Speciation characteristics, ecological risk assessment, and source apportionment of heavy metals in the surface sediments of the Gomishan wetland.

Metal contamination is one of the worldwide environmental issues. The main aim of this study was to evaluate the concentration, probable environmental risk, and source of investigated elements (Al, As, Co, Cr, Cu, Fe, Mn, Ni, and Zn) in sediments and water of the Gomishan wetland. Sediment contamination indices revealed sediments were solely polluted by As. The potential ecological risk index (RI), toxic risk index (TRI), and chemical speciation assessments indicated no major ecological hazards for investigated metals. Correlation analysis and principal component analysis (PCA) indicated that all studied metals in the Gomishan wetland sediments derived from natural sources. HPI, and HEI indices showed that the water quality in terms of hazardous components was inappropriate for aquatic life.

Simultaneous dairy wastewater treatment and bioelectricity production in a new microbial fuel cell using photosynthetic Synechococcus / Tratamiento simultáneo de aguas residuales lácteas y producción de bioelectricidad en una nueva celda de combustible microbiana utilizando Synechococcus fotosintético

Photosynthetic microbial fuel cell (PMFC) is a novel technology, which employs organic pollutants and organisms to produce electrons and biomass and capture CO2 by bio-reactions. In this study, a new PMFC was developed based on Synechococcus sp. as a biocathode, and dairy wastewater was used in the anode chamber. Different experiments including batch feed mode, semi-continuous feed mode, Synechococcus feedstock to the anode chamber, Synechococcus-Chlorella mixed system, the feedstock of treated wastewater to the cathode chamber, and use of extra nutrients in the anodic chamber were performed to investigate the behavior of the PMFC system. The results indicated that the PMFC with a semi-continuous feed mode is more effective than a batch mode for electricity generation and pollutant removal. Herein, maximum power density, chemical oxygen demand removal, and Coulombic efficiency were 6.95 mW/m2 (450 Ω internal resistance), 62.94, and 43.16%, respectively, through mixing Synechococcus sp. and Chlorella algae in the batch-fed mode. The maximum nitrate and orthophosphate removal rates were 98.83 and 68.5%, respectively, wherein treated wastewater in the anode was added to the cathode. No significant difference in Synechococcus growth rate was found between the cathodic chamber of PMFC and the control cultivation cell. The heating value of the biocathode biomass at maximum Synechococcus growth rate (adding glucose into the anode chamber) was 0.2235 MJ/Kg, indicating the cell’s high ability for carbon dioxide recovery. This study investigated not only simultaneous bioelectricity production and dairy wastewater in a new PMFC using Synechococcus sp. but also studied several operational parameters and presented useful information about their effect on PMFC performance.(AU)

Development and application of novel risk indices for assessing heavy metal pollution in aquatic sediments.

This study presents the development of a new sediment individual risk index (SIRI) and sediment complex risk index (SCRI) to assess heavy metal pollution in Anzali Wetland sediments. SIRI incorporates total metal concentrations, bioavailability, and sediment quality guidelines. SCRI, derived through principal component analysis (PCA), integrates SIRI for a comprehensive risk assessment. The newly developed indices were systematically classified. Results showed varying risk levels with SIRI values of Zn, Cr, Cu, Pb, Ni, As, Cd, and Hg as 0.82, 1.32, 0.98, 0.71, 1.41, 1.37, 0.79, and 0.79, respectively. Pb, Cd, and Hg posed very low risk, Cu and Zn posed low risk, and Cr, Ni, and As posed moderate risk. SCRI yielded an index value of 1.02, indicating a moderate level of risk for the studied stations. Pearson correlation analysis validated SCRI with a highly significant and strong correlation coefficient (0.923) with metal bioavailability, serving as a risk indicator.

Investigating heavy metal pollution in Anzali coastal wetland sediments: A statistical approach to source identification.

In this study, the pollution and bioavailability of heavy metals in the sediments of Anzali Wetland were measured by analyzing data from sequential chemical extraction of sediments, risk assessment code (RAC), and sediment pollution indices. The average RAC results indicated that the risk from Zn, Cr, Cu, and Hg was low, while the risk from Pb, Ni, As, and Cd was moderate. To identify the sources of heavy metal pollution in the sediments of Anzali Wetland, multivariate statistical techniques such as Pearson correlation analysis, cluster analysis (CA), and principal component analysis (PCA) were employed. The results of the statistical analyses at a high significance level revealed that Zn, Cr, Cu, Pb, Ni, and As were attributed to natural sources. Additionally, the statistical analyses demonstrated that the concentrations of Cd and Hg in the sediments of Anzali Wetland were influenced by non-oil organic sources and atmospheric deposition, respectively.

