# Identification of Neuroactive Chemicals in Crude Oil-Derived Water-Accommodated Fractions

## TL;DR

This study identifies neuroactive chemicals in crude oil fractions using zebrafish behavior to understand how these chemicals affect nervous system function.

## Contribution

The study introduces a novel integration of chemical fractionation, behavior phenotyping, and mode-of-action fingerprinting to dissect complex environmental mixtures.

## Key findings

- WAF exposure caused concentration-dependent behavioral changes in zebrafish larvae.
- PAHs, MAHs, and NAP fractions impaired habituation learning and disrupted specific receptors.
- Resin fractions showed diverse chemical profiles and distinct behavioral effects.

## Abstract

Crude oil-derived water-accommodated fractions (WAFs)
are complex
mixtures containing bioavailable constituents. We applied an automated
zebrafish behavior-based assay to assess potential neuroactivity following
exposure to WAF and chemical fractions including polycyclic aromatic
hydrocarbons (PAHs), resin, naphthalene (NAP), monoaromatic hydrocarbon
(MAH), and saturate fractions. Zebrafish larvae were exposed to WAF
concentrations (9.8–100%, 1 g/L loading) and assessed using
the 26-end point visual and acoustic motor response assay at 5 day
postfertilization. WAF exposure elicited concentration-dependent behavioral
effects, including reduced dark-period activity, impaired acoustic
startle responses, and inappropriate activity during light and typically
quiescent interstimulus periods. All WAF fractions were neuroactive,
eliciting dark-phase hypoactivity and fraction-specific hyperactivity
patterns. Exposure to PAH, MAH, or NAP fractions also impaired habituation
learning. Comprehensive two-dimensional gas chromatography–mass
spectrometry identified phenanthrene, 2-methylanthracene, and ethyl
4-ethoxybenzoate as the dominant PAHs. In contrast, the resin fraction
was chemically diverse. Behavioral profiles of zebrafish exposed to
PAH fraction constituents or an artificial mixture recapitulated WAF-like
effects. Neurobehavioral fingerprinting predicted that WAF neuroactivity
may arise from structurally diverse chemical classes disrupting multiple
molecular targets, including disruption of peroxisome proliferator-activated
receptor delta- or gamma-aminobutyric acid type A receptor-dependent
signaling. Taken together, integration of chemical fractionation,
high-resolution behavior phenotyping, and mode-of-action fingerprinting
supports mechanistic dissection of environmentally relevant mixtures.