# Multi-endpoint assessment of tunnel wash water and tyre-particle leachate in zebrafish larvae

## TL;DR

This study shows that untreated tunnel wash water is more toxic to zebrafish larvae than treated water, highlighting the need for better environmental safeguards.

## Contribution

The study compares the toxicity of untreated and treated tunnel wash water using zebrafish larvae and identifies specific pollutants like 6PPDq.

## Key findings

- Untreated tunnel wash runoff (UTWR) caused higher toxicity in zebrafish larvae than treated runoff (TWR).
- Exposure to UTWR and TWR led to increased mortality, developmental issues, and altered swimming behavior in zebrafish larvae.
- Chemical mixtures in tunnel wash water and tyre-particle leachate reduced larval swimming and increased oxygen consumption.

## Abstract

Washing of road tunnels is essential for removing accumulated pollutants such as tyre wear particles, brake dust, exhaust residues, and road debris to ensure visibility and safe driving. Tunnel washing generates large volumes of contaminated runoff known as untreated tunnel wash runoff (UTWR). Some countries filter UTWR through a sedimentation process before release to reduce contamination, generating what is known as treated tunnel wash runoff (TWR). This study investigates the potential environmental impact of diluted UTWR (25 %) and TWR (50 %) by evaluating their toxicity in fish and comparing the effect to tyre-particle leachate (TPL, 2 g/L). UTWR was collected during tunnel cleaning, and TWR was collected after 14 days of filtration through sand sediments, from the Bodø tunnel in Norway. Zebrafish larvae, used as a fish model, exposed to contaminated runoff exhibited increased mortality, impaired growth, developmental anomalies, altered swimming behaviour, and changes in gene expression. Both UTWR and TWR exposure induced significant toxicity in zebrafish larvae, though the toxicity caused by TWR was notably lower than that of UTWR. This study shows that current filtration methods of tunnel wash water reduce the levels of most pollutants, however, more research is needed on how tunnel wash-water runoff affect aquatic ecosystems.

•High levels of heavy metals, PAHs and 6PPDq found in untreated tunnel wash runoff.•Tunnel wash runoff and tyre-particle leachate increased oxygen consumption.•All chemical mixtures reduced larval swimming.•Untreated tunnel wash runoff has higher toxicity compared to treated tunnel runoff.

High levels of heavy metals, PAHs and 6PPDq found in untreated tunnel wash runoff.

Tunnel wash runoff and tyre-particle leachate increased oxygen consumption.

All chemical mixtures reduced larval swimming.

Untreated tunnel wash runoff has higher toxicity compared to treated tunnel runoff.