Bioavailability of Barium to Plants and Invertebrates in Soils Contaminated by Barite Dane T. Lamb, †,‡ Vitukawalu P. Matanitobua, †,‡ Thavamani Palanisami, †,‡ Mallavarapu Megharaj,* ,†,‡ and Ravi Naidu †,‡ † Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia ‡ Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC CARE), University of South Australia, Mawson Lakes, SA 5095, Australia ABSTRACT: Barium (Ba) is a nonessential element to terrestrial organisms and is known to be toxic at elevated concentrations. In this study, the bioavailability and toxicity of Ba in barite (BaSO 4 ) contaminated soils was studied using standard test organisms (Lactuca sativa L. “Great Lakes”, Eisenia fetida). Contamination resulted from barite mining activities. Barium concentrations in contaminated soils determined by X- ray fluorescence were in the range 0.13-29.2%. Barite contaminated soils were shown to negatively impact both E. fetida and L. sativa relative to control soil. For E. fetida, pore-water concentrations and acid extractable Ba were linearly related to % body weight loss. In L. sativa, pore-water Ba and exchangeable Ba were both strongly related to shoot Ba and shoot biomass production. A negative linear relationship was observed between shoot Ba content and shoot weight (P < 0.0004, R 2 = 0.39), indicating that Ba accumulation is likely to have induced phytotoxicity. Plant weights were correlated to % weight loss in earthworm (r = -0.568, P = 0.028). Barium concentrations in pore-water were lower than predicted from barite solubility estimates but strongly related to exchangeable Ba, indicating an influence of ion exchange on Ba solubility and toxicity to E. fetida and L. sativa. ■ INTRODUCTION Barium (Ba) is a group 2 element that shares several chemical characteristics with calcium (Ca), strontium (Sr), and lead (Pb). Barium is used in the production of soaps, explosives, fire extinguishers, drilling fluids, and even insecticides. 1-3 Barium is not an essential nutrient to animals and plants but instead is known to cause several deleterious effects in most organisms. Exposure to high quantities of Ba in humans may cause hypokalaemia, acute hypertension, vomiting, diarrhea, cardiac arrhythmia, and even death if not treated. 4,5 The Australian National Environmental Protection Council (NEPC) has not provided human health guidance values, although it does provide an ecological investigation level of 300 mg kg -1 . 6 The NEPC value is on par with the U.S. ecological soil screening levels of 330 mg kg -1 for soil invertebrates but not wildlife (2000 mg kg -1 ). 7 Speciation of Ba is well-known to influence solubility. 3,8 Chloride, acetate, perchlorate, and nitrate salts of Ba are readily soluble in water, but barite (BaSO 4 ) is a highly insoluble mineral. 9,10 Barite is insoluble in water, acids, and bases and on its own is unlikely to cause a risk to humans or the environment. Barite is orally administered to patients deliberately as a radiological tool to visualize the gastrointestinal tract. As has been noted, 4 despite the deliberate oral supply of barite, little is known about the risk posed by barite to humans and ecological receptors from environmental media, although it is generally stated to be of little to no risk. 3 Barium may be highly mobile in soil, as Ba primarily associates with soil colloids by ion exchange, 3,11 and is not known to form stable complexes with dissolved organic matter. 12 In montmorrilonite, Ba was shown to predominantly be adsorbed to permanently charged basal surfaces. However, Zhang et al. 11 reported that Ba 2+ sorbed to montmorrillonite by outer-sphere and inner- sphere complexes using extended X-ray absorption fine structure spectrometry (EXAFS) and Lee et al. 13 reported inner-sphere adsorption to muscovite. The available data indicate that Ba does not complex (no sharing of electrons) appreciably with humic substances or clay minerals. 11,13,14 However, barite solubility is extremely important on the toxicity of Ba in the environment. Barium is known to be toxic to plants and soil invertebrates when soluble. Kuperman et al. 15 reported toxicity benchmark values for Eisenia fetida, Folsomia candida, and Enchytaeus crypticus at Ba concentrations in soil in the range 165-2000 mg kg -1 . Similarly, Ba is known to accumulate to significant concentrations in aerial plant tissues. Critical tissue Ba concentrations in Panicum maximum (Tanzania guinea grass) were reported in the range 156-383 mg kg -1 when grown in nutrient culture. Similarly, significant Ba accumulation was observed in aerial shoot parts of Bertholletia excelsia (Brazil nut) (5.00 to 325 mg kg -1 ), with the higher concentrations found in Received: May 23, 2012 Revised: February 12, 2013 Accepted: March 13, 2013 Published: March 13, 2013 Article pubs.acs.org/est © 2013 American Chemical Society 4670 dx.doi.org/10.1021/es302053d | Environ. Sci. Technol. 2013, 47, 4670-4676