All original research articles on the impact of plastic waste on human health in low-income countries meeting the following eligibility criteria were included: 1) research with a quantitative, qualitative or mixed design; 2) articles published in English or French; and 3) limited to low- or middle-income countries based on the World Bank Listing June 2022 [29] . The World Bank defines low-income economies as those with a gross national income (GNI) per capita of $1025 (US dollars) and middle-income economies as those with a GNI per capita between $1026 and $4035 [30] .

The exclusion criteria were as follows: 1) commentaries, review articles, letters, discussion papers, posters, conference abstracts, conference reports, dissertations and systematic reviews; and 2) studies written in languages other than English and French, articles without abstracts and inaccessible full text, and those not addressing the impact of plastic waste.

We searched the following electronic databases due to their wide range of scientific publications and multidisciplinary content. These include PubMed, CINAHL, Global Health, Embase and Web of Science. The search was limited to the English or French language and human subjects. Additional searches were carried out in the bibliography of the retained articles. Manual searches were also conducted in academic journals to identify other relevant studies.

We used the PICO method to identify the keywords of the research question. We then developed a search equation adapted to search PubMed, CINAHL, Global Health, Embase and Web of Science (Table 1).

After combining the PICO components, we have refined our search equation for greater efficiency and precision, which is now as follows:

(“Humans” [Mesh] OR “human population*” OR “Persons” [Mesh] OR “People” AND “Plastics” [Mesh] OR “plastic trash” OR “plastic waste*” AND “Health Impact Assessment” [Mesh] OR “Population Health” [Mesh] OR “Health effect*” OR “Health outcome*” OR “Health concern*” OR “Health impact*”).

We searched the PubMed, CINAHL, Global Health, Embase and Web of Science databases from January 31 to March 13, 2023. Overall, 3779 articles were retrieved from these five (5) electronic databases.

The searches were carried out on all five databases, and the articles identified in the searches were exported to Rayyan software. After removing duplicates, 3167 items were retained for review.

The selection of relevant articles about our research question and inclusion criteria was made gradually. Before the selection process, to improve its reliability, all reviewers participated in a preparatory meeting with an example taken from an article to facilitate reading. The selection process involved the title, abstract, and full text. Initially, the group leader divided the researchers into three subgroups (WSR, TB and AWVA; GA and NB; GKKP and CK) and selected articles based on their titles and abstracts. Of the 3167 articles examined, 3141 were excluded at this stage based on all the exclusion criteria. We obtained the full texts of the potentially eligible studies by at least one of the reviewers. We compared and validated the results through a consensus session. Disagreements were resolved by discussion and consensus involving all the investigators and with the help of a third reviewer if the disagreement could not be resolved. The articles selected based on their titles and abstracts were imported into the ZOTERO software.

Full-text articles were then selected in three stages. In the first stage, researchers were divided into two subgroups (WSR, GKKP, TB and AWVA) and (GA, CK and NB) to review at least one article and decide on their inclusion to harmonize views on the article selection and quality analysis grids. The researchers selected the remaining articles independently and separately in the second stage. The third stage involved comparing the selected articles to resolve discrepancies by consensus. To reach a consensus, six articles were evaluated by a senior team member (PN). A flow chart summarizing the study selection process was drawn. At the end of this process, twenty-six (26) full texts were retained after the titles and abstracts were read:

The characteristics of the excluded studies are also available in Appendix 1. Uncertainties and disagreements over inclusion were resolved by discussion between the seven (7) investigators. The following flowchart illustrates the selection process and is represented by Figure 1: [31] .

An extraction grid was developed by a reviewer (WSR) and validated by all team members. The subgroup data were independently extracted from the selected studies using the MMAT extraction grid [32] . Data were extracted according to the following variables : 1) title of the article, 2) name of the first author, 3) year of publication of the study, 4) location of the study, 5) aim or objectives of the study, 6) type of study, 7) duration of the study, 8) data collection, 9) collection tools, 10) analysis methods, 11) primary results or main outcomes, 12) participants, 13) sex ratio and 14) sample size. Some of these extracted data are tabular in shape in the Results section.

The main results focus on plastic waste’s impact on developing countries’ human population. Plastic waste can cause serious environmental and health hazards both directly and indirectly. The impact that plastics can have on human health has been the subject of numerous studies, with the main findings focusing on the following points:

1) Exposure to BPA and BPS through the gut. Plastic contains chemicals that may enter the human body and harm human health.

