2231 © IWA Publishing 2011 Water Science & Technology | 63.10 | 2011 Sources and leaching of manganese and iron in the Saigon River Basin, Vietnam Nguyen Thi Van Ha, Satoshi Takizawa, Kumiko Oguma and Nguyen Van Phuoc ABSTRACT High concentrations of manganese and iron in the Saigon River are major problems for the water supply in Ho Chi Minh City (HCMC), Viet Nam To identify their sources and leaching processes, we surveyed water quality along the Saigon River and ran batch leaching tests using soil and sediment samples Two important leaching processes were identified: acidic leaching from acid sulfate soil Nguyen Thi Van Ha (corresponding author) Nguyen Van Phuoc Faculty of Environment, Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Viet Nam E-mail: ntvha2003@gmail.com (ASS) in the middle reaches of the river, and Mn dissolution and Fe reduction from sediments in the downstream reaches Low pH caused the concurrent release of Fe and Mn from the ASS In contrast, anoxia caused the release of Fe but not Mn from the sediments, whereas low pH facilitated Mn dissolution Sediments are a more important source of Mn because of their higher Mn contents (10 times) and release rates (14 times) than those from ASS Key words Satoshi Takizawa Kumiko Oguma Department of Urban Engineering, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan | acid sulfate soil, iron leaching, manganese leaching, pH-Eh diagram, redox condition, sediment INTRODUCTION Manganese and iron are common metals found in Earth’s crust and in natural water Excessive exposure to Mn is associated with adverse health effects and neurotoxicity, and retards the intellectual development of children (Wasserman et al ) The health-based Mn guideline value for drinking water is recommended at 0.4 mg/L (World Health Organization (WHO) ) and 0.3 mg/L (US EPA ) In many countries, the guideline values for Fe and Mn are set at lower concentrations than the health-based guidelines The Vietnamese environmental standards for Fe (QCVN 08:2009, A2) and for Mn (TCVN 5942: 1995, A) are set at mg/L and 0.1 mg/L, respectively; and the US EPA’s levels are 0.3 mg/L and 0.05 mg/L, respectively Saigon River is the second most important source of water for HCMC and Binh Phuoc Province However, it is facing water quality problems of low pH, high turbidity, and high concentrations of Mn, ammonia and total coliform Tan Hiep water treatment plant (WTP) reported that Fe and Mn concentrations in the river water frequently exceed the Vietnamese standards for water supply The monthly average concentration of Mn was about 0.16 mg/L in the dry season from 2005 to 2008, and in the rainy season it has reached 0.24 mg/L in the rainy season, exceeding several times the US EPA health risk level doi: 10.2166/wst.2011.460 of 0.3 mg/L High Mn caused difficulties in operation of the WTPs (Kohl et al ) In rivers and lakes receiving industrial effluents, heavy metals and Mn are deposited in the sediments (Youger & Mitsch ) The amounts of Fe and Mn leaching depend on their concentrations in the top sediment layer (Guerios et al ), pH and redox condition (Eh) (Davison ) There is limited information about sources of Mn and Fe in the Saigon River A better understanding of the Mn and Fe sources and their leaching processes is required to predict when and where its high concentrations will occur The objective of this study was to identify the main sources and transport of Mn and Fe entering the Saigon River to assist development of river basin management strategies for controlling point and diffuse sources of Mn and Fe inputs into the river MATERIALS AND METHODS Study sites The Saigon River has a total length of about 280 km, its catchment covers about 4,717 km2 and its average flow rate is 85 m3/s The upstream Dau Tieng Reservoir is the N T Van Ha et al 2232 | Sources and leaching in the Saigon River Basin Water Science & Technology | 63.10 | 2011 DT9 and DT7) and 11 from the Saigon River (SG4 to SG22, of which some points were skipped) On May 9th, 2008 seven river surface water samples (SG9 to SG20) and seven canal water samples (ThT, RM, RBC, RBB, RBL, RT, VT) were collected at the same depths We measured pH, turbidity and DO on-site by using a Horiba W-23XD probe, and measured total Mn and total Fe with a DR820 