Simultaneous dairy wastewater treatment and bioelectricity production in a new microbial fuel cell using photosynthetic Synechococcus.

Photosynthetic microbial fuel cell (PMFC) is a novel technology, which employs organic pollutants and organisms to produce electrons and biomass and capture CO2 by bio-reactions. In this study, a new PMFC was developed based on Synechococcus sp. as a biocathode, and dairy wastewater was used in the anode chamber. Different experiments including batch feed mode, semi-continuous feed mode, Synechococcus feedstock to the anode chamber, Synechococcus-Chlorella mixed system, the feedstock of treated wastewater to the cathode chamber, and use of extra nutrients in the anodic chamber were performed to investigate the behavior of the PMFC system. The results indicated that the PMFC with a semi-continuous feed mode is more effective than a batch mode for electricity generation and pollutant removal. Herein, maximum power density, chemical oxygen demand removal, and Coulombic efficiency were 6.95 mW/m2 (450 Ω internal resistance), 62.94, and 43.16%, respectively, through mixing Synechococcus sp. and Chlorella algae in the batch-fed mode. The maximum nitrate and orthophosphate removal rates were 98.83 and 68.5%, respectively, wherein treated wastewater in the anode was added to the cathode. No significant difference in Synechococcus growth rate was found between the cathodic chamber of PMFC and the control cultivation cell. The heating value of the biocathode biomass at maximum Synechococcus growth rate (adding glucose into the anode chamber) was 0.2235 MJ/Kg, indicating the cell's high ability for carbon dioxide recovery. This study investigated not only simultaneous bioelectricity production and dairy wastewater in a new PMFC using Synechococcus sp. but also studied several operational parameters and presented useful information about their effect on PMFC performance.

Health risk assessment and source apportionment of potentially toxic metal(loid)s in windowsill dust of a rapidly growing urban settlement, Iran.

Rapid industrialization and urbanization have resulted in environmental pollution and unsustainable development of cities. The concentration of 12 potentially toxic metal(loid)s in windowsill dust samples (n = 50) were investigated from different functional areas of Qom city with the highest level of urbanization in Iran. Spatial analyses (ArcGIS 10.3) and multivariate statistics including Principal Component Analysis and Spearman correlation (using STATISTICA-V.12) were adopted to scrutinize the possible sources of pollution. The windowsill dust was very highly enriched with Sb (50 mg/kg) and Pb (1686 mg/kg). Modified degree of contamination (mCd) and the pollution load indices (PLIzone) indicate that windowsill dust in all functional areas was polluted in the order of industrial > commercial > residential > green space. Arsenic, Cd, Mo, Pb, Sb, Cu, and Zn were sourced from a mixture of traffic and industrial activities, while Mn in the dust mainly stemmed from mining activities. Non-carcinogenic health risk (HI) showed chronic exposure of Pb for children in the industrial zone (HI = 1.73). The estimations suggest the possible carcinogenic risk of As, Pb, and Cr in the dust. The findings of this study reveal poor environmental management of the city. Emergency plans should be developed to minimize the health risks of dust to residents.

Determining the appropriate mixing ratio in a multi-substrate anaerobic digestion of organic solid wastes employing Taguchi method.

The current research proposed a method for optimally combining feed input ratios in order to improve the quantity and quality of daily biogas production through optimizing the variable response level in the Taguchi method. The anaerobic digestion (AD) process of an existing plant in Iran was simulated through a set of two-stage pilot reactors under mesophilic temperature conditions in order to achieve optimal operational performance. Three common substrates (organic fraction of municipal solid wastes, fruit and vegetable wastes, and horse manure) along with two recirculated materials; the post-digestion sludge and the secondary digester slurry, were investigated in 16 experimental runs based on four different pre-surface hypotheses. Comparison of the results of daily biogas energy (J/d/g-VS) in Run#9, to which the actual yield of hydrogen sulfide was minimal in parallel to a methane yield above 100 mL/g-VS, with the result of the optimal run with the ratios provided by the model, showed that the daily biogas energy was improved by 50% comparing to the control Run that had similar conditions to which was being applied in the full-scale existing AD plant.

Integrated model for land-use transformation analysis based on multi-layer perception neural network and agent-based model.

