Download - SDMS DOCD 11 Ammonium Perchlorate
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Ammonium Perchlorate SDMS DOCID# 1137733
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What Exposure Pathways did the Aerojet Human Health Risk Assessment Quantify?
Direct Contact with Perchlorate in Soils:
- Young child plays in the yard everyday except for a 2 week holiday
- Swallows 200 milligrams dirt containing perchlorate per day
- Acceptable level of perchlorate in soils for child play = 28 ppm (parts per million)
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What Exposure Pathways did the Aerojet Human Health Risk Assessment Quantify?
Indirect Contact with Perchlorate in Soils due to Soil Leaching Perchlorate to Groundwater:
- Perchlorate moves from moist soils to underlying groundwater (GW) - Pregnant woman drinks 8 glasses of GW everyday except for a 2 week holiday
- 60 % of her perchlorate exposure is from GW - 40 % of her perchlorate exposure is from food
- Acceptable level of perchlorate in soils for leaching to GW pathway = 60 ppb
(parts per billion)
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What Exposure Pathway Does the Aerojet CAG Want the Human Health Risk Assessment to Quantify? Home gardening exposure pathway
- Perchlorate can move from soil to plant when water containing perchlorate is absorbed in the root - People may be exposed to perchlorate when they consume vegetables grown in soils containing perchlorate
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“While a potentially complete pathway, homegrown produce is not quantitatively evaluated, as significant land preparation, including the addition of topsoil / amendments, would be required for backyard gardening” (Aerojet Risk Assessment White Paper)
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Estimating a perchlorate concentration level in soils that would be protective of home gardening exposures is complex and the results would be very uncertain.
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Uncertainty No. 1 – How much perchlorate will be taken up by vegetables? Field vs. Lab Concentrations in Soil Soil Conditions Seasonal Factors Weather Conditions Vegetable Type
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Uncertainty No. 2 – How much homegrown vegetables do people consume? Types and Proportions of Vegetables Consumed
- Leafy (lettuce and cabbage) - Roots (carrot and potato) - Fruits (tomato and squash) - Flower Buds (broccoli and cauliflower)
Garden Plot Size and Yield Number of Growing Seasons Percent of Total Produce that is from the Garden
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Open for Discussion
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Soil Concentration (µg ClO4 per kg dry soil) Vs. Soil Water Concentration (µg ClO4 per liter)
Bioconcentration
Consumption
A
B
C
Some Challenges in Quantification– Kevin Mayer
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Soil Moisture (A) Perchlorate may dissolve completely, like a salt. Volume of Pore Space per kg of Soil about 2-300 ml, or more Pores full of water? Field Capacity? Wilting Point? Concentration root “sees” could be 3 or 4 x higher than soil
concentration (60 µg/kg = 200 µg/l). Flushing?
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Plant Uptake – Bioconcentration (B) Lab studies usually testing perchlorate in irrigation water. Lettuce – perhaps 300X root solution(old leaves), 80X (young). So, 60 µg/kg Soil= 200 µg/l = 16-60 mg/kg dry wt. lettuce. Fresh weight of lettuce less than 10% solids (0.8-3 mg/kg lettuce) Field conditions less defined.
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Human Consumption(C) Lettuce and leafy vegetables are not the only garden produce eaten. EPA NCEA exposure factors handbook (September 2011, on line). Women aged 13-49 and children 3-5. Consume 0.23 grams (not kg) of lettuce per kg body weight per day. For a soil concentration of 60 µg/kg , exposure to perchlorate
through lettuce may be 0.2 – o.7 µg ClO4/kg body weight per day. EPA IRIS Reference dose is o.7 µg ClO4/kg body weight per day.