Miljøprojekt, 1152 – Pesticidtruslen mod grundvandet fra pesticidpunktkilder på oplandsskala

Pesticidtruslen mod grundvandet fra pesticidpunktkilder på oplandsskala

Summary

The project concerns development of a database and programs for use in a risk assessment tool for the evaluation of pesticide point sources in relation to pollution of groundwater resources.

A pesticide database containing physical chemical properties of pesticides and their transport and fate in the environment has been prepared. The database contains the data that is relevant for risk assessment and prioritisation of point sources to pesticides in groundwater resources. The data is selected to give the best possible description of the fate of pesticides in soil and groundwater under Danish conditions. This information is used directly in the risk assessment tool.

Pesticide database

The pesticide database contains basic data for 173 compounds comprising pesticides and their degradation products, since these compounds are included in the analytical package for groundwater samples in Denmark. The basic data includes the common pesticide name, CAS-no., the Danish STANDAT code (used for national reports), systematic IUPAC name, and molecular formula.

61 of the 173 compounds have been found in Danish groundwater samples and for these compounds, the database includes information on the physical chemical properties of the pesticide and degradation rates in different media and under different conditions. Chemical structures and metabolite pathways are described for some compounds.

The database does not include information on products, manufacturers, application and dosage, since this information is found in other databases. Web-links to these are provided in the database.

For many of the compounds, no appropriate values are found in the literature. Extensive literature searches have only been carried out for critical parameters, which are needed for the risk assessment tool. These critical parameters include partition coefficients in soils and aquifers (K_d-values) and degradation rates (DT₅₀) in groundwater aquifers.

For many compounds, no literature values have been identified and for use in the risk assessment tool, an estimate for the expected level has been defined based on similar compounds.

For other parameters, many values have been found in the literature and a “best bet” is defined for each parameter dependent on the measurement conditions.

The pesticide database is web-based and can be accessed on www.pesticiddata.dk using a standard internet browser.

A user manual describing use of the database and the protocol used during data collection and registering of the data is presented in the report.

Risk assessment tool

The overall objective for the risk assessment tool has been to develop an IT-tool, so that a user with general background knowledge of pesticide point sources and with access to GIS themes for water catchments areas can within one day carry out a trustworthy and dynamic assessment of a water catchment area for a waterworks. The risk assessment tool is based on existing knowledge and therefore can be carried out for point sources with detailed information on conditions and pollution levels as well as for point sources with little or no information. Based on the data available, the risk assessment tool demonstrates the best possible description of pesticide loads in a catchment area.

The advantage with the risk assessment tool is that a quick simulation of different conditions and the consequences for different remedial actions in a catchment area can be evaluated.

The risk assessment tool has two main menus; site data and risk assessment. The risk assessment is carried out in three steps, in which the 1^st. step comprises registration of site data in a database and the 2^nd and 3^rd step comprise an actual risk assessment.

Step 1	Registration or revision of site data for the potential point sources in a catchment area. Information on a site is entered in a database with details on the actual levels of contamination found in groundwater, soil or on recorded spills on site.
Step 2	Selection of the catchment area to be evaluated using the GIS themes and selection of the point source loads for the individual sites in a catchment area. The risk assessment tool is designed so that minimum, maximum, or average concentrations can be selected to represent the point sources and thereby sensitivity tests can be carried out. If the point source load is based on a soil concentration or a spill, a calculation module to model the vertical transport in the unsaturated zone is activated. For different types of pesticide point sources, a series of default values have been derived, so that the tool can be used by a user without actual information on the levels of pollution expected. These are based on experience collected from investigations of all types of pesticide point sources.
Step 3	Calculation and graphical visualisation of the horizontal transport in a catchment area. Construction of a series of reports in the form of maps and tables describing the pesticide contribution from individual point sources to the catchment area or to the individual wells in the catchment area.

The pesticide database is web-based and can be accessed using a standard internet browser, but the calculations are based on prepared GIS-tables, which typically are prepared by the regional authorities. Application of the risk assessment tool therefore requires that the user is registered and has access to the required GIS-themes and that these are linked to the risk assessment tool on the web server.

Use of the risk assessment tool is described in a detailed user manual and an example is presented in the report.