Supporting Information
Simulation of the plant uptake of organophosphates and other emerging pollutants for greenhouse experiments and field conditions
Stefan Trapp, Trine Eggen
Table of Content
Methods 2.3 Model parameterization for greenhouse experiment
Table SI 1a. Soil and plant input data for the simulation of greenhouse experiments.
Methods 2.4 Field simulation study and model parameterization
Table SI 2. Meteorological input data.
Table SI 3. Properties of soil layers.
Table SI 4. Plant parameters for the field simulation.
Results 3.1 Simulation of greenhouse experiments
Figure SI 1. Input data greenhouse scenario.
Results 3.2 Simulation of the field scenario
Water balance
Figure SI 2. Elements of the water balance.
Discussion 4.1 Bioaccumulation in field simulation versus greenhouse studies
Definition bioconcentration factor BCF
Table SI5. Bioconcentration factors obtained from the greenhouse study
Table SI6. Bioconcentration factors for the field scenario
Discussion 4.2 Mass balance
Table SI7. Mass balance for the input to soil layer 5
Appendix to Methods, 2.2 Model approach
Tipping Buckets model for transport of water in soil
To Methods 2.3 Model parameterization for greenhouse experiment
Table SI 1a. Soil and plant input data for the simulation of greenhouse experiments.
Parameter / Barley 2009 / Carrot 2009Soil mass g / 4 000 / 4 000
Soil OC % / 0.7 / 0.7
Root g dw / 3.1 / 0.9 - 5.0 (5.0)
Leaves g dw / 11.8 / 0.9
Seeds g dw / 34.9 / nn
Water content roots % / nd (75) / 72.9 - 80.5 (77)
Water content leaves + stem % / nd (66.3) / 66.3
Water content seeds % / 6.3 / nn
Transpiration coefficient kg fw/L / 100 / 100
nd: no data; nn: not needed; in brackets: selected as input data for the simulations
To Methods 2.4 Field simulation study and model parameterization
Table SI 2. Meteorological input data, averaged per half-month, measured in Feucherolle, France, between 1999 and 2000.
Month / End day (d) / Precip (L/d) / Evap (L/d) / Air temp (°C)Aug / 15 / 6.31 / 1.71 / 22.1
Aug / 31 / 0.30 / 1.60 / 19.8
Sep / 46 / 2.71 / 1.39 / 20.7
Sep / 61 / 4.86 / 0.94 / 17.2
Oct / 76 / 1.19 / 0.69 / 13.5
Oct / 92 / 1.88 / 0.56 / 11.7
Nov / 107 / 1.52 / 0.34 / 9.2
Nov / 122 / 1.31 / 0.21 / 5.6
Dec / 137 / 3.25 / 0.23 / 7.0
Dec / 153 / 6.34 / 0.19 / 4.7
Jan / 168 / 0.72 / 0.19 / 5.3
Jan / 184 / 0.50 / 0.23 / 3.7
Feb / 199 / 1.67 / 0.28 / 6.2
Feb / 212 / 1.97 / 0.48 / 6.7
March / 227 / 0.67 / 0.63 / 8.0
March / 243 / 1.85 / 0.74 / 9.0
April / 258 / 3.28 / 0.88 / 9.5
April / 273 / 3.20 / 1.04 / 12.8
May / 288 / 3.89 / 1.33 / 18.2
May / 304 / 2.20 / 1.24 / 16.8
June / 319 / 2.95 / 1.39 / 18.6
June / 334 / 0.04 / 1.78 / 19.8
July / 349 / 6.21 / 1.21 / 18.0
July / 365 / 3.09 / 1.53 / 19.0
Table SI 3. Properties of soil layers. Depth, dry density S,dry, field capacity FC, permanent wilting point PWP and organic carbon OC of soil layers; typical values, except OC.
Soil layer / Depth / S,dry / FC / PWP / OCcm / kg/L / L/L / L/L / g/g
1 / 0-20 / 1.3 / 0.35 / 0.15 / 0.007
2 / 20-40 / 1.3 / 0.35 / 0.15 / 0.0035
3 / 40-60 / 1.3 / 0.35 / 0.15 / 0.0035
4 / 60-80 / 1.3 / 0.35 / 0.15 / 0.0035
5 / 80-100 / 1.3 / 0.35 / 0.15 / 0.0035
Table SI 4. Plant parameters for the field simulation (year 1999/2000).
