**3.2 Levels of heavy metals in little Akaki River water**

As presented in **Table 2**, the concentration levels of heavy metals (Pb and Cd) were ranged between (2.5–3.9 mg/L) and (0.03–0.4 mg/L) respectively. But Cr and Cu were found below the detectible concentration limits of the laboratory instrument (ICP-OES) in all three sampling locations along Little Akaki River. The detectible concentration limits of ICP-OES for both heavy metals (Cr and Cu) are 0.005 mg/L [18]. The result has revealed that the contamination level of the river water with Chromium and Copper was very low. Woldetsadik et al. has reported Cr (0.02– 0.029 mg/L) and Cu (0.028–0.039 mg/L) around Lekuanda and Mekanisa respectively and (Aschale, 2015) also reported Cr (0.0074 mg/L) and Cu (0.0056 mg/L)


**Table 1.** *The descriptive statics.* *Concentration Levels of Heavy Metals and Selected Ions in the Irrigation Water: The Case… DOI: http://dx.doi.org/10.5772/intechopen.103677*


#### **Table 2.**

*Concentration of heavy metals in (mg/L).*

around Kera [9]. This shows that previous studies also confirmed that the level of chromium and copper in the Little Akaki River was very low this is because the possible reasons are it could be the presence of hydrological process of the river water. In the natural aquatic environments or surface water, chromium does not persist for long in the dissolved states and is precipitated as a suspension in the river water and the soluble species of chromium are readily adsorbed by Phyto and zooplankton.


Cadmium ion found in the ranges between (0.03 and 0.4 mg/L) with an average value of 0.1566 mg/L (**Figure 2**). The study shows that cadmium was found extremely higher than the maximum recommended permissible limit of FAO (0.01 mg/L) guidelines for irrigation uses in the catchment irrigated areas.

In addition, the concentration of cadmium was very higher upstream around lekuanda (0.4 mg/L) and it has decreased downstream of the river around Gelan (**Figure 3**). This is because the possible reason is that the concentration of cadmium in the upper catchment is influenced by naturally occurring sources like weathering of parent materials, sources of soils, and rocks than the anthropogenic effects. Cadmium is also governed by the types and extent of land use in the catchment areas. However, cadmium is decreasing downstream of the river. This is due to the presence of

**Figure 3.**

*Concentration level of sodium ion in mg/L between sampling locations of little Akaki River stream.*

complex physic-chemical interaction and hydrological processes of the river water. The river flow rate also can determine the concentration of heavy metals, in a lower rate of river flow intensity, heavy metals become deposited at the bottom of the rivers and can be adsorbed with different suspended particulate matter that could be deposited in the bottom of the river flow while the heavy metals are transported in the longdistance along with the river flow. The other point is Cadmium concentration is highly influenced by the pH and other physic-chemical parameters of the river water. Because heavy metals like Cadmium are strongly adsorbent with the organic and inorganic matter in alkaline conditions. So, the analysis result also supported this assumption that pH, selected ions (chloride, Na, Ca, and Mg), TDS, and ECw are higher downstream of the river and they can influence the dissolution rate of cadmium downstream. Woldetsadik et al. has reported a similar trend of Cadmium concentration along the river streams that cadmium was higher in Kera (0.00282 mg/L) and Lafto (0.00148) but the very lower value of cadmium in Akaki (0.00033 mg/L) and it was also extremely lower than the current study result (0.03–0.4 mg/L) which indicated that the problem of cadmium concentration is progressively increasing in Little Akaki River water [9].

Lead (Pb) was also found in ranges between (2.5–3.9 mg/L) with an average value of (3.23 mg/L). The concentration level of lead was higher (3.9 mg/L) in the middle catchment around Gofa followed by the upper catchment in the lekuanda sampling location and it was lower downstream of the river (**Figure 4**).

