Multi-element effects on arsenate accumulation in a geochemical matrix determined using µ-XRF, µ-XANES and spatial...

Area of Science:

• Environmental Science
• Geochemistry
• Soil Science

Background:

• Soils critically regulate trace element environmental impacts.
• Direct measurement of reaction mechanisms in complex soil systems is challenging.
• Understanding arsenate accumulation and speciation in soils is vital for environmental risk assessment.

Purpose of the Study:

• To develop methods for assessing how co-localized geochemical matrix elements affect arsenate accumulation and speciation in soil.
• To investigate the role of iron, aluminum, calcium, titanium, and zinc in controlling arsenate behavior within soil microsites.

Main Methods:

• Synchrotron X-ray fluorescence microprobe (µ-XRF) imaging to map element distribution.
• Spatial and non-spatial regression models to correlate arsenic accumulation with matrix elements.
• Time-of-flight secondary ion mass spectrometry (ToF-SIMS) for elemental correlation analysis.
• Microscale X-ray absorption near-edge structure (µ-XANES) spectroscopy to determine arsenate chemical speciation.

Main Results:

• Strong positive correlations found between accumulated arsenic (As) and soil iron (Fe) (r' = 0.77, 0.64).
• Regression models indicated a dominant contribution of Fe and minor contributions of Ca and Ti in predicting As accumulation.
• µ-XANES analysis suggested Fe and Al (hydr)oxides control As(V) speciation, with potential minor augmentation from Ti, Ca, and Zn.

Conclusions:

• Iron and possibly aluminum (hydr)oxides are dominant in controlling arsenate accumulation in soil microsites.
• Minor contributions from co-localized titanium, calcium, and zinc to arsenate accumulation were inferred.
• The study demonstrates effective microscale analytical approaches for elucidating trace element behavior in complex soil matrices.