VNU ỉo u rn a l of Science, F.arth Sciences 24 (2008) 87-95 Effects of using wastewater as nutrient sources on soil chemical properties in peri-urban agricultural systems N g u y e n M a n h K h a i1'4, P h a m T h a n h T u a n 2, N g u y e n C o n g V in h 3, I n g rid O b o r n Coỉỉcgc of Science, VNU Department o f Environmental Impact Asscssmcnt and Appraisal, M inistry o/N aturaỉ Resources and Environmcnt ( MONRE) ’ Soils and Fertiỉizers ỉnstitutc Department of Soil Sãcnces and Environment, Sĩocdish University of Agriadturaỉ Scicnccs (SLU) Kcccivod 27 M ay 2008; rcccivcd in rcviscd ío rm July 2008 A bstract R cu sing d o m estic w a stc w n te r for irrigation and a p p ly in g bio so lid s as a íertiliser in crop p ro d u ctio n a rc com m on practiccs in pcri-u rban arcas of V ietnam T his stu d y investigatcs thc cffects o f u sin g d o m cstic w a stc w ater in ficld cxpcrim cnts on riu v iso ls soils in pcri-urban arcas of l ỉanoi an d N am D inh cities VVe co m p a rc d long-tcrm (30-50 ycars) w a sto w ater-irrig atcd ricc-dom inated íarm in g sy stem s U sing w a stc w a tc r for irrigation signiíicantly affcctcd pl 1, electrical conductivity (KC), exchan g eablc K a n d N a a n d rc v ersc aqun rí$/rt-digestiblc (Rcv Aq R cịị) co p p c r (Cu), lcad (Pb) an d zinc (Zn) in the in v e stig a tc d a rc a s com pared \vith troi plots irrigntcd using riv er w atcr ĩh c rc w crc n o sig n iíican t cffccts o f w astcw atcr irrigation o n th c NI I N O vextrnctablc íraction of c ad m iu m (C d) and o th c r trac c m ctals, but th c r.D T A -extractable íraction of C u # Pb a n d Zn w as sig n iíican tly in crcascd Kci/ĩOữrds: SF A sia; hcnvy m ctals; irrigation; p a d d y soils; tracc elem onts Introduction The advantagos of reusing w astew ater arc that it providcs a convcnient disposal of w aste products and has the beneíicial aspects of ad d in g valuable plant nutrients and organic m atter to soil Purthcrm ore, the reusc of w astow atcr for irrigation as a íertiliser source is a com m on and popular practice, cspocially in pcri-urban aroas W astowater is often the only source of w atcr for irrigation Evon in arcas vvhere w astew ater is not the solc vvater source for agricultural irrigation, íarm crs still proíor using sew age for irrigation by rcason of its nutritivc valuc, vvhich ređuccs expcnditurc on chcm ical ícrtilisers [10,17] Urbanisation and industrialisation are leading to pro d u ctio n of a h u g c volum e of eííluents in m any countries Industrial, agricultural and dom estic cffluents such as biosolids and w astow ater are eith er d u m p cd on land or used for irrigation an d íertilisation purposes, vvhich creates both o p p o rtunitics and problem s [24] * Corrosponding author Tcl.: 84-4*5583306 K-mail: khainm ểvnu.vn 87 Ngm/cn Maiĩh Khni ctnl / VNU Ịountnl o f Science, Eartlt Sciences 24 (2008) 87-95 88 Hovvever, as vvastes are products of hum an society, onhancod concentrations of potential toxic substances including traco m etals are generally ío und in waste\vater, w hich m ay lim it the long-term usc of effluents for agricultural p u rp o ses due to the likclihood of phytotoxicity, hoalth and envừonm ental effects (1, 14] Anothcr problem of w astcw atcr disposal on agricultural land is tho potentially phytotoxic naturc of organic vvastes, m ainly as a result of com bination of íactors such as high salinity or excess of am m onium ions, organic com pounds or low m olccular w eight íatty acids, vvhich e.g m ay inhibit soed germ ination | , 10] If the content of trace m ctals increascs above a ccrtain critical concentration due to theừ accum ulation