This is because in the middle catchment the anthropogenic activities such as industries and other commercial activities are higher and lead is accumulated in the river water through various sources such as industrial emission; burning of lead-containing gasoline etc. the concentration of leads has been reduced to the down catchment it is because of different hydrological process and interaction of other physicochemical properties in the river water. The low-intensity water flow downstream can reduce its carrying energy causing lead has to be adsorbed on suspended particles and become deposited in the bottom of the river and river banks. The downstream river water is also diluted with different small tributaries which are joining to the main river stream at the down catchment. Factors such as pH, Alkalinity of water, TDS, and ECw affect the concentration of leads in the down catchment. In the downstream, the pH is relatively higher and has a slightly alkaline nature than the upper catchment. So, this slightly alkaline water content tends to the heavy metal ions converted to poorly soluble forms and to adsorb on the suspended matter in the river water. And heavy

*Concentration Levels of Heavy Metals and Selected Ions in the Irrigation Water: The Case… DOI: http://dx.doi.org/10.5772/intechopen.103677*

#### **Figure 4.** *Concentration levels of Lead ions between the sampling points across the little Akaki River streams.*

metals like leads have strongly adsorbent properties and can be retained at river banks, aquatic vegetation, hydro-engineering structures, suspended particles, and other solid bodies in the river water. pH above 7 in irrigation water sources inactivate the heavy metals and reduce their mobility and availability to crops (Office, F A O Regional and Cairo, 2003). However, under acidic conditions (pH < 7) heavy metals could be a problem. The correlation analysis (**Table 3**) also supported these assumptions because Pb is perfectly (100%) correlated with Alkalinity and has a negative association. Woldetsadik et al. have reported a similar trend along the river stream that the level of lead was higher in Lafto (0.0369 mg/L) and kera (0.0477 mg/L) whereas the value was lower in 0.0168 mg/L) in Akaki [9]. The result of previous studies has revealed similar concentration trends along the catchment of the Little Akaki River and their result was extremely lower than the current study result. This shows that the concentration of heavy metals especially Pb and Cd are progressively increasing in Little Akaki River irrigation water. And the current study shows that the existing concentration level of lead somehow seems to be hazardous for irrigation agriculture to produce vegetables because the value was found nearly lower than the maximum recommendation limits of FAO (5 mg/L) guidelines for irrigation water. So, however, currently, it was found below the permissible limits of FAO for irrigation water, the possible hazardous condition should not be overlooked because it is persistent and highly toxicant heavy metals to plants and human health even at lower concentrations.

### **3.3 Heavy metals variations between sampling locations**

Variation of heavy metals concentration levels between the three water sampling locations along Little Akaki River streams were tested with ANOVA and the result is illustrated in **Table 4**.

The research Hypothesis was that Ha: the concentration of heavy metals has a significant concentration variation between the sampling locations at 0.05. According to the ANOVA test, the alternative hypothesis is rejected because the F calculated value (1.079) is less than the F tabulated value (5.14325). So, it is confirmed that there is no statistically significant concentration variation of heavy metals (Pb and Cd) at 0.05 and 0.01 between the sampling locations along the river stream.


*\*Correlation is significant at the 0.05 level (2-tailed).*

*\*\*Correlation is significant at the 0.01 level (2-tailed).*

#### **Table 3.**

*Correlation coefficient.*


#### **Table 4.**

*The analysis of variation (ANOVA) for heavy metals.*

#### **3.4 Selected ions of water sample**

The concentration levels of selected ions such as chloride, calcium, Sodium, and Magnesium were presented in **Table 5**.

