244th ACS National Meeting | August 19th to 23rd

, 2012 | Philadelphia, PA 

Monitoring and predicting leaching 

and transport of a metabolite from a 

field to drinking water abstraction 

points 

R Sur*, T Oertel†, M Himml‡, G Görlitz§ 

*Bayer CropScience LP, Environmental Exposure Assessment, RTP, NC

§Bayer CropScience AG, Environmental Modelling, Monheim, Germany

†Stadtwerke Duisburg AG, Germany

‡GEOBIT Ingenieurgesellschaft mbH, Aachen, Germany

EMPM, March 19th, 2013 | Washington DC
Slide 2 

 N,N-dimethylsulfamide (DMS) is a prominent soil metabolite of the 

fungicidal a.i. tolylfluanid 

 DMS is neither harmful to man nor to the environment (non-genotoxic, 

non-toxic, non-ecotoxic, non-pesticidal) 

 Regulatory recommendations (wholesomeness limits) for drinking water

concentrations of DMS in Germany (Federal Environment Agency): 

 1.0 μg/L (permanently) 

 10 μg/L (temporarily for max. 9 years) 

 Long-term application of the fungicide EUPAREN M on an orchard has 

resulted in significant amounts of DMS in the groundwater catchment of 

water works Duisburg (Germany, North Rhine-Westphalia)

 Concerns were raised by the water works whether the threshold value 

for DMS in drinking water could be exceeded

Introduction

R Sur et al | Drinking Water Modelling | 
Slide 3 

Objective

 Develop generic modelling approach for drinking water exposure assessment 

(case study)

 Predict duration and distribution of future DMS groundwater contamination in 

catchment for water management purposes

 Derive dilution/transfer factors between DMS in groundwater and drinking water

2D-modelHYDRUS

1D-model

PEARL 

R Sur et al | Drinking Water Modelling | 

regulatory approval:

PECgw or measurement

in 1 m depth under

treated field

aquifer

monitoring well drinking water well

dilution

raw water

drinking water

protection:

measured

concentration
Slide 4 

Tolylfluanid

DMST 

DMST-acid

DMS

 Minor Metabolites

 Bound Residues

 CO2, H2O, mineral salts

DT50 = 0.7 d

DT50 = 1.8 d

DT50 = 1.2 d

DT50 = 127 d

1st Metabolite:

2nd Metabolite:

3rd Metabolite:

25%

86%

 Formation fraction tolylfluanid 

 DMS is 22% (molar)

 Koc = 0 L/kg

 No degradation in aquifer

Soil Degradation of Tolylfluanid

(20°C, pF 2) 

ideal 

tracer

R Sur et al | Drinking Water Modelling | 
Slide 5 

significant contributions

from non-contaminated

downstream water, 

surrogate wells in the

upstream area of the

galleries were considered

for predictive dw modelling

( )

Catchment

Northern 

drinking water 

well gallery

Southern 

drinking water 

well gallery

DMS

Source

Observation 

Wells

2.2 km

 Groundwater from several 

wells within two galleries 

is abstracted, mixed and 

processed before supply 

as drinking water

Hydraulic Gradient: 

ca. 1 m /600 m

GW Flow

 Due to the large 

spatial distribution

of dw wells, varying

mixing ratios and

R Sur et al | Drinking Water Modelling | 
Slide 6 

Soil 1 Soil 2 Soil 3 Soil 4 Soil 5

Soil 

1 - 18

Cropping History on 18 Plots

 determines application

Source

Soil No. 1+3 (36%)

Soil No. 2 (25%)

Soil No. 4 (25%)

Soil No. 5 (13%)

1 

 3 kg/ha

 1.5 kg/ha

 6 kg/ha

 5 kg/ha

Application Rates

(Euparen M WG, 50% a.s.)

14.4 ha

Euparen M 

use from 1993 

R Sur et al | Drinking Water Modelling | to 2006
Slide 7 

Cropping History at Source

R Sur et al | Drinking Water Modelling | 
Slide 8 

Soil Distribution at Source

Soil Distribution on Orchard

27%

25%

9%

25%

13%

1%

Soil 1 Soil 2 Soil 3 Soil 4 Soil 5 Soil 6/7

-200

-150

-100

-50

0

min max min max min max min max min max

1 1 2 2 3 3 4 4 5 5

Soil Profile No.

