Patterns and Trends of the Pesticide Pollution of the Shallow Nile Delta Aquifer (Egypt)

Two hundred forty-nine groundwater samples collected from 55 irrigation water supply wells in Al-Mahala Al-Kubra, Samannoud, and Al-Santa districts of the Gharbiya Governorate (Egypt) during a monitoring survey carried out in January, June, and in November in 3 years (2013–2015). The prime objective was to document, for the first time, the status and sustained trends in the concentrations of pesticides in the shallow Nile Delta aquifer. The non-parametric Mann–Kendall and Thiel–Sen trend statistical tests were applied for detection and estimation of trends and their magnitude. Violation of standards clarified emergence of methyl parathion (98.1%), endrin (97.9%), endosulfan sulfate (96.5%), dieldrin (55.3%), atrazine (42.3%), and simazine (40.4%), in decreasing order of abundances. Malathion obeyed the permissible limits (900 μg L−1) in all samples. Methyl parathion showed an average rate of deterioration (μg L−1 year−1) of 0.82 that was largest in Al-Santa (1.0) followed by Al-Mahala Al-Kubra (0.63). Malathion proved the second largest rate emerging in Al-Mahala Al-Kubra (0.67) followed by Al-Santa (0.65). Endosulfan sulfate came third in deterioration rate (av. 0.37) followed by endrin (av. 0.32), atrazine (av. 0.32), dieldrin (av. 0.25), and simazine (av. 0.23). Groundwater improvements of pesticide contents propagated faster eastward and northward associated with larger surface water recharge rates from dense complex irrigation canals through thicker topmost silty clay layer and thicker peat layers inter-bedded in the sediments. For sustainable agriculture to alleviate negative impacts on groundwater resources and the environment, the use of ecofriendly bio-degradable or quickly deactivated pesticides along with awareness of farmers with the health hazards and the protective measures while handling pesticides are strongly recommended.