracy in certificationof specific causes of death among elderly peo-ple. The mortality analysis included theperiod of occurrence of the alleged cluster(from 1984).
Postcodes were used to locate cases anddeaths within circles of interest around theplant, and to link them to census enumerationdistricts; valid postcodes were available for89-3% of cancer registrations and over 99% ofdeaths in Wales over the 11 years of the study.Population data (for the calculation of rates)were obtained from the small area statisticsfor the 1981 census; at the time of study,small area statistics for the 1991 census wereunavailable. Within 7-5 km, from the 1971 to1981 census, there was a decline in popula-tion of 3 1%, and a further decline of 1I7%between 1981 and 1991. This decline wasmore noticeable within 2 km (14% from 1981to 1991).
Figure 1 Circles of 3 and 7 5 km centred on the Baglan Bay works, BP Chemicals Ltd.
Because of the change in coding betweenthe eighth and ninth revisions of theInternational Classification of Diseases(ICD), bridge codes were used for cancerincidence to ensure comparability over time 6;as all deaths were coded to the ninth revision(ICD-9), slightly different codes were used forthe mortality analysis. The cancers studied forboth incidence and mortality (ICD codes)were all cancers (140-207, ICD-8; 140-208,238-6 ICD-9, except 202.2-202-6, 202.9 forincidence), laryngeal cancer (161), and allleukaemias (204-207, ICD-8; 204-208,ICD-9). The mortality study also includedsome cancers chosen previously for study-forexample, other lymphatic and haematopoieticcancers, blood disorders, and some solidtumours possibly associated with chemicalexposure to petroleum products7 15 that is,cancers of liver (155) and lung (162), all lym-phatic and haematopoietic cancers (200-208,238 6), blood disorders (238-7, 284-8, 284-9,285-8, 287-3, 287-5, 288-0, 288.8), all lym-phatic and haematopoietic cancers and blooddisorders combined, non-Hodgkin's lym-phomas (200, 202), Hodgkin's lymphoma(201), multiple myeloma (203, 238 6), lym-phoid leukaemia (204), and myeloidleukaemia (205).To allow for possible socioeconomic con-
founding, a deprivation score, shown else-where to be a powerful predictor of cancerrates,16 was calculated for each census enu-meration district in Great Britain from 1981census data on unemployment, overcrowding,and social class of the head of the household.Specifically, each of these variables wasadjusted to have zero mean and unit variance.Z Scores were obtained for each enumerationdistrict, and the deprivation score of the enu-meration district was calculated as the sum ofthe three Z scores. Counts of cancer caseswere obtained for enumeration districts withinnational quintiles of the deprivation score,and for a small (sixth) stratum where datawere insufficient to provide a score. Expectednumbers were obtained by applying appropri-ate year, age, sex, and deprivation specificnational rates to the population data, andsumming up over strata. Effects of the socio-economic stratification were examined bycomparing the ratios of the expected valuesstratified or unstratified for deprivation. Thus,for cancers with higher incidence in moredeprived areas-for example, laryngeal can-cer, and all cancers combined-this ratio ofexpected values is higher in more deprivedareas. For some cancers-for example, alllymphatic and haematopoietic cancers com-bined and leukaemias-there is essentially norelation between incidence and deprivation,whereas for others-for example, multiplemyeloma-lower disease rates are seen inmore deprived areas.16 Sex, year, and diseasespecific standardised registration (or mortal-ity) ratios for Wales were also calculated fromnational rates stratified by the deprivationindex. These were used to adjust for regionaldifferences in registration levels, completenessof postcoding, and incidence (or mortality) by
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*Expected numbers based on rates from Great Britain (incidence) and England and Wales(mortality).tRegional adjustment factor standardised for age and index of deprivation, average males andfemales.i-Standardised for age, sex, index of deprivation, and adjusted for region.§For definition of blood disorders, see text.
multiplying the expected values by thisregional factor. Rates of cancer incidence andmortality were also examined for WestGlamorgan (where Baglan Bay is located) rel-ative to the regionally adjusted national rates.
