1. Scientific Issue and Objective
15th International Conference RAMIRAN, Versailles, France, June 3-5th 2013
Predictive modelling of the long-term accumulation of trace metals in tropical soils amended with organic wastes – field trial validation
Oustrière Nadège1*, Lahbib-Burchard Taos1, Doelsch Emmanuel2, Feder Frédéric3,4, Poïny-Toplan Stéphanie1, Wassenaar Tom1, Bravin Matthieu N.1
1 CIRAD, UPR Recyclage et risque, F Saint-Denis, La Réunion, France
2 CIRAD, UPR Recyclage et risque, F Aix-en-Provence, France
3 CIRAD, UPR Recyclage et risque, Dakar, Sénégal
* Corresponding author: CIRAD, UPR Recyclage et risque, F Montpellier, France
Scientific Issue and Objective
Agricultural recycling of waste as fertilizer and soil amendment is a good alternative to manage the growth of agricultural, industrial and urban wastes.
The environmental impact of such agricultural recycling practices had to be controlled since it can result in a significant accumulation of trace metals.
Models were already developed to predict the accumulation of trace metals in soils amended with organic wastes but none of the studies were validated with field experiments or conducted on tropical areas .
We aimed to adjust the parameterization of an accumulation model to the specific conditions of the tropical island of La Reunion and to validate the model against mid-term field trials
Modelling and methodology
Estimation of trace metals
leached or uptake by plant
Modelling
Field experiment for model validation
Modeled trace metals concentration in soil were compared to measured values from field experiments.
Measure : concentration in plants edible organs, soil, organic wastes and mineral fertilizer
Option n°1 from the literature : multi-linear regression model with the formalism
Trace metals uptake by plants = a ln Cst + b pH + c [1]
Trace metals leached = A log Cst + B log som + C pH + D [2]
Option n°2 from measured values : median from the field experiment data
Cst = Cst-1 + (Iow +Imf – Op+Ol)
(10 ρ dp)
Upper
soil layer
Lower Ol Op
Iow
Imf
pig slurry compost
Lactuca sativa
Daucus carota
Lycopersocon esculentum
Phaseolus vulgaris
Brassica oleracea
Poultry litter compost
NPK fertilizer
Zn leached (µg l-1)
Zn uptake (mg kg-1)
Literature
Measured
Median
213 90
102 19
>
>
Regression model (literature) was not able to predict adequately the range of Cd, Cu, Ni and Zn leached or uptake by plant (measured).
Consequently, we chose to use the median of measured values as the predicator of trace metals leached or uptake by plants
ρ and dp : soil depth and soil density / Cst : traces metals concentration
Iow, Imf : traces metals input by organic wastes or mineral fertilizers
Op and Op : traces metals output by leaching and plant uptake
Model validation
Balance of input and output
of trace metals
210
230
250
270
290 1 2 3 4 5 6 7
Time (Years)
Legend :
Measured Zn concentration amended with poultry litter compost
Modeled Zn concentration amended with poultry litter compost
Measured Zn concentration amended with mineral fertilizer
Modeled Zn concentration amended with mineral fertilizer
Zn mass [mg/m²]
Iow
Imf Ol Op 5 50
500
5000
50000
Iow>>Imf=Ol>OP
Initial Zn mass in soil layer
Zn input by organic wastes (Iow) and mineral fertilizer (Imf) represent 2 and 0,13 % of initial Zn mass in soil layer
Mass balance between Imf and Ol is equilibrate whereas it is not between Iow and Ol
Zn output by plant uptake (Op) represent 4*10-5 % of initial Zn mass in soil layer
Iow, Imf and Ol can cause trace metals balance on the long-term whereas Op will not
Soil Zn concentration [ mg/kg]
Zn and Cu concentration ◊ in soil amended by pig slurry and poultry litter compost ◊ slightly decreasing in soil amended by mineral fertilizer
Ni and Cd concentration ◊ stay constant in soil amended by pig slurry, poultry litter compost and mineral fertilizer
For all modalities, the model simulates pretty well the tendency of
measured values. The adjusted model would be adapted to the
specific climate and soil conditions of la Réunion.
Similar results are obtained for Cd, Cu and Ni
Take-Home Message
We validate our model against a filed trial in the specific climate and soil conditions of La Réunion
The adjustment with data from the field experiment avoided the overestimation of trace metals output from trace metals uptake by plants or trace metals leached.
The model could be now applied to compare different scenarios of organic wastes recycling to further assess the ecotoxicological issue of trace metals accumulation in agricultural soils on a long-term perspective.
Literature
[1] Efroymson, R.A., Sample, B.E., Suter II, G.W., Uptake of inorganic chemicals from soil by plant leaves: regressions of field data. Environmental Toxicology and Chemistry 20,
[2] Sauvé, S., Hendershot,W., Allen, H.E., Solid-solution partitioning of metals in contaminated soils: dependence on pH, total metal burden, and organic matter. Environmental Science & Technology 34,
This study was performed within the two frameworks of the “Réseau PRO” CasDAR research project coordinated by ACTA and INRA and within the “PILMO” research project. It was co-funded by ADEME (Minister of Agriculture, Food and Forestry), the ministry of Agriculture & Fisheries and by Région Réunion