Assessing the Industrial Effluent Effect on Irrigation Water Quality and Farm Soil near Kombolcha Town, Ethiopia

Department of Hydraulic Engineering, College of Architectural and Civil Engineering, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia Department of Environmental Engineering, College of Biological and Chemical Engineering, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia Department of Biotechnology, College of Biological and Chemical Engineering, Addis Ababa Science and Technology University, Addis Ababa 16417, Ethiopia


Introduction
Water is one of the most important natural resources essential for the survival of all living things including human beings. Irrigation is a vital use, but some dissolved or suspended substances found in water affect its suitability. e scarcity of surface and groundwater for irrigation is also an ever-increasing problem around the world. In many lowincome countries, wastewater is discharged commonly into water bodies with little and no treatment as there are limited treatment facilities [1]. e use of wastewater for agriculture chemical, and biological properties [7]. Irrigation by effluents containing high salinity made soil secondary salinization easy and enhanced total alkalinity and sodium alkalinity sharply in the soil, causing soil hardening and soil permeability decrease [8]. e problem seems to exacerbate in the town, where farmland soil type is clay, compared to other types which state low-quality irrigation water is hazardous on clay soil [9,10], while the same water could be used satisfactorily on the sand and/or permeable soils.
In Ethiopia, urbanization and industrialization are occurring rapidly throughout the year [11]. Due to the rapid increase in the urban population, urban agricultural activities are being recognized as an important source of food, nutrition, and income for the urban poor. However, irrigation is challenged with a lack of water, and the experience of using polluted rivers for irrigation is becoming a common practice near urban areas. In Kombolcha town of Ethiopia, the "Worka" and "Leyole" rivers, tributaries of the "Borkena" river, have been receiving untreated industrial effluents directly or indirectly, and local farmers are irrigating without any treatment. For instance, the electric conductivity (EC) for the steel processing effluent was found to be higher compared to the other industries (i.e., steel products industry � 4000µS/cm, textile industry � 800µS/cm, tannery industry � 2200µS/cm, and BGI brewery industry � 2100µS/ cm) [12].
Moreover, results indicated that median concentrations of Cr in the tannery effluent and Zn in the steel processing effluents were as high as 26,600 and 155,750 µg/l, respectively, much exceeding both the United States Environmental Protection Agency (USEPA) and the Ethiopian emission guidelines. Cu concentrations were low in all effluents, whereas Pb concentrations were high in tannery effluents [12]. e quantification of the pollutants found both in irrigation water and farm soil is an important aspect. Additionally, more industries are being installed which will increase the amount of wastewater with high pollution load unless properly treated. ere is no research done for the specified site in identifying the concentration of the pollutants both in irrigation water and farm soil. Hence, the main objective of this study is to assess the effect of industrial effluents on the quality of Borkena river irrigation water and farm soil for selected parameters.

Area Description.
e study area is found near Kombolcha town located in the north-central part of Ethiopia placed immediately southeast of Dessie town in the Amhara Region. It is 377 km away from Addis Ababa (capital city) and is geographically located at 11 o 06′N, 39 o 45′E. River Borkena, which crosses the town, receives industrial effluents indirectly through its tributaries named "Worka" and "Leyole." Most of the industries are found close together in the middle of the town near the tributaries of Borkena ( Figure 1).
e Kombolcha basin has a semiarid climate with an average annual rainfall of 1,030 mm, and the mean annual monthly temperature ranges from 24°C in January to 28°C in August. Kombolcha has two wet seasons, with the early wet season from February to April and later in the summer from July to September. e rains in the early wet season have been very low in recent years because of recurrent droughts with high annual potential evapotranspiration, reaching up to 3,050 mm/year in 2018. e rainfall in the wet season of June to September has remained relatively heavy and extensive (with a monthly average of 710 mm) compared with the early wet season (having an average rainfall of 130 mm) [13]. e landform of the study area includes rolling and undulating hills, with high plateaus to the west, the graben in the center, and the southward sloping ground to the Borkena River. e elevation of the land ranges from 1,750 m above sea level in the alluvial plain up to greater than 2,000 m above sea level in the uplands. Large parts of the built-up areas of the Kombolcha city have slope from 2.6% to 10%, and the slope of the hilly area increased to greater than 20%. e local soils comprise alluvial/lacustrine deposits covering a large part of the town, with fluvisols at the banks of the tributaries of Borkena, colluvial screed deposits found mostly at the foot of hilly areas of the town and where Cambisols are developed, and Vertisol on the top of the alluvial or colluvial deposits, and covering most parts of the catchment areas [12].

