# Assessment of Pesticide Contamination of Groundwater from Titu-Sarata Plain, Romania
## 3 Results  
### Occurrence and Distribution of Pesticides in the Groundwater Sample from Titu-Sarata Plain, Romania  
In the collected groundwater samples, OPs as well as OCPs were identified and quantified. The results show that, out of all of the groundwater samples collected from 27 locations, only 9 groundwater samples exceeded the maximum permissible concentration for individual OPs in drinking water (0.1 ug/L per pesticide), as specified by current regulations [44]. Furthermore, in five of the groundwater samples, the total pesticide concentration also surpassed the cumulative limit of 0.5 ug/L.  
Using Geostatistical Analyst extension from ArcGIS 10.8, Inverse Distance Weighting (IDW) interpolation method was used to predict the spatial distribution of total pesticide concentration in Titu-Sarata Plain (Equation (7)):  
\[Z(x_{o})=\frac{\sum_{i=1}^{n}\frac{x_{i}}{d_{i}^{\mathrm{t}}}}{\sum_{i=1}^{n} \frac{d_{i}^{\mathrm{t}}}{d_{i}^{\mathrm{t}}}}, \tag{7}\]  
where \(Z(x_{o})\) is the estimated value of pesticide concentration in the water sample from the _ith_ dug well, \(x_{i}\) is the measured value of the pesticide concentration in the _ith_ well, \(n\) is the number of dug wells located around the predicted location; \(d\) is the distance between dug wells, and \(i\) and \(0\) and \(k\) are the weights assigned to each measured pesticide concentration, which is usually considered equal to two.  
The spatial distribution of the total pesticide concentration in the groundwater from the studied areas is presented in Figure 2.  
The OP and OCP concentrations determined in the collected groundwater samples are presented in Supplementary Data (Table S2 and Table S3, respectively).  
For data analysis, Microsoft Excel 2021 and Python 3.10.9 were used. Descriptive statistics (Supplementary Table S4, Figure 3) analysis was used to interpret the results.  
The order of the median concentrations of OPs in groundwater samples was Carbaryl; Simazine < Bentazon < 3,5-Dichlorobenzoic acid < Prometin < Aldicarb sulfoxide < Thionazine < Dichlorprop < Phosdrin < Phorate.  
With the exception of Aldrin and ppDDE, respectively, very strong positive skewness values and high or very high kurtosis values were observed for the detected pesticides, which showed a lot of very low values and few high concentration values. This is linked to the effects of the factors mainly originating from agricultural anthropogenic sources and geogenic conditions of the sampling sites.  
Figure 2: Spatial distribution of the total pesticide concentration in the Titu-Sarata Plain, Romania.  
To assess the relationships between pesticides present in the groundwater samples, a Pearson correlation analysis was performed and the obtained correlation matrix is presented in Figure 4.  
Strong positive correlations were identified between Bentazon, Carbaryl, Simazine, Atrazine, and Prometin, and between Dieldrin and alfa endosulfan (r > 0.9), respectively, indicating potential common contamination sources. A moderate correlation (r = 0.5-0.6) was observed between Aldrin and Bentazon, Carbaryl, Simazine, Atrazine, and Prometin, respectively, while weak or non-significant correlations (r < 0.40) indicate distinct contamination sources.  
Figure 4: Pearson’s correlation matrix of pesticides in groundwater, \(p\) < 0.05.  
Figure 3: Box-plot diagram of pesticide concentrations (\(\mu\)g/L) in groundwater samples.  
There is no significant relationship between the water depth and total pesticide concentration (Figure 5), as indicated by the very low R\({}^{2}\) value (0.0292). Most data points, clustered between 2 and 10 m in depth, exhibit relatively low pesticide concentrations, generally below 0.4 \(\mu\)g/L. A few outliers, such as the point near 1.4 \(\mu\)g/L, are observed but appear to be isolated incidents. These may suggest localized contamination, potentially linked to intensive pesticide use in nearby agricultural areas.