Environmental Sustainability Impacts of Solid Waste Management Practices in the Global South

Solid waste management (SWM) is one of the key responsibilities of city administrators and one of the effective proxies for good governance. Effective SWM mitigates adverse health and environmental impacts, conserves resources, and improves the livability of cities. However, unsustainable SWM practices, exacerbated by rapid urbanization and financial and institutional limitations, negatively impact public health and environmental sustainability. This review article assesses the human and environmental health impacts of SWM practices in the Global South cities that are the future of global urbanization. The study employs desktop research methodology based on in-depth analysis of secondary data and literature, including official documents and published articles. It finds that the commonplace SWM practices include mixing household and commercial garbage with hazardous waste during storage and handling. While waste storage is largely in old or poorly managed facilities such as storage containers, the transportation system is often deficient and informal. The disposal methods are predominantly via uncontrolled dumping, open-air incinerators, and landfills. The negative impacts of such practices include air and water pollution, land degradation, emissions of methane and hazardous leachate, and climate change. These impacts impose significant environmental and public health costs on residents with marginalized social groups mostly affected. The paper concludes with recommendations for mitigating the public and environmental health risks associated with the existing SWM practices in the Global South.


Introduction
Solid waste management (SWM) continues to dominate as a major societal and governance challenge, especially in urban areas overwhelmed by the high rate of population growth and garbage generation. The role of SWM in achieving sustainable development is emphasized in several international development agendas, charters, and visions. For example, sustainable SWM can help meet several United Nations' Sustainable Development Goals (SDG), such as ensuring clean water and sanitation (SDG6), creating sustainable cities and inclusive communities (SDG11), mitigating climate change (SDG13), protecting life on land (SDG15), and demonstrating sustainable consumption and production patterns (SDG12) (https://sdgs.un.org/goals, accessed on 26 September 2022). It also fosters a circular urban economy that promotes reductions in the consumption of finite resources, practices toward policy and practical recommendations for a more sustainable SWM sys-tem, with the Global South as the study boundary. This stage also helped identify relevant keywords to search for during the literature review in the second stage.
The second stage involved identifying and collecting relevant literature from online sources. The researchers utilized Google Scholar and Scopus databases to identify peerreviewed academic works (peer-reviewed articles, conference proceedings, and books) as well as the gray literature. The literature that satisfied the following three inclusion criteria was identified and downloaded: (1) It is related to the study's objective; (2) it is in the English language; and (3) it was published within the last twenty years, although some old documents about established concepts and approaches were also accessed. The downloaded gray literature includes newspaper articles, statistics, technical reports, and website contents from international development organizations such as the World Health Organization (WHO), the United Nations, and the World Bank.
In the last stage, the authors organized, analyzed, and synthesized the data collected from the literature. The downloaded works were organized according to the similarity of topics, even though some fit in more than one category. Then, each document was thoroughly examined, and themes concerned with SWM practices and their human and environmental impacts were collated, synthesized, and harmonized. Finally, the themes were summarized in Tables (see Appendix A) and discussed. Implications and recommendations of the findings are then highlighted.  The second stage involved identifying and collecting relevant literature from online sources. The researchers utilized Google Scholar and Scopus databases to identify peerreviewed academic works (peer-reviewed articles, conference proceedings, and books) as well as the gray literature. The literature that satisfied the following three inclusion criteria was identified and downloaded: (1) It is related to the study's objective; (2) it is in the English language; and (3) it was published within the last twenty years, although some old documents about established concepts and approaches were also accessed. The downloaded gray literature includes newspaper articles, statistics, technical reports, and website contents from international development organizations such as the World Health Organization (WHO), the United Nations, and the World Bank.
In the last stage, the authors organized, analyzed, and synthesized the data collected from the literature. The downloaded works were organized according to the similarity of topics, even though some fit in more than one category. Then, each document was thoroughly examined, and themes concerned with SWM practices and their human and environmental impacts were collated, synthesized, and harmonized. Finally, the themes were summarized in Tables A1-A3 (see Appendix A) and discussed. Implications and recommendations of the findings are then highlighted. Table 1. Common MSW management practices by country's level of economic development (adapted from [34]).