Colorimeter fourth biggest reservoir in Vietnam, with a storage capacity of 1.48 Â 109 m3 The Dau Tieng – Saigon River system is the largest irrigation system in Vietnam and an important water supply source At two water intakes in the middle section (SG15 and SG16 in Figure 1), about 326,000 m3 per day is withdrawn for supply to HCMC and Binh Duong Province The tidal effect sometimes went up to the location of SG9 (Figure 1) There is about 16,670 of ASS around the water intakes in Cu Chi District in HCMC The Thi Tinh River (ThT), the Rach Tra (RT) Canal and the Vam Thuat (VT) Canal are the main tributaries of the Saigon River The ThT and VT receive wastewater from industrial zones in Binh Duong Province and HCMC, respectively The RT Canal collects most of the drainage from potential acid sulfate soil (PASS) in the Saigon River basin and acidic drainage from actual acid sulfate soil (AASS) in the Vam Co Dong River basin Three undisturbed ASS samples were collected at locations S1 to S3 from two depths: 0–25 cm and 25–50 cm Fourteen sediment samples were taken along the river and kept in plastic bags at C until the batch leaching tests were conducted Total Mn and Fe were measured following the US EPA method 3051 (US EPA ) and expressed in mg/kg dry weight Water sampling and analysis Batch leaching test On August 20th, 2006 we collected three surface water samples (at 0.5 m) from the DT Reservoir (denoted as DT1, About 30 g of air-dried soil was mixed with 150 mL Milli-Q water or 150 mL acid solution at about pH 1.5 Figure | Map of study area, sampling sites and distributions of acid sulfate soil Soil and sediment sampling and analysis W N T Van Ha et al 2233 | Sources and leaching in the Saigon River Basin (Mehlich extraction solution: 0.025 N H2SO4 and 0.05 N HCl) in serum bottles, shaken for on a reciprocating shaker at 180 oscillations per min, and then incubated at room temperature in aerobic conditions Leachates were sampled at 1, 18, 72 and 168 h after mixing to measure pH and dissolved Mn and Fe by inductively coupled plasma atomic emission spectrometer (ICPAES) Four sediment samples containing high amounts of Mn and Fe (SG15, SG17, SG18 and SG19) were used for batch leaching tests following the American Society for Testing and Materials (ASTM) () method About g of wet sediment was put into 120 mL serum bottles with 100 mL synthetic Saigon River water (Naỵ, 80.9 mg/L; Mg2ỵ, 15.6 mg/L; Kỵ, 17.2 mg/L; Ca2ỵ, 10.5 mg/L; Cl, 95.7 mg/L; NO , 3.5 mg/L; and SO4 , 19.7 mg/L; pH 5.78; EC, 17.61 mS/cm; DO, 7.9 mg/L; oxidation–reduction potential (ORP), 216 mV) Duplicate samples were prepared for aerobic (denoted as A) and anaerobic (denoted as An) leachants with (denoted P) and without (no annotation) pH amendment, to 4.29 Control samples contained only synthetic Saigon River water The anaerobic bottles were sealed with Teflon-coated rubber stoppers and aluminium caps, and then purged with pure N2 gas for at 60 mL/min The aerobic bottles were capped with oxygen-permeable caps made of silicone foam rubber All bottles were gently shaken by bio-shaker (BR-300LF) at 30 C at a horizontal shaking rate of 30 rpm for month Leachates were taken at 1, 18, 72, 168 and 720 h after mixing for the analysis of Mn, Fe and Ca by ICP-AES and of SO4 by ion chromatography The initial and final leachates were measured for pH, electricity conductivity (EC), dissolved oxygen (DO) and ORP, which was converted to Eh later Data were plotted on the Eh–pH diagrams of the Fe-O-H or Mn-O-H-C system (M ¼ 10À5 mol/L, W Figure | Profiles of pH, DO, Mn and Fe in surface water of Saigon River Water Science & Technology | 63.10 | 2011 298.15 K, and P(CO2) ¼ 0.00035 atm) using FACTSAGE software, v 6.1 RESULTS AND DISCUSSION Water quality variation along the Saigon River Overall, pH, DO, Mn and Fe varied similarly in both river surveys in August 2006 and May 2008, although there were some differences at a few sampling locations The water was slightly acidic: pH varied from 5.2 to 6.2 (Figure 2(a)) and from 5.5 to 6.5 (Figure 2(b)), and was lower in the middle section (SG13 to SG16) in both periods The ThT and RT canals had pH values of ,5.7, which increased the acidity in the middle section The low pH in the middle section and the anoxia in the downstream section are