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HEALTH CONSULTATION

Use of Well Water for Garden Irrigation

ST. REGIS MOHAWK RESERVATION
HOGANSBURG, FRANKLIN COUNTY, NEW YORK


BACKGROUND AND STATEMENT OF ISSUES

The Environmental Protection Agency (EPA) and St. Regis Mohawk requested the Agency for Toxic Substances and Disease Registry (ATSDR) to evaluate the public health implications of ingesting vegetables grown on the St. Regis Mohawk Reservation using salt-containing private well water.

Salt water has intruded into a shallow aquifer in the St. Regis Mohawk Reservation. The aquifer is used as a drinking private-well water supply by the tribe. ATSDR previously evaluated the public health implications of ingesting salt-containing water and using the water for cooking and bathing [1, 2]. ATSDR concluded 1) the levels of sodium in private well water may be of health concern for those tribal members who have, or are at risk, for hypertension, and 2) the levels of strontium concentrations may be of public health concern for children if the children are exposed for several years or more. These residents are provided bottled drinking water. However, residents are using well water for cooking and irrigating vegetable gardens.


ENVIRONMENTAL DATA

ATSDR reviewed results of well water samples collected from approximately 67 private wells in the affected area by EPA Region II from April 7, 1999, through April 28, 1999, in this health consultation(1). Levels of strontium in private well water ranged from 0.0165 to16.9 milligrams per liter (mg/l). Levels of sodium in private well water ranged from 3.6 to 351 mg/l.


DISCUSSION

St. Regis Mohawk residents' dose of sodium and strontium from consuming vegetables grown with salt-containing water depends on several factors, including 1) background soil concentration of sodium, strontium, and calcium, 2) rate of well water irrigation, 3) rate of contaminant dilution from rainfall, 4) the rate of sodium and strontium uptake by the crops, and 5) rate of consumption of home-grown vegetables.

Soil strontium competes with calcium for plant uptake(2). Scientists studying the effects of the Chernobyl accident have determined that strontium-90 is relatively immobile in soil, particularly where calcium is present in the soil [1]. (Naturally occurring non-radioactive strontium was found in the St. Regis Mohawk ground water, not strontium-90. Strontium-90 is mentioned because its movement in the environment is believed to be similar to that of naturally occurring strontium.)

The background levels of strontium and calcium levels in the affected area are not known. However, calcium levels in private well water ranged from 39 to 197 mg /l in April 1999 well water sampling data. Therefore, strontium uptake by plants from well water will be limited since the calcium levels are two to tenfold greater than the strontium levels. The bio-availability of strontium in humans is also limited by adequate intake of dietary calcium [2].

Sodium in soil and irrigation water is not readily taken-up by leafy vegetables(3). Therefore sodium levels in leafy vegetables grown in the St. Regis Mohawk Reservation are expected to be similar to levels normally found in leafy vegetables. Typical sodium levels found in raw leafy vegetables range from less than 1 to 10 mg of sodium per 100 grams (g) of vegetable [3].

Levels of sodium in other vegetables typically range from 2 mg per 100 g of raw potatoes to 83 mg in 100 g of raw celery [3]. The sodium dose from consumption of non-leafy vegetables would not present a health concern even if irrigation with salt-containing well water resulted in increased sodium uptake. The estimated daily maximum sodium dose will be less than 500 mg, based on the following:

  • a conservative consumption rate of homegrown vegetables (uncooked) of 476 grams (approximately 1 pound) per day. This rate represents the 95th percentile for persons in the Northeastern United Stated, based on 70 kilogram person [4].

  • conservatively estimating a maximum sodium concentration of 100 mg per 100 gram of vegetables.

The American Heart Association recommends that healthy adults limit their sodium intake to 2,400 mg of sodium per day [5]. Therefore, consuming homegrown vegetables that were grown with salt-containing water would represent less than 25 percent of the recommended daily maximum intake. Consumption of home-produced vegetables is likely to result in lower sodium in-take than ingesting canned or frozen vegetables because of salt added to those foods.


ATSDR CHILD HEALTH INITIATIVE

ATSDR considers children in the evaluation of all exposures. ATSDR uses health guidelines that are protective for children. In evaluating any potential health effects from ingestion of home produced vegetables, children were considered as a special population. In formulating conclusions for this health consultation, ATSDR considered children to be more sensitive than adults to excessive intake of strontium.


CONCLUSIONS

The use of sodium and strontium containing well water for irrigation of produce in the St. Regis Mohawk community may result in sodium and strontium exposure to