# Multiple Sources of Riparian Wetland Suspended Solids during Episodic Rain Events: Influence on Uranium Transport

## TL;DR

This study shows how different types of suspended particles during rain events affect uranium transport in contaminated wetlands.

## Contribution

The study reveals dynamic changes in suspended solids and their uranium adsorption capacity during rain events.

## Key findings

- Initial suspended particles were Fe-flocs with high uranium content due to adsorbed uranyl species.
- Later particles had lower uranium content and were composed of minerals like quartz and kaolinite.
- Uranium solid to liquid ratios exceeded 72,000 (μg/kg)/(μg/L) in Fe-flocs.

## Abstract

Suspended solids can be the primary vector for transporting
contaminants
in streams. The objective of this study was to determine whether changes
in the properties of suspended solids during rain events impacted
contaminant transport. Stream water was collected during five episodic
events downstream from a U-contaminated wetland located in South Carolina,
USA. The suspended particles were initially composed of Fe-flocs (particles
formed in situ prior to the rain event) that had
significantly greater Fe, Mn, organic-C, and U content than particles
collected later during a sampling rain event. XANES and EXAFS revealed
that U in the Fe-flocs was U­(VI) and that it was not incorporated
in a mineral structure but existed as inner- or outer-sphere adsorbed
uranyl species associated with organic matter and Fe-oxides. The uranyl
had an extraordinarily high affinity for the suspended solids, with
solid to liquid U ratios of >72,000 (μg/kg)/(μg/L).
After
the initial flush of Fe-flocs, a greater fraction of the suspended
solids had lower organic-C, Fe, Mn, and amorphous phases and were
composed of more quartz, kaolinite, and gibbsite, resulting in lower
U concentrations than those in the solids collected earlier in the
rain event. This study highlights the importance of understanding
suspended solids as transport vectors and their potential dynamic
nature during rain events.