Development of an extraction method for perchlorate in soils Jaclyn E. Can˜as,* Rashila Patel, Kang Tian and Todd A. Anderson Received 10th November 2005, Accepted 25th January 2006 First published as an Advance Article on the web 8th February 2006 DOI: 10.1039/b515978d Perchlorate originates as a contaminant in the environment from its use in solid rocket fuels and munitions. The current US EPA methods for perchlorate determination via ion chromatography using conductivity detection do not include recommendations for the extraction of perchlorate from soil. This study evaluated and identified appropriate conditions for the extraction of perchlorate from clay loam, loamy sand, and sandy soils. Based on the results of this evaluation, soils should be extracted in a dry, ground (mortar and pestle) state with Milli-Q water in a 1 : 1 soil : water ratio and diluted no more than 5-fold before analysis. When sandy soils were extracted in this manner, the calculated method detection limit was 3.5 mg kg 1 . The findings of this study have aided in the establishment of a standardized extraction method for perchlorate in soil. Introduction Perchlorate originates as a contaminant in the environment from solid salts of ammonium, potassium, and sodium per- chlorate used in the manufacture of matches, solid rocket fuels, munitions, and pyrotechnics. 1 Since it was initially detected in groundwater at low levels in 1997, perchlorate has become a widespread contaminant in groundwater and some surface waters across the United States. Perchlorate is currently listed on the US EPA’s Contaminant Candidate List for drinking water. 2 There has been much debate over what level of perchlorate may potentially pose a hazard to human health and the environment. The National Academy of Science National Research Council evaluated existing toxicological information and recommended a reference dose for perchlorate of 0.7 mg kg 1 day 1 which corresponds to a Drinking Water Equiva- lent Level (DWEL) of 24.5 mgL 1 . 3 The new reference dose and DWEL will be used to establish target levels for Super- fund cleanups, which would include remediation of contami- nated soils. There is concern regarding perchlorate contamination be- cause perchlorate has the potential to competitively inhibit iodide uptake into the thyroid via the sodium-iodide sym- porter, thus resulting in a decrease in circulating thyroid hormones. 4 As a result, researchers have looked for and detected perchlorate in water, vegetation, animal tissues, and food items such as lettuce and milk. 5–13 However, few studies have reported on the occurrence of perchlorate in soil. 7,9 There is a need to explore this data gap because once in the soil, the potential exists for perchlorate to leach into the water table or to be taken up into plants. Despite the lack of occurrence data, researchers have eval- uated the fate of perchlorate in soils. Under typical environ- mental conditions, significant sorption of perchlorate does not generally occur in most soils. 14,15 Perchlorate has only been observed to adsorb slightly to soils in low pH environments with higher anion exchange capacities. 16 Urbansky and Brown 15 calculated perchlorate anion exchange capacities (PAECs) to be between 4 and 150 nmol g 1 with most soils in the 20–50 nmol g 1 range. Soil anion exchange capacities (AECs) range from 1 to 10 mmol g 1 , which would make PAECs about 1/100 to 1/50 of typical soil AECs. This further supports the idea that perchlorate sorption to soils does not significantly influence perchlorate fate. It has been demonstrated that perchlorate degrades rela- tively quickly in soil under specific soil conditions 6,14,17 and therefore, biodegradation can significantly affect perchlorate transport in soil. However, intrinsic perchlorate remediation is not limited by microorganism capabilities but rather by sui- table environmental conditions (complete anoxia and suffi- cient electron donor source) for optimal microorganism function. Perchlorate degradation is reduced in the presence of nitrate which is preferentially used as an electron acceptor before perchlorate. Therefore, the presence of nitrate may explain the persistence of perchlorate in the environment, especially when perchlorate is typically found at concentra- tions lower than nitrate. Currently only two analytical methods, ion chromato- graphy and liquid chromatography with electrospray tandem mass spectrometry detection (LC/ESI/MS/MS), have been used for the determination of perchlorate in soil. With the exception of one study, the existing soil studies used ion chromatography with conductivity detection according to EPA Method 314.0, 18 which is a method published by the US EPA Office of Water for perchlorate determination in water. EPA Method 9058, an equivalent procedure published by EPA’s Office of Solid Waste, can also be used for the determination of perchlorate in water and extracts of solid matrices. 19 However, both methods currently do not include an extraction method for perchlorate in solid matrices, parti- cularly soil. Therefore, the goal of the studies outlined here Department of Environmental Toxicology, The Institute of Environmental and Human Health, Texas Tech University, P. O. Box 41163, Lubbock, TX, USA 79409. E-mail: jaclyn.canas@tiehh.ttu.edu This journal is  c The Royal Society of Chemistry 2006 J. Environ. Monit., 2006, 8, 399–405 | 399 PAPER www.rsc.org/jem | Journal of Environmental Monitoring