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 Cd:P ratios
Nziguheba and Smolders, 2008

3. Where the story begins...
Nauru

4. 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).

5. Archived soil samples illustrate rising soil Cd concentrations
Archived soil samples illustrate rising soil Cd concentrations. Sources: soil Cd in Broadbalk, Rothamsted ( ) Jones et al., 1987

6. 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
Hutton and Symon, 1986
Moolenaar and Lexmond, 1998
Input
P-fertiliser
Atm. dep.
Other 8 3 4 1 2
Output
Crop offtake
Leaching
n.d.
0.6
1.6
Net balance
2-5
(measured)
<8

7. 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

8. Measured deposition: factor 4 decrease over about 20 years
Wet-only deposition collector approved by EMEP

9. P-fertilizer consumption in EU: factor 1.4 decrease over last 15 years

10. Soil acidity (pH) is main driver for the Cd leachingOH
OCd+ OH
OCd+ O O Ca
+ 4Cd2+ Cd
+ 3H+ +Ca2+ O O OH
OCd+
More H+ (lower pH): reaction to the left=Cd more soluble
Solid:liquid distribution of Cd in soil expressed in KD=Cdsoil/Cd soil solution (concentration ratio)

11. Pore water KD values of Cd in 151 European soils
Degryse et al. 2009

12. 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

13. Key changes between the 2002 assessment and current assessment
factor change
Input
Atmospheric deposition (g/ha/y) 1.5 (0-3) fold lower
Fertiliser use (kg P2O5/ha/y) fold lower
Lime/manure/sludge (g Cd/ha/y) marginal increase
Output
Average soil pH fold 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 15%depletion

14. Trends of wheat grain Cd in Sweden: from accumulation to depletion
Kirchmann et al. 2009

15. 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