Hazardous Waste Management: An African Overview

: Hazardous waste materials and their management are of prime importance to society. This article gives an overview of the current practices that relate to hazardous waste management. It looks at issues concerning the transboundary or international movement of harmful materials from industrialized nations to the developing and emerging world. This study has shown that Africa, most notably Nigeria, has become a dumping ground for hazardous waste materials as a result of the high importation of scrap computers and electronic devices into the country. The public health hazards, such as birth deficiencies, cancers, and even infectious diseases such as human immunodeficiency virus (HIV) and Hepatitis B and C, respectively, have been traced to the improper management of these waste materials. The review highlights a few models on hazardous waste management as developed by previous literature, which gives a hierarchy, ranging from source reduction, recycling, and landfill options. Studies reveal that hazardous waste management in Africa must revolve around wealth creation, economic, and environmental sustainability. The study provided evidence that the recycling option has high potentials in the areas of energy recovery. The data collected show South Africa to be the most advanced in the African continent in the field of hazardous waste management. For a sustainable environment, keen attention must be paid to hazardous waste management globally.


Introduction
The day to day generation of hazardous waste in many parts of the world poses tremendous threats to humans, animals, and the ecosystem at large. The increase in waste generation can be strictly linked to the rise in the global population, thus leading to a rapid boost in industrial activities [1], which are a significant source of hazardous contaminants in the world. According to research by the United Nations Environment Programme (UNEP), about 400 million tons of hazardous waste are generated globally every year, which is estimated to be about 60 kg for every individual in the world [2,3].
On a global scale, several studies have been conducted on hazardous waste materials, which have indicated the rate of generation of unsafe contaminants. China, for example, faces critical challenges in the control of dangerous pollutants, both domestically and internationally. In 2005, about 11.62 million tons of industrial hazardous waste (IHW) was produced, of which an average of approximately 43.4% was recycled, 33% was stored, and 23% was disposed of. This accounts for about 70,000 tons of IHW that were discharged to the environment with no form of control [4]. According to studies carried out by [5], 1.4% of about 13 million tons of industrial waste generated in Portugal as of the year 2001 was reported to be hazardous. This study showed that 5% to 7% of municipal solid waste is considered to be hazardous [5]. Elsewhere in India, about 9.3 million metric tons (MT) of hazardous waste is generated, of which 1.35 million MT is recyclable, 0.11 million MT is incinerable, and 0.49 million MT is sent away for safe disposal [6]. Some other studies have been able to deal with the quantification of hazardous waste generated at the household and national levels [7][8][9]. Recent estimations show that 3,000,000 tons/year of industrial waste is produced in Chile, of which 129,918 tons/year of hazardous waste has been reported [10]. Data from research suggest that 100,000-250,000 tons of household hazardous waste (HHW) were expected to be disposed of in the United Kingdom, without considering electronic waste materials [7][8][9].
