Dissolved Barium Causes Toxicity to Groundwater Cyclopoida.

Area of Science:

• Environmental Toxicology
• Hydrogeology
• Ecotoxicology

Background:

• Barium (Ba) dissolution and mobilization in groundwater are primarily controlled by sulfate due to barium sulfate (BaSO4) low solubility.
• Elevated Ba concentrations in groundwater can stem from anthropogenic activities and geogenic sources.
• No toxicity data currently exist for Ba concerning groundwater organisms (stygofauna).

Purpose of the Study:

• To assess the toxicity of barium to two stygobiont cyclopoid species from New South Wales, Australia.
• To determine the influence of sulfate concentration on barium toxicity.
• To evaluate the risk of elevated dissolved Ba concentrations to groundwater ecosystems.

Main Methods:

• Toxicity testing of Ba on two stygobiont cyclopoid species over 28 days.
• Experiments conducted in waters with varying sulfate concentrations (<1-100 mg SO4/L).
• Measurement of cyclopoid survival and observation of BaSO4 precipitation dynamics.

Main Results:

• Dissolved Ba was toxic to cyclopoids, while precipitated Ba was not toxic to the Wellington species.
• Toxicity values for dissolved Ba included a 21-day no-effect concentration of 3.3 mg/L and an effective concentration of 4.8 mg/L for 5% mortality.
• Sulfate presence led to rapid BaSO4 precipitation, reducing dissolved Ba until sulfate depletion.

Conclusions:

• Elevated dissolved Ba concentrations may pose a significant risk to groundwater organisms.
• Further toxicity testing on diverse stygobiont species is recommended for comprehensive risk assessment.
• Developing Ba guideline values for groundwater contaminant risk assessments is crucial.