Assessing Event-Driven Dynamics of Pesticides and Transformation Products in an Agricultural Stream Using Comprehensive Target, Suspect, and Nontarget Analysis

A comprehensive assessment of pesticide transport in
surface waters
is challenging due to discharge characteristics and the occurrence
of transformation products (TPs). Detailed long-term sampling of pesticide
concentrations, including rainfall and pesticide application events,
is still lacking to better predict pesticide transport pathways and
toxicity within agricultural catchments. In the present study, pesticide
and TP transport dynamics were evaluated over a three-year monitoring
period, which included 12 stormwater events and 7 dry events. An extensive
target screening for 328 pesticides was conducted, while simultaneously
performing suspect and nontarget analysis (SNTA) using liquid chromatography
high-resolution mass spectrometry. Twenty-one pesticides and two TPs
associated with the main crop, rice, were identified as the major
pollutants. The risk assessment results, based on the stepwise toxicity
data collection, suggested that insecticides, primarily neonicotinoids,
exhibited severe ecological risk. Additionally, SNTA revealed the
presence of 8 parent compounds and 46 TPs. TPs occurred following
parent peak periods, indicating that integrated pesticide monitoring
is a practical approach to risk assessment. A precautionary approach
using SNTA of parent pesticides and TP identification suggests that
the potential aquatic effects of pesticide TPs may be underestimated
by a conventional pesticide monitoring strategy.