Irrigation with Treated Municipal Wastewater on Artichoke Crop

18 Pages·2017·1.26 MB·English

water
Article
Irrigation with Treated Municipal Wastewater on
Artichoke Crop: Assessment of Soil and Yield Heavy
Metal Content and Human Risk
GiuseppeGatta1,* ID,AnnaGagliardi1 ID,GraziaDisciglio1,AntonioLonigro2,
MatteoFrancavilla1,EmanueleTarantino1andMarcellaMichelaGiuliani1 ID
1 DepartmentofAgricultural,FoodandEnvironmentalSciences,UniversityofFoggia,71122Foggia,Italy;
[email protected](A.G.);[email protected](G.D.);[email protected](M.F.);
[email protected](E.T.);[email protected](M.M.G.)
2 DepartmentofAgriculturalandEnvironmentalScience,UniversityofBari,70121Bari,Italy;
[email protected]
* Correspondence:[email protected];Tel.:[phone]
Received:3February2018;Accepted:26February2018;Published:1March2018
Abstract:Industrialandmunicipalwastewatersareoftenusedforirrigatingagriculturalfieldsinarid
andsemi-aridcountries,representingthemostattractiveoptiontoalleviatepressureonfresh-water
resources. However, thewastewatermaycontainvariouspotentiallytoxicelementsandorganic
matters with highly harmful effects on human and animal health. During two growing seasons
ofglobeartichoke,theeffectsofirrigationwithsecondary(SWW)andtertiary(TWW)municipal
wastewater on heavy metal soil and plant content were evaluated, together with the consequent
humanriskfromartichokeheadconsumption. Theheavymetalcontents(i.e.,Al,Cd,Co,Cr,Cu,Fe,
Ni,Pb,Zn,andMn)oftheirrigationwater,soil,plant,andyieldwereanalyzed. Totalandextractable
heavymetalswerequantifiedtodeterminethebioaccumulationfactors,andthehealthriskstoadults
andchildrenweredeterminedaccordingtohazardindices. Theheavymetalcontentsoftheartichoke
headsharvestedafterSWWandTWWirrigationwerelowerthantheinternationalthresholdvalues,
andlowbioaccumulationfactorssuggestedthattheseheavymetalsdidnotaccumulateintheedible
partoftheartichokecrop. Thehazardindicesthatwerebasedontheconsumptionoftheartichoke
headsremained<1.0forbothadultsandchildren,thusindicatingthatthehealthrisksinvolvingthe
differentheavymetalsarenotsignificant.
Keywords: globe artichoke; treated wastewater re-use; irrigation; heavy metal; risk assessment;
bioaccumulationfactor
1. Introduction
Water scarcity is the primary reason for the increasing trend toward wastewater re-use in
agricultureworldwide. Industrialandmunicipaltreatedwastewatersareoftenusedforirrigation
ofagriculturalfields,particularlyinaridandsemi-aridcountries,becausethisrepresentsthemost
attractiveoptionforalleviatingthepressureonfreshwaterresources[1–4].Moreover,wastewatersmay
representasignificantnutrientsourceforplantsthataregrowninlowfertilitysoils[5,6]. However,in
additiontoplantnutrients,wastewatersmaycontainvariouspotentiallytoxicmineralelementsand
organicmatter,andthesecomponentscanhaveharmfuleffectsonhumanandanimalhealth[7]. Asfor
heavymetals,whilelowconcentrationsinthesoilareoftenbeneficialtothegrowthandmetabolismof
plants,theycanhaveundesirableeffectsathigherconcentrations[8,9]. Althoughtheheavymetals
contentinwastewaterthatisusedforirrigationmustcomplywiththelegallimits,continuoususe
ofwastewatercanleadtotheirsoilenrichment. Accumulationoftoxicheavymetalscausestressin
Water2018,10,255;doi:10.3390/w10030255 www.mdpi.com/journal/water
Water2018,10,255 2of18
plantsduetointerferencewiththemetabolicactivitiesandphysiologicalfunctioningoftheplants[10].
Excessivelevelsofmetalscanalsoresultinthedegradationofsoilquality,reductioninmarketable
cropyield,and/orpoorqualityofmarketableagriculturalproducts,andtheseeffectscanalsopose
significanthazardstothehealthofhumans,animals,andtheecosystem[9,11].
The leafy parts of vegetables tend to accumulate higher amounts of heavy metals than the
fruits [12]. Studies on the plants heavy metals uptake have shown that they can be transported
fromrootstoshootsthroughthexylemvessels[13],whiletheygenerallyhavepoormobilityinthe
phloem [14]. Plant storage organs, such as fruits and seeds, have low transpiration rates and do
notaccumulateheavymetalsbecausetheyarelargelyphloem-loaded. Theaccumulationofheavy
metalsinagriculturalsoilsthroughwastewaterirrigationmightnotonlyresultinsoilcontamination,
but might also affect food quality and safety [15]. Adverse effects of soil and vegetables heavy
metalscontaminationonhumanhealthhavebeenwidelyreported[9,16,17]. Majordamagetohealth
is strongly correlated with heavy metal toxicity, which can cause tissue damage, kidney tubule
dysfunction, skeletal damage, osteoporosis, cancer of the blood and lungs, metabolic disorders,
anaemia,andhypochromicanaemia[18].
The risks that are related to the uptake of heavy metals by food crops depends more on the
increaseoftheiravailablefractionthanonthetheirtotalconcentrationinthesoil[19],ontheheavy
metalsspeciationandsolubility,andonthecropsthatarecultivated[20].
