Suicide in Australian pesticide-exposed workers

Occupational Medicine 2011;61:259–264 Advance Access publication on 18 April 2011 doi:10.1093/occmed/kqr031 Suicide in Australian pesticide-exposed workers E. MacFarlane, P. Simpson, G. Benke and M. R. Sim Department of Epidemiology and Preventive Medicine, Monash University, The Alfred Hospital, Commercial Road, Melbourne 3004, Australia. Correspondence to: E. MacFarlane, Department of Epidemiology and Preventive Medicine, Monash University, The Alfred Hospital, Commercial Road, Melbourne 3004, Australia. Tel: 161 3 9903 0593; fax: 161 3 9903 0556; e-mail: Background Epidemiological research has observed that workers with exposure to anticholinesterase pesticides, and particularly those with a history of acute overexposure, may be at increased risk of depression. However, there is little published research about the risk of suicide in relation to pesticide exposure. ................................................................................................................................................................................... Aims To investigate risk of suicide in relation to metrics of pesticide exposure and type of work. ................................................................................................................................................................................... Methods A nested case–control study was performed within a retrospective cohort study of pesticide-exposed workers from various industries. Ninety male suicide deaths and 270 male controls were matched by age bands, state of residence and live status. Cholinesterase inhibition was determined using subjectspecific biomonitoring records collected at the time of exposure. ................................................................................................................................................................................... Results Suicide risk was not significantly elevated in relation to exposure to any particular pesticide classes nor in relation to pesticide overexposure, confirmed by blood test. While the risk of suicide associated with a history of cholinesterase inhibition was raised, this was not significant (odds ratio 5 1.90, 95% confidence interval 5 0.73–4.93). ................................................................................................................................................................................... Conclusions This study did not find an elevated suicide risk associated with use of any major class of pesticide and there was little evidence that overexposure was associated with increased risk of suicide. A nonsignificant association between overexposure to anticholinesterase pesticides may be consistent with previous research showing increased depression in workers with a history of cholinesterase inhibition and warrants further investigation. ................................................................................................................................................................................... Key words Cholinesterase; nested case-control studies; occupational epidemiology; pesticide exposure; suicide. ................................................................................................................................................................................... Introduction Suicide is a recognized problem in the farming community both in Australia and elsewhere [1–5] and evidence suggests that farm workers have a higher risk of suicide than workers in almost any other major industry [6,7]. Although evidence of excess suicide risk in farmers is extensive, it is not universal [3,8,9]. The farm suicide phenomenon is complex and likely to be multifactorial [10] and evidence suggests that a wide range of factors such as age, remoteness, social support, lethal vector availability and farm job type are likely to be involved [3,8–11]. The problem is likely to be under-represented in mortality statistics since coroners may be reluctant to assign a finding of suicide to deaths where intentionality is not completely clear [12,13] and in farming families [7]. There is evidence that farmers are less likely than others to leave definitive proof of intentionality in the form of a suicide note [11]. Much of the research on mental illness and suicide in the farming population has focused on stress, resilience and coping mechanisms in farmers, as well as family and social dynamics in farming communities and access to care [2,7]. Because agricultural workers are less likely than others to acknowledge mental health problems, less likely to seek help and tend to select the most lethal suicide vectors, to which the farm workplace provides ready access, suicidal behaviour in this population is characterized by a high ratio of completed suicides [14]. Epidemiological research has observed that workers with a history of overexposure to anticholinesterase insecticides such as organophosphates (OPs) may be subject to long-term neuropsychological changes, including depression and depressive symptoms [15–17]. Steenland et al. [18] and Savage et al. [19] reported significant changes in mood among subjects who had experienced OP poisoning from 3 to .10 years prior to evaluation. In a study of farm pesticide users, Stallones and Beseler [20] found that overexposure events serious enough to cause symptoms of toxicity were associated with a high incidence of depressive symptoms independent of other
The Author 2011. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: ................................................................................................................................................................................... 260 OCCUPATIONAL MEDICINE Methods The case–control study was nested within a cohort study of pesticide-exposed workers assembled from archive records, belonging to the New South Wales and Victorian state governments. Extensive state government programmes in the 1960s to 1980s offered free regular biomonitoring to pesticide-exposed workers. The programmes provided ongoing occupational health surveillance and identification of possible overexposure cases requiring follow-up. Personal identifiers including name, address, date of birth, job information and interview dates were collected from archive records. The cohort consisted of 14 601 eligible workers, of whom 92% were male. The cohort included pesticideexposed workers with jobs in agriculture and primary production, pesticide manufacturing/distribution and maintenance of municipal and sporting facilities, ornamental gardens and public utilities [29]. Relevant identifier variables for each cohort member were supplied to the Australian Institute of Health and Welfare (AIHW) for linkage to the National Death Index (NDI) for the years 1983–2004. For subjects matched to the N (...truncated)