The concentration of chloride was varying between 284 to 394 mg/L with an average value of 334.66 mg/L in Little Akaki River irrigation water. The result revealed that the value of chloride was surpassed the maximum permissible limit


*Concentration Levels of Heavy Metals and Selected Ions in the Irrigation Water: The Case… DOI: http://dx.doi.org/10.5772/intechopen.103677*

#### **Table 5.**

*Selected ions in little Akaki River water (mg/L).*

of FAO for irrigation water (350 mg/L) in the middle catchment (**Figure 5**). The Excess amount of chloride in the middle catchment is due to domestic and industrial wastes have been discharged into the river streams. Chloride is originating from natural resources, sewage, and industrial effluents, excessive chloride concentrations increase rates of corrosion of metals in the irrigation structure system, The excessive chloride ions in irrigation water have great impacts on the accumulation of chloride ions in soil solution through long time irrigation uses and can affect the vegetable production since excessive chloride in soil solution is very toxic to plants.

#### **3.5 SAR and Sodium hazard**

The computed SAR value of the water samples ranged between 3.68 to 4.25 and it is found below the Maximum limits of FAO (6) for irrigation water (**Figure 6**). SAR of the irrigation water has explained the impact of sodium in the destruction of soil structure and water infiltration problems through the application of contaminated irrigation water for long periods. The computed value of the Na/Ca ratio from (**Table 6**) was 3.64. In this regard, however, the computed SAR value is lower than the maximum limit of FAO, sodium ions can cause toxicities to sodium-sensitive crops at a lower SAR value in sodium-dominated irrigation water (ratio of Na/Ca > 3:1). At a

#### **Figure 6.**

*Computed SAR between sampling locations across Little Akaki River stream.*


#### **Table 6.**

*Physic-chemical characteristics of Little Akaki River water (mg/L).*

given SAR value, the potential effect of sodium toxicity and soil water infiltration problems increases in sodium-dominated irrigation water (Na/ca >3:1).

Sodium-ion concentration was found in ranges between 66.32 and 87.9 mg/L with an average of 78.52 mg/L which is surpassed the maximum limit of FAO (69 mg/L) in the middle and downstream of the river for irrigation and the concentration is increasing to the downstream of the river (**Figure 3**). Sodium-ion concentration is told us the extent of its toxicity for plants. Therefore, according to the analysis result, sodium ion concentration is reached at the middle to slight restriction level for vegetable production in the study area because it has a significant toxicity effect on plants at higher concentration levels. The concentration of Sodium ions in the aquatic system is mainly derived from atmospheric deposition and silicate weathering [19].

#### **3.6 Variation of selected ions between sampling locations**

Variation of selected ions (Chloride, Sodium, Calcium, and Magnesium) concentration levels between the three sampling locations along the river streams were tested with ANOVA and the result is illustrated in **Table 7**.

The research Hypothesis was that Ha: the selected ions have a significant concentration variation between the sampling locations at 0.05. According to the ANOVA test, the alternative hypothesis is rejected because the F calculated value (1.538) is less than the F tabulated value (4.45897). So, it is confirmed that there is no statistically significant concentration variation of selected ions (Chloride, Na, Ca, and Mg) at 0.05 and 0.01 between the sampling locations along the Little Akaki River stream.

*Concentration Levels of Heavy Metals and Selected Ions in the Irrigation Water: The Case… DOI: http://dx.doi.org/10.5772/intechopen.103677*


**Table 7.**

*Analysis of variation (ANOVA) test for selected ions.*

#### **3.7 The physic-chemical characteristics of Little Akaki River water**

As indicated in **Table 6**, COD has been decreased downstream of the rivers from 295.6 mg/L at Lekuanda to 168.9 mg/L at Gelan. Whereas, the other parameters such as Alkalinity, pH, TDS, and EC were increased across the downstream (**Table 3**). This is because the COD content was diluted and attenuated across the path of the river course from upstream to downstream. The physical and chemical properties of the river water are characterized by several interdependent interactions and their relationships are extremely complex. The hydrological process is also the most determinant factor that influence the concentration of the physic-chemical parameters of the river water.