Taking into consideration the various types of hazardous waste sources, such as e-waste and biomedical waste, several studies have revealed some critical data concerning their generation. About 500 million PCs (personal computers) are said to have reached the end of their service lives between 1994 and 2003 [11]. These PCs are reported to contain an average quantity of 2,872,000 tons of plastics, 718,000 tons of lead, 1363 tons of cadmium, with an average lifespan decreasing from about six years in 1997 to two years as of the year 2005 [11,12]. Figure 1 shows a global map with the quantity of hazardous waste generation globally. From Figure 1, Russia generates the highest amount of hazardous waste in the world, at about 139,194,000 tons per annum, with the United States following behind at 37,033,000 tons per annum. Most of Africa still shows a low hazardous waste generation rate [13,14].  Table 1 gives a summary of hazardous waste generated in African countries and the hazardous waste generated per capita in Africa and other parts of the world. Table 1 also highlights the same information from randomly selected countries which cut across other regions of the world.  Gabon  27  20  Cuba  941  83  Gambia  29  20  Argentina  2530  67  Ghana  419  20  Belize  1  3  Guinea  172  20  Bolivia  573  67  Guinea-Bissau  29  20  Brazil  11,740  67  Kenya  643  20  Chile  1039  67  Lesotho  37  20  Colombia  2897  67  Liberia  66  20  Costa Rica  273  67  Libya  110  20  Iraq  15,091  616  Madagascar  345  20  Iran  168  2  Malawi  243  20  Kazakhstan  130  8  Mali  257  20  Kiribati  1  14  Mauritania  57  20  Kuwait  25  10  Mauritius  0  0  Kyrgyzstan  6780  1329  Morocco  987  33  Laos  80  14  Mozambique  378  20  Puerto Rico  260  67  Namibia  41  20  Saint Kitts and Nevis  3  67  Niger  24  2  Saint Lucia  0  3   Nigeria  2469  20  St Vincent and The  Grenadines  7  67   Rwanda  170  20  Trinidad and Tobago  87  67  Sao Tome and Principe  4  20  Hungary  3413  345  Senegal  202  20  Iceland  13  45  Seychelles  2  20  Ireland  492  126  Sierra Leone  98  20  Italy  4279  74  Somalia  194  20  Latvia  93  40  South Africa  915  20  Liechtenstein  4  118  Sudan  672  20  Lithuania  111  32  Swaziland  22  20  Luxemburg  101  253  Togo  98  20  Panama  206  67  Tunisia  198  20  Paraguay  380  67  Uganda  511  20  Peru  1785  67  Tanzania  741  20  Suriname  27  67  Western Sahara  6  20  Uruguay  226  67  Zambia  219  20  Venezuela  1678  67  Zimbabwe  261  20  Israel  325  52 From Table 1, Nigeria is reported to generate the highest amount of hazardous waste in Africa, at 2,469,000 tons per annum, followed by Egypt, at about 1,440,000 tons per annum. Africa is reported to have an average per capita hazardous waste generation of 20.1 kg/person/annum [13,14]. The Benin Republic and Morocco are reported to have the highest per capita hazardous waste generation at 65 and 33 kg/person/annum [13,14]. Table 1 also gives an insight into the per capita generation rates of other regions of the world. Estonia, for example, has the highest per/capita generation of hazardous waste, at 4774 kg/person/year [13,14].
This review identifies the hazardous waste situation in some African countries, based on available data and its impact on public health in the African continent. Challenges faced by Africa in the effective management of hazardous waste materials are identified with potential mitigative measures. By utilizing a basic model, this review provides a process flow of hazardous waste materials that could be adopted by African nations based on the peculiarities of their countries.

The African Scenario
The case in the African continent differs from that of the developed world. Africa is said to be the dumping ground of preowned and disregarded electronic materials from the developed world [15][16][17][18]. Moreover, [16,19] reported that the enormous hazardous waste generated in developed countries is usually sent across to African nations as a result of the high cost of disposing of these wastes in their nations and due to the less stringent environmental laws and regulations in Africa. As of the year 1988, it cost between USD 100-USD 2000 per ton to dispose of hazardous waste in the Organization for Economic Cooperation and Development (OECD) countries, as compared to USD 2.50 to USD 50 per ton to dispose of this same waste in developing countries [19,20]. About 20-50 million tons of e-waste are produced annually, of which most of these are shipped to developing countries, including second hand and inferior e-waste [21]. As a result of these weak regulations, wastes are dumped or incinerated in an unhealthy manner to both humans and the environment [21][22][23]. To further bolster this point, a study carried out by the Basel Action Network (BAN) in Nigeria revealed that about 500 containers containing approximately 800 monitors and CPUs enter into the country through the Lagos port every month [17,24]. These values indicate that, on average, 400,000 s-hand or scrap computers enter into the country via the Lagos seaport with an estimated weight of about 60,000 MT per annum [24]. In comparison, [25,26] reports that about 1,200,000 tons of electronic materials are imported into Nigeria, with about 6,800,000 tons of electronic equipment being used annually. This study shows that 1,100,000 tons of e-waste is generated in Nigeria, with Ghana following closely, at about 179,000 tons.  This influx of electronic materials, which is eventually converted to e-waste, is a result of weak legislation on e-waste control in African nations. Studies have shown that there is little legislation in Africa regarding the effective management of electronic waste [27,28]. Reviews by [25,29] have revealed that West Africa has the highest population of people covered by legislation on e-waste at about 53%, with Northern and Southern Africa having no data to show. Figure 3 shows the population of people in Africa covered by the law on e-waste disposal. In third world countries, sacrifices are often made in the areas of environmental preservation to achieve a short-term economic goal [30]. This is said to be the cause of poverty that several developed nations have exploited. For example, China, for a fee of USD 50 per ton, accepted containers conveying waste materials in the early 1990s [18]. This is not new in the African continent, as there are similar cases, such as the dumping of toxic waste in the Koko fishing village in Nigeria by an Italian firm in 1987 [18,[31][32][33][34][35]. In this case, a landowner for a small monthly rent accepted the stacking of toxic radioactive waste by an Italian company on his property [19].
