Humic acids increase dissolved lead bioavailability for marine invertebrates

Area of Science:

• Environmental Chemistry
• Marine Ecotoxicology
• Biogeochemistry

Background:

• Dissolved organic matter (DOM), particularly humic acids (HA), is generally thought to reduce metal bioavailability by binding metal ions.
• This binding is presumed to lower the concentration of free metal ions in natural waters, thereby decreasing metal toxicity.

Purpose of the Study:

• To investigate the complexation of lead (Pb) by humic acids (HA) in artificial seawater.
• To assess the impact of HA on Pb uptake by marine invertebrate tissues.
• To evaluate the effect of HA on Pb toxicity to marine invertebrate larvae.

Main Methods:

• Square wave anodic stripping voltammetry (SWASV) was used to study Pb complexation with HA.
• Pb uptake was measured using excised gills of the mussel Mytilus edulis.
• Pb toxicity was assessed using the Paracentrotus lividus embryo-larval bioassay.

Main Results:

• Lead complexation by HA was confirmed in artificial seawater.
• Both Pb uptake by mussel gills and Pb toxicity to sea urchin larvae increased in the presence of HA.
• The observed increase in Pb uptake and toxicity was concentration-dependent, being higher at elevated HA concentrations.

Conclusions:

• Dissolved organic matter, specifically humic acids, can enhance, rather than reduce, the uptake and toxicity of lead in key marine invertebrate species.
• These findings challenge the universal applicability of the free ion activity model for predicting metal bioavailability and deriving environmental water quality criteria for metals.