The efficacy of land-use changes on aquatic ecosystems has been extensively studied in recent decades. Water resource management needs to understand the relationship between land-use change patterns and water quality, especially in urban areas. Hence, recognizing spatial-temporal changes in land use is required for sustainable development and proper water resource management. This research has developed an integrated model based on agent-based model (ABM) and multi-layer perceptron (MLP) neural network technique to predict the future land-use transformation tested on the North Ahvaz watershed, Iran. Random forest-supervised classification technique was applied to derive the land-use maps using Landsat 1989, 2004, and 2019 images in the Google Earth Engine (GEE) platform. The overall accuracy of classified land-use images was 0.82, 0.81, and 0.84, respectively, with the kappa coefficient of 0.74, 0.72, and 0.78. Land-use change analysis and generating transition potential maps were carried out in land change modeler (LCM) through MLP based on seven driving factors. Then, the land-use map for 2019 (for validation) and 2040 was simulated using the transition potential map and an agent-based approach. The ABM scenario was farmers' and urban landowners' decisions to convert undeveloped and unprotected lands to residential lands. The results showed that residential areas and pasture lands would grow by 67.96 km2 and 64.63 km2, and agricultural and barren lands would degrade about 84.19 km2 and 47.98 km2 during 2019-2040, respectively. Predicting land-use change through the integrated MLP-ABM model may be used to evaluate the effects of land-use change coming out of human decision-making.

Exposure risk assessment, pollution level, and source identification of arsenic in soil: A case study of the Bardsir Plain (southeastern Iran).

In this study, we investigated the total arsenic concentration in the soil and the related human exposure risks in the central part of the Bardsir Plain in southeastern Iran. The results show that the average total arsenic concentration in agricultural soil is 50.26 mg/kg, which is 2.5 times higher than the maximum acceptable limit (20 mg/kg) recommended by the European Community. The natural portion of the arsenic concentration was larger than the anthropogenic portion. The high total arsenic concentration could be due to a combination of geogenic sources and irrigation with polluted groundwater. The average values of Igeo, Ipoll, and IB for agricultural soils were 1.10, 0.14, and 0.15, respectively; which are characterized as moderately polluted. The average non-carcinogenic hazard (HI) values for children and adults were 2.27 and 0.24, respectively, suggesting that children are exposed to non-carcinogenic risks. The total carcinogen risk (CR) value was 1.16E-04, which indicates a high risk of harmful effects to inhabitants.

Measurement and ecological risk assessment of heavy metals accumulated in sediment and water collected from Gomishan international wetland, Iran.

This study aimed to measure and ecologically assess heavy metals, including As, Cr, Pb, Cd, and Ni in water and sediment samples taken from Gomishan, an international wetland located in Golestan, Iran. Four sampling stations were selected to cover all parts of the wetland. The analyses of the heavy metals were performed by ICP-MS. Based on the content of the heavy metals in the sediments, the values of risks for individual heavy metals, as Er, and for total heavy metals, as IR, were estimated. Igeo and EF also presented the soil quality in terms of accumulated contamination. The average content of the heavy metals in water was 23.12, 4.14, 10.04, 6.71, and 94.48 µg/L for As, Cd, Cr, Ni, and Pb, respectively. The heavy metal concentrations in sediments were decreased in the following order: Pb (2130 ppb) > As (655 ppb) > Cr (295 ppb) > Ni (148.8 ppb) > Cd (148.8 ppb). The potential risk values for individual heavy metals were in the low range, Er < 40, except for Cd, which mostly posed a moderate ecological risk. The values of EF and Igeo showed that the sediments sampled from the Gomishan wetland were minimally enriched and contaminated. As the Gomishan wetland has a moderate risk of heavy metal contamination, conservative and monitoring activities should be performed.

The thermodynamic stability, potential toxicity, and speciation of metals and metalloids in Tehran runoff, Iran.

Surface runoff is the most significant source of water in dry cities like Tehran. The surface runoff is polluted by heavy metals, which their risk level is a function of their speciation. Herein, Tehran runoff quality and the speciation of metals and metalloids were investigated. The results of quality showed that oxidation-reduction potential (Eh) and pH ranged from + 186 to + 230 mV and from 7.31 to 10.29, respectively. Cluster analysis indicated that Cr, Si, Mn, Fe, Pb, Se, Th, Ba, Ni, Li, and Sr had similar behaviors and origins, and salinity played an active role in restricting their concentrations. Eh and dissolved oxygen (DO) negatively affected the concentrations of all the studied elements. The speciation model (according to HSC Chemistry program) exhibited that all the studied elements are stable; however, in two cases, they would become unstable (pH < 7, Eh < - 480 mV or Eh > 1100 mV) and (pH > 10, Eh < - 570 mV or Eh > 970 mV). Also, Ba, Cd, Li, Mn, Al, As, Sr, Cr, Si, and Se are present in bioavailable species and As and Cd in the runoff exist in high toxic oxidation states of + 3 and + 2, respectively. The linear regression of Cu, Co, Cd, Zn, and As with Eh provided a good fit, and all of these metals were significant at levels 1 and 5%. Finally, it is recommended to continuously monitor the Eh-pH changes for investigating the potential toxicity of metals and predicting the metal pollution by regression equations in any other stations.

