Cancer incidence, morbidity and geothermal air pollution in Rotorua, New Zealand.

BACKGROUND The New Zealand city of Rotorua sits on a geothermal field. However, little is known about the possible health impacts of the geothermal emissions. This was an ecological study that examined cancer incidence and morbidity data for Rotorua. METHODS Cancer registry and hospital discharge (morbidity) data were obtained for the decade 1981-1990. Standardized incidence ratios (SIR) were calculated comparing Rotorua residents with those living in the rest of New Zealand. Diagnostic categories examined were based on known target organ systems of hydrogen sulphide toxicity. RESULTS Of the cancer sites, there was an elevated rate for nasal cancers. However, this was based on only four cases. The SIR for cancers of the trachea, bronchus and lung in Maori women was 1.48 (95% CI: 1.03-2.06). This was not explained by higher smoking rates. In the hospital discharge data, a number of diseases showed elevated SIR, notably diseases of the nervous system and the eye. To some extent, these effects were characteristic of effects induced by hydrogen sulphide and also mercury compounds. However, there were few data with which to assess whether significant mercury exposures had occurred, and other explanations were possible. CONCLUSIONS There are inadequate exposure data for Rotorua to permit conclusions on likely causal associations. However, some of the elevated disease rates were at least consistent with what one might expect to find if sufficient exposures to hydrogen sulphide and/or mercury were occurring.