Published in J. Environ. Qual. 33:458-464 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA
TECHNICAL REPORT
Ecological Risk Assessment
Dredged Illinois River Sediments
Plant Growth and Metal Uptake
R. G. Darmody*,a,
J. C. Marlinb,
J. Talbottb,
R. A. Greenc,
E. F. Brewerd and
C. Stohre
a Dep. of Natural Resources and Environ. Sciences, Univ. of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801
b Waste Management and Res. Center, Illinois Dep. of Natural Resources, 1 E. Hazelwood Dr., Champaign, IL 61820
c College of Agricultural, Consumer, and Environ. Sciences, Univ. of Illinois, 1222 Plant Sciences Laboratory, 1201 S. Dorner Dr., Urbana, IL 61801
d Illinois Natural History Survey, 607 E. Peabody Dr., Champaign, IL 61820
e Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, IL 61820
* Corresponding author (rdarmody{at}uiuc.edu).
Received for publication May 6, 2003.
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ABSTRACT
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Sedimentation of the Illinois River in central Illinois has greatly diminished the utility and ecological value of the Peoria Lakes reach of the river. Consequently, a large dredging project has been proposed to improve its wildlife habitat and recreation potential, but disposal of the dredged sediment presents a challenge. Land placement is an attractive option. Previous work in Illinois has demonstrated that sediments are potentially capable of supporting agronomic crops due to their high natural fertility and water holding capacity. However, Illinois River sediments have elevated levels of heavy metals, which may be important if they are used as garden or agricultural soil. A greenhouse experiment was conducted to determine if these sediments could serve as a plant growth medium. A secondary objective was to determine if plants grown on sediments accumulated significant heavy metal concentrations. Our results indicated that lettuce (Lactuca sativa L.), barley (Hordeum vulgare L.), radish (Raphanus sativus L.), tomato (Lycopersicon lycopersicum L.), and snap bean (Phaseolus vulagaris L. var. humillis) grown in sediment and a reference topsoil did not show significant or consistent differences in germination or yields. In addition, there was not a consistent statistically significant difference in metal content among tomatoes grown in sediments, topsoil, or grown locally in gardens. In the other plants grown on sediments, while Cd and Cu in all cases and As in lettuce and snap bean were elevated, levels were below those considered excessive. Results indicate that properly managed, these relatively uncontaminated calcareous sediments can make productive soils and that metal uptake of plants grown in these sediments is generally not a concern.
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INTRODUCTION
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THE ILLINOIS RIVER is a major tributary of the Mississippi River (Fig. 1)
. Before major modifications of midwestern drainage patterns caused by glaciation during the Pleistocene, the lower Illinois River channel was the path of the upper Mississippi River. Consequently, the river is underfit for its valley, and for much of its length the river is sluggish and has a broad flood plain. It drains about 75000 km2, flowing for 680 km from the Des Plains River out of Chicago to the Mississippi River. A more recent modification of the river occurred about 100 yr ago, when the Chicago Sanitary and Ship Canal was constructed to channel the city's waste water away from Lake Michigan by sending it down the Des Plains River and into the Illinois River. At about the same time, navigation projects in the Illinois River were initiated, culminating with the construction of a lock and dam at Peoria designed to pool water for navigation. Over the same period, changes in land use converted much of the Illinois River watershed from natural forests and prairies to the modern mixture of urban and rural uses. Row crops, stream channelization, urban storm water runoff, and other factors have increased erosion and sediment loads to the river.
Sedimentation is a significant problem in lakes and reservoirs anywhere surface water bodies are impacted by soil erosion. Because of rapid sedimentation into Illinois surface water impoundments, removal and utilization of sediment is a concern. Previous work in Illinois has shown that agricultural use of dredged sediments is a possibility (Darmody and Marlin, 2002). Their high fertility and favorable moisture holding capacity are beneficial for plant growth. Similarly, sediments removed from Lake Springfield and from Lake Paradise in central Illinois were shown to have potential for increasing plant growth on eroded soils (Olson and Jones, 1987; Lembke et al., 1983a, 1983b).
