Effect-Based Water Quality Assessment in an Urban Tributary under Base Flow and Storm Conditions

Storm events can mobilize organic contaminants from hard
surfaces
in urban areas and can impact receiving water quality. Traditional
water quality assessments predominantly rely on chemical analysis,
which inadequately capture the collective effects of diverse chemical
mixtures released during storm events. We applied effect-based methods
(EBM) to detect arylhydrocarbon receptor (AhR) activity, estrogenic
activity, neurotoxicity and oxidative stress response in water samples
from an urban tributary during a storm event and compared it with
base flow conditions. AhR activity and neurotoxicity peaked during
the storm event, with neurotoxicity exceeding the interim effect-based
trigger value and showing a high specificity of effect. This suggests
unacceptable water quality during the storm event. Conversely, estrogenic
activity was relatively low, and there was little difference between
base flow conditions and the storm event. The absence of wastewater,
industrial and agricultural inputs in the catchment suggests that
the observed bioactivity was related to road runoff, specifically
from two adjacent major motorways. The effects on AhR and neurotoxicity
were linearly correlated with detected concentrations of 15 tire additive
chemicals from an accompanying study. This study demonstrates that
EBM provides complementary information to chemical analysis for water
quality monitoring and that there is an increased chemical pressure
on receiving water bodies during rain events in urban areas.