of 42
BioavailabilityEffect of pH on bioavailability of Ni for oats
a case study
General introduction
What is bioavailability?Used in different disciplinesVarious definitions
Soil Quality: nutrients/contaminants in soil actually available to receptor organisms (uptake)
The journey of a chemical
Adsorbed/precipitatedSoil solutionBiomembraneBiological responseinputphysical-chemical reactions transport uptake relocation effects
Popular theories
Free Ion Activity Model (FIAM)free metal ion activity is the parameter that determines the effects
Bio-Ligand Model (BLM)uptake is a result of competition for binding of the chemical by all reactive components (abiotic & biotic)
What processes/factors affect bioavailability?Abiotic--Physical chemical factorssoil composition, pH, structure, etc.
Biotic factors species, root activity, cellular compartment, etc.
Case study
Reading materials Effects of soil characteristics on Ni toxicity to oats1. pH effects2. Soil composition effects
This lecture focuses on the pH effects
Why pH?pH: -log(H+) wide range in soilcan be manipulated affecting both the physical chemical and the uptake process
pH effects on basic uptake processWater culture using nutrient solutionavoid implication from soil
(almost) all Ni is free Ni2+ ion
Bioavailability, water cultureWhat factors might affect the uptake of metal ions?
Metal ion concentration??pH ??Other factors??
00.5 pH 40.25Plant growth and Ni concentration in WaterConcentrations in mg/l Ni1 2 4 8
Effect Ni conc. on plant growthpH40.00.20.40.60.81.01.21.4050100150[Ni-nutrient solution] (M) shoot dry weight (g/plant)1 week2 week3 week
Effect Ni conc. on plant growth0.40.60.81.01.21.4050100150[Ni-nutrient solution] (M) shoot dry weight (g/plant)pH61 week2 week3 week
pH 5
pH effects on Ni toxicity in water 1 mg/liter Ni pH4 pH5 pH6 pH7
pH effects0%20%40%60%80%100%120%0102030405060[Ni-nutrient solution] (M)
relative dry weight pH7pH6pH5pH4 EC50
From effects to uptakeGrowth is one of the plant responses to Ni toxicityIn most cases, the extent of the physiological responses is related to the chemical concentration in tissue (uptake)
What are the effects on uptake?
Relationship between pH, Ni conc. and uptakepH4pH5pH7pH6root
Relationship between pH, Ni conc. and uptakepH4pH7shoot
pH dependent uptakeNote uptake scale is logarithmicLow Ni concentration big pH effectHigh Ni concentration very small pH effect
What could be the reason of the fact that the pH dependence of the uptake vanishes at [Ni]>1 mg/l ? See photograph.
Uptake equationpH dependent uptake can be described using linear equations
shoot:
log[Ni-shoot] = 1.15 + 0.65log[Ni2+-free] + 0.11 pH
Conclusions water cultureNi at higher concentration is toxicNi is taken up by the roots and transported to the shootsNi uptake is dependent on the pH and [Ni]Higher pH, higher uptake, higher toxicity!
What would happen in soil?
Bioavailability of Ni in soilWhat chemical forms (species) will Ni take when added to soil? solid/solution?Will pH affect Ni distribution among these chemical forms?If we assume pH effects on plant uptake remain the same, What would be the final pH effects on Ni toxicity in soil?
