Electrochemical and microbiological effects of dumpsite leachates on soil and air quality

2.1 Description of the study area

The study was conducted within the Anambra, Delta, and Bayelsa states of Nigeria, as displayed in Figure 1. Delta and Bayelsa states are located in the Niger Delta wetlands of south-southern Nigeria [29]. Similarly, Anambra state is a major commercial hub in Nigeria, which is situated in the south-eastern region of Nigeria, with weakly consolidated subsoils prone to gully erosion [30]. The studied region’s climate can be categorized into wet “rainy” and dry seasons. According to the estimates of the National Population Commission, Anambra, Delta, and Bayelsa states have populations of about 5.7 million, 6.1 million, and 2.4 million, respectively [29,31]. Table 1 presents the prevailing climatic and environmental conditions of the dumpsites locations.

Figure 1

The map of the study area showing the respective dumpsites (D1 – dumpsite 1, D2 – dumpsite 2, D3 – dumpsite 3, D4 – dumpsite 4).

Additionally, there are few government-monitored solid waste disposal and management structures (dumpsites) in the region. These dumpsites receive their municipal/domestic waste materials, mainly through private sector partnerships, that facilitate the collection of these wastes from the individuals/parastatals and convey them in trucks to the dumping point. These dumpsites are poorly managed, leading to the acute emission of offensive odor, poisonous gases, and pathogenic microorganisms into the environment [33]. Remarkably, dumpsites are predisposed to wildfires, particularly during dry seasons, releasing large volume of toxic substances into the atmosphere [25,26].

2.2 Sample collection and preparation

Subsoil (0.4 m depth) samples were carefully sampled from five spatial locations within the vicinity of an unlined dumpsite for the four unlined dumpsites evaluated in this current research. Four spatial points were situated approximately 250 m north, south, east, and west from the epicenter of the dumpsite, while the fifth point was located at the center of each dumpsite. The four unlined dumpsites used to achieve the aim of this study include three active sites and one passive site. Active sites are those dumpsites that are still receiving waste materials, while passive sites are those dumpsites that are nonfunctioning (not receiving waste materials again). Typically, government tends to shut down (reallocate) active dumpsites, primarily due to rapid urban expansion and ecological issues. These passive dumpsites rely heavily on natural remediation to clear the environment [33]. This has resulted in toxic compounds and pathogens persistence, within the proximity of passive dumpsites. Remarkably, the passive site chosen in this research was closed down approximately 2 years ago by the government.

Furthermore, the Delta state site (dumpsite) received approximately 150,000 tons of waste weekly, while each of the Anambra state sites received roughly 200,000 tons of municipal solid waste weekly. The larger volume of waste generated at Anambra state can be attributed to the high daily influx of people into the state due to its high socio-commercial activities [31]. Specifically, the active dumpsites were more than 15 years old, and each covers an area of 30,000 m². The wastes received by these sites consist mostly of domestic, medical, industrial, and electronic wastes [33]. These dumpsites lack proper waste sorting and recycling structures; hence, their dumpsites and landfills are littered with organic and inorganic materials.

In order to define the pollution level and pollution index of the dumpsite on the environment, a reference point (control) 3 km upland from the dumpsite was selected. The control location (reference point) had no documented records of the presence of a waste yard for the past decade. The soil samples were located from the designated points by using a soil auger, poured into sterilized containers, labeled accordingly, and transported to the laboratory.

2.3 Laboratory analyses

Table 2 shows the recap of the specimens, factors tested, and the testing techniques adopted to accomplish the research goals.

2.4 Air quality determination

The air quality at the various dumpsites was measured by using a portable gas detector (model GC310, Henan Chicheng Electric Co., Ltd, China) at a height of 2 m above the ground level, and sampling duration of 1 h per sampling time. Sampling was done at three defined periods of 7–8 a.m., 12–1 p.m., and 6–7 p.m. for all locations. CO (carbon (ii) oxide), CH₄ (methane), NH₃ (ammonia), NOx (nitrogen oxide), VOCs, and SO₂ (sulfur dioxide) were measured in ppm and converted to μg/m³, with a conversion factor of 1,000 [26].