Similarly, a reported contract of about $600 million was offered to Guinea-Bissau in 1988, to dispose of 15 million tons of toxic waste for five years [36]. Although this contract did not pull through due to public concerns, the contract amount was reported to be roughly four times Guinea-Bissau's gross national product [36]. Other similar activities by developed nations include the storage of nuclear waste in Sudanese desert locations by the Americans and Germans in 1985 [31], the construction and operation of a toxic waste incinerator by a Swiss-based firm in Mozambique in 1992 [31], and the shipping of tons of mercury by the British and Americans into South Africa, thus leading to unacceptable mercury standards (1000-1900 times higher than the World Health Organization standards) [31]. A report by the US National Intelligence Council, as contained in [37], shows that there is a yearly turnover that ranges between 12 to 15 billion Euros in illegal trafficking of hazardous waste. Figure 4 displays the identified and suspected routes of e-waste dumping, as obtained from [38,39].

Identification and Classification of Hazardous Waste
Hazardous waste can be characterized as waste that can substantially add to an increase in death or an increase in irreversible or debilitating reversible ailment, or represent an ensuing or potential danger to human wellbeing or the Earth when inappropriately treated, moved or discarded [35]. Hazardous waste is waste that has or can have the potential of having properties such as being corrosive, ignitable, flammable, toxic [35], carcinogenic [36], infectious, radioactive [37,38]. According to the United States Environmental Protection Agency (USEPA), solid waste is said to be hazardous when it is explicitly categorized into one of the listed four (4) categories as contained in the code of Federal Regulations (CFR) (F, K, P, and U) [39]. i.
The F list categorizes waste from conventional engineering and industrial processes as hazardous; examples include spent solvent residues, agents used for wood preservation, and others.
ii. The K list categorizes hazardous wastes from sectors of industry and manufacturing and is source-specific waste. Industries that generate this class of waste are iron and steel production, pesticide manufacturing, wood preservation.
iii. The P list and U list comprises hazardous waste of pure and marketable grade formulations of certain unused substances that are to be disposed of Hazardous waste materials can also be classified based on the threat levels they pose. A study by [40] ranked hazardous waste into high-risk wastes, intermediate risk wastes, and low-risk wastes.
iv. High-risk waste: Materials that contain high concentrations of toxic, mobile bioaccumulative constituents, such as chlorinated solvents and cyanide waste PCB (polychrome biphenyl). v.
Transitional risk wastes: These wastes contain metal hydroxide sludges. vi.
Low-risk wastes: Waste that provides a high volume of low hazard waste and some putrescible waste.
Hazardous wastes are not just peculiar to industries and medical facilities, but are also common in households. A study carried out by [41,42] classifies household hazardous waste materials into six classes, as given in Figure 5.

