Investigating the Impact of Humic Acid on Copper Accumulation in Sinonovacula constricta Using a Toxicokinetic–Toxicodynamic Model

TL;DR

This study uses a model to show how humic acid affects copper accumulation and toxicity in a bivalve species, highlighting the role of dissolved organic carbon in aquatic ecosystems.

Contribution

The study introduces a toxicokinetic–toxicodynamic model to evaluate the effects of humic acid on copper bioavailability and toxicity in Sinonovacula constricta.

Findings

At low DOC levels, Cu bioavailability decreases due to speciation shifts, reducing Cu accumulation in bivalves.

High DOC levels enable colloidal Cu–HA complexes to enter the bivalve digestive system, but with lower toxicity than water-phase Cu.

Higher DOC concentrations increase bivalve survival, indicating a protective effect against Cu toxicity.

Abstract

In aquatic ecosystems, the interaction between heavy metals and dissolved organic carbon (DOC) plays a pivotal role in modifying the bioavailability of these metals. This study, employing a toxicokinetic–toxicodynamic model, delves into the interactive effects of humic acid (HA), a significant component of DOC, on the bioaccumulation and toxicity of copper (Cu) in the estuarine economic bivalve Sinonovacula constricta. Utilizing the stable isotope 65Cu as a tracer, we evaluated Cu uptake in S. constricta under varied DOC concentrations in a controlled laboratory setting. Our findings reveal that at DOC concentrations below 3.05 mg L−1, the bioavailability of Cu is reduced due to shifts in the speciation distribution of Cu, resulting in decreased bioaccumulation within S. constricta. Conversely, at DOC levels exceeding 3.05 mg L−1, the formation of colloidal Cu–HA complexes allows its entry into the bivalves’ digestive system. Moreover, toxicity assays demonstrate an increase in S. constricta survival rates with higher DOC concentrations, suggesting a protective effect of DOC against Cu toxicity. The integration of accumulation and toxicity data infers that Cu–HA complexes, when ingested via the digestive tract, exhibit lower toxicity compared to Cu directly assimilated from the water phase. These findings emphasize the need to consider environmental DOC levels in assessing Cu pollution risks and provide insights for managing heavy metal toxicity in estuarine aquaculture.

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