Grantee Research Project Results

2000 Progress Report: The Particle Size Distribution of Toxicity in Metal-Contaminated Sediments

EPA 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
Current Institution: Colorado School of Mines , Colorado State University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001 (Extended to September 30, 2002)
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $372,795
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text |  Recipients Lists
Research Category: Sustainable and Healthy Communities , Land and Waste Management , Air , Safer Chemicals

Objective:

The overall project 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. The major hypothesis of the work is that the size distribution of acid-extractable metals will significantly affect both organism exposure to, and toxicity of, oxic metal-contaminated sediments. The size distribution of metal sorbing phases, such as organic matter or oxides, also may influence exposure. This hypothesis depends largely on two assumptions. First, in some cases dietary routes of exposure dominate over dissolved metal exposure, and second, sediment composition varies with particle size. Due to the influence of specific surface area on metal sorption, particle size could still play a major role when dissolved metal exposure is the more important process.

Progress Summary:

Sediment Characterization. We are examining sediments from streams that have been impacted by historical mining of metal
sulfide ores. The current field site is located on the North Fork of Clear Creek, located in the Front Range of Colorado.
Sediments are dominated by iron oxyhydroxide precipitates, which form during the neutralization of low-pH, metal-rich tailings
and mine effluents. A number of toxic metals are associated with the sediments as a result of sorption and coprecipitation. The
size distribution of trace metal content may be important if size-selective feeding by benthic and water-column organisms
occurs. Furthermore, both sediment transport and surface-area dependant reactions such as sorption and dissolution depend
on particle size. We have been using traditional (sieving and sedimentation) and newly-developed (SPLITT) methods to size
fractionate sediments prior to chemical analysis. An example of the affect of particle size on trace metal composition of a Clear
Creek sediment that was fractionated by traditional methods is given in Table 1. Results demonstrate that significant variations
in sediment composition occur among the different size classes.

Toxicity Testing. Toxicity tests are being performed that have been designed to examine the relative importance of dietary
exposure versus exposure to dissolved metals. Two approaches to this are being taken. One approach to control the relative
amount of exposure to dissolved versus sediment-associated metals is to examine different pH conditions. By increasing pH,
dissolved metals concentrations are reduced by sorption and precipitation reactions. Thus, by comparing experiments with
sediment suspensions performed at low and high pH, the degree of dissolved metals can be varied while sediment metal
concentrations are constant.

Table 1. Size dependence of element composition of Clear Creek suspended sediments

Element	<5 micron		5-25 micron		>25micron
	Average	Std. Dev.	Average	Std. Dev.	Average	Std. Dev.
	ppm (mg/kg)	(from 3 reps.)	ppm (mg/kg)	(from 3 reps.)	ppm (mg/kg)	(from 3 reps.)
Al	27300	300	21100	920	28200	1700
Cd	37	0	20	1	30	1
Cr	49	10	50	2	80	2
Cu	1500	20	790	30	860	40
Fe	85700	1700	59000	2260	68500	3400
Mn	4100	50	3010	120	5500	100
Ni	460	410	100	2	270	180
Pb	540	10	310	9	250	10
Si	5840	120	5500	450	5070	120
Zn	8030	90	3810	170	3600	190
S	24500	1940	27000	1820	65250	1130

Another approach is to compare toxicity of water samples that contain sediments to ones that have had the sediments removed.
Assuming the waters are in equilibrium with the sediments, the amount of dissolved metals will be the same in both cases, but in
one case sediment-associated metals also are available to the organisms. An example of such an experiment, using Daphnia
magna, is shown in Table 2. It is clear that greater toxicity occurs when sediments are present, which demonstrates the
importance of a dietary route of metal exposure.

Table 2. Toxicity results for Daphnia magna using an undiluted and a 10:1 dilution of a suspension of North Fork
sediments

Duration of Toxicity Tests		24 hours	48 hours	24 hours	48 hours
		With sediment		Without sediment
North Fork Water Sample	# inactive (of 15)	6	11	0	7
	% effect	40	73	0	47
10:1 Dilution	# inactive (of 15)	2	10	0	5
	% effect	13	67	0	33
DI Water Control	# inactive (of 30)	1	3
	% effect	3	10

Sublethal effects of metals also are being examined. For example, the effect of sediment metal concentrations on the growth of
benthic organisms is being studied. Table 3 and Figure 1 show sediment metal concentrations and their effect on survival and
growth of Chironomous tentans for a 10-day experiment where contaminated North Fork sediments were mixed with
uncontaminated Poudre River sediments. Decreases in both survival and weight gain are seen with increasing sediment metal
concentrations.

Size Fractionation Method Development. Future toxicity experiments will focus on size-fractionated sediments. Both
traditional and newly developed methods of preparative-scale size fractionation will be used to prepare these fractions.
Therefore, a method is needed to analyze the size distributions within each size fraction. Furthermore, we wish to characterize
the distribution of metals in these size fractions.

Table 3. Metal concentrations in North Fork sediment, Poudre River sediment, and mixture of the two sediments

	Metal Concentration (mg/kg sediment)
	Poudre River Sediment	North Fork Sediment	Mixture
Fe	8,500	71,000	23,000
Mn	100	1,200	400
Al	4,400	16,000	6,400
Zn	80	2,300	660
Cu	10	600	160
Pb	BDL	210	50

Figure 1. Effect of sediment zinc and copper concentration on survival and weight gain of chironomid tentans

Field-flow fractionation (FFF) methods are being developed that can provide high resolution size analysis and fractionation of
the sediments. Coupling FFF directly to ICP-AES provided the information on metal distributions that will assist in the
interpretation of toxicity data. Figure 2 shows the results for the FFF analysis of a mixture of spherical polystyrene standards
and a standard clay sample. A UV detector is used to determine the approximate mass of particles eluting from the FFF versus
time. Addition of an online single particle counter provides additional characterization for the sediments. In future work, we will
couple ICP to the FFF to examine the size distribution of metal content of the sediments. The resulting characterization will be
used to interpret sediment toxicity test results.

Figure 2.

Future Activities:

Current standard sediment toxicity test methods require considerable amounts of sediment. Given that the size fractionation methods may produce insufficient quantities for standard test, we are developing methods that require less sediment mass. We are beginning experiments with size fractionated sediments and are including a greater number of species in the toxicity tests. Additional field sites are being investigated to expand the scope of the study.

Journal Articles:

No journal articles submitted with this report: View all 14 publications for this project

Supplemental Keywords:

sediments, bioavailability, heavy metals, aquatic, environmental chemistry., RFA, Scientific Discipline, Air, Waste, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Ecosystem/Assessment/Indicators, Ecosystem Protection, Contaminated Sediments, Environmental Chemistry, Chemistry, Fate & Transport, Ecological Effects - Environmental Exposure & Risk, Engineering, Chemistry, & Physics, Biology, Ecological Indicators, EPA Region, fate and transport, ecological exposure, ecosystem modeling, particle size, sediment contaminant effects, acid volatile sulfide, sediment toxicity, contaminated sediment, ecological modeling, sediment, exposure, chemical composition, metal contaminated sediment, simultaneously extracted metals, Region 8, flourescent bacteria, ecological risk, benthic macroinvertebrates, heavy metal contamination, exposure assessment

Progress and Final Reports:

Original Abstract

1999

2001

Final Report