Public Health Concerns
Developed, developing, and underdeveloped nations genuinely understand the threats that this influx and generation of hazardous waste materials could cause. Harmful contaminants that escape into the environment have a high tendency of polluting both water and surrounding air, thus causing significant harm to humans, animals, and the ecosystem [43,44]. Hazardous wastes usually contain toxic chemical substances such as mercury, lead, sulfur, arsenic, and cyanide, which are dangerous both to individuals and the ecosystem. Exposures to these elements, for example, can be seen as a result of mining activities in Zamfara and Plateau states in Nigeria [45]. A report shows that over 400 children were affected by lead contaminations in Zamfara state in 2013. Similarly, lead poisoning has led to the death of about 28 children so far in the Rafin Local Government of the Niger state in Nigeria, due to small scale gold mining in the area [46]. Exposures to lead can lead to an increase in blood pressure, sleep disorders, kidney damage, nerve disorders, amongst others [21]. Similarly, Mercury is known to be a neurotoxin in several forms, which could lead to mental deficits in low exposure levels and severe neurologic effects at extreme levels of exposure [47]. A study carried out by [47,48] on the artisanal mining of gold in Zimbabwe and Tanzania reveals that about 1.46 g of Mercury (Hg) is lost to the environment for every gram of gold mined, of which 70-80% of these goes to the atmosphere. Several other studies have shown that women and children are the most vulnerable due to their engagements in gold mining activities in Africa [47]. The mining and sale of gold have been described as all-women activities in Gaoua, Burkina Faso [47,49]. The proportion of these artisanal miners, which comprises women and infants, can range from as low as 5% in South Africa to 50% in Mali (i.e., n = 500 to n > 100,000) [49]. Another study by [50] on 248 patients in Malaysia revealed some high levels of toxicity due to exposures to arsenic-contaminated water [51]. Other manifestations ranged from burning eye sensations, leg swelling, liver fibrosis, chronic lung disease to skin cancer [52].
Furthermore, research has shown that the improper treatment and disposal of medical waste, for example, could expose humans to potentially harmful microorganisms [53]. The World Health Organization (WHO) in a report revealed that, as of the year 2010, unsafe injections accounted for about 33,800 new HIV infections, 1.7 million hepatitis B infections, and 315,000 hepatitis C infections [54,55]. A research study conducted in Egypt showed that the lack of written policies and protocols in the country has led to deficiencies in the processing of hazardous biomedical waste in hospitals and primary health care facilities [56]. Hazardous waste requires a high level of monitoring and management, as humans interact with them every day. An action as simple as burning hazardous waste is reported to release dioxins, which are said to be one of the most toxic chemicals known [57][58][59]. Hazardous waste management is extremely critical for a healthy environment. There are reportedly increased risk of cancer mortality in US counties containing dangerous waste dumpsites [60,61]. This is similar to research conducted in Europe by [62], which shows that there is a raised risk of congenital abnormality in newborn babies whose mothers reside close to sites that handle hazardous waste materials. Figure 6 gives a summary of some hazardous materials and the potential health threats they pose when humans and other living organisms are exposed to them [38].

Management and Control of Hazardous Waste in Africa
The management and control of toxic, hazardous waste should be of the utmost priority to any nation, to foster a healthy living amongst its citizens and, in the long run, enhance environmental sustainability. In most developing countries such as Nigeria, a well-recognized system for the separation, storage, collection, transportation, and disposal of hazardous waste materials has been highly neglected [63]. In Nigeria, quite a few regulations concerning waste management include the Environmental Impact Assessment Act, 1992; the National Environmental Standards and Regulations Enforcement Agency Act, 2007; and the Harmful Waste Act, 1988 [42,64]. The Harmful Waste Act of 1988 in Nigeria outlaws the trade and generation of toxic, lethal, and potentially harmful substances [42,64].
Furthermore, no legislations are guiding the effective handling of e-waste, thus leading to an overall complacency in waste and its management generally [24]. The situation has deteriorated further as a result of governments' complacency towards the trans-boundary movement of electronic waste materials into the nation and the regular sub-standard recycling activities. Governments and administrators in many unindustrialized countries seem to be uninvolved in the material flow and ecological repercussions of e-waste importations into their different nations [24,65]. This has led to the low-level management of e-waste in Nigeria, such as open dumps, backyard recycling, and ocean dumping [24,66]. Inadequate financing and the lack of a unified structure on the subject of the monitoring and control of toxic, hazardous waste have also caused significant weaknesses to the efficient management of these waste materials [24]. This situation has led to slow growth and development in technologies to curb these toxic waste materials.
