Adsorption of mercury species on river sediments ? effects of selected abiotic parameters

Cen al Eu opean Jou nal o Chemis y * E-mail: [email p o ec ed] Cen . Eu . J. Chem. •8(1) • 2010 • 116–125 DOI: 10.2478/s11532-009-0128-6 116 Adso p ion o me cu y species on i e sedimen s – e ec s o selec ed abio ic pa ame e s Recei ed 11 June 2009; Accep ed 18 Augus 2009 Abs ac : Abio ic pa ame e s (pH, empe a u e, cu en eloci y, me cu y species concen a ion, and sedimen and aqueous media composi ion) in luence me cu y species (MeHg+, E Hg+, PhHg+ and ino ganic Hg2+) adso p ion on i e sedimen s. The highes amoun o adso bed MeHg+ and E Hg+ (82-93% and 85-91% o s a ic and agi a ed sys em, espec i ely) occu ed a pH 3-4. Fo PhHg+ he maximum adso p ion (90% and 95% o s a ic and agi a ed sys ems) was loca ed o e he b oad 3-10 pH ange, while o Hg2+ (94% and 97% o s a ic and agi a ed sys ems) i was a pH ~ 3. Tempe a u e (4.5-60°C) in luenced he adso p ion a e bu no he quan i y. Bo h a e and quan i y inc eased in he o de : s a ic < agi a ed ≤ s i ed sys ems. The aqueous medium composi ion a ec ed bo h a e and quan i y. Sul a e caused he la ges adso p ion dec ease o o ganome cu y species (15-25% dec ease); sul ide educed Hg2+ adso p ion abou 67%. Ca ions a pH 5.2 educed ei he he adso p ion a e (Ca2+, Al3+) o he o al adso p ion (Zn2+, Fe3+). Posi i e co ela ions we e ound be ween sedimen C, N, S con en as well as ca ion exchange capaci y (CEC) wi h me cu y adso p ion (R = 0.45-0.66, 0.56-0.89, 0.45-0.61 and 0.55-0.73, espec i ely) while nega i e co ela ions we e obse ed wi h Fe and Al (R = -0.63 o -0.90 and -0.65 o -0.86, espec i ely). Keywo ds: Me cu yspecies•Adso p ion•Ri e sedimen s ©Ve si aWa sawandSp inge -Ve lagBe linHeidelbe g. 1Depa men o Chemis yandBiochemis y,MendelUni e si yo Ag icul u eandFo es y, 61300B no,CzechRepublic 2 Depa men o Chemis y,Masa ykUni e si y, 61137B no,CzechRepublic 3 Depa men o FoodBiochemis yandAnalysis,TomasBa aUni e si yinZlín, 76272Zlín,CzechRepublic Pa lína Pelco á1, Jana Ma ge íno á1, Tomáš Vaculo ič2, Jose Komá ek2, Vlas imil Kubáň2,3* Rese ch A icle 1. In oduc ion Na u al bio-geochemical cycles desc ibe he anspo , beha io and a e o me cu y in he en i onmen . They a e cha ac e ized by e apo a ion o he elemen om soil and su ace wa e s, ollowed by a mosphe ic anspo , deposi ion back o land and su ace wa e s and so p ion by soil o sedimen . Pa icula e-bound me cu y can be con e ed o insoluble me cu y sul ide o bio-con e ed in o mo e ola ile o soluble o ms ha e-en e he a mosphe e o bioaccumula e [1,2]. The cycle is complica ed by nume ous me cu y species (e.g. Hg0, Hg2+, Hg2 2+ and o ganome cu y species RHg+, R2Hg) p esen . Sedimen s play a majo ole in he dynamics o na u al aqua ic sys ems. The mobili y and a e o me cu y depends la gely on sedimen mine alogy and su ace chemis y as well as he wa e en i onmen [3]. Be e unde s anding o adso p ion/deso p ion p ocesses and a es is necessa y o assess and p edic pollu ion [4]. Pa i ion among dissol ed and pa icula e phases is he ou come o compe i ion among ligands in solu ion ( uly dissol ed), colloidal pa icles, and o ganic