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Workplace
Original article
Depressive symptoms and severity of acute occupational pesticide poisoning among male farmers
  1. Jaeyoung Kim1,
  2. Yousun Ko2,
  3. Won Jin Lee2
  1. 1Department of Preventive Medicine, College of Medicine, Keimyung University, Daegu, South Korea
  2. 2Department of Preventive Medicine, College of Medicine, Korea University, Seoul, South Korea
  1. Correspondence to Dr Won Jin Lee, Department of Preventive Medicine, College of Medicine, Korea University, Seoul 136-705, South Korea; leewj{at}korea.ac.kr

Abstract

Objectives Limited evidence suggests the association between severity of acute occupational pesticide poisoning and depressive symptoms in farmers. The aim of this study was to investigate the association between occupational pesticide exposure and depressive symptoms among male farmers in South Korea.

Methods A nationwide sampling survey of male farmers was conducted in South Korea. A total of 1958 male farmers were interviewed in 2011. Severity of occupational pesticide poisoning was evaluated according to symptoms, types of treatment and number of pesticide poisonings per individual. Depressive symptoms were assessed using the Geriatric Depression Scale. A survey logistic regression model was used to estimate the multivariate OR and 95% CIs.

Results Among total farmers, 10.4% (n=197) reported depressive symptoms. After controlling for potential confounders, occupational pesticide poisoning in the previous year was positively associated with the risk of depressive symptoms (OR=1.61; 95% CI 1.10 to 2.34). Cases of more severe pesticide poisoning, such as moderate- or severe-symptom cases (OR=2.81; 95% CI 1.71 to 4.63), outpatient or hospitalisation cases (OR=2.52; 95% CI 1.15 to 5.53), and multiple poisoning cases (OR=1.82; 95% CI 1.19 to 2.76) showed higher risks of depressive symptoms than did milder cases. Among the pesticides causing the poisonings, paraquat dichloride was found to be a significant predictor of depressive symptoms. No significant association was found with cumulative lifetime pesticide application and depressive symptoms.

Conclusions Our findings suggest that the risk of depression appears to be related to the severity of symptoms of poisoning, type of care received and the number of previous episodes of acute poisonings.

https://doi.org/10.1136/oemed-2012-101005

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    What this paper adds

    • Previous studies have not examined the impact of different levels of pesticide poisoning on depressive symptoms.

    • Understanding the effect of severity of pesticide poisoning on depressive symptoms is important to extend previous knowledge about the causality.

    • The results showed the pattern of increased likelihood of depressive symptoms among farmers with occupational pesticide poisoning was related to its severity, type of care received and number of episodes of poisoning.

    • Among pesticide, paraquat dichloride was identified to significantly contribute to depressive symptoms which deserve further studies.

    • This paper implies the necessity of timely intervention may be critical to prevent subsequent depression.

    Introduction

    Pesticide exposure has been reported to increase the risk of depression among farmers. Occupational pesticide poisoning was associated with depressive symptoms among Colorado farm residents in both a cross-sectional study1 and from a cohort study.2 Banana plantation workers in Costa Rica with a history of organophosphate poisoning demonstrated greater psychiatric distress and suicidal ideation.3 A US prospective cohort study reported a history of pesticide poisoning to be significantly associated with physician-diagnosed depression among female spouses of pesticide applicators.4 The Agricultural Health Study has additionally suggested that both acute pesticide poisoning and cumulative exposure are significantly associated with depression in pesticide applicators.5

    Chronic occupational exposure to pesticides has also been reported to increase depressive symptoms among Nicaraguan cotton farmers,6 Egyptian pesticide formulators,7 women on Louisiana farms,8 Iowan and North Carolinian pesticide applicators,5 and vineyard workers in France,9 but not among male fruit farmers in New Jersey10 and British male users of sheep dip.11 While the effect of pesticide poisoning on depression seems consistent, the impact of chronic occupational exposure on depression may be subtle.