Parameter / Unit / Value / SourceTranspiration coefficient / L kg fw-1 / 100 / Larcher (1996)
Final root mass / kg fw-1 m-2 / 2.35 / Legind et al. (2012)
Final mass of stem / kg fw-1 m-2 / 2.33 / Legind et al. (2012)
Final leaf mass / kg fw-1 m-2 / 0.26 / Legind et al. (2012)
Final mass of grains / kg fw-1 m-2 / 1.45 / Legind et al. (2012)
To Results 3.1 Simulation of greenhouse experiments
Figure SI 1 (top) shows the growth of barley roots, leaves and grains (fruits; stem equals leaves). After about 60 days, most of the biomass of roots and leaves has established, and grains (fruits) start to develop. The last 30 days is the ripening phase, with declining plant growth and transpiration. This growth pattern has consequences for the concentration in plant, as can be seen for the simulated concentration of TCPP in barley leaves (Figure SI 1, middle). Initially rapid uptake of TCPP with the transpiration wateroccurs. A maximum level of TCPP in leaves is reached at day 20. By growth dilution and loss processes (volatilization, metabolism), the concentration decreases. Reduced growth of leaves at day 60 and peak transpiration day 84 have some effect on the curve. Concentrations in roots are higher than those in soil and both decrease over the simulation period (Figure SI 1 bottom). The most important loss process for TCPP from soil is uptake into plant, because the pot is relatively small (4 kg weight, soil to plant ratio 80 kg/kg). Concentration in grains (fruits) remain low. Growth dilution is the same for all chemicals, but the overall decline depends on the chemical-specific loss processes, i.e. degradation and volatilization.
Figure SI 1. Mass (kg) of barley roots, leaves and grains (fruits) (top) versus time; simulated concentration of TCPP (mg/kg fw) in leaves (middle) and in soil, roots and fruits (bottom), greenhouse scenario.
To Results 3.2 Simulation of the field scenario
Water balance. The water balance is shown in Figure SI 2 a b c. Precipitation occurs all over the year, but with a minimum in June and high rainfall in July (Figure SI 2a). Evaporation from soil surface is highest in August 1999 and spring 2000, but none in summer 2000. This is because the water in the top soil layer is depleted. Transpiration of water occurs as long as the plant grows, that is from May to June, with peak end of May. Leaching of water to groundwater occurs in the cold season, from October to April, but stops as soon as transpiration gets higher.
The water content WC of the soil layers at the end of the half-month periods is seen in Figure SI 2b. All layers start with WC at the permanent wilting point (WC is 0.15 L/L, not shown), but soil layer 1 (top) and 2 are filled up within the first 15 days, due to heavy rainfall the first August weeks. It takes until October to refill layer 3,4 and 5, and in this order. Until the start of the growth season, the soil remains water-saturated. Then the soil layers are rapidly depleted, starting with the top soil layer in March and all layers until May. In July, due to heavy rainfall and while the plants are ripening, the 3 top layers refill partly.
The driver for the depletion of the soil layers from water is the transpiration. Figure SI 2c shows the water uptake by roots for the five soil layers in the period between March and July. The difference between FC and PWP corresponds to 40 L water per layer, and that is the maximum that can be taken up during a period of two weeks. During March, the crops can satisfy their water needs from the top soil layer 1. In April, layer 2 is also depleted. In May, transpiration peaks with up to 12 L/d, and water is drawn from all five layers. Second half of May, the soil layers are empty, and additional 134 L of water are taken from below 1 m depth. Rainfall in June provides water for uptake in layer 1 and (little) 2. End of June is dry, and very little water is available. However, plants get into the ripening phase, where the water needs is low (see Fig. SI 2a).
Figure SI 2. Elements of the water balance. Periods last 1/2 month each. Top a) Precipitation, actual evaporation, leaching out of soil layer 5, transpiration by plants, all in L/d. Middle b) Water content of the five soil layers over time, unit L/L; upper limit field capacity is 0.35 L/L, lower limit permanent wilting point at 0.15 L/L. Bottom c) transpiration separated for the five soil layers. Unit is L (per period, 1/2 month).
To Discussion 4.1 Bioaccumulation in field simulation versus greenhouse studies
Definition bioconcentration factor BCF
Greenhouse study:
BCF = concentration (mg/kg dw) in plants at harvest / initial concentration in soil (mg/kg dw)
Field study:
BCF-values for the field simulation are more difficult to define, because the concentrations of the chemicals differ in the five soil layers and are not constant over time. Principally, the BCF should be defined by using the concentration ratio between plants at harvest and the concentration in soil, but which concentration in soil? The BCF can be related to the concentration in top soil (this is justified because the crop takes up most water from the top layer, Fig. SI2) or to the maximum or to the average concentration of all five soil layers. Over time, the concentration in soil can be a) the maximum concentration (i.e. after sludge application) of the simulation period, or b) the concentration at the time when the plants start to grow (March), or c) the concentration at harvest.