2.5 Heavy metal analysis

The specimens were air-dried in the research laboratory, crumpled, and sifted using a 1 mm sieve. Two grams of the sifted dried soil were digested in 10 mL of concentrated acids (trioxonitrate(v) acid, hydrochloric acid, and tetraoxosulfate(vi) acid) in a mixture ratio of 4:1:1, at a temperature of 90°C to achieve a transparent solution. The digested product was strained using a standard filter paper (Grade 42) into a volumetric bottle and diluted to 100 mL using deionized water. Thereafter, the As, Pb, Ni and Cd levels in the solution were measured by atomic adsorption spectrometry, and the results are presented in mg/kg (ppm) [11].

3.1 Dielectric constant and EC

The dielectric constant (ɛʹ) of each soil specimen was determined in agreement with ASTM D150 approved guidelines at a constant frequency of 10.0 GHz. Additionally, the soil EC level, which is the measure of the amount of salt ions in the soil, was determined following standard guidelines [34,35,36].

3.2 Electrical resistivity

The electrical resistivity level of the soil was measured in harmony with the standard procedures explained in previous studies [36,37], as shown in Figure 2. Thereafter, the soil resistance (R) and resistivity (ρ) were computed using equations (1) and (2), respectively:

where A is the soil column area and L is the soil column length.

Figure 2

Structural diagram of the testing unit [36].

3.3 Microbial analysis of the soil

The plate count method was used to measure the total bacterial count (TBC) of each sample by plating serial dilutions of 5 g of the soil specimen, in agreement with the processes explained by Frączek et al. [38]. TBC was then quantified as colony-forming units per gram (cfu/g). Thereafter, the population of Staphylococcus aureus, Escherichia coli, Pseudomonas spp., Bacillus spp., Arthrobacter spp., and Streptococcus spp. in the soil samples was determined by using the culture-based methods. S. aureus was evaluated using the mannitol salt agar, E. coli was determined using the eosin methylene blue agar, Pseudomonas spp. was evaluated using the Cetrimide agar, Bacillus spp. was measured using the nutrient agar (spore-forming), Arthrobacter spp. was evaluated using the Actinomycetes isolation agar, and Streptococcus spp. was determined using the blood agar [7,38].

3.4 Evaluation of pollution indices

The pollution level of HMs was determined using the contamination factor and pollution load index (PLI).

3.5 Contamination factor (CF)

This pollution evaluation index was calculated using equation (3).

where X ₁ and X ₂ are the concentrations of HMs at the dumpsite and control point, respectively.

Soil CF is classified as follows: low – Cf < 1, moderate – Cf > 1 < 3, considerable – Cf > 3 < 6, and very high – Cf ≥ 6 [33].

3.6 PLI

The PLI was computed using equation (4):

PLI is classified as follows: PLI > 1 indicates a polluted condition, and PLI < 1 specifies nonpolluted situation [33].

3.7 Health hazard assessment

3.8 Statistical analysis

The relationship between the parameters investigated and sampling locations was evaluated using the SPSS software (version 20.0, Chicago, IL, USA). The analysis of variance was used to evaluate the significant effects on the dumpsite activities, soil PTMs, and microbial and electrical properties status (levels). The average values were separated by Duncan’s multiple range test (DMRT) at a 95% confidence level. Additionally, apart from the air quality measurement, most of the tests were repeated three times, and the average documented.

4.1 Air quality assessment

The results of the air quality of the dumpsites regions in comparison to the reference points are presented in Table 3. In the three active dumpsites (D1, D3, and D4) investigated, tt was highlighted that the average SO₂, NOx, NH₃, VOC, CO, and CH₄ concentrations ranged from 99.50 to 242.20 μg/m³, 60.60 to 85.60 μg/m³, 1376.80 to 1812.20 μg/m³, 10663.30 to 18097.90 μg/m³, 32.40 to 73.00 μg/m³, and 3365.40 to 3823.30 μg/m³, respectively. Remarkably, the results revealed that the volume and concentration of gaseous emission around the dumpsite locality were considerably greater than the results verified at the reference points. This confirmed previous findings that emissions from decomposing organic and inorganic materials are loaded with hazardous compounds [25]. According to Uguru et al. [26], substances released from ineffectively managed dumpsites contain large percentages of CO, methane, ammonia, and VOCs. Interestingly, the results indicated that the high concentrations of SO₃ and NOx recorded around the active dumpsites (1, 3, and 4) exceeded the maximum allowable limits approved by World Health Organization (WHO, 2024) for residential areas.

