Atmospheric Error Propagation Methodology

The mean total and bioavailable Fe concentration in the soil samples were below the USEPA maximum permissible limit of 5500mg/kg for agricultural soils. This result of

the mean Fe concentration is similar to the one reported by Ruqia et al., (2015). The ANOVA results revealed that residual fraction (F5) is more significant and dorminant than carbonate and oxidizable fractions, though F5 is dorminant over F3 (reducible) fraction, but the relationship was not significant (appendices ii-iv). The results also showed that non-residual fractions constituted over 50% of the available Fe (Fig. 4.9).

This level of iron in the study area may be related to the composition of the parent soil material and the impact of the coal ash deposits. The results revealed that the concentration of Fe in the study area is higher than the control area. The solubilty and mobility of Fe is affected by hydrolysis, complexation and pH (Kabata and Pendias, 1992). Iron (Fe) is essential for all organisms, it is a co-factor in enzymes and heme protein, and is involved in photosynthesis and nitrogen fixation. High level of Iron concentration is found in residual and non residual fractions, but they were still within the USEPA permissible range.

Mean extractable managanese is above the maximum permissible limit of 300mg/kg, (USEPA, 1996), but the bioavailable fraction was below the permissible limit (Table 4.6).

Similar results were reported by Obasi et al., (2012). The high percentage of Mn in the residual fraction may be attributed to the soil parent material as well as the pH condition.

Though total Mn was above the permissible limit, but the percentage bioavailable fractions and other non residual fractions were 5.68% and 37% respectively, this means that the non residual fraction was below 50% of the extractable managanese in the study area. Since only few managanese may be available for plants up take, there may not be Mn toxicity threat to the soil environment. The result also revealed that managanese accumulate more in the surface between 5cm – 25cm under the ground in accordance with the report of kabata and pendias, 1992. Managanese is essential for production of oxygen in plant chloroplasts, it is also essential in the human diet.

The results in Table 4.6, and Fig. 4.9 revealed that both the mean total and bioavailable

prominent than other fractions, as the non residual fraction was just 18% of the extractable nickel(appendices II-IV). However, the result did not agree with that of Haluschak et al (1998), who reported that most available nickel in the soil may be that associated with Fe and Mn oxides. Since the residual fraction is not easily soluble, only few Ni may be available for plant uptake. The correlation of the axis was positive and significant, which implied that the origin of nickel in the study area was the same. Also, the correlation with the control sample results showed that Nickel concentration was more on the surface of the soil and decreases down. The implication is that certain amount of nickel might have been introduced into the study area by anthropogenic activities. Nickel bioavailablity decreases as soil pH increases, nickel is required by animals and it may also be essential for human health (Mograth and Simth, 1990). The available Ni may not pose any danger in the study area, since the bio-available fractions were far below the permissible limit.

Mean extractable lead (Pb) in the soil of the study area was above the USEPA, 1986 set limit of 30 – 300mg /kg, while the mobile fractions were within the set limit. Results also revealed that more than 50% of the lead was found in the non- residual fractions. 37.44%

of the total lead concentraction is associated with the mobile phase (Table 4.6). The ANOVA results revealed the dorminance of the acid soluble fraction followed closely with the reducible and organic phases, though the relationship were not significant(Appendices II-IV). The high level of mobile phase and other non – residual fractions may be related largely to the impact of coal ash deposit and the composition of the parent soil materials. Similar results were reported by Obasi et al (2012). The correlation of results from the four axis was positive and significant, showing that the source of lead in the study area was the same. Naturally lead is the least mobile of the heavy metals (Kabata and Pendias, 1992) and it accumulates more on the surface of soil which is in agreement with result of our depth profile analysis (Fig. 4.27). Lead is most available under acid condition and it is non essential element to all living things. The high level concentration of lead in the mobile phase and other non residual fractions means

that more lead may be available for plants uptake, thereby posing toxicity danger to the environment through food chain.

Mean extractable and bioavailable cadmium were above the 3mg/kg USEPA set limit 1986 and 5mg/kg set limit by some European communities (Kabata and Pendias 2001).