in soil, this can have negative environm ental effccts, which can includc negative effccts on soil biota and honce on m icrobial and íaunal activity [7ị Furthermoro, tracc m etals can affect crop grow th and quality, and thus pose risks for hum an health [2, 6, 12] Thereíorc, thc risk of contam ination by trace m otals m ust bc considcred vvhon wastcvvater is applicđ and understanding of thc behaviour of m ctals in thc soil is essential for assessing environinental risks of ap p lying w astew ater in agro-ocosystem s T h e m ain objective (>f this papor w as to q u an tiíy thc cffects of reuse of vvastowatcr as n u tricn t sources by: (i) invcstigatúig the effccts of long-term vvastcvvatcr rigation on soil pH , EC, organic carbon, total nitrogcn and trace m etals (cadm ium (Cd), copper (Cu)y lcad (Pb) and zinc (Zn)); (ii) invcstigating the cííects of application of w astcw atcr, espocially as rcgards tracc mctal accum ulation and solubility M ate rials and m eth o d s 2.7 Locatiou of thc rcscarch arcas Soil sam ples w cro collccted from periu rb an arcas in tvvo provinces of V ietnam , including Hanoi, N am Dinh (Table 1) Tho sam p led arcas are locatod in dclta and low land areas vvith a tropical m onsoon clim ate T he annual rainíall is 1500-2000 m m , and m orc than 50% of thc rainíall is concentrated during Junc to A ugust T he m ean m onthly tem porature varies betvveen 17 and 29"c, w ith tho w arm cst pcriod from Junc to A ugust and the coldest d u rin g Decombor and January T able D cscription of w a stc w a tc r (full-scale case s tu d ic s) in cx p e rim en ts on P luvisols in p cri-u rb an arcas o f H anoi and N a m D inh citics, V ictnani No Location Soil irrig atc d by Posỉtion N am c C ro p A p p licatio n S am p lin g tim c Ilan o i F luvisols W astcw atcr N: 20°57.52' K: 105°49.68' T rc a tm e n t Ricc Since 1960s Ju n c 2004 R iver w ntcr N: 20°58.12' E: 105°48.15’ C e n tra l Rice W a stc w atcr N: 20°44.93’ E: 106°20.98' T re atm en t Rice R ivcr w atcr N: 20°43.43' Con troi Rice Ju n c 2004 N am D inh F luvisols E: 106o20.68’ Sincc 1980s Ju n c 2004 Ju n c 2004 N^UI/CIÌ M anh Khai ct nị / VNU Ịourtml o f Sãencc, ĩ.nrth Sciences 24 (2008) 87-95 2.2 Wastaoatcr irrigation in pcri-urban agriailtural production systems The sevvage rig atio n study arcas are located ừi u rb an rcgions dovvnstream from Hanoi City and N am Dinh City Tho soil typcs arc Eutric Fluvisol at tho Hanoi site, and H um i-E ndogleyic Fluvisol (Eutric) at tho Nam Dinh sito according to tho World Rcíorcnce Baso for Soil Resources T he soils are íertile and suitable for grow ing crops Rice has been th e m ain crop in these areas, but therc is a ten d en cy of changing from rice to vegotable p ro d u ctio n d u e to incrcasing dcm and from the innor City m arkots of Hanoi and Nam Dinh At tho Hanoi site, sevvage w atcr has been usod for irrigation since thc 1960s Bocause o f vvater scarcity, agricultural land has boen irrigated by sevvage from Kim Nguu River, w hich runs thrọugh tho urban arca to rural agricultural land [8, 9] At the Nam Dinh site, irrigation using vvastevvater started in thc 1980s as a rosult of increasing urbanisation Tho sow agc m ainly com prises dom cstic w ater but also includes vvastovvater and dischargcs from industrial activities in the urban areas |4, 20] In N am Dinh, the soil sam ples vvere takcn in the íields vvhore the DANIDA-IWMI project on vvastevvater reuse in agriculturc in V ietnam w as carried out [20] 2.3 Soil sampling stratcgy and sainplc prcparation For assessment of the im pact of wastovvater, soil sam ples w erc takcn from the topsoil (0-20 cm) of all