Source Reduction
Low per capita waste generation rates, no organized SWM program, high reuse rate.
Some source reduction elements but rarely incorporated into an organized SWM program.
SWM programs emphasize the three "Rs": reduce, reuse, and recycle. More producer responsibility.
Collection Infrequent and inefficient. Serves mainly high visibility areas, the wealthy, and businesses willing to pay.
A high fraction of inert and compostable waste impact collection. The overall collection is less than 50%.
Improved collection and transportation in residential areas. Large vehicle fleet and mechanization. The overall collection rate is from 50% to 80%. Transfer stations are gradually incorporated into the SWM system.
More than 90% collection rate. Compactor and well-mechanized trucks, and transfer stations are common. Waste volume is a major consideration. Aging collection workers are often considered in system design.

Recycling
Informal sector recycling by scavengers is dominant. High recycling rates for local and international markets. Imports of materials for recycling, including hazardous goods such as e-waste and shipbreaking. Recycling markets are unregulated and include several "middlemen". Large price fluctuations.
Informal recycling, high technology sorting, and processing facilities. Relatively high recycling rates. Materials are often imported for recycling. Recycling markets are mostly regulated. Material prices fluctuate considerably.
Recyclable material collection, high-technology sorting, and processing facilities are common and regulated. Increased attention towards long-term markets. Overall, recycling rates are higher than in middle-and low-income countries. Informal recycling still exists (e.g., collecting aluminum cans). Extended product responsibility is common. It is not widespread. Largescale composting facilities are mostly unsuccessful because of contamination and operating costs (little waste separation); some small-scale composting projects at the community/neighborhood level are more sustainable than the large-scale. Growing use of anaerobic digestion.

It is widespread in backyard and
large-scale facilities. The waste consists of smaller portions of organic matter than low-and middle-income countries. More source segregation makes composting easier. Anaerobic digestion is gaining popularity. Odor control is critical.

Incineration
It is uncommon and mostly unsuccessful due to high capital, technical, and operation costs, the high moisture content in the waste, and the high proportion of inert waste.
A few incinerators operate but experience financial and operational difficulties. Air pollution control equipment is not advanced and is often bypassed. Lack of emissions monitoring. Facilities are often driven by subsidies as construction and operation costs are prohibitive.
Predominant in areas where land is scarce or expensive (e.g., islands). It is mostly subjected to environmental control to regulate and monitor emissions. It recovers energy but it is about at least three-folds the cost of landfilling per ton.

Landfilling and open dumping
Open dumping of waste and low-technology landfill sites. High pollution to nearby aquifers, water bodies, and communities. Regularly receive medical waste. Waste is often burned. Significant health impacts on workers and residents.
Sanitary landfills with some environmental controls often exist.
Open dumping of garbage is widespread. Projects for landfill gas collection under clean development mechanism are commonplace.
Sanitary landfills combined with liners, leak detection, and leachate collection systems. Gas collection and treatment systems. It is often problematic to open new landfills due to concerns of neighboring residents. Post-closure use of sites is increasingly important, e.g., golf courses and parks.

Costs
Waste collection costs represent 80-90% of the municipal SWM budget.
Local governments regulate waste fees, but the fee collection system is inefficient. Only a small proportion of the budget is allocated toward disposal.
Collection costs represent 50% to 80% of the municipal SWM budget. Some local and national governments regulate waste fees and more innovation in fee collection, e.g., included in electricity or water bills. More mechanized collection fleets and disposal expenditures are higher than in low-income countries.
Collection costs can represent less than 10% of the budget. Large budget allocations to intermediate waste treatment facilities. Upfront community participation reduces costs and increases options available to waste planners (e.g., recycling and composting).

(b) Irregular Waste Collection and Handling
Uncollected and untreated waste has socioeconomic and environmental costs extending beyond city boundaries. Environmental sustainability impacts of this practice include methane (CH 4 ) emissions, foul odor, air pollution, land and water contamination, and the breeding of rodents, insects, and flies that transmit diseases to humans. Decomposition of biodegradable waste under anaerobic conditions contributes to about 18% and 2.9% of global methane and GHG emissions, respectively [54], with the global warming effect of about 25 times higher than carbon dioxide (CO 2 ) emissions [55]. Methane also causes fires and explosions [56]. Emissions from SWM in developing countries are increasing due to rapid economic growth and improved living standards [57].
Irregular waste collection also contributes to marine pollution. In 2010, 192 coastal countries generated 275 million metric tons of plastic waste out of which up to 12.7 million metric tons (4.4%) entered ocean ecosystems [58]. Moreover, plastic waste collects and stagnates water, proving a mosquito breeding habitat and raising the risks of dengue, malaria, and West Nile fever [56]. In addition, uncollected waste creates serious safety, health, and environmental consequences such as promoting urban violence and supporting breeding and feeding grounds for flies, mosquitoes, rodents, dogs, and cats, which carry diseases to nearby homesteads [4,19,59,60].
In the global South, scavengers often throw the remaining unwanted garbage on the street. Waste collectors are rarely protected from direct contact and injury, thereby facing serious health threats. Because garbage trucks are often derelict and uncovered, exhaust fumes and dust stemming from waste collection and transportation contribute to environmental pollution and widespread health problems [61]. In India's megacities, for example, irregular MSW management is one of the major problems affecting air and marine quality [62]. Thus, irregular waste collection and handling contribute to public health hazards and environmental degradation [63].