and ino ganic ma e ials. Hg2+, MeHg+ and 2-me hoxye hylme cu y adso p ion and deso p ion kine ics on soils and sedimen s ha e been in es iga ed [4-9]. I was assumed ha h ee concu en eac ions, i.e., one apid and e e sible, ano he slow and e e sible, and an i e e sible eac ion P. Pelco á e al. 117 117 (maximum dep h 15 cm), placed in plas ic bo les, s o ed in coole s, and anspo ed o he labo a o y. They we e lyophilized unde acuum a –51 ± 1°C o 48 h. Sedimen agg ega es we e manually c ushed in a bo osilica e mo a and sie ed h ough a 2 mm high densi y polyp opylene (HDPP) sc een. All expe imen s we e conduc ed using he <2 mm sedimen ac ion. 2.3. Adso p ion o me cu y species on sedimen s Sedimen samples (20 ± 0.01 g DM) we e weighed in o 500 mL b own sc ew-cap glass bo les and 250 mL o 20 o 50 µg L-1 me cu y species wo king s anda d was added. Samples we e shaken using an o bi al shake (BioSan, Riga, La ia) a 180 pm and 10 mm ampli ude, o s i ed a 600 pm wi h PTFE magne ic s i e s (3.5 cm × 1.0 cm) wi h a MM 2A magne ic s i e (Labo a o ní přís oje, P ague, Czech Republic). A wa e ba h was used o con ol he empe a u e. A p e-selec ed ime in e als 300 µL aliquo s we e collec ed and il e ed h ough 0.45 µm PTFE il e s in o b own ials, hen immedia ely measu ed. The di e ence be ween me cu y added and ha emaining in he il a e was a ibu ed o adso p ion by he sedimen . Values epo ed a e he a e age o h ee de e mina ions. Me cu y adso p ion on he glasswa e was negligible in compa ison wi h adso p ion by he sedimen . 2.4. Chemical analyses Sedimen S, P, Si, Mn, Fe, Mg, Al and Ca con en s we e de e mined by ICP-OES a e usion and acid diges ion. Sedimen (0.25 g) was mixed wi h 0.75 g o Spec omel A20 (Me ck, Ge many) in a P dish and used o 15 minu es. A e cooling he mel was dissol ed in 100 mL 0.7 M HNO3 (Me ck, Ge many) and analyzed by a JY 170 Ul ace ICP-OES spec ome e (Jobin Y on, F ance) wi h la e ally iewed plasma (15 mm abo e induc ion coil). Condi ions we e: gene a o 40.68 MHz (c ys al con olled); powe inpu 1200 W; a gon gas lows (L min-1): ou e 12.0, in e media e 0.6, shea h 0.2, ca ie 0.6; 1 m Cze ny-Tu ne monoch oma o ( o S and P); Paschen-Runge polych oma o ( o Si, Mn, Fe, Mg, Al, Ca); spec al lines S 181.978 nm, P 213.618 nm, Si 251.611 nm, Mn 257.610 nm, Fe 259.940 nm, Mg 280.274 nm, Al 308.215 nm, and Ca 393.366 nm. A T uSpec CHN Analyse (LECO, S . Joseph, MI, USA) was used o de e mine sedimen o al ca bon and ni ogen. Sample (0.3 g) was di ec ly weighed in o a combus ion boa and au oma ically inse ed in o he CHN Analyze . Combus ion empe a u e was 950°C. Accu acy was con olled by analyses o e e ence a ec ed adso p ion/deso p ion, since h ee di e en kinds o eac i e si es a e p esen on soil o sedimen [5,9]. O ganic ma e , salini y, he amoun and na u e o pa icles and pH seem o play impo an oles in he adso p i e beha io o ino ganic me cu y (Hg2+) and me hylme cu y on sedimen [10-12]. Humic and ul ic subs ances, which o m e y s ong complexes wi h me cu y species, also in luence hei adso p ion [13]. Howe e , epo s desc ibing me cu y adso p ion unde di e en condi ions a y. Li le in o ma ion on