Pollution of heavy metal threat posed by e-waste burning and its assessment of human health risk

Improper treatment during recycling of e-waste materials by means of open burning is on the rise which has led to an increase in air pollution. This study looked at heavy metal concentrations, concentrations in relation to threshold values, and assessments of risk for noncarcinogenic and cancer risk threat. The Microwave Plasma-Atomic Emission Spectrometry (MP-AES 4210) series instrument of Agilent Technology, United States of America (USA), was used in analyzing heavy metal (Cd, Cu, and Pb) concentrations. The result of the analysis of the Kuka Bulukiya treatment point revealed that Pb has the highest mean concentration of 0.0693 ppm, Cu 0.0525 parts per million (PPM), and Cd 0.0042 ppm. The mean concentration at PRP Gidan Ruwa for Cd was found to be 0.0059 ppm, Cu 0.0363 ppm, and Pb 0.049 ppm. The result of the adult and children population calculated shows that the hazard quotient (HQ) and hazard index (HI) values are not up to 1 in all the pathways (inhalation, ingestion, and dermal) at both treatment points (1.2 ˟ 10−4 and 9.8 ˟ 10−5) and (6.4 ˟ 10−4 and 5.9 ˟ 10−4), respectively. The cancer risk for Kuka Bulukiya 6 ˟ 10−10 and PRP G/Ruwa 5 ˟ 10−10 for adults and 7 ˟ 10−10 and 4 ˟ 10−10 for children were both lower than the threshold set for cancer risk by the United States Environmental Protection Agency (USEPA). This meant that both adults and children were not at risk of cancer and noncarcinogenic threat based on the assessment in this study. The study concluded that informal e-waste burning has substantially helped in the relatively high levels of air pollution identified in the treatment points and in turn posed environmental and public health concerns to people around the area. This study recommends that samples of the vegetable products at the PRP G/Ruwa treatment point should be investigated immediately and adequate restrictions and regulations should be enacted and enforced in order to safeguard the environment and the populace. There is need for caution from the authorities to avert the possible implications (e-waste extractors and the public) of being affected with noncarcinogenic or carcinogenic ailments over time.