2) Home waste storage is associated with houseflies in the kitchen (r = 0.17, p < 0.0001). The presence of houseflies in the kitchen during cooking is correlated with the incidence of childhood diarrhea (r = 0.36, p < 0.0001). Inadequate solid waste facilities result in the indiscriminate burning and burying of solid waste. There was an association between waste burning and the incidence of respiratory health symptoms among adults (r = 0.25, p < 0.0001) and children (r = 0.22, p < 0.05). Poor handling and disposal of waste are major causes of environmental pollution, which creates breeding grounds for pathogenic organisms and the spread of infectious diseases.

3) Health hazards associated with the use of plastic bags.

The methodological quality of the three studies included in this synthesis was assessed using the Mixed Methods Appraisal Tool (MMAT) (see Appendix 2). The MMAT is a critical appraisal tool designed for mixed systematic reviews, i.e., qualitative, quantitative and mixed methods studies. It assesses the methodological quality of five categories of studies: qualitative research, randomized trials, quantitative studies, descriptive studies and mixed-method studies [32] [33] . The MMAT criteria list includes two triage questions and five questions per study category. In addition, the document consists of indicators that explain and illustrate certain criteria. For each question, the authors answered by ticking “Yes,” “Do not know,” or “No.”

The main results of the studies were analyzed and summarized in narrative form. A systematic narrative synthesis was carried out using the information presented in the text and tables to summarize and explain the characteristics and results of the included studies.

A total of 3779 articles were retrieved through various electronic database searches. After eliminating duplicates (n = 612), 3167 articles were reviewed based on title and abstract. Of these reviewed articles, 26 were retained for full-text review, and 23 articles were excluded for the following reasons: full texts not found (n = 2), articles excluded for comments (n = 2), a systematic review (n = 1), articles carried out outside developing countries (n = 14), and articles excluded because analyses were not carried out in humans but rather in animals or laboratory tests (n = 4). The flow and number of studies examined at each stage of this systematic review are presented according to the PRISMA diagram in Figure 1.

The articles included were published in English between 1939 and 2023. Appendix 1 provides a brief overview of the main characteristics of the included studies. The articles included in our systematic review used different types of studies, including cross-sectional studies and a quantitative randomized trial. The study duration and data collection periods varied from article to article.

All studies were conducted in middle- and low-income countries. All three articles were in English. The size of the study population was 1766, including 556, 25 and 960 participants. The sex ratio favored women in all three studies, with 0.9 and 0.6 in two (2) studies and an exclusively female presence in the other.

The studies were generally of high quality. Consensus responses to all MMAT methodological quality criteria were “yes” for the three included studies (Appendix 2).

The primary search strategy identified 3779 potentially relevant studies. After an initial screening based on abstract titles, 26 studies were selected for full-text review. At this stage, 23 studies were excluded, as summarized in Appendix 3. The methodological quality of the remaining three studies was assessed. No studies were excluded based on quality assessment.

The articles included in our systematic review included different types of studies, including cross-sectional studies (2) and randomized quantitative studies (1). The study duration and data collection periods varied. Details can be found in Appendix 4. The types of studies in our selected articles were all quantitative. The data collection methods used in all these studies included interviews with a structured questionnaire (2) and interviews with 960 female heads of household (1).

The included articles were published as early as 2005 and as recently as 2021. One article was published in 2021, one (1) in 2013 and one (1) in 2005.

The three studies included in the review were conducted in India (Varanasi and Mangalore), and the last was in Ghana (Accra). The objectives of each of these articles are as follows:

• This cross-sectional survey aimed to assess the use of plastic in contact with food, awareness of the health hazards of plastic chemicals, and warning labels on plastic items among a sample population in Varanasi.

• This study examined household-level waste management and disposal practices in the Accra metropolitan area, Ghana.

• This study was performed to determine people’s awareness of the health hazards associated with the use of plastic bags and their perceptions of legislation prohibiting plastic bags.

To assess the quality of the articles included, we used the MMAT. The methodological quality of our three articles included in this synthesis was assessed using the mixed methods appraisal tool (MMAT). It is a critical appraisal tool designed for mixed systematic reviews, i.e., reviews that include quantitative, qualitative and mixed methods studies. It assesses five categories of methodological quality: qualitative research, randomized controlled trials, nonrandomized studies, quantitative descriptive studies and mixed-method studies. The tool is divided into two parts. First, the tool was suitable for this study because it was explicitly developed for the quality assessment of systematic reviews involving qualitative, quantitative and mixed-method designs. The MMAT criteria list includes indicators that explain and illustrate specific criteria. Our three articles evaluated were all quantitative studies. The articles involved 556 adult visitors, 960 female heads of household and 250 women (160) and men (90).

