Int. J. Environ. Sci. Tech., 7 (2), 327-336, Spring 2010 ISSN: 1735-1472 A. Biati et al. © IRSEN, CEERS, IAU Role of metal species in flocculation rate during estuarine mixing 1 3 2 1 2 *A. Biati; A. R. Karbassi; A. H. Hassani; S. M. Monavari; F. Moattar 1 Department of Environmental Science, Graduate School of the Environment and Energy, Science and Research Branch, Islamic Azad University, Tehran, Iran 2 Department of Environmental Engineering, Graduate School of the Environment and Energy, Science and Research Branch, Islamic Azad University, Tehran, Iran 3 Graduate Faculty of the Environment, University of Tehran, Tehran, Iran Received 3 January 2010; revised 2 February 2010; accepted 28 February 2010; avaiable online 1 March 2010 ABSTRACT: Flocculation can be considered as an effective mechanism in self-purification of metals during estuarine mixing. In the present investigation, flocculation of metals during mixing of Minab River water with the Strait of Hormuz (The Persian Gulf) water is studied for the first time. Flocculation behavior of metals (except for Pb) is governed by dissolved organic carbon. The source of dissolved organic carbon is terrigenous in the estuarine waters of study area. The general pattern of flocculation of studied metals is manganese (180 µg/L) > zinc (88 µg/L)> nickle (73 µg/L)> copper (30 µg/L)> lead (19 µg/L). The results of present study show that metal species are a very important factor in overall flocculation rate. It is found that solids and oxides have the highest and lowest flocculation levels, respectively. Eh-pH diagram indicated that lead is present as lead oxide in Minab River water and the least flocculation rate is attributed to this element. The results also showed that flocculation rate of metal species could be as solids > free ions ≈ hydroxides > oxides. The amount of metal flocculation is about 30.5, 6.6, 25.3, 10.4 and 62.5 ton/y for zinc, Pb, Ni, Cu and Mn, respectively. Keywords: Environment; Estuary; Flocculation; Metal; Pollution; River; Species; Water INTRODUCTION Fluxes of materials (dissolved and particulate 1988; Samarghandi et al., 2007). These two matters) find their way into lakes and seas through counteractive, non biological mechanisms are rivers (Meybeck, 1988). Estuaries are the major desorption of metals from resuspension of riverine biogeochemical interfaces between land and sea where particles and flocculation of metals-humate from terrigenous elements born by river on their way to the solution (Li et al., 1984). Controlling mechanisms of sea under go various changes (Sharp et al., 1982; flocculation process have been investigated Breuer et al., 1999). Mixing of river and seawater results intensively. In wetlands, flocculation is enhanced by in flocculation of trace metals especially in the upper increased pH, turbulence, concentration of suspended part of the estuary where lower salinity regimes are matters, ionic strength and high algal concentration found (Gerringa et al., 2001; Karbassi et al., 2008a; (Matagi et al., 1998; Zvinowanda et al., 2009). Biati et al., 2010). Due to the flocculation process a Flocculation mechanisms are mainly due to colloidal large portion of the dissolved metals supplied by the stability, surface properties, humic acids, salinity and river come into particulate phase (Eckert and Sholkvitz, pH (Hunter, 1983; Zhiging, et al., 1987; Featherstone 1976; Boyle, 1977; Sholkovitz et al., 1977; Karbassi et and O’Grady, 1997; Karbassi et al., 2007). Removal of al., 2008b; c). Thus, estuarine processes can influence significant amounts of reiverine dissolved organic elemental composition of the sea water (Sillen, 1961; carbon (DOC) may occur due to flocculation or Mackenzie and Garrels, 1966; Mackenzie, 1975; Troup precipitation reactions that result in the conversion of and Bricker, 1975; Nouri et al., 2008a). The two important DOC to particulate organic carbon and their mechanisms affecting the concentration and subsequent settlement on to the sediments (Sholkovitz, distribution of trace metals during estuarine mixing have 1976; Nouri et al., 2008b). Production of autochthonous been successfully modeled by water-column mixing DOC in estuaries may also occur through several experiments (Sholkovitz, 1976; Comans and Van Dijk, processes (Sharp, 1991; Aliabadi et al., 2006). Although *Corresponding Author Email: [email protected] many studies have reported conservative mixing of Tel./Fax: +989123777164 DOC during estuarine transport (Moor et al., 1979; A. Biati et al. Laane, 1980; Sharp et al., 1982; Mantoura and MATERIALS AND METHODS Woodward, 1983; Aminot et al., 1990), some Strait of Hormuz is an important corridor that investigations displayed a relatively