Release of heavy metals under pre-set redox potentials in Musa estuary sediments, northwestern of Persian Gulf.

Sediments are capable of adsorbing and desorbing heavy metals (HMs) under various environmental conditions. This study investigated the impact of pre-set redox potential (Eh) on the release dynamics of HMs (Co, Cr, Cu, Ni, Pb, V, and Zn) from sediment in an automated biogeochemical microcosm. The release of Co, Pb, and V under reducing conditions increased that may increase the potential risks in the aquatic environment. This phenomenon could be attributed to the decrease in pH, the reductive dissolution of FeMn oxides, and the complex of HMs with dissolved organic carbon (DOC). However, the soluble Cr, Cu, Ni, and Zn decreased at redox potentials as low as -150 mV. Co, Ni, Pb, and Zn were observed in mobile fractions while Cu primarily existed in the residual fraction (indicating lithogenic source). HPI and HEI indexes showed that water quality concerning HMs would become more unsuitable for aquatic life by reducing Eh.

Impacts of land use and land cover change on the interactions among multiple soil-dependent ecosystem services (case study: Jiroft plain, Iran).

The spatial and temporal distribution pattern is an outstanding feature of the relationship among ecosystem services (ESs) that explains links between human activities and disturbed chemical composition of ecosystems. This study investigated the spatiotemporal variation of land use/cover changes (LUCC) and quantifies the change in four essential ecosystem services with an emphasis on soil (nutrient delivery ratio, carbon storage, crop production, and water yield) and their relationships in the Jiroft plain, Iran, during 1996-2016 through analytical tools including Land Change Modeler, and the Integrated Valuation of Ecosystem Services and Tradeoff. During the 20-year concentrate period, there was a considerable overall gain in cropland (5396 km2) and urban (1787 km2), loss of unused land (5692 km2), water (2088 km2), and forest (1083 km2). As a result of LUCC, while crop production and nutrient delivery ratio showed a rising trend, overall carbon storage and water yield decreased. The spatiotemporal trade-off between carbon storage and crop production, the temporal trade-off between crop production and water yield, and synergy between water yield and crop production were widespread in Jiroft plain. These results showed that the interaction among ESs mutates over time and can be changed under planning and policies. This study will enrich the research of the geographical distribution of ESs interaction in dryland ecosystems to provide practical ecosystem management under local conditions.

Study of speciation and spatial variation of pollutants in Anzali Wetland (Iran) using linear regression, Kriging and multivariate analysis.

Multivariate statistical techniques and geostatistical methods are among the important tools used in surface water quality management. They are widely used in interpreting data, identifying the pollution sources, understanding the spatial variation of parameters, and determining the places of monitoring stations. Therefore, in this study, spatial variation of water quality and pollutants in the Anzali Wetland water (Iran) was evaluated using multivariate statistical and Kriging methods. The values of different water quality parameters measured in six stations in the wetland water were subjected to cluster analysis (CA) and principal component analysis (PCA). Cluster analysis reduced the number of stations from six to four. The results of PCA showed that industrial and agricultural pollution sources could be responsible for the Anzali Wetland water quality. Then, the spatial variation maps of the PCA scores were generated using Kriging geostatistical method in the geographical information system (GIS) to investigate the pollution sources affecting the wetland parts. These maps illustrated that a great part of the wetland body was under the effect of agricultural sources, while the industrial sources affected the outlet and central parts. Finally, a comparison between two models (multiple linear regression (MLR) and Kriging) was made to assess their ability in predicting water quality parameters in the study area. The results showed the improvement of prediction using MLR, which was by 25%-97%, compared with Kriging. The results of the present study can be effectively used in the planning and implementation of future monitoring networks in the Anzali Wetland and other similar aquatic systems.

A comparative study of elemental pollution and health risk assessment in urban dust of different land-uses in Tehran's urban area.