Ni conc. effect on plant growth in soilpH4.7
Ni conc. effect on plant growth in soilpH6.0
pH effects in soilpH4.7 pH5.2 pH6.0 pH6.8100 mg Ni/kg soil
pH effects in soilbased on total metal contentpH4.7pH5.2pH6.0pH6.8EC50
Why the pH effects differ from those in water culture?To understand it, we need to separate the effects on soil from those on uptake
Uptake via soil solution0.01 Molar CaCl2 extraction
EC50Soil CaCl2, versus nutrient solution0102030408EC50 (M)CaCl2 extractionNutrient solutionsoil
Chart1
0.72244.71.41.4
1.32295.20.60.6
4.13165.75.7
9.95256.82.82.8
421.8969335605
513.8858603066
66.2793867121
71.3918228279
Ni CaCl2 soil solution
free Ni2+ nutrient solution
pH
solution EC50 (M)
soil EC50 (mmol/kgsoil)
Sheet1
Sheet1
0.04490.20511.0114000000
0.04660.25341.0572000000
0.04250.22440.9508000000
0.04060.15510.6929000000
0.03190.09730.3028000000
0.02560.04830.054000000
0.0230.02820.021000000
1 week
2 week
3 week
[Ni-nutrient solution] (M)
shoot dry weight (g/plant)
pH4
Sheet2
0.8909000.03750.17550.8909000000
0.9791000.03290.18920.9791000000
0.8997000.03840.18890.8997000000
0.552000.03710.16110.552000000
0.4133000.04210.13430.4133000000
0.1734000.0470.08310.1734000000
0.0955000.040.05630.0955000000
21 day
7 day
14 day
21 day
[Ni-nutrient solution] (M)
shoot dry weight (g/plant)
pH6
Sheet3
10001000
1.04528376514.25894378194.25894378194.25894378190.9836612474.25894378194.25894378194.2589437819
0.94008305328.51788756398.51788756398.51788756390.91799928228.51788756398.51788756398.5178875639
0.685089974317.035775127817.035775127817.03577512780.675502551417.035775127817.035775127817.0357751278
0.299386988334.071550255534.071550255534.07155025550.279063591234.071550255534.071550255534.0715502555
0.053391338768.143100511168.143100511168.14310051110.067144769268.143100511168.143100511168.1431005111
0.0207632984136.2862010221136.2862010221136.28620102210.0132076398136.2862010221136.2862010221136.2862010221
17.614991482117.614991482117.614991482117.614991482117.614991482117.614991482117.614991482117.6149914821
22.896081771722.896081771722.896081771722.896081771722.896081771722.896081771722.896081771722.8960817717
01000100
2.1294718911.10533480812.1294718912.1294718912.1294718910.99350385052.1294718912.129471891
4.25894378191.1720411814.25894378194.25894378194.25894378190.96157065674.25894378194.2589437819
8.51788756390.91619161078.51788756398.51788756398.51788756390.80368250818.51788756398.5178875639
17.03577512780.362971156317.035775127817.035775127817.03577512780.401118606417.035775127817.0357751278
34.07155025550.23321705134.071550255534.071550255534.07155025550.098759288434.071550255534.0715502555
68.14310051110.049008763768.143100511168.143100511168.14310051110.01761309768.143100511168.1431005111
00100010
1.0732538331.0732538331.09900101021.0732538331.0732538331.0732538330.95050633281.073253833
2.1294718912.1294718911.00987765182.1294718912.1294718912.1294718910.86310003662.129471891
4.25894378194.25894378190.61959815924.25894378194.25894378194.25894378190.67138752224.2589437819
8.51788756398.51788756390.46391289718.51788756398.51788756398.51788756390.39835010728.5178875639
17.035775127817.03577512780.194634639117.035775127817.035775127817.03577512780.176657580217.0357751278
34.071550255534.07155025550.107194971434.071550255534.071550255534.07155025550.065011925934.0715502555
00010001
0.5281090290.5281090290.5281090290.74982692970.5281090290.5281090290.5281090290.7738436567
1.0732538331.0732538331.0732538330.64434060231.0732538331.0732538331.0732538330.6059293472