The work reported here is in anticipation of the dredging of the Peoria Lakes portion of the Illinois River to restore habitat diversity and recreation (Bhowmik et al., 2000). The project could produce as much as 119 x 106 m3 of sediments needing environmentally and economically sound management (Demissie and Bhowmik, 1986). An extensive sampling program recently documented levels of some metals in the sediments as somewhat elevated above background soil levels (Cahill, 2001). Sediment quality issues typically involve concerns about water pollution or the impact on aquatic ecosystems; but here we are concerned with beneficial agricultural utilization. The fertility and general suitability of sediments to serve as agricultural soils has been demonstrated elsewhere (Darmody and Marlin, 2002); however, there is no long-term agricultural track record or clear regulatory tradition of sediment utilization as there is for biosolids (Gaskin et al., 2003). The primary intent of this research was to determine suitability of the sediments from the Peoria Lakes region of the Illinois River as a growth medium for selected plants. Secondarily, we wanted to obtain preliminary data on uptake of metals by those plants.
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MATERIALS AND METHODS
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Experimental Design
Sediment samples were collected in the Peoria Lakes between Peoria and Chillicothe, IL, where proposed dredging will occur. These were calcareous "fresh" and "weathered" sediments. The fresh sediment was collected from the upper 60 cm of sediment where the water was about 75 cm deep in the lake. At the time of sampling, the fresh sediment was a viscous fluid. Weathered sediment was collected from an island constructed of dredged sediments by the U.S. Army Corps of Engineers. It is located within the Woodford State Fish and Wildlife Area and was built as part of the Environmental Management Program in 1994. This weathered sediment was exposed to air, vegetative growth, freezing and thawing, and wetting and drying. The weathered sediment was taken from about the first 25 cm and was no longer fluid, but showed some evidence of soil structure development. Natural topsoil, Drummer A horizon silty clay loam (fine-silty, mixed, superactive, mesic Typic Endoaquolls), was used for comparison. This is the most common, highly productive soil in East Central Illinois. The reference soil and sediments were dried, ground, and mixed with an equal volume of horticultural grade perlite, a conventional practice to enhance aeration and drainage in greenhouse pots. The mixtures were placed into 15-cm greenhouse clay pots. Prior work (Darmody and Marlin, 2002) indicated that sediments from the Illinois River have high clay content and would be expected to benefit from perlite additions when confined in pots, as is the case with natural, fine-textured, upland topsoils like Drummer. We also tested one plant, barley, in weathered sediment without perlite addition to determine the effect of perlite on plant growth. As perlite is not water-soluble and adds no nutrients to the soil, it was not expected to significantly influence soil chemistry.
Plants grown in sediments in greenhouse pots included: cardinal barley, snap bean, cherry belle radish, black seeded simpson lettuce, and patio type cherry tomato. The snap bean plants were inoculated with the appropriate Rhizobium species. Agronomic parameters measured included germination, dry mass yield, and where appropriate, number of fruit. A randomized complete block design was used, with three greenhouse benches serving as the blocks. Four replications per plant type in each of the three blocks were used, giving 12 pots per plant type. The pots were rotated weekly on each greenhouse bench so that plants were equally exposed to environmental conditions. Germination and growth rates were documented and the plants were thinned to one plant per pot in the case of tomato and two plants per pot for the other species. Plants were watered as needed. Each pot was fertilized with Peters 20–10–20 (20–4.37–16.6, N–P–K) at a rate of 200 mg kg–1 N each week after thinning. After the plants grew for 4 to 5 wk, they were harvested and dried overnight at 60°C to determine dry mass yield. Fresh tomato fruits were used for evaluation of metal uptake, and tomato fruits from residential vegetable gardens in Champaign and Peoria counties, Illinois, served as reference samples. Dried, aboveground portions of the bean, lettuce, and barley plants were also analyzed for total metal content and used in the uptake evaluation. The stems and leaves were not washed, but had little or no visible soil on them. This would more closely mimic a situation where vegetables are eaten right out of a garden. Whole radishes were harvested and the roots washed before drying and analysis.
Laboratory Analyses
All laboratory soil analyses followed standard methods as appropriate (Klute, 1986). Extractable nutrients including Ca, Mg, K, P, and Na were determined in a Mehlich 3 extracting solution (Mehlich, 1984). Cation exchange capacity (CEC) was estimated by summation of the extractable bases. Because of the presence of free carbonates in some of the sediments, i.e., mollusk shells, etc., CEC values may be exaggerated in those soils. Soil pH was determined both in distilled water and in 0.01 M CaCl2 (McLean, 1982).
Dried, ground soil materials used in greenhouse experiments were prepared for analyses using a modified version of USEPA SW846 microwave digestion Method 3051A in which nitric acid and hydrogen peroxide, without hydrochloric acid, were used (USEPA, 1998). Digestion batch quality control (QC) samples for soils included reagent blanks, duplicates, matrix spikes, and a Standard Reference Material (SRM) from the National Institute of Standards and Technology (NIST) (Montana soil no. 2710). Soil digestates were initially screened for total recoverable metals by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) using a semi-quantitative "elemental screen" approach, which has a maximum uncertainty of ±50%. Quantitative analyses by ICP-MS followed semi-quantitative identification of contaminant metals.