Globeartichoke(CynarascolymusL.)isanirrigatedcropthatiswidespreadinMediterranean
areas,anditisofparticularimportanceintheMediterraneandiet. Inareasinwhichcropsareirrigated
withwastewateritisrelevanttoevaluatetheaccumulationofindividualheavymetalsintheedible
parts in order to estimate potential risks to human health. To the best of the authors’ knowledge,
noinformationareavailable,inthescientificliterature,ontoxicheavymetalcontaminationofglobe
artichokecropirrigatedwithtreatedwastewaterneitherontheriskstohumanhealththatmaybe
associatedwithsuchcontamination.
Theaimofthepresentstudywastoevaluatetheaccumulationofheavymetalsinthesoil,with
specificreferencetotheexchangeablefraction,andintheediblepartoftheartichokecropirrigated
with fresh, secondary (SWW), and tertiary (TWW) municipal wastewater. Moreover, it was also
evaluatedthebioaccumulationfactorsandthenthehumanriskthatisrelatedtotheconsumptionof
artichokeheads.
2. MaterialsandMethods
2.1. SiteDescriptionandAgronomicConditions
TheresearchwasconductedintheApuliaregionofItaly(Trinitapoli,41◦21(cid:48) N,16◦03(cid:48) E;altitude
10ma.s.l.) onglobeartichoke(Cynaracardunculus(L.),subsp. scólymusHayek),cultivar‘Violettoof
Provenza’overtwocroppingcycles(2012–2013and2013–2014). Theexperimentaltrialwasperformed
inaloamsoil(UnitedStatesDepartmentofAgricultureclassification)withthefollowingphysicaland
chemicalcharacteristics: sand,45.3%;silt,30.0%;clay,24.7%;fieldcapacity(measuredbypressure
plateapparatusat−0.03MPa)of30.7%dryweight(dw);wiltingpoint(measuredbypressureplate
apparatusat−1.5MPa)of15.2%dw,andabulkdensityof1.45Mgm−3;organicmatter,1.2%(Walkley
andBlackmethod);availablephosphorus(Olsenmethod),114.0mgkg−1;totalpotassium,1.27gkg−1
(determinatedbycoupledplasmaopticalemissionspectrometer,Agilent,ICP-OES720);totalnitrogen,
0.91 (Kjeldahlmethod).
(cid:104)Threetypesofirrigationwaterwereappliedtothecrop: freshwater(FW),secondarymunicipal
wastewater (SWW), and tertiary municipal wastewater (TWW). The FW was obtained from the
irrigationnetworksystemthatisnormallyusedbythefarmersintheareaforcropirrigation;theSWW
andTWWwerefromsecondaryandtertiarymunicipalwaterrecyclingplantthatwaslocatednear
theexperimentalsite. Arandomizedcompleteblockdesignwiththreereplicationshasbeenused.
Overall, nine plots of dimensions 16.8 m × 6.0 m were defined. In the first growing season (GS ),
1
Water2018,10,255 3of18
theartichokeplantswereplantedasoffshootson15July2012inrows1.20mapartandwith1.20m
spacingwithintherowstoprovideadensityof6944plantsha−1. Inthesecondgrowingseason(GS ),
2
theplantswerere-awakenedon20July2013byapplyingwaterinordertoestablishsoilfieldcapacity.
Adripirrigationsystemwasusedwithdripperlinesplacedalongeachrow. Thein-linedripperswere
located0.40mapart;thedripperflowratewas4Lh–1atanoperatingpressureof1.5bar. Irrigation
wasperformedwheneverthewaterwaslost(excludingtheusefulrainfall)bycropevapotranspiration
(ET )inthesoillayercontainingtherootsreachedapredeterminedlevel(30mm,i.e.,~50%ofavailable
c
waterdepletion). Thewateringvolumeusedrestored100%ofthewaterlost. DuringtheGS andGS
1 2
growingcycles,theseasonalwaterirrigationvolumesappliedwere3300m3ha–1and3000m3ha–1,
respectively. Duringthesetwogrowingseasons,standardagronomicpracticesforartichokecrops
werefollowed.
2.2. Water,SoilandPlantSampling
Water samples were collected and analyzed six times during the two growing seasons.
Inparticular,duringGS watersamplesweretakenat5,71,128,191,247,300daysaftertransplanting
1
(S –S ), while during GS , they were taken at 2, 58, 113, 185, 245, 303 days after transplanting
W1 W6 2
(S –S ). The samples were taken as three replications using 1000 mL sterile glass bottles,
W7 W12
transportedinrefrigeratedbagstothelaboratory,andwerestoredinarefrigeratorat4◦C.Toprevent
microbialactivity,1mLconcentratedHNO wasaddedtoeachwatersample.
3
Soil samples were collected randomly from each experimental plot before transplanting time
(S ,fordeterminationofbackgroundsoilheavymetalcontent)andattheendofthefirst(S )and
S1 S2
second(S )artichokegrowthcycles. Thesoilsampleswerecollectedatdepthsof0–40cm(H )and
S3 1
40–80cm(H ). H representedthehighrootdensityzone(i.e.,topprofile),whileH representedthe
2 1 2
deeperpartoftherootzone(i.e.,bottomprofile). Soilsampleswereair-dried,crushed,andpassed
througha2-mmsievepriortochemicalanalysis. Thefullsoilsamplingcomprisedonesampleper
plot × 9 plots (i.e., 3 irrigation treatments × 3 replicates) × 3 sampling dates × 2 soil depths × 2
growingseasons,yieldingatotalof108soilsamples.
Sampling of the artichoke heads (i.e., the portion of the plant that is edible to humans) was
performed three times (in November, March and May), in each growing season by picking five
marketableartichokeheadsperexperimentalplot. Attheendofeachgrowthcycle,threerandomly
selectedplantswerecollectedfromeachplotanddividedintoleavesandstems. Theartichokeplant
andheadsamplesweredriedinanovenat70◦Cfor24h,groundintofinepowder,sievedthrough
2-mm mesh, and were stored at room temperature. The full sampling comprised five heads per
plot×9plots(i.e.,3irrigationtreatments×3replicates)×3samplingdates×2seasons,yieldinga
totalof270artichokeheads.
