Background
Non-communicable diseases (NCDs) have recently become a global public health concern and are estimated to contribute to more than 70% of deaths worldwide [
1] which is equivalent to 41 million people who die each year [
2]. In low and middle income countries, these NCDs accounts for about 75% of all causes of death and about 86% causes of premature mortality in these countries [
2]. The World Health Organization (WHO) has categorized key groups of NCDs including chronic respiratory diseases among others.
Environmental risks, particularly air pollution increases a considerable burden on NCDs [
3,
4]. WHO estimated that indoor air pollution resulting from biomass fuel use causes about 4 million premature mortality each year [
5]. NCDs are influenced by the people’s lifestyle factors such as unhealthy diets, physical inactivity, tobacco use, the harmful use of alcohol [
2], and poor working environments [
6]. Air pollution alone puts 90% of people at increased risk for NCDs including cancer, chronic obstructive pulmonary diseases (COPD) and cardiovascular diseases [
7]. Studies conducted in 2018 in India reported an increased threat of developing COPD because of air pollutants from use of biomass solid fuels [
8]. Air pollutants like PM, NO
2, O
3 and SO
2 emitted from burning of biomass fuel have the ability to affect the respiratory system and cause respiratory symptoms like phlegm, cough and bronchial hyper responsiveness [
9].
COPD imposes a substantial economic burden on providers of health care service and on patients themselves while negatively affecting the daily lives of patients, impairing the wellbeing of an individual, reducing productivity and functional status with a major economic impact [
10]. Inefficient combustion of biomass fuel emits high level of air pollutants like PM and CO [
11]. Nowadays, the focus of air pollution has risen because particulate matters (PM
2.5) have the ability to penetrate lung tissue and induce local and systemic effects. Particles with 10 microns diameters or below (PM
10) and those with 2.5 microns diameter or below (PM
2.5) may enter deeply in the lungs, hence causing damage to health [
12].
Evidence has shown that exposure to biomass smokes increase both respiratory and non-respiratory diseases [
13]. A longitudinal study conducted in Kenya has established an association between inhalation of polluted air caused by biomass use and acute respiratory infections [
14]. For a human to be exposed to pollutants from air depends on indoor and outdoor amounts of air pollutants, the environment and time of exposure in such conditions [
15]. Air pollution from cooking places with poor ventilation tends to result in due decline of lung function [
8].
Tanzania is committed to achieve the sustainable development goal number 7, by which the country through the ministry of energy and minerals promote use of clean and affordable energy in many ways, including the establishment of Rural Energy Agency (REA) which ensures affordability and availability of electricity in rural areas [
16]. Furthermore, the Tanzanian government through health sector strategic plan (2021–2026) they have a plan in strengthening Public Private Partnership (PPP) in addressing the health effects of air pollution from business and commercial activities [
17]. However, biomass fuel is still the source of energy in homes and businesses [
18] due to its affordability and availability. Few cross-sectional studies have measured the lung function of people at risk in Tanzania who use biomass fuel [
19]. A cross-sectional study conducted in Simiyu region in Tanzania, reported 99.5% of the households used biomass fuels for cooking and the prevalence of COPD was estimated at 17.5% [
19]. Another study conducted in an informal urban environment reported the prevalence of COPD at 8.13% [
20]. A study done in Bagamoyo showed the prevalence of acute respiratory illness were 54% among women involved in cooking [
21]. It is hypothesized that fish vendors exposed to biomass smoke, fumes and heat when frying fish are at high risk of respiratory diseases.
In Tanzania there is a legal framework which ensures health and safety in the community and workplaces. The national policy on energy use of 2003 emphasizes on availability of reliable, affordable and environmentally sound energy sources. The policy aims to lower the impact of using biomass fuel (firewood) both in domestic and at workplaces by replacing it with the use of clean energy [
22]. Also, the national environmental management Act of 2004 [
23] provides the mandate to public health inspectors in both local and central government authorities to enforce and monitor air quality standards in all premises. Fish processing settings are among the premises that are required to adhere with the stipulated standards as provided in the national Air quality standard regulation of 2007 [
24]. Despite the presence of legal framework, however its implementation is challenging due to inadequate coordination, and facilities to monitor air quality in workplaces. Thus, there is a need to rethink on the best way that can ensure effective monitoring of air quality in workplaces.
There is limited information in the country on the occupational impact from air pollution exposure among small-holder fish vendor’s who almost always rely on biomass fuel for frying fish prior to selling them. This study assessed the prevalence of COPD and associated factors among small-holder fish vendors along coastal areas in Tanzania. The study would provide information about the lung health of participants which is valuable information for decision makers, medical practitioners and health-care planners to promote quality of life, better health and reduce or prevent morbidity and mortality from COPD.