Representative samples of tomato from the various growth media and reference gardens were obtained by pureeing tomato in a blender. The tomato puree and representative portions of other dried, ground plant tissues were then acid digested using the microwave digestion procedure described above for soils (USEPA, 1998). Among the full complement of QC samples prepared with each batch of plants tissues were two different reference materials, NIST Tomato Leaves SRM no. 1573a, and NIST Durum Wheat RM no. 8436. The quantitative ICP-MS approach used for determination of metals in plant tissue digestates generally is accurate to within 10% of true values. Dry weights were determined on a second portion of the tomato puree so that results could be reported on a dry-weight basis. Mercury analyses were performed by atomic fluorescence spectroscopy and are expressed on a dry weight basis. Statistical comparisons were done at the 
= 0.05 level using ANOVA (SAS Inst., Cary, NC).
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RESULTS AND DISCUSSION
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Soil and Sediment Fertility
The Peoria Lake sediments used were typical of the fine-silty textured sediments from that portion of the Illinois River (Darmody and Marlin, 2002; Cahill, 2001), and they were similar to the topsoil used in the experiment. Silt contents were 65, 69, and 62% and clay contents were 30, 28, and 28% for the topsoil, fresh sediment, and weathered sediment, respectively. The sediments had a water pH of 7.5 and organic matter content of about 2.65%, about the same as the topsoil (Table 1). However, compared with the reference topsoil, the sediments were more fertile. They were higher in exchangeable bases and most extractable nutrients. Although extractable K and Mg were about the same in the sediments as in the topsoil, the sediments had a greater amount of extractable P, Na, and particularly Ca. The weathered sediment had the highest P content, perhaps because large numbers of birds frequented the site. The greater Ca content in the sediments was largely due to biogenic accumulated Ca in the form of mollusk shells. The sediment higher Na content was not enough to be an agronomic concern (Univ. of Illinois Extension, 1998). The general conclusion from the soil fertility data is that the sediments have high natural fertility, as good as or better than the naturally fertile and productive soils of Illinois from which they are largely derived.
Soil Metal Content
Metal levels in sediments from the Illinois River will vary with location in the river and sediment sample depth. The sediments used in this study had total recoverable metal contents typical of Peoria Lake (Table 2) (Cahill, 2001). Because of cost considerations and the existing extensive database available on the chemical characteristics of Illinois River sediments (Cahill, 2001), we did not replicate our analyses. However, some general observations can be made. Compared with the topsoil, the sediments had higher levels of most elements measured, particularly Ca and Mg, which are biologically magnified in the sediments by mollusks, etc., and greater concentrations of some of the industry related metals, such as Cd, Zn, and Pb. When compared with the fresh sediment, the weathered sediment had somewhat lower Ca and Mg contents, but was generally somewhat higher in the other elements measured.
The effect of perlite on soil chemistry was investigated by analyzing weathered sediment with and without perlite addition. Concentration of total metals in perlite itself was very low with the exception of Na, K, Ca, and Al, and addition of perlite generally had only a small impact on the total recoverable metal content of weathered sediment. A dilution effect can be assumed because of the lower concentrations shown in the samples with perlite; however, because of the very low density of perlite (
0.03 g cm–3), its effect on a weight basis is small. Sodium is an exception; it is increased by the addition of perlite. However, because these are total metal levels, not plant available, the impact of perlite on the chemistry is not considered biologically significant.