he adso p ion/deso p ion o phenyl- o e hylme cu y on sedimen is a ailable. The in luences o selec ed abio ic pa ame e s (sedimen /aqueous phase a io, me cu y concen a ion, pH, empe a u e, mo emen o he sedimen /wa e mix u e in he bio eac o , and sedimen and aqueous phase composi ions) on he adso p ion o me cu y species (MeHg+, E Hg+, PhHg+ and Hg2+) by i e sedimen we e in es iga ed. Bo h he a es and quan i ies o me cu y species adso p ion as well as hei di e ences we e examined. Bac e ial ans o ma ions o me cu y in he sys ems examined we e negligible. 2. Ma e ials and me hods 2.1. Chemical and eagen s Ino ganic me cu y calib a ion s anda d (1.000±0.002 g L- 1 Hg2+ in 2% / HNO3) was ob ained om he Czech Me ological Ins i u e (P ague, Czech Republic). Me hylme cu y chlo ide (MeHg+) and phenylme cu y chlo ide (PhHg+) we e pu chased om Sigma-Ald ich. E hylme cu y chlo ide (E Hg+) was pu chased om Supelco (Munich, Ge many). S ock s anda d solu ions o MeHg+, E Hg+ and PhHg+ (c = 1 g L-1 ) we e p epa ed in me hanol. Wo king s anda ds (20 and 50 µg L-1 ) we e p epa ed om he s ock solu ions by dilu ing wi h deionized wa e (AquaDem-02, AquaOsmo ic, Tišno , Czech Republic) u he pu i ied in a Millipo e Milli-Q sys em (Bed o d, MA, USA). The esis i i y was g ea e han 16 MΩ cm. Analy ical g ade HCl, HNO3, NaOH, NaCl, Na2SO4, Na2S, FeCl3, Fe2(SO4)3, MnSO4, MnCl2, AlCl3, ZnCl2, Na3PO4, u ea, hiou ea, L-cys eine we e pu chased om Pen a (Ch udim, Czech Republic). All glasswa e was bo osilica e glass. I was soaked o e nigh in 10% HNO3 and insed wi h DI wa e jus be o e use. Hyd ochlo ic acid, ni ic acid and sodium hyd oxide we e used o adjus he pH. 2.2. Sedimen samples Sedimen samples we e collec ed om ou Mo a ian i e s du ing Oc obe 2007. The GPS posi ions and da es a e gi en in Table 1. Su ace samples we e aken Adso p ion o me cu y species on i e sedimen s – e ec s o selec ed abio ic pa ame e s 118 Table 1. Sedimen chemical analyses Samplea S C N P Si Mn Fe Al Ca Mg pH CEC MeHg+Hg2+ [%] [mmol kg-1] [mg kg-1] Jihla a 0.04 0.69 0.07 0.33 63.5 0.10 5.34 12.0 2.91 4.48 6.63 141 0.004 0.052 ZL806 0.21 2.17 0.24 0.23 68.4 0.09 3.71 9.50 1.61 1.04 7.33 344 0.005 0.115 ZL1306 0.46 3.53 0.26 0.39 66.4 0.07 3.89 9.24 2.29 1.04 7.30 428 0.01 0.314 ZL1506 0.11 1.82 0.16 0.20 70.1 0.12 4.41 10.6 1.69 1.34 7.04 305 0.012 0.344 ZL1606 0.30 1.75 0.16 0.11 75.0 0.06 3.24 8.40 0.77 0.86 6.50 268 <LOD 0.059 R.S.D. alues (n = 3) a e: S 0.17–9.30%, C 0.19–1.96%, N 1.79–8.06%, P 0.73–2.80%, Si 0.1–1.5%, Mn 0.07–1.90%, Fe 0.24–1.8%, Al 0.01–1.60%, Ca 0.07–2.40%, Mg 0.58–1.90%, CEC 5.08–8.25%, MeHg+ 4.80–7.53%, Hg2+ 5.38–8.54%) aJihla a i e - [49°5´55.165´´N, 16°11´45.962´´E], Mo a a i e - wo samples ZL1606 [49°4´2.281´´N, 17°26´16.33´´E], ZL1306 [49°10´58.071´´N, 17°31´3.15´´E], Dře nice i e - sample ZL 806 [49°12´31.545´´N, 17°33´33.231´´E] and he Če ťák cu o o he Mo a a i e – sample ZL 1506 [49°4´5.746´´N, 17°26´11.767´´E]) ma e ials 502-082 and 502-062 wi h decla ed con en s o N 2.45%, C 45.81% and N 0.097%, C 0.84%, espec i ely. Ca ion exchange capaci y (CEC) was de e mined by Mehlich 3 ex ac ion. The sedimen pH was de