Discussion
This study is the first to be conducted along coastal areas among fish vendors’ work environment (Bagamoyo and Kunduchi fish markets) assessing occupational exposure in Tanzania. In these working environments all fish vendors (100%) practice open burning in frying fish for business purposes. These findings are consistent with the Tanzania demographic health survey data which presents that more than 94% of Tanzanians use biomass fuel in cooking practices mainly charcoal and wood [
29]. The use of wood has also been reported in many parts of the world as a primary cooking fuel in South Asian, African and South American countries with open fires most common in Tanzania, Pakistan, Colombia and Zimbabwe [
30]. These findings are similar to many studies in Africa where availability and affordability of biomass fuel have been mentioned as a major reason for using biomass fuel [
31]. The constituents of biomass smoke are known to be toxic and cause irritation of the respiratory system. These constituents include Carbon monoxide, Particulate matter, Sulfur dioxide, Nitrogen dioxide, Formaldehydes, Volatile Organic Compounds, Polycyclic Aromatic Hydrocarbons, free radicals and chlorinated dioxins [
32]. Multiple risk factors for COPD have also been reported in Africa. A cigarette smoker may be exposed to air pollutants or occupational exposure [
20] hence in this study multiplicity of risk factors may have resulted in the findings observed as all participants were occupationally exposed to air pollutants and 32% were cigarette smokers.
For this occupation, the number of men are higher than that of women as many men engage in fish frying. This is different from findings from other cross sectional studies conducted in different parts of the world which reported biomass smoke exposure to women and mothers who are more responsible in cooking practices at homes [
33‐
35] while in the process of fish frying in Tanzania men are more exposed to air pollution from burning of firewood as an occupational exposure. Other studies have also reported high exposure of biomass smoke to women as they are responsible for cooking at home at their early age and hence cumulative exposure over time which lead to early manifestation of the disease [
32].
Almost all fish vendors reported having respiratory symptoms (cough, breathlessness, wheezing and sputum production) which interfere with their daily activities in one way or another. The reported respiratory symptoms of this study are higher than reported findings from a cross sectional study in rural areas of Tanzania [
19] which reported higher percentages of all of this symptoms with 51.7% of participants had cough, 35.6% had sputum production, 32.3% had wheezing, 25% reported breathlessness, 84.6% reported walking slower than others of same age, 69.2% they had to stop for breath when walking and 46.2% had shortness of breathing when at rest. A previous study assessing the effect of household cooking smoke reported cold as the most common symptom (46%), coughing (46.6%), phlegm production (21.2%) [
36] similar to respiratory symptoms reported in this study.
The reported respiratory symptoms were similar to respiratory symptoms reported elsewhere [
19,
31,
36‐
39]. A study done in South East Asia in Brunei Darussalam reported that cooking vendors who use biomass fuel where having higher respiratory symptoms and the symptoms were thrice more for those who have work for more than 10 years [
40] same as this study where working duration of more than ten years were associated with higher respiratory symptoms. This may be because the working duration and increased working days per week increases the chance of getting higher respiratory symptoms as a results of cumulative occupational exposure overtime.
Both male and females reported experiencing higher respiratory symptoms. There are also some studies on the effect of biomass smoke and respiratory symptoms among adults for which higher risk of those symptoms reported among male same as this [
20,
41] and the reason was cigarette smoking. Higher risk of respiratory symptoms among the female gender associates with the double exposure as they are responsible for cooking at homes while also exposed to biomass smoke at work. Thus the cross exposure could balance the exposure risk related to gender [
20]. Some symptoms were significantly related to smoking (coughing, sputum production, wheezing and breathlessness when walking uphill) same as other studies at household level which reported an association between chronic respiratory symptoms with smoking [
41,
42]. It appears that the respiratory symptoms could have results from the daily exposure to biomass smoke while also other risk factors play a role. The results of this study could be explained by the fact that firewood smoke contain many pollutants which are dangerous to health such as carbon monoxide, particulate matter, formaldehydes, sulfur dioxide, nitrogen dioxide, volatile organic compounds, polycyclic aromatic hydrocarbons, free radicals and chlorinated dioxins. Exposure to wood smoke has been associated with respiratory effects including acute and chronic changes in the lung function. Respiratory symptoms like coughing and breathlessness resulted from high exposure to firewood smoke pollutants and may aggravate lung disease and reduce the strength of the immune system. Thus alternative energy use can contribute to reduction of respiratory symptoms and COPD development. However only longitudinal studies over several years can fully account for the relationship between biomass smoke and self-reported respiratory symptoms among fish vendors.
The prevalence of current smokers and ex-smokers were higher in this study, however a cross sectional study assessing COPD in rural areas of Tanzania at household settings reported the prevalence of ex-smokers to be 25.2% higher than the one found in this study while the prevalence of current smokers were 5.4% lower than the one found in this study [
19]. The previous study at household setting reported the prevalence of those who had previous history of TB to be 3.63% [
19] which is higher than the one reported by this study.