2.3. DeterminationofHeavyMetalsintheWater,SoilandPlantSamples
Allofthesamples(water,soil,plants,andartichokeheads)wereanalysedforthetraceelements
Al,Cd,Co,Cr,Cu,Fe,Ni,Pb,Zn,andMn. Inthesoilsamples,theextractablemetalfractionswerealso
determined. Theelementsanalysedarehereinafterreferredtoas‘heavymetals’. Allofthesamples
wereanalysedintriplicatetoensuredataaccuracy,andthemeansofthreeinstrumentalreplicates
wereusedindatainterpretation. Thechoiceoftheheavymetalsforanalysisinthesoilandinthe
plant marketable yield (i.e., artichoke heads) was based on their concentrations in the three types
of irrigation water that were used. Thus, the metals that were below the limit of detection in the
irrigationwatersamples(i.e.,PbandCd)werenotanalysedinthesoilandintheartichokeplantand
headsamples.
For the analytical determination of the heavy metal water content, each sample was filtered
througha0.20-µmsyringefilterconsistingofacelluloseacetatemembraneanddiluted,ifnecessary,
with ultrapure water (Milli-Q). The levels of the heavy metals were determined using inductively
coupled plasma optical emission spectrometer (Agilent, ICP-OES 720). Soil samples (0.5 g dw)
Water2018,10,255 4of18
were mineralized in 10 mL 70% (v/v) HNO in a microwave oven (CEM-Mars6). After cooling,
3
thedigestedsamplesweretransferredinto50-mLflasksandbroughttothefinalvolumewithMilli-Q
water[21],andthananalyzedbyICP-OES.Theextractablemetalfromsoilsampleswereobtained
using diethylenetriaminepentaacetic acid (DTPA) solution, according to ISO 14870 method [22].
About10gofeachsoilsamplewasextractedwith100mL0.005MDTPAfor30min,undershakingat
180oscillations/min. ThemixturesobtainedwerefiltredandanalyzedbyICP-OES.
Foranalyticaldeterminationofthetotalheavymetalconcentrationsintheartichokeplantsand
heads,thesamples(about0.5gdw)weremineralizedin10mLHNO /H O (3:1;v/v)inamicrowave
3 2 2
oven(CEM-Mars6). Aftercooling,thedigestedsamplesweredilutedwithMilli-Qwaterto50mL[23]
andwereanalyzedbyICP-OES.
2.4. QualityAssuranceandQualityControl
Appropriatequalityassuranceproceduresandprecautionswerefollowedtoensurethereliability
of the data. All of the reagents used were of analytical grade. Glassware was cleaned thoroughly
withdetergentandwasrinsedseveraltimeswithdeonizedwater. Milli-Qwaterwasusedforallof
thedilutionsthroughoutthestudy. Blankreagentdeterminationswereusedtocorrectinstrument
readings. Toensuredataquality,thesampleswereanalysedintriplicate,andonestandardsample
wasanalysedforeverythreeexperimentalsamples. Tomaintaininstrumentcalibration,blankand
driftstandardswererunaftereveryfivedeterminations.
2.5. BioaccumulationFactorandCharacterizationofHumanRisk
The bioaccumulation factor (BAF) is an index related to the accumulation in food of a
particular metal with respect to its concentration in the soil; here, it was calculated according to
Cuietal. (2004)[24],asdefinedinEquation(1).
BAF =C /C (1)
M Mplant Msoil
whereC andC representthetotalconcentrationsofaparticularheavymetalintheedible
Mplant Msoil
partsoftheplantandinthesoil, respectively, ondryweightbasis. Inthepresentstudy, BAFwas
calculatedbothrelativetothetotalmetalconcentration(BAF)andalsorelativetothe‘extractable’
t
heavymetalsconcentration(DTPA-extractablemetalfraction;BAF ).
e
Thehazardindices(HIs)usedtodeterminethenon-carcinogenicriskstohumanhealthwere
estimatedbycomparingthedailyintakeofaparticularmetal(DI )throughtheediblepartofthe
M
artichoke crop with the corresponding oral reference dose (RfD ) [9,24–26]. Thus, the HIs for the
M
consumptionoftheartichokeheadswerecalculatedusingEquation(2)[27].
Ef×Ed×DI
HI= (2)
RfD×BW×ET
whereEfisthefrequencyofexposure(thefrequencyofartichokeconsumption)intheexperimental
area(240daysyear−1),Edistheexposureduration(82years,equivalenttothemeanlifespanofmalesand
femalesinItaly)[28],DIisthedailymetalintake(mgperson−1day−1),RfDistheamountofthechemical
elementthatcanbeingesteddailyoveralifetimewithoutcausingharmfulhealtheffects(mgkg−1day−1),
BWisthemeanbodyweightoftheconsumer(kg),andETisthemeanexposuretimefornon-carcinogens
(280daysyear–1×numberofexposureyears,assuming50yearsinthisstudy).InEquation(2),DIforeach
particularheavymetal(DI )wascalculatedbymultiplyingthedailyfreshartichokeheadconsumption
M
(kgperson−1day−1)bytheaverageamountofthatheavymetalintheartichokeheads(mgkg–1fresh
matter). The mean daily vegetable intakes for adults and children were considered to be 0.021 and
0.0105 kg person−1 day−1 [29], respectively, and the mean adult (18 years of age or over) and child
(8yearsofage)bodyweightswereconsideredtobe70.2kgand31.9kg,respectively[30,31]. TheRfD
foreachheavymetal(RfD )wasderivedfromtheUSEnvironmentalProtectionAgency[32]guidelines
M
Water2018,10,255 5of18
(http://www.epa.gov).Finally,theadditiveHIs(AHIs)forthetotalheavymetalcontaminantsforboth
adultsandchildren[32]hasbeencalculated,asreportedinEquation(3).
n
∑
AHI= HI (3)
i=1
InEquation(3),HIisdefinedfortheindividualnheavymetalsasshowninEquation(2).