Furthermore, the elevated concentrations of VOCs, CH_4, and NH₃ detected around D1, D3, and D4 vicinity can be primarily attributed to emissions from degrading (decomposing or burning) organic materials, paints, tyres, petroleum-based materials, and pesticides [26]. These findings aligned with the previous observations made by researchers in previous studies [25,39,40], where activities correlated with dumpsites released significant amount of toxic compounds and greenhouses gases into the ecosystems. Distinctively, considerable SO₂, NOx, NH₄ and CH₄ levels, documented at the reference point, can be linked to the emissions from other anthropogenic activities with the control point’s locality. High SO₂, NH₃, and NOx concentrations are highly lethal, posing significant health challenges to human survival. Some health challenges linked to higher levels of SO₂, NOx, NH₃, CO, CH₄, and VOCs in the atmosphere include respiratory issues and cardiovascular diseases [26,39].

4.2 Heavy metal parameters

The results of the effect of the dumpsite leachate on the subsoil heavy metal content are shown in Table 4. Table 4 shows that D1–D4 actions had significant effect (p ≤ 0.05) on the Ni, Pb, Cd, and As concentrations in the subsoil. This indicates negative implications of solid waste effluents on public health and human safety. At dumpsite 1, it was observed that the subsoil specimens had mean Cd, Pb, Ni, and As concentrations that ranged from 0.66 to 1.86 mg/kg, 35.30 to 72.53 mg/kg, 8.65 to 20.13 mg/kg, and 1.33 to 7.67 µg/kg, respectively. In dumpsite 2, the samples recorded average Cd, Pb, Ni, and As concentrations that varied from 0.04 to 0.1 mg/kg, 31.87 to 76.73 mg/kg, 3.91 to 7.12 mg/kg, and BDL to 6.33 µg/kg, respectively. Then, at dumpsite 3, it was noted that the subsoil had mean Cd, Pb, Ni and As contents that ranged from 0.46 to 1.70 mg/kg, 26.56 to 66.08 mg/kg, 0.74 to 5.24 mg/kg, and BDL to 6.67 µg/kg, respectively. Additionally, at dumpsite 4, the average Cd, Pb, Ni, and As concentrations ranged from 0.24 to 2.75 mg/kg, 17.01 to 75.48 mg/kg, 15.51 to 34.26 mg/kg, and 3.33 to 233.33 µg/kg, respectively. The wide HM concentration difference observed among D1–D4 can be attributed to several factors, such as the soil's geotechnical properties, the region’s topography, and the soil’s hydraulic conductivity [7,42].

Furthermore, the results indicated that the PTM – cadmium, nickel, lead and arsenic – levels in the dumpsite locality soils were significantly greater than those in the control location. Notably, the PTM concentrations verified at the passive dumpsite (D2) were considerably lower than those recorded in the active dumpsites (Dumpsites 1, 3, and 4). This buttressed earlier reports, which stated that solid waste effluent tends to contribute immensely to heavy metal pollution and its associated health issues [43,44]. Hosseini Beinabaj et al. [14] gave a concise view that there is strong correlation between PTM level, dumpsite age, and dumpsite volume. Additionally, bioremediation activities occurring in D2 greatly help in weakening the PTM concentration, consequently, leading to overall lower metal concentrations [45].

The elevated concentrations of the PTMs recorded at the dumpsite center could be attributed to the significant amount and concentration of leachate, emitted from the metallic and non-metallic wastes deposited in the localities [7,33]. When metallic objects corrode, they emit harmful minerals, including toxic metals, into the environment leading to ecological contamination; this further elevates the PTM toxicity of the ecosystems [10]. Peculiarly, Cd and Ni levels in this study were lower than those recorded by Abd-Elhalim et al. [44] for soils located around waste yard vicinities; on the contrary, the Pb and Cd levels in this study were greater than those found in previous studies [42,44]. Correspondingly, the Cd levels documented in this research were less than that (2.31 mg/kg) obtained for other region's dumpsites’ soils [46]. The mean Ni concentrations found here were greater than those of Magaji et al. [47] but aligned with observations made by Uguru et al. [7]. Notably, the Cd concentrations in the D2 and D3 subregions were substantially lower than those in previous studies [48,49]. However, the Cd and Pb values found here were confirmed to be greater than those reported by Omo-Irabor et al. [43] for an unlined landfill.