(c) Landfilling and Open Dumping
Most municipal solid waste in the Global South goes into unsanitary landfills or open dumps. Even during the economic downturn during the COVID-19 pandemic, the amount of waste heading to landfill sites in Brazil, for example, increased due to lower recycling rates [64]. In Johor, Malaysia, landfilling destroys natural habitats and depletes the flora and fauna [65]. Moreover, landfilling with untreated, unsorted waste led to severe public health issues in South America [66]. Based on a study on 30 Brazilian cities, Urban and Nakada [64] report that 35% of medical waste was not properly treated before disposal, which poses a threat to public health, including the spread of COVID- 19. Landfills and open dumps are also associated with high emissions of methane (CH 4 ), a major GHG [67,68]. Landfills and wastewater release 17% of the global methane emission [25]. About 29 metric tons of methane are emitted annually from landfills globally, accounting for about 8% of estimated global emissions, with 1.3 metric tons released from landfills in Africa [7]. The rate of landfill gas production steadily rises while MSW accumulates in the landfill emissions. Released methane and ammonia gases can cause health hazards such as respiratory diseases [37,[69][70][71]. Since methane is highly combustible, it can cause fire and explosion hazards [72].
Odors from landfill sites, and their physical appearance, affect the lives of nearby residents by threatening their health and undermining their livelihoods, lowering their property values [37,38,68,[82][83][84]. Moreover, the emission of ammonia (NH 3 ) from landfill sites can damage species' composition and plant leaves [85]. In addition, the pollutants from landfill sites damage soil quality [73,84]. Landfill sites also generate dust and are sources of noise pollution [86].
Air and water pollution are intense in the hot and rainy seasons due to the emission of offensive odor, disease-carrying leachates, and runoff. Considerable amounts of methane and CO 2 from landfill sites produce adverse health effects such as skin, eyes, nose, and respiratory diseases [69,87,88]. The emission of ammonia can lead to similar problems and even blindness [85,89]. Other toxic gaseous pollutants from landfill sites include Sulphur oxides [89]. While less than 20% of methane is recovered from landfills in China, Western nations recover up to 60% [90].
Several studies report leachate from landfill sites contaminating water sources used for drinking and other household applications, which pose significant risks to public health [36,43,53,72,75,83,[91][92][93][94][95]. For example, Hong et al. [95] estimated that, in 2006, the amount of leachates escaping from landfill sites in Pudong (China) was 160-180 m 3 per day. On the other hand, a properly engineered facility for waste disposal can protect public health, preserve important environmental resources, prevent clogging of drainages, and prevent the migration of leachates to contaminate ground and surface water, farmlands, animals, and air from which they enter the human body [61,96]. Moreover, heat in summer can speed up the rate of bacterial action on biodegradable organic material and produce a pungent odor [60,97,98]. In China, for example, leachates were not treated in 47% of landfills [99].
Co-mingled disposal of industrial and medical waste alongside municipal waste endangers people with chemical and radioactive hazards, Hepatitis B and C, tetanus, human immune deficiency, HIV infections, and other related diseases [59,60,100]. Moreover, indiscriminate disposal of solid waste can cause infectious diseases such as gastrointestinal, dermatological, respiratory, and genetic diseases, chest pains, diarrhea, cholera, psychological disorders, skin, eyes, and nose irritations, and allergies [10,36,60,61].