Incident cases and deaths from leukaemiain children, including any cases in the vicinitywith invalid postcodes, were checked by theChildhood Cancer Research Group in Oxfordagainst data on their own files. The Office ofPopulation Censuses and Surveys and theWelsh cancer registry checked registrationdetails of the incident cases of adultleukaemias. Copies of death certificates wereprovided for all leukaemias, non-Hodgkin'slymphomas, and multiple myeloma.
STATISTICAL METHODSThe main hypotheses identified at the startconcerned, for both sexes combined, the inci-dence (1974-84) of all cancers and cancer ofthe larynx at all ages and ages 0-64, as well asleukaemias in children (0-14), adults(15-64), and at all ages. The main analyses ofmortality were for both sexes combined atages 0-74, as well as all cancers, leukaemias,and blood disorders at ages 0-14.Two sets of data (not independent) were
examined for each cause. Firstly, for descrip-tive purposes, observed (0) and expected (E)values, observed/expected (O/E) ratios, andtheir 95% confidence intervals (95% CIs)(assuming a Poisson distribution) wereobtained for the entire 7-5 km study area, andfor an area close to the source, chosen at thestart to be from 0-3 km. Secondly, 0, E, andO/E ratios were obtained for eight bandsdelimited by circles up to a radius of 7-5 km,chosen at the start to give four circles close tothe plant (within 3 km) with the rest enclosingbands of roughly equal areas. Thus eightbands were defined between circles of radii0.5, 1-0, 2-0, 3-0, 4-6, 5-7, 6-7 and 7-5 km.Tests of significance, based on thosedescribed by Stone,'7 used data from these
eight bands to test for decline in risk at some(unspecified) distance from the plant. Thisapproach partly overcame problems of infer-ence associated with the arbitrary choice ofboundaries as data are examined and testedsimultaneously over all distance bandsincluded in the study, and a single P value isobtained. Significance levels were obtained byMonte Carlo methods based on 999 simula-tions. The tests may give significant resultseven where there is no overall excess in thearea considered.Two tests were done, referred to here as the
unconditional and conditional tests. For theunconditional test, the null hypothesis wasthat the relative risk in each of the bands wasequal to one. An isotonic alternative includesany pattern of non-increasing risk over thebands. The null hypothesis can be rejectedeither because of a raised relative risk over thestudy area as a whole-that is, within7-5 km-or because of a decline in risk withdistance. The data were further explored byuse of the conditional test'8 19 that corrects forthe overall level of risk by constraining thesum of expected numbers over the (7-5 km)study area to be equal to the sum of theobserved numbers.The study, particularly of mortality,
included exploratory analyses of a number ofcancer sites, as well as subgroups of cancers,and analysis by sex and age. This involvedover 75 unconditional Stone's tests, althoughnot all were independent. Care has to betaken when interpreting the results of multiplesignificance tests, where many tests were per-formed. If the 75 tests were truly indepen-dent, with a significance level of 5%, up toseven significant results might be expected bychance alone.
ResultsThe population within 7-5 km of the plantwas 115 721 at the 1981 census (56 302males and 59 419 females) and it was 26 206within 3 km. There were 12 133 boys and11517 girls aged 0-14 within 7-5 km in 1981,and 2681 and 2499 respectively within 3 km.The area within 7-5 km was more deprivedthan the average for Great Britain as a whole,especially from 0-5-1 km, where ratios ofexpected values stratified or unstratified bythe deprivation index were 1-11 for the inci-dence of all cancers and 1-32 for cancer of thelarynx. Results in the tables are given for bothsexes combined and for the age groups identi-fied at the start as of most interest. An appen-dix with age and sex specific results isavailable on request.
