Year of Award

2021

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Systems Ecology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Benjamin P. Colman

Commitee Members

Alysia Cox, Bob Hall, Nancy Hinman

Keywords

Aquatic geochemistry, metals and metalloids, colloidal particles, dissolved, mine-waste, single particle ICP-MS

Subject Categories

Terrestrial and Aquatic Ecology

Abstract

Metals and metalloids (metal(loid)s) in aquatic ecosystems are often described through measures of their concentrations in whole and filtered waters. The filtered fraction is operationally defined as “dissolved,” and assumed to be primarily composed of free metal(loid) ions or of ions bound by low molecular weight organic matter. This definition ignores that the dissolved fraction also likely contains colloidal particles (1 to 1000 nm) that can pass through commonly used filters. This colloidal fraction can also be preferentially removed from the water column by algae and other aquatic organisms compared to free metal(loid) ions and organic bound metal(loid)s. Though they may be important in describing the bioavailability and toxicity of contaminants, the abundance and composition of colloidal particles is not well described. To better understand the abundance and elemental composition of colloidal particles in aquatic ecosystems, we used single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) to simultaneously characterize and quantify a range of elements in individual colloidal particles. We collected samples from eight mainstem sites and two tributaries to the Clark Fork River, Montana, which has a legacy of metal(loid) contamination in its sediments and surface waters from past mining and ore processing. Colloidal particles were abundant in all samples, with 144 different particle types detected. The most common particle types contained Fe and Mn. Single-element particles were more abundant than multi-element particles, however our estimate of multi-element particles is likely conservative due to the small size of the single-element particles (median 83 nm) which may limit detection for minor components. Multi-element colloidal particles mostly consisted of Fe and Mn in combination with other metal(loid)s, indicating Fe and Mn may serve as vectors for more toxic metal(loid)s. Our data suggest biogeochemistry drove the presence of the abundant Fe and Mn containing particles, which contrast with the Al and Si rich sediment. The small size of the colloidal metal(loid) particles suggests that that contaminant exposure to organisms occurs as complex assemblages of colloidal particles. Loads of elements in colloidal particles increased for many elements from upstream to downstream, though the exact mechanisms behind this increase are unknown. The abundance of colloidal particles in this study suggests that they may be important to the fate and transport of metal(loid) contaminants, and that they may be important to consider when examining exposure, accumulation, and toxicity of metal(loid) contaminants in aquatic ecosystems.

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