Water and Soil Sampling
Method. Samples of irrigation water and farmland soils were collected within one irrigation period, in three months, of the study area. Guidelines for Interpretation of Water Quality for Irrigation standard [14] and calibrated instruments were used during sample collection. Two sampling points, one in the upstream and the other in the downstream, were selected, i.e., upstream (A * ) Guragoye and downstream (B * ) Workiya, as shown in Supplementary Table S1. Composite water samples were taken from the two sampling locations, i.e., from the upstream and downstream of the Borkena River, between April and June. e intention was to characterize during the wet period (June) and the dry period (May). Representative soil samples were collected randomly using shovel slices at 20 different spots within the demarcated farmlands. One surface composite sample was collected in each irrigation phase, and a total of 3 composite surface samples were collected from the downstream-irrigated farmland. One composite surface soil sample from 20 different spots was collected for the upstream-irrigated farmland as the control. e samples were collected in a plastic bucket, and after thoroughly mixed, 0.5 kg of composite soil samples was used. Subsurface soil samples were collected from a 5 m × 5 m area by digging a V-shaped cut. ree pits were dug downstream of the farmland randomly, which is representative of the farmland soil sample. Nine soil samples were taken from the downstream-irrigated farmland in one irrigation phase within different depths (from 0 to 30 cm, 30 to 60 cm, and 60 to 90 cm). Totally, 27 subsurface soil samples were taken in three irrigation phases (one crop life) from the three pits' excavated area at the downstream irrigation farmland. ree subsurface soil samples were taken from the upstream-irrigated farmland as a control in the 2 nd irrigation phase. Finally, samples of 500 gm soil were collected at 30 cm intervals along with the depth. e summary of water and soil samples collected in the study area is presented in Supplementary Table S2.

Physicochemical Analysis of Water and Soil Samples.
pH, electric conductivity (EC), calcium (Ca +2 ), magnesium (Mg +2 ), sodium (Na + ), chloride (Cl − ), alkalinity, and heavy metals were analyzed by following the standard procedures as outlined by USSL staff [15]. Total dissolved solids (TDS) and sodium absorption ratio (SAR) were calculated by formulas suggested in the FAO [14]. e physicochemical characteristics of the collected water samples were analyzed using the standard method [16]. e methods of physicochemical analysis of water and soil samples are summarized in Table 1.

Statistical
Analysis. SPSS statistical software version 18 was used to determine the descriptive statistics to obtain the means, standard deviations, and coefficient of variances. e mean comparison was done using a t-test to find out whether there was any significant difference, at a 95% confidence interval, between the calculated means.

Chemical Characteristics of Sampled Water.
Physicochemical characteristics of downstream Borkena water quality in different irrigation phases and during the dry and wet season are reported in Tables 2 and 3, respectively. Most of the parameter results were above the permissible limit of the FAO [14] standard (Table 4) except Ca + , Fe, Mn, Pb, and SAR during April at different irrigation levels as there was no rainfall, but water sampled from the downstream of Borkena was below the permissible limit of irrigation water quality, in the wet (June) period, except for the concentration of CO 3 −2 and HCO 3 -. e EC of downstream Borkena irrigation water had 0.77, 0.67, and 0.68 dS/ m and 1.25, 1.05, and 1.15 dS/m during wet and dry periods at different irrigation phases. High EC value is predominant with Na + and Cl − concentrations [17]. e highest EC (1.15 dS/m) value was recorded during the dry period, and the lowest was 0.48 ds/m at the upstream which is below the permissible limit of the FAO. In general, downstream Borkena irrigation water exceeds the permissible limit of the FAO standard (Table 4).
As shown in Table 3, the mean values of CO 3 −2 and HCO 3 for downstream irrigation water were 1.75 mg/l and 10.22 mg/l during the dry period and 0.95 mg/l and 8.15 mg/l for the wet period. e results were above the permissible limit of the FAO's irrigation standard. High alkalinity concentration in irrigation water causes Ca +2 and Mg +2 ions to form insoluble minerals, leaving sodium as the dominant ion in the solution [18]. Mean pH at downstream Borkena irrigation water was 8.72 and 8.42 for dry and wet periods, respectively. e value of pH during the dry period was higher than the wet period (8.65-8.75), which is above the FAO irrigation water quality standard (6.5-8.4). High pH values are often caused by high CO 3 −2 and HCO 3 concentrations known as alkalinity [19,20]. pH values of 4 or less and 12 or high cause death to most fish Journal of Chemistry species [21,22].
e observed values reflected that downstream Borkena irrigation water is unsuitable for irrigation purposes. e concentrations of heavy metals for the selected site are reported in Table 3. Results showed that higher concentration was recorded during the dry period except for Mn, and Cr showed high seasonal variation. e higher concentration of Fe, Pb, Cu, Cr, and Cd during the dry period might be due to no dilution as there is no rainfall. Similarly, Islam et al. [23] reported that Cd, As, Cr, Cu, Pb, and Ni are identified as the priority control metals. erefore, this study provides quantitative evidence demonstrating the critical need for strengthened wastewater discharge regulations.