Table 1 shows standardized O/E ratios forWales and for West Glamorgan, both for inci-dence and mortality. Rates for Wales as awhole were consistent with national rates;however for West Glamorgan, in comparisonwith (Welsh) regionally adjusted nationalrates, there was evidence for an excess of can-cer registrations for all cancers combined(O/E 1-05; 95% CI 1-04-1-07) and laryngealcancer (1-24; 1.07-1-43).
Sans, Elliott, Kleinschmidt, Shaddick, Pattenden, Walls, et al
Table 2 Observed (0) and Expected (E) * numbers of incident cases within 3 km and 7 5 km of the Baglan Bay petrochemical plant, 1974-84: OIEratios, 95% CI, and P values for Stone's unconditional and conditional tests for all cancers, cancer of the larynx, and all leukaemias, both sexes combined
0-3 km 0-75 km Stone's test
Cause 0 E OlE (95% CI) 0 E OlE (95% CI) Unconditional Conditional
*Standardised for age, sex, index of deprivation, and adjusted for region.tOne extra case within 3 km was misallocated to the 3-4-6 km band, and one case, also one within 0-3 km, was not included as it had a non-valid postcode. If thesecases are added to the 0-3 km band the figures are observed 4, expected 2-13, O/E 1-87 (95% CI 0-51-4-81) (see text).
Table 2 gives cancer incidence from 0-3 kmand 0-7 5 km of the Baglan Bay plant andresults of Stone's tests. Figure 2A shows theeight band data and (log scale) cumulative 0and E with distance; (log1o) cumulative O/Eratios are represented by differences betweeno and E on the log scale. During 1974-84, atotal of 5417 cancers with a valid postcodewas registered within 7 5 km of the plant, v5030 expected (O/E 1-08; 1 05-1 11). This8% excess is consistent with the 5% excessover the same period for the county of WestGlamorgan (table 1). Although Stone'sunconditional test was highly significant(P = 0-001), the conditional test was not sig-nificant (P = 0 49) reflecting an O/E ratiogenerally above one, rather than evidence ofdecline in risk with distance from the plant(table 2 and fig 2A).For cancer of the larynx, there were 70
cases registered within 7-5 km v 52-7expected (O/E 1-33; 1-05-1P68) but Stone'stest was not significant (table 2 and fig 2A).Again, this apparent excess generally in thearea was consistent with the 24% excessrecorded in West Glamorgan as a whole(table 1).
Within 7-5 km, there were 119 leukaemiacases in the 11 years of study against 106-3expected (O/E 1-12; 0-94-1-34), and 51 and38i8 respectively at ages 15-64 (1 32;1 00-1 73) with no evidence of decline in riskwith distance from the plant (table 2). A closeexamination of all the 119 incident leukaemiaregistrations was undertaken in collaborationwith the Office of Population Censuses andSurveys. Two duplicate registrations and onetriplicate were found (all at ages 15-64).Among children (0-14) 10 leukaemia caseswere observed within 7-5 km (9-9 expected),two of which were within 3 km (2- 1expected); again there was no evidence ofdecline in risk with distance (table 2).
Review of the childhood cases by theChildhood Cancer Research Group showedtwo on the database of the Small Area HealthStatistics Unit that had incorrect postcodes(one boy, one girl), both of which should havebeen located within 3 km. One of these caseshad been included in the band 3-4-6 km; theother had a non-valid postcode as the addressat registration was incorrect, and hence thecase was excluded from this analysis. Correct
allocation of these two cases would have givenfour rather than two cases within 3 km (O/E1-87; 0-51-4-81); Stone's test of the reviseddata remained non-significant (unconditionaltest P = 0.61).
