Published June 23, 2014

Journal of Environmental Quality

TECHNICAL REPORTS Special Section Sustainable Use of FGD Gypsum in Agricultural Systems

Effects of Gypsum on Trace Metals in Soils and Earthworms Liming Chen, Dave Kost, Yongqiang Tian, Xiaolu Guo, Dexter Watts, Darrell Norton, Richard P. Wolkowski, and Warren A. Dick*

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ypsum (CaSO4·2H2O) has a number of beneficial functions as a soil amendment in agriculture (Chen and Dick, 2011; EPRI, 2006; Wallace, 1994). It is a soluble source of the essential plant nutrients Ca and S and can improve overall plant growth. Gypsum amendments can also improve the physical and chemical properties of some soils. Physical properties improved by application of gypsum include promotion of soil aggregation, reduced dispersion of soil particles, reduced surface crust formation, promotion of seedling emergence, increased water infiltration rates, deeper movement of Ca and S through the soil profile, and reduced erosion losses of soils and nutrients. Chemical properties improved by application of gypsum include those associated with subsoil acidity and Al toxicity. This can enhance deep rooting and the ability of plants to take up adequate supplies of water and nutrients during drought periods. Gypsum is also a commonly used amendment for sodic soil reclamation. A large amount of flue gas desulfurization (FGD) gypsum is produced by removal of SO2 from flue streams when energy sources (generally coal) containing high concentrations of S are burned (American Coal Ash Association, 2011). Flue gas desulfurization gypsum has a higher CaSO4·2H2O content and lower concentrations of many trace elements than commercially available mined gypsum (Dontsova et al., 2005; Srivastava and Jozewicz, 2001). Flue gas desulfurization gypsum may be used beneficially in agriculture (EPRI, 2006; Chen and Dick, 2011; Fisher, 2011). However, FGD gypsum contains higher concentrations of Hg and Se (Dontsova et al., 2005). In terms of agricultural function, the source of gypsum is not important. A potential constraint controlling use of a particular gypsum for agriculture is its trace element content. The higher concentrations of Hg and Se in FGD gypsum than in soils and mined gypsum have been identified as potential elements of concern when using FGD gypsum as an agricultural amendment (EPRI, 2011). Arsenic (As) is also cited as a potential element of concern due to its toxicity, although concentrations in FGD

Mined gypsum has been beneficially used for many years as an agricultural amendment. A large amount of flue gas desulfurization (FGD) gypsum is produced by removal of SO2 from flue gas streams when fuels with high S content are burned. The FGD gypsum, similar to mined gypsum, can enhance crop production. However, information is lacking concerning the potential environmental impacts of trace metals, especially Hg, in the FGD gypsum. Flue gas desulfurization and mined gypsums were evaluated to determine their ability to affect concentrations of Hg and other trace elements in soils and earthworms. The study was conducted at four field sites across the United States (Ohio, Indiana, Alabama, and Wisconsin). The application rates of gypsums ranged from 2.2 Mg ha−1 in Indiana to 20 Mg ha−1 in Ohio and Alabama. These rates are 2 to 10 times higher than typically recommended. The lengths of time from gypsum application to soil and earthworm sampling were 5 and 18 mo in Ohio, 6 mo in Indiana, 11 mo in Alabama, and 4 mo in Wisconsin. Earthworm numbers and biomass were decreased by FGD and mined gypsums in Ohio. Among all the elements examined, Hg was slightly increased in soils and earthworms in the FGD gypsum treatments compared with the control and the mined gypsum treatments. The differences were not statistically significant except for the Hg concentration in the soil at the Wisconsin site. Selenium in earthworms in the FGD gypsum treatments was statistically higher than in the controls but not higher than in the mined gypsum treatments at the Indiana and Wisconsin sites. Bioaccumulation factors for nondepurated earthworms were statistically similar or lower for the FGD gypsum treatments compared with the controls for all elements. Use of FGD gypsum at normal recommended agricultural rates seems not to have a significant impact on concentrations of trace metals in earthworms and soils.

Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

L. Chen, D. Kost, Y. Tian, X. Guo, and W.A. Dick, School of Environment and Natural Resources, The Ohio State Univ./The Ohio Agricultural Research and Development Center, Wooster, OH 44691; Y. Tian, Dep. of Vegetable Science, College of Agronomy and Biotechnology, China Agricultural Univ., Beijing, 100193, China; X. Guo, Key Laboratory of Advanced Civil Engineering Materials, Tongji Univ., Shanghai, 200092, China; D. Watts, USDA–ARS, National Soil Dynamics Lab., Auburn, AL 36832; D. Norton, USDA–ARS, National Soil Erosion Research Lab., West Lafayette, IN 47907; R.P. Wolkowski, Dep. of Soil Science, Univ. of WisconsinMadison, Madison, WI 53706. Assigned to Associate Editor Géraldine Sarret.

J. Environ. Qual. 43:263–272 (2014) doi:10.2134/jeq2012.0096 Received 5 Mar. 2012. *Corresponding author ([email protected]).

Abbreviations: EC, electrical conductivity; FGD, flue gas desulfurization.

