Road-runoff pollution in English surface drains: Chemical composition and potential associated environmental risk(s).

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Water Quality Assessment

Background:

• Surface waters globally are contaminated by diverse chemicals, notably from road runoff originating from tyre wear, exhaust emissions, and brake abrasion.
• Over 170 road runoff-associated chemicals have been identified in scientific literature, but their ecological impacts remain poorly understood.
• A significant knowledge gap exists regarding the ecotoxicological effects of these contaminants on aquatic organisms in the UK.

Purpose of the Study:

• To assess the concentrations of 70 chemicals in UK surface drains using Environment Agency data from 2000-2024.
• To compare monitored chemical concentrations against existing literature values and established toxicity thresholds.
• To evaluate the potential risk posed by road runoff chemicals to aquatic life in UK surface waters.

Main Methods:

• Literature review of 23 studies to identify 170+ road runoff chemicals and their concentrations.
• Analysis of 25-year monitoring data (2000-2024) for 70 chemicals in UK surface drains by the Environment Agency.
• Comparison of monitored concentrations with minimum and maximum reported concentrations from literature.
• Assessment against the lowest effect concentration for 50% lethality (LC50) for fish and aquatic invertebrates.

Main Results:

• 43 out of 70 monitored chemicals in UK surface drains exceeded reported minimum concentrations from literature.
• 19 chemicals surpassed the highest measured concentrations found in existing studies.
• Twenty monitored chemicals exceeded the LC50 thresholds for fish and/or aquatic invertebrates.
• Concentrations suggest a potential risk to aquatic organisms, contingent on dilution in receiving river systems.

Conclusions:

• Road runoff introduces a significant load of potentially harmful chemicals into UK surface drains.
• Many monitored chemicals are present at concentrations exceeding established safe limits and literature values.
• These findings indicate a substantial ecotoxicological risk to aquatic life in UK surface waters, necessitating further investigation into dilution effects and mitigation strategies.