Future trends in soil cadmium concentration under current cadmium fluxes to European agricultural soils

1
Future trends in soil cadmium concentration
under current cadmium fluxes to European
agricultural soils Erik Smolders and Laetitia
Six Katholieke Universiteit Leuven, Belgium
2
Mineral P fertilisers contain traces of Cd
derived from rock P with different CdP ratios
Nziguheba and Smolders, 2008
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Where the story begins...
Nauru
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Soil Cd increases with cumulative application of
P-fertilisers in experimental plots in Australia.
The HCl soluble soil Cd increases from 0.03 to
0.06 mg kg-1 soil (Williams David, 1974).
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Archived soil samples illustrate rising soil Cd
concentrations. Sources soil Cd in Broadbalk,
Rothamsted (1846 -1980) Jones et al., 1987
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Natural stock of Cd in topsoil 100-1000 g Cd/ha
Annual Cd mass balances in European agricultural
topsoils in g Cd/ha/year
  Rothamsted UK 1846-1980 Hutton and Symon, 1986 Moolenaar and Lexmond, 1998
Input P-fertiliser Atm. dep. Other   8 3 4 1 4 2 1
Output Crop offtake Leaching   n.d. 2 0.6 1.6
Net balance 2-5 (measured) lt8 2
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2003 proposal for a Cd limit in EU mineral
fertilisers based on mass balance calculations
Predicted change in soil Cd in European
agricultural soil after 100 years application of
inorganic P fertilizers at different Cd levels.
Means (? ) and 10th -90th percentile of different
simulations Calculations in the CSTEE report
(2002) a, right side, updated 2013
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Measured deposition factor 4 decrease over about
20 years
Wet-only deposition collector approved by EMEP
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P-fertilizer consumption in EU factor 1.4
decrease over last 15 years
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Soil acidity (pH) is main driver for the Cd
leaching
OH
OCd
OCd
OH
O
O
3H Ca2
4Cd2
Ca
Cd
O
O
OCd
OH
More H (lower pH) reaction to the leftCd more
soluble Solidliquid distribution of Cd in soil
expressed in KDCdsoil/Cd soil solution
(concentration ratio)
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Pore water KD values of Cd in 151 European
soils Degryse et al. 2009
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Predicted change in soil Cd over 100 years in 540
potential European scenarios soil pH is the main
driver Average scenario 15 depletion
Six and Smolders, 2014
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Key changes between the 2002 assessment and
current assessment 2002 2012 factor
change Input Atmospheric deposition (g/ha/y) 1.5
(0-3) 0.35 4-fold lower Fertiliser use (kg
P2O5/ha/y) 1.6 0.80 2-fold lower Lime/manure/slu
dge (g Cd/ha/y) 0 0.15 marginal
increase Output Average soil pH 6.5 5.8 2.3-fo
ld increase Cd output KD model two
models new model prediction of new in
between that of two earlier models
Change in soil Cd in 100y at average fertiliser
Cd slight accumulation 15depletion
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Trends of wheat grain Cd in Sweden from
accumulation to depletion
Kirchmann et al. 2009
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• Conclusion
• Cd input to European soils has decreased due to
  lower emissions and lower mineral P use
• Cd output from soil may be higher than initially
  estimated average soil pH (CaCl2 0.01M) is 5.8
  in arable soils
• Burden of fertiliser on foodchain Cd has reduced
  but political pressure on setting strict limits
  remains