Table 3 and fig 2B show the results of themortality analysis for the 11 years 1981-91.For all cancers combined within 7-5 km, therewere 2458 deaths v 2387 expected (O/E 1-03;0-99-1-07). There was no evidence of anexcess, nor decline in risk of death with dis-tance, for any of the solid tumours examinedin this study (larynx, lung, liver, table 3). Forlymphatic and haematopoietic cancers andblood disorders within 7-5 km, there were 179deaths v 156-7 expected (1-14; 0-99-1-32,table 3). There were four deaths fromleukaemia among children (1 19; 0 33-3 06),two of which were also included in the inci-dence analysis; two of the four deathsoccurred within 3 km (one lymphoid, onemyeloid) v 0-7 expected (2-74; 0 33-9 90,table 3). The Stone's tests were not significantin all these analyses (table 3).
For multiple myeloma, adjustment fordeprivation resulted in expected values lower(and hence O/E ratios higher) by up to 5%, asnational reference rates are lower in moredeprived areas. Forty two deaths from multi-ple myeloma were recorded within 7-5 kmduring 11 years v 28-2 expected (O/E 1-49;1-10-2 01, table 3 and fig 2B. All these deathswere over the age of 55 (62% over 65 years),13 were within 3 km (2-15; 1-25-3-67, table3) and 25 were among women; analysis by sexshowed that the excess within 7* 5 km was pre-dominantly among women (2-01; 1 -36-2-97).Over the same period, the standardised mor-tality ratio for multiple myeloma in WestGlamorgan was 0 94 (table 1). When data forall eight bands were examined, the combina-tion of Stone's tests (both sexes combined,unconditional P = 0-057 and conditionalP = 0-36; women, P = 0-014 and P = 0-65,respectively) suggested a general excess ofmultiple myeloma in the area, especiallyamong women, rather than decline in riskwith distance, because the unconditional, butnot the conditional test assumes that thebackground risk is 1 0-that is, the regionalaverage; table 3 and fig 2B, (data for womennot shown). Among women aged 15-74 (datanot shown), there was an excess within
Cancer incidence and mortality near the Baglan Bay petrochemical works, South Wales
A04F
All cancers
l-
103a)
Ca)
c0)C.)C
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Distance from plant (km) Dist
Larynx cancer
:__1
2 4 6Distance from plant (km)
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2 4 6stance from plant (km)
All leukaemias
- Observed--- Expected
2 4 6Distance from plant (km)
Lung cancer
2 4 6Distance from plant (km)
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2 4 6Distance from plant (km)
04 rLymphatic,
haematopoetic,and blood disorders
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Non-Hodgkin'slymphomas
2 4 6
Distance from plant (km)
Multiple myeloma
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r - -
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Figure 2 Graphs of cumulative observed and expected numbers of cases (log scale) with distance from the plant.
7-5 km of deaths from lymphatic andhaematopoietic cancers combined (includingmultiple myeloma) (O/E 1-36; 1 09-1 69), butagain the combination of Stone's tests did notindicate decline in risk with distance (uncondi-tional P = 0-039, conditional P = 0 40).
Fifty one deaths from non-Hodgkin's lym-phomas were found within 7-5 km (50-8expected; table 3 and fig 2B. These comprisedthree reticulosarcomas, three lymphosarco-mas, one malignant hystiocytosis, and theremainder were lymphomas of unspecified
Sans, Elliott, Kleinschmidt, Shaddick, Pattenden, Walls, et al
Table 3 Observed (O) and Expected (E) * numbers of deaths within 3 km and 75 km of the Baglan Bay petrochemical plant, 1981-91: OlE ratios,95% CI, and P values for Stone's unconditional and conditional tests, both sexes combined
0-3 km 07-5 km Stone's test
Cause 0 E OIE (95% CI) 0 E OIE (95% CI) Unconditional Conditional
*Standardised for age, sex, index of deprivation, and adjusted for region. tFor definition of blood disorders, see text.
morphology (ICD-9 code 202 8).Unconditional (P = 0O045) and conditional(P = 0O023) Stone's tests for the eight bandssuggested decline in risk with distance, signifi-cant at the 5% level (table 3 and fig 2B.Analysis by sex showed a significant declinefor women (Stone's unconditional testP = 0-021, conditional P = 0008) but notmen (unconditional P = 0O60).
