Ammonium Perchlorate SDMS DOCID# 1137733

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)

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)

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

“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)

Estimating a perchlorate concentration level in soils that would be protective of home gardening exposures is complex and the results would be very uncertain.

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

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

Open for Discussion

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

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?

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.

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.