2.1294718912.1294718912.1294718910.39745586712.1294718912.1294718912.1294718910.4151670806
4.25894378194.25894378194.25894378190.2201453794.25894378194.25894378194.25894378190.2451759207
8.51788756398.51788756398.51788756390.15143648328.51788756398.51788756398.51788756390.1293884743
17.035775127817.035775127817.03577512780.069833852517.035775127817.035775127817.03577512780.0636709936
pH4
pH5
pH6
pH7
Fit Curve-pH4
Fit Curve-pH5
Fit Curve-pH6
Fit Curve-pH7
[Ni-nutrient solution] (M)
relative dry weight
1000
0.9836612474.25894378194.25894378194.2589437819
0.91799928228.51788756398.51788756398.5178875639
0.675502551417.035775127817.035775127817.0357751278
0.279063591234.071550255534.071550255534.0715502555
0.067144769268.143100511168.143100511168.1431005111
0.0132076398136.2862010221136.2862010221136.2862010221
17.614991482117.614991482117.614991482117.6149914821
22.896081771722.896081771722.896081771722.8960817717
0100
2.1294718910.99350385052.1294718912.129471891
4.25894378190.96157065674.25894378194.2589437819
8.51788756390.80368250818.51788756398.5178875639
17.03577512780.401118606417.035775127817.0357751278
34.07155025550.098759288434.071550255534.0715502555
68.14310051110.01761309768.143100511168.1431005111
0010
1.0732538331.0732538330.95050633281.073253833
2.1294718912.1294718910.86310003662.129471891
4.25894378194.25894378190.67138752224.2589437819
8.51788756398.51788756390.39835010728.5178875639
17.035775127817.03577512780.176657580217.0357751278
34.071550255534.07155025550.065011925934.0715502555
0001
0.5281090290.5281090290.5281090290.7738436567
1.0732538331.0732538331.0732538330.6059293472
2.1294718912.1294718912.1294718910.4151670806
4.25894378194.25894378194.25894378190.2451759207
8.51788756398.51788756398.51788756390.1293884743
17.035775127817.035775127817.03577512780.0636709936
Fit Curve-pH4
Fit Curve-pH5
Fit Curve-pH6
Fit Curve-pH7
[Ni-nutrient solution] (M)
relative dry weight
-0.16694000870.62894000870.62894000870.6289400087
0.11762462740.92997000430.92997000430.9299700043
0.24172386541.2311.2311.231
0.49620709741.53202999571.53202999571.5320299957
0.95883261651.83305999131.83305999131.8330599913
1.39337555662.1340899872.1340899872.134089987
0.327910013-0.14919387030.3279100130.327910013
0.62894000870.06136408620.62894000870.6289400087
0.92997000430.31913608870.92997000430.9299700043
1.2310.50400513241.2311.231
1.53202999570.57177450241.53202999571.5320299957
1.83305999130.86986968821.83305999131.8330599913
0.03034054950.0303405495-0.07002999570.0303405495
0.3279100130.3279100130.26909004960.327910013
0.62894000870.62894000870.33933947480.6289400087
0.92997000430.92997000430.46778490330.9299700043
1.2311.2310.56006211221.231
1.53202999571.53202999570.75874526141.5320299957
-0.2776383062-0.2776383062-0.2776383062-0.1321946064
0.03034054950.03034054950.0303405495-0.0488269097
0.3279100130.3279100130.3279100130.1430536927
0.62894000870.62894000870.62894000870.3261751652
0.92997000430.92997000430.92997000430.463572615
1.2311.2311.2310.5582907779
pH4
pH5
pH6
pH7
[Ni-nutrient solution] (logM)
[Ni-shoot] (logmmol/kg)
244.71.41.4
295.20.60.6
3165.75.7
256.82.82.8
421.8969335605
513.8858603066
66.2793867121
71.3918228279
Ni CaCl2 soil solution
free Ni2+ nutrient solution
pH
EC50 (M)
244.71.41.4
295.20.60.6
3165.75.7
256.82.82.8
421.8969335605
513.8858603066
66.2793867121
71.3918228279
Ni CaCl2 soil solution
free Ni2+ nutrient solution
pH
EC50 (M)
00000
00000
00000
00000
00000