2.6. StatisticalAnalysis
Thedatasetsweretestedaccordingtothebasicassumptionsofanalysisofvariance(ANOVA).
The normal distribution of the experimental error and the common variance of the experimental
errorwereverifiedthroughShapiro-WilkandBartlett’stests,respectively. Whenrequired,Box-Cox
transformations[33]wereappliedpriortoanalysis.
Forallofthedatasets,theANOVAprocedurewasperformedaccordingtoarandomizedcomplete
block design with three replicates. For irrigation water data, two-way ANOVA was performed
(irrigationwater×watersamplingdate). Theirrigationwaterwasconsideredtobeafixedfactor,
and the water sampling date was considered a random factor. Each soil heavy metal content was
subjectedtoathree-wayANOVAprocedure(irrigationwater×soildepth×soilsamplingdate)when
consideringthetypeofirrigationwaterandthesoildepthasfixedfactorsandthesoilsamplingdate
asarandomfactor. Fortheheavymetalcontentoftheartichokeplants,combinedanalysisofthedata
wasperformedtodeterminethemeanirrigationwaterresponseoverthetwogrowingseasons.
Lastly,thedataonbioaccumulationfactors(BAF andBAF )andhazardindices(HIandAHI)
t e
weresubjectedtoaone-wayANOVAprocedureinwhichthetypeofirrigationwaterwasconsidered
the only effect. The statistical significance of the differences in the means was determined using
Tukey’s honest significance difference post hoc test at the 5% probability level. Bivariate statistical
methodswereappliedtoverifythedataforcorrelationsamongthedifferentheavymetalcontents
forirrigationwater,soil,andmarketableyield. TheANOVAandbivariatestatisticalmethodswere
performedusingtheJMPsoftwarepackage,version8.1(SASInstituteInc.,Cary,NC,USA),andfigures
wereconstructedusingSigmaPlotSoftware(SystatSoftware,Chicago,IL,USA).
3. ResultsandDiscussion
3.1. HeavyMetalContentofIrrigationWater
TheANOVAofthedataforthethreeirrigationwatersshowedsignificantdifferencesinheavy
metalcontentforboth,irrigationwatertype(IW)andwatersamplingdate(S )aswellasfortheir
W
interaction. Figure1showsthelevelsofindividualheavymetalsinFW,SWWandTWWmeasuredon
the12samplingdates(GS ,S –S ;GS ,S –S ). TheCdandPbcontentswerenotconsidered
1 W1 W6 2 W7 W12
beingbelowthedetectionlimits(0.001and0.008mgL−1,respectively)probablybecauserecycled
municipalwastewatersdonotusuallycontaintheseindustrialwastecontaminants[15,34].Asexpected,
theconcentrationsofallheavymetalsinFWwerelowerthantheconcentrationsinSWWandTWW
(Figure1). TheheavymetalcontentofSWWandTWWshowedhighvariabilityasafunctionofwater
samplingdate. Inparticular,theCr,Cu,Zn,andMncontentsweresignificantlyhigher(p<0.05)at
S andS (July2012andJuly2013,respectively)thanattheothersamplingdates(Figure1).
W1 W7
Thisvariabilitymightbeduetoseasonalvariabilityinthequalityofthewaterthatformedtheinput
tothewastewatertreatmentplant. Indeed,theinputwaterforthewastewatertreatmentplantcame
fromTrinitapoli,whichisasmalltownof15,000inhabitants[28],whichincreaseduringthesummer
holidays(July–August);thismightresultinvariationinthechemicalcharacteristicsofthewastewater.
The Co content (about 0.007 mg L−1) did not show significant differences as a function of
watersamplingdate,withtheexceptionofS andS forSWWandTWW,respectively(Figure1).
W7 W9
The Al and Fe contents of SWW and TWW were highly variable, ranging from 0.075 mg L−1 to
0.005mgL−1andfrom0.20mgL−1to0.05mgL−1,respectively. Comparisonofthemeasuredheavy
Water2018,10,255 6of18
metal concentrations with national [35] and international (United Nations Food and Agriculture
Organization(FAO),USEnvironmentalProtectionAgency)guidelinesshowedthatthelevelsofheavy
metalsinSWWandTWWwerebelowtherecommendedthresholdvalues(Table1).
Water 2018, 10, x FOR PEER REVIEW 6 of 18
The heavy metal concentrations in the irrigation water that were used in this study are in
agreement with the report of Shiekh et al. (1987) [36] on the efficiency of municipal wastewater
The heavy metal concentrations in the irrigation water that were used in this study are in
treatmenatgprreoemceesnste swfiothr tthhee rreedpuorctt ioofn Sohfiehkeha vety aml. e(t1a9l8c7o) n[3te6n] to.nI ntdhee eedff,ichiiegnhcyc oonf tmenutnsiocifphale awvaystmeweatatelsr are
normallytrfeoautmnednitn prinocdeusssetsr ifaolr stehwe raegdeuectfifloun eonf th,ewavhye rmeeatsalt hcoenctoenntc. eInndtreaetdi,o hnisgho fcothnteesnetsm oef thaelasviyn mdoetmalse stic
wastewaaterer snaorremgaellny efroaulnlyd loinw infdoullsotwriailn gsetwhaegsee ettflfilnuegnot,f wsohleirdesasd uthrei ncgontrceeanttrmateionnts[ 3o7f ].thHesoew meevtearl,s hine avy
metalacdcuommeusltaict iwonasitnewthateersso ialrde ogeesnenroatllye xlcolwu sfiovlelolywdinegp tehned soetntlitnhge olef vseollsidosf dhuerainvgy mtreeattamlsenint [t3r7e]a. ted
However, heavy metal accumulation in the soil does not exclusively depend on the levels of heavy
wastewater; italsodependsontherateofirrigationandonthesoiltype[38]. Therefore,although
metals in treated wastewater; it also depends on the rate of irrigation and on the soil type [38].