Introduction
Electrical electronic equipment (EEE) that has reached the unwanted stage known to be e-waste is about the fastest rising waste stream globally (Tsydenova and Bengtsson 2011;Ikhlayel 2018). E-waste is considered a hazardous substance because of its composition of heavy metals, flame retardants, and other substances (Tsydenova and Bengtsson 2011). Studies have identified sites where e-waste is recycled and its surrounding to be the key source of numerous escaped pollutants (Chen et al. 2018;Shen et al. 2019), and the concentration of related pollutants is more in urban areas (Huang et al. 2013). However, in spite of the potential toxicity of pollutants that is becoming obvious, data on their environmental happening and exposure to human still remains mainly unfamiliar (Li et al. 2020).
As of now, informal recycling centers have dominated the e-waste industry and treated 90% to 95% of generated e-waste in an unfriendly manner in developing countries (Vats and Singh 2014). However, informal sectors do not follow the set guidelines by authorities but use the crude method of disposal such as open burning in order to recover valuable resources such as gold, silver, palladium, iron, and plastics and release toxic metals such as lead, arsenic, cadmium, chromium, and mercury at the treatment sites (Vats and Singh 2014) causing undue public and environmental health concerns. E-waste burning in an open place releases dioxins and polycyclic aromatic compounds which is grossly more toxic than burning of domestic waste (Dave et al. 2016). However, only 78 countries are covered globally by e-waste policy, legislation, or regulation (Forti et al. 2020); this is part of the challenges faced in terms of its generation, collection, and disposal.
Public and environmental health is a thing of concern due to the fast growth of e-waste materials and the intricate composition and unsafe nature of metals contained in them (Dave et al. 2016). As of 2019, about 53.6 million metric tons of e-waste was generated and it was estimated to go beyond 74 Mt by 2030 (Forti et al. 2020). This implies that e-waste is increasing at a disturbing rate and the potential danger posed is quite enormous. It is an alarming threat to the extractors that dismantle the e-waste to get valuable metals (Dave et al. 2016) and the people living closer to the dismantling, recycling, and treatment points. The workers and people around e-waste recycling areas are uninformed of the harmful nature of the materials and the action of the extractors as they are not using protective equipment (Li et al. 2008).
Lead and cadmium in glass panels, gaskets, circuit boards, chip resistors, and semi-conductors result in damage in the kidney and adverse effects on children's brain development, and copper in copper wires and PCBs results in nausea, liver damage, Wilson's disease, or stomach cramps (Monika and Jugal Kishore, 2010;Padiyar 2011). However, dismantling with bare hands and separation of components of e-waste cannot be unconnected with skin and other respiratory diseases. It was asserted that the major route of e-waste contaminants is through air by means of inhalation, ingestion, and dermal absorption (Priyadarshini 2011). However, addressing the pressing threat e-waste posed to the extractors and the people living around the treatment points prompted us to undertake this study. This will add to the pool of knowledge of the enormous hazardous nature of burning of e-waste in an open place and its respective public health concerns.
It is asserted that burning of e-waste in an open place releases various metal(loids) into the environment which has a call for concern globally (Cao et al. 2020). For extraction of valuable resources, e-waste materials are burned at the two treatment points identified in the study area (Kuka Bulukiya and PRP G/Ruwa). In other words, the study of Gangwar et al. (2019) has indicated that the recycling of e-waste presented a tremendous threat to the populace and the environment. Luo et al. (2011) has highlighted that the metal concentration at soils of e-waste burning sites is highest in relation to the surrounding areas in China. However, these studies and others prompt the need to explore the potential health risk the extractors and the public around the treatment points in this study are exposed to.
This method of calculating the threat associated with taking in air from burning of e-waste materials was recommended by USEPA. The idea behind it all is to see the potential risk the extractors and the public around the treatment points are exposed to. So, this method best suits that idea. It is better than other methods in the sense that it best suits the aim of the study. Other methods used aimed at determining whether the people around the treatment area have developed noncarcinogenic ailments or carcinogenic risks due to having taken in contaminated air from e-waste activities by taking blood or urine samples of the extractors or the residents around the treatment points. This requires studying the people under study over a long period of time to make sure other factors or substances did not play a role in determining the outcome of the study, and this is not the interest of this study as it adopts the method used in this study. This is a novel research in the study area as nothing on e-waste activities has been investigated or determined. What is interesting is the ability of undertaking the research and identifying the treatment points. It has been established by the results that the concentration of heavy metals at the treatment points is way higher than the samples away (control) from the points. It has also been asserted that the results of some of the samples were higher than the results in other studies and in set threshold values by authorities. Another interesting thing is that the results of samples from Kuka Bulukiya are higher than the results from PRP G/Ruwa due to the frequency of activities at Kuka Bulukiya, and this corroborates the actual situation on the ground. Notwithstanding, the concentration and other factors (physiological and anatomical conditions of adults and children) combined used in the calculation revealed that there is no noncarcinogenic and carcinogenic threat posed by their activities as of now. This implies that the public around the treatment points and the extractors is safe for now which is very much interesting. But the results also revealed the need for caution in their activities in order to safeguard the environment and the populace.
This study aims at identifying e-waste activities and the treatment points where the contamination of the surrounding environment especially air is taking place. The study revealed that there is hazard identification in the study area or any area globally with similar activities. Exposure assessment and toxicity (dose response) assessment were revealed based on the concentration. A risk characterization of the assessments was undertaken, and this helped reveal the potential danger of being infected with noncarcinogenic or carcinogenic ailments. What this has added to the pool of literature is that depending on the concentration of the contaminants and other factors, it cannot be vividly said one is going to be infected with certain ailments (carcinogenic and noncarcinogenic) without subjecting a phenomenon to some measurements or test.
Notwithstanding, this study looked at heavy metal concentrations in the air at the treatment points in order to identify the hazards. The concentrations were measured in relation to the set threshold by the National Environmental Standards and Regulations Enforcement Agency (NES-REA), United States Environmental Protection Agency (USEPA), and National Ambient Air Quality Standards (NAAQS). An assessment of risk for noncarcinogenic and carcinogenic threat through pathways such as inhalation, ingestion, and dermal contact was undertaken in this study (at the two treatment points identified). This highlighted the danger of unsound e-waste burning practices and its toxicity in cities of developing countries.

