A Desorption Electrospray Ionization Mass Spectrometry Imaging Approach to Monitor Toxic Ionic Liquids in Zebrafish (Danio Rerio)

Ambient mass spectrometry imaging has become an increasingly powerful technique for the direct analysis of biological tissues in the open environment with minimal sample preparation and fast analyses times. In this study, we introduce desorption electrospray ionization mass spectrometry imaging (DESI-MSI) as a novel, rapid and sensitive approach to monitor toxic ionic liquids in zebrafish (Danio rerio). AMMOENG 130, distearyldimethylammonium chloride, is used as a surfactant in commercialized personal care products. AMMOENG 130 is toxic to zebrafish exhibiting an LC50 of 5.2 mg/L, causing extensive damage to gill secondary lamellae and increasing membrane permeability. Zebrafish were exposed to AMMOENG 130 in a static 96 hour acute toxicity study in concentrations below and near the LC50 ranging from 1.25-5.0 mg/L. DESI-MS analysis of zebrafish gills revealed the appearance of a metabolite in all concentrations of exposure. The metabolite was further characterized with a high resolution hybrid LTQ-Oritrap mass spectrometer as the stearyltrimethylammonium ion of m/z 312. Whole body zebrafish tissue from exposure concentrations were mapped for AMMOENG 130 and its dealkylated metabolite, accumulation was mainly found in the nervous and respiratory systems suggesting that AMMOENG 130 and its metabolite were capable of penetrating the blood brain barrier of zebrafish brain uncovering potential neurotoxic effects. To evaluate DESI-MS as a potential environmental IL monitoring tool, AMMOENG 130 was spotted in varying concentrations onto PTFE surfaces and the limit of detection found was 10 g/L. Hence, we demonstrate here the simultaneous characterization, accumulation and metabolism of a toxic IL in whole body zebrafish analyzed by DESI-MSI. This ambient ionization mass spectrometry technique shows great promise for the direct analysis of biological tissues to monitor toxic and persistent environmental pollutants in aquatic organisms for qualitative analysis with future potential for quantitative analysis.