    However, the differences in study populations and exposure measurements sustain the controversy surrounding the link between pesticide exposure and depression. Previous studies also have not examined the impact on depressive symptoms of different levels of pesticide poisoning, although understanding the effect of severity of pesticide poisoning on depressive symptoms is required in order to establish the causal link. Furthermore, there is a lack of epidemiological evidence regarding the effect of pesticide poisoning on depression in East Asian countries.

    The objective of this study, therefore, was to explore the association between depressive symptoms and occupational pesticide exposure according to its severity by using nationwide survey data for male farmers in South Korea.

    Materials and methods

    Study population

    The details of this study design and population have been previously described.12 In brief, a nationwide sampling survey of male farmers residing in rural areas in South Korea was conducted during February and March of 2011. Stratified multistage probability sampling methods were designed with the frame used by the 2010 Korean Agricultural Household registry data. Data were collected through inperson interviews with selected households. Overall, 1958 households were interviewed among the 2000 samples selected for the study. After excluding subjects missing information related to key variables such as depressive symptoms, income, perceived health status and years of farming or pesticide application (n=63), the remaining 1895 persons were included in the final analyses.

    This study was reviewed and approved by the Institutional Review Board of Korea University (KU-IRB-11-7-A-2). Informed written consent was voluntarily obtained from all individual study participants.

    Pesticide poisoning and pesticide use

    The main predictor in this study was episode of acute occupational pesticide poisoning during 2010. For screening pesticide poisoning, 21 symptoms and signs were selected based on a pilot study13 and reference reviews. These symptoms include nausea, vomiting, diarrhoea, sore throat, runny nose, dyspnoea, headache, dizziness, hyperactivity, profuse sweating, blurred vision, paraesthesia, slurred speech, paralysis, chest pain, syncope, muscle weakness, skin irritation, eye irritation, lacrimation and fatigue. Respondents were queried as to whether they had experienced any of these symptoms within 48 h of using pesticides. If they had suffered any of the 21 listed symptoms or signs and it had occurred within 48 h of occupational pesticide use, it was defined as an acute occupational pesticide poisoning.

    The severity of cases was classified according to the proposal of Thundiyil et al.14 Severe cases were defined as any cases including symptoms of paralysis or syncope, while moderate cases were defined as suffering symptoms including vomiting, diarrhoea, dyspnoea, blurred vision, paraesthesia, slurred speech and chest pain. The remaining cases were classified as mild cases. Information regarding the treatment of pesticide poisoning (ie, untreated, self-medicated, outpatient and hospitalised) and number of episodes of pesticide poisoning was also collected in order to categorise the severity of pesticide poisoning.

    Subjects were further asked about the pesticide products associated with causing poisonings, workdays lost due to poisoning, lifetime history of hospitalisation due to pesticide poisoning, size of farm, years and type of farming, and demographics. Detailed information on pesticide use, such as years of pesticide use, average days per year of use, average hours per day of use, pesticide application methods, use of personal protective equipment and safety behaviours, was also included.

    Depressive symptoms

    The primary outcome variable in this study was depressive symptoms measured by the Korean version of the Geriatric Depression Screening Scale short form (GDS-15). Considering our relatively old farming population, GDS-15 was chosen for an adequate screening instrument for detecting major depressive episodes as defined by criteria from the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, with outpatients 60 years old and older.15 The validity and reliability of the GDS-15 in Asia has been tested in a number of countries.16–18 Individuals were asked whether they experienced specific depressive symptoms during the past week. Each item was rated as ‘no’ (0) or ‘yes’ (1), and total scores were calculated.

    While a cut-off value of 5 or 6 has most often been used in Western countries,19 a slightly higher cut-off point has been adopted for Asian countries16 ,20 ,21 in consideration of cultural issues. In South Korea, a score of 8 has been used most frequently as the optimal cut-off point score to screen major depression.22 ,23 Therefore, respondents with GDS scores over 8 were defined in this study as having depressive symptoms.

