Arsenic speciation in the River Zenne, Belgium

Area of Science:

• Environmental Chemistry
• Aquatic Chemistry
• Geochemistry

Background:

• The Zenne River, a tributary of the Scheldt estuary, receives sewage contamination.
• Understanding arsenic (As) speciation is crucial for assessing aquatic ecosystem health and contamination.
• Previous studies on the Zenne River's arsenic levels and speciation were limited.

Purpose of the Study:

• To determine the distribution and speciation of arsenic in the Zenne River.
• To investigate the relationship between arsenic species, dissolved oxygen, and iron.
• To identify dominant arsenic species under varying environmental conditions.

Main Methods:

• Water samples were collected from the Zenne River in winter 2003.
• Total dissolved and particulate arsenic concentrations were measured.
• Arsenic species (As(III), As(V), methylated As) were analyzed.
• Dissolved iron and oxygen levels were quantified.
• Redox potential (Eh) was measured and compared with calculated values.

Main Results:

• Highest total dissolved arsenic concentrations (up to 3.6 microg L(-1)) were found in the middle Zenne River.
• Particulate arsenic increased towards the river mouth (up to 2 microg L(-1)).
• A strong correlation was observed between dissolved arsenic and dissolved iron, both decreasing with increasing dissolved oxygen.
• Arsenic(III) was the dominant species in the oxygen-depleted middle section (below 1 mg L(-1) O2), while Arsenic(V) dominated elsewhere.
• No methylated arsenic species were detected.

Conclusions:

• Dissolved oxygen levels significantly influence arsenic speciation in the Zenne River.
• The interplay between arsenic, iron, and oxygen suggests specific geochemical processes at play.
• Arsenic speciation is primarily controlled by redox conditions, with As(III) prevalent under low oxygen environments.