## 4 Discussion
In this sense, previous studies have demonstrated that employment of the ELISA test for the detection of DDT and glyphosate in water samples is a feasible technique [48; 49], and provides results comparable to other methods. For example, [PERSON] et al. [50] assessed DDT pollution in water samples from different sources (i.e., channels, borewell, and lake) in southern India, by employing ELISA and gas chromatography (GC) techniques, concluding that statistically comparable results were obtained with both techniques. [PERSON] et al. [51] compared the performance of the ELISA test and liquid chromatography tandem mass spectrometry (LC/MS/MS) for glyphosatequantification in more than 700 water samples across Ontario (Canada), concluding that the ELISA test was a cost-effective approach to enhance the spatial and temporal resolution of a water quality monitoring surveys. [PERSON] et al. [52] compared the performance of the ELISA test and high-pressure liquid chromatography (HPLC) for glyphosate quantification in different types of water samples (i.e., nanopure, tap, and river water), concluding that, regardless of the water type, there was no statistical difference between the two methods. Both pesticides have very different chemical properties (e.g., DDT is less soluble in water than glyphosate, and their half-lives in soil are different too; see fact sheets in PubChem [53] and [PERSON] et al. [5]), and their spatial distribution pattern was also very different. Its spatial distribution is a consequence of the environmental characteristics of each river basin and associated channel, as well as past and present land use and management practices. Negative correlation between glyphosate and DDT-DDE, and the significant correlation with EC for both pesticides, was observed (Table 2). Inverse correlation among pesticides concentration for the whole study area seems to be more related with local land use and management than a potential interaction between both pesticides. As spatial analyses will reveal, this inverse correlation may denote differences in the past and present application (and environmental availability) of each pesticide. Additionally, significant correlations of EC with pesticides (positive for DDT-DDE and negative for glyphosate) is due to the characteristics of river basins and associated channels instead of a cause-effect relationship. These results suggest that different spatial patterns could be found and need to be investigated. The sequence of spatial analyses developed in this research (see Table 3, Figures 2 and 3) was needed to elucidate the spatial pattern of both pesticides. They provided valuable information about the expected autocorrelation range for each variable. The Getis-Ord statistic results revealed a clear high-high cluster of DDT-DDE located close to the artificial mouth the Vinalopo River, between both protected wetlands (Figure 2e). As previously noted, this region of southeast Spain had endemic malaria until 1960s [54]. The presence of large wetlands and irrigation channels, where _Anopheles_ mosquitoes may have reproduced led to the intensive use of insecticides (especially DDT, in the past). Wetlands comprised of a large reservoir of mosquitoes, and efforts to combat malaria must have focused particularly on them. This may explain the higher abundance of residual DDT-DDE. The current presence of remarkably high concentrations of DDT and metabolites in surface waters is frequent in areas where malaria was endemic, as our study area or locations were as remote as South Africa [55]. Although DDT could be currently banned (or strictly regulated), extensive history of DDT application has left a permanent mark on the environment [55]. Glyphosate is an herbicide used in many environments, not only in rural areas, but also in urban and peri-urban areas to control weeds (e.g., roadsides). This could explain the fact that we did not find a clear pattern for its spatial distribution, influenced by the great presence of urban settlements and disperse houses.