important characteristics for water quality In the upstream and middle sections, it varied from 1.1 to 6.9 mg/L in 2006 and from 2.1 to 6.8 mg/L in 2008 In the downstream section it was depleted owing to urban drainage from Thu Dau Mot Town and HCMC DO depletion was more distinct and Fe concentration was lower in August 2006 than in May 2008 This is because, in early rainy season in May, water contained low Fe in runoffs and therefore less Fe oxidation occurred Fe concentrations varied from 0.5 to 2.33 mg/L in 2006 and from 0.65 to 1.67 mg/L in 2008 Concentrations were higher in the middle section owing to the erosion of Fe-rich soil in the basin In the downstream section, because of the high pH (! 6), most of the ferrous iron was oxidized and precipitated, resulting in a decrease of Fe concentration downstream The canal drainages N T Van Ha et al 2234 | Sources and leaching in the Saigon River Basin Water Science & Technology | 63.10 | 2011 (Abesser et al ) The amounts of Mn leached varied among the soil types (Table 1): S3 (AASS) had the lowest pH, 2.13, the highest dissolved Mn concentration in the leachates, 9.34 mg/L, and the highest Mn release percentage (30%) S1 had the highest pH and the lowest Mn leaching rate, 1.36 mg/L, or 3.5% Similar to Mn, total Fe contents did not differ between the two soil layers but differed greatly among soil types S3 had the highest Fe contents, of 29,800 mg/kg dry top-soil, and the highest Fe leaching rates of 925 mg/L S1 had the lowest Fe leaching rates, which were nearly negligible compared with their total contents (17.9 mg/L, or ,0.1%) The similar leaching results between Mn and Fe implied that they were associated with each other in the soil samples The lower pH leachants increased metal leaching rates from PASS Acidic leachant (pH ∼ 1.5) dramatically increased Mn and Fe leached at S1 After a week Mn and Fe concentrations in leachates increased about 10 times and 14 times, respectively (RM, RBC and RBL) and tributaries (ThT and RT) in the middle section had low pH and high Fe concentrations, indicating that acidic leachates from ASS contribute to the Fe inputs and acidification of the Saigon River The acidic drainage from ASS contained Al, Mn and Fe (Green et al ) Mn concentrations in DT Reservoir varied from 0.007 to 0.099 mg/L, lower than those in the Saigon River due to less impact from ASS, which means that DT Reservoir was not an important source of Mn Iron was at a peak at SG18 in August 2006 due to receiving more acidic drainages from Vam Thuat Canal, and more turbulence which resuspended Fe sediments, than those occurring in the early rainy season in 2008 In contrast to Fe, Mn concentrations increased in the downstream Dissolved Mn, which is oxidized very slowly at pH 6, remained in the water, when dissolved Fe was readily oxidized and precipitated Mn and Fe releases from ASS Mn, Fe and SO4 releases from sediments The pH of the soil leachates varied from 2.13 to 4.94 depending on soil type and acidity (Table 1) During leaching tests, pH of S3 leachate remained stable in both soil layers, while pH of S2 leachate increased slightly Periodic inputs of such acidic water acidified Saigon River because of its low buffering capacity Mn and Fe are likely to be the major trace metals released by the oxidation of ASS (Welch et al ) and in soil water Table | Total Fe contents in surface sediments did not vary significantly along the Saigon River, 31,300–61,220 mg/kg, while total Mn contents varied greatly, 261–1,370 mg/kg Mn contents in the downstream sediments at SG18, SG19 and SG20 were 1,000 mg/kg, about 10 times higher than that in ASS Sediment SG19 had a slower Mn release rate than SG17 and SG18, and the lowest concentration of released pH and dissolved Mn and Fe concentrations of soil leachates and total Mn and Fe contents in top-soils (0–25cm) Mn concentrations in leachates (mg/L) Site pHa hour 168 S1 4.06 4.94 S2 2.92 3.79 2.29 2.13 S3 Total Mn mg/kg Water Acidic leachantsb leachantsc Fe concentrations in leachates (mg/L) Water Total Fe mg/kg 168 168 143 1.1 1.36 9.43 13.2 65 1.13 0.88 1.52 1.58 120 7.26 9.34 7.30 9.11 29,800 a leachantsb Acidic leachantsc 168 168 16,600 0.55 17.9 38.7 246 20,600 8.23 218 107 519 692 925 924 1,220 b c Note: pH of water leachants pH of acidic