e mined in a 1:5 sedimen /solu ion a io wi h 0.01 M CaCl2 [14]. T iplica e 100 µL samples we e analyzed o o al me cu y concen a ion using an Ad anced Me cu y Analyze AMA 254; he a e age was aken as he me cu y concen a ion. The same ins umen was used o sedimen o al me cu y de e mina ions concen a ions. Homogenized solid samples we e di ec ly weighed (ca. 100 mg) in o combus ion boa s and au oma ically inse ed in o he ins umen . The samples we e d ied a 120°C o 90 s and he mally decomposed a 550°C o 180 seconds unde an oxygen low. The selec i ely apped me cu y was eleased om he amalgama o by b ie hea ing and quan i ied (measu ing cycle, 60 s) as Hg0 by a omic abso p ion spec ome y a 253.65 nm. The de ailed me hod o me cu y species de e mina ion is desc ibed elsewhe e [15]. To summa ize: 1.5–3.0 g o sedimen sample was ex ac ed o 10 min (6 M HCl + 0.1 M NaCl) in a high-p essu e mic owa e diges ion uni (E hos SEL, Miles one, I aly). A e il a ion (pape No. 389, 12.5 cm) he il a es we e injec ed in o he HPLC/ CV-AFS (HPLC: Pe kin Elme , No walk, USA; AFS: P.S. Analy ical L d., O ping on, UK). The me cu y species we e sepa a ed on a Hype sil BDS C18 column (3 µm pa icle size, 2×125 mm, Agilen , Palo Al o, CA, USA). Isoc a ic elu ion was pe o med a 0.15 mL min-1 wi h a mobile phase con aining 7% ( / ) CH3OH and 0.05% ( / ) 2-me cap oe hanol in pH 5 ace a e bu e . CH3OH con en was inc eased o 100% a 15 min. Accu acy was con olled by analyses o sedimen s anda d e e ence ma e ial CRM 580. The esul s a e p esen ed in Table 1. 3. Resul s And Discussion 3.1. E ec o mo emen o sedimen /wa e mix u e The eac ion o me cu y species wi h sedimen in ol es bo h chemical eac ions and di usion. Di usion is o en he a e-limi ing s ep o adso p ion in s a ic sys ems. Th ee sys ems (s a ic, agi a ed and s i ed) imi a e mo emen in aqua ic ecosys ems. The s a ic sys em imi a ed pond ecosys ems while he agi a ed and s i ed sys ems imi a ed i e s. Mo emen o he sedimen / wa e mix u e inc eased bo h adso p ion a es and amoun s in he o de : s a ic < agi a ed ≤ s i ed sys ems (Fig. 1). Inc easing in ensi y o sedimen /wa e mix u e mo emen inc eased bo h a es and amoun s o adso p ion, showing ha agi a ion acili a es access o adso p ion si es. 3.2. E ec o sedimen o solu ion a io Changes in he sedimen /solu ion a io ( om 1:12.5 o 1:100 keeping he ini ial me cu y concen a ion cons an a 20 µg L-1 ) did no al e he adso p ion o any me cu y species. On he o he hand, educing he amoun o sedimen dec eases adso p ion due o he educ ion o su ace a ea and numbe o binding si es. The quan i y o adso bed me cu y species is con olled by sedimen su ace a ea and numbe o binding si es a he han sedimen /solu ion a io. P. Pelco á e al. 119 119 3.3. E ec o me cu y species concen a ion The a io be ween adso bed me cu y and ha emaining in solu ion can be ep esen ed by he F eundlich equa ion, which assumes ha he me cu y concen a ion in sedimen is p opo ional o ha in solu ion [4]. Howe e , he expec ed e ec o concen a ion changes (20 and 50 µg L-1 ) on he quan i y o me cu y adso bed was no obse ed (samples Jihla a and ZL1306). Me cu y concen a ion in