Acute pesticide poisoning amongst adolescent girls and women in northern Tanzania

Acute pesticide poisoning (APP) is documented as a serious public health problem in Tanzania [1, 2] and other parts of the world [3‐9] due to its adverse human health effects. Evidence of APP occurring in women is documented in studies from Tanzania [2, 10], Uganda [11], Kenya [12], South Africa [13, 14], India [15], China [16], Nepal [17], Sri Lanka [18], Iran [19] and Ethiopia [20]. A 2002 review of APP globally suggested that pesticide-related morbidity and mortality is under-reported amongst women [21]. As a result, the Burden of Disease due to pesticide exposure, particularly amongst women, may be substantially underestimated. Similarly, amongst children, APP may be an under-reported problem globally. A WHO study reported that over 30% of the global burden of disease amongst children can be attributed to environmental factors, pesticides being a major contributor [22]. Childhood acute pesticide poisoning is documented in several countries including South Korea [23], South Africa [24], Canada [25], Turkey [26], and India [27]. Apart from accidental and occupational poisoning, adolescent risk-taking behavior can lead to attempted intentional pesticide self-poisoning. Reasons for adolescents’ intentional poisoning include emotional trauma from family stress or failed relationships with the opposite sex [28].

APP may also signal increased risk for long-term chronic health effects associated with pesticide exposure. For example, individuals surviving a single APP episode involving an OP are at risk of neuropsychiatric and neurological sequelae years after the episode [29, 30].

Age and gender are said to affect physiological susceptibility to the effects of exposure to toxic pesticides [31]. Biological factors, notably body size, and differences in physiological, hormonal, and enzyme functions between women and men, and between adults and children influence susceptibility to health hazards from exposure to pesticides [31]. With a generally higher proportion of body fat, women are more likely to store those pesticides that are fat-soluble in their tissues, which, if mobilized to become biologically active, can act as a continuous source of internal exposure linked to adverse chronic health outcomes [32]. Moreover, at particular stages of their lives, such as pregnancy, lactation, and menopause, women’s bodies undergo physiological changes that may also change their vulnerability to health effects from toxic chemicals [31].

Studies suggest that women’s exposure to pesticides in pregnancy is associated with miscarriages [33], premature births, birth defects, and low birth weight [31], largely because of trans placental exposure, as well as transfer via breast milk during post-partum breast-feeding [31].

Other health effects linked with pesticide exposure in women include pregnancy complications as reported in Tanzanian horticulture [2], depressed cholinesterase levels due to Organophosphate (OP) exposure as reported amongst South African female farm workers [34], and respiratory problems, including asthma, as reported in Brazil [35] and South Africa [34]. Hormonally-related cancers in females, including breast, thyroid, and ovary, were reported amongst women in North Carolina, USA [36]. Adolescent females are also at risk to the impacts of endocrine disrupting chemicals, and many pesticides have been linked to adverse impacts on sexual development amongst both boys and girls [37].

Exposure pathways for women are diverse. Women can be exposed to pesticides directly through poor pesticide handling in agriculture, ingestion involving deliberate swallowing of pesticides or their concentrates, inappropriate handling in pesticides retail shops and consumption of pesticide-contaminated food. Dermal absorption can occur with exposure to contaminated clothing, dust or residues on floors and other surfaces or objects. Other possible sources for exposure include pesticide drift and unattended empty pesticide containers [5]. While many pathways for women’s exposure may be similar to men’s, some pathways may be gender-specific. For example, women may also be exposed to pesticides through washing their husbands’ contaminated work clothes, or re-entering fields to conduct work earmarked for women following spray application [38].

Research on APP amongst women in Tanzania suggests that, firstly, agents reported to be responsible for poisoning include hazardous pesticides, particularly OPs used on food crops [2]. Secondly, although reports of occupational pesticide poisoning are uncommon in health facility records [1], studies have suggested that women may be at high risk for APP, given that women comprise of 80% of the agricultural labour force in Sub-Saharan Africa where pesticides are applied regularly [39].

Despite the prevailing reliance on pesticides for pest control [40], Tanzania currently has no surveillance system for APP. Poisoning is reported in the health management information system within Tanzanian hospitals with non-standardised information on the causative agent. Previous studies have reported the lack of specificity of reporting of pesticide poisoning in hospital information systems [10].