Pollution levels of potentially toxic metals (PTMs) were studied performing enrichment factor, geo-accumulation index and ecological risk index. The most enriched elements which categorize as very high and extremely high enriched in different land-uses were in order of: commercial Cu (73.79)>Hg (66.55)>Pb (55.73)>Zn (46.15)>Cd (37.31); residential Pb (48.35)>Zn (34.79)>Cu (27.69)>Hg (22.96)>Cd (22.61) and industrial Zn (55.43)>Pb (51.52)>Cu (40.20)>Cd (26.29). In green lands sampling points, there weren't any elements with enrichment factor more than twenty. Based on the result of geo-accumulation index, commercial land-use appeared to be highly polluted with Cu, Pb and Zn. Residential land-use were highly polluted just in case of lead and industrial land-use were categorized as highly polluted in case of Zn, Pb and Cu. Hakanson's ecological risk index classified all of the land-uses except for green lands as very high ecological risk category. Factor analysis revealed that Cr, Mn, Ni, Fe and to a lesser extent Pb, Zn and As are from similar anthropogenic sources. Carcinogenic risk of Cr, Pb, As, Ni and Cd were found to be negligible for all land-uses for adult and children except for chromium in commercial land-use which exceed the safe level and need more attention in the future.

Contamination and cancer risk assessment of polycyclic aromatic hydrocarbons (PAHs) in urban dust from different land-uses in the most populated city of Iran.

Due to population growth and the considerable increase in usage of the resources, Human environment quality has been highly threatened by pollutants in recent decades. Polycyclic aromatic hydrocarbons (PAHs) are widespread, persistent organic pollutants which are of great concern due to their carcinogenicity. The present study is the first investigation that assesses contamination, sources and cancer risk of 16 priority PAHs proposed by US EPA in urban dust samples (n = 80) taken in different land-uses of Tehran metropolis, the capital of Iran. Gas chromatography-mass spectrometry (GC-MS) is used to measure PAHs concentrations. The results showed that the average concentration of the total 16 PAHs and the average Benzo[a]pyrene total potency equivalency were 566 µg kg-1 dry weight and 36.4 µg kg-1, respectively. In the commercial and residential land-uses high molecular weight (HMW) PAHs were dominated, whereas in green lands, light molecular weight (LMW) PAHs showed maximum contribution. The highest concentration of total PAHs were observed in the commercial areas due to limited air circulation and heavy traffic loads. Incremental Lifetime Cancer Risk (ILCR) model was applied to evaluate the cancer risk of exposure to PAHs contaminated dust. Based on the results, Tehran's residents (children and adults) in various land-uses except for green lands, are in high potential cancer risk of PAHs via ingestion and dermal contact exposure routs. Ace, Chr, Pyr, and BghiP which are indicators of traffic emissions, were found to be predominant PAH contributors in urban dust of commercial areas. Also, Ace, Fl, Phe, and BghiP which are derived from fossil fuel combustion, were mainly observed in the industrial land-use. Based on the results of factor analysis and diagnostic ratios, Diesel/gasoline engine vehicular emissions and combustion were found to be the main sources of PAHs in urban dust of Tehran.

The role of the estuarine zone on the river particulate toxicity.

Annually, a great volume of sediment and suspended particulate matters (SPMs) enters into the seas through estuaries. In the estuarine zone, metals present in SPMs may undergo conservative or non-conservative changes. In the present study, oxidation-reduction potential (ORP) as the most complex chemical parameter of open sea water and its relationship with the behavior of t metals in the estuarine area were investigated. Dissolved oxygen was used as a strong oxidant to increase the ORP. According to the absorption and desorption experiment, Mn and Cu are desorbed from SPMs during estuarine mixing. However, Zn and Pb are absorbed into the SPMs. In addition, the analysis results were indicative of the conservative behavior of Ni. The results of the three-step chemical partitioning of the SPMs revealed that Mn and Cu are desorbed from the SPMs physically, whereas Zn is absorbed into the SPMs chemically. Also, results showed that Pb is physically desorbed from the SPMs, while it is absorbed into SPMs chemically. All metals, except for Ni and Zn, whose reactions with the SPMs are not affected by an increase in the ORP, are affected by the escalation of this parameter.

Temporal metal concentration in coastal sediment at the north region of Persian Gulf.

