Grantee Research Project Results
2000 Progress Report: The Particle Size Distribution of Toxicity in Metal-Contaminated Sediments
EPA Grant Number: R826651Title: 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 projectSupplemental 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 assessmentProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.