Characteristic of Water Quality Parameters in the ree Irrigation Phases.
e result in Table 2 shows the physicochemical characteristics of downstream Borkena irrigation water. e samples taken in the 2 nd irrigation phase had higher concentrations and were above the permissible limits of the FAO's standard. is is due to the lack of rainfall and industrial effluents released directly to the Borkena River without being diluted with rainwater. In the 3 rd irrigation phase, water sampled from downstream Borkena was below the permissible limit of irrigation water quality except for the concentration of CO 3 −2 and HCO 3 -. Minimum concentration was recorded in this period due to the dilution with rainwater, and the medium value was recorded in the 1 st irrigation phase (Table 2).   Journal of Chemistry e average physicochemical characteristics of water from upstream and downstream Borkena are presented in Table 4. pH, both in upstream and downstream, was higher than the limit values; Mg +2 � 5.27 me/l, CO 3 −2 � 1.25 me/l, HCO 3 -� 9.10 me/l, Cu � 0.21 mg/l, Cr � 0.31 mg/l, and Cd � 0.03 mg/l were above the permissible limit of the FAO's irrigation water quality standard. e mean concentration of EC � 0.96 ds/m, Na + � 3.35 me/l, Cl − � 7.67 me/l, and TDS � 612.98 mg/l is a moderate restriction for irrigation, and the value of Fe is very close to the limit (Table 4). e others are below the permissible limit of the FAO's standard. However, prolonged application of this water under a poorly managed irrigation system could lead to the accumulation of these elements in the soil profile [23,24]. Table 5 presents the t-test comparison of upstream and downstream water quality, and there were significant differences (at p ≤ 0.05) for the mean concentration of Mg +2 , Cl − , Pb, and Cu. However, there were no significant differences for pH, EC, Ca + , Na + , HCO 3 -, CO 3 −2 , Fe, Mn, Cr, Cd, Ni, and TDS.

Levels of Pollutants in the Farm Soil.
e physicochemical characteristics of sampled soils from the downstream of Borkena irrigated farmland in different irrigation  phases and different depths are presented in Table 6. e average concentration of physicochemical parameters during the dry period (May) in the 2 nd irrigation phase is higher than from the rain period (June). is is because industrial effluents are discharged without being diluted with rainwater and might be due to the weak adsorption nature in the soil. e concentration of pH, CO 3 −2 , HCO 3 -, and SAR is increasing within the depth. However, the concentration of EC, Mg +2 , Ca +2 , Na + , Cl − , Fe, Mn, Pb, Cu, Cr, Cd, and Zn is decreasing along with the depth. is shows the movement of the chemical parameter, especially for heavy metals, is very slow, and the seepage level is minimal [25].
According to the FAO soil classification, soils showing EC < 0.7 ds/m, ESP < 15%, SAR<10, and pH from 6.5 to 8.5 are classified as normal soils. e average concentration of EC ranges from 0.8 to 0.9 ds/m during the dry period and from 0.6 to 07 ds/m during the rainy period but decreased along with the depth during the dry and rainy period. is shows that the EC of the downstream of Borkena irrigated farmland soil is a moderate restriction for irrigation (i.e., above the permissible limit of the FAO). e CO 3 −2 concentration ranges from 0.9 to 0.5 me/l during the dry and rainy periods which is above the permissible limit of the FAO. Generally, the concentrations of CO 3 −2 , Cr, and Cd were above the permissible limit of the FAO. However, the average concentrations of Mg +2 , Ca + , Na + , Cl − , pH, HCO 3 −2 , Fe, Mn, and Pb were below the permissible limit of the FAO. Similarly, Kumar and Chopra [26] reported the increment of the concentrations of pH, EC, Cl − , HCO 3 -, CO 3 2-, Na + , K + , Ca 2+ , Mg 2+ , Fe 2+ , Zn, Cu, Cd, Pb, and Cr in the soil after irrigating with paper mill effluent for 12 weeks. Other studies also reported the increase in the concentrations of Ca, K, and Mg in the soil due to the wastewater application in irrigation [27,28].