It is interesting to note that the PTM levels around the dumpsite neighborhood soils were below the maximum acceptable concentrations values, approved by WHO and European Union for human safety. However, their elevated concentrations present considerable risks to food safety and electrical installations. Toxic metal pollutants have the ability of causing numerous diseases in humans by their accumulation in the food chain and food web [14,43]. Food poisoning resulting from PTM toxicity is a leading cause of human mortality, as it poses a severe hazard to humanity [44]. PTMs have the potential of accumulating in the soil, vegetation, and human bodies, resulting in chronic health issues such as system failures, memory loss, nervous disorders, and cancer diseases [7,50]. Cadmium primarily enters in the environment through leachates from electroplated materials and electronic components [7]; while leachate from battery circuit boards and semiconductors are significant contributors to nickel pollution in the soil [14]. Anthropogenic sources such as leachate from paint materials, pesticides, batteries, and tires are the major contributors of Pb contamination in the environment [51]; while industrial chemicals, electronic waste, batteries, and photovoltaic cells are the major sources of arsenic in the soil [7].

Based on the impact of these dumpsite actions on engineering infrastructures, the high PTM concentrations in the soil can significantly impact the functionality of telecommunication facilities [53]. According to ref. [21], metallic ions facilitate corrosion, thereby diminishing the material proficiency in numerous electrical and electronic components. PTMs (mostly Pb and Cd) have the ability of increasing the soil moisture’s salinity level, leading to corrosion of metallic circuits and connectors, which in turn undermines the electrical integrity of the system [52]. Corrosion is enhanced by high soil EC, resulting in interference with signals and energy transmission. This subsequently leads to telecommunication and grounding system interruptions and failures [53,54]. These conditions are associated with signal degradation, leading to deprived connectivity and service consistency.

4.3 Microbial analysis

Table 5 presents the microbiological analysis of the dumpsite and its environmental soil samples. The average TBC in the dumpsites regions varied between 7.54 × 10⁶ and 128.30 × 10⁶ cfu/g, while the load of S. aureus ranged from 1.76 × 10³ to 15.26 × 10³ cfu/g. The population of E. coli was between 7.25 × 10³ and 33.92 × 10³ cfu/g. whereas the count of Pseudomonas spp. fluctuated from 5.55 × 10³ to 45.74 × 10³ cfu/g. Likewise, the mean Bacillus spp. load was between 6.91 × 10³ and 91.02 × 10³ cfu/g, while the Arthrobacter spp. population varied from 3.66 × 10³ to 28.12 × 10³ cfu/g. Finally, the mean population of Streptococcus spp. ranged from 1.59 × 10³ to 8.77 × 10³ cfu/g. The results revealed that the bacteria population at the central area and in the vicinity of the dumpsites were significantly highly than the results obtained from the reference points. This is an indication that leachates from the waste materials immensely lead to microbial infestation of the environment.

Remarkably, out of the six bacteria isolated from the dumpsite soil samples, Bacillus spp., Pseudomonas spp., and E. coli have the highest prevalence, regardless of the sampling location and dumpsite. At D3, Streptococcus recorded the highest frequency of isolation, while Bacillus spp. was dominant in dumpsite 2. The Pseudomonas spp. population at D4 was significantly greatest compared to the populations observed at Dumpsites 1–3, while Arthrobacter spp. and E. coli had the highest isolation frequency at dumpsites 4 and 1, respectively. The high bacteria prevalence in the dumpsite soils portrayed the harmful impact of inappropriate WM practices on the ecosystems. These findings are consistent with the observations previously made in Refs [55,56], where it was noted that the organic material effluent has extremely large population of Streptococcus spp., Bacillus spp., E. coli, and Pseudomonas spp., subsequently causing massive environmental pollution. Uguru et al. [26] critically observed during their investigation into public health that a strong correlation existed between emissions from organic waste and microbial contamination of the environment.

