Sediment Contamination with Heavy Metals around Demolished Floriculture Farms of Central Ethiopia

Abstract

Assessing the sediment contamination with heavy metals; which indicates the contamination of fresh water ecosystem is one of the challenges strongly influence the sustainable development and ecosystem health in Ethiopia in general and in the central part of Ethiopia in particular. The main objective of this study was to investigate sediment contamination with heavy metals around Holeta and Sebeta demolished floriculture farms of central Ethiopia. The sediments from 30 sampling points were acid digested and the level of selected heavy metals: Cd, Pb, Cu, Zn, Ni, Cr, Co and Mn were determined by Flame Atomic Absorption Spectroscopy (Agilent technologies 200 series AA). Heavy metal pollution and their ecological risks in the sediment were assessed by Contamination factor, Pollution load index, geo-accumulation index and potential ecological risk index. The average metal concentrations (mg/kg) in the sediments were increased as follows: Cu<Co<Ni<Cr<Zn<Mn in both dry and rainy season. The spatial concentration (mg/kg) ranges of the trace metals were 3.1-34.8 for Cu, 1.9-71.4 for Co, 26.2-146.4 for Ni, 12.9-148.2 for Cr, 57.56-121.32 for Zn and 663.4-3579.4 for Mn. Except for Mn, the average concentrations of all selected heavy metals in the rainy season were higher than the dry season. In both seasons, almost the calculated geo-accumulation values indicated that the sediments from the 30 sampling points were found to be in the class 0, thus which observed in the uncontaminated standard level. The mean potential ecological risk index value for the study area was 11.27 for the dry season and 18.53 for the rainy season, indicating low ecological risk of the sediment with heavy metals. The contamination factor values of all selected heavy metals in the two seasons were observed between low contaminations to considerable contamination. In the rainy season the values of pollution load index were observed greater than 1(one) at many sampling points which indicates sediment was observed n the polluted standard level with heavy metals. The comparison of the mean concentration of examined heavy metals with sediment quality guidelines were reflects that, the sediments were moderately polluted to heavily polluted with Ni and Cr in both dry and rainy seasons. These pollution status in study area would not stay static, as floriculture activity continuous and waste control mechanisms have less attention, more pollution was emerging; even the activity is finished, residues of wastes could be contaminate the stream ecosystem as a whole. To establish sustainable conditions for the society around the demolished floriculture industries and reduce ecological risks, an immediate plan for mitigation and remediation and the periodic monitoring are must be carried out.