Review of related studies
Depending on the type of electrical and electronic equipment, there is a wide range of precious metals and other base metals contained in those devices (Ghosh et al. 2015;Cucchiella et al. 2015). On the other aspect of the components, there are toxic substances contained in electrical and electronic devices which are harmful to the environment and humans as well. Improper disposal or unsound management of e-waste leads to undesirable contamination of the environment and severe health-related challenges (Cesaro et al. 2019). In a real sense, waste electrical and electronic equipment (WEEE) need to be collected, sorted, extracted, treated, transported, and disposed properly with environmental and human safety as the main goal.
However, the informal WEEE recycling points are usually done in unsound and crude conditions at the backyard of urban environments or at informal collection points with the central goal of extracting precious metals such as gold and silver (Ceballos and Dong 2016) especially in developing countries. The e-waste is usually dismantled and separated manually to acquire its valuable components, and sometimes WEEE are subjected to treatments before extracting the valuable components. Usually, these treatments are mostly acid treatment and open burning (Cesaro et al. 2019). Since sound environmental conditions are not followed, there is a likelihood of severe potential health risks to the extractors and the public living around the treatment points. Nevertheless, recent studies (Table 1) have revealed the contamination of air, water, and soil from e-waste-related activities (Tue et al. 2016); various concentrations of heavy metals and other toxic substances have been detected within the informal treatment points and the surrounding area (Awasthi et al. 2016). This scenario has posed risks to human health, that is, to both those that engaged in e-waste activities and those residing in vicinities close to the treatment point, due to the mixture of e-waste toxic substances and other environmental contaminants leading to more severe health and environmental hazards (Bakhiyi et al. 2018).

Treatment of WEEE through open burning
The open burning of e-waste to recover copper from cable wires and other component from different devices is apparent (Cesaro et al. 2019). This is often done on bare surfaces and at relatively low temperatures, and this is identified as the most reported crude method of recycling e-waste (Perkins et al. 2014). Open burning of e-waste has a direct implication on the environment by releasing toxic substances into the atmosphere, contaminating the soil on which it was burnt, and polluting the nearby water bodies through runoff (Alcantara-Concepcion et al. 2016). This implies that the effects on human health come either directly during processing and treatment or indirectly through taking contaminated water or through the food chain. Imran et al. (2017) have revealed that air is the most significant medium of transportation of contaminants during open burning and have asserted that both the workers and people around the area have trouble breathing. Such situations have exposed the environmental concerns there in considering the number of the workers were exposed to during the burning activity. The study also found that increased amounts of burnt e-waste significantly influenced the concentrations of coarse and fine particles emitted Cao et al. (2020) Bioaccessibility and human health risk assessment of metal(loid)s in soil from an e-waste open burning site in Agbogbloshie, Accra, Ghana In human health risk assessments (HHRAs), oral ingestion of soil can be a major route of exposure to many immobile soil contaminants. The hazard index was above the threshold value (> 1) for 5/10 samples, Potential environmental health consequences of these toxic metals and organic compounds are described Liu et al. (2021) Heavy metals in soil-vegetable system around e-waste site and the health risk assessment Results indicated that both adults and children were suffering potential health risks Mowla et al. (2019) Health risk assessment of heavy metals in e-waste recycling shops in Dhaka, Bangladesh The amount of hazardous material in the dust samples surrounding these areas was determined and the potential health risk was found using some empirical co-relations Ngo et al. (2020) Environmental health risk assessment of heavy metal exposure among children living in an informal e-waste processing village in Vietnam The findings revealed that levels of the total average daily intake (ADI) of the five heavy metals collected from a child at the exposed village were 3.90 times higher than that of a child at the reference village. The total noncarcinogenic risk and carcinogenic risk in an exposed child were 1.63-and 4.70-fold higher than their respective risks in a reference child Oguri et al. (2017) Exposure assessment of heavy metals in an e-waste processing area in northern Vietnam Garden soil and floor dust were estimated to be mainly contributors to daily Pb intake, as indicated by calculations using bioaccessible metal concentrations and the U.S. Environmental Protection Agency soil plus dust ingestion rate Singh et al. (2018) Health risk assessment of the workers exposed to the heavy metals in e-waste recycling sites of Chandigarh and Ludhiana, Punjab, India High concentration of Ba, Cu, Pb 13 and Zn was observed in the soil and dust samples. Cr, Pb, and Zn were observed in high 14 concentrations in dermal samples Zhang et al. (2019) Heavy metals in human urine, foods and drinking water from an e-waste dismantling area: identification of exposure sources and metal-induced health risk Risk assessment predicted that dust ingestion of Cd, Pb, Cu, and Zn via food consumption poses health risks to local residents of e-waste dismantling areas (EDAs), and the urinary concentrations of analyzed metals were significantly (Pearson correlation coefficient: r = 0.324-0.710; p < 0.01) associated with elevated 8-OHdG, a biomarker of oxidative stress in humans hours spent at the treatment or recycling points and how frequent one visits. Table 1 shows the review of related studies.