    Data analysis

    The distributions of major demographic characteristics and farming-related variables between depressed and non-depressed farmers were compared using raw frequencies and weighted percentages. Sampling weights were calculated as the inverse of the selection probabilities, and age was considered for poststratification adjustments. To account for the sampling design, SEs were calculated using a linearisation method.24

    Based on the risk factors of pesticide poisoning, depression or both, as reported in the literature, we considered the following covariates to be potential confounders in the analysis: socio-demographic (age, income, education, marital status), job-related (farm size, type of farming, application methods, use of personal protective equipment, safety behaviour when applying pesticides), medical (physician-diagnosed health condition, perceived health status) and health behaviours (smoking, drinking, obesity).

    In the multivariate analysis, we began with a full logistic regression model that included pesticide poisoning and all other variables with p<0.2 in the univariate analysis. Variables that failed to reach statistical significance at the p≤0.05 level were removed but subsequently retained if their removal altered the magnitude of the main effect by more than 10%. The final model included age, income, marital status, smoking, comorbidity and perceived health status as covariates.

    To ensure the temporal relationship between exposure and outcome, as well as to reduce the potential for previous depression to affect the likelihood of pesticide poisoning and current depressive symptoms, we excluded those respondents diagnosed with depression prior to 2010 (n=6) in the subgroup analysis. In order to separate the effect of cumulative occupational pesticide exposure on depressive symptoms among farmers with no history of pesticide poisoning, we also conducted a further analyses after excluding the pesticide poisoning cases (n=449). All analyses were performed using SAS V.9.2 (SAS Institute Inc., Cary, North Carolina, USA). A statistically significant association between exposure and outcome was declared when the p value was less than 0.05.

    Results

    The demographic characteristics of the study population by depressive symptoms are summarised in table 1. A total of 197 farmers showed a GDS score of 8 or above, yielding a 10.4% prevalence of probable depression among male farmers in South Korea. Depressed farmers were more likely to report older age; less education; lower levels of family income; a marital status of separated, divorced or widowed; poor perceived health status; comorbidity; and ever diagnosed with depression.

    View this table:
    Table 1

    Demographic characteristics of male farmers surveyed nationwide in South Korea, 2010

    The distribution of farming characteristics by depressive symptoms is depicted in table 2. Chronic pesticide exposure indices including lifetime years, days or hours of pesticide application did not show significant differences between farmers with and without depressive symptoms. The results were similar when the analysis was conducted after excluding defined pesticide poisoning cases (data not shown). Among application methods, the use of manual backpack sprayers showed a higher risk for depressive symptoms compared with non-use. Failure to wear personal protective equipment at work and an absence of safety behaviours also accounted for an increased risk of depressive symptoms.

    View this table:
    Table 2

    ORs and 95% CIs for depressive symptoms by farming characteristics among South Korean male farmers, 2010

    Table 3 presents the ORs of depressive symptoms by occupational pesticide poisoning. Farmers who experienced pesticide poisoning at work over the past year demonstrated significant increased risk of depressive symptoms (OR=1.61; 95% CI 1.10 to 2.34). Greater symptom severity of pesticide poisoning cases appears to be associated with greater depressive symptoms. Cases with poisoning requiring a medical visit showed a higher risk of depressive symptoms than cases in which treatment was not pursued. Similarly, farmers with more than a single episode of occupational pesticide poisoning in the preceding year or a greater number of lost work days due to pesticide poisoning were found to be more depressed. Excluding the subjects who had been diagnosed with depression prior to the time of pesticide poisoning did not change this result (data not shown).

    View this table:
    Table 3

    ORs and 95% CIs for depressive symptoms by acute occupational pesticide poisoning indices among South Korean male farmers, 2010

    To explore the consequences on depressive symptoms of poisoning by specific pesticide, individual pesticides and the functional, chemical classes of pesticide used when farmers were poisoned was examined (table 4). Herbicide poisoning was positively associated with the risk of depression, but other chemical classes of pesticide at poisoning did not show significant results. Among the individual pesticides that caused acute poisoning, paraquat dichloride showed a significant increased risk for depressive symptoms after controlling covariates.