There are no generally agreed upon standards for metal contamination in sediments intended for land application (Darmody and Marlin, 2002). One approach would be comparison with background soil levels. The only potentially toxic heavy metals that we found that exceeded a national survey of uncontaminated agricultural soils were Cd, at 4.4 vs. 2.0 mg kg–1, and Zn at 306 vs. 264 mg kg–1 (Holmgren et al., 1993). However, based on a statewide survey of Illinois soils (Illinois EPA, 1994), none of the metals in the sediments exceed concentration ranges observed. Another approach would be to look at the USEPA critical values for metal contaminants in its 503 regulations for the land disposal of sewage sludge (USEPA, 1995). Under those regulations, none of the metals in the sediment exceeds regulatory levels. Other regulations include the Illinois' Tiered Approach to Corrective Action Objectives (TACO), which provide industrial site cleanup standards for a variety of chemicals (Illinois EPA, 1997). While these TACO standards do not apply to sediment, they are frequently referenced in discussions about potential use of sediment. Metals in Peoria Lakes sediments meet the TACO standards. Another approach is simply statistical; the Illinois EPA classifies an analyte in sediments as elevated if its concentration is between one and two standard deviations above the state-wide mean and as highly elevated if it is greater than two standard deviations above the mean (Mitzelfelt, 1996). By this measure, the sediments we used had elevated levels of Ni and elevated to highly elevated levels of Cr and Ag. Other potential chemical contaminants in the sediments are under study. With any approach, the method of determining the metal levels, total, recoverable, or by some extractant, is critical and not necessarily a good predicator of plant uptake (Singh et al., 1996; Vandecasteele et al., 2002a).
Plant Growth and Metal Uptake
There were no statistically significant differences in seed germination among the soil treatments with any of the plants grown (data not shown). Plants grew well in all the soil treatments. Barley growth was no different among the perlite-treated samples (Table 3). Barley yields were highest in the nonperlite fresh sediments, but there was no statistically significant barley yield difference between the reference topsoil and the weathered sediments. The perlite/no perlite barley growth rates are not directly comparable because they were grown at different times, but they indicate that perlite additions were not necessary to achieve good plant growth in the sediments.
Lettuce growth showed some statistical differences; it grew better on weathered sediment and reference topsoil. Radish yield did not differ among the materials. Snap bean produced the same quantity of fruit on all three materials and the total plant mass produced also did not differ among growth media (Table 4). The number of tomato fruits produced did not differ on the materials, but the fruit mass produced was least from the topsoil (Table 5).
The metal content of tomato grown on different media varied and did not present clear trends, although values from the sediment-grown plants indicate that metal uptake was inhibited, possibly due to the higher pH of the sediments or to the presence of less available forms of the metals (Table 6) (Tack et al., 1996). There were no statistically significant differences in the contents of Pb, Cr, Cu, Mn, Ni, Ti, Zn, Sr, or Zr among the tomato. With Cd, the statistically lowest concentration was found in the plants grown in the topsoil. However, Cd content of the tomato from local gardens had about the same amount of Cd as found in plants grown on the sediments in the greenhouse. Cadmium levels measured were within the range considered uncontaminated in a U.S. food survey (Wolnik et al., 1985), and an Australian "market basket survey" (Reilly, 1991); however, the level was higher than reported for tomato in the U.S. FDA "Total Diet Study" (0.18 ± 0.13 mg kg–1) (U.S. Food and Drug Admin., 2003).
Tomato grown on the topsoil had the highest content of Co, while Co levels from other growth media did not differ. Barium content was highest in tomato from the topsoil and the reference gardens and lowest in the weathered sediment samples. Likewise, Mo was highest on the topsoil and lowest in the weathered sediment tomatoes. Selenium and Rb contents were highest with the fresh sediment and lowest with the topsoil. Tomato from both the fresh sediment and the Peoria garden had Se contents higher than reported for tomato in the FDA total diet study (0.036 ± 0.089) or in the USDA National Nutrient Database (0.064 ± 0.024 mg kg–1) (USDA, 2003). Because other food groups may have a substantially greater range of a given metal contaminant and because that food group may be consumed in substantially greater quantities than the vegetables grown in this study, it is essentially meaningless to limit the discussion to a comparison of identical vegetables. For example, Se levels in various food groups in the Australian "Market Basket Study" ranged from <0.001 to 0.34 mg kg–1 (Reilly, 1991). Only one of our samples, from a topsoil pot, had detectable Hg (0.001 mg kg–1) (Table 6). Chromium was only found in two samples, one tomato grown in Champaign garden soil (3.4 mg kg–1) and one grown in topsoil (3.3 mg kg–1). Overall, metals detected in tomato grown in the sediments were all at a very low levels and within typical levels observed in agricultural crops and foodstuff (Sharp, 1987; Kabata-Pendias and Pendias, 1992; Reilly, 1991).
Other plants analyzed for metal content were only grown in reference topsoil and weathered sediment, because of the similarities of the two sediments, and most elements did not differ by soil type (Table 7). However, when averaged over all plants, Ba and Mn were statistically lower, and As, Cd, Cu, Se, Tl, Zn, and Mo were statistically higher in the plants grown in sediment than in the reference topsoil. These differences are not necessarily important because the levels remain below those considered excessive (Kabata-Pendias and Pendias, 1992; Förstner, 1995) and within ranges reported in the FDA Total Diet Study (U.S. Food and Drug Admin., 2003).