The pH value of water samples ranged between7.8 to 8.4 and it has a mean value of 8.01. The value of pH also increases downstream of the river this is because the alkalinity and ECw of river water also increase downstream of the river and have a significant contribution to raising the pH of the river water downstream because they have a positive correlation. Hence the result indicated that Little Akaki River irrigation water is slightly alkaline and it lies in the acceptable ranges of FAO guidelines (6.5–8.4). pH is the most determinant factor for the quality of irrigation water and it can greatly influence the toxicity of heavy metals and other impairing selected ions. Alkaline irrigation water prohibits the solubility and bioavailability of heavy metals.

Electrical conductivity (ECw) of the river water was varied between (288–1584 μS/cm) with an average of 791 μS/cm and the value was increased to the downstream of the river from 288 to 1584 μs/cm and it is found below the permissible limits of FAO (3000 μS/cm) for irrigation uses (**Figure 7**).

#### **Figure 8.**

*Levels of TDS in mg/L between sampling locations across Little Akaki River streams.*

The total dissolved solids (TDS) of water samples were varied between 198 and 1036 ppm with an average of 519 mg/L and it has a higher value in the downstream (1036 mg/L) and the concentration is decreased to the upstream of the river (**Figure 8**). TDS is found below the maximum recommended limit of FAO (1400–2000 mg/L) for irrigation water. But relatively the higher value is obtained downstream of the river and it indicated the presence of a higher amount of basic or alkaline compounds like bicarbonates, sulfates, chlorides, etc. In general, according to the result in (**Figures 7** and **8**), the value of EC and TDS illustrated that salinity is not a serious problem in the existing condition in Little Akaki River irrigation water.

#### **3.8 The variation of physic-chemical parameters**

Variation of physic-chemical parameters (COD, Alkalinity, pH, TDS, and ECw) between the sampling locations along the river streams were tested with ANOVA and the result is illustrated in **Table 8**.

The research Hypothesis was that Ha: the physic-chemical parameters have a significant concentration variation between the sampling locations at 0.05. According to the ANOVA test, the alternative hypothesis is rejected because the F calculated value (2.085346) is less than the F tabulated value (4.45897). So, it is confirmed that there are no statistically significant variations in the physic-chemical parameters (COD, Alkalinity, pH, TDS, and ECw) at 0.05 and 0.01 between the sampling locations along the Little Akaki River stream.


#### **Table 8.**

*Analysis of variation (ANOVA) for physic-chemical parameters.*

*Concentration Levels of Heavy Metals and Selected Ions in the Irrigation Water: The Case… DOI: http://dx.doi.org/10.5772/intechopen.103677*

**Figure 9.** *Correlations between TDS and ECw.*

#### **3.9 Correlation of heavy metals and other physic-chemical parameters**

The correlation analysis is conducted to show the relationship and interaction of heavy metals and other physic-chemical properties of the river water. The interaction between the heavy metals and other properties are the major factor for their concentration variations in the river water. Therefore, the correlation result is presented in **Table 3**.

The concentration of heavy metals and other selected ions were correlated with some physic-chemical interactions and different hydrological processes of the river water. The scatter plot analysis also depicted that ECw and TDS have positive associations and are strongly correlated with each other (**Figure 9**).

TDS concentration describes the presence of inorganic salts and organic matter in the irrigation water and EC is the measure of irrigation water capacity to conduct electric current. Both EC and TDS are very determinant irrigation water quality parameters, which are used to describe the salinity level of the irrigation water [20]. These two parameters are correlated and usually expressed by a simple equation: TDS (mg/L) = k\*EC (μS/cm in 25°C. The value of k will increase along with the increase of ions in water. However, the relationship between conductivity and TDS is not always directly linear; it depends on the activity of specific dissolved ions in the liquids and ionic strength [21].

Accordingly, the TDS/ECw ratio of the water samples in the Little Akaki River was = 519/791 = 0.656 or it can be written as equation TDS = 0.656\*EC. This indicates that the correlation of both parameters is strongly influenced by the EC values. Unlike freshwater, the correlation between TDS and EC in wastewater cannot be described well because the water is heavily influenced by many contaminants [21].
