The Particle Size Distribution of Toxicity in Metal-Contaminated SedimentsEPA Grant Number: R826651
Title: The Particle Size Distribution of Toxicity in Metal-Contaminated Sediments
Investigators: Ranville, James , Clements, William , Macalady, Donald L. , Ross, Phillipe
Institution: Colorado School of Mines , Colorado State University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 1998 through September 30, 2001 (Extended to September 30, 2002)
Project Amount: $372,795
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text | Recipients Lists
Research Category: Sustainability , Land and Waste Management , Air , Engineering and Environmental Chemistry
The overall objective is to determine whether significant improvement in predicting ecosystem risk can be obtained by applying current test methods for metal-contaminated sediments to size fractionated sediments. A hypothesis of the proposed work is that the size distribution of acid-extractable or total metals will significantly affect both organism exposure to, and toxicity of, oxic metal-contaminated sediments. Similarly the size dependence of acid volatile sulfide (AVS) and simultaneously-extracted metals (SEM) will be important for anoxic/reduced sediments. This effect may arise from either a.) the dependence of the metal-release rate (desorption from oxic sediments or sulfide oxidation following re-suspension or seasonal changes in redox) on particle specific surface area which increases with decreasing size, and/or b.) size selective feeding behavior of aquatic organisms. The former case may be important for organisms whose main metal exposure route is through passive uptake of dissolved metals. The latter case may be important when the main exposure route is through sediment ingestion. The size distribution of metal sorbing phases such as organic matter or oxides may influence both exposure routes.
A unique aspect of the work is the application of new size separation (SPLITT fractionation) and analysis (single particle counting) methods to metal-contaminated sediments. SPLITT provides accurate, high-resolution size fractionation in the range of 0.5 - 20 micrometers. No standard methods (sieving, settling, etc.) have equivalent versatility or resolution in this size range. By performing toxicity tests on SPLITT fractions we can directly examine the influence of particle size on toxicity of fine-grained sediments. Chemical analysis (acid-extractable and total metals; acid-volatile sulfide and simultaneously extracted metal) of SPLITT fractions can provide the information necessary to interpret the toxicity data. Single particle counting provides high-resolution size distributions of whole sediment and size fractions. This data can provide further information that may relate sediment physical properties to toxicity. Experiments will compare toxicity of benthic macroinvertibrates to fluorescent bacteria (MicroTox). Statistical correlation of toxicity to sediment characteristics will be performed.
The results of this study will have the following identifiable benefits and utilities: (1) improved scientific basis and computational models for the prediction of the effects of particles on the toxicity of metals in natural water systems, (2) evaluation of the degree of sediment characterization required to accurately predict risk from metal-contaminated sediments, (3) expansion of the current database on sediment toxicity, (4) protocols for the application of new experimental techniques (e.g. SPLITT, single particle counting) to the investigation of the nature and effects of fine sediments on toxicity, and (5) an experimental database which will provide additional information on the toxicity of metal contaminated sediments and the comparability of MicroTox to aquatic organism toxicity.