Location
The treatment points are found within Kano metropolis on latitude 12.00782 and longitude 8.50407 (Dala Kuka Bulukiya) and latitude 12.0388697 and longitude 8.5409142 (PRP G/Ruwa, Brigade) respectively in the Sudan Savanna region of Nigeria. It is about the most evident e-waste treatment points in the region where e-waste open burning takes place in order to get the valuable resources in them. There is a large population of people surrounding the treatment points as it is found within the vicinity of cities in developing countries.

Climate
The study area is known for its four distinct seasons: the dry and cool season known as Kaka (Winter period), the dry and hot season known as Bazara (Spring period), the wet and warm season referred to as Damuna (Summer period), and the dry and warm season known as Rani (Fall or Autumn period).

Nature and sources of data
Quantitative data type was from the laboratory analysis conducted. The air data was collected at the treatment points where open burning of e-waste is usually done.

Air sample collection
Two treatment points were chosen, and they were identified as the hotspots in Kano metropolis. The air was captured at 3 different times (December, 28, 2020, January 11 and 18, 2021) at different intervals (0 m, 5 m, and 10 m) in the treatment points (each of the site) during the day. 9 samples were collected (for each treatment points) and homogenized into 3, that is, 3 times for each interval. The Scientific Kit Corporation (SKC) air sampling sidekick pump with a flow range of 5-3000 ml/min developed by SKC Limited, United Kingdom, was used to collect the heavy metals in the particulate matter from the treatment points on the filter paper inserted (Kim et al. 2010). The Gelman Sciences (Ann Arbor, Michigan, USA) filter was inserted on the pump, and the air was collected in order to capture the heavy metals. The filters were stored in desiccators until the mass became constant and weighed in a 0.1-mg unit scale; they were dried, weighed, and kept in the desiccators for analytical purposes. The control was collected about 100 m away from the treatment points.

Air preparation and analysis
In the analysis of the captured metals, the filter was pretreated with a hot plate. The USEPA method of digestion was adopted (USEPA 2016a lab manual revised). The filters were put in a conical flask to which 5 ml of 98% stock solution of nitric acid and 5 ml deionized water were added. Thereafter, the opening was closed; the samples were decomposed with the hot plate digestion system. However, in the decomposition process the temperature was at 170 °C for 15 min during the first step. Hydrogen peroxide 75% solution was added to neutralize the acid; 100 ml of deionized water was used to dilute the solution and was put back onto the hot plate until the yellow fumes stop for the second step. In the third step, the solution was taken down and allowed to cool to room temperature for about 120 min. The Microwave Plasma-Atomic Emission Spectrometer (MP-AES 4210 series) instrument of Agilent Technology, USA, was used for the concentration of heavy metal (Cd, Cu, and Pb) analysis.

Exposure assessment
The study assessed the health risk threat to certain heavy metals like Cd, Cu, and Pb in e-waste treatment points through burning which might lead to noncarcinogenic and carcinogenic ailments. The exposure assessment calculated the average daily intake (ADI) and the lifetime average daily dose (LADD) of metals identified all the way through inhalation, ingestion, and dermal pathways by adults and children in the two treatment points. The noncarcinogenic threshold that is RfD (reference dose) and the CSF (cancer slope factor) (which is a potential carcinogen factor) are two substantial toxicity indexes used in this study. The equations used in this study were recommended by USEPA (1989).

Inhalation of heavy metals
ADI inh is the average daily intake of heavy metals inhaled, which is the quantity of contaminants (mg/kg day), and for evaluating carcinogenic impurities, it is referred to as lifetime average daily dose, LADD, while for noncarcinogenic contaminants it is known as average daily dose, ADD or ADI; C is the concentration in the media of interest (mg kg -1 ); IR air is the rate of inhalation (m 3 day -1 ); EF is the frequency of exposure (days year -1 ); ED is the duration of exposure (years); BW is the weight of the body (kg); PEF is the particulate emission factor in cubic meters per kilogram; ET is the time of exposure in hours per day; AT is the average time equals 25,550 days based on a life time of 70 years for cancer risk; and for noncarcinogens, averaging equals ED (years) multiplied by 365 days per year.

Ingestion of heavy metals
ADI ing is the average of daily intake of the heavy metals ingested, which is the amount of contaminants (mg/kg day); C is the concentration in the media of concern (mg kg -1 ); IR is the ingestion in milligrams per day; EF is the frequency of exposure (days year -1 ); duration of exposure is ED (years); BW is the weight of the body (kg); AT is the average time period in days; and CF is the factor of conversion in kilograms per milligram.