The findings in this study highlighted that the non-active dumpsite typically had the lowest bacteria population. This could be linked to the favorable bacteria habitat conditions created by decomposition solid waste residues. Pseudomonas spp., Bacillus spp., and Arthrobacter spp. are heavy metal-resistant pathogens, while Staphylococcus and Pseudomonas spp. are biofilm-forming bacteria. Therefore, these microorganisms can thrive successfully in contaminated environmental conditions [33,57,58]. Additionally, the variation observed in microbial loads both within and among dumpsite neighborhoods can be correlated with the composition of the waste materials. Waste type (organic, inorganic, or toxic), environmental conditions (temperature, moisture, pH, and oxygen levels), as well as the remediation processes, tend to influence microbial reproduction and survival in the soil [56,59]. The outflow from organic materials tends to enhance the survival and performance of microorganisms [26,60]. On the contrary, seepages from synthetic or hazardous sources tend to hinder microbial growth and favorability [26,60].

Despite the pathogenic nature of Bacillus spp. and Pseudomonas spp., these bacteria can play bioremediation roles, mainly due to their resilience to degrading toxic compounds [58,61]. E. coli, Bacillus spp., and Pseudomonas spp. dominance in the polluted soils depicts colossal microbial diversity alteration. This context can be correlated with potential response to environmental stressors, which is caused by the waste materials’ seepage into the landscape [62]. The significant bacteria population recorded at the control points could be attributed to activities associated with anthropogenic actions, such as agricultural production and domestic activities [26].

4.4 Electrical property parameters

The results of the electrical properties of the soil samples are presented in Table 6. The results highlighted that the subsoil’s EC values at dumpsites 1, 2, 3, and 4 varied from 26.06 to 70.15 mS/m, 22.93 to 46.57 mS/m, to 21.31 to 65.06 mS/m, and 32.57 to 76.02 mS/m, respectively; while their ρ varied between 7.61 and 12.04 Ω m, 12.25 and 17.23 Ω m, 9.08 and 15.26, 8.64 Ω m and 15.31 Ω m, respectively. Likewise, their ɛʹ values at dumpsites 1, 2, 3, and 4 ranged from 2.46 to 3.54, 2.64 to 3.23, 2.75 to 3.64, and 2.58 to 3.32, respectively. Generally, the results revealed that the soils around the dumpsites had higher EC values, along with decreased ɛʹ and resistivity values compared to the soil samples at the reference points. This is an indication that leachate actions successfully initiate an increment in the soil’s ability to conduct electrons and electrical charges throughout the soil mass. This action can be linked to the presence of large amount of HMs in the soil, performing the function of electron transporters, thereby facilitating the electron mobility and increasing EC of the soil in the process [17].

Furthermore, the results show that anthropogenic activities – leachate from the waste products – interfere with the soil's ρ values, which is similar to the findings of ref. [19]. High metallic concentrations of the soil tends to improve electrons’ conductive routes, hence reducing the soil’s electrical resistivity [62]. These findings highlighted that the dumpsite discharge reduces the soil’s insulating capability, thereby creating conductive bridges within the soil mass. Depreciation of the soil ρ, particularly around the dumpsite surroundings, will adversely affect the electrical earthing performance of electrical installations constructed in these areas. These conditions result in a higher occurrence of electrical faults and electrical accessories/systems malfunctions [37].

The smaller ɛʹ values documented at the dumpsite neighborhood, compared to the reference point, can be attributed to the higher PTM levels recorded within the dumpsite area. Heavy metal pollution has the potential to cause significant alteration in the soil structure and moisture retention ability. Consequently, this will lead to an increase in the soil’s ion concentration, causing substantial reduction in the ɛʹ rates [64,65]. Notably, the high EC levels detected in the soils around the waste yards could foster corrosive conditions, which accelerate rapid deterioration of electrical and mechanical installations.