00000
00000
10000
0.99560631090000
0.97808602190000
0.9216035150000
0.18693149840000
0.01879119080000
0.00475680390000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
00000
01111
00.88917690230.99857210250.99999937221
00.33598977550.92743173320.99995050180.9999999992
00.09130481330.55150068470.99936337260.9999999734
00.03092447440.18933447890.99611215370.9999996933
00.01293922820.06049620480.98432635670.9999979563
00.00629688130.02197787780.95217356640.9999903757
00.00341559280.00914317890.88286709180.9999643269
00.00200846820.00425002140.76467513280.9998890362
00.0008260360.0011753620.4433583270.9992611664
00.00039947420.00041049850.20159559790.9965300799
00.00021609840.00016860320.08725234830.9872579164
00.00016413860.00011320940.05828383940.9773270934
00.00012690430.00007799370.03958039810.9613999834
00.00007935090.00003951130.01924281470.9015085523
00.00006396460.00002891660.01376365310.8525298571
00.00005213490.00002150430.0100005550.7889554802
00.00003565360.0000124030.0055102860.6244781236
00.00002986320.00000959540.00416982030.5326544642
00.00002520260.00000750480.00319212270.4425276091
00.00002141720.00000592890.00246993290.3594260185
00.00001831690.00000472740.00193015870.286755755
00.00001363120.00000308170.00121090530.1763846122
00.00001035310.00000206910.00078432740.1064613896
00.00000800430.00000142540.00052239880.0644093003
00.00000500470.00000072210.00024877630.0246755315
00.00000328810.0000003930.00012809830.0102272758
00.00000224860.00000022670.00007026730.0045754771
00.00000158950.00000013710.00004061260.00218933
00.00000115520.00000008640.00002452630.0011100373
00.00000085970.00000005630.00001537590.0005915961
00.00000050480.0000000260.00000662880.0001902506
pH5.2
response line pH4.7
response line pH5.2
response line pH6.0
response line pH6.8
[Ni-added] (mmol/kgsoil)
relative dry weight of shoot
-0.3804184503-0.3804184503-0.9727580839-0.9727580839-0.0554374372-0.9727580839-0.9727580839-0.9727580839
-0.137397321-0.137397321-0.6717280882-0.67172808820.2550768255-0.6717280882-0.6717280882-0.6717280882
0.06597331950.0659733195-0.3706980926-0.37069809260.4931577548-0.3706980926-0.3706980926-0.3706980926
0.52265673220.5226567322-0.0696680969-0.06966809690.9308720175-0.0696680969-0.0696680969-0.0696680969
0.99935831910.99935831910.23136189880.23136189881.25551961350.23136189880.23136189880.2313618988
1.64516441551.64516441550.53239189440.53239189441.53070054290.53239189440.53239189440.5323918944
-0.6717280882-0.380477671-0.0876565078-0.380477671-0.6717280882-0.0876565078-0.6717280882-0.6717280882
-0.3706980926-0.1048429790.1875244215-0.104842979-0.37069809260.1875244215-0.3706980926-0.3706980926
-0.06966809690.01352386020.43090535080.0135238602-0.06966809690.4309053508-0.0696680969-0.0696680969
0.23136189880.42169359690.89511961350.42169359690.23136189880.89511961350.23136189880.2313618988
0.53239189441.12040201181.18973387621.12040201180.53239189441.18973387620.53239189440.5323918944
0.83342189011.67101032831.45431480551.67101032830.83342189011.45431480550.83342189010.8334218901
-0.3706980926-0.3706980926-0.5053966665-0.3706980926-0.2470755785-0.5053966665-0.2470755785-0.3706980926
-0.0696680969-0.0696680969-0.3904219515-0.06966809690.0351720175-0.39042195150.0351720175-0.0696680969
0.23136189880.23136189880.02529190550.23136189880.37041961350.02529190550.37041961350.2313618988
0.53239189440.53239189440.103187710.53239189440.62440054290.103187710.62440054290.5323918944