(d) Open Burning and Incineration
Open burning of MSW is a main cause of smog and respiratory diseases, including nose, throat, chest infections and inflammation, breathing difficulty, anemia, low immunity, allergies, and asthma. Similar health effects were reported from Nepal [101], India [87], Mexico, [69], Pakistan [52,73,84], Indonesia [88], Liberia [50], and Chile [102]. In Mumbai, for example, open incineration emits about 22,000 tons of pollutants annually [56]. Mongkolchaiarunya [103] reported air pollution and odors from burning waste in Thailand. In addition, plastic waste incineration produces hydrochloric acid and dioxins in quantities that are detrimental to human health and may cause allergies, hemoglobin deficiency, and cancer [95,104]. In addition, smoke from open incineration and dumpsites is a significant contributor to air pollution even for persons staying far from dumpsites.

(e) Composting
Composting is a biological method of waste disposal that entails the decomposing or breaking down of organic wastes into simpler forms by naturally occurring microorganisms, such as bacteria and fungi. However, despite its advantage of reducing organic waste by at least half and using compost in agriculture, the composting method has much higher CO 2 emissions than other disposal approaches. In Korea, for example, composting has the highest environmental impact than incineration and anaerobic digestion methods [105]. The authors found that the environmental impact of composting was found to be 2.4 times higher than that of incineration [105]. Some reviews linked composting with several health issues, including congested nose, sore throat and dry cough, bronchial asthma, allergic rhinitis, and extrinsic allergic alveolitis [36,106].

Implications and Recommendations
As discussed in the section above, there are many negative impacts of unsustainable SWM practices on the people and the environment. Although all waste treatment methods have their respective negative impacts, some have fewer debilitating impacts on people and the environment than others. The following is the summary of key implications of such unsustainable SWM practices.

•
Uncollected organic waste from bins, containers and open dumps harbors rodents, insects, and reptiles that transmit diseases to humans. It also produces odor due to the decomposition of organic wastes, especially in the summer, and leachates that migrate and contaminate receiving underground and surface waters.

