Basic Standards for Surface Water Molybdenum Standards • 2010 Basic Standards for Surface Water. - Water Supply/Human Health Mo=210 µg/L. - Agriculture/Cattle Mo=300 µg/L. • 2016 Basic Standards Issues for Molybdenum (Mo): - Resolve EPA disapproval of agriculture standard and adopt appropriate standard for agriculture. - Adopt appropriate human health standard. 1
Water Supply/Human Health Standard Basic Standards for Ground Water • 1987 Basic Standards for Ground Water – Commission adopted 100 µg/L. • 1990 Basic Standards for Ground Water – Commission deleted 100 µg/L. (Commission believed that the information submitted at the 1987 hearing was inadequate to support any numerical standard at that time. Reg. 41.14.B.2). • 2007 Basic Standards for Ground Water: - Division proposed, and Commission adopted 35 µg/L based in part on 1993 EPA RfD for Mo. - EPA RfD based on Kovalskiy 1961 in Armenia which has been discredited. - EPA RfD has not been revised and is outdated. • 2010 Basic Standards for Ground Water – Commission adopted 210 µg/L based on Fungwe study. 2
2010 Basic Standards for Surface Water Water Supply/Human Health Standard • Division proposed 35 µg/L - consistent with Ground Water Standard at that time. • Climax suggested 210 µg/L which Commission adopted. • 210 µg/L based on Fungwe 1990 – NOAEL=0.9 mg/kg/day. Best information available at time. • Based on application of equation in Commission Policy 96-2: DWS/MCLG, µg/L = RfD x 70 x 1000 µg/mg x RSC 2 x UF Where: RfD = verified reference dose for non-carcinogens, mg/kg-day (based on Fungwe) 70 = weight of an average adult, kg 2 = daily drinking water consumption, liters/day RSC = relative source contribution (0.2 is default value) UF = Uncertainty Factor of 1.0 • Commission adopted 210 µg/L in all Water Supply segments in subsequent Basin Hearings. 3
International Molybdenum Association Sponsored Studies Summary • IMOA sponsored studies to meet the requirements of multiple international regulatory initiatives in the absence of reliable scientific studies on molybdenum . • IMOA sponsored study results were internationally accepted independent studies - 90-Day Sub-chronic Toxicity Study (2013) - Prenatal Developmental Toxicity Study (2014) - Pending Two-Generation Reproductive Toxicity Study (2015) 4
Molybdenum Study Comparisons Calculated LOAEL vs. Performed Data Regulatory Study Date Reproducible Type Standard Comment NOAEL On Endorsement Suitability (µg/L) (mg/kgBW/day) Basis for Current IRIS 1961 Humans No Population Survey 35 None No 0.14 (LOAEL) Kovalskiy Number 90-Day Dose 1990 - Fungwe 1990 Rats No 210 None No PhD Dissertation 0.9 (NOAEL) Response 90-Day Sub-chronic Peer Murray, et al 2013 Rats Yes 3967 OECD Yes 17 (NOAEL) Toxicity Study Reviewed/Published Prenatal Peer Murray, et al 2014 Rats Yes Developmental 9333 OECD Yes 40 (NOAEL) Reviewed/Published Toxicity Study Two-Generation Pending Peer Review Murray, et al 2015 Rats Yes Reproductive TBD OECD Yes TBD and Publication Toxicity Study 5
2014 Colorado River Basin Hearing • WQCD did not take issue with the results of the IMOA sponsored studies but applied different uncertainty factors in developing a standard. • Commission adopted 210 µg/L with “Current Conditions” temporary modification to 12/31/16 in Tenmile Creek, Blue River Segment 14. • Climax agreed to support a third Two Generation Developmental Toxicity study to be sponsored by IMOA. • Two generation study will be done in 2015 with results expected by end of 2015 in time for potential revised Water Supply/Human Health based proposal in Basic Standards Hearing Notice. 6
Is Mo Basic Standard to Protect Human Health Necessary? • National – No 304(a) criteria under the Clean Water Act. EPA recently determined not to pursue a maximum contaminant level for Mo under the Safe Drinking Water Act. • Colorado – WQCD statewide data shows very low Mo levels. • If a human health standard is necessary: - What is the appropriate scientific basis? and - What is the appropriate uncertainty factor? • What is the appropriate standard to protect Human Health/Water Supply? 7
The Agriculture Standard Concern – Molybdenosis in cattle – Reported in 1950’s in the Blue River drainage. No • known subsequent occurrences in Colorado. • Based on equation developed by WQCD during 2010 Basic Standards: Cu diet X DIR + Cu w X WIR + Cu sup - (Mo diet X DIR) TVS = Cu: Mo Safe Ratio WIR Where: WIR = Water Intake Rate DIR = Dietary Intake Rate Cu:Mo Safe Ratio = 4:1 Equation assumed, among other things, that Cu:Mo safe ratio = 4:1 and Cu • supplementation. • Climax disagreed with 4:1 but did not challenge the resulting 300 µg/L standard which was adopted by the Commission. • EPA disapproved 300 µg/L in 2011 – because it assumed Cu supplementation. EPA has no criteria for Mo. • 8
After EPA Disapproval • WQCD deleted Cu supplementation assumption in Mo equation unless evidence that supplementation is universal. • Basin Hearings: 2012 San Juan/Gunnison Mo=160 µg/L. 2013 Arkansas/Rio Grande Mo=160 µg/L 2014 Upper and Lower Colorado Mo=160 µg/L • Exceptions: - Urban segments where no cattle are present - Upper Gunnison 9 and 11 – Agriculture classification but no cattle - Upper Arkansas 1b – Not classified agriculture - Blue River 13 and 14 – Agriculture classification but no cattle - Williams Fork Upper Colorado Segment 8 – 190 µg/L 9
2014 Colorado River Basin Hearing • Climax noted error in WQCD molybdenum standard equation. • Climax proposal based on corrected WIR and DIR values. • Mo WIR and DIR varies for different animals: Type/Body Weight DIR WIR Mo WQS Kg/d L/d µg/L Juvenile (225 – 250 kg) 6.8 24.7 346 Pregnant cow (409 kg) 12.0 31.4 480 Lactating cow (409 kg) 16.8 54.9 385 Adult bull (727 kg) 13.6 40.9 418 • Climax proposed 300 µg/L. • Commission adopted 160 µg/L despite acknowledged error. 10
EPA Similar Approach but Broader Range 600 EPA Min 500 EPA Max 400 Existing 300 Basic Std 200 Juvenile Finishing Pregnant Lactating Bull • WQCD: Must protect most sensitive animal: Lactating cow at 236 µg/L. • WQCD: Site Specific Standard for Williams Fork = 190 µg/L based on assumption of 80° temperature at Kremmling (WIR based on temperature). • Climax: The standard is a chronic value. The temperature in Kremmling is not 80° year round or even a 24 hour average in the summer. • Must the standard protect the most sensitive individual animal? • If a standard is necessary, what is the appropriate scientific basis and what is the representative life stage to consider? Must the standard apply the most conservative assumptions in every instance? 11
Colorado State University Study • Goal to develop scientifically based Mo water quality standard for cattle. • Study to be done in 2015 with results available for 2016 Basic Standards. Critical Issues for Basic Standards • Does Colorado need a Basic Standard for Mo to protect agriculture? • If so, what should the standard be? • Is it possible to develop single number agriculture standard given all the variables? • Narrative standard in Regulation 31.11(1)(a)(ii) prohibits discharges that “are harmful to the beneficial uses or toxic to . . . animals . . .” Is the narrative standard sufficient? 12
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