0.83342189010.83342189010.81145015650.83342189010.91724813890.81145015650.91724813890.8334218901
1.13445188571.13445188571.48104932661.13445188571.31609573491.48104932661.31609573491.1344518857
-0.0696680969-0.0696680969-0.0696680969-0.592450343-0.0696680969-0.0696680969-0.3287613158-0.3287613158
0.23136189880.23136189880.2313618988-0.3611905410.23136189880.2313618988-0.1118803865-0.1118803865
0.53239189440.53239189440.5323918944-0.12627252040.53239189440.53239189440.21100054290.2110005429
0.83342189010.83342189010.83342189010.02143584720.83342189010.83342189010.47204813890.4720481389
1.13445188571.13445188571.13445188570.3792442451.13445188571.13445188570.93979573490.9397957349
1.43548188141.43548188141.43548188141.32056026561.43548188141.43548188141.38280999761.3828099976
pH4.7 measured
pH5.2 measured
pH6.0 measured
pH6.8 measured
pH4.7 predicted
pH5.2 predicted
pH6.0 predicted
pH6.8 predicted
log[Ni-soil] mmol/kg
log[Ni-straw] mmol/kg
0.64177442240.62894000870.62894000870.6289400087
0.80695718880.92997000430.92997000430.9299700043
1.03661298551.2311.2311.231
1.25734479231.53202999571.53202999571.5320299957
1.41281358631.83305999131.83305999131.8330599913
1.55653003012.1340899872.1340899872.134089987
0.3279100130.6690199320.3279100130.327910013
0.62894000870.95184948970.62894000870.6289400087
0.92997000431.21739772180.92997000430.9299700043
1.2311.41859403711.2311.231
1.53202999571.34864741081.53202999571.5320299957
1.83305999131.42689965241.83305999131.8330599913
0.03034054950.03034054950.88179303970.0303405495
0.3279100130.3279100131.20297127640.327910013
0.62894000870.62894000871.24418915580.6289400087
0.92997000430.92997000431.25698750020.9299700043
1.2311.2311.18375855031.231
1.53202999571.53202999571.2529950981.5320299957
-0.2776383062-0.2776383062-0.27763830621.0210492999
0.03034054950.03034054950.03034054951.2859958615
0.3279100130.3279100130.3279100131.5126014438
0.62894000870.62894000870.62894000871.6860985053
0.92997000430.92997000430.92997000431.6330678418
1.2311.2311.2311.2262248338
pH4
pH5
pH6
pH7
[Ni-nutrient solution] (logM)
[Ni-root] (logmmol/kg)
-0.16694000870.62894000870.62894000870.6289400087
0.11762462740.92997000430.92997000430.9299700043
0.24172386541.2311.2311.231
0.49620709741.53202999571.53202999571.5320299957
0.95883261651.83305999131.83305999131.8330599913
1.39337555662.1340899872.1340899872.134089987
0.327910013-0.14919387030.3279100130.327910013
0.62894000870.06136408620.62894000870.6289400087
0.92997000430.31913608870.92997000430.9299700043
1.2310.50400513241.2311.231
1.53202999570.57177450241.53202999571.5320299957
1.83305999130.86986968821.83305999131.8330599913
0.03034054950.0303405495-0.07002999570.0303405495
0.3279100130.3279100130.26909004960.327910013
0.62894000870.62894000870.33933947480.6289400087
0.92997000430.92997000430.46778490330.9299700043
1.2311.2310.56006211221.231
1.53202999571.53202999570.75874526141.5320299957
-0.2776383062-0.2776383062-0.2776383062-0.1321946064
0.03034054950.03034054950.0303405495-0.0488269097
0.3279100130.3279100130.3279100130.1430536927
0.62894000870.62894000870.62894000870.3261751652
0.92997000430.92997000430.92997000430.463572615
1.2311.2311.2310.5582907779
pH4
pH5
pH6
pH7
[Ni-nutrient solution] (logM)
[Ni-shoot] (logmmol/kg)
4.70.72
5.21.32
64.1
6.89.95
18.2800
17.289333333300
16.590333333300
15.723666666700
5.798666666700
0.70600
0.093333333300
mean
Ni in soil (mg/kg)
dry weith shoot (g/pot)
19.342666666700
18.34300
16.18900
15.75400
13.404666666700
0.52100
0.075666666700
#REF!
