Chromium redox speciation in natural waters.

Area of Science:

• Environmental Chemistry
• Water Quality Analysis
• Chromium Speciation

Background:

• Hexavalent chromium (Cr(VI)) is a significant environmental pollutant.
• Understanding chromium speciation in aquatic environments is crucial for ecological risk assessment.
• Previous studies in 1993 established baseline chromium levels in the Humber catchment.

Purpose of the Study:

• To determine dissolved hexavalent chromium concentrations in the Humber catchment's river, estuarine, and coastal waters.
• To assess the stability of hexavalent chromium during sample storage.
• To evaluate the proportion of hexavalent chromium relative to total dissolved chromium and compare with historical data.

Main Methods:

• Water samples were collected from river, estuarine, and coastal sites within the Humber catchment.
• Samples were filtered and extracted on-site.
• Dissolved hexavalent chromium concentrations were measured after storage for up to eight days.

Main Results:

• Dissolved hexavalent chromium concentrations showed no significant change (p=0.05) after storage for up to eight days.
• Total chromium concentrations in the catchment were below 1.0 microg l(-1), considered low relative to proposed Environmental Quality Standards.
• Hexavalent chromium constituted 27% to 100% of total dissolved chromium, averaging approximately 50%.

Conclusions:

• Dissolved hexavalent chromium is stable in filtered river, estuarine, and coastal waters of the Humber catchment under the tested conditions.
• Chromium levels in the Humber catchment are generally low, with a substantial proportion existing as hexavalent chromium.
• Oxidizable organic matter and organic ligands are key factors influencing chromium redox speciation in natural waters.