BCF-values calculated from the options a, b and c are shown in the Tables SI 6a,b,c. The use of soil concentrations in top soil at begin of plant growth 1st of March (Tab. SI 6b) leads to very high BCF-values of TCEP and also of DEET. The reason is certainly that TCEP and DEET have leached to lower soil layers by this time. The use of the maximum concentration in soil at harvest (concentrations and layers shown in Table 4) leads to rather high BCF for all compounds (Tab. SI 6c). The reason here is that the compounds have been lost from soil at the end of the simulation period, also due to plant uptake. Thus, the use of the concentration in soil at its maximum in time, i.e. directly after sewage sludge application in September (values shown in Table 3), seems the most reasonable way to calculate the BCF (Tab. SI 6a) and leads to BCF-values that are comparable in value to the BCF from the greenhouse study (Table SI5).
Table SI5a. Bioconcentration factors obtained from the greenhouse study with barley, measured and simulated (kg/kg dw); meas. = measured, sim. = simulated.
Root meas / Root sim / Leaf+stem meas / Leaf+stem sim / Grains measTCEP / 0.615 / 0.012 / 25.5 / 37.4 / 0.034
TCPP / 0.74 / 0.77 / 6.38 / 5.83 / 0.11
TBP / 1.39 / 1.18 / 1.23 / 1.16 / 0.01
NBBS / 0.025 / 0.014 / 0.075 / 0.053 / 0.005
DEET / 0.81 / 0.08 / 7.46 / 0.89 / 0.00
Table SI5b. Bioconcentration factors obtained from the greenhouse study with carrots, measured and simulated (kg/kg dw); meas. = measured, sim. = simulated
Carrot meas min / Carrot meas max / Carrot sim / Leaf+stem meas / Leaf+stem simTCEP / 0.26 / 0.68 / 0.45 / 42.0 / 28.1
TCPP / 9.21 / 20.2 / 5.41 / 17.4 / 21.1
TBP / 0.37 / 4.56 / 1.13 / 0.56 / 0.71
NBBS / 0.20 / 0.45 / 0.15 / 0.52 / 0.45
DEET / 0.35 / 2.61 / 1.43 / 4.10 / 8.14
Table SI6a. Bioconcentration factors (kg/kg dw) calculated for the field scenario using the maximum concentration in top soil (after sewage sludge application in September).
Root / Stem / Leaves / SeedsTCEP / 0.21 / 2.25 / 69.9 / 1.76
TCPP / 0.34 / 0.24 / 1.23 / 0.08
TBP / 0.19 / 2.23 / 4.62 / 0.03
NBBS / 0.0010 / 0.0012 / 0.0089 / 0.0004
DEET / 0.22 / 0.36 / 6.82 / 0.46
Table SI6b. Bioconcentration factors calculated for the field scenario using the concentration in top soil 1st of March (when plants start to grow).
Root / Stem / Leaves / SeedsTCEP / 28.5 / 304 / 9451 / 238
TCPP / 4.3 / 3.1 / 15.7 / 1.0
TBP / 1.2 / 14.6 / 30.2 / 0.23
NBBS / 0.22 / 0.27 / 2.0 / 0.09
DEET / 5.4 / 9.0 / 169.5 / 11.4
Table SI6c. Bioconcentration factors calculated for the field scenario using the maximum concentration of all soil layers at the harvest date (31st July).
Root / Stem / Leaves / SeedsTCEP / 6.9 / 74 / 2296 / 58
TCPP / 14.5 / 10.5 / 53.0 / 3.4
TBP / 3.1 / 35.8 / 74.2 / 0.6
NBBS / 2.7 / 3.2 / 24.3 / 1.1
DEET / 5.3 / 8.8 / 166 / 11.2
To Discussion 4.2 Mass balance
Table SI7. Mass balance for the input to soil layer 1 (mg/m2/year and %).
Compound / sewage sludge / with rain / dry particle depositionTCEP / 0.51
82.5% / 0.062
10.0 % / 0.046
7.4 %
TCPP / 10.3
94.1 % / 0.63
5.8 % / 0.016
0.1 %
TBP / 0.38
66.9 % / 0.17
29.9 % / 0.018
3.2 %
Appendix to Methods, 2.2 Model approach
Tipping Buckets model for transport of water in soil
adapted from Legind et al. (2012)
The discrete Tipping Buckets water balance model considers five soil layers located above the groundwater table, for which the water balance is calculated. The soil layers are considered to be a series of "tipping buckets", which have an upper and lower limit for water storage capacity: the water content at the upper limit is the field capacity FC (L), that at the lower limit is the permanent wilting point PWP (L). Flow is discontinuous, i.e. the soil layers are considered as buckets that can be filled up to field capacity, after which they tip, and by putting the soil layers in series, tipping buckets arise that transport water and solutes. Transpiration, i.e. water extraction by plants, is calculated from plant growth (see there). It is assumed that plant roots always extract water from the highest possible soil layer, and until the PWP is reached. Precipitation, evaporation and transpiration were considered and calculation was done in eight steps as detailed in the following. All calculations were done for an area of 1 m2.
