Using Pollution Load Index (PLI) and Geoaccumulation Index (I-Geo) for the Assessment of Heavy Metals Pollution in Tigris River Sediment in Baghdad Region

Abstract

Six stations along Tigris river in Baghdad region were chosen to collect and assess the Mn, Ni, Pb, Cu and Cd contamination in sediments by using pollution load index (PLI) and geo-accumulation index (I-geo). Cd was found at the lowest concentration ranged between 0.3-1.3 µg/g dry weight. Whereas, Mn was the highest ranging between 166 -426 µg/g dry weight. Geo-accumulation index indicates that the sediment in the most of studied stations were slightly polluted (grade 1) with respect to Pb and Cd, while the sediments in all studied stations were unpolluted (grade 0) with respect to Mn, Cu and Ni. The values of Pollution Load Index (PLI) were found to be very low, and varied between 0.301-0.970, indicating that the studied stations in Tigris river were unpolluted by total of studied heavy metals. Introduction In the recent past, there have been increasing interests regarding heavy metal contaminations in the environments, apparently due to their toxicity and perceived persistency within the aquatic systems (1). There are basically three reservoirs of metals in the aquatic environment: water, sediment and biota (2). The analysis of river sediment is a useful method of studying environmental pollution with heavy metals (3,4). Heavy metals accumulate in the sediments through complex physical and chemical adsorption mechanisms depending on the nature of the sediment matrix and the properties of the adsorbed compounds (5). The occurrence of elevated concentrations of trace metals in sediments found at the bottom of the water column can be a good indicator of man induced pollution rather than natural enrichment of the sediment by geological weathering (6). The assessment of sediment enrichment with elements can be carried out in many ways. The most common ones are the index of geo-accumulation (I-geo) and pollution load index (PLI). The I-geo has been widely utilized as a measure of pollution in freshwater sediment (7), while the pollution load index (PLI) represents the number of times by which the heavy metal concentrations in the sediment exceeds the background concentration, and gives a summative indication of the overall level of heavy metal toxicity in a particular sample (8). Concentrations of metals in sediment of the Iraqi waters have been documented by (9, 10, 11, 12 and 13). This study can be considered the first attempt to evaluate the heavy metals pollution in sediments of Tigris River sediment by using pollution load index and geo-accumulation index.