Because the magnitude of APP in adolescent and adult females in Tanzania is unknown, this study was undertaken with the aim of estimating the burden from APP and characterizing the patterns of APP amongst adolescent and adult females in Tanzania. Because Tanzania currently lacks a comprehensive surveillance system for acute pesticide poisoning, this study also could potentially generate recommendations to address this surveillance gap.

In the period of 1 year this study identified 108 acute pesticide poisoning cases involving adolescent girls and adult women in 8 of the 10 facilities in this study. The fact that most facilities visited reported poisoning indicates that APP in women is widespread in the study area. Given that APP is under-reported in many developing countries [1, 13, 45], particularly amongst women [1], it is likely that there are further cases which are not captured due to the absence of an adequate surveillance system.

The most commonly recorded circumstance of poisoning in this study was suicide (60.2%). This proportion is lower than that reported among females in Sri Lanka (88.7%) [18] but higher than reported in Kenya (14.6%) [12]. The higher proportion of suicide in Sri Lanka women could be due to the Sri Lankan study including only rural facilities in areas of high pesticide use whereas this study included both rural and urban facilities (Additional file 1).

Occupational exposure as circumstance for APP was very low for females (only 8.3% of the cases reported). Again, this may be a function of under-reporting resulting from the absence of a comprehensive surveillance system for APP in Tanzania as well as misdiagnosis of signs and symptoms of pesticides exposure. Previous research suggests that occupational cases may be missed [1] since farmers do not present to hospitals, especially for less severe poisonings, but rather wait to recover or use alternative treatments [10].

The age distribution of APP in females suggests that the highest proportion of cases was found in the age group 20–29 years. This is broadly consistent with findings from studies in India [46, 47], South Africa [48] and Nepal [49] although the Nepalese and South African studies included females in the younger age range. Females aged 15 to 40 years may be involved in pesticide handling and may attempt suicide using pesticides as a result of easy access to toxic chemicals. Suicide risk in this age group is exacerbated by factors such as physical or sexual abuse, persistent psychosocial stresses, loss of social support, financial hardship, and heavy seasonal workloads. Similarly, depression arising from OP exposure [50, 51] may also contribute to increase risk for suicidal attempts.

Organophosphates (OPs) emerged as the single most important group of agents responsible for poisoning in females in this study. This pattern is consistent with studies conducted in India [47], Sri Lanka [18] and Nepal [49] and reflects the widespread use of organophosphate insecticides in Tanzania [52]. Previous research suggest that, broadly speaking, usage patterns appear to be correlated with APP in Tanzania [40].

Poisoning with OPs was significantly associated with older age (PRR Adult women/ Adolescent girls = 1.3, 95% CI =1.01–1.6). Adult women may be more likely to handle pesticides, both directly while working in the farm and indirectly through handling contaminated containers and clothing than adolescent girls and therefore have a higher chance of coming into contact with OP products. The lower frequency of handling pesticides in adolescent girls could also arise because of legislative measures to limit child labour and tasks associated with pesticide exposure of children [53].

The study also suggested an association between suicide and poisoning by OPs (PRR Suicide/Non Suicide = 1.35, 95% CI – 1.1 – 1.6). OP’s are freely available in Tanzania in various pesticide retail shops and can be easily used in suicide attempts. Controlling easy access to OPs may therefore be an important measure to prevent suicide. Investigating the causative factors in suicide attempts might also help to inform preventive strategies.

Other agents reported in APP cases included paraquat, Endosulfan and zinc phosphide, all of which are significant hazards. Endosulfan is associated with adverse male and female reproductive effects. Endosulfan metabolites bio-accumulate in adipose tissue, depending on their lipophilicity [54]. Endosulfan is said to be a neurotoxin, haematoxin, genotoxin, nephrotoxin and carcinogenic, causing both acute and chronic toxicity in males and females, with some laboratory evidence suggesting greater susceptibility amongst females [55]. As a chemical endocrine disruptor [56, 57] exposure to even small concentrations of Endosulfan can lead to serious health effects. Endosulfan has been banned in Tanzania for health risks since 2013 and it has also been earmarked for elimination under the Stockholm Convention on Persistent Organic Pollutants (POPs) and listed under the Rotterdam Convention on Prior Informed Consent [58].