Step 1: Initial (absolute) water content in the top soil layer (soil layer 1) WIni1 (L) is obtained from initial volumetric water content W,Ini1 (L L-1) and the volume of soil layer 1 VS1 (L) as
WIni1 = W,Ini1 x VS1(1)
Step 2: Infiltration Inf (L d-1) is calculated from precipitation P (L d-1) and evaporation E (L d-1) (soil layer 1):
(2)
Step 3: After infiltration, a new water content WInf1 (L) is established in soil layer 1:
WInf1 = WIni1 + Inf x ∆t(3)
where ∆t (d) is the length of the time period.
Step 4: Leaching from soil layer 1, Leach1 (L), occurs if the water content is now above field capacity FC (L):
(4)
Step 5: After leaching, the water content of soil layer 1 changes to WLeach1 (L):
WLeach1 = WInf1 - Leach1(5)
Step 6: Transpiration, i.e. water flux to plants from soil layer 1 q1 (L), takes place if the water content is now above the permanent wilting point PWP1 (L):
(6)
where Q (L d-1) is the total transpiration of the plant in this period (see next section).
Step 7: After transpiration, again a new water content Wq1 (L) is established in soil layer 1:
Wq1 = WLeach - q1(7)
Step 8: Finally, remaining transpiration qTotal-1 (L), i.e. transpiration water that needs to be taken from deeper soil layers, is obtained by:
qTotal-1 = Q x ∆t – q1(8)
For the next soil layers (soil layer i, with i> 1), steps 3 to 8 are repeated. However, Step 3 (Eq. 3) is the new water content of layer i due to leaching from above:
WInf,i = WIni,i + Leachi-1(9)
Step 6 (Eq. 6) changes to
(10)
and Step 8 (Eq. 8) changes to
qTotal-i = qTotal-(i-1) – qi(11)
The water balance was established iteratively for all soil layers i in each time period p. The calculated water content after transpiration from one time period (Wq,i,p) was entered as initial water content for the following time period (WIni,i,p+1).
If the plant does not find sufficient water in the five soil layers (i.e., Q > qi), it is assumed that the remaining water required for transpiration is drawn from groundwater. This does not affect water or substance content of the five soil layers. In the present model formulation we assume that the groundwater has the same substance concentration as the lowest soil layer.
Solute transport in soil
Solutes passively follow the water movement. The change of solute concentration in soil is given by input from air and pulse emissions (amendment application) to soil layer 1 minus loss of solute by leaching and plant uptake via transpiration. As heavy metals are considered in this study, loss by degradation and by volatilization from the top layer are not of relevance. In discrete form, the concentration in soil layer 1, C*S,1 (mg L-1) (referred to the volume of bulk soil, VS), at time t is:
(12)
where C*S,1(t-1) is metal concentration in soil layer 1 at time t-1 (preceding time period), AS (1 m2) is the surface area of the soil, vdep (m d-1) is the deposition velocity of particles, CA,p (mg m-3) is the total concentration at particles in air (mg m-3), PAS is the diffusive (gas) exchange velocity between soil and air (gaseous concentration in air is neglected), Rain is the precipitation in the period (L d-1), CRain is the concentration in rain (mg L-1) and I (mg) is a pulse input (from amendment application). The water to dry soil partition coefficient KWS1 (-) in soil layer 1 was calculated as
(13)
where Kd (L kg dw-1) is the dry soil to water partition coefficient and ρS,dry is the density of dry soil. The change of concentration in the second and following soil layers (index i, with i > 1) is given by influx of solute from the upper soil layer via leachate minus loss by leaching to deeper soil layers and transpiration. Soil concentration C*S,i at time t is accordingly:
(14)
The volume-based concentrations in bulk soil, C*S (mg L-1) can be converted to soil dry weight, CS (mg kg dw -1), by dividing by the dry soil density ρS,dry (kg dw L-1). For solutes, the Courant criterion needs to be fulfilled, which says that in one step not more compound can flow out of a layer than is in it. This limits thickness of the layers and time step.
1