Derivation of Proposed 2007 Draft Matrix Soil Standards for Barium Glyn R. Fox Environmental Management Branch Environmental Protection Division September 24, 2007 Victoria, British Columbia Table of Contents Page 1. Introduction ……………………………………………………………………… 4 2. Details Related to Derivation of Proposed 2007 Draft Matrix Soil Standards 2.1 Derivation of Human Health Protection Standards – Intake of contaminated soil ………………………………………………………….. 7 2.2 Derivation of Human health Protection Standards – Groundwater used for drinking water ……………………………….…………….......... 7 2.3 Derivation of Environmental Protection Standards – Toxicity to soil invertebrates and plants ……………………………………….......... 9 2.4 Derivation of Environmental Protection Standards – Livestock ingesting soil and fodder ………………………………………………… 9 2.5 Derivation of Environmental Protection Standards – Major microbial function impairment ………………………………….……… 10 2.6 Derivation of Environmental Protection Standards – Groundwater flow to surface water used by aquatic life ..…………………………… 10 2.7 Derivation of Environmental Protection Standards – Groundwater used for livestock watering ……………………………………………… 11 2.8 Derivation of Environmental Protection Standards – Groundwater used for irrigation ………………………………………………………… 12 2.9 CSST “Background” Adjustment ……………………..……………… 12 2.10 Application of CSST Rounding-off Rule ……………………………… 12 3. References …….…………………………………………………………………… 13 2 Table of Contents (continued) Page 4. Exhibits Exhibit 1. Proposed 2007 Draft Matrix Soil Standards for Barium ……..… 19 5. Tables Table 1. Comparative Solubility and LD50 Values for Selected Barium Compounds ………………………………………………………… 21 6. Appendices Appendix A. Members of the Barite-Barium Issues Technical Advisory Committee ……………………..………………. 23 Appendix B-1. Details of Derivation: Human Health Protection – Intake of contaminated soil, 2007 Draft Matrix Standards for Barium …………………………………….. 24 Appendix B-2. Exposure Terms for Various Classes of Toxic Substances and Land Uses ……………………………….. 25 Appendix C1. Details of Derivation: Environmental Health Protection – Livestock ingesting Soil and Fodder, 2007 Draft Matrix Standards for Barium ……………………… 26 Appendix C2. Calculation of Barium TRV for Cattle …………………… 27 Appendix D. Groundwater Model Parameter Values Used to Calculate Barium Preliminary 2007 Matrix Soil Standards to Protect Groundwater ……………………… 28 3 1. Introduction Barium is used in a number of industries including: optical glass, paint and rubber manufacture, (Patty, 1981). Various barium compounds are also used in the electronic, friction materiel, pesticide, pharmaceutical, pyrotechnic and speciality paper industries (Alberta Environment, 2004a; CCME, 1999). Barite (barium sulphate) is the most commonly used barium mineral in industry. It has been estimated that between 80% (Energy, Mines and Resources Canada, 1993) and 95% (Patty, 1981) of the world’s annual production of barite is used by the petroleum producing industry as a “weighting agent” in oil and gas well drilling mud compositions (Wikipedia, 2007). The toxicity of barium per os is attributed to the barium ion (Ba+2) and therefore, the toxicity of a particular barium compound is related to that compound’s respective solubility (ATSDR, 2005; Dibello et al., 2003; US EPA, 1997; WHO, 1990). As shown in Table 1, the oral toxicity of barium compounds, as reflected by acute LD50 values in adult rats, tends to decrease commensurate with corresponding decreased water solubility. However, Table 1 also shows that while both barium chromate and barium sulphate are virtually insoluble in water, barium chromate in contrast to barium sulphate retains some degree of toxicity. Thus, only barium sulphate is essentially non-toxic to rats (Boyd & Able, 1966)1 and humans (ATSDR, 2005; US EPA, 1994) via the oral route of exposure. 2 Although in general, the solubility of barium compounds increases with decreasing pH (ATSDR, 2005; WHO, 1991), barium sulphate is only very sparingly soluble in alcohol, alkalis and weak or dilute acids (Alberta Environment, 2004b; Merck & Co., 1976; Patty, 1981; US EPA, 1994). Consequently, the ministry recognizes that barite (barium sulphate) is unique among barium compounds in being demonstratively insoluble and non-toxic under most environmental conditions. It is also recognized that use of the current Strong Acid Leachable Metals (SALM) in Soil (B.C. Ministry of Environment, 2007a) extractive analytical method can result in considerable over-estimation of soluble barium concentrations in soil containing barium sulphate when compared to more environmentally relevant extractive methods. Over-estimation of soluble barium attributable to barium sulphate in soil by the SALM method is of particular concern at oil and gas well sites where large amounts of barite is used. 1 Note that the toxic effects provoked by barium sulphate in the Boyd & Able, 1966 study were physical/mechanical (i.e. gastric fistula/fissure and intestinal occlusion) rather than chemical in nature. 