Public Concerns Regarding the Effect of Nantygwyddon Landfill Site
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Public concerns regarding the effect of Nant-y-Gwyddon Landfill Site (NYG) on the incidence of Non Hodgkin’s Lymphoma (NHL) in the South Wales Rhondda Valley Steward JA, Wright M, White C, Wade R Welsh Cancer Intelligence & Surveillance Unit, Cardiff (WCISU), Wales, UK Background In response to public concern about the health effects of living close to Nant-y- Gwyddon Landfill site (referred to in this document as NYG), WCISU were asked by the local resident campaign group, RANT (Rhondda Against Nant-y-Gwyddon Tip) and also the Welsh Assembly, to investigate a possible link between residence close to the site and the incidence of Non-Hodgkin’s Lymphoma (NHL). The landfill site opened in January 1988 and was closed due to public pressure in March 2002. Emissions from the Nant-y-Gwyddon landfill site Landfill gas is produced by the decomposition of organic material contained in the waste. Environmental monitoring at the site commissioned by the Environment Agency identified 117 different compounds in the raw landfill gas at NYG1. Very high levels of hydrogen sulphide were reported and several other compounds – styrene, dimethyl styrene, ethylbenzene and C4 alkyl benzenes – were found at concentrations exceeding those reported at other UK landfill sites. On four occasions between July and September 1997 community air samples were collected for detailed analysis. The results showed that with the exception of benzene, the carcinogenic agents present in the raw landfill gas sampled were not found at measurable concentrations in the community. Benzene is a colourless liquid with a sweet odour. It evaporates into the air very quickly and dissolves slightly in water. Outdoor air contains low levels of benzene from tobacco smoke, automobile service stations, exhaust from motor vehicles and industrial emissions. Indoor air quality contains higher levels of benzene from products that contain it, such as glues, paints, furniture wax and detergents. A major source of benzene exposure is tobacco smoke. Long term 2,3 exposure to high levels of benzene in the air can cause leukaemia Average ambient air concentration is between 5-20µg/m3(WHO). The air quality standard accepted by the Government recommended by the Expert Panel on Air Quality Standards is 16.25µg/m3 [5 parts per billion (ppb)]. However, they also recommend that the Government should work towards a running annual average of 1ppb. The current long term Environmental Assessment Level (EAL) is set at 3.24µg/m3 (1ppb). 1 Benzene was observed in concentrations exceeding its long term EAL in three of the air samples collected in areas away from the landfill (500m-1km) – measurements of 17.9µg/m3, 12µg/m3 and 5.8µg/m3 were recorded. Modelling suggests that the contribution of benzene to the community air from landfill gas is in the order of 1.1 ppb (3.24µg/m3) - less than benzene derived from other sources (e.g. vehicle emissions). Air around the site was monitored again following the closure of the site. Between January and June 2002 monitoring took place weekly4 Three areas around the site were compared to two control locations in Pontypridd. The mean (maximum) concentrations of benzene found at Jones Street (Blaenclydach), Berw Road (Tonypandy) and Primrose Hill (Gelli) were 0.22ppb(1.71ppb), 0.4ppb(4.65ppb) and 0.0ppb(0.00ppb) respectively. In the Sardis Road and Llanfair Road control sites levels were 0.58ppb(2.24ppb) and 0.06ppb(0.8ppb) respectively. Comparison of levels will only be sensible if the study and control sites are comparable (with respect to traffic volume for example). Toulene and Xylene levels were also monitored. Levels of these were no different in the NYG area to those observed in Pontypridd. All were within the current WHO guidelines. A toxicological review by the Institute for Environment and Health (IEH) for the independent investigator5 considers all possible pathways of exposure including gasses, contamination of water sources and dispersal of dust and concludes that apart from benzene and hydrogen sulphide there is little evidence of exposure. The independent investigator’s report6 (Purchon report) itself does not provide specific evidence of exposure although it appears to raise some doubts about the quality of environmental monitoring in the past. Clinical terminology - Non Hodgkin’s lymphomas – NHL Malignant lymphomas are malignant neoplasms arising in the lymphatic tissues mainly from B-cells. Lymph nodes are an integral part of the body’s immune system and it seems paradoxical that malignancy should arise in it. Some types of lymphoma are indistinguishable from the lymphoid leukaemias which originate in bone marrow. Hodgkin’s disease (C81) is distinguished by clinical features suggestive of chronic infection, an epidemiology with links to Epstein-Barr virus (EBV) and a characteristic histology which includes the Reed-Sternberg cells. The Non-Hodgkin’s lymphomas (NHL) are basically all the others, a heterogeneous group of neoplasms with a complex classification7. The usual clinical presentation of NHL is enlargement