Effect of Industrial Effluent on the Irrigated Farm Soil.
As shown in Table 4, the salt concentration in the downstream of Borkena irrigation water was 0.96 ds/m which is a : bicarbonate; Mg +2 : magnesium; Mn: manganese; Na + : sodium; Ni: nickel; Pb: lead; SAR: specific absorption rate; TDS: total dissolved solids; < L.D: less than the limit of detection; F: statistics computed from sample variance for Levene's test; Sig.: significance; t: value of t-test (single value obtained after reduction of the entire sample by the t-test procedure); df: degree of freedom; Sig. (two-tailed): significance for two-tailed test.
slightly moderate restriction on its use. In the case of the soil sample, the value of EC ranges from 0.67 to 0.79 ds/m. erefore, based on EC values of irrigation water, it is a slightly moderate restriction for irrigation, and a moderate salinity problem was developed which required leaching. SAR (8.59 to 8.68) value of water in downstream Borkena irrigated farmland soil samples showed no restriction for use. Soils with SAR values greater than 10 are usually considered sodic. According to the FAO soil classification of the normal soil, as stated above, results of the downstream Borkena irrigated farmland soils are considered normal. Other studies reported that the accumulation in soil was insignificant compared to being added, and a difference might be only noticeable in the long term [29][30][31][32].    e mean value of physicochemical characteristics of the soil sampled in different irrigation phases in different sample stations from the upstream-and downstreamirrigated farmland is presented in Table 7. e result shows that the concentration of CO 3 −2 , HCO 3 -, Cr, Cd, and Ni was above the permissible limit of the FAO and not suitable for irrigation. In the case of cations, Na + is the dominant ion followed by Ca +2 and Mg +2 . e concentration of pH, CO 3 −2 , HCO 3 -, and SAR was increased, while the others decreased with depth. For this study, the order of heavy metals' concentrations is observed as follows: Fe > Cu > Pb > Cu > Mn > Cr > Cd > Zn. However, Marr et al. [33] reported Fe was the highest, while Cd was the least, Kumar and Chopra [26] reported the order of Pb > Cr > Cd > Zn > Cu after reirrigating with paper mill effluent for 12 weeks, and Tiwari et al. [34] reported the order of Fe > Mn > Zn > Cd > Cu > Pb > Cr > As after irrigating with industrial wastewater. e difference might be due to the differences in the wastewater characteristics used for irrigation and farm soil property. Generally, the long-term application of untreated and treated wastewater has resulted in the increment of pollutants in the soil [35][36][37].

Conclusions
e present study concludes that the industrial effluent drained to the Borkena River has affected the quality of irrigation water and farm soil.
e river water quality of downstream showed higher concentrations of EC, Mg +2 , pH, CO 3 −2 , HCO 3 −2 , Cu, Cr, Cd, and TDS which were above the permissible limit of the FAO. Higher concentrations of heavy metals were also recorded during the dry period except for Mn, but Cr showed high seasonal variation. e soil analysis showed higher concentration of CO 3 −2 , HCO 3 -, Cr, Cd, and Ni which was above the permissible limit of the FAO. In the case of cations, the dominancy is in the order of Na + > Ca +2 > Mg +2 . Along with the depth of the soil, the concentration of pH, CO 3 −2 , HCO 3 -, and SAR increased, and the order observed for heavy metals was Fe > Cu > Pb > Cu > Mn > Cr > Cd > Zn. Generally, there are significant (at p ≤ 0.05) differences for the mean value of Mg +2 , Cl − , Pb, and Cu. e seasonal water application had some slight influence on soil chemical properties, i.e., the concentration of cations (Na + , Ca +2 , and Mg +2 ) was slightly lower than those in the dry period. Soils in the dry period, however, exhibited higher pH and HCO 3 than those in the wet period. Hence, prolonged application of the polluted river under a poorly managed irrigation system could lead to the accumulation of these elements in the soil profile. To alleviate the problem, industries should be forced to treat their wastewater to the standard.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare no conflicts of interest.