2 If inhaled, barite dust acts as a physical respiratory irritant and can cause associated inflammatory pulmonary disease e.g. baritosis, a benign pneumoconiosis (NIOSH, 1999). 4 To address this issue of extractive bias related to barium sulphate, the ministry with the assistance of the British Columbia Laboratory Quality Assurance Advisory Committee (BCLQAAC) has now developed a more environmentally appropriate chemical extractive method. The new Soluble Barium by Calcium Chloride Extraction method (BC Ministry of Environment, 2007b) is based on cation exchange associated extraction of soil rather than the more traditional strong acid digestive extraction used in the SALM method. Compared to the SALM, the new calcium chloride method is much less “aggressive” in its ability to extract barium from barite in soil. The new method however, is still able to ensure complete extraction of barium from other more soluble and therefore more toxic, barium compounds which may be present in soil. Full details related to the development and validation of the calcium chloride method are presented in the following reports: • Development of BC CSR Analytical Method for Soluble Barium, Phase 1: Evaluation of Viable Analytical Methods for Soluble Barium., Hugdahl et al., 2007a, • Development of BC CSR Analytical Method for Soluble Barium, Phase 2: Optimization and Ruggedness Testing for Soluble and Total Barium Methods., Hugdahl et al., 2007b, and • Development of BC CSR Analytical Method for Soluble Barium, Phase 3: Inter- laboratory Testing of the Analytical Methods for Soluble Barium and BC SALM Barium., Hugdahl et al., 2007c. The new environmentally relevant calcium chloride extraction method for barium has been designed and validated strictly for use at barite sites.3 At barite sites only, barium concentrations in soil may be determined using the Soluble Barium by Calcium Chloride Extraction method. For all sites other than barite sites, barium concentrations in soil must be determined using the Strong Acid Leachable Metals (SALM) in Soil method. Administrative rules related to determining if a site is barite site will be provided at a future date in the following Director’s protocol: • Director’s Protocol 14, Requirements for Determining Barite Sites and Rules of Application for Soluble Barium by Calcium Chloride Extraction Analytical Method., (B.C. Ministry of Environment, 2007c). 3 A barite site is a site at which it can be demonstrated to the satisfaction of the Director of Waste Management that the only form of barium used for commercial/industrial purposes at the site was barium sulphate. 5 Generic soil quality standards for barium are currently provided in Schedule 4 of the Contaminated Sites Regulation (British Columbia, 2005). The ministry with the assistance of the British Columbia Upstream Petroleum Environmental Committee, Barite-Barium Issues Technical Advisory Committee, (Appendix A) has now developed and is proposing for use under the Regulation, proposed 2007 draft matrix soil quality standards for barium. 6 2. Details Related to Derivation of 2007 Proposed Draft Matrix Soil Standards This report provides details related to the derivation of the proposed 2007 draft matrix soil quality standards for barium presented in Exhibit 1. The proposed 2007 draft standards were developed in accordance with the Contaminated Sites Standards Task Group (CSST) Procedures for the Derivation of Soil Quality Matrix Standards for Contaminated Sites, (B.C. Environment, 1996). 2.1 Derivation of Human Health Protection Standards – Intake of contaminated soil Details related to the CSST, 1996 equations and parameter values used to derive human health protection - intake of contaminated soil, preliminary soil standards for barium are presented in Appendix B. The US EPA (IRIS) Integrated Risk Information System oral reference dose (RfDo) of 0.2 mg/kg/d for barium was used as the tolerable daily intake (TDI) in developing preliminary soil ingestion standards for barium. Scientific details related to the derivation of the US EPA, RfDo for barium can be found in US EPA, 2005a; 2005b. The ministry considers barium to be a threshold toxicant (i.e. a non-carcinogenic substance) by ingestion based on conclusions by the US EPA that, “adequate chronic oral exposure studies in rats and mice have not demonstrated carcinogenic effects” (US EPA, 2005a) and “barium is considered not likely to be carcinogenic to humans following oral exposure” (US EPA, 2005b). To protect humans from inadvertent intake of barium