Nigeria and several other nations in the African continent have been plagued with a low level of awareness when it comes to hazardous waste management. A study carried out by [42] amongst students of tertiary institutions revealed that the majority of people within the Sub-Saharan regions of Africa do not read the labels on purchased products, which gives details on the efficient management of these products. Their study targeted an age group of people between 15-40 years in Nigeria, South Africa, and Kenya. The study revealed that the participants in Nigeria had the highest level of awareness on household hazardous waste materials at a 69% level of consciousness, followed closely by South Africa at 68%, and the least was reported in Kenya, which only had a level of awareness of 36%. In the area of management, 62% of participants in South Africa were able to manage their HHW. In comparison, 48% of participants in Nigeria could do the same, and 32% of the participants from Kenya could achieve their HHW. Figures 7 and 8 give the charts for the level of awareness and management knowledge and ability, as contained in [42].  Furthermore, a comprehensive study was carried out by the United Nations Economic and Social Council on four African countries, namely Ghana, Egypt, Kenya, and the Zambia [67]. The report investigates the management practices of waste materials and hazardous waste materials within those countries. The selected nations cut across the different regions of Africa. The findings from this study are summarized in Table 2.
From Table 2, African countries have been able to develop some legal frameworks for the control of hazardous waste substances, although challenges, especially in the areas of enforcement and overlapping objectives, persist [67]. Furthermore, African nations are signatories to treaties, such as the Basel Convention and the Stockholm Convention on Persistent Organic Pollutants. These treaties give general guidelines on the handling of hazardous waste disposal and the transboundary movement of hazardous waste [71,72]. As a result, African regulations on the processing of hazardous waste are modeled to correspond to international standards. Further down in 1998, the Bamako convention came into force to bridge the gap of the Basel convention within Africa, with about 27 parties [73]. The Bamako convention prohibits the importation of hazardous waste into Africa, prohibits the incineration of hazardous waste materials, and gives provision for the efficient management of hazardous waste within the African continent [73]. This shows that a lot of African countries possess adequate laws and regulations on the handling of hazardous waste, but are limited due to several factors, such as lack of data, financial instability, lack of waste management infrastructure, lower recycling rates, and weak law enforcement [74][75][76][77].
Developed communities have been able to tackle their hazardous waste management issues more efficiently due to the availability of adequate data and infrastructure to manage these waste materials. For example, [78] reports that there are about 155 installations for hazardous waste treatment in about 11 European countries. These hazardous waste management installations have been able to reduce CO2 emissions by about 4 million tons/year, achieve a high degree of material recovery, and are responsible for over 630,000 MWh in energy recovery [78]. Furthermore, seven (7) European countries have been able to close the gap between the hazardous waste generated and treated within their borders. These seven countries are reported to have a gap of less than 20% on hazardous waste generated and treated [79]. Table 3 gives a summary of seven European countries with close to optimal hazardous waste management, as reported by [79]  The highlighted European countries in Table 3 show an impressive gap between hazardous waste generated and that treated within their borders. A country like Germany is still able to handle over 3 million imported hazardous waste materials with an impressive gap of 15% [79]. This is not the case throughout Europe as countries like Luxemburg, Malta, and Ireland have generation to treatment gaps of over 95% [79]. On the European level, the average gap is about 28% (29 million tons), up from 26% in 2012 (26 million tons) [79].
In North America, the United States has developed a highly sophisticated guideline on the management and handling of hazardous waste materials. These laws and guidelines are contained in [80]. Globally, the hazardous waste service industry is seen as a profitable source of revenue for countries. The United States has specifically created the largest market for hazardous waste at over 34%, thus accounting for over $45 billion in revenue [81]. This proves that, if professionally managed, hazardous waste could potentially become a source of revenue for developing nations. Table 4 gives a summary of hazardous waste revenue generated in the United States, as reported by [82].

Revenue of Hazardous Waste Treatment and Disposal
Year From Table 4, the revenue derived from hazardous waste management in the United States was about $9 billion in 2018. This signifies a 182.88% increase in revenue from the year 2000.
