Chemical Assessment of Effects on Invertebrates Using High-resolution Mass Spectrometry

Poster Presentation

Prepared by C. Moschet1, T. Anumol2, S. Hasenbein1, B. Lew1, T. Young1
1 - UC Davis, One Shields Ave., Davis, CA, 95616, United States
2 - Agilent Technologies, 2850 Centerville Rd, Wilmington, DE , 19808, United States

Contact Information:; 530-752-1755


The Cache Slough complex is an area of tidal sloughs in the Sacramento–San Joaquin River Delta of California (USA) and is an important habitat for endangered fish species (e.g., the endemic Delta Smelt). Existing pesticide data are sufficient to demonstrate a risk to aquatic invertebrates upon which several fish species depend. However, traditional chemistry and toxicity testing methods inadequately characterize the risk, and it has been difficult to show causality of the effects. For example, a targeted pesticide monitoring is prone to miss chemicals that can be the cause of observed toxicity. This study involved deployment of a sensitive amphipod species, Hyalella azteca, an important fish prey in the study area, combined with a complete chemical screening of water samples during different storm events in winter 2015/2016. The use of high-resolution mass spectrometry thereby not only allowed the detection of target chemicals but also the screening of unknown chemicals.

Water samples were concentrated by solid phase extraction. Non-polar pesticides were analyzed on an Agilent GC-QTOF-MS/MS. Negative chemical ionization (NCI) mode was selected for the target screening of pyrethroids and fipronil due to its low sensitivity. To identify further suspected pesticides without having a reference standard, samples were measured in electron impact (EI) mode using an accurate mass spectral database for pesticides containing 750 chemicals (Agilent Technologies). Polar chemicals were analyzed on an Agilent LC-QTOF-MS/MS using electrospray ionization (ESI) in both positive and negative mode. 35 target chemicals were selected in order to validate the method. An accurate mass MS/MS database consisting of 1700 pesticides and related chemicals was used to screen for other pesticides and transformation products.

Finally, molecular features of all chromatograms were extracted to look at true unknowns in the sample. Features with significant differences between affected and non-affected samples were extracted using Agilent Mass Profiler Professional (MPP) software. Obtained data will provide crucial information about chemicals that were the cause of observed toxicity to deployed H. azteca, which will represent a valuable resource for future watershed management towards the protection of the fragile delta ecosystem.