4.5 Heavy metal health hazards

4.5.1 Non-carcinogenic and carcinogenic risks

The results of the non-carcinogenic risks (EDI, HQ, and HI) and carcinogenic risks (CR and TCR) of the PTMs are presented in Table 7 and Figures 3 and 4. It was observed that the EDI values for Cd, Pb, Ni, and As were found as follows: 8.51 × 10⁻⁷ – 1.07 × 10⁻⁵ mg/kg/day, 1.26 × 10⁻⁶ – 1.11 × 10⁻⁴ mg/kg/day, 8.28 × 10⁻⁶ – 7.22 × 10⁻⁵ mg/kg/day, and 2.90 × 10⁻⁸ – 7.33 × 10⁻⁷ mg/kg/day, respectively. Basically, the EDI values obtained at the center of the dumpsites were greater than those found around the vicinity of the dumpsites. This reflects the emissions from the waste materials dumped at these waste yards; this builds on previous investigation of ref, [7], which identified the detrimental impact of emissions from waste materials on the environment. According to the results, the HQs of the Cd, Pb, Ni, and As varied from 8.51 × 10⁻⁴ to 1.07 × 10⁻², 3.60 × 10⁻³ to 3.17 × 10⁻², 4.14 × 10⁻⁴ to 3.61 × 10⁻³, and 9.67 × 10⁻⁵ to 4.90 × 10⁻⁴, respectively. Likewise, the HI values for the PTMs revealed varied levels of risk, depending on the age group and contamination point. At the dumpsite center, the HI values were 4.85 × 10⁻² for children and 9.72 × 10⁻³ for adults; within the dumpsites’ neighborhood soils, the documented HI values were 2.48 × 10⁻² and 4.96 × 10⁻³ for the children and adult age categories, respectively (Figure 3). These results show that though the HI values were considerably high, they did not exceed the threshold (HI ≥ 1), which is associated with non-carcinogenic health risks linked to prolong exposure to heavy metal assimilation. Typically, an HI value less than 1 is an indication that prolonged exposure to these harmful PTMs will not pose any significant non-carcinogenic health risk to humans [7].

Table 7

Non-carcinogenic and carcinogenic risks of PTMs

PTM	Location	EDI (mg/kg/day)		HQ		CR
		Children	Adults	Children	Adults	Children	Adults
Cd	Central	1.07 × 10−5	2.14 × 10−6	1.07 × 10−2	2.14 × 10−3	4.07 × 10−6	8.13 × 10−7
	Locality	4.25 × 10−6	8.51 × 10−7	4.25 × 10−3	8.51 × 10−4	1.62 × 10−6	3.23 × 10−7
Pb	Central	1.11 × 10−4	2.23 × 10−5	3.17 × 10−2	6.37 × 10−3	9.44 × 10−7	1.90 × 10−7
	Locality	6.29 × 10−5	1.26 × 10−5	1.80 × 10−2	3.60 × 10−3	5.35 × 10−7	1.07 × 10−7
Ni	Central	7.22 × 10−5	1.44 × 10−5	3.61 × 10−3	7.20 × 10−4	6.06 × 10−5	1.21 × 10−5
	Locality	4.14 × 10−5	8.28 × 10−6	2.07 × 10−3	4.14 × 10−4	3.48 × 10−5	6.96 × 10−6
As	Central	7.33 × 10−7	1.47 × 10−7	2.44 × 10−3	4.90 × 10−4	1.10 × 10−6	2.21 × 10−7
	Locality	1.45 × 10−7	2.90 × 10−8	4.83 × 10−4	9.67 × 10−5	2.18 × 10−7	4.35 × 10−8

Figure 3

The HI values of PTMs.

Figure 4

The TCR values of PTMs.

Furthermore, the carcinogenic risks results for Cd, Pb, Ni, and As were observed to be within the following ranges: 3.23 × 10⁻⁷ to 4.07 × 10⁻⁶, 1.07 × 10⁻⁷ to 9.44 × 10⁻⁷, 6.96 × 10⁻⁶ to 6.06 × 10⁻⁵, and 4.35 × 10⁻⁸ to 1.10 × 10⁻⁶, respectively. The results further highlighted that children and the center of the dumpsites had higher CR values compared to the adults and soils sampled from the vicinity of the dumpsites. This finding is in conformity with previous observations reported by Hu et al. [69] and Uguru et al, [7]. Additionally, the TCR results (Figure 4) show that at the dumpsite center, the TCR values for children and adult were 6.67 × 10⁻⁵ and 1.33 × 10⁻⁵, respectively, while within the dumpsite locality, the TCR values were 3.72 × 10⁻⁵ and 7.43 × 10⁻⁶ for children and adults, respectively. Based on the health safety standard, the TCR values obtained in this study, regardless of the sampling point and age category, do not exceed the minimum allowable limit of 1 × 10⁻⁴, as stipulated by the USEPA for metropolitan areas [66]. Interestingly, the TCR results portrayed that there are no carcinogenic health hazards, which can be linked to prolong exposure to the pollutants (PTMs) emitted in the form of leachate from both the active and passive dumpsites studied. This depicted a relatively lower environmental and health concern, related to PTM lethality from poorly managed dumpsites.

4.6 Evaluation of the pollution rate