Of all the potentially toxic metals measured, Cd showed the greatest consistent increase in the plants grown in sediments compared with those grown in topsoil. Increase in concentrations over the topsoil control ranged from 5.5 times background for barley to 4.8 times background for snap bean. Leafy vegetables like lettuce are well known accumulators of Cd, and lettuce grown in sediment showed the highest overall concentration of Cd at 2.40 mg kg–1 (Table 7). We found no published standards for unacceptable Cd levels in vegetables and references vary as to "normal" food Cd contents. For example, Cd in iceberg lettuce in the FDA Total Diet Study was 2.2 ± 1.2 mg kg–1 (U.S. Food and Drug Admin., 2003), Wolnik et al. (1983) report an upper limit of 1.9 mg kg–1 Cd for lettuce grown in "uncontaminated" soils, and published Cd concentrations in various plant materials range from 0.2 to 0.8 mg kg–1 for "normal" and from 5 to 30 mg kg–1 for "contaminated" plants (Kabata-Pendias and Pendias, 1992). Therefore, Cd concentration in the lettuce we grew was within the reported range for lettuce by the USFDA (2003), above the "uncontaminated" range of Wolnik et al. (1983), and below the reported "contaminated" range for those various plants reported by Kabata-Pendias and Pendias (1992).
There were individual differences in metal uptake by plant species. The plants with the highest amount of particular elements were: snap bean for Ba and Tl; radish for B, Co, Mo, and Hg; lettuce for Cd and Pb; and barley for Cu, Mn, Se, Zn, and Ti. The levels of these elements are within normal ranges observed in plants (Pais and Jones, 1996; Sharp, 1987). Despite the "elevated" levels of Ni and "highly elevated" levels of Cr and Ag in the sediments, none of these metals showed an increase in plant uptake over the topsoil.
References to total diet and market basket survey in the preceding paragraphs hint at the difficulty in assessing relative risks to humans from toxic elements in food. The FDA does not have a universal regulatory level for toxic metals in all foods but there are a few specific guidance or action levels. For example, there are guidance levels for Cd in shellfish and for Cd extracted from imported pottery containers for food (U.S. Food and Drug Admin., 1993, 2000a, 2000b). A single regulatory level for all foods would be difficult to deal with because there are many factors to be taken into consideration. These factors include the average daily dietary intake of each particular food stuff, age of the individual, regional variations in dietary consumption, and other factors for assessing potential risk. Generally the FDA provides guidance on the amount of a particular food group that should be consumed during a given time period only under special circumstances. For example, the FDA may recommend that pregnant women limit consumption of shellfish to no more than a few servings per week to limit exposure to Hg in the shellfish, a known accumulator of Hg.
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CONCLUSIONS
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Sediments from the Peoria Lakes reach of the Illinois River are essentially equal to highly productive natural topsoil from central Illinois in terms of fertility and plant productivity in the greenhouse. Because of their initially poor soil structure and fluid consistency immediately after dredging, crusting and sealing of the surface may be a problem at first, but should become less of an issue after weathering or tillage. Addition of materials to improve tilth, such as perlite, compost, biosolids, or similar materials, may be helpful in the development of soil structure and the avoidance of compaction in the field. In the greenhouse, where we crushed the dried and caked sediment and added perlite, compaction and tilth proved not to be significant and there was no difference between fresh and weathered sediment in plant growth.
Plant metal uptake, as indicated by tomato fruit and barley, snap bean, lettuce, and radish plants grown on sediments in the greenhouse, was not excessive. Metal levels in the tomato grown on the sediments were essentially the same as those grown on natural topsoils in the greenhouse or from local gardens. Metal levels, although elevated in some of the plants relative to those grown in topsoil, were below levels considered excessive, and well below those from more industrial areas (Tack et al., 1996; Vandecasteele et al., 2002a, 2002b). In summary, we found no chemical or physical reason that these relatively uncontaminated, calcareous dredged sediments from the Peoria Lakes in the Illinois River, properly managed, should not make an excellent plant growth medium. Further work needs to be done to determine if these results, based on short-term greenhouse studies, hold up under long-term field conditions or if other potential contaminants, such as organic compounds, may limit the beneficial use of dredged Illinois River sediments.
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JEQ 2004 33: 413-418.
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TOP
ABSTRACT
INTRODUCTION
of plants grown in dredge sediments and reference materials.