GIS Ecoregion and Soil Crosswalks
The term crosswalk means using GIS to do similarity analysis on soil climates across continents or “crosswalks.” The main objective of a GIS crosswalk is to find similar soils under similar conditions in ecoregions or agricultural areas that enable registrants (manufacturers of pesticides) to demonstrate that foreign test site conditions could exist in either Europe or North America. In a typical crosswalk, both soil and climate properties are considered. This can be accomplished by either using the OECD ENASGIPS tool (Europe – North American Soil Geographic Information for Pesticide Studies) or local datasets.
OECD’s ENASGIPS tool (final as of January 2016) ) is a GIS based application that enables users to quickly determine at an ecoregion level if similar ecoregions exist in Europe or North America. This tool uses long-term annual total rainfall, average precipitation, soil texture, soil pH and soil organic matter to calculate a similarity index. Waterborne has been involved in reviewing and testing this tool since 2010. As no “all above” listed parameters may influence chemical behaviors, we successfully argued for the inclusion of a weight-of-evidence approach in which the user selects just the parameters that affect their chemical.
Conducting a crosswalk enables a registrant to quickly determine if foreign test site conditions are likely to occur in the areas of interest. Such an assessment is quick and can be conducted at much lower cost compared to TFD (Terrestrial Field Dissipation) or laboratory study. For example, if a client had to do a field study in Europe in order to get their product (i.e. pesticide) registered in the US, which could be very expensive, they can perform a study or use the crosswalk approach to demonstrate that similar soils and climate conditions occur in the US, without even having to travel to Europe. Being able to demonstrate that similar conditions occur can result in decreased requirements for additional field or laboratory study.
In addition to using the ENASGIPS tool, Waterborne conducts crosswalks using higher resolution soils data from the USDA NRCS SSURGO (US Department of Agricultural Natural Resource Conservation Service Soil Survey Geographic Database), Canada Soil Landscape and EU Member state data. These include data not available in the OECD database, such as soil taxonomy. By establishing a set of criteria based on the test site locations, we use GIS to determine similar areas. In all of our studies, the results demonstrate that terrestrial field studies conducted at sites in Europe and Canada or laboratory environmental fate studies using soils from Europe and Canada are relevant and applicable to soils in the United States, particularly those soils in USEPA regions with high reported usage. In addition we have calculated a similarity index using the OECD method, but using the higher-resolution dataset for selected ecoregions.