    View this table:
    Table 4

    ORs and 95% CIs for depressive symptoms by causative pesticides of acute occupational poisoning among South Korean male farmers, 2010

    Discussion

    We found that farmers suffering pesticide poisoning at work during the preceding year show a higher risk of depressive symptoms compared with those with no such reported episode, after controlling for other risk factors. The pattern of increased likelihood of depressive symptoms among farmers with occupational pesticide poisoning was accordingly substantive by symptom severity, type of care received and number of episodes of poisoning. The results remained consistent when the analyses were repeated after excluding subjects diagnosed with depression prior to pesticide poisoning.

    Our findings of depressive symptoms and pesticide poisoning at work are consistent with previous studies reporting a higher level of depressive symptoms or depression among individuals with a history of pesticide poisoning.1 ,2 ,5 Our results also contributed that the severity of acute pesticide poisoning is incrementally related with the risk of depressive symptoms. Farmers who experienced moderate to severe pesticide poisoning showed a significantly increased risk of depressive symptoms. Farmers with acute pesticide poisoning requiring a medical visit to a doctor or hospitalisation were found to be at higher risk for depressive symptoms than were farmers experiencing self-medicated or untreated pesticide poisoning. Moreover, if farmers experienced more than a single pesticide poisoning at work, this also increased their odds of being depressed over farmers with one or no occupational pesticide poisonings. This finding reflects that the risk of subsequent depression after occupational pesticide poisoning depends on the severity of the pesticide poisoning. It also implies that the necessity of timely intervention may be critical to prevent postpoisoning depression.

    Among specific pesticides, we found that herbicides, principally paraquat dichloride, were significantly associated with depression. Although no direct epidemiological or experimental study has been undertaken related to paraquat poisoning and depression, paraquat exposure has been strongly suggested to increase the risk of Parkinson's disease,25 ,26 which is often characterised by comorbid neuropsychiatric symptoms such as anxiety and depression. Paraquat exposure also has been shown to induce alterations in non-motor symptoms27 and neuropsychiatric function in rats,28 which may also link with depression. Depressive cases have been reported following chronic pesticide intoxication in South Korea, although the particular kind of pesticide was not specified.29 Further studies are warranted to better investigate the effects of paraquat on depressive symptoms among farmers.

    Cumulative pesticide exposure measured by lifetime pesticide application hours, days or years did not show any meaningful association with depressive symptoms. This could reflect that while the index of chronic pesticide use may explain exposure level, it may not directly relate with health effects (ie, farmers who apply pesticides but had no poisoning history may not yet have reached the point leading to depression). While there is some controversy regarding depression following chronic pesticide use in the absence of acute poisoning,30 it appears that the evidence suggests that depression may more strongly relate to the indices of acute pesticide poisoning than to that of cumulative pesticide exposure.

    While the adverse impact of pesticide poisoning over the preceding year showed an increased risk of depression, lifetime hospitalisation due to poisoning appeared to include no significant effect on depression. The potential explanation for this may be that the depressive effect of pesticide poisoning may not persist long enough to be measured in lifetime depression, and hence the effect of lifetime poisoning on depression may be more likely to be complicated by other life events. One cohort study reported a similar finding that when attenuating the effect of pesticide poisoning on depression over time, the depression rate was the highest in the first year subsequent to pesticide poisoning and decreased over the following 3 years.2

    Although there are no available epidemiological data regarding depression among Korean farmers, rural residents in Korea have been suggested to show a range of depressive symptom prevalence of 9%–33%.31 Depressive symptom prevalence among male farmers in this study appears to be slightly lower than among overall rural residents in South Korea. Limiting the study subjects to male farmers may partly explain the difference, although the diversity of measures of depressive symptoms and study populations make it difficult to directly compare our results with others.