sedimen inc eased only un il all su ace binding si es we e sa u a ed. Comple e sa u a ion occu ed a 0.2 mg L-1 me cu y species. Inc easing me cu y concen a ion om 20 o 50 µg L-1 ex ended he equilib ium adso p ion ime o o ganic me cu y species om 60 o 1440 min. Fo Hg2+ i inc eased om 5 o 60 min. This can be explained by a slow adso p ion s ep ollowed by a as adso p ion s ep. Yin e al. [4] desc ibed a e e se obse a ion and cha ac e ized he adso p ion kine ics by a biphasic pa e n - a as s ep ollowed by a slow s ep. A dec ease in concen a ion inc eased he equilib a ion ime. The dependence o he adso p ion a e on Hg2+ concen a ion was explained by di usion, which has been equen ly epo ed as a e-limi ing o me al adso p ion. Howe e , ou expe imen s we e pe o med in s i ed sys ems, which signi ican ly educed limi a ions due o di usion. Wi h inc easing concen a ion, he mos ac i e (s ong) adso p ion si es become sa u a ed i s ( as s ep) and he less ac i e (weake ) binding si es domina e la e (slow s ep). 3.4. E ec o empe a u e Highe empe a u e inc eased only he a e o adso p ion, no he quan i y. When he empe a u e o he sedimen /wa e mix u e was inc eased om 4.5 o 60°C, equilib a ion ime in an agi a ed sys em dec eased om 1440 min o 120 min (o ganome cu y species) and om 7 min o 2 min o Hg2+ (Fig. 2). Tempe a u e also inc eased di usion in a s a ic bio eac o . In compa ison wi h agi a ed and s i ed sys ems, he s a ic sys em showed he g ea es educ ion o equilib ium ime ( o o ganome cu y species om 2880 min o 1440 min and om 1680 min o 900 min o Hg2+). Me cu y adso p ion Figu e 1. E ec o sedimen /wa e mix u e mo emen o (1) s a ic sys em, (2) agi a ed sys em, (3) s i ed sys em. 20 g o ZL 1606 sedimen , T= 22.3°C, 250 mL o wa e , pH 5.2, Hg concen a ion 0.2 mg L-1 ; s i ed sys em ab cd Adso p ion o me cu y species on i e sedimen s – e ec s o selec ed abio ic pa ame e s 120 in eal wa e ecosys ems could be in luenced by season empe a u e changes in he same manne . Schuhmache e al. [16] obse ed ha me cu y concen a ion in wa e and sedimen was lowe in summe han in win e , bu did no in es iga e adso p ion a e. Thei esul s we e explained by inc eased mic oo ganism ac i i y and as e bio- ans o ma ions a ele a ed empe a u e. 3.5. E ec o pH The e ec o pH on Hg2+ and MeHg+ adso p ion has been desc ibed [7,17-21], bu li le in o ma ion on i s e ec on PhHg+ o E Hg+ is a ailable. Adso p ion as a unc ion o pH o s a ic and agi a ed sys ems is shown in Fig. 3. The ela ionships ha e simila shape o all me cu y species, bu he maxima di e . The same maxima we e obse ed o agi a ed and s i ed sys ems. Fo MeHg+ and E Hg+ he maxima (82-93% and 85-91% o s a ic and agi a ed sys ems) occu ed o e he na ow pH ange 3-4. Fo PhHg+ he co esponding maxima (90% and 95%) we e loca ed o e he b oad ange o 3 – 10, due o i s highly non-pola s uc u e. The adso p ion maxima o Hg2+ (94% and 97%) we e obse ed a pH ~ 3. When he pH was adjus ed wi h HNO3 ins ead o HCl, abou 12% mo e me cu y was adso bed. Reduced adso p ion a lowe pH alues was a ibu ed o p o on compe i ion and o a smalle ex en (when using HCl o pH adjus men ) o he e ec o chlo ide ions, which o m soluble chlo o- complexes [7,19,20]. Reduc ions in adso bed me cu y a highe pH a e a ibu ed o: i) complexa ion o me cu y species wi h o ganic ligands, since hei chela ion abili y inc eases wi h pH [20], ii) inc eased o ma ion o Hg(OH)2 o RHgOH, which a e poo ly adso bed [7,20], and iii) change o sedimen su ace po en ial [17,19]. 