dynamic DOC pool connects Iran and other oil producing economic (Doering et al., 1994). Redox processes is of major countries (OPEC) to the world’s open seas. Strait of concern for mobilization of trace metalsin estuaries where Hormuz has a width of 50 to 60 Km. Maximum depth of an oxygen gradient exists in addition to the salinity water in strait of Hormuz is 100 m. Minab Rive has a gradient (Gerringa et al., 2001;Abdel-Ghani et al., 2009). length of 200 Km and its average annual discharge is 3 A combination of high organic matter content and a 10.99 m / s. Minab River is formed by two main branches long residence time, may result in development of anoxic named Rudan in western part and Jaghin in eastern conditions that may be either restricted to the sediments part. It lies between longitude of 57º 07´ and Latitude (Westerlun d et al., 1986; Kerner and Wallmann 1992) or of 27 º 09´. Various municipal and industrial waste water can occur in the water column (Zwolsman and Van Eck, containing heavy metals and organics along with 1993; Zwolsman et al., 1997; Shiller and Mao, 1999). agricultural fertilizers, pesticides and herbicides enter Sulfides of elements (e.g. zinc (Zn) and cadmium (Cd)) into the Minab River. Fresh and saline water samples may precipitate in anoxic conditions (Malakootian et were collected in pre-cleaned 25 L polyethylene bucket al., 2009). In more saline parts of the estuary, some from the Minab River upstream and Strait of Hormuz elements (e.g. Zn and Cd) are released in to the water as (16 Km away from river mouth), respectively (Fig. 1). th. a result of oxidation (Sholkovitz, 1976; Duinker and Water sampling was carried out on 5 October 2008. Nolting, 1978; Duinker et al., 1983;Wollast, 1988; Regnier On the same day, water samples were filtered through and Wollast, 1993; Chiffoleau et al., 1994; Paucot and 0.45 µm MilliporeAP and HAfilters.About one liter of Wollast, 1997). Flocculation process has been studied filtered fresh water was acidified with concentrated in northern part of Iran (Haraz, Sefidrud, Chalus, Talar, HNO3 to a pH of approximately 1.8 and stored in Tadjan and Gorgan rud rivers) (Karbassi and Nadjafpour, polyethylene bottles in a refrigerator prior to analysis 1996; Karbassi et al., 2007, 2008a). Such investigations of dissolved metals. Filtered river water and seawater has not been carried out in southern part of Iran. Present were mixed together at room temperature (ca. 25 ºC) in study would fill up such gap for southern coasts of Iran. nine proportions yielding salinities of 3.3-29.7. The 28º50’0”N 28º30’0”N Iran Faryab 28º10’0”N Ziarat ali 27º50’0”N Ghale Ganje Minoujan 27º30’0”N Bandar Abbas Minab 27º10’0”N Minab river land 26º50’0”N m Is Strait of Hormuz Qesh 26º30’0”N Persian Gulf 26º10’0”N Sampling Stations City River 25º50’0”N Boundary of water shed basin 25º30’0”N Sea of Oman 0 15 30 60 90 120 Km 25º10’0”N 55º0’0”E 56º0’0”E 57º0’0”E 58º0’0”E 59º0’0”E 60º0’0”E Fig. 1: Locations of water samples from Minab River and Strait of Hormuz 328 Int. J. Environ. Sci. A. Tech.,Biati et7 (2),al. 327-336, Spring 2010 Table 1: Methods and apparatus used for measurement of various parameters Parameter Method/ apparatus of measurement Mn, Cu, Pb, Zn, Ni ICP (JOBINYVON model JY138 ULTARCE Ca, Mg AAS (Varian, model Spectraa. 200) Na Flame photometer pH/Eh pH meter (Metrohm 744) EC Conductimeter (CRISON GLP32) DO DO meter (Inolab WTW) DOC Photo cathalitical oxidation method (ANATOCTM SERIES II) Chloride Argentometric method (4500-Cl¯) (APHA, 2005) -2 Sulfate Turbidimetric method (4500- SO4 ) (APHA, 2005) Alkalinity of phenol and methyl Titration method (2320) (APHA, 2005) Salinity, carbonate, bicarbonate, total alkalinity Titration method (APHA, 2005) Temp. of water Thermometer (accuracy of 1Cº) Table 2: Flocculants of trace metal contents (laboratory scale) along with pH, Eh, EC, temperature, salinity, DO and DOC – laboratory condition Parameter DOC DO Salinity T EC Eh Mn Cu Ni Pb Zn aquarium pH (Mg/L) (mg/L) (ppt) (C°) (µs/cm) (m V) (µg/L) (µg/L) (µg/L) (µg/L) (µg/L) No. River 4.31 6.3 0.72 20.85 1900 -89 8.84 259 36 88 50 117 water Seawater 3.13 5.3 37.5 23 59500 -60 8.32 75 3 15 3 12 1 4.60 6.6 3.3 22.3 6500 -77 8.67 85 14 55 5 37 2 0.97 6.7 8. 3 22.3 14000 -72 8.63 133 20 56 19 28 3 2.66 6.7 9.1 22.3 15000 -72 8.55 76 26 58 13 46 4 0.21 6.9 11.4 22.3 19000 -67 8.49 175 10 59 6 52 5 2.39 6.9 14.5 22.3 22575 -66 8.47 109 8 73 7 29 6 1.84 6.9 18.5 22.3 29500 -65 8.47 180 5 54 4 50 7 0.48 6.9 26.7 22.3 41500 -68 8.48 170 28 30 4 41 8 1.39 6.9 28.8 22.3 44500 -68 8.52 74 30 18 7 33 9 1.36 6.9 29.9 22.3 46250 -66 8.45 78 30 16 13 88 Total - -- - - - - 1414 210 522 131 533 samples were kept for 24 h with occasional stirring.