DISTRIBUTION OF PESTICIDES IN GROUNDWATER FLOOD-IMPACTED UNCONNECTED COMMUNITIES IN SOUTH TEXAS FOLLOWING HURRICANE HANNA

Over the years, there has been an increasing concern regarding the water quality of the surface (SW) and groundwater (GW), especially after heavy rainfall and intense storms. Hurricane Hanna produced extensive damage to infrastructure and agriculture in many counties across the Rio Grande Valley. This area has one of the largest colonias in South Texas, predominantly Hispanic low-income semirural communities near the Texas-Mexico border. Lack of potable water and sanitary sewer systems is an issue in these colonias, and they rely on GW as drinking water.

This study collected SW and GW samples after the hurricane for one year. Samples were extracted by solid-phase extraction (SPE) followed by ultrahigh-pressure liquid chromatography (UPLC) and ion chromatography (IC) coupled to Orbitrap Fusion Tribrid mass spectrometer system (OT-FTMS). Preliminary results using an in-house database of 700 pesticides (suspect screening) identified 6 intact pesticides by UPLC-OT-FTMS (positive mode) and 28 intact pesticides and herbicides matching the pesticides molecular mass database for IC-OT-FTMS (negative mode). DEET (N,N-diethyl-m-toluamide), Ethephon, Isoprocarb, Indole-3-butyric acid, Carbetamide, and Carbofuran were detected by LC and confirmed by in silico fragmentations. In the case of IC, cymoxanil, quizalofop-p, and MCPA-butoxyethyl ester were potentially identified, and their chemical structures will be verified using both in-silico fragmentations and pesticide standards. Mainly, SW shows higher abundant intensity for pesticides detected than in GW, excluding DEET. DEET only shows significant changes over time in GW, but no differences between SW and GW samples. At the beginning of September 2020, DEET shows over 160 times higher concentration than the first sampling in mid-August 2020. Contrarily, isoproparb shows a graduate decrease by a factor of 4 within a month from the first sampling period.