DiscussionThis report presents an analysis of the inci-dence of cancer (1974-84) and mortality(1981-9 1) within 7 5 km of the petrochemicalworks at Baglan Bay and follows reports of analleged cluster (from 1984) of cancers in thearea, especially cancer of the larynx andleukaemias. The petrochemical industryinvolves exposure to benzene, which is a
recognised cause of leukaemias at least in an
occupational setting,7 where exposures are
likely to be many times higher than thoseexperienced by residents living in the vicinityof a petrochemical plant. For children, an
association of leukaemia and non-Hodgkin'slymphomas with occupational exposure offathers to benzene in the preconceptionalperiod has been reported,20 and in this age
group the geographical distribution ofleukaemia and non-Hodgkin's lymphomasshows evidence of spatiotemporal clustering.21In this enquiry, however, there was no evi-dence of decline in leukaemia incidence or
mortality with distance, at all ages or inchildren.Our finding of an excess incidence of all
cancers and cancer of the larynx within the7.5 km study area is consistent with a generalexcess of these cancers in West Glamorgan.There was no apparent decline in risk with
distance from the plant and we found noevidence of excess mortality from these can-cers. For cancers with prolonged survival suchas cancer of the larynx (or childhoodleukaemias) it is recognised that mortalitydata are a poor proxy for cancer incidence.The study was by design centred on the
Baglan Bay petrochemical plant, althoughmany other possible sources of industrial pol-lution are located nearby. These include theBritish Steel plant at Port Talbot (fig 1), con-taining coking works, and an oil refinery atLlandarcy, within 4 km of the Baglan Baypetrochemical plant. Thus any trend of riskwith distance may be obscured by other possi-ble (environmental) risks operating near theplant.The general excess of cancers in West
Glamorgan needs to be viewed in the contextof cancer registration in Wales, for whichthere have been recent concerns about dupli-cation of records in the National CancerRegistry.22 In our study, scrutiny of all 119leukaemia registrations found two duplicateregistrations and one triplicate. Examinationof incidence relative to mortality gives an indi-cation of the degree of possible over (orunder) registration. Recent data indicatehigher incidence to mortality ratios in Walesthan for any other region of England andWales.22 For West Glamorgan in our study, incomparison with regionally adjusted nationalrates, there was a 5% excess incidence for allcancers but a 2% deficit of mortality, duringthe respective study periods of 1974-84 and1981-91; in contrast, for cancer of the larynx,the standardised ratio estimates for both inci-dence and mortality were raised (1 -24 and1 - 13 respectively). To our knowledge, anassociation between benzene exposure or thepetrochemical industry and cancer of the
Cancer incidence and mortality near the Baglan Bay petrochemical works, South Wales
larynx has not been reported; the main knownrisk factors for this cancer are cigarettesmoking and alcohol drinking, althoughoccupational risks-for example, mustard gasand asbestos-are also described.23 24The mortality study included other causes
of death possibly associated with the petro-chemical industry. We found an excess gener-ally of multiple myeloma within the 7-5 kmstudy area, but Stone's tests were not indica-tive of decline in risk with distance from theplant. Relative mortality from multiplemyeloma in West Glamorgan as a whole wasless than one (standardised mortality ratio094). The excess mortality was found espe-cially among women, whereas previous stud-ies in England and Wales found higher ratesin men than women.25 The reasons for thehigher mortality in women in our study areunclear, and may represent a chance finding.Mortality from multiple myeloma tends toreflect reported incidence well, because fatal-ity is high and median survival time is onlytwo or three years26; 97% agreement has beenreported between death certification and hos-pital diagnosis of multiple myeloma.2' Noerrors or inconsistencies in coding were foundon review of death certificates of the 42 cases ofmultiple myeloma included in our study.
Associations between multiple myelomaand benzene exposure have been reported,again in an occupational setting, for example,in case series9 28 and studies of chemical work-ers.7 15 It has been postulated that low cumula-tive exposures to benzene may produce a welldifferentiated cancer such as multiplemyeloma, whereas higher exposures may leadto leukaemia.'29 In our study, there seems tobe no clear explanation for the apparent localexcess of multiple myeloma; the possibility of achance finding should be considered in viewof the multiple tests of significance carried outin the study.We also found a significant decline in mor-
tality from non-Hodgkin's lymphomas, espe-cially in women, although there was no excessoverall within 7 5 km. The high proportion ofunspecified lymphomas (44/51) is indicativeof likely misclassification among these can-cers. Results of occupational studies that wereexamined for possible associations betweenchronic benzene exposure and non-Hodgkin'slymphomas are inconsistent."3 14 30 No clearexplanation is apparent for the decline in riskoflymphomas reported here; again it may be achance finding.
Limitations in the data and methods havebeen discussed elsewhere.' 2 These includefirstly, varying degrees of incompleteness andduplication in cancer registration, which mayhave been a particular problem in our studygiven both incomplete postcoding and evi-dence of duplicates, at least among theleukaemia registrations. The non-availabilityof the 1991 census small area statistics at thetime of the study did not affect the study ofcancer incidence (up to 1984 only) althoughexpected numbers of deaths may have beenoverestimated because of population declinebetween 1981 and 1991. Also, population
migration" is likely to have reduced estimatesof possible risk.
Secondly, we used a radial dispersionmodel of decline in risk with distance, uni-form in all directions, in the absence ofhistorical exposure data, although recentmonitoring in the area-for example of ben-zene-was not suggestive of generallyincreased levels near the plant.5 Thirdly, thestudy of cancer incidence near a single indus-trial site generally lacks statistical power forrare diseases, and the retrospective nature ofthe statistical tests for the cancers of initialconcern-that is, all cancers, cancer of thelarynx, and leukaemias-greatly complicatestheir interpretation. Fourthly, for some can-cers, including the that of larynx, there is theproblem of possible residual socioeconomicconfounding despite attempts to correct for itby use of the deprivation index. Despite theselimitations, a major strength of the approachof the Small Area Health Statistics Unit is theability to examine the available statistics forsmall areas close to an industrial plant, andwhere necessary, to replicate the study else-where if the findings warrant further investiga-tion.
In summary, the apparent excess incidenceof all cancers and cancer of the larynx within7.5 km of the BP Chemicals Ltd works wasconsistent with an excess of these cancers inWest Glamorgan. Although the cancer inci-dence data available for this study (1974-84)did not cover the period during which theapparent cluster of cancers in the Baglan Bayarea was alleged (from 1984), some reassur-ance is gained from the absence of significantdecline in the earlier period, as well as fromthe finding of no excess mortality from thesecancers during the period of concern. A studyof lymphatic and haematopoietic cancers nearoil refineries in Great Britain is to be under-taken, which will help put the findings of ourstudy in wider context.
The Small Area Health Statistics Unit is funded by grantsfrom the Department of Health, Department of theEnvironment, Health and Safety Executive, Scottish Homeand Health Department, Welsh Office, and Northern IrelandDepartment of Health and Social Services. We thank theOffice of Population Censuses and Surveys (OPCS) and theInformation and Statistics Division of the Scottish HealthService, who made the postcoded cancer data available to us.We also thank OPCS for checking registration details of spe-cific cases and for providing copies of death certificates. Weare grateful for the efforts of the separate cancer registries thatsubmit data to the national cancer registration scheme,especially the Welsh cancer registry; and to Dr Gerald Draper(Childhood Cancer Research Group) for checking cancerrecords of children in the study, and, with other members ofthe Small Area Health Statistics Unit Steering Committee, forhelpful comments on earlier drafts.
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