theheavymetallevelsintheirrigationwastewaterusedinthisstudyarebelowtherecommended
Therefore, although the heavy metal levels in the irrigation wastewater used in this study are below
thresholds,itremainsimportanttoevaluatethesoilbioaccumulationofthesemetalsoverboththe
the recommended thresholds, it remains important to evaluate the soil bioaccumulation of these
mediummanetdalslo onvgert ebromth. the medium and long term.

Figure 1.FigHuerea v1y. Hmeeavtayl mcoetnatle cnotnsteonftst hoef tthher etehrierer iigrraitgiaotnionw wataetrer tytyppeess aapppplliieedd aas sfufnucnticotnio onf owfawtera ter
samplingsadmapteli,nsgh doawtei, nshgotwhiengir trhige airtriiognatwiona twerat×er w× wataetrers saammppllee ddaattee inintetrearcaticotnio (nIW(I ×W SW×). TShe) d.aTtah earde ata
W
arethemtheae nmse±ansst a±n sdtaanrddaerrdr oerrrsoorsf tohf rtehereree prelipclaictaetse.s.G GSS1,, fifirrsstt ggrroowwiinngg sseeaassoonn; ;GGS2S, s,esceocnodn gdrogwroinwg ing
1 2
season.Sseas–oSn. SW1a–rSeWt1h2 earwe athtee rwsaatmerp slainmgpldinagte dsaftoers tfhoer tfihres tfi(rSst (S–WS1–SW)6)a anndd sseeccoonndd ((SSW7–S–WS12) gr)ogwroinwg ing
W1 W12 W1 W6 W7 W12
seasons. Honest significant differences (HSDs) calculated according to Tukey’s test are also
seasons.Honestsignificantdifferences(HSDs)calculatedaccordingtoTukey’stestarealsoreported.
reported.
Water2018,10,255 7of18
3.2. HeavyMetalContentoftheSoil-PlantSystem
3.2.1. HeavyMetalContentoftheSoil
Table 2 lists the mean concentrations of individual heavy metals in the soil as a function of
irrigation water type (IW), soil depth (H), and soil sampling time (Ss). Only the soil depth had
significanteffectsonthetotalmetalcontents(p≤0.05),whilenosignificantinteractionswerefound
between these different experimental factors. The Co soil content was not determined because it
wasbelowthedetectionlimitof0.015mgkg−1;ontheotherhand,alsointheirrigationwaterthe
Cocontentwas, ingeneral, verylow(about0.007mgL−1). Alsoforthesoil, alltheheavymetals
examined were lower than the threshold values (Table 1) that were listed in the national [39] and
international[40]guidelines.
Table1.Nationalandinternationalguidelinesformaximumlimitsofheavymetalsinirrigationwater,
soilandcultivatedvegetables.
WastewaterGuidelines SoilGuidelines VegetableGuidelines
HeavyMetals (mgL−1) (mgkg−1 ) (mgkg−1 )
dryweight freshweight
1IGw 2FAO 3USEPA 4IGs 5EUs 6IR 7FAO/WHO
Al 1.0 5.0 5.0 - - - -
Cd 0.005 0.01 0.005 2.0 3.0 3.0e 0.1(0.050)
Co 0.05 0.05 0.05 20 - 50e 50
Cr 0.10 0.10 0.10 150 150 100e 2.3
Cu 1.0 0.20 0.2 120 140 100e 73
Fe 2.0 5.0 5.0 - - 50,000f 425
Ni 0.20 0.20 0.20 120 75 50e 67
Pb 0.10 0.50 0.50 100 300 100e 0.3(0.1)
Zn 0.50 0.20 2.0 150 300 300e 100
Mn 0.20 0.20 0.20 - - 2000f 500
Note: ThemaximumlimitsforvegetablesaccordingtoEuropeanguidelines,EC1881/2006[41],arereported
inparentheses. 1IGw,Italianguidelinesforagriculturalwastewaterreuse:MinisterialDecreen. 185/2003[35].
2Ayers,R.S.;Westcot1985[42]. 3UnitedStatesEnvironmentalProtectionAgency,Washington,DC,2012[43].
4IGs,Italianguidelinesforsoilcontent:MinisterialDecreen. 152/2006[39]. 5EUs,Europeanunionstandards
(EU2002)[40].6IR,Internationalreferences.7FAO/WHO,2001.Foodadditivesandcontaminants[44].eEwers,
1991[45].fPendiasandPendias,1992[46].-noprescribedlimits.
Table2. Maineffectsoftheirrigationwaters,soildepths,andsoilsamplingdatesonthetotalsoil
heavymetalcontents.
