**3. Results**

**2.3. Sample preparation**

702 Environmental Risk Assessment of Soil Contamination

three days (72 hours).

**2.4. Metal analysis**

fluorescence Spectroscopy (EDXRF) method [21].

intensity by the Zr-K is subtracted for each sample.

for the analysis of K, Th, Y, Zr, Nb and Mo.

International Atomic Energy Agency (IAEA).

labeled.

press.

ADC – card.

sample.

Plant samples were washed with tap water and then with distilled water to remove debris and surface contamination. Samples were then bulked and air dried to remove excess moisture. Similarly, samples of the soils collected were bulked into composite samples and air dried for

Dried plant and soil samples were ground using a porcelain mortar and pestle and sieved to attain a uniform particle size. Each sample was put in a small transparent polythene bag and

Analysis of the elemental content of the samples was done using the Energy dispersive X-ray

The samples were ground manually to powder with an agate mortar and pestle to grain size of less than 125µm. Pellets of 19mm diameter were prepared from 0.3-0.5kg powder mixed with three drops of organic liquid binder and pressed at 10 tons of pressure in a hydraulic

Measurements were performed using an annular 25mCi 109Cd as the excitation source, that emits Ag – K rays (22.1 KeV) in which case all elements with lower characteristic excitation energies are accessible for detection in the samples. The system consists furthermore of Si (Li) detector, with a resolution of 170eV for the 5.90KeV line, coupled to a computer controlled

Quantitative analysis of the sample was done using the Emission Transmission (E-T) method and that involves the use of pure target material (Mo) to measure the absorption factors in the

The Mo target served as a source of monochromatic X-rays, which are excited through the sample by primary radiation and then penetrate the samples on the way to the detector. In this way, the absorption factor is experimentally determined which the program uses in the quantification of concentration of the elements. In addition, the contribution to the Mo-K peak

Sensitivity calibration of the system was performed using thick pure metal foils (Ti, Fe, Co, N, Zn, Nb, Zr, Mo, Sn, Ta and Pb) and stable chemical compounds (K2CO3), CaCO3, Ce2O3), WO3, ThO2, U3O3). The spectra for the samples were collected for 3000s with the 109Cd source and the spectra were then evaluated using the AXIL-QXAS program [22]. 109Cd source was used

The accuracy and precision of the measurements was confirmed though an analysis of IAE – V10 (hay powder) and IAEA – 259 (cabbage) certified reference material, distributed by

#### **3.1. Metal concentration in soils and plant samples**

In the soils around the Zobe dam catchment, the mean concentration of metals generally followed the order Fe>Mn>Zn>Cr>Cu>Ni>Cd and Fe>Mn>Zn>Ni>Cr>Cu>Cd in dry and wet seasons respectively. In soils in the environs of the Katsina Steel Rolling Mill (KTSRM), the mean wet season concentration trend followed the order Fe>Mn>Zn>Cr>Ni>Cu>Cd and Fe>Mn>Zn>Cu>Cr>Ni>Cd in the dry season (Table 2; Fig 4). Differences in soil concentrations of all the metals between seasons were not statistically significant (P=0.05)

#### **3.2. Chromium**

The soil around the Zobe dam catchment had a mean Cr concentration of 66.00 mg/kg and 70.53 mg/kg, in dry and wet seasons respectively (Table 2; Fig 4). The mean Cr concentration in the environs of the Katsina Steel Rolling Mill was 46.67 mg/kg in the dry season and 70.53mg/ kg in the wet season. The wet season concentrations were observed to be higher than acceptable limits for soils in Canada and the Netherlands (Table 3).


Differences in soil heavy metal content were not significant (ns) between seasons in both locations.

**Table 2.** Mean Seasonal Heavy Metal Concentration (mg/kg) and T-test P-values of Soils collected from Zobe dam catchment and the environs of Katsina Steel Rolling Mill (KTSRM)


**Table 3.** International Recommended Levels of Heavy Metals in Soils (mg/kg)

In the plant samples, the highest concentration of Cr was recorded in *Senna siberiana* (2.64 mg/ kg) in the dry season and *Englerina gralicinus* and *Terminalia mollis* (3.30 mg/kg) in the wet season (Fig 5). "Normal" concentration of Cr in plants is described as being from 0.1 to 0.5 mg/ kg, while concentrations between 5 to 30 mg/kg as "Excessive" and 75 to 100 mg/kg, "Phyto‐ toxic" (Table 4).