3.6. E ec o anions Ino ganic and o ganic ligands in solu ion exe a conside able in luence on me cu y adso p ion on soil and sedimen , including kaolin, goe hi e e c. The e ec o chlo ide on Hg2+ and MeHg+ adso p ion has been desc ibed [3,7,13,17-20], bu li le in o ma ion desc ibing he e ec o o he anions is a ailable. Thus, he e ec s o Cl-, SO4 2-, sul ide and phospha e a 0.2 g L-1 we e e alua ed. Despi e he expec a ion ha adso p ion will be ma kedly lowe in he p esence o chlo ide ions due o HgCl4 2- and RHgCl o ma ion [13], his hypo hesis was Figu e 2. E ec o empe a u e o (1) s a ic sys em, (2) agi a ed sys em, (3) s i ed sys em (agi a ed sys em, 20 g o ZL 1606 sedimen , 250 mL o wa e , pH 5.2, Hg concen a ion 0.2 mg L-1 ) a b cd P. Pelco á e al. 121 121 Figu e 3. E ec o pH (s a ic sys em and agi a ed sys em, 20 g o ZL 1606 sedimen , 250 mL o wa e , Hg concen a ion 0.2 mg L-1 , T = 22.3°C); (1) MeHg+, (2) E Hg+, (3) PhHg+, (4) Hg2 no con i med. O ganome cu y adso p ion was no ma kedly in luenced by NaCl addi ion a pH 5.2. The adso p ion o Hg2+ was abou 11% highe in he p esence o 0.2 g L-1 NaCl and an inc ease in Cl- concen a ion o 10 g L-1 had li le e ec (Fig. 4). Simila esul s o pH 3 we e epo ed by Yin e al. [17]. They epo ed ha a neu al o alkaline pH, only a small amoun o chlo o- complexes o med, and adso p ion la gely depended on he balance be ween he in e ac ion o o he me cu y species wi h he soil su ace and complexa ion wi h dissol ed o ganic ma e . Ba ow and Cox [19] also epo ed ha he e ec o chlo ide a ied wi h he me cu y concen a ion. Some au ho s [7,19] epo ed ha Cl- dec eased Hg adso p ion a low pH, bu Yin e al. [17,20] ound ha he e ec o Cl- on Hg adso p ion by soil a acid pH depended on soil o ganic ma e con en . The adso p ion o me cu y in he p esence o 1 g L-1 Cl- was also pH dependen . We es ed only h ee pH alues (1, 5 and 12). The addi ion o 1 g L-1 Cl- a e y low o e y high pH did no a ec he quan i y o me cu y adso bed, bu equilib ium was delayed abou 60 min. No e ec o Cl- on adso p ion was obse ed a high pH since me hylme cu y hyd oxo species p edomina e [17,20]. The la ges adso p ion was obse ed a pH 5 o all species. The e ec o Cl- is e y complex and depends on many pa ame e s (e.g., me cu y o m and concen a ion, chlo ide concen a ion, sul ide concen a ion, sedimen o ganic ma e con en , pH, e c.). Sul a e anions a pH 5.2 dec eased he o ganome cu y adso p ion abou 15-25% (Fig. 4), bu did no in luence he quan i y o Hg2+ adso bed. Howe e , he Hg2+ equilib a ion ime was ma kedly longe ( om 2 min o 60 min) in he p esence o 0.2 g L-1 SO4 2-. A e e se e ec was obse ed in he p esence o sul ide; i dec eased Hg2+ adso p ion a pH 5.2 by abou 67%, bu did no in luence o ganome cu y adso p ion. The equilib a ion o Hg2+ was delayed om 2 min