ExperimentalFactor TotalHeavyMetalContent(mgkg−1)
Al Co Cr Cu Fe Ni Zn Mn
Irrigationwater(IW) ns ns ns ns ns ns ns
FW 2827.9±45.8 nd 21.4±1.7 21.0±1.7 18,007.6±298.1 18.3±1.8 51.8±3.1 504.1±13.9
SWW 2839.8±45.2 nd 22.7±1.7 21.6±1.8 17,554.4±193.2 19.3±1.5 50.3±2.7 528.0±133
TWW 2915.6±57.8 nd 22.3±0.6 21.1±0.9 18,228.1±244.4 19.1±0.5 51.9±4.1 524.9±12.1
Soildepth(H) *** *** *** * *** *** ***
H1 3007.2±24.9a nd 24.3±0.8a 25.8±2.2a 17,615.1±183.4b 20.4±0.9a 56.7±2.3a 562.3±6.5a
H2 2715.1±33.3b nd 20.0±0.9b 18.3±0.3b 18,244.7±214.7a 17.5±1.0b 46.2±1.5b 475.8±6.7b
Soilsamplingdate(SS) ns ns ns ns ns ns ns
SS1 2959.4±54.2 nd 22.2±1.6 21.2±1.7 18,179.5±288.8 18.2±1.4 51.6±2.5 517.7±13.3
SS2 2845.8±53.1 nd 22.3±1.9 22.3±1.8 17,632.2±226.3 19.4±1.6 51.5±4.2 516.2±12.7
SS3 2832.2±42.3 nd 21.8±0.7 22.1±1.0 17,978.2±247.8 19.2±0.9 50.9±3.5 523.1±13.7
Note:Dataaremeans±standarderror(n=3).Foreachexperimentalfactor,datafollowedbydifferentsuperscripted
letters(aandb)withineachcolumnaresignificantlydifferent(p≤0.05;Tukey’stest);ns,notsignificant. FW,
freshwater;SWW,secondarytreatedwastewater;TWW,tertiarytreatedwastewater;H1,topsoilprofile(0–40cm);
H2,bottomsoilprofile(40–80cm).SS1,SS2,SS3,first(beforetransplanting),second(endofGS1),andthird(endof
GS2)soilsamplingdates,respectively;nd,notdetected;*p≤0.05;***p≤0.001(Fisher’stest).
TheconcentrationsofAl,Cr,Cu,Ni,Zn,andMnweresignificantlyhigher(p≤0.05)inH (top
1
soilprofile)thaninH (bottomsoilprofile). Incontrast,higherconcentrationsofFewerefoundinH
2 2
thaninH (18,244.7vs. 17,615.1mgkg−1).
1
Water2018,10,255 8of18
InordertodeterminetheBAF,manystudiesrefertotheconcentrationsofaheavymetalinthe
soilasthe‘total’amount. Tothebestoftheauthors’knowledge,veryfewstudieshaveconsidered
the concentrations of the ‘extractable’ heavy metals using DTPA, or other methods. Because total
heavymetalcontentisnotanefficientpredictoroftheavailabilityandmobilityofheavymetalsin
soils[47],inthisstudy,thepotentiallyplant-availableheavymetalcontents,asrepresentedbythe
DTPA-extractablecontents, werealsoevaluatedtodeterminewhethertheycanmoveintothesoil
anduptakebythecrop. TheDTPA-extractablemetalsdonotrepresentthetotalsoilmetalsthatare
availablefortheplant,however,theyaregoodindicatorsofthepotentialmetalsquantitiesthatthe
cropmayuptake[48].
The effects of type of irrigation water used, soil depth, and soil sampling time (IW, H, S
S
experimentalfactors)onthemeansoilconcentrationsofDTPA-extractableheavymetalsarereported
in Table 3. Also, in this case, Co content was not determined as it was below the detection limit
(0.015mgkg–1). DTPA-extractableAl,Cu,Ni,andZnlevelsweresignificantlyhigher(p≤0.05)in
SWW and TWW than in FW. The concentrations of Cr in TWW was not significantly higher than
thoseinFW.
Table3.Maineffectsofirrigationwaters,soildepths,andsoilsamplingdatesontheexchangeablesoil
heavymetalcontents(afterDTPAextraction).
ExperimentalFactor ExchangeableHeavyMetalContent(mgkg−1)
Al Co Cr Cu Ni Zn
Irrigationwater(IW) *** * ** *** **
FW 0.64±0.02b nd 0.34±0.01b 3.02±0.15b 0.29±0.02b 6.78±0.28b
SWW 0.74±0.01a nd 0.41±0.02a 3.52±0.20a 0.41±0.02a 7.60±0.24a
TWW 0.70±0.02a nd 0.39±0.02ab 3.55±0.20a 0.38±0.01a 8.39±0.57a
Soildepth(H) *** *** ** *** *
H1 0.73±0.01a nd 0.44±0.01a 3.56±0.18a 0.40±0.01a 7.33±0.20b
H2 0.66±0.02b nd 0.33±0.02b 3.17±0.13b 0.32±0.02b 7.95±0.25a
Soilsamplingdate(Ss) ns ns *** ns ns
SS1 0.71±0.02 nd 0.38±0.02 2.53±0.08b 0.34±0.02 7.79±0.17
SS2 0.67±0.03 nd 0.39±0.02 3.71±0.16a 0.35±0.02 7.39±0.37
SS3 0.70±0.02 nd 0.36±0.03 3.86±0.17a 0.37±0.02 7.60±0.39
Note:Dataaremeans±standarderror(n=3).Foreachexperimentalfactor,datafollowedbydifferentsuperscripted
letters(a,bandab)ineachcolumnaresignificantlydifferent(p≤0.05;Tukey’stest). FW,freshwater;SWW,
secondarytreatedwastewater;TWW,tertiarytreatedwastewater;H1,topsoilprofile(0–40cm);H2,bottomsoil
profile(40–80cm);SS1,SS2,SS3,first,second,andthirdsoilsamplingdates,respectively;ns,notsignificant.;nd,not
detected;*p≤0.05;**p≤0.01;***p≤0.001(Fisher’stest).