Similar results were obtained by Obasi et al (2012). Over 50% of the extractable Cd is associated with the non- residual fraction, while the bioavailable fractions contributed 35.39% of the available cadmium (Table 4.6 and Fig. 4.9). The ANOVA results also revealed a positive non-significant relationship among all the fractions (Appendices ii-iv). Correlation of the results among the four axis in appendix ix were positvely significant, which implied that cadmium has the same source in the study area. There is no known biological function related to cadmium. It can rapidily accumulate in live stock and other animals, partcularly in kidney, it is a potential hazard for human consumption (CCRM, 1995). The high level of cadmium in the non-residual fractions means that more Cd may be available for plants uptake. Moreso, the level of Cd in the soil of the study area may be largely attributed to the impact of coal ash deposit and the composition of the soil parent materials.

Mean extractable cobalt is above the maximum allowable concentration of 50mg/kg recorded by Kabata-Pendias and Pendias (2001). However the bioavailable fraction which consituted 14.32% of the total cobalt figure 4.23 is below the set limit. The result also revealed that non- residual fractions made up 42% of the total cobalt in the study area. Similar results were obtained by Andreu (1991). ANOVA result also revealed that the residual fraction was more significant and dorminant over the mobile fractions (Table 4.6). The correlation of cobalt in the four axis revealed a positive relationship which indicated that cobalt concentration in the study area comes from the same source. The high level of residual fraction may be related to the composition of the parent soil materials, and little input from the coal ash deposit. The lower percentage of the mobile

essential for plant growth when the concentration is within the allowable limit, it is also an essential element for some animals Kabata and Pendias (1992).

Mean extractable and bioavailable zinc in the study area were below 300mg/kg set limit by USEPA, 1986. 40% of the total zinc was associated with the non residual fractions (Table 4.6). The dorminace of residual fraction agrees with the ANOVA result which revealed that residual fraction is more significant and prominent than other fractions (appendices ii-iv). The results of the mobile fraction is similar to the one reported by Obasi et al (2012). The high level of residual fraction may be attributed to the composition of the parent soil materials, while the mobile phase may be related to the impact of coal ash deposit. Since zinc is more soluble in the soil than other metals, it is therefore likely that most of the zinc that came with the coal ash might have been converted to soluble zinc and taken away through different sources, hence the low mobile phase (Kabata and Pendias (1991 ). As long as the mobile phase is below the permissible limit, zinc toxicity is not implicated. Mean while zinc is required for several enzymes in animals, it is also essential for energy metabolism in humans (Kiekans, 1990).

Total chromium concentration in the study area is below the maximum allowable concentration of 200mg/kg reported by kabata – pendias and pendias (2001) for agricultural and domestic soils, and 750mg/kg USEPA set limit. Chromium was mostly associated with the residual fraction as was shown also in the ANOVA results(Table 4.6 and appendices II-IV). The mobile phase consituted only about 2.87% of the total chromium which is too low to make any meaningful impact in chromium containmation or plant uptake in the study area (Fig. 4.23).

The dorminance of the residual fraction may be related to the composition of the parent soil materials. The result is also in agreement with the report of Kabata-Pendias and Pendia (1992), that chromium is resistant to weathering and only slightly soluble under very acid condition. Chromium (Cr) is required for removal of excess glucose in mamals (Scott, 1972) and deficiences have been found to occur in humans and animals (NRCC, 1976), while Cr⁺⁶ is toxic to both plants and animals (Kabata, 1992).

Total and bioavailable copper concentrations in the study area were below the maximum permissible limit of 100 – 300mg/kg set limit by USEPA, 1986 for agricultural lands.

Similar result were reported by Obasi et al (2012) and Obasi et al (2013). The result indicated that copper concentration was mostly associated with the residual fraction, which is in agreement with the ANOVA results which revealed dorminance of residual fraction over other fractions (Table 4.6). Since the bioavailable fraction is just 11.28% of the total copper and the concentration of other non residual fractions were low, it means that the area is not at risk of copper containination, as less copper will be available for plants up take. Copper in soil can be fixed by adsorption, precipitation organic chellation and complexation and basically the solubilty of copper decreases at pH 7 – 8 ( kabata and pendias 1992). Copper is necessary in animal nutrition where it plays role in oxidase functions (Kabata and Alloway, 1972). In this research the dorminance of residual fraction may be related to the composition of parent soil material.

