Basic Standards for Surface Water Molybdenum Standards

Transcription

1 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 Basic Standards Issues for Molybdenum (Mo): - Resolve EPA disapproval of agriculture standard and adopt appropriate standard for agriculture. - Adopt appropriate human health standard. 1

2 Water Supply/Human Health Standard Basic Standards for Ground Water 1987 Basic Standards for Ground Water Commission adopted 100 µg/l 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 B.2) 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 - EPA RfD has not been revised and is outdated Basic Standards for Ground Water Commission adopted 210 µg/l based on Fungwe study. 2

3 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

4 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

5 Molybdenum Study Comparisons Study Date Performed On Reproducible Type Calculated Standard (µg/l) Data Endorsement Regulatory Suitability Comment LOAEL vs. NOAEL (mg/kgbw/day) Kovalskiy 1961 Humans No Population Survey 35 None No Basis for Current IRIS Number 0.14 (LOAEL) Fungwe 1990 Rats No 90-Day Dose Response 210 None No PhD Dissertation 0.9 (NOAEL) Murray, et al 2013 Rats Yes Murray, et al 2014 Rats Yes Murray, et al 2015 Rats Yes 90-Day Sub-chronic Toxicity Study Prenatal Developmental Toxicity Study Two-Generation Reproductive Toxicity Study 3967 OECD Yes 9333 OECD Yes TBD OECD Yes Peer Reviewed/Published Peer Reviewed/Published Pending Peer Review and Publication 17 (NOAEL) 40 (NOAEL) TBD 5

6 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

7 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

8 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

9 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 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 µg/l 9

10 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 Kg/d WIR L/d Mo WQS µg/l Juvenile ( kg) Pregnant cow (409 kg) Lactating cow (409 kg) Adult bull (727 kg) Climax proposed 300 µg/l. Commission adopted 160 µg/l despite acknowledged error. 10

11 EPA Similar Approach but Broader Range Juvenile Finishing Pregnant Lactating Bull EPA Min EPA Max Existing Basic Std 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

12 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