Introduction

1. There have been very few epidemiological studies published which investigated cancer incidence or mortality amongst individuals living in proximity to incinerators in Great Britain.(1, 2) The COC was asked during 1993-4 to comment on a study undertaken by the Small Area Health Statistics Unit (SAHSU) which investigated the cancer incidence of over 14 million people living near to 72 solid waste incinerators. This investigation had been initiated following the publication of several reviews of the potential health risks associated with incineration which highlighted the lack of appropriate epidemiological investigations of cancer risk.(1, 3,4) and was published in the scientific literature in 1996.(5) However, before drawing any conclusions on the SAHSU study, the Committee requested further information in respect of the data on liver cancer; namely a histopathological and case-note review of primary liver cancer cases. The Committee considered the report of this latter investigation during 1998 and at its March 1999 meeting. This statement presents some background information on municipal solid waste incineration in the UK, a review of the SAHSU investigations of cancer incidence near to municipal solid waste incinerators and conclusions reached by the Committee regarding the risk of cancer associated with living near to municipal incinerators.

Municipal solid waste incineration in the UK

2. According to the Department of the Environment, Transport and the Regions (DETR), currently around 26 million tonnes of municipal waste is produced in the UK each year; around 10% of which is disposed via incineration. In the UK all municipal waste incinerators (MWIs) are regulated by the Environment Agency or local authorities. Since 1 December 1996, all MWIs have been required to meet the standards in the Municipal Waste Incineration Directives 89/369/EEC and 89/429/EEC and this resulted in the closure of the majority of the existing incinerators and the upgrading of the remainder. A dioxin emission limit of 1 nanogram per cubic metre (ng m-3) was imposed at the same time although, in practice, most existing plants already achieve dioxin emissions close to 0.1 ng m-3. There are currently 11 MWIs in operation in the UK, with another due to start operating in 2000. The Committee was informed that there is expected to be a significant increase in UK incinerator capacity over the next 10-20 years to meet the requirements of the proposed EC Landfill Directive which sets limits for the percentage of biodegradable waste which may be landfilled (it has been estimated that a further 16 MWIs may be required by 2006).(6) However, the draft Waste Incineration Directive currently being discussed within the EU seeks to reduce further emissions of key pollutants from incineration processes, including particulates, dioxins, and heavy metals.

SAHSU studies of municipal solid waste incinerators.

A. 1996 Investigation of health statistics

3. The cancer incidence of over 14 million people living near to 72 municipal solid waste incinerators in Great Britain was examined from 1974-1986 (England), 1974-1984 (Wales), and 1975-1987 (Scotland).(1) The study was conducted in two stages: the first involved a stratified sample of 20 incinerators and the second considered the remaining 52 incinerators. Overall there was a statistically significant decline in risk with distance from incinerators for all cancers combined and for stomach, colorectal, liver and lung cancers. The excess risk in people living within 1 km of a MWI for these cancers after allowing for a 10 year lag period, was estimated from the second stage investigation to vary from 5% (colorectal) to 37% (liver; 0.95 excess cases 10-5 year-1). SAHSU estimated a total of 23 excess cases of liver cancer in the 0-1 km zone from the second stage of the analysis. There was evidence of residual confounding which the authors suggested was a likely explanation for the findings for all cancers, stomach and lung, and also to explain at least part of the of the excess of liver cancer. For this reason and because of the substantial level of misdiagnosis (mainly secondary tumours) believed to occur among registrations and death certificates for liver cancer, the COC asked for a further investigation. This was to comprise a histological review of the liver cancer cases identified in the first study, in order to determine whether or not an increase in primary liver cancer had occurred.

B. Histological and case-note review of primary liver cancer cases

4. This diagnostic histopathological and case-note review considered 235 cases (155 males, 80 females) registered with primary liver cancer and included all 87 cases within 1km of a MWI, and random samples of 74 cases from 1-7.5 km and 74 from the rest of Great Britain. Diagnostic material was available for 94 cases (of which 26 also had clinical notes available) and medical records only were available for 25 additional cases. Histopathological slides were reviewed independently by three pathologists and any discrepancies resolved at case conferences. The medical records were reviewed independently by one senior clinician.

5. Primary liver cancer was confirmed in 66/119 cases (55%, 95% CI 46-64%) while 21 cases (18%; 95% CI 11-24%) were considered to be definite secondary cancers. The remaining cases could not be distinguished between primary and secondary cancers (26 cases) or no malignant tissue was found in the specimens available (6 cases). There was no evidence to suggest that the proportion of cases confirmed as having primary liver cancer, nor of those with evidence of cirrhosis and associated risk factors, differed with distance from incinerators. The Committee agreed that the confirmation of 55% of registered primary liver cancer cases following diagnostic review, is in accordance with a previous study in Great Britain.(7) The Committee agreed that the finding of a high concordance between cancer registration and death certificate data for the confirmed primary liver cancer cases (80%) was unexpected but important new information which suggested that the use of death certificates was acceptable in epidemiological investigations of liver cancer.

