Potentially Toxic Trace Element Contamination of the Little Akaki River of Addis Ababa, Ethiopia

In this study, river water samples taken from 26 different locations along the course of the Little Akaka River in Addis Ababa were analyzed to determine potentially toxic trace element concentrations. The mean concentrations in ?g L-1 for Mn 1540.04, Fe 1075.92, B 383.04, Sr 336.75, Ba 132.17, Cr 67.04, Sb 42.80, Zn 25.50, Ni 6.66, Cu 5.61, V 4.87, Pb 3.13, Co 2.62, As 1.46, Cd 0.06 and Hg <0.05. Overall metal concentration were in the order Mn > Fe > B > Sr > Ba > Cr > Sb > Zn > Ni > Cu > V > Pb > Co > As > Cd > Hg. A strong positive correlation was observed between several of the trace elements indicating common sources. The concentrations of Cr, Mn, Sb, B and Pb exceeded the permissible limits of the Ethiopian, European Community and WHO for drinking water quality guidelines. Fe and Sr exceeded the permissible limits of the Ethiopian drinking water guideline and Sr exceeded the WHO thresholds. The concentration of Cr, Zn, Cu and Pb exceeded the annual average thresholds for surface waters set in SI 272 of 2009. The concentration of Cr, Mn and Sr were also higher than the international guidelines value for irrigation water. The pollution of the river water is increasing alarmingly and poses serious threat to human health. Many of the concentrations were higher than previously reported. It is, thus, necessary to take serious and essential measures from the concerned bodies. Adoption of adequate measures to remove the heavy metal load from the industrial waste water and upgrading of sewage treatment plants are suggested to avoid further deterioration of the river water quality. Keywords: River water, Potential toxic elements, Heavy metal contamination, Drinking water standard

Assessment of Potentially Toxic Elements in Vegetables Grown along Akaki River in Addis Ababa and Potential Health Implications

The present study was carried out to assess contamination of vegetables from five farmlands in Addis Ababa with toxic and potentially toxic elements (Cd, Pb, As, Cu, Zn, Cr, Co, Ni, Ba, B, Sr, V, Fe and Mn) and health risk concerns to consumers of these vegetables as well as farm soils and water used to irrigate the vegetables. Pollution levels were varied with metals and vegetable types. The average total metal accumulation (mg kg-1) in the vegetables was potato (245.54) > carrot (202.20) > Swiss chard (52.42) > lettuce (47.43) > cabbage (38.04) > Ethiopian kale (30.17). Results also revealed that the average concentrations (mg kg-1) of all elements in the vegetables were found in order of Pb (744.10) > Fe (288.5) > Mn (51.66) > Sr (50.12) > Zn (38.81) > Ba (35.51) > B (21.65) > Cu (7.95) > Cr (1.97) > Ni (1.14) > V (0.54) > Co (0.20) > As (0.08) > Cd (0.08). Many of the concentrations were higher than previously reported. The average metal concentration (mg kg-1) of vegetables by farm was Burayu (136.58) > Akaki (125.00) > Kolfea (54.19) > Goffa (37.11) > Kera (29.40). The concentration of Cr, Cd, Pb and Fe in most vegetables surpassed the maximum recommended levels. From health standpoint consuming lettuce, Swiss chard, carrot and potato may cause serious health risk to consumers than cabbage and Ethiopia kale due to the high level of toxic metal accumulation. Elevated levels of some heavy metals were detected in the soil and irrigation water (Cd, Pb, As, Cu, Zn, Cr, Co, Ni, Ba, B, Sr, V, Fe and Mn) suggesting contamination from various the industrial and municipal discharges to the local river network. The present study highlights the immediate need for proper treatment and disposal of wide range of effluents and waste materials that currently enter the Akaki River and its tributary and farmlands as well as regular monitoring of potential contaminants in soil, water and vegetables and enforcement of standards. Keywords: Potentially toxic elements, contamination, plant uptake, health ris