Temporal and Spatial Variations on Heavy Metals Concentration in River Mojo, Oromia State, East Ethiopia

This study was aimed to reveal the temporal and spatial concentration variations of trace heavy metals in extreme wet rainy season, semi wet and semi - dry period (autumn), and extreme dry season (winter). The experimental results of this study unveiled that the level of As increases from the wet to dry periods of the year showing the dilution effects. Except for a single result, all analyzed results of As are above WHO Drinking Water Guidelines (DWG) (0.01mg/l). Cd pollution load is observed to be low in all study locations and sampling periods (mean value = 0.12 0.075mg/l). All the experimental results of Hg are significantly (p = 0.043, p less than 0.05) greater than the WHO/FAO set standards for fresh water (0.05mg/l) and maximum acceptable DW for livestock (0.003mg/l). The analytical results of Pb, pointed out that more than half the analyzed results are above the maximum permissible limit of WHO for DWG (0.01mg/l). The mean registered value for Cr was 2.515.94mg/l and half of the results lie below FAO set standard for surface water for irrigation (0.1mg/l) and WHO DWG (0.05mg/l) but all results fall above the FAO set standard for fresh water set standard (0.005mg/l). The findings warns that much care and precaution has to be taken especially on the use of water from River Mojofor vegetable irrigation, livestock watering and for different domestic uses by the local dwellers. Investigation on the implication of these high concentrations of heavy metals in water uptake by irrigated vegetables is decidedly recommended.