assessment of sources and concentration of metal contaminants in marine sediments of musa estuary, persian gulf

introduction we can obtain useful information about aquatic systems by studying heavy metals in surface sediments. marine sediments can bring out the aquatic contamination. due to heavy metal toxicity, hard biodegradation and easy bioaccumulation in aquatic ecosystems, various indices have been developed such as sediment quality guidelines (sqgs), enrichment factor (ef), pollution load index (ipoll) and index of geo-accumulation (igeo). sediment-bound heavy metals may be desorbed from surface sediment and accumulated on fine grained particles which finally move into the depositional. grain size is an important factor to evaluate heavy metals concentration in the sediment. the recommended size for particles is cr(43%) > co(34%) > sr(33%) > ni(31%) > mn(24%) > zn(19%). the values obtained from ipoll index are indicative of a broad range (from no pollution to strong pollution) for various studied elements. cluster analysis (ca) is a statistical method which identifies the group of samples that behave similarly or show a significant relationship between different clusters.   figure 1. dendrogram showing clustering of metals and loi based on dendrogram, three distinct clusters are identifiable: (a) loi-cu, (b) co-zn-al-cr-ni, and (c) as-ba-mn-sr. the cluster analysis revealed that ni joined to cr by high similarity coefficient which indicates that cr could be originated from oil sources. dendrogram also shows that a part of cr and ni are derived from lithogenous source as they are linked to al. pearson coefficient amongst zn, al, and ni shows that zn is probably originated from both lithogenous and oil sources. sr and mn joined together with a relatively high coefficient that is indicative of a common source. since loi is linked with the other clusters at an insignificant level, it can be inferred that the organic contents do not play a major role in elemental concentrations. in order to consider the possible additive toxicity effects of the combined toxicant groups in different concentration, mean sqg quotients were calculated as follows:                                                                                                             (4) where, ci is the sediment concentration of compound i, ermi is the respective effect range median for compound i and n is the number of compound i. based on the classification of metals contamination, all sediment samples can be categorized as medium-low priority sites with 30% probability of toxicity. conclusion the mean enrichment factor values for various metals were between minimal and extremely high enrichment. the maximum mean ef value was for as (as=42.6) showing the extremely high enrichment, and also the minimum mean ef value was for co (co=1.2) indicating the minimal enrichment. the unpolluted igeo designation is obviously not confirmed by the other methods for calculating the metal pollution impact in musa estuary. a considerable amount of cu and cr was found in lithogenous portion. the results of partitioning studies revealed that the arrangement of anthropogenic portions for the metals are as follows: cu (96%) > cr(43%) > co(34%) > sr(33%) > ni(31%) > mn(24%) > zn(19%). the ca revealed that ni joined to cr by high similarity coefficients, which is indicative of oil origin for these two elements.