Dermal contact
ADI derm is the dermal contact exposure (mg/kg day); C is the concentration in the media of concern (mg kg -1 ); AF is the soil adherence factor in milligrams per square centimeter; SA is the exposed skin area in square centimeters; ABS is the fraction of the applied dose absorbed on the skin; and BW, ED, AT, EF, and CF are as defined in Eq. (2).

Noncarcinogenic risk assessment
Noncarcinogenic threats are known as hazard quotient (HQ). This is expressed as a unitless value that shows the possibility of someone developing an adverse health effect. This is defined as the quotient of ADI divided by the toxicity threshold value (RfD), which is the persistent reference dose in milligrams per kilogram per day of a specified heavy metal.
For n number of heavy metals, the noncarcinogenic effect of the population is the summation of HQs due to different metals known as hazard index (HI). (2) In a situation where the HI value is not up to 1, the exposed population is not likely to experience the occurrence of adverse health effects. Meanwhile, if the HI value is more than 1, there might be issue regarding noncarcinogenic effects. The HQ which is the summation of average daily index by the reference dose is the independent variables while HI depends on their outcome.

Cancer risk assessment
The cancer risk is estimated as the possibility of a person developing a cancer over a lifetime exposure to potential contaminants.
The Risk is a unitless value. ADI in (mg/kg day) and CSF in (mg/kg day) −1 are the average daily intake and the cancer slope factor of n heavy metals, respectively. The average daily index and the cancer slope factor are the independent variables while the cancer risk depends on their outcome.
The total lifetime cancer risk was calculated from the input of different heavy metals in all the pathways as follows: where Risk inh , Risk ing , and Risk derm are the risk contributors in inhalation, ingestion, and dermal pathways.

Results and discussion
The results revealed the rationale behind this study which is to ascertain the pollution level of e-waste activities (burning of e-waste at treatment points) posed to the extractors and the people around the treatment points. It reveals the concentration of heavy metals (Cd, Cu, and Pb) therein, the concentration in relation to set threshold, and the assessment of human health risks (carcinogenic and noncarcinogenic) people are exposed to.
The e-waste burning engaged by the extractors is solely for economic gain as valuable resources are extracted from the burnt materials which cater for the livelihoods of the extractors and their family. The government also gains from this activity by collecting tax and revenue from the extractors and agents that are engaged in e-waste activities. Notwithstanding, their activities pollute the environment and posed a threat to the well-being of the extractors and the public residing around the treatment points. This is a thing of concern and has prompted us to undertake this study in order to safeguard the environment and the populace.

Heavy metal concentration at e-waste burning sites
The heavy metal concentrations were revealed, and risk assessments for noncarcinogenic and carcinogenic ailments were analyzed.
The heavy metal concentration (Cd, Cu, and Pb) is shown in Table 2 in the various samples analyzed at the two treatment points (Kuka Bulukiya and PRP G/Ruwa). The results of the analysis at the Kuka Bulukiya treatment point revealed that Pb has the highest mean concentration of 0.0693 ppm, followed by Cu 0.0525 ppm and Cd 0.0042 ppm. However, the control concentration of heavy metal was relatively lower than the concentration of the samples at the treatment points. Cd was found to be 0.0015 ppm, Cu 0.0037 ppm, and Pb 0.0052 ppm; this might not be unconnected with pollution from other sources within the urban environment. This implies that there are heavy metal pollution activities taking place at the treatment points, which is a thing of concern for the extractors, public, and environmental health. The concentrations at PRP G/Ruwa were found to be similar to the ones at Kuka Bulukiya, but the mean concentration of Cd which was found to be 0.0059 ppm is slightly (significantly) more than the concentration at Kuka Bulukiya. However, the mean concentration of Cu which was 0.0363 ppm and Pb which was 0.049 ppm is slightly lower than the concentrations at Kuka Bulukiya, as seen in Table 2. The Cu concentration for control at PRP G/Ruwa was found to be 0.0027 ppm which was slightly lower, and for Pb it was 0.0097 ppm which was higher than the control concentration at Kuka Bulukiya. However, the Cd concentration at PRP G/ Ruwa was not detected (ND); this implies that the concentration might be negligible and below the detection limit of the equipment. The result of the analysis (Table 2) in the two treatment points (K/Bulukiya and PRP G/Ruwa) is higher than the concentrations of Cu 2.468 µg/m 3 (0.00247 ppm) and Cd 0.008 µg/m 3 (0.000008 ppm) in the study of Kim et al. (2010) on the characteristics of atmospheric heavy metals in a subway station in Seoul. This implies the contributions of e-waste burning materials in the results of the analysis obtained. However, the study of Adaramodu et al. (2012) on the concentration of metals of surface dust in e-waste components of the Westminster electronic market, Lagos for Pb (outdoor dust) 15.90 mg/kg and Cd (outdoor dust) 1.80 mg/kg, is way higher than the result in this analysis (Table 2). Other similar studies on exposure to the heavy metals of e-waste workshops and recycling point are those by Xu et al. (2015) and Wu et al. (2016).