o 60 min by 0.2 g L-1 sul ide (Fig. 4) jus as o 0.2 g L-1 SO4 2-. Hg2+ adso p ion also ma kedly dec eased (abou 29%) in he p esence o sul ide a pH > 10 (Fig. 5). Ino ganic me cu y (Hg2+) p obably o med e y s able non-adso bing species in excess sul ide in he pH ange 5.2-12, which dec eased Hg2+ adso p ion. The o ma ion o me cu y sul ide was no obse ed in s ongly acid media; sul a e did no in luence he adso p ion o any me cu y species a pH ≤ 1, bu equilib a ion o Hg2+ was delayed abou 8 min. Phospha e had no e ec . 3.7. E ec o ca ions The p esence o ca ions in an aqueous ecosys em may also in luence me cu y adso p ion on sedimen s. Howe e , ca ions do no complex wi h me cu y species. They p obably a ec adso p ion ia compe i ion o ac i e si es and p ecipi a ion o spa ingly soluble hyd oxo-complexes a alkaline pH. The e ec o 0.2 g L-1 Ca2+, Zn2+, Mn2+, Al3+ o Fe3+ was in es iga ed. Ca ions in he bio eac o a pH 5.2 ei he slowed adso p ion (Ca2+, Al3+) o educed o al adso p ion (Zn2+, Fe3+). Hg2+ equilib a ion was delayed abou 58 min in 0.2 g L-1 Ca2+, bu o ganome cu y adso p ion was no a ec ed. The e e se esul was obse ed in he p esence o Al3+. The equilib ium o ganome cu y concen a ion was es ablished abou 57 min la e bu Hg2+adso p ion was no a ec ed by 0.2 g L-1 Al3+. The p esence o 0.2 g L-1 Zn2+ o Fe3+ educed adso p ion o all me cu y species by abou 4-30% o 12-20%, espec i ely (Fig. 6). This can be explained by compe i ion o adso p ion si es. Fe3+, Mn2+, Al3+ (0.2 gL-1) in s ongly alkaline medium pH > 10) inc eased sedimen Hg2+ adso p ion by abou 15%, 20% and 10%, espec i ely. This can be a ibu ed ei he o he dec eased o ganic ma e solubili y caused ab Adso p ion o me cu y species on i e sedimen s – e ec s o selec ed abio ic pa ame e s 122 Figu e 4. E ec o anions (agi a ed sys em, 20 g o ZL 1606 sedimen , 250 mL o wa e , pH 5.2, Hg concen a ion 0.2 mg L-1 , T = 22.3°C); (1) wi hou anion addi ion, (2) 0.2 g L-1 NaCl, (3) 10 g L-1 NaCl, (4) 0.2 g L-1 sul a e, (5) 0.05 g L-1 sul a e, (6) 0.2 g L-1 sul ide Figu e 5. E ec o sul ide a di e en pH on Hg2+adso p ion (agi a ed sys em, 20 g o ZL 1606 sedimen , 250 mL o wa e , Hg concen a ion 0.2 mg L-1, T = 22.3°C) ; (1) pH 5.2, wi hou sul ide, (2) pH 5.2, 0.2 g L-1 sul ide, (3) pH 1, wi hou sul ide, (4) pH 1, 0.2 g L-1 sul ide, (5) pH 12, wi hou sul ide, (6) pH 12, 0.2 g L-1 sul ide a b cd P. Pelco á e al. 123 123 Figu e 6. E ec o Zn2+ and Fe3+ a pH 5.2 (agi a ed sys em, 20 g o ZL 1606 sedimen , 250 mL o wa e , pH = 5.2, Hg concen a ion 0.2 mg L-1, T = 22.3°C); (1) wi hou ca ion addi ion, (2) 0.2 g L-1 Zn2+, (3) 0.2 g L-1 Fe3+ by ca ions as no ed by Yin e al. [20] o Ca2+, o o p ecipi a ion o hyd oxo-complexes, which ha e la ge adso p ion capaci y. Regnell e al. [22] obse ed a subs an ial dec ease in me cu y mobili y in he p esence o i on and manganese hyd oxides, p obably due o hei la ge su ace a ea and high adso p ion capaci y. This e ec was no obse ed o o ganome cu y species. Based on he a ailable esul s, we a e unable o d aw de ini e conclusions. 