In India, hazardous waste management possesses similarities to what is attainable in many African countries. The informal sector is responsible for the management of most of India's waste including hazardous waste, thus leading to inconsistency in India's hazardous waste management data [84]. Although India possesses some stringent rules on hazardous waste management, such as huge fines and imprisonment for negligence, the country still suffers from poor enforcement, lack of data, and inadequate infrastructure [85]. Furthermore, [85] reports a significant shortage in hazardous waste treatment facilities in India. India is said to have about 220 recycling facilities, 88 incinerators for hazardous waste, and two engineered landfills. However, this is not enough, as 70% of India's hazardous waste does not receive any form of treatment [84,85].
Developed society has embraced some hazardous waste management strategies, which could serve as recommendations for the developing community. A study carried out by [86] suggested the following: i.
Establishment of public enlightenment on the potentials of hazardous materials recycling. ii.
Source reduction from the point of generation iii.
Development of human capacity on effective recycling technologies. iv.
Assessment and evaluation of management schemes alongside reporting platforms. v. Improvement of suitable structure, practical awareness, and know-how. vi.
Solidification and restructuring of current regulatory structures. vii.
The endowment of finance for the development of modern infrastructure to curb these hazards viii.
Provincial hazardous waste control systems.
Besides, the gaps identified in hazardous waste management within the continent of Africa can be bridged by following a systematic approach, as suggested in Figure 9. This approach, coined from several studies, would aid in the sustainable management of all sorts of hazardous waste products and solid waste in general [67,87,88]. From Figure 9, African nations need to develop a sophisticated legal framework for the management of hazardous wastes and on the transboundary movement of hazardous waste materials from one country to the other. Strict enforcement methods must be put in place to tackle defaulters and noncompliant industries or institutions regarding hazardous waste management. Secondly, national governments would have to identify relevant stakeholders and properly coordinate their practices. This stakeholder participation would include private sector coordination and other international NGOs.
Additionally, communities must be given public awareness of identifying hazardous waste materials or products and given adequate training on how to handle toxic substances. Lastly, finance or capital must be injected into the management of hazardous waste materials, such as transportation, disposal, recycling, or reuse processes. These will ensure that profits are being recovered from huge hazardous waste management investments. Moreover, African institutions and their global partners must ensure that hazardous waste management schemes are sustainable for the African continent, and not just a direct copy and paste from the worldwide community. This approach can quickly be adopted by any developed or developing nation, with emphasis given to the most significant shortcomings of each country. The situation in country A will be peculiar to that country and will require tweaking these management strategies to suit the nation optimally.

Hazardous Waste Models and Process Flow
Several studies have been done on hazardous waste management, and models have been arrived at. Notably, [88] explains hazardous waste management as a carefully organized system that hazardous waste materials pass through up to their final disposal. Moreover, [87] developed a similar but more sophisticated model. In their study, a hierarchy of waste management was employed with a greater emphasis on source reduction, which would involve processes such as the design of new products, product changes, and source elimination. Furthermore, [40], in a study on hazardous waste management, suggests that it is of the utmost importance to consider how system components interact with one another to attain a dangerous optimum waste management scheme. For example, it would be more efficient to opt for a treatment option which generates less residue, such as incineration, in the case where there are limited landfill capacities [40]. Other methods, such as chemical fixation, might pose fewer threats to the environment when compared to incineration, but have a higher residue generation [40,89]. Furthermore, a mixed-integer programming model was developed by [90] for the location-routing of industrial hazardous waste materials. This model is tasked with the objective of total cost minimization and transportation risk minimization. The model developed by [90] can enable decision-makers to quickly identify waste treatment, recycling, and disposal facilities, thus giving waste routes between these facilities at optimal costs. A similar location-routing model was developed by [91], to identify where best treatment facilities can be situated, where disposal facilities can be sited, and how to find the best facility for a selected type of identified hazardous waste material.
