An investigation on pollution intensity, risk release and bioavailability of heavy metals in aquatic fresh water,coastal zones and their relation with sediment characteristics(size and composition)
Executor of project: Dr. Raziye Lak
Project Associates: Dr. Ali Vosoogh - Prof.Dr.Mohsen Saeedi
Heavy metals are potentially toxic for environment and microorganism. Sediments in aquatic ecosystems(fresh or saline) can adsorb more parts of inorganic contaminants (heavy metals) and some organic pollutants.Some parameters like size.mineralogy and composition of sediments affect on heavy metals risk assessment and risk release.So,in this research,pollution intensity,risk release and bioavailability of heavy metals in aquatic fresh water and their relationship with sediments physical and chemical characteristies(size and composition) have been studied. In order to study,surface sediment samples from rivers(40 stations from 15 rivers),wetland (2stations from 2wetlands) and coastal sediments(5stations)have been collected. Physical(sediments size) and chemical(XRD and total concentration of heavy metals)were determined.Due to different geological formation,all of river sediments divided into two categories(east-central and west) by using fuzzy clustering and Fe,Al,Ca,Sr concentrations.At the next step, pollution intensities of sediments in different sizes calculated by cumulative ecological risk index(RI). The results showed that the maximum values of ecological risk index was for particle sizes 63-125 microns.In wetland sediments the greatest values was in particles under 38 microns. Ecological risk index for coastal sediments showed that the highest values of the samples blonges to stations near Anzali port. To determine risk release of sediments, seqeuntioal extraction experiments were perfomed on selected samples. Metals existence in different bonds.exchangeable,carbonate,Fe and Mn oxides,organic and residual have been shown in perncent. The results indicated that Cd had highest percentage of heavy metals in loosely bonds in river sediments less than 63 microns and for particles bigger than 63 microns.Pb and Co were the highes amounts.In the wetland sediments, the results were different with river sediments.In particles less than 63 microns,Cu,Cr.Cd,V and Co were the maximum participation with loosely bond.Ni and Pb in partiles bigger than 63 microns were the highest.Finally, because of high participations of Pb, Ni,Cd and Co in loosely bond, the mobility and thus the risk release of these metals were higher than other. For evaluating risk rease of metals in different sizes,modified risk assessment code(MRAC) has been used.In wetland sediments, the highest amount of mRAC was for particles less than 38 microns. Particles between 63-125 microns have a maximum mRAC amounts in coastal sediments. In the next step,bioavailability of size fractionated sediments were determined by single extraction with EDTA.