Motor neuron disease mortality and lifetime petrol lead exposure: Evidence from national age-specific and state-level age-standardized death rates in Australia

Background: The age standardized death rate from motor neuron disease (MND) for persons 40 to 84 years of age in the Australian States of New South Wales, Victoria, and Queensland increased dramatically from 1971 to 2013. Nationally, age-specific MND death rates also increased over this time period, but the rate of the rise varied considerably by age-group. The historic use of lead (Pb) additives in Australian petrol is a candidate explanation for these trends in MND mortality (International Classification of Disease (ICD)-10 G12.2). Methods: Leveraging temporal and spatial variation in petrol lead exposure risk resulting from the slow rise and rapid phase-out of lead as a constituent in gasoline in Australia, we analyze relationships between 1) national age-specific MND death rates in Australia and age-specific lifetime petrol lead exposure, 2) annual between-age dispersions in age-specific MND death rates and age-specific lifetime petrol lead exposure; and 3) state-level age-standardized MND death rates as a function of age-weighted lifetime petrol lead exposure. Results: Other things held equal, we find that a one percent increase in lifetime petrol lead exposure increases the MND death rate by about one-third of one percent in both national age-specific and state-level age standardized models of MND mortality. Lending support to the supposition that lead exposure is a driver of MND mortality risk, we find that the annual between-age group standard deviation in age-specific MND death rates is strongly correlated with the between-age standard deviation in age-specific lifetime petrol lead exposure. Conclusion: Legacy petrol lead emissions are associated with age-specific MND death rates as well as state-level age-standardized MND death rates in Australia. Results indicate that we are approaching peak lead exposure attributable MND mortality.