3.8. E ec O U ea, Thiou ea And L-Cys eine Me cu y has a s ong a ini y o sul u . We es ed he e ec s o he sul u con aining compounds hiou ea and L-cys eine on sedimen me cu y adso p ion a pH 5.2. O ganome cu y adso p ion dec eased abou 2-8% in 0.2 g L-1 u ea and abou 6-20% in 0.2 g L-1 hiou ea. This educ ion was no obse ed o Hg2+. The p esence o u ea o hiou ea had li le e ec on all abso p ion a es. In 0.2 g L-1 L-cys eine equilib a ion o all me cu y species was delayed abou 58 min compa ed wi h hiou ea, and he o ganome cu y adso p ion dec eased abou 10- 25% (Fig. 7). Compounds con aining S-H g oups keep o ganome cu y species in solu ion o much longe ime due o hei s ong a ini y o Hg. Howe e , SO4 2- dec eased o ganome cu y adso p ion as well as did L-cys eine, and sul ide dec eased Hg2+adso p ion much mo e han S-con aining compounds. Facile sedimen adso p ion o Hg-cys eine explains his. 3.9. E ec O Sedimen Composi ion I is well known ha sedimen composi ion plays an impo an ole in me cu y adso p ion, al hough his has been chie ly examined quan i a i ely o soil o ganic ma e [23]. Posi i e co ela ions we e ound be ween C, N, S con en s as well as ca ion exchange capaci y (CEC) wi h me cu y adso p ion (R = 0.45-0.66, 0.56- 0.89, 0.45-0.61 and 0.55-0.73, espec i ely). Inc easing C, N and S con en s inc eased adso p ion since mo e unc ional g oups (e.g. -COOH, -SH, -NH3 , e c.) and hus adso p ion si es a e a ailable. Inc easing he ab c d Adso p ion o me cu y species on i e sedimen s – e ec s o selec ed abio ic pa ame e s 124 Figu e 7. E ec o u ea, hiou ea and L-cys eine (agi a ed sys em, 20 g o ZL 1606 sedimen , 250 mL o wa e , pH 5.2, Hg concen a ion 0.2 mg L-1, T = 22.3°C); (1) wi hou S-compound, (2) 0.2 g L-1 u ea, (3) 0.2 g L-1 hiou ea, (4) 0.2 g L-1 L-cys eine sedimen Al and Fe dec eased adso p ion; R anged om -0.63 o -0.90 and om -0.65 o -0.86. Compe i i e occupa ion o adso p ion si es by aluminum o i on ions is esponsible. 4. Conclusions Sedimen s a e sensi i e indica o s o me cu y con amina ion o he aqua ic ecosys em. The beha io o me cu y s ongly depends on i s chemical o m and on a ious physical, chemical and biological ac o s. Thus knowledge o adso p ion/deso p ion beha io unde di e en condi ions is impo an in unde s anding he me cu y bio-geochemical cycle. Adso p ion o me cu y on sedimen a ies ma kedly among indi idual me cu y species. Some abio ic pa ame e s in luenced only he a e o adso p ion ( empe a u e, me cu y species concen a ion, composi ion o aqueous media – e.g. p esence o Ca2+, Al3+); o he abio ic pa ame e s in luenced he quan i y adso bed (pH, composi ions o sedimen and aqueous media – e.g. p esence o SO4 2-, S2-, Zn2+ o Fe3+ a pH 5.2; p esence o Fe3+, Mn2+ o Al3+ in s ongly alkaline medium, e c.). Finally, sedimen adso p ion/deso p ion o me cu y species is a e y complex p ocess ha depends on a numbe o physico-chemical pa ame e s. The a icle p esen s new and mo e complex in o ma ion abou me cu y adso p ion on i e sedimen s. Ex ension o u he obse a ions o me cu y pho o- and bio ans o ma ion and bioaccumula ion in he wa e en i onmen is desi able. A mul i ac o expe imen o de elop a mo e de ailed desc ip ion o me cu y species adso p ion is in p og ess [24]. ab cd