•
Open dumps and non-engineered landfills release methane from decomposing biodegradable waste under anaerobiotic conditions. Methane is a key contributor to global warming, and it can cause fires and explosions.
• Non-biodegradable waste, such as discarded tires, plastics, bottles, and tins, pollutes the ground and collects water, thus creating breeding grounds for mosquitoes and increasing the risk of diseases such as malaria, dengue, and West Nile fever. • Open burning of MSW emits pollutants into the atmosphere thereby increasing the incidences of nose and throat infections and inflammation, inhalation difficulties, bacterial infections, anemia, reduced immunity, allergies, and asthma. • Uncontrolled incineration causes smog and releases fine particles, which are a major cause of respiratory disease. It also contributes to urban air pollution and GHG emissions significantly. • Incineration and landfilling are associated with reproductive defects in women, developmental defects in children, cancer, hepatitis C, psychosocial impacts, poisoning, biomarkers, injuries, and mortality.
Therefore, measures toward more sustainable SWM that can mitigate such impacts must be worked out and followed. The growing complexity, costs, and coordination of SWM require multi-stakeholder involvement at each process stage [7]. Earmarking resources, providing technical assistance, good governance, and collaboration, and protecting environmental and human health are SWM critical success factors [47,79]. As such, local governments, the private sector, donor agencies, non-governmental organizations (NGOs), the residents, and informal garbage collectors and scavengers have their respective roles to play collaboratively in effective and sustainable SWM [40,103,107,108]. The following are key practical recommendations for mitigating the negative impacts of unsustainable SWM practices enumerated above.
First, cities should plan and implement an integrated SWM approach that emphasizes improving the operation of municipalities to manage all stages of SWM sustainably: generation, separation, transportation, transfer/sorting, treatment, and disposal [36,46,71,77,86]. The success of this approach requires the involvement of all stakeholders listed above [109] while recognizing the environmental, financial, legal, institutional, and technical aspects appropriate to each local setting [77,86]. Life Cycle Assessment (LCA) can likewise aid in selecting the method and preparing the waste management plan [88,110]. Thus, the SWM approach should be carefully selected to spare residents from negative health and environmental impacts [36,39,83,98,111].
Second, local governments should strictly enforce environmental regulations and better monitor civic responsibilities for sustainable waste storage, collection, and disposal, as well as health hazards of poor SWM, reflected in garbage littering observable throughout most cities of the Global South [64,84]. In addition, violations of waste regulations should be punished to discourage unsustainable behaviors [112]. Moreover, local governments must ensure that waste collection services have adequate geographical coverage, including poor and minority communities [113]. Local governments should also devise better SWM policies focusing on waste reduction, reuse, and recycling to achieve a circular economy and sustainable development [114,115].
Third, effective SWM requires promoting positive public attitudes toward sustainable waste management [97,[116][117][118]. Therefore, public awareness campaigns through print, electronic, and social media are required to encourage people to desist from littering and follow proper waste dropping and sorting practices [36,64,77,79,80,82,91,92,119]. There is also the need for a particular focus on providing sorting bins and public awareness about waste sorting at the source, which can streamline and optimize subsequent SWM processes and mitigate their negative impacts [35,45,46,64,69,89,93]. Similarly, non-governmental and community-based organizations can help promote waste reduction, separation, and sorting at the source, and material reuse/recycling [103,[120][121][122]. In Vietnam, for example, Tsai et al. [123] found that coordination among stakeholders and appropriate legal and policy frameworks are crucial in achieving sustainable SWM.
Fourth, there is the need to use environmentally friendly technologies or upgrade existing facilities. Some researchers prefer incineration over other methods, particularly for non-recyclable waste [44,65]. For example, Xin et al. [124] found that incineration, recycling, and composting resulted in a 70.82% reduction in GHG emissions from solid waste in Beijing. In Tehran city, Iran, Maghmoumi et al. [125] revealed that the best scenario for reducing GHG emissions is incinerating 50% of the waste, landfilling 30%, and recycling 20%. For organic waste, several studies indicate a preference for composting [45,51,75] and biogas generation [15,42,68]. Although some researchers have advocated a complete ban on landfilling [13,42], it should be controlled with improved techniques for leak detection and leachate and biogas collection [126,127]. Many researchers also suggested an integrated biological and mechanical treatment (BMT) of solid waste [66,74,95,119]. In Kenya, the waste-to-biogas scheme and ban on landfill and open burning initiatives are estimated to reduce the emissions of over 1.1 million tons of GHG and PM2.5 emissions from the waste by more than 30% by 2035 [42]. An appropriately designed waste disposal facility helps protect vital environmental resources, including flora, fauna, surface and underground water, air, and soil [128,129].
Fifth, extraction and reuse of materials, energy, and nutrients are essential to effective SWM, which provides livelihoods for many people, improves their health, and protects the environment [130][131][132][133][134][135][136]. For example, recycling 24% of MSW in Thailand lessened negative health, social, environmental, and economic impacts from landfill sites [89]. Waste pickers play a key role in waste circularity and should be integrated into the SWM system [65,89,101,137], even to the extent of taking part in decision-making [138]. In addition, workers involved in waste collection should be better trained and equipped to handle hazardous waste [87,128]. Moreover, green consumption, using bioplastics, can help reduce the negative impacts of solid waste on the environment [139].
Lastly, for effective SWM, local authorities should comprehensively address SWM challenges, such as lack of strategic SWM plans, inefficient waste collection/segregation and recycling, insufficient budgets, shortage of qualified waste management professionals, and weak governance, and then form a financial regulatory framework in an integrated manner [140][141][142]. Effective SWM system also depends on other factors such as the waste generation rate, population density, economic status, level of commercial activity, culture, and city/region [37,143]. A sustainable SWM strives to protect public health and the environment [144,145].

Conclusions
As global solid waste generation rates increase faster than urbanization, coupled with inadequate SWM systems, local governments and urban residents often resort to unsustainable SWM practices. These practices include mixing household and commercial garbage with hazardous waste during storage and handling, storing garbage in old or poorly managed facilities, deficient transportation practices, open-air incinerators, informal/uncontrolled dumping, and non-engineered landfills. The implications of such practices include air and water pollution, land degradation, climate change, and methane and hazardous leachate emissions. In addition, these impacts impose significant environmental and public health costs on residents with marginalized social groups affected mostly.
Inadequate SWM is associated with poor public health, and it is one of the major problems affecting environmental quality and cities' sustainable development. Effective community involvement in the SWM requires promoting positive public attitudes. Public awareness campaigns through print, electronic, and social media are required to encourage people to desist from littering and follow proper waste-dropping practices. Improper SWM also resulted in water pollution and unhealthy air in cities. Future research is needed to investigate how the peculiarity of each Global South country can influence selecting the SWM approach, elements, aspects, technology, and legal/institutional frameworks appropriate to each locality.

Conflicts of Interest:
The authors declare no conflict of interest in conducting this study.

Odor generation Water and air contaminations
The use of conditioning treatments, such as composting, is essential before using the residues for agricultural uses. The wastes must be fully categorized before using for agricultural purposes.