Heavy metal concentration in relation to set threshold and its implications
However, the result of the analysis in relation to NESREA standards for point source maximum emission limit for facilities and process, and for ambient air quality standards is shown in Table 3. The analysis discovered that the concentrations of Cd, Cu, and Pb at the two treatment points (Kuka Bulukiya and PRP G/Ruwa) are lower than the NES-REA (2014) set threshold for the point source maximum emission limit for facilities and process from any source (Table 3). More so, the ambient air quality standards set by NESREA (2013) for concentrations of Cd (0.38 ppm) and Pb (3759 ppm) are higher than the concentrations of Pb (0.063 ppm and 0.049 ppm) and Cd (0.0042 ppm and 0.0059 ppm) at both the Kuka Bulukiya and PRP G/Ruwa treatment points, respectively. The USEPA (2016b) National Ambient Air Quality Standards (NAAQS) for lead stipulated the primary and secondary standards to be 0.15 µg/m 3 for 3 months in average which is lower than the concentration obtained in this study for the two treatment points. The European Commission (2000) assigned 0.2 to 2.5 ng/m 3 for This study Kamunda et al. (2016) ambient air pollution by cadmium at the urban background which is lesser than the mean concentration for the two treatment points in this study. Of importance is the consideration for the extractors/collectors, public, and environmental health that need to be checked (Plate 1). There is tendency of accumulation of these heavy metals over time which might result in a myriad of health and environmental problems. Of concern is that there are lots of buildings (houses and schools) surrounding the treatment points at K/Bulukiya, a football field where football is played by both children and adults; children who come to the pond to catch fish and swim and inhale the burnt e-waste are at risk or might potentially face several health challenges (Plate 1). There is the Kuka Bulukiya Primary School and Government Junior Secondary School (GJSS) (Plate 1) nearby that house children (which are vulnerable) during school hours while these burning (e-waste) activities takes place.
Of interest is that at the PRP G/Ruwa treatment point during the burning of e-waste materials, air or smoke settles or moves over the nearby vegetable farmland which might lead to bioaccumulation of these metals (Cd, Cu, and Pb) on the farm produce with the potential of causing unforeseen danger to the consumers and nearby houses. Liu et al. (2021) indicated that the results of a study conducted on heavy metals in the soil/vegetable system close to e-waste sites in China showed that both adults and children were suffering from health risks. It further narrated that the consumption of lettuce and sweet potato caused the most health risk and also revealed that cowpea and cabbage were moderately safe. Another study by Yin et al. (2021) revealed that there is a reasonable pollution of PBDEs and heavy metals there in the vegetables in a regulated e-waste recycling site in Eastern China.
Another public health implication of burning of e-waste materials in open places is that the extractors/collectors and people living around the area do not use any form of protection (face and hand gloves) for safety during burning, and this poses a health-related menace to the extractors, environment, and the public.
However, it is worth noting that children residing close to the PRP G/Ruwa treatment point especially come to the treatment point to sell sachet water and in the process inhale and ingest the contaminants there in the burning activities, and another activity worth noting is that there are wood cutters just about 1.5 m to the treatment point by which this open burning will be a threat to their well-being.
The major implication of these heavy metals is that they are toxic at low levels of exposure. In addition, both acute and chronic exposures are a threat to humans and the environment, that is, a single exposure to harmful substances Plate 1 Collection of air samples at the K/Bulukiya treatment point and those that occur over a long period of time and that its health effects are cumulative. Similarly, they tend to build up in crucial organs like the kidney, brain, liver, and bones, for a number of years leading to serious health problems once they are absorbed by the body (Kamunda et al. 2016). The effect of over time accumulation of inhaled cadmium is adverse kidney, bone, and liver damage and cancer, and that for lead is delays in neurological development, physical development and damage, damage of renal function, hearing loss, anemia, and blood pressure (World Health Organization 2007). Furthermore, Pb disturbs the functioning of kidneys and the reproductive and nervous systems and induces renal tumor. Severe exposure to Cd has its effect such as emphysema, alveolitis, and bronchiolitis (Pendias 2011). Cd may also lead to kidney malfunction, hypertension, bone fracture, and cancer (Khan et al. 2013). Anemia, cardiovascular diseases, reduced fertility, arthritis, cirrhosis, and strokes are seen as some of its effect in a long run (Kamunda et al. 2016). Excessive exposure to Cu may lead to noncarcinogenic effects on human health; meanwhile, they are crucial to human life, and its surplus has been linked with liver damage (Cao et al. 2010).