For each question, the authors answered by ticking “yes” or “no,” “do not know,” or “comments.” Regarding the methodological quality of the articles, three studies scored 6/6 (100% high quality), indicating overall high methodological quality (see Table 2).

In this systematic review, we screened 3167 journal articles and selected three articles containing quantitative information about the impact of plastic waste on human health in low-income countries. Plastic pollution threatens the environment, human health, and future generations. Humans are exposed to many toxic chemicals and microplastics through inhalation, ingestion, and direct skin contact throughout the plastic lifecycle. Although the health impacts of plastics are still a relatively new research area, scientific results indicate that the toxic chemical additives and pollutants in plastics threaten human health globally. Given the heterogeneity in quantitative study design and outcome measures, we could not conduct meta-analyses. Thus, we synthesized the findings narratively.

Generally, men engage in practices likely to result in oral exposure to plastic chemicals that harm their health. This may be due to a lack of information or misinformation about the possible impact of plastics on human health. Most of the participants in our study admitted to following common plastic container practices that can cause plastic chemicals to leach into their edible products. Washing plastic containers in the heat of a dishwasher can also leach chemicals and should, therefore, be avoided.

Plastic materials contain specific chemical compounds that can infiltrate the human body, leading to adverse health effects. Research indicates plastic chemicals are more hazardous to children’s health, particularly infants. Moghadam et al. (2012) conducted a study on the impact of bisphenol A in BPA-free baby feeding bottles. They discovered that children’s immaturity makes their gut more susceptible to damage triggered by these products [36] . The World Health Safety Agency banned BPA in baby cups and bottles due to increasing apprehension about the health risks of BPA [36] .

Even though in current daily practices, plastic can release harmful chemicals and expose people to the impact of these chemicals on human health, the willingness to reduce the use of plastic routinely and to prefer plastic substitutes was not observed in most participants. Although most people have heard that plastic and microwaves are not mixed, it is uncommon for people to reheat their food in plastic containers, such as Tupperware.

Plastic bags preserve and store food in the home, collecting waste before disposal. The storage of waste in plastic containers within homes or their immediate vicinity promotes the presence of flies, which transmit germs, resulting in diarrhea. Domfeh et al. (1999) reported, in research conducted in Accra (Ghana), that infectious diseases leading to diarrhea and associated poor hygiene were frequently reported health issues in the city’s outpatient health centers [35] . This situation may be explained by the fact that households do not have a home collection service, and those with a low capacity are inadequate. A lack of funding in the rapidly expanding cities of many low- and middle-income countries leads to extensive informal waste recycling [33] . According to a survey in Kinshasa, most respondents (69%) managed their waste by landfilling. Ninety-six percent of respondents said no infrastructures were available for waste management [37] .

Waste burning-related air pollution poses health hazards to nearby populations [33] , exposing them to respirable airborne particles such as carbon monoxide, nitrogen oxide, and sulfur dioxide. A study in Jakarta [10] showed a correlation between uncollected garbage and the onset of respiratory illness in mothers and children who burned their garbage.

In rural areas, a few more affluent residents might have their waste collected and taken to alternative sites for disposal or burning. However, 34 out of 48 residents can burn waste in their backyards or dispose of it locally (in streets, riverbeds, scrubland or informal central landfills). Therefore, the open burning of garbage is a common risk reduction strategy, although the impacts on local air quality, human health, and climate remain primarily ignored [38] .

This systematic review emphasizes the hazards of using and disposing of plastic containers. These containers come in various shapes and sizes, serving multiple purposes, such as holding food, drinking water, and household waste. The use of plastics poses health risks due to the penetration of chemical substances into the intestines and lungs, resulting in various health issues.

It is worth mentioning that while the hazards of plastics are well documented, there is a regrettable lack of awareness and information among the public. Emphasis should be placed on increasing awareness among various people about the harm caused by plastics and the availability of alternatives.

This systematic literature review confirmed that plastics threaten human health and the environment. The quality of the studies reviewed was intriguingly methodological. Behavior-change communication must be enhanced with the public, governmental organizations, and nongovernmental organizations. However, developing countries have undertaken minimal work on plastic waste hazards, and necessary measures to improve human and environmental protection are either lacking or poorly enforced.

Our study of the impact of plastic waste on human health has several limitations. First, we may have omitted relevant studies by retaining only articles published in English or French. We may have missed some relevant studies, as unpublished and gray literature is inaccessible in most low- and middle-income countries.