leachants was about 1.5 and did not change significantly; soil: milli-Q water ¼ 1:5; soil: Mehlich solution ¼ 1:5 Table | Amount of Mn and Fe released from sediments leaching test Mn released (mg/kg) Iron released (mg/kg) Moisture total Mn 1h 720 h Total Fe Sediment (%) mg/kg (A) (An) (A) 1h (An) mg/kg (A) (An) (A) SG15 45 573 119 124 SG17 56 619 258 367 SG18 57 1,020 399 378 716 580 55,297 64 SG19 57 1,374 44 41 187 180 58,391 17 720 h (An) 197 190 50,288 21 27 14 1,582 504 558 61,220 30 46 34 3,045 94 19 1,862 19 18 856 N T Van Ha et al 2235 | Sources and leaching in the Saigon River Basin Mn (167–244 mg/kg), although it had the highest total Mn content, i.e., Mn species in SG15, SG17 and SG18 sediments were mostly in the readily leachable form, whereas Mn at SG19 was more slowly leachable Sediment SG19 was contaminated by industrial and municipal effluents from HCMC, whereas SG17 and SG18 were located in agricultural areas and received drainage from ASS paddy fields in Saigon and VCD River basin Unlike Mn, Fe was slow to dissolve into the leachants at low content pH adjustment was too minor to bring any significant effects on releasing rate The anaerobic condition had a significant influence on the amount of Fe released (t-test, P , 0.001), but had no effect on Mn leaching After 168 h, anaerobic leachates had pH more than and zero DO, which could facilitate the Fe releasing process (Figure 3(b)) Sediments SG17 and SG18 had higher sulfate release rates (14.3–28.8 g/kg), indicating deposition of SO4-rich particles derived from ASS at those locations Figure | Leaching of Mn, Fe and SO4 from the sediments Water Science & Technology | 63.10 | 2011 The release of Mn from sediments was about 14 times that from the soils, indicating sediments are a more important source of Mn in the Saigon River In contrast, the amounts of Fe leached from sediments varied from 21 mg/kg in aerobic tests to 124 mg/kg in anaerobic tests, far less than that from soils, 2,390 mg/kg This suggests that Fe was derived mainly from soil erosion and leaching from soil rather than from sediment Effects of pH and Eh on Mn and Fe release from sediments Figure shows the effects of pH, Eh and concentrations, and distribution of Fe and Mn species in the final sediment leachates Sediments SG15, SG17 and SG18 were more acidic, explaining the lower pH and higher Eh of the aerobic samples than those of the control samples, whereas sediment SG19 showed a pH increase and an N T Van Ha et al 2236 Figure | | Sources and leaching in the Saigon River Basin Water Science & Technology | 63.10 | 2011 Eh-pH diagram of Fe and Mn plotted with the data of the final sediment leachates (The open and solid symbols are aerobic and anaerobic samples and the asterisks are control samples Additional lines were drawn in (a) for aqueous Fe concentration from 10À10 to 10À2 mol/L and in (b) for aqueous Mn ¼ 10À2 mol/L at P(CO2) ¼ 0.00035 atm, and 0.0035 atm.) Eh decrease Aerobic treatment moved the pH–Eh conditions along the border between Fe2O3 and Fe2ỵ, i.e., moving to lower pH with higher Eh (Figure 4(a)) Hence, it did not promote dissolution of Fe In contrast, anaerobic treatment raised pH and lowered Eh During the course of the batch leaching tests, Eh was lowered before pH was increased, so that the anaerobic condition accelerated the dissolution of Fe from sediments The aqueous concentation of Fe also affects its state; the Fe2ỵ area gradually narrows as the aqueous Fe concentration increases from 10À10 to 10À2 mol/L Fe tends to remain in solid form in soil and sediment owing to the higher aqueous Fe concentration in pore water, but, when soil is eroded into river water or when sediment is resuspended, Fe can be dissolved if pH and Eh are lower in the Fe2ỵ area of Figure 4(a) Most Mn leaching data fell in the Mn2ỵ area (Figure 4(b)), indicating that Mn in the sediments is readily soluble in water, as proved by the batch leaching tests This contrasts with Fe, which can be dissolved only if the sediments are placed under strong anaerobic, i.e reducing, conditions Around the area plotted with the data of the final leachate, variation of Eh has less effect than pH The concentration of aqueous Mn2ỵ and partial pressure of carbon dioxide P(CO2) also affected the leaching of Mn (Figure 4(b)) In