Health risk exposure assessment
The health risk exposure assessment in this study comprises both noncarcinogenic and carcinogenic assessments of health risks in the burning of e-waste materials at the K/ Bulukiya and PRP G/Ruwa treatment points. Exposure of the extractors and the people living around the treatment points who likely inhaled and ingested and had dermal contact with the contaminated air is considered in this assessment. This assessment predicts the possible noncancerous and cancerous health risks exposed by adult and children at both treatment points by integrating data generated (Tables 4 and 5) to arrive at the estimates of hazard indices and cancer risk through different pathways (inhalation, ingestion, and dermal contact) of identified heavy metals (Cd, Cu, and Pb) therein.

Noncarcinogenic risk of heavy metals
Based on the RfD values (Table 5) and ADI values (Table 6), the noncarcinogenic risks for adults and children were calculated. The results for the pathways (inhalation, ingestion, and dermal) were all expressed in terms of hazard quotient (HQs) and its summation expressed in terms of hazard indices (HI) in Table 6. The HQs and HI gave the prediction of the potential noncarcinogenic health risk exposed by the populace. The standard is that when HQ and HI values are not up to 1, it means there is no clear potential risk of noncarcinogenic effects to the population, though if these values surpass 1, there may be concerns (USEPA 2004). The result of the adult population calculated shows that the HQ (Figs. 1, 2, 3, and 4) and HI values are less than 1 in all the pathways Table 4 Heavy metal concentration at e-waste treatment points (burning) ND not detected    (Table 6). Figures 1 and 2 show the hazard quotient for Kuka Bulukiya for adult and children for all the pathways (inhalation, ingestion, and dermal) and for the contaminants under study (Cd, Pb, and Cu). The standard for the values used in the conversion of the figures was 1 ˟ 10 −6 .
This meant that the populations are not at risk of noncarcinogenic effects. However, dermal and ingestion contributed more followed by inhalation in that order at both treatment points. In essence, the result for the children revealed that the HQ and HI are less than 1, for all the pathways at both treatment points at Kuka Bulukiya 6.4 ˟ 10 −4 and PRP G/Ruwa 5.9 ˟ 10 −4 (Table 6). This meant child populations are not at risk of noncarcinogenic health effects based on the calculation of health risk assessment due to the concentration of the heavy metals in this study. Figures 3 and 4 show the hazard quotient for PRP G/ Ruwa for adult and children for all the pathways (inhalation, ingestion, and dermal) and for the contaminants under study (Cd, Pb, and Cu). The standard for the values used in the conversion of the figures was 1 ˟ 10 −6 .

Cancer risk assessment of heavy metals
Based on the carcinogenic risk assessment values calculated, the lifetime average daily dose (LADD) values in Table 7 and cancer slope factor (CSF) in Table 4 revealed the health risk threat faced by the extractors and the public. The lifetime risk assessment for adults and children contributed by different heavy metals for all the pathways is shown in Table 7.
The carcinogenic risk was calculated for Cd, Cu, and Pb where Pb was found to be the major contributor in this assessment (Figs. 5,6,7,and 8  considers 1 ˟ 10 −6 to 1 ˟ 10 −4 to be the range of the standard for cancer risk purposes. The cancer risk for Kuka Bulukiya 6 ˟ 10 −10 and PRP G/Ruwa 5 ˟ 10 −10 for adults and 7 ˟ 10 −10 and 4 ˟ 10 −10 for children (Table 7) were both lower than the threshold set for cancer risk. Figures 5 and 6 show the cancer risk potential for Kuka Bulukiya for adult and children for all the pathways (inhalation, ingestion, and dermal) and for the contaminants under study (Cd, Pb, and Cu). The standard for the values used in the conversion of the figures was 1 ˟ 10 −9 . This meant that both adults and children are not at risk of cancer based on the assessment in this study at the treatment points. The ingestion contributed more to cancer risk assessment followed by inhalation pathways. However, due to the nonavailability of the cancer slope factor (CSF) for the dermal pathway, it was not part of the assessment, though there is need for caution since there is hazard identification at the treatment points and authorities should act accordingly. Figures 7 and 8 show the cancer risk for PRP G/Ruwa for adult and children for all the pathways (inhalation, ingestion, and dermal) and for the contaminants under study (Cd, Pb, and Cu). The standard for the values used in the conversion of the figures was 1 ˟ 10 −9 .
Lead toxicity is apparent as it contributes more in the results revealed followed by cadmium, and copper contributed the least in the calculation at both the Kuka Bulukiya and PRP G/Ruwa treatment points.

