# Oil spill surface washing agents and chemical herders drive microbial community structure impacting biodegradation

## TL;DR

This study shows how oil spill treatment agents affect microbial communities and oil breakdown in lab experiments.

## Contribution

The study reveals how surface washing agents and chemical herders influence microbial community structure and biodegradation of oil.

## Key findings

- Microbial communities degraded spill treating agents, with higher CO2 production in oil and STA treatments.
- Surface washing agents caused persistence of higher molecular weight n-alkanes over 40 days.
- Chemical herders initially limited oil bioavailability but were degraded within 72 hours.

## Abstract

Spill treating agents (STAs) may be authorized for use during an oil spill response; however, the impact of certain classes of agents on oil biodegradation is poorly understood. Microcosms comprising an oil-degrading microbial consortium were amended with weathered crude oil and treated with two STAs: a surface washing agent or chemical herder, alongside single-agent treatments. The microbial community readily degraded the STAs, evidenced by microbial growth and respiration. Carbon dioxide production was higher than expected in treatments containing oil and STA together, suggesting synergistic co-metabolism of otherwise recalcitrant compounds or dead-end metabolites. Within 14 days, n-alkanes and polycyclic aromatic hydrocarbons were biodegraded in oil-containing treatments by 90% and 57%, respectively. However, over the 40-day study, a fraction of higher molecular weight n-alkanes persisted in the oil treatment amended with the surface washing agent. The chemical herder initially confined the oil, limiting its bioavailability, but within 72 hours, the chemical herder was degraded, releasing oil hydrocarbons for subsequent biodegradation. Pronounced shifts in the microbial community were observed in all treatments with distinct differences between the total and active populations. Known contaminant-degrading families Sphingomonadaceae and Rhodobacteraceae were well represented in crude oil treatments, while groups such as Gordonia, Rhodococcus, and Methylophaga flourished in treatments containing STA. These findings demonstrate the outsized impact STAs have in shaping the activity and structure of the oil-degrading microbial community under laboratory conditions. However, uncertainty remains regarding the influence of these agents on oil biodegradation in real-world applications.

Spill treating agents offer oil spill responders alternative measures to reduce the overall impact of oil in the environment. Although the environmental implications of chemical dispersant use have been exhaustively studied under various conditions, this study aims to close knowledge gaps regarding lesser-known spill treating agents that may inhibit oil biodegradation. Results of this study demonstrated an impact on hydrocarbon degradation, highlighting significant differences in microbial community structure among the treatments. However, these agents were also readily biodegraded, potentially yielding limited influence on oil biodegradation in the environment. These findings broaden current understanding of how oil-degrading microbial communities may be affected by the use of spill treating agents, beyond chemical dispersants, ultimately aiding personnel tasked with operational decision-making during the critical stages of an oil spill response.