river sediments, Mn is estimated to remain as MnCO3 because of higher Mn2ỵ and P(CO2) in pore water, whereas in the Saigon River Mn can be easily dissolved because of lower aqueous Mn2ỵ and P(CO2) than in the pore water of the sediments CONCLUSIONS Two major sources of Mn and Fe inputs into the Saigon River were identified: (1) acidic leaching from ASS in the middle river section, and (2) dissolution from Mnand Fe-enriched sediments downstream Fe leaching from ASS was more critical than Mn leaching Low pH was a determinant cause of Mn and Fe leaching from ASS Reducing pH from to 1.5 increased Mn leaching from PASS by 10 times and Fe leaching by 14 times The acidic pH in river water, especially in the rainy season, facilitates Mn dissolution and its release from sediments, whereas anoxia and low pH facilitate Fe release Aquatic Mn concentration and CO2 partial pressure also contribute to Mn dissolution ASS-derived sediments (SG17 and SG18) had faster and higher Mn and Fe leaching rates than the other sediments Land management and improvement of water quality in the rainy season to avoid the acidification and DO depletion will help to reduce Mn and Fe leaching into the river water ACKNOWLEDGEMENTS The Japan Society on Promotion of Science and the HCMC Department of Science and Technology are greatly appreciated for funding to conduct this study 2237 N T Van Ha et al | Sources and leaching in the Saigon River Basin REFERENCES Abesser, C., Robinson, R & Soulsby, C Iron and manganese cycling in the storm runoff of a Scottish upland catchment Journal of Hydrology 326, 59–78 American Society for Testing and Materials (ASTD) Standard Test Methods for Shake Extraction of Solid Waste with Water ASTMD-3987, American Society for Testing and Materials, Annual Book of ASTM Standards v.11.04, pp 24–27 Davison, W Iron and manganese in lakes Earth-Science Reviews 34, 119–163 Green, R., Waite, T D & Melville, M D Characteristics of the acidity in acid sulfate soil drainage waters, MCLeods Creek, Northeastern NSW, Australia Environmental Chemistry 3, 225–232 Guerios, B B., Machado, W., Lisboa-Filho, S D & Lacerda, L D Manganese behavior at the sediment-water interface in a Mangrove dominated area in Sepetiba Bay – Abstract, SE Brazil Journal of Coastal Research 19 (3), 550–559 Kohl, P M., Medlar, S J & AWWA and USEPA Occurrence of Manganese in Drinking Water and Manganese Control American Water Works Association, IWA Publishing, Denver, Colorado, 184 pp Water Science & Technology | 63.10 | 2011 US EPA Method 3051A – Microwave Assisted Acid Digestion of Sediments, Sludge, Soils and Oils (Revision 1) US EPA Washington, District of Columbia, 25 pp US EPA Drinking Water Health Advisory for Manganese, Report 822-R-04–003, US EPA, Washington, District of Columbia, 34 pp Available from: http://www.epa.goc/ safewater/cci/pdf/dwadvisory (accessed 10 October 2006) Wasserman, G A., Liu, X., Parvez, F., Ahsan, H., Levy, D., FactorLitvak, P., Kline, J., Geen, A V., Salvkovich, V., Lolacono, N J., Cheng, Z., Zheng, Y & Graziano, J H Water manganese exposure and children’s intellectual function in Araihazar, Bangladesh Environmental Health Perspectives 114 (1), 124–129 Welch, S A., Christy, A G., Kirste, D., Beavis, S G & Beavis, F Jarosite dissolution I – Trace cations flux in acid sulfate soils Chemical Geology 245, 183–197 World Health Organization (WHO) Manganese in Drinking Water – Background Document for Development of WHO Guidelines for Drinking-Water Quality WHO/SDE/WSH/ 03.04/104, World Health Organization, Geneva, 21 pp Youger, J D & Mitsch, W J Heavy metal concentration in Ohio Revier sediments – Longitudinal and temporal patterns Ohio Journal of Science 89 (5), 172–175 ... | Sources and leaching in the Saigon River Basin REFERENCES Abesser, C., Robinson, R & Soulsby, C Iron and manganese cycling in the storm runoff of a Scottish upland catchment Journal of. .. RT) in the middle section had low pH and high Fe concentrations, indicating that acidic leachates from ASS contribute to the Fe inputs and acidification of the Saigon River The acidic drainage... of lower aqueous Mn2ỵ and P(CO2) than in the pore water of the sediments CONCLUSIONS Two major sources of Mn and Fe inputs into the Saigon River were identified: (1) acidic leaching from ASS in