Climate change adaptation
According to the Intergovernmental Panel of Climate Change (2022), "adaptation refers to adjustments in ecological, social, or economic systems in response to actual or expected climatic stimuli and their effects or impacts. It refers to changes in processes, practices, and structures to moderate potential damages or to benefit from opportunities associated with climate change." Adaptation to climate change is given increasing international attention as the confidence in climate change projections is getting higher     (Mertz et al. 2009). This study has highlighted the threat posed by burning of e-waste materials, and this contributes to climate change due to the chemicals released. This implies that the released chemicals (heavy metals, polybrominated biphenyls, and toxins) accumulate in the air and pose severe health implications to the environment, crop/plant, humans, and animals. E-waste being a contemporary area of study has limited studies on its activity's adaptation to climate change. Climate change adaptation has to do with an environmentally friendly method of extracting valuable materials that should be at the forefront of policies that will be specifically enacted on e-waste management in developing countries. For example, Fahad and Jing (2018) and Fahad and Wang (2018) suggest that awareness on the impacts of climate change and disseminating of research findings related to climate change in various communities is of paramount importance in adapting to climate change impacts, whereas according to Ozturk et al. (2019), preventing corruption improves climate change adaptation. Taking back systems and encouraging environmentally sound recycling and refurbishing alternatives will help in climate adaptation. Regulations should be in place to promote sustainable e-waste dismantling and extraction (by discouraging or stopping open burning of e-waste) facilities and on how to capture the contaminants released into the air. Tree planting should be encouraged, and a formal e-waste treatment points should be identified and allow only environmentally friendly activities to take place, and a penalty should be set aside for policy and regulation averters.

Conclusion and recommendation
The results of this study and the discussion herein have highlighted the hazard caught up in open e-waste material burning and their environmental implications and public health concerns, though the concentration was found to be below the set threshold by NESREA. The analysis at the Kuka Bulukiya treatment point revealed that Pb has the highest mean concentration of 0.0693 ppm, followed by Cu with 0.0525 ppm and Cd with 0.0042 ppm. Although the concentrations of heavy metals at the control points were lower than those at the treatment points, the concentrations of heavy metals at the treatment points remained relatively high. Herein, the carcinogenic risk was calculated for Cd, Cu, and Pb where Pb was found to be the major contributor in this assessment. There is need for caution and regulations in informal open e-waste material burning. The health risk assessment calculated has revealed for now that there are no noncarcinogenic and carcinogenic concerns with respect to the extractors and people living around the treatment points for both adults and children. The study concluded that informal burning of e-waste has substantially led to the relatively high levels of air pollution identified in the treatment points and in turn posed environmental and public health threats to the extractors and residents around the study area. Climate change adaptation has to do with an environmentally friendly method of dismantling, extracting, refurbishing, and recycling of valuable materials that should be at the forefront of policies that will be specifically enacted on e-waste management in developing countries. If not, the adverse effects on the environment, humans (damage to the reproductive and nervous systems, kidney, liver, and heart and also birth defects and diseases), and animals will be enormous. Therefore, this study recommends that the government should identify a suitable location for e-waste collection and treatment points to avert the danger posed to the agricultural practices at the PRP G/ Ruwa treatment point and the pond at the Kuka Bulukiya treatment point. This research served as a wake-up call to the authorities in setting up a standard treatment point with the extractors, public, and environmental health concerns in mind and a call for enforcement of regulations or its enactment in the study area. Specific e-waste management policies (dismantling, extraction, recycling facility, and refurbishment) should be in place and enforced to curtail future consequences of e-waste activities, and the government should provide proper support to the communities' concern in the shape of access to information and extension services on climate change and adaptation. In the wake of the alarming issues of e-waste and climate change, these findings will help policymakers implement stringent policies. The limitation is that the study had wanted to use a hands-on instrument that will measure the concentration of heavy metals at the spot (treatment points) but was unavailable.
Data availability All data generated or analyzed during the study are included in the published article(s) cited within the text and acknowledged in the reference section.

Declarations
Ethics approval and consent to participate This study neither involved human/animal participation, experiment, nor human data/tissue.

Consent for publication
This study did not involve children or individual details, but 100% data usage.

Competing interests
The authors declare no competing interests.