Multivariate Tiered Approach To Highlight the Link between Large-Scale Integrated Pesticide Concentrations from Polar Organic Chemical Integrative Samplers and Watershed Land Uses.

This paper presents a multi-step methodology to identify relationships between integrative pesticide quantifications and land uses on a given watershed of the Adour-Garonne Basin (Southwestern France). In fact, a large amount of pesticide concentration data was collected from 51 sites located in the Adour-Garonne Basin for a 1 year monitoring period in 2016. The sampling devices used here were polar organic chemical integrative samplers (POCIS), which provided time-weighted average concentration estimates. For each study site, its associated watershed and land cover distribution were determined using Corine Land Cover 2012 (CLC 2012) and Geographic Information System (GIS). The large-scale data were analyzed using multivariate statistical analyses, such as hierarchical cluster analysis (HCA) and principal component analysis (PCA). HCA grouped the 51 sites into five clusters with similar primary land uses. Next, the integrated pesticide concentration and land use distribution data sets were analyzed in a PCA. The key variables responsible for discriminating the sample sites showed distribution patterns consistent with specific land uses. To confirm these observations, pesticide fingerprints from sites with contrasting land uses were compared using a waffle method. The overall multivariate approach allowed for the identification of contamination sources related to their likely initial use, at the watershed level, that could be useful for preventing or containing pesticide pollution beyond simply acting on areas at risk.