#### **3.3. Copper**

Mean concentrations of Cu in the soil samples collected around the Zobe dam catchment was 29.66mg/kg in the dry season and 7.92 mg/kg in the wet season. Around the environs of KTSRM, the mean Cu concentration was observed to be 56.91 mg/kg in the dry season and 12.05 mg/kg in the wet season (Table 2; Fig 4). Only soil samples collected from the en‐ virons of KTSRM in the dry season were observed to have mean Cu concentration above the acceptable limits of the WHO (30 mg/kg), Germany, the Netherlands and Sweden (40 mg/kg) Table 3).

In plant samples collected, the highest concentration of Cu was observed in members of the genus *Diospyros, D. piscatoria*, 10.41 mg/kg and *D. mespiliformis* 10.40 mg/kg in the dry season. In the wet season, the concentration of Cu was generally higher in the plants, with the highest concentration recorded in *Combretum mucronatum* (34.58 mg/kg) (Fig 5). Concentrations

between 20 to 100 mg/kg in plants have been described as being excessive (Table 4).

**Recommending Agency/Country Cr Cu Ni Cd Fe Mn Zn WHO [24]** 100 30 80 NA NA NA 200 **Mexico (Agricultural soils) [25]** NA NA 1600.00 37.00 NA NA NA **USA [26]** 3, 000 4, 300 75.00 NA NA 7500 **Japanese MOE [27]** 250 NA NA 150 NA NA NA

**Austria [29]** 100 60 to 100 50 t0 70 1 to 2 NA NA NA **Germany [29]** 60 40 50 1 NA NA NA **France [29]** 150 100 50 2 NA NA NA **Luxembourg [29]** 100-200 50 to 140 30 to 75 1 to3 NA NA NA **Netherlands [29]** 30 40 15 0.5 NA NA NA **Sweden [29]** 60 40 30 0.4 NA NA NA **United Kingdom [29]** 400 135 75 3 NA NA NA

In the plant samples, the highest concentration of Cr was recorded in *Senna siberiana* (2.64 mg/ kg) in the dry season and *Englerina gralicinus* and *Terminalia mollis* (3.30 mg/kg) in the wet season (Fig 5). "Normal" concentration of Cr in plants is described as being from 0.1 to 0.5 mg/ kg, while concentrations between 5 to 30 mg/kg as "Excessive" and 75 to 100 mg/kg, "Phyto‐

Mean concentrations of Cu in the soil samples collected around the Zobe dam catchment was 29.66mg/kg in the dry season and 7.92 mg/kg in the wet season. Around the environs of KTSRM, the mean Cu concentration was observed to be 56.91 mg/kg in the dry season and 12.05 mg/kg in the wet season (Table 2; Fig 4). Only soil samples collected from the en‐ virons of KTSRM in the dry season were observed to have mean Cu concentration above the acceptable limits of the WHO (30 mg/kg), Germany, the Netherlands and Sweden (40

In plant samples collected, the highest concentration of Cu was observed in members of the genus *Diospyros, D. piscatoria*, 10.41 mg/kg and *D. mespiliformis* 10.40 mg/kg in the dry season. In the wet season, the concentration of Cu was generally higher in the plants, with the highest

**Table 3.** International Recommended Levels of Heavy Metals in Soils (mg/kg)

**Agriculture** 64 63 50 14 NA NA NA **Residential/Park** 64 63 50 10 NA NA NA **Commercial** 87 91 50 22 NA NA NA **Industrial** 87 91 50 22 NA NA NA

**Canadian CCME [28]**

704 Environmental Risk Assessment of Soil Contamination

NA — Not available

toxic" (Table 4).

mg/kg) Table 3).

**3.3. Copper**

Fig. 4. Seasonal variation in heavy metal concentration (mg/kg) in soils of Zobe dam catchment and the environs of Katsina Steel Rolling Mill (KTSRM)(**a**, Cu, Cr and Ni; **b**, Mn and Zn; **c**, Fe; and **d,** Cd). **Figure 4.** Seasonal variation in heavy metal concentration (mg/kg) in soils of Zobe dam catchment and the environs of Katsina Steel Rolling Mill (KTSRM)(a, Cu, Cr and Ni; b, Mn and Zn; c, Fe; and d, Cd).

9

**Table 4: Range Values of Heavy Metals in Vegetation (mg/kg)** 


**Table 4.** Range Values of Heavy Metals in Vegetation (mg/kg)