Moreover,forallofthemetalsconsidered,withtheexceptionofZn,theDTPA-extractablecontent
washigherinthetopsoilprofilethaninthebottomone. Finally,asforsoilsamplingdate(S ,S ,S ),
S1 S2 S3
onlyCushowedadifferentDTPA-extractableheavymetalcontent. ThemeanCucontentofthesoil
sampledattheendofthefirst(S )andsecond(S )artichokecropcyclesexceededthebackground
S2 S3
value(S ). ThismightbeduetotheplantsuptakeCuataratethatislowerthantherateatwhichit
S1
wassuppliedbytheirrigationwater.
The DPTA-extractable soil content of Fe and Mn varied significantly with type of irrigation
water and soil depth (IW × H interaction; Figure 2A,B). In the top soil profile (H ), SWW and
1
TWW both significantly increased the Fe and Mn soil content (3–5 mg kg−1 and 10–15 mg kg−1,
respectively;p≤0.05forboth)comparedtoFW.Incontrast,inthebottomsoilprofile(H )therewere
2
nosignificanteffects(p>0.05)ofSWWorTWWontheFeandMnsoilconcentrations. Thesedata
areinagreementwiththeresultsreportedbyAchahetal. (2014)[15],whofoundacloserelationship
betweenFecontentintheirrigationwaterandFecontentofthesoilandvegetablesamples. Also
Al-Lahhametal. (2007)[34],inastudyontomatocropsirrigatedwithwastewater,reportedincreased
concentrationsofMn,andFeinthesoilcorrelatedwiththehighconcentrationsofthesemetalsinthe
wastewaterusedforirrigation.
Water 2018, 10, x FOR PEER REVIEW 9 of 18
rWeapteorr2t0e1d8 ,i1n0c,2re55ased concentrations of Mn, and Fe in the soil correlated with the high concentrat9ioofn1s8
of these metals in the wastewater used for irrigation.
IInn tteerrmmss ooff tthhee SSS ×× HH inintteerraacctitoionn eeffffeecctsts ((FFigiguurree 22CC,D,D)), ,tthhee DDTTPPAA--eexxttrraaccttaabbllee FFee aanndd MMnn ssooiill
S
ccoonntteenntt iinn tthhee ttoopp ssooiill pprroofifillee ((HH1)) iinnccrreeaasseedd ffrroomm SSS1 ((33..2266,, 1100..5555 mmgg kkgg−−11, ,rreessppeeccttiivveellyy)) ttoo SSS3 ((44..4433,,
1 S1 S3
1155..3322 mmgg kkgg−−1,1 ,rerespspeectcitviveleyly),) ,ininddiciacatitningg ththaat tththeessee mmeetatalsls aaccccuummuulalatetedd ggrraadduuaalllyly inin tthhee ttoopp ssooiill;; nnoo
ssuucchh eeffffeecctt wwaass oobbsseerrvveedd ffoorr tthhee bboottttoomm ssooiill pprrooffiillee ((HH2)).. TThhee aaccccuummuullaattiioonn ooff FFee aanndd MMnn iinn tthhee ttoopp
2
soil profile was related to the higher content of Fe and Mn in SWW and TWW (Figure 1), and to the
soilprofilewasrelatedtothehighercontentofFeandMninSWWandTWW(Figure1),andtothe
low mobility of these heavy metals, especially in alkaline soils (pH ~ 8) [38]. Moreover, combining
lowmobilityoftheseheavymetals,especiallyinalkalinesoils(pH~8)[38]. Moreover,combining
this with the irrigation water demand of artichoke plants defined in terms of the active root depth
thiswiththeirrigationwaterdemandofartichokeplantsdefinedintermsoftheactiverootdepth
(40–50 cm), the heavy metals that were present in the added SWW and TWW would be expected to
(40–50cm),theheavymetalsthatwerepresentintheaddedSWWandTWWwouldbeexpectedto
accumulate specifically in the top soil profile.
accumulatespecificallyinthetopsoilprofile.

Figure 2. Diethylenetriaminepentaacetic acid (DTPA)-extractable soil content of iron (A,C) and
Figure 2. Diethylenetriaminepentaacetic acid (DTPA)-extractable soil content of iron (A,C) and
manganese (B,D) according to the first-order interaction factors irrigation water × soil depth (A,B)
manganese (B,D) according to the first-order interaction factors irrigation water × soil depth (A,B) and
andsoilsamplingdate×soildepth(C,D).Differentletters(a–b)indicatesignificantdifferences(p≤0.05;
soil sampling date × soil depth (C,D). Different letters (a–b) indicate significant differences (p ≤ 0.05;
Tukey’stest).Thedatashownarethemeans±standarderrorsofthreereplicates.S ,S ,S referto
S1 S2 S3
Tthuekfieyrs’st, tseesct)o.n Tdhaen ddattah isrhdoswoinl saarme tphlein mgedaantess ±, rsetsapnedcatirvde elyr.roFrWs ,offr ethshrewe areteprl;icSaWteWs. ,SsSe1,c oSnS2d, SarS3y rterfeeart etod
the first, second and third soil sampling dates, respectively. FW, fresh water; SWW, secondary
wastewater;TWW,tertiarytreatedwastewater;H ,topsoilprofile(0–40cm);H ,bottomsoilprofile
1 2
t(r4e0a–t8e0d cwma)s.tewater; TWW, tertiary treated wastewater; H1, top soil profile (0–40 cm); H2, bottom soil
profile (40–80 cm).
3.2.2. HeavyMetalContentofthePlantsandoftheMarketableYield
3.2.2. Heavy Metal Content of the Plants and of the Marketable Yield
Artichokeplantsandheadsirrigatedwithdifferenttypesofwaterdifferedinalloftheheavy
Artichoke plants and heads irrigated with different types of water differed in all of the heavy
metalcontentsthatwereconsidered,exceptforCo(Figure3).
metal contents that were considered, except for Co (Figure 3).
