The impact of rice cultivation systems in a Mediterranean wetland: Evaluation of the occurrence, behavior and fate of pesticides and their transformation products.

L'Albufera Natural Park, in Valencia (Spain), is a Mediterranean wetland mainly devoted to rice cultivation. Therefore, it is crucial to assess the impact of pesticides on the environmental compartments (water, sediments and biota) affected by agricultural activities. Moreover, the accumulation of organic pollutants has considerably degraded these areas, which may adversely affect human health. The objective of the study was to evaluate pesticides accumulating in rice growing areas including identification of major metabolites. The study included the identification of the main transformation products of pesticides. The sampling campaign was performed from May to September 2021 during the rice harvest period. Samples were collected every week to compare the emissions of pesticides. Four sampling cases were considered: a local spring (called Ullal), one organic production system and two other sampling points with traditional crop production systems (Sollana and Alfafar) to obtain information regarding the accumulation, transport, and degradation of pesticides in water and sediments. Pesticide application history in this field has been recorded. Pesticides were extracted from water samples by solid phase extraction and sediments by the citrated buffered QuEChERS. Pesticides were determined by LC-HRMS in an Orbitrap Exploris 120 mass spectrometer. Pesticides and their transformation products were determined using wide target screening against a positive list of compounds and non-target screening by applying ddMS2 of the four more intense ions in each cycle. The target analysis was focused on 10 pesticides used during rice cultivation (azoxystrobin, cyhalofop-butyl, 2-methyl-4-chlorophenoxyacetic acid, penoxulam, propanil, difenoconazole, bentazone, cyhalofop acid, imazamox and acetamiprid) as well as their transformation products. The results revealed the presence of pesticides in varying amounts in water and sediments, even within organic parcels employing eco-friendly planting strategies. The occurrence of these pesticides is directly associated with irrigation water that, in many cases, goes from one field to another and the proximity to crops from conventional production systems. However, Ullal showed very low pesticide levels in comparison to conventional systems.