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gypsum are typically low and similar to those in soil and mined gypsum (Chaney, 2011; Pier, 2007; Dontsova et al., 2005). Trace elements added to the soil with gypsum or any soil amendment may be concentrated in food chains as the elements are consumed and passed from one trophic (feeding) level to another level (Duffy and Gulledge, 2011). Some of the potential food chain effects of gypsum as a soil amendment may be evaluated by measuring elemental uptake by organisms living in the amended soil. This is done routinely by measuring element concentrations in plants growing on the amended soil, but animals may also be used to measure element uptake. Earthworms form the base of various food chains because they are preyed on by many species of snakes, mammals, and invertebrates (Edwards and Bohlen, 1996). Earthworms are also good indicators of soil chemical quality and are bioindicators of potential element availability (Paoletti, 1999). They have close contact with the soil, which they ingest during feeding and burrowing activities, and have relatively long life spans that allow for bioaccumulation to occur through time. By feeding directly on soil, earthworms may short-circuit the usual pathways by which elements are concentrated in food chains. The usual pathways involve absorption of the elements by plants and then feeding by herbivores on the live plants or by soil animals after the plant has died and been converted into detritus. Earthworms also absorb trace elements by ingesting detritus derived from plants along with the soil. The purpose of this study, conducted at several field sites in the United States, was to evaluate the effect of FGD and mined gypsums as agricultural amendments on earthworm numbers and biomass and concentrations of trace metals, with special emphasis on Hg, Se, and As in soils and earthworms.

soils were sampled from the control and the highest rates of FGD and mined gypsums treatments. The gypsum rates for this study were generally considered to be at least double (in some studies 10 times) the presumed optimal agricultural application rate of gypsum to increase the likelihood of producing measurable effects. The mined gypsums were pelletized products consisting of the specific mined gypsum plus binding materials to form the pellets. A summary of the sites and treatments involved in this study is provided in Table 1. Because of the greater scrutiny of Hg, As, and Se in FGD gypsums, these elements are singled out in the results and discussions that follow. Concentrations in gypsums of Hg, As, and Se are shown in Table 2. Concentrations of Hg in the FGD gypsum samples were approximately 75 to 2000 times higher than those of the corresponding mined gypsums, with the FGD gypsum used in Wisconsin having the highest concentrations. Concentrations in gypsums of 12 other trace elements (Table 3) show Ba and Sr were lower in the FGD gypsums than in the mined gypsums. The other elements were also either generally similar or lower in the FGD gypsum compared with the mined gypsum.

Earthworm Sampling The lengths of time from gypsum application to soil and earthworm sampling were 5 mo (2008) and 18 mo (2009) in Ohio, 6 mo in Indiana, 11 mo in Alabama, and 4 mo in Wisconsin. At all study sites except Indiana, earthworms were collected from two sample points in each plot. At each sampling point, a block of soil (30 cm × 30 cm × 10 cm deep) was excavated with a spade and placed in a plastic bag to return to the laboratory for hand sorting of earthworms. Then 3 L of a mustard solution was applied to the soil pit to drive out deeper burrowing earthworms and bring them to the surface. The mustard stock solution was prepared by mixing 106 g of dry mustard into 1 L of 5% acetic acid (vinegar) and shaking overnight. The stock solution was diluted in the ratio of 15 mL stock solution to 1 L of water to make the field sampling solution (Chan and Munro, 2001). The mustard solution was applied slowly to each hole, but there was always some ponding of the solution depending on the infiltration rate of the soil. Each hole was observed for at least 10 min for the emergence of earthworms. Earthworms expelled by the mustard solution were rinsed in water and placed in glass jars with moist soil for return to the laboratory. Soil from the excavated blocks was stored at room temperature in the laboratory for a maximum of 8 d before earthworms were extracted from the soil. Earthworms were hand sorted from the two soil blocks per plot and combined into one sample with the earthworms from the same plot expelled by mustard. Earthworms were placed in tared glass bottles, rinsed repeatedly

Materials and Methods Study Sites and Experimental Design Field studies were conducted at four sites across the United States to study the effects of gypsum amendments on soil quality, crop yield, and crop quality. The sites were located at (i) Canfield, OH; (ii) Kingman, IN; (iii) Crossville, AL; and (iv) Arlington, WI. At each site, a standard protocol involved a comparison of FGD gypsum with commercial mined gypsum each at three rates plus a zero rate control treatment. The gypsums were surface applied without incorporation except at the Wisconsin site, where these materials were lightly tilled into the top 10 cm of soil. The treatments were replicated four times in a completely randomized (Indiana site) or a randomized complete block design (all other sites). The gypsum rates varied at the different sites depending on the intended effects on soil properties (Chen and Dick, 2011). At each site, earthworms and

Table 1. Description of sites and treatments used for earthworm and soil sampling. Location Canfield, OH Kingman, IN Crossville, AL Arlington, WI 264

Date of gypsum application

Date of sampling

% 2.7

Gypsum rates Mg ha−1 0, 20

May 2008

2.1 0.8 2.4

0, 2.2 0, 20 0, 9.0

May 2008 May 2008 May 2009

Oct. 2008 Dec. 2009 Dec. 2008 Apr. 2009 Sept. 2009

Crop

Soil series

pH

Total C

pasture

Wooster silt loam

5.8 7.2 6.1 7.1

corn Russell and Yeddo silt loams bermuda-grass Hartsells fine sandy loam alfalfa Ringwood and Hunstville silt loams

Journal of Environmental Quality

Table 2. Concentrations of mercury, arsenic, and selenium in gypsums. Element

Gypsum source

Ohio

Indiana

Alabama

Hg, mg kg−1

FGD† mined

376 2.7

198 0.1

589 0.8

As, mg kg−1

FGD mined FGD mined

Se, mg kg−1

Effects of gypsum on trace metals in soils and earthworms.

Mined gypsum has been beneficially used for many years as an agricultural amendment. A large amount of flue gas desulfurization (FGD) gypsum is produc...
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