of one or more lymph nodes with progressive general malaise, weight loss, intermittent fever and night sweats. The categorisation of NHL (using WHO International Classification of Disease (ICD108)) includes follicular NHL (C82), diffuse NHL (C83), T cell lymphomas 2 (C84), other unspecified NHL (C85) and other unspecified lymphoid and haematopoietic neoplasms (C96). Many pathologists and clinicians now use the more detailed Revised European American classification of lymphoid neoplasms (REAL). Most epidemiological studies of NHL are necessarily “broad brush” as they group diverse diseases together. In the 10 year period, 1989-98, NHL was the 8th most common cancer in males and 10th in females in Wales. The corresponding crude rates were 15.9 and 12.9 per 100,000 population per annum, respectively. Brief review of the research literature The literature shows unexplained worldwide increases in the incidence of NHL. Most studies suggest that this increase is related to calendar period effects (cross-sectional) rather than birth cohort effects (longitudinal). Some workers consider that this is an artefact of classification changes but most agree that the increase is a real effect, presumably of some unknown environmental factor9,10. Various potential risk factors have been investigated. By far the strongest association with NHL is with immunodeficiency, whether that be amongst patients with the rare inherited primary disorder, or those with a secondary disorder such as that consequent on HIV infection or taking immunosuppressive drugs e.g. to facilitate transplant. Virus infection has been considered but the association with EBV infection is not so strong as with Hodgkin’s disease, with the exception of lymphomas associated with immunosuppression. The rare adult T-cell lymphoma has been linked to infection by the human retrovirus HTLV-1 that is prevalent in certain tropical areas. Other types of medical treatment may be associated with NHL. Some studies have suggested links with BCG vaccination, blood transfusion, certain anti-epileptic drugs and cancer chemotherapy. There is weak evidence for a link with medical radiation from the well known Court-Brown and Doll study of ankylosing spondylitis. Various cohort and case-control studies have highlighted a number of occupations, which are identified as being at increased risk of NHL. These include painters, carpenters, brick and stone masons, plumbers and roofers, rubber workers, chemists, chemical workers, dry cleaners, petroleum refinery workers, printing workers, abattoir workers, beauticians, farmers and wood workers. Amongst the specific risk factors identified in such studies are exposure to chlorophenols/ phenoxyacetic acids, wood dust, thinner, white spirits, solvents, mineral/cutting/lubricating oil, benzene, arsenic, hair dye and pesticides. The association with farming may not be an effect of increased exposure to agri-chemicals although organophosphates, as for example in sheep dips, are immuno-suppressive. Some studies show veterinary surgeons also have a high incidence of NHL. Perhaps animal exposure per se could be a risk factor e.g. by some unknown zoonotic infection? In fact the strongest dietary association with NHL is with the consumption of milk, which is puzzling but could be linked with the latter hypothesis. High dietary intake of fats and certain meats and low intake of vegetables (particularly cruciferous) have also been found to be risk factors as with some other cancers. Cigarette smoking, tricyclic antidepressants, aspirin, amphetamine or cocaine use, adult-onset diabetes and low birthweight have all been reported in the literature as being associated with excess NHL risk. Other suspected risk factors such 3 as exposure to ethylene oxide, residence proximal to nuclear installations, exposure to sunlight and consumption of tea and coffee have all been found to have no association with NHL after repeated epidemiological studies. Across the literature on aetiology, many studies present contradictory conclusions however. For example, one study showed no NHL association with exposure to benzene and another stated chorophenols were not a risk factor. Nitrate levels in drinking water, phenoxy-herbicides and alcohol consumption have also caused debate. One problem may be the lack of diagnostic precision available to epidemiological studies and difference in case classifications. 10 Methods The statistical analysis of putative sources poses several well-known problems 11,12. There is no universally approved method. Thus a variety of methods were employed in an attempt to acquire a robust overview of the situation. All NHL cases (1983-2001) were extracted from the WCISU database as frozen at May 2002. Using postcodes, the incidence was allocated to defined geographical boundaries, the 1991 census wards in Wales. Numbers of cases, expected numbers, and age-standardised incidence rates (using Wales as the standard population) were examined for wards whose centroid was within 2.5km of NYG. A distance of 2.5km was chosen on the basis of a literature review of distances used in similar studies, and the perceived area of risk identified by RANT.