Total and bioavailable arsenic in this study were above the maximum allowable concentration of 15 – 20mg/kg for agricultural soil, (Kabata and Pendias, 2001). The results of mean arsenic level in this study was similar to the one obtained by (Halluschak et al (1998). ANOVA results revealed dorminance of mobile phase over residual phase (Appendices II-IV). Correlation of results from the axis indicated a positive and significant correlation which implied that arsenic concentration in the study area has the same source (Appendix XIV). Also the mean arsenic concentration in the study area is higher than the control samples. The mobile phase has 44.15% of the total arsenic in the study area, while the residual fraction is associated with only 5.53%. the high level concentration of the mobile phase may be related to the impact of coal ash deposit.

Arsenic minerals and compounds are soluble, but there is limited movement of As in the soil because it is adsorbed by hydroxides, clays and organic matter (Kabata and Pendias, 1992). Solubilty of arsenic is affected by pH, unlike most trace elements, the inorganic

has not been determined, also it is not a requirement for animals or humans. The result indicated that the study area is in a high risk of arsenic contamination.

Mean extractable molybdenum in the study area was above the maximum allowable concentration range of 4-10mg/kg for agricultural soils in some European communities (Kabata and Pendias, 2001). Mean while the result revealed that the bioavailable fractions were below the set limit. The result of ANOVA revealed dorminance of the oxidizable fraction followed by reducible and the residual fractions (Appendices II-IV). The least concentration was associated with the mobile fractions which is 5.22% of the available molybdenum in the study area. The results obtained in this study were less than the ones obtained by Halluschak 1998, Obasi, 2012 and 2013. More than 50% of the total molybdenum was associated with the non – residual fractions which implied that, though, the bioavailable fractions were below the set limit, but the area may be prone to molybdenum contamination, as high level of molybdenum may be available for plant up take when there is slight change in pH condition. The high level of molybdenum in the oxidizable and reducible fractions may be related to the composition of parent soil material and the impact of coal ash deposit. Hence, the conversion of mobile fractions to precipitates, oxides and complexes during aging may be the reason for reduced level of the mobile fraction (Kabata and Pendias, 1992). Molybdenum is essential in animal nutrition (MCBRIDE, 1994) and can result in copper toxicity if present in deficient amounts (Kabata and Alloway, 1972).

Total selenium concentration in the study area was above the trigger action value of 3 – 10mg/kg for agricultural soils in some European communities (Kabata and Pendias, 2001).The result also showed that the bioavailable fractions which contributed only 10.75% of the total selenium were within the approved range. However other non – residual fractions were associated with more than 50% of the total selenium in the study area. The correlation of the results from the four axis was positively significant, which implied that the source of selenium was the same (Appendix XVI). Elevated selenium concentration associated with the oxidizable and residual fractions may be attributed to

selenites and selenium sulfides in the composition of the parent soil material and to the impact of coal ash deposits. The dorminance of oxidizable and residual fractions means that unless there is suden change of pH, their availability for plant, uptake may be limited (Kabata and Pendias, 1992). Selenium is essential in human, and can lead to cardiomyopathy and tubular bone changes if deficient (Kabata and Pendias, 1992). Toxic levels in humans may lead to malformation in children, miscarriages and dermatitis (Marier and Jaworski, 1983).

Total mercury concentration in the study area was above maximum allowable concentration range of 0.5 – 5mg/kg for agricultural soils in some European communities (Kabata and Pendias 2001). Apart from the resiual and oxidizable fractions, other fractions were below the detectable limit of the instrument.

The dorminance of the residual fraction may be attributed the composition of the parent material and little contribution from the coal ash deposit. Though the total mercury is above the set limit but the available mercury for plants uptake may be limited since the bioavailable fractions were below detection limit.