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System for Predicting the Environmental Impact of Pesticides

System for Predicting the Environmental Impact of Pesticides

Introduction :

SyPEP was developed by S. Pussemier for Belgian conditions and crops. The SyPEP model uses equations to model a predicted environmental concentration in groundwater and surface water. After this predicted environmental concentration has been calculated, it is compared to the maximum permissible concentration of the chemical that is allowed in that specific environmental compartment (however, NOEC toxicity values may be substituted for the maximum permissible concentrations). In this comparison, the maximum permissible concentration values are divided by the predicted environmental concentration. That quotient is then ranked on a 1-5 scale to arrive at a SyPEP score for each compartment.

References:

  • Pussemier, L. 1999. A system for predicting the environmental impact of pesticides in Belgium. In J. Reus, P. Leendertse, C. Bockstaller, I. Fomsgaard, V. Gutsche, K. Lewis, C. Nilsson, L. Pussemier, M. Trevisan, H. van der Werf, F. Alfarroba, S. Blümel, J. Isart, D. McGrath, T. Seppälä (eds), Comparing Environmental Risk Indicators for Pesticides: Results of the European CAPER Project. Utrecht, The Netherlands: Centre for Agriculture and the Environment.
  • Reus, J., Leendertse, P., Bockstaller, C., Fomsgaard, I., Gutsche, V., Lewis, K., Nilsson, C., Pussemier, L., Trevisan, M., van der Werf, H., Alfarroba, F., Blumel, S., Isart, J., McGrath, D., Seppala, T. 2002. Comparison and evaluation of eight pesticide environmental risk indicators developed in Europe and recommendations for future use. Agriculture, Ecosystems, and Environment 90, 177-187.


Equations :

  1. PEC gw = (APEBOD*1000/recharge groundwater)
    GUS = log DT50*(4-logKoc)
    CSPER1 = 163.51-181.28(GUS) + 52.88(GUS)2 -3.42 (GUS)3
    APEBOD = CSPER1*(actual dose/reference dose)*soil correction factor

In equation (1) APEBOD is the amount of pesticide potentially exportable below one meter depth. The recharge groundwater variable is approximated by dividing the annual rainfall amount at the site by 3. This default value approximation is given in the SyPEP model. GUS is the groundwater ubiquity score, CSPER1 is the amount of pesticide able to leach under 1 m depth according to the Dutch standard scenario, and the soil correction factor is a factor taking into account rainfall amounts and soil types included in SyPEP (see SyPEP Table 1).

SyPEP Table 1: SyPEP Soil Correction Factors

Soil Type
Rainfall < 750mm
750mm<Rainfall<850mm
Rainfall>850mm
Sandy
0.67
0.95
1.00
Loam
0.10
0.14
0.38
Humous
0.33
0.43
0.48

SyPEP also calculates a predicted environmental concentration in surface water according to the following equation:

  1. PEC sw = PCOW*(1-BFI)
    PCOW = APESUW / (rainfall*SPR)


  2. PEC sw-lt = Average PEC sw


  3. PEC sw-st = Maximum PEC sw

In equation (1) PCOW is the predicted concentration in out flowing water. The BFI variable is the Base Flow Index that represents the fraction of river water not directly linked to rainfall (and thus originating from groundwater). For our research, a SyPEP default value of 0.50 was used as the BFI value. APESUW is the amount of pesticide potentially exportable to surface waters. It is calculated by adding pesticide losses to surface water such as drift, runoff, drainage, and direct losses.

After the PEC values are obtained they are converted into Toxicity Exposure Ratios (TERs).

  1. TER gw = 0.1/PECgw


  2. TER sw-lt = NOEC water organism /PECsw-lt


  3. TER sw-st = NOEC water organism * 10 /PECsw-st


  4. Total Risk = TER gw + TER sw-lt + TER sw-st

In equation (1) the 0.1 value reflects the drinking water quality standard of 0.1 g/L. In equation (2) NOEC toxicity values are used in lieu of maximum permissible concentrations (MPCs) as MPC values were difficult to find. This substitution is specifically allowed under the SyPEP system.

After TER scores are obtained they are converted into environmental impact scores based on the following rationale:

TER <0.1
score = 5
TER <1
score =4
TER<10
score=3
TER<100
score=2
TER<1000
score=1
TER>1000
score=0

These scores are then added across each of the environmental compartments considered (groundwater, short-term surface water risk, and long-term surface water risk) to arrive at a final SyPEP score (It should be noted that this final summation of risk is not specifically included in the SyPEP model. However, this summation has been used in other research to show the total environmental risk score predicted by SyPEP).

SyPEP List of Symbols :

Symbol
Description & Units
Actual Dose amount of pesticide active ingredient applied (g/ha)
APEBOD amount of pesticide a.i. potentially exportable below 1 m (g/ha/year)
APESUW amount of pesticide a.i. potentially exportable to surface water (g/ha)
BFI base flow index
CSPER1 amount of pesticide a.i. able to leach under 1 m depth for the Dutch standard scenario (g/ha/year)
GUS groundwater ubiquity score
PCOW predicted concentration of pesticide a.i. in outflowing water (g/L)
PECgw predicted concentration of pesticide a.i. in groundwater (g/L)
PECsw predicted concentration of pesticide a.i. in surface water (g/L)
PECsw-st acute concentration of pesticide a.i. in surface water (g/L)
PECsw-lt long term concentration of pesticide a.i. in surface water (g/L)
Rainfall amount of rainfall (m3)
Recharge Groundwater new groundwater influx (m3)
Reference Dose recommended amount of pesticide a.i. applied (g/ha)
Soil Correction Factor Factor for the pedo-climatic condition of the region
SPR standard percentage runoff (%)


Analysis :

In order to operate this model, some assumptions may have to be made. First, SyPEP requires rainfall data fortnightly. To arrive at these fortnightly amounts (if the researcher has only monthly rainfall data), monthly rainfall amounts may have to be divided by two. Second, some pesticides could have a PECgw of 0. However, a 0 value results in the toxicity exposure ratio score equation (equation v) not working (one cannot divide by 0). Thus, if a pesticide has a 0 PECgw value, then a value of 1e-9 (or similar low value) may have to be used so that the environmental impact score of the pesticide can be calculated. Third, a default value of 0.5 may have to be used for the Base Flow Index variable (which is the fraction of river water not directly linked to rainfall). This default value is included in the SyPEP article. Fourth, a default value of 0.333 may have to be used for the Standard Percentage Runoff (which is the fraction of rainfall that will reach a river via runoff and drainage). This default value is included in the SyPEP article. Fifth, following the rationale in the article, a "correction factor of 1 (based on yearly rainfall amounts>850mm and a sandy type of soil) was assumed. This "correction factor variable is used to calculate the PEC gw.

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