Mapping Arsenic Risks in the Ayeyarwady (Irrawaddy) Delta, Myanmar: Implications for Public Health

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• The Ayeyarwady Delta, home to 12 million people, suffers from extensive arsenic contamination.
• Arsenic contamination is primarily caused by the reductive dissolution of iron minerals under anoxic conditions, fueled by organic carbon.

Purpose of the Study:

• To investigate the influence of drainage density and hierarchical recharge pathways on arsenic distribution in the Ayeyarwady Delta.
• To assess arsenic contamination levels in groundwater across a 170 km transect of the delta.

Main Methods:

• Utilized digital elevation model (DEM) data to analyze drainage density and recharge pathways.
• Compiled and analyzed data from 136 wells (depth up to 215 m) along a west-to-east transect.
• Examined national screening data from over 123,000 wells.

Main Results:

• Identified arsenic hotspots in the mid-central delta, correlating with high drainage density and focused recharge.
• While 21% of studied wells exceeded the local 50 μg/l limit, 71% exceeded the WHO's 10 μg/l guideline.
• National data shows 8% of wells exceed Myanmar's 50 μg/l limit, but 71% exceed the WHO's 10 μg/l guideline.

Conclusions:

• Arsenic contamination is widespread and poses a significant risk, especially to rural populations, as current national standards are less stringent than WHO guidelines.
• Variability in arsenic concentration is driven by complex redox dynamics and groundwater flow, necessitating targeted screening in hotspot regions.
• A comprehensive screening program is crucial to prevent unwitting exposure to unsafe drinking water.