    Lower income, marital status of getting separated, divorced and widowed, and smoking status of former or current smoking, self-rated health and comorbidity were independent risk factors in the association between pesticide poisoning and depression. Previous studies have found that individuals who have low socioeconomic status or poor health status have an increased risk of depression among elderly both from South Korea32 and other countries.33

    Our results showed that personal protective equipments and safety behaviours had protective effects for depressive symptoms among pesticide applicators; therefore, promoting use of personal protective equipments and education for safety use of pesticide could be encouraged as important methods to reduce pesticide exposure. Although a recent Korean law recommend safety training for farmers using pesticides this is not mandatory. Priority should be given to other more effective strategies of exposure reduction such as eliminating toxic pesticides and reducing pesticide use through integrated pest management.

    There are certain limitations to this study. Although we covered some risk factors for depression, the survey does not provide information on other potential confounding variables, including family history and additional stressful life events outside farming. This lack of data limited the ability of further analysis to explore the mechanism between pesticide poisoning and depressive symptoms. However, we believe that these unmeasured confounding variables would not affect differentially among farmers. Reverse causality also could be a concern because this is a cross-sectional survey; however, the results were unaltered when we excluded farmers who had been diagnosed with depression prior to 2010. Low prevalence of physician-diagnosed depression history in our study may be due to reverse causation and healthy worker selection34 in that depressive farmers experienced more pesticide poisoning than non-depressive farmers. Other potential explanations may be poorer availability of mental healthcare facilities in rural areas compared with urban areas and cultural issues about stigmatisation among small farming communities which may prevent reporting depression in a face-to face survey. It is also known that depression is often masked as psychosomatic symptoms in the elderly.35

    In addition, the self-reported nature of the information in this study may introduce potential recall bias, which is a common phenomenon with survey data. Self-reported information on pesticide use in general among farmers, however, has been reliable for epidemiological study in South Korea.36 In our case definition, symptoms related to pesticide poisoning might be due to other work-related factors or physical disorders as well as pesticide poisoning. Thereby, our pesticide poisoning cases may be overestimated especially in mild cases; however, moderate or severe cases and lifetime hospitalisation cases may not be greatly affected.

    Despite these limitations, this study retains certain strengths. First of all, this is the first nationwide survey sampling study exploring depression and pesticide poisoning among male farmers in South Korea. Second, we include detailed pesticide exposure and poisoning related information, allowing the categorisation of the severity of poisoning by symptoms, numbers of poisonings and type of treatment received. Third, we used a Geriatric Depression Scale to appropriately measure depression among the elderly who make up our major study population.

    In summary, our findings suggest that depressive symptoms were significantly associated with a history of acute occupational pesticide poisoning and that the relationship was associated with the severity of the symptoms of poisoning among male farmers. Of the pesticides used, paraquat dichloride was identified as significantly contributing to depressive symptoms, which deserves further study. These findings emphasise a need for timely intervention for reducing pesticide poisoning through restrictions on certain pesticides and promotion of and training in the use of personal protective equipment; this would have the effect of reducing the burden of depression associated with pesticide poisoning.

    Acknowledgments

    We thank Ms Ji Hyun Kim and Ms Cha Eun Shil for data analysis support and Dr Hyun Joong Kim for generous comments on an early version of the manuscript.

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    Footnotes

    • Contributors All authors of this manuscript have directly participated in the planning, execution or analysis of the study, and in the preparation of the manuscript and have approved this final submitted version.

    • Funding This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2010-0021742) and by the Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ007455), Rural Development Administration, Republic of Korea.

    • Competing interests None.

    • Patient consent Obtained.

    • Ethics approval Ethics approval was provided by the Institutional Review Board of Korea University (KU-IRB-11-7-A-2).

    • Provenance and peer review Not commissioned; externally peer reviewed.