stu d y sitcs in pcri-urban arcas of Hanoi (n=4) and N am Dinh (n=8) u sing a soil auger At cvery sam p lin g point, to subsamplos w crc takon from approxim ately 250 m and m ixed to obtain a bulk sam plc Nonvvastewater irrigatcd soils ("natural" river irrigation) w ere also sam plcd for com parison (n=4 for Hanoi, an d n=8 for N am Dinh) 89 A íter air drym g at room tcm peraturo, thc soil sam plos vvere ground and sievod to rem ovc particlos > m m , and then stored in plastic bags The soil sam plos w crc brought to Sw edon (SLU) for analysis 2.4 Soil analysis Total N (Ntot) and total organic carbon (TOC) vvas detorm incd on íinoly ground sam plcs on a LECO CH N analyser (Lcco CH N*CHN 932 analyser) Prior to the analyses, tho sam plos worc trcatcd by 4M HC1 (1:1 soil:solution ratio) for dissolution of carbonates T he soil EC and pH vvere m oasurcd in deionisod H :0 (1:5 soil:solution ratio), and pHcaci: vvas doterm inod aftcr addition of 0.5M CaC l; [18] Tho soil sam plcs wcru cxtractod w ith IM N H jN O j for hours (1:2,5 soil:so!ution ratio) to quantiíy thc exchangoablo and spociíically adsorbod íraction of trace m ctals (i.c Cd, Cu, Pb, Zn) |3| Potentially bioavailable metals wcro extracted vvith 0.025 M (Na):EDTA (1:10 soilisolution ratio) for 1.5 h |19| The reversc acịua rcgia (3:1 HNO.;:HCl ratio)-digestible ừaction (Rcv Aij Rcg) of C d ; Cu, Pb and Zn w as extracted using a m ethod dcscribcd by Stcvens et al [18] Aíter contriíugation, íiltration an d dilution (if neccssary) m etal concentrations vvere determ ined by inductivcly couplcd plasm a-m ass spoctrometry (ICP-MS, Perkin Elmer ELAN 6100) 2.5 VVatcr sampling and ĩoatcr analysis In N am Dinh and Hanoi, vvater samples w ere colloctcd in su m m er 2004 from the Red Rivèr and w astew ater channcls, which wcre the irrigation sourcos at the study sites The pH and EC in these vvatcr sam ples vvere dcterm ined directly after sam pling Polyethylene bottles that had been pre- N guyên Manh Khni et a i / VNU Ịounml of Science, Lnrth Sciences 24 (2008) 87-95 90 w ashed w ith acid and distilled w ater and dricd wero used, and aíter sam pling, a few drops of concentratcd HC1 vvere added prior to chem ical analysis VVater sam ples vvcre analysed for thcừ total concentrations of Ca, Cd, Cu, K, Mg, N, p, Pb and Zn O n e aliquot of the sam ples vvas digested w ith boiling concentrated H N O beíore determ ination of the total conccntration of K by ílam e spectrom otry; Ca, Mg and Na, by atom ic ad so rp tio n spcctrophotom etry (AAS, Perkin Elm er 300); Cd, Cu, Pb and Zn by ICP-MS, an d total p by H N O digestion followod by detcrm in atio n of PO 4-P w ith the ascorbic acid m ethod [5] Total N vvas quantiíied as described elsevvhere [9Ị with the river vvater Tho \vastow ator also had signiíicantly highcr conccntrations of nutricnts and traco m ctals com parcd vvith the river w ater This indicatcd that non-treatcd vvastcwater containod both nutrients that are of value for irrigation of crops in agricultural system s, and potontial toxic elem ents that can aííect soil production capacity an d crop quality A com parison botweon w astew aters in H anoi and N am Dinh show ed that the conccntrations in Hanoi vvastevvater w ere significar>tly higher for m ost elcm ents included in the study (i.c Cd, Cu, K, Na, N,„„ P1o1/ Pb, Zn) 3.2 Effccts o f applying ĩoastaoater on soil pH and elcctrical conductivity 2.6 Statistical analysis Data from tho experim ents wero analyscd using the G eneral Lincar Modcl (GLM) procedure of M initab Softw are version 14 T reatm ent m ean s w hich shovvòti signiíicant differenccs at th e probability level of p