Soil depth (cm)

Loam Sandy loam Clay loam Sand

 5 different main soil

profiles on orchard

 Loamy top soil layer

(0.7 – 1.8 m) followed

by sandy/gravel bottom

layer down to 

groundwater table 

(4.5 – 6.5 m)

 Significant variability in 

thickness of loamy top 

soil layers 

R Sur et al | Drinking Water Modelling | 
Slide 9 

 Discretise orchard in ca. 50 sub-plots with same soil and crop (use) history 

 Calculate mass of DMS and water volume at depth of groundwater table for

each sub-plot

 Select soil hydraulic parameters based on texture class (ROSETTA PTF)

 Atmospheric boundary condition: Local weather data

 Lower boundary condition: Free drainage (variable groundwater table) 

 Combine results to calculate area weighted average concentration of DMS for

single plots and entire orchard

1-D Modelling Approach (PEARL)

R Sur et al | Drinking Water Modelling | 
Slide 10

DMS in Leachate (mean over entire orchard)

0 

5 

10

15

20

25

Apr-95Apr-97Apr-99

Apr-01

Apr-03Apr-05Apr-07Apr-09Apr-11

Apr-13

Apr-15

Apr-17

DMS in Leachate (μg/L)

Simulation Wet Scenario Simulation Dry Scenario

real weather prediction

 Nearly complete dissipation of DMS from soil by 2011

final application

Cmean = 12 μg/L

R Sur et al | Drinking Water Modelling | 
Slide 11

Validation of Leachate Simulation

Mean (area weighted) over all plots with measured data on DMS in leachate

Good agreement between observed and simulated DMS in leachate

final application

21 leachate 

monitoring 

sites

R Sur et al | Drinking Water Modelling | 
Slide 12

-25

-20

-15

-10

-5

0

0 250 500 750 1000 1250

Hydraulic conductivity (m/d)

Depth below ground surface (m)

Keff - Aggregated Mean (optimised)

Keff - Aggregated Mean (data set)

Horizontal Hydraulic Conductivities Aquifer

Experimental Results from 10 observation wells across catchment

 Lognormal distribution of hydraulic conductivities

 Conductivity increases with depth, high variability between wells

∑

= ∑

i

ii

eff h, d

dK

K

R Sur et al | Drinking Water Modelling | 
Slide 13

2D Modelling Approach (HYDRUS) 5 m 10 m

Ø 40 m/d

Ø 300 m/d

Ks -0.5 Pressure head (m) 14.5

∆ 5 m

2800 m

15 m

DMS Observation Nodes

















=

















= 1.00

01

K0

0K

A

2

A

A 1 K

Tensor of

Hydraulic Anisotropy

Porosity: 0.2

Dispersivity - long: 10 m

Dispersivity - vert: 0.1 m

Integral: 1.5 × 10-3 m/s 

R Sur et al | Drinking Water Modelling | 
Slide 14

DMS in aquifer below orchard - observed vs. simulated

17 monitoring 

 wells DMS (aquifer) / DMS (leachate) = 1:8

DMS in upper third of aquifer

R Sur et al | Drinking Water Modelling | 
Slide 15

DMS at remote monitoring wells - observed vs. simulated

Source 4 Wells 4 Wells

1.6 km

R Sur et al | Drinking Water Modelling | 
Slide 16

Source 4 Wells 4 Wells

DMS at remote monitoring wells - observed vs. simulated

2.2 km

R Sur et al | Drinking Water Modelling | 
Slide 17

Vertical Cross-Section of Aquifer

snap-shot June 2008 

DMS Concentration

 Gradual vertical mixing of DMS with increasing distance from source

 Reduced water flow in upper part of aquifer 

 Monitoring wells close to source overpredict DMS concentrations in aquifer

monitoring wells 

(sampling water from upper aquifer) 

orchard drinking water well

R Sur et al | Drinking Water Modelling | 
Slide 18

Overall Dilution of DMS

treated 

field

distance to 

groundwater

background 

concentration aquifer

drinking 

water

abstraction

monitoring wells

12 μg/L

12 μg/L

1.5 μg/L 0.5 μg/L

 Transfer factor of 20 between concentr. in leachate and drinking water well

PECgw

(EU regulatory 

concentration)

Leachate

R Sur et al | Drinking Water Modelling | 
Slide 19

Conclusions and Outlook

 The coupled 1D-2D model can adequately describe the observed

concentrations of DMS in leachate below the site of application and in 

remote drinking water wells

 Significant leaching of DMS into aquifer predicted/verified to terminate

in 2011

 Exposure of drinking water predicted to remain constant until 2015 and

to terminate about 2025

 DMS will not exceed the threshold value in drinking water

 In total, a dilution/transfer factor of ca. 20 between the concentration of

DMS in groundwater recharge and in drinking water was calculated

 The modelling approach presented has been extensively validated and

can be useful to estimate drinking water concentrations also of other

agrochemicals

R Sur et al | Drinking Water Modelling | 
Slide 20

Thank you! 

(robin.sur@bayer.com)

R Sur et al | Drinking Water Modelling |