TheheavymetalcontentoftheartichokeplantsresultedhigherunderSWWandTWWirrigation
The heavy metal content of the artichoke plants resulted higher under SWW and TWW
whencomparedtoFWirrigation,althoughthesealwaysremainedbelowthevegetableguidelines
irrigation when compared to FW irrigation, although these always remained below the vegetable
(Table1). Al,Fe,andNishowedthesamebehavior,withsimilarSWWandTWWvaluesthatwere
guidelines (Table 1). Al, Fe, and Ni showed the same behavior, with similar SWW and TWW values
significantlyhigherthanFW.Instead,Cr,Zn,andMn,showedthehighestvaluesunderSW,without
that were significantly higher than FW. Instead, Cr, Zn, and Mn, showed the highest values under
significantdifferencesbetweenTWandFW.Finally,onlyCushowedsignificantdifferencesamongthe
SW, without significant differences between TW and FW. Finally, only Cu showed significant
threeirrigationwatertypes,havingSWWwithhighestvalueandFWthelowest.
differences among the three irrigation water types, having SWW with highest value and FW the
Theheavymetalconcentrationsintheartichokeheadswereonaverageabout20%lowerthan
lowest.
those in the artichoke plants. Several studies have indicated that edible plant organs are not the
Water 2018, 10, x FOR PEER REVIEW 10 of 18
Water2018,10,255 10of18
The heavy metal concentrations in the artichoke heads were on average about 20% lower than
those in the artichoke plants. Several studies have indicated that edible plant organs are not the
mmaaiinn ssiittee ooffa caccucmumulualtaiotinono fohfe ahveyavmye tmalest[a7ls,4 9[7];,4in9s];t eiands,tehaeda,v yhemavetya lmsaeptaplesa raptopeaaccr utmo ualcacteummuailnatley
minatihnelys hino otthsea snhdoorotso tasnodf prolaontst so,fa npdlalnotws, earnldev leolwsaerre legveenlesr aalrley gfoenuenrdalilny tfhoeunmda rikne tthabe lemyairekledta[1b4le].
yInieplda r[t1ic4u].l aInr, pAalratincdulCaru, sAhlo awnedd Cthue sshaomweedbe thhaev sioarm,we ibtehhsaivmioilra,r wSWithW simanidlaTr WSWWWv aalnude TsiWgnWifi cvaanlutley
shiiggnhiefircathnatlny FhWig.hIners tethadan, CFrW,F.e ,InZsnt,eaadnd, CMrn, ,Fseh, oZwne,d ahnidg hMesnt,v ashluoewseudn dheigrhSeWst wviatlhuoeust usingdneifir cSaWnt
wdiiftfheoreunt cseigsnbiefitcwaneet ndiTffWereanncdesF bWet.wFeineanl lTyW, o nanlyd NFWi s.h Foiwnaeldlys, iognnliyfi Ncain sthdoiwffeedre snicgensifaicmanotn dgitfhfeeretnhcreees
airmriognatgi otnhew thatreere tiyrpriegahtaiovnin wgaStWerW tytphee hhaivgihnegs tSvWalWue tahne dhiFgWhetsht evlaoluwee astn.d FW the lowest.

FFiigguurree 33.. HHeeaavvyy mmeettaall ccoonntteenntt ooff aarrttiicchhookkee ccrrooppss aass ppllaannttss ((rriigghhtt,, ggrreeeenn bbaarrss)) aanndd aass aarrttiicchhookkee hheeaaddss
((lleefftt,, bblluuee bbaarrss)),, aass aa ffuunnccttiioonn ooff tthhee ttyyppee ooff iirrrriiggaattiioonn wwaatteerr uusseedd.. DDiiffffeerreenntt lleetttteerrss ((aa––bb)) iinnddiiccaattee
ssttaattiissttiiccaallllyy ssiiggnniiffiiccaanntt ddiiffffeerreenncceess ((pp ≤≤ 00.0.055; ;TTuukkeeyy’’ss tteesstt)).. TThhee vveerrttiiccaall bbaarrss iinnddiiccaattee ssttaannddaarrdd eerrrroorrss
((nn == 66,, 33 rreepplliiccaatteess ×× 22 ggrorowwiningg sseeaassoonnss).) .
GGeenneerraallllyy,, tthhee aarrttiicchhookkee hheeaaddss ccoonnttaaiinneedd llooww ccoonncceennttrraattiioonnss ooff hheeaavvyy mmeettaallss,, bbeellooww tthhee lliimmiittss
ssppeecciiffiieedd iinn tthhee EEuurrooppeeaann [[4411]] aanndd iinntteerrnnaattiioonnaall [[4444]] gguuiiddeelliinneess ffoorr vveeggeettaabblleess uusseedd ffoorr hhuummaann
ccoonnssuummppttiioonn ((TTaabbllee 11)).. IInnddeeeedd,, tthhee hheeaavvyy mmeettaall ccoonntteennttss ooff aarrttiicchhookkee hheeaaddss uunnddeerr SSWWWW aanndd TTWWWW
iirrrriiggaattiioonn wweerree aabboouutt 1122--ffoolldd aanndd 5500--ffoolldd lloowweerr tthhaann tthhee iinntteerrnnaattiioonnaall tthhrreesshhoolldd vvaalluueess ffoorr ZZnn ((88 vvss..
110000 mmgg kkgg−−1 1frfereshsh wweeigighht)t )aanndd FFee (9(9 vvss. .442255 mmgg kkgg−1− f1refsrehs whewigehigth),t r),ersepsepceticvtievlyel. y.