The purpose of this article is to study, result of metal concentration in two-sediment cores from Persian Gulf. Age of sediment is determined by C14 isotope method and bulk concentration is determined by ICP. This research output shows that, age of BandareAbbas core back to 9660 and Bushehr core to 15,600 years ago. Also,concentration in BandareAbbas and Bushehr cores respectively change as, As (1.08-11.76 Vs 5.2-13.09), Ba (15.03-129.5 Vs 73.9-120.4), Cd (0.09-0.46 Vs 0.09-0.18), Li (5.66-58.5 Vs 15.3-33.4), Mo (0.3-0.75 Vs 0.3-0.8), Mg (7928.4-15,503.9 Vs 13,102.8-17,227.8), Mn (110.6-566.4 Vs 279.3-429.1), Na (8905.47-27,993.3 Vs 9357.7-27,541.4), Ni (13.3-110.3 Vs 37.1-88.4), Pb (0.5-42.5 Vs 2.5-13.6), Sr (407.5-1773.2 Vs 440.3-1596.9), Zn (13.05-71.2Vs22.4-50.5), Fe (0.46-4.07 Vs 1.7-3.18), Ca (9.25-23.3 Vs 13.8-19.2) and Al (0.62-8.15 Vs 2.48-4.65). Moreover different pollution index investigation represent that except Ca, the rest of the metal elements do not show pollution.

Removal of mercury from contaminated saline wasters using dithiocarbamate functionalized-magnetic nanocomposite.

In this study, an efficient adsorbent was proposed for the removal of mercury from saline water contaminated with mercury ions. Fe3O4 nanoparticles were modified using tetraethylenepentamine and carbon disulfide to incorporate dithiocarbamate functional group on the surface of the adsorbent. CHNS analysis confirmed successful modification of magnetic nanoparticles. The XRD pattern of adsorbent indicated a proper match with the standard XRD pattern of cubic Fe3O4. The saturation magnetization of final adsorbent was 27 emu g-1. The morphology of bare and silica-coated Fe3O4 and final product were investigated using FE-SEM analysis. For optimizing the adsorption process, response surface methodology was applied, which was resulted in a significant quadratic model. The effect of adsorbent dosage and initial concentration of Hg (II) was much more significant than that of pH. Different concentrations of dissolved solids up to 2000 mg L-1 had no adverse effect on the adsorption process due to the strong interaction between dithiocarbamate functional group of adsorbent and Hg (II). The least values of RMSE (0.0950) and χ2 (0.0009) were observed for Radke-Prausnitz, Redlich-Peterson, and UT isotherms. Maximum adsorption capacities calculated using Langmuir and UT models were 109.5 and 95.07 mg g-1, respectively. The investigation of adsorption isotherm was conducted at the pH range of 2.0-6.5. The results showed an increase in the adsorption capacity by increasing pH. Thermodynamic studies demonstrated that the nature of the adsorption process was spontaneous and endothermic. Recovery of adsorbent was successfully carried out using HCl 0.5 mol L-1. The prepared adsorbent was successfully applied for mercury removal from a real groundwater.

Fate of toxic metals during estuarine mixing of fresh water with saline water.

Metals are among the most common environmental pollutants, and their presence in high concentration in waters and biota have devastating effects on flora, fauna, and human health. Flocculation process of metals during estuarine mixing can reduce the environmental hazards of metals and also can provide micronutrients to the aquatic system. The present investigation provides a thorough study of eliminating colloidal elements of copper, manganese, nickel, lead, and zinc during estuarine mixing of Shalmanrood River water with Caspian Sea water in Iran. The processes of flocculation were carried out in six different salinity regimes (0.45-2.4 ppt). The obtained result is indicative of non-conservative behavior of the studied metals. Higher flocculation resulted in a lower salinity regime. The obtained results indicated that most of the metals were eliminated during the initial mixing of fresh water with sea water at 0.45-0.9 ppt salinity interval. The trend of flocculation rates of elements is as follows: Zn (59.3%) > Pb (47.6%) > Mn (37.5%) > Cu (29.2%) > Ni (27%).The annual average load of copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) from Shalmanrood River to Caspian Sea decreases as a result of flocculation process from 9.9, 7.7, 8.9, 5.1, and 23.2 tons per year to 7, 4.8, 6.5, 2.7, and 9.4 tons per year, respectively. According to the cluster analysis, parameters such as temperature, pH, and Eh do not have any impact on flocculation of elements expect for Pb. The only parameter that influences the flocculation of Mn is the salinity. Metal speciation studies that are carried out by Eh-pH software show that the studied metals are present as oxides (Zn, Cu, and Ni) and hydroxides (Mn and Pb).