Ni in soil (mg/kg)
dry weight shoot (g/pot)
18.2067473594.71.41.4
19.08261101845.20.60.6
15.867111121265.75.7
9.67685000896.82.82.8
421.8969335605
513.8858603066
66.2793867121
71.3918228279
free Ni2+ CaCl2 soil solution
free Ni2+ nutrient solution
pH
EC50 (M)
244.71.41.4
295.20.60.6
3165.75.7
256.82.82.8
421.8969335605
513.8858603066
66.2793867121
71.3918228279
Ni CaCl2 soil solution
free Ni2+ nutrient solution
pH
solution EC50 (M)
soil EC50 (mmol/kgsoil)
Reason for the difference??Practical point of view, simple to have just one EC50 independent of pH !!
Theoretical insight needed to explain the difference
Ni speciation in CaCl2 extractFree metal ion considered to be the bioavailable speciesNi forms complexes with dissolved organic matter: fulvic, humic acid etc.Measuring free Ni with the DMT technique
Relationship between Ni in CaCl2 versus free Ni2+
Log [Ni2+-free] = 0.76 + 1.09log [Ni2+-CaCl2] - 0.14 pH Free Ni2+ concentration in CaCl2 extraction decreases with increasing pH.
EC50free Ni2+ in CaCl2 extract, nutrient solutionNi2+ nutrient solutionNi2+ CaCl2 extraction
Adsorption isothermLog[Ni-adsorbed] = -1.89 + 0.77 log [Ni-CaCl2] + 0.6 pH (1)From CaCl2 extraction, we derived:Relationship between Ni-CaCl2 and free Ni2+:(1) + (2) gives:Log[Ni-adsorbed] = -1.35 + 0.71 log[Ni2+-free] + 0.70 pHLog [Ni2+-free] = 0.76 + 1.09log [Ni2+-CaCl2] - 0.14 pH (2)
Plant uptake equation from nutrient solution experimentlog[Ni-shoot] = 1.15 + 0.65log[Ni2+-free] + 0.11 pH (1)
Soil adsorption isotherm From CaCl2 extractionLog[Ni-adsorbed] = -1.35 + 0.71 log[Ni2+-free] + 0.70 pH (2)
Conclusion soil adsorption versusuptakeBoth biotic uptake and binding to soil increase with increasing pH
Bioavalibility in nutrient solution increases with increasing pH
pH effect for soil is bigger than for uptake
Result is that the bioavailability when expressed on Ni bound to soil (app. total Ni) decreases with increasing pH
Model approach to link soil metal content to metal uptakeQM-soil = Ks (Me2+)ms (H+)as(1)QM-biota = Kb (Me2+)mb(H+)ab(2)(1) + (2) gives, assuming Me(total)=QM-soilQM-biota = KbKs-(mb/ms) QM-total(mb/ms) (H+)(ab-as(mb/ms))
Outcome modelLog[Ni-shoot] = 3.41 + 0.92 log[Ni-soil] - 0.53 pH
Outcome model prediction of Ni uptake in soil-1.0-0.50.00.51.01.52.0-1.5-1.0-0.50.00.51.01.52.0log[Ni-soil] mmol/kg log[Ni-shoot] mmol/kgpH4.7pH5.4pH6.2pH6.8
What have we found about the pH effects on Ni bioavailability?