Zinc phosphide is extremely toxic, causing acute respiratory distress in exposed persons due to the release of phosphine gas when it comes into contact with moisture [59]. However, it is not registered for use in Tanzania and its distribution is therefore illegal, its use being mainly for domestic rats control [1]. Because the main use of this highly hazardous product occurs within households, the proximity to human habitation is likely to increase risks for human poisoning. The illegal distribution also means that control of this hazard will require methods of enforcement different to products registered in Tanzania.

Paraquat is another pesticide commonly used as herbicide in Tanzania but also commonly misused for suicide attempts [1]. The concentrated product is highly toxic, has no antidote and, as a result, has been responsible for many fatal poisonings in Tanzania [1]. Poisoning of women using paraquat is also reported in Sri Lanka [18].

This study reported a relatively high proportion of APP cases (60.2%) with no data on the responsible agents, a proportion much higher than studies amongst women in Sri Lanka [18] and California [60]. This difference could result from the existence of better surveillance systems in Sri Lanka and California compared to Tanzania. For example, the study by Pearson and colleagues, which demonstrated how close collaboration between stakeholders in Sri Lanka made use of surveillance data to implement effective policies to prevent pesticide poisoning, confirms the presence of a robust surveillance system for APP in that country [61]. Absence of information on the poisoning agent was associated with younger age in that adolescent girls were more likely to be involved in an APP where the agent was unknown (PRR Adolescent girls/Adult women = 1.9, 95% CI =0.9–3.9). This higher proportion of unknown poisoning agents in adolescent girls could be linked to inexperience in pesticides handling in that they are less likely to identify the poisoning agents. Similarly, restriction of hazardous forms of child labour implies that young workers in agriculture will rarely handle pesticides. This may be another factor explaining why adolescents may be unable to identify poisoning agents.

Population-based APP incidence rates in this study (5.1/100,000) were far lower than reported in Nepalese females aged 15 to 50+ years (77.5/100,000) [47] and South Korean females aged 0 to 65+ years (27.4/100,000) [62]. This could be explained by (a) poorer hygiene resulting in unsafe pesticide handling practices in Nepal or (b) under-reporting due to the lack of a surveillance system in Tanzania. For the Korean study, there were also age differences in the study population including children aged 1 to 10.

Conversely, the incidence rates found in this study were about three times higher than reported in a US study [9] where better preventive practices and legislation in the US may explain this difference.

The APP cases found in this study may signal a problem of long-term adverse effects from pesticide exposures. Endosulfan is an example of an organochlorine insecticide which is fat soluble, may bio-accumulate in both environmental media and human tissues and has many adverse long-term effects. Those surviving APP may be left with residual neurologic impairment, particularly if the poisoning resulted in multi-organ failure or nervous system hypoxia. Research suggests that patients with a history of a single acute organophosphate or other pesticide poisoning are at risk of long-term neuropsychiatric sequelae [29]. Thus, while the absolute numbers of women and adolescent girls affected by acute poisoning is not that high, it may be the tip of an iceberg of wider exposures needing investigation.

To address the surveillance gap, hospital based surveillance data can be supplemented by promoting the community based self-reporting of APP whereby the community will capture mostly minor APP injuries. Similarly, forensic data source in Tanzania under the Ministry of Health can also be included to provide data on severe APP, particularly involving suicide and homicide cases. Tanzania lacks a comprehensive system such as the SENSOR-Pesticides surveillance program in the US which utilizes a very wide range of data sources and variables, such as poison center calls, workers’ compensation claims, and variables related to current job, crops worked, and pesticide handling status [8].

The study indicates that acute pesticide poisoning is common among women in northern Tanzania with estimated IR of 5.1/100,000, MR of 0.2/100,000 and CFR of 3.7%. The most common known agents were WHO Class I and II pesticides including a number of Organophosphates. The most common circumstances for APP in women were suicide for women of the age group 10–29 years. To reduce suicide related to APP, attention should be paid to addressing the causes of suicide, safer storage, (storage far away from home premises), improved hygiene measures and control of access to toxic pesticides. Occupational APP and APP associated with child labour, though uncommon amongst hospital admissions, need to be addressed by improving safe handling conditions and notification systems, and stronger child labour regulation and enforcement. Multifaceted intervention efforts are needed to reduce acute pesticide poisoning among women in Tanzania.