Overview
Water samples collected at six stations along the Modjo River (Modjo Town to Koka Dam confluence, Ethiopia) show Cr(VI) concentrations above the FAO irrigation limit of 0.1 mg/L in reaches downstream of tannery effluent discharge. The river receives untreated or minimally treated wastewater from tanneries, abattoirs, poultry farms, and domestic waste, rendering it unsuitable for irrigation in lower reaches without treatment. The computed irrigation water quality index (IWQI) of 30.6 places the river in the medium suitability class, and sodium adsorption ratios (SAR 57.6 to 122.3) further indicate salinity and permeability hazards. This study is directly relevant to supply-chain risk for agricultural produce irrigated with tannery-affected river water in Ethiopia and similar sub-Saharan African industrial zones.
Key numbers
- Cr(VI) limit for irrigation (FAO): 0.1 mg/L
- Cr(VI) in lower reaches of Modjo River: above 0.1 mg/L (downstream of Ethiopia Leather Factory PLC effluent)
- SAR range across stations: 57.6 to 122.3
- IWQI: 30.6 (medium suitability class: 22–37)
- Six sampling stations from upstream bridge (1,742 m elevation) to terminal before Koka Dam (1,591 m elevation)
- Analytical method for Cr(VI): Palintest Chromicol colorimetric method (measures hexavalent Cr specifically)
- Composite samples collected in triplicate from three cross-sectional points per station
Methods (brief)
Physicochemical analysis of surface water per standard methods. Cr(VI) measured by Palintest Chromicol colorimetric method (hexavalent-specific). SAR calculated from Na, Ca, Mg concentrations in meq/L. IWQI computed as weighted sum of five hazard groups (salinity, permeability, specific ion toxicity, trace elements, miscellaneous effects). Cluster analysis and PCA performed on the full parameter dataset. Single-investigator study; limited temporal replication (sampling over one period, 2022).
Implications
Certification: Documents tannery-derived Cr(VI) contamination of irrigation water exceeding FAO limits; relevant to supply-chain risk assessment for crops irrigated with affected water in Ethiopia and comparable contexts. Courses: Concrete case study linking industrial effluent (tannery) to agricultural water quality failure; useful for supply-chain due-diligence curriculum. App: No direct food concentration data; informs supply-chain risk flags for Ethiopian-origin produce from tannery-adjacent regions. Microbiome: Not directly relevant.
Related evidence
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