No any participant had a previous spirometry test or any diagnosis of lung function same as the previous study at household level [
19]. A study conducted in informal urban environment report the prevalence of COPD to be 8.13% [
20] Although this is a different setting, but still the prevalence of lung obstruction in the current study based on the FEV1/FVC less than the LLN [
43] is much higher as in every ten fish vendors three individual have lung obstruction. A study conducted in Malawi on use of biomass fuel among household participants found 40% of participants with abnormal spirometry but mainly restrictive lung diseases [
37,
42] which is different from this study as the higher proportion of abnormal spirometry was found among participants with obstructive lung disease. The same study in Malawi found the prevalence of lung obstruction to be 8.7% (95% CI, 7.0–10.7) [
42] which is lower than the findings of this study. The higher prevalence of lung obstruction among fish vendors may be because of daily exposure to firewood smoke, which may have a major public health implication in occupational settings and the community at large. Majority of participants with lung obstruction had mild to moderate lung obstruction. From these findings it shows that fish vendors are affected by firewood smoke. And since lung obstruction is progressive disease, if no immediate intervention is put in place the prevalence of respiratory symptoms will increase year to year.
The reason for observed higher prevalence may be due to occupational exposure which results from day to day exposure for 8 to 10 h. The lower numbers of females who participate in this study make generalization of findings difficult. Avoiding sex bias by including a similar number of both sex was difficult as females who participated in this occupation in Tanzania are smaller in number compared to men. The prevalence of lung obstruction in this working population suggests a hidden health problem and may be a potential for major health consequences in the future if immediate intervention is not taken into account. Major priority has to be prevention of exposure by promotion of self-awareness among fish vendors on the harmful effects of firewood smoke and among health-care workers and policy makers [
44].
In logistic regression analysis age, gender, working duration, being underweight and having a previous history of tuberculosis were associated with COPD although the association were non-significant. This shows that there are some other factors responsible for lung obstruction including exposure to air pollutants of biomass smoke. As COPD was found to be associated with age, this may be due to cumulative risk over time both biologically and epidemiologically plausible thus higher risk of lung obstruction as the person ages [
20,
45] but in the current study the association was non-significant. The association of lung obstruction with female gender may be explained by social cultural reasons as females are more exposed at early age in homes than males [
34,
35,
46] and hence double exposure. Interestingly, participants who were obese seems to have reduced odds of COPD which is different from other studies which reported an association between obesity and COPD [
47,
48].
In this study population, COPD is higher compared to previous reports in Africa as 3–4 participants out of 10 have COPD. Air pollution is a major determinant of COPD though other risk factors such as age, gender, smoking history, having previous TB history and working duration play a role. For all air pollutants measured, the average pollutant concentration before and after fish frying was below the recommended standards. Environmental air pollutants at the fish markets were higher than the WHO recommendations for both particulate matter and carbon monoxide exposure during fish frying. A study conducted in Malawi assessing air pollution at household level found the day to day air pollution exposure was approximately three times the WHO upper safety limits [
42] same as the results of this study. Improving the working environment and use of clean energy remains an important strategy in controlling COPD in this population.
Findings from this study indicate that biomass use is still common in occupational settings including fish frying working environment. Health risks associated with this have been documented in many studies [
13,
18,
21,
33,
45,
49] hence there is a need for immediate action to protect this workforce.
This study reports an occupational exposure to firewood smoke and respiratory symptoms among fish vendors. These findings are concurrent with other studies in Africa [
19,
42,
45] which reported exposure to biomass smoke and higher respiratory symptoms among household members, among food venders and in the community. The findings of this study may be due to daily occupational exposure to firewood smoke.
Given that there is much evidence on the health effect of air pollution and the extent of public health impact of this environmental risk factor, immediate intervention to reduce the exposure and improving air quality are needed to protect public health, which require both multidisciplinary and multi-sectoral approaches.
The strength of the study is that it is the first study performed among fish vendors in Tanzania where spirometry and environmental measurements were conducted. This was a descriptive cross sectional study that described the fish vendor’s work environment, and its associated occupational exposure and the effects on the respiratory system. The study opens up for the follow up or cohort studies to be conducted in this area.
The study has some limitations, as this occupation involves more men than women, hence our results are not appropriate for some cultures where more women are involved in fish frying. As the study was only descriptive we did not measure the causal association between air pollutants and lung function values, hence a bigger study with a different design will be useful. The results of the study might also be affected by small sample size as this study uses fish vendors from Bagamoyo and Kunduchi fish markets, with only 103 participants, hence may not represent all fish vendors in the country who are exposed to biomass smoke. However, most fish vendors in the country have a similar working environment and similar exposure. The findings and reported measure of association could be limited due to the selection of the sample that shared a similar exposure from the general population.
There is also a need to detect if those with lung obstruction have a risk of progressive disease and hence there is a need for longitudinal study to observe disease progression and understand any other risk of progressive disease.
Therefore, based on the nature of the fish vendor’s working environment, it is reasonable to believe that respiratory symptoms were the result of daily exposure to air pollutants.
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