More routing models were developed by [92,93]. Another study carried out by [94] utilizes data such as spatial data, laws, extensive socioeconomic, and environmental data to design a multi-criteria analysis technique. These data, coupled with the capabilities of GIS, aids the system to identify the best disposal sites for hazardous waste materials [94]. There is a similar approach being developed in Iran, as defined in a study carried out by [95]. A model that investigates the general profitability of an entire hazardous waste management system was developed by [96]. This model is a polluter pay system, which tries to locate hazardous waste generation centers and processes the extent to which the polluter would be involved in the waste management processes [96]. For the prediction of healthcare and medical waste generation, an optimized artificial neural network model was developed by [97]. Figure 10 gives a simple process flow for hazardous waste management, that could be utilized by developing African communities.
In summary, the first step will be to identify the source from where the hazardous waste material is being generated. This will involve determining the type of industry and nature (e-waste, radioactive waste, or medical waste) of hazardous waste produced. The municipalities will further rate the source handling of these hazardous waste materials if it meets regulations. This will enable the city to determine the best sanctions it can place on the waste generator.
With source handling meeting regulations, the next step will be to locate appropriate treatment facilities based on the type of waste generated, and then transporting or hauling these wastes to the points of processing. This transportation of hazardous waste materials might involve the transboundary movement of hazardous waste materials, and thus must follow national guidelines. Processing options might require recycling if the waste material can be reused, or landfill operations using engineered landfills or incineration. The model developed by [91] has been utilized in Turkey and it shows great potential for African countries if professionally integrated. The model will help reduce expenses in the overall management of hazardous waste, which will be an optimal solution for Africa. The model finds solutions to problems, such as the best location for treatment facilities, the best technologies to be adopted for the treatment of hazardous waste, where disposal facilities can be located, and routing hazardous waste from the source of generation to disposal, thus effectively reducing the cost while efficiency is increased [91]. The model suitable for African countries must revolve around cost-effectiveness, environmental sustainability, job creation, and community empowerment, based on the peculiarities of each African country. This is shown in Figure 11. Huge hazardous waste investments might not be necessary for Africa, given the present economic situation of the continent. This implies that models must be able to determine the best management outcomes with the poor economic situation of Africa. Figure 11. Critical issues that an African hazardous waste management model must tackle.

Landfill Operations
Landfilling is said to be an easy and cheap method of waste disposal. Landfill, when not managed properly, can deteriorate into open dumps [98,99]. According to [40], landfills may be classified into common, approved, and secured landfills, respectively. Secured landfills that are designed explicitly for waste with hazardous contaminants are further classified into open dumps, control landfills, and closed landfills with control and closed landfills absorbing weakly toxic and highly toxic substances, respectively [40]. The lack of engineered landfills could lead to devastating effects on the environment, because a lot of toxic waste materials will end up finding its way to the environment [100]. According to [101], the major shortcoming of this method in Africa begins with sorting at the point of generation. As a result, hazardous waste materials are easily found in African landfills, which has led to groundwater contamination in some cases [101]. Furthermore, African landfills have significant shortcomings in handling hazardous waste, with ratings from low hazard to hazard being dumped in non-engineered landfills [102]. Table 5 gives a summary of landfills in Africa and their classification, based on the level of compliance with international regulations. Table 5. A review of landfills in Africa and their ranking, based on the level of agreement to international rules [101][102][103].

S/N Level of Landfill Control
Rating Landfills Characteristics  Table 5, most identified landfills in Africa fall within the zero-rating level, which signifies a no level of control or supervision of disposal into these dumps [103]. These landfills can be categorized as open dumps and cannot handle hazardous waste materials. For example, the Lapite landfill in Oyo state Nigeria has no form of leachate collection, cover materials, with studies showing groundwater contamination as a result of toxic substances from unsorted waste. There is also a high presence of Zn and Mn; levels which are unacceptable according to WHO and the Nigerian environmental regulatory body NESREA [101,104]. Similarly, in Port Harcourt Nigeria, the Eneka landfill shows a higher degree of groundwater contamination, due to higher levels of rainfall in the area. It could require quick rehabilitation to protect public health [105].
