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Geographical distribution of crop protection agents used in agriculture: relationship between use and emission to surface water

Issue 16-08-2012Acting on behalf of Flanders Environment Report (MIRA), the Flemish Institute for Technological Research (VITO) has investigated 22 pesticides for their use in agriculture and emission to surface water. New in this study is the geographical detailing of the use (per agricultural land unit) for 12 crop groups, whose emission to surface water has been estimated. The relationship between use and emission to surface water constitutes a key instrument for underpinning and evaluating the water policy with regard to priority substances.

Detailed picture of the use

Pesticides are found in surface water in concentrations that exceed the threshold values and as such pose a threat to the aquatic environment. By identifying the relationship between use and emission to surface water, it becomes possible to place responsibility on the user of pesticides.

The study estimates the geographical distribution of the use of crop protection agents in agriculture and the gross emission to surface water for 22 active substances. For 12 crop groups, both overall numbers for Flanders and figures for each agricultural land unit are available. The calculations are based on sample data representing the use of pesticides by 700 or so farms from the Agricultural Monitoring Network for the period 2007-2009, as provided by the Monitoring and Study Division of the Department of Agriculture and Fisheries (AMS). VITO has extrapolated the sample data as a function of the type of agricultural land unit and the available data.

Gross emission to surface water estimated

For the calculation of the gross emission to surface water, different emission routes are taken into consideration: losses due to drift, direct losses, erosion, drainage, volatilisation, interception by the plant, and leaching to groundwater. The first 4 partial emissions make up the gross emission to surface water (Figure 1). The partial emissions are estimated with emission factors that depend on the active substance and, where appropriate, the crop group, the agricultural area, and the geographical location. For the derivation of these emission factors, an existing methodology was extended to 22 active substances and 12 crop groups. Subsequently, the partial emissions and the gross emission were determined for the 22 active substances for the total Flemish agricultural area. For the direct losses, the following 2 scenarios are taken into account: a best-case scenario with an annual application of the substance and a worst-case scenario with the maximum number of applications per year of a substance (according to Fytoweb). The results of the best-case scenario were incorporated into the final calculations.

Figure 1: Diagram of the different routes from use to emission for crop protection agents in agriculture

Diagram of the different routes from use to emission for crop protection agents in agriculture

The gross emission for the 22 substances on average amounts to 0.6 % of the use. There are 5 predominant substances, which together account for 78 % of the emission and 77 % of the use: terbutylazine, thiram, glyphosate, metamitron and mancozeb. Except for lenacil, erosion is the primary emission route for gross emission (39 to 86 %), followed by direct losses. Losses due to drainage are also substantial for substances with a high Groundwater Ubiquity Score (GUS), such as lenacil (48 %), ethofumesate (9 %), metamitron (8 %) and terbutylazine (11 %).

Figures 2 and 3 show the use and the gross emission of glyphosate in agriculture. This total herbicide is used in all crop groups. The emission is greatest in the erosion sensitive southern part of Flanders, due to the high contribution of erosion to the gross emission.

Figure 2: Use of glyphosate in agriculture (Flanders, 2007-2009)

Map Use of glyphosate in agriculture (Flanders, 2007-2009)

Figure 3: Gross emission of glyphosate to surface water in agriculture (Flanders, 2007-2009)

Map Gross emission of glyphosate to surface water in agriculture (Flanders, 2007-2009)

Further application

VMM uses the results of this study in the WEISS emission model WEISS, which converts gross emission to loads and concentrations in the surface water with a high geographical resolution. In this way, it becomes possible to correlate the use of pesticides with their occurrence in the surface water. The continuous monitoring of pesticides in surface water would, in the future, enable better validation and even model calibration.

Read the English summary of the Dutch report ‘Geographical distribution of crop protection agents used in agriculture: relationship between use and emission to surface water’

Study commissioned by MIRA, the Environment Reporting Unit
Research report MIRA/2012/03 - VITO/2012/RMA/R/81

researchers: Leen Van Esch, Ingeborg Joris, Guy Engelen, Piet Seuntjens, VITO

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