6. Two cases of angiosarcoma were diagnosed on histopathological review within 7.5 km of a MWI (cf 0.26 expected based on a national register (p<0.05)), but there was no evidence more generally of clustering near incinerators of cases ascribed to angiosarcoma in a national register. Neither of these two cases had been diagnosed previously, both being registered as hepatocellular carcinoma, and neither was an industrial case. The Committee noted that there was no background information on the extent to which angiosarcoma was misdiagnosed routinely as hepatocellular carcinoma or carcinoma (not otherwise specified) in the general population. The Committee agreed that SAHSU had adopted an acceptable approach to the evaluation of the significance of the two cases of angiosarcoma given the limitations in the national register data used

7. The histopathology diagnostic review allows a range of estimates to be made of possible (absolute) excess of "true" primary liver cancer near incinerators, based on relative risk estimates from the previous study. Assuming that primary liver cancer was the correct diagnosis in 55% of all registered cases then the excess number of cases among the population living within 1 km of an incinerator is reduced from 23 to 12.6, i.e. an excess of 0.53 excess cases 10-5 year-1. With only definite secondary cancer cases excluded (18%) then the excess within 1km is reduced to 18.8 cases, i.e. 0.78 excess cases 10-5 year-1.(8)

COC evaluation of SAHSU studies

8. The Committee was informed that there have been considerable reductions in the levels of emissions of pollutants from incinerators in recent years. The Royal Commission on Environmental Pollution recognised that epidemiological studies are much less likely to reveal any health effects in relation to current standards of controls on emission of pollutants from MWIs.(1) Thus estimates of the relative risk derived from the SAHSU investigations would, if causally associated with exposure to emissions, be related to accumulated exposures prior to the introduction of the controls implemented through the 1989 Municipal Waste Incineration Directives

9. The Committee agreed that there were a number of factors that should be considered in deriving conclusions on the SAHSU studies of MWIs: i) accuracy of health statistics, ii) accuracy of cancer diagnosis, iii) potential confounding factors for individual cancers, and iv) a number of environmental variables particular to incineration such as type of waste burnt, geographical and meteorological conditions, and controls placed on the emission of pollutants.

10. With regard to the 1996 study of cancer incidence, the Committee agreed that the excess of all cancers, stomach, lung and colorectal cancers were due to socio-economic confounding as has been reported by the SAHSU group following adjustment of the data by use of a deprivation index. Post-hoc analyses which compared cancer incidence prior to establishment of an incinerator with cancer incidence following a 10 year lag period since first exposure was consistent with this conclusion.

11. With regard to the diagnostic histopathology study of liver cancer, the Committee agreed that whilst the excess of primary liver cancer near incinerators was not readily explained by known confounding or other factors, residual confounding by socio-economic factors could not be excluded in view of the strong association of deprivation with liver cancer incidence.

Conclusions

12. The Committee agreed the following overall conclusions with respect to the SAHSU investigations of cancer incidence near MWIs:

i) The SAHSU studies found a small excess of primary liver cancer near municipal solid waste incinerators (estimated to be between 0.53-0.78 excess cases 10-5 year-1). It is not possible to conclude that this small increase in primary liver cancer is due to emissions of pollutants from incinerators, as residual socio-economic confounding cannot be excluded. The Committee agreed that an excess of all cancers, stomach, lung and colorectal cancers was due to socio-economic confounding and was not associated with emissions from incinerators.

ii) The finding of two cases of angiosarcoma during the histopathology review in individuals who were resident within 7.5 km of a municipal solid waste incinerator was unexpected. The Committee considered that the evaluation of this finding was difficult given the limitations in the registration of angiosarcoma and lack of information regarding accuracy of diagnosis in the general population. The Committee, however, agreed that there was no evidence more generally of clustering near incinerators of cases ascribed to angiosarcoma in a national register.

iii) The Committee was reassured that any potential risk of cancer due to residency (for periods in excess of 10 years) near to municipal solid waste incinerators was exceedingly low and probably not measurable by the most modern epidemiological techniques. The Committee agreed that, at the present time, there was no need for any further epidemiological investigations of cancer incidence near municipal solid waste incinerators.

March 2000

References

1. Royal Commission on Environmental Pollution (1993). Seventeenth report: Incineration of waste. Chairman Hougthon J, HMSO, London.

2. Elliott P, Hills M, Beresford J, Kleinschmidt I, Jolley D, Pattenden S, Rodrigues L, Westlake A and Rose G (1992). Incidence of cancer of the larynx and lung near incinerators of waste solvents and oils in Great Britain. Lancet, 339, 854-858.

3. British Medical Association (1991). Hazardous waste and human health. A report from the BMA Professional and Scientific Division. Oxford University Press, Oxford. pp242.

4. Hattermer-Frey HA and Travis C (1991). Health Effects of municipal waste incineration. CRC Press, Boca Raton, pp 387.

5. Elliott P, Shaddick G, Kleinschmidt I, Jolley D, Walls P, Beresford J and Grundy C (1996). Cancer incidence near municipal solid waste incinerators in Great Britain. British Journal of Cancer, 73, 702-710.

6. Regulatory and environmental impact assessment of the proposed waste incineration directive. Final report from Entec UK Ltd to DETR, March 1999.

7. Jenkins D, Gilmore IT, Doel C and Gallivan S (1995). Liver biopsy in the diagnosis of malignancy. Q J Med, 88, 819-825.

8. Elliot P, Eaton N, Shaddick G and Carter R (2000). Cancer Incidence near Municipal Solid Waste Incinerators in Great Britain 2 : Histopathological and Case Note Review of primary liver cancer cases. Br J Cancer, 82(5) p1103-1106.

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