Furthermore, the semi-controlled landfills in Africa show similar characteristics to landfills, without any level of control. These types of landfills may possess some equipment or unskilled staff force who oversee the daily operation of the landfill [103]. For example, the Solous landfill in Lagos handles over 820,000 tons of municipal solid waste, with occasional compaction and staff put in place [101]. This landfill lacks a leachate collection system, and thus frequent groundwater pollution is recorded [106]. This is similar to the Granville Brooke and Garankuwa landfills in Sierra Leone and South Africa, respectively [101,107].
Medium or controlled landfills in Africa, such as the Olusosun and Dompoase in Lagos Nigeria and Kumasi Ghana, do conform to some international regulations and possess an adequate leachate collection system. Nevertheless, they still fall short in areas of proper monitoring and the control of waste that is being disposed of. If well-coordinated, a controlled landfill could be able to handle some hazardous waste [101,108].
Studies have shown that only South Africa and Botswana can boast of engineered landfills in Africa, as shown in Table 5. These landfills can handle some hazardous waste materials if sorted adequately, due to their efficient liner and leachate collection system with groundwater monitoring facilities. For example, the Robinson deep in South Africa is equipped with a bentonite modified coating that protects groundwater from leachate infiltration. The Bellville south and Coastal Park in South Africa both possess groundwater monitoring systems [109,110].
Governments and investors should pay more attention to developing engineered landfills and state of the Art facilities for waste management, with the high consideration of hazardous waste management. This will help protect public health among its citizens.

Recycling
Another management technique is the recycling of hazardous waste materials. Most waste has become regarded as having typical value and could be recovered and reused for valuable goods [28]. This involves the reprocessing of hazardous waste materials as raw materials for technical procedures or a substitute for a marketable product, which in turn is economically optimal and advantageous to public health [87]. Recycling could have potential positives to a nation's economy. For example, studies have shown that recycling 10 kg of aluminum not only provides a 90% energy saving, but also averts the formation of 13 kg of bauxite residue, 20 kg of CO2 gas, and 0.11 kg of SO2 gas [38,111]. Likewise, recycling iron and steel offers 74% of energy saving, a 86% decrease in air pollution, 40% decrease in water use, 76% in decline in water contamination, 97% decrease in mining wastes, and a 90% saving in virgin materials use [38,112]. Notably, [111] reports that, for every 10,000 tons of materials disposed of annually, computer reuse creates 296 more jobs.
Resources obtained from the United Nations Statistics Division show some data on hazardous waste materials that have been landfilled, recycled, and incinerated. These statistics, as depicted in Table 6, represent data collected from national statistical offices and ministries of the environment of the choice nations.

Conclusion and Recommendation
The management of hazardous waste materials is highly crucial to the sustenance of an environment and preservation of sound health practices amongst humans. Developed and developing countries have a significant role to play in hazardous waste management. These roles will range from sound regulatory practices by government institutions to technological advancements in the areas of recycling and reuse, energy recovery, and much more. Responsibilities could be placed on the producers of hazardous waste such as paints and toxic chemicals, on the post monitoring of their products after it leaves their shelves. Similarly, a national recall program can be put in place to recall all unused drugs, electronic wastes, and many other expired products to foster proper management [86]. Furthermore, an emphasis should be placed on data collection and storage on the present nature of waste in African countries, as African countries suffer from data needs.
The involvement of all stakeholders, such as producers, managers, decision-makers, waste processors, and the formal and informal sectors at large, will go a long way in the development of a suitable and sustainable waste management plan. Table 7 gives a summary of the challenges faced by most African Nations in hazardous waste management and a possible way forward for decision-makers. Hazardous waste management, although challenging in Africa, can be tackled with effective measures considering the peculiar nature of each African country, and not just a copy and paste approach. Wealth creation must be at the center of the African hazardous waste management industry, to maximize economic benefits. Funding: This research received no external funding.

Acknowledgments:
The authors appreciate the management of Covenant University for providing an enabling environment for carrying out this research work. We also appreciate the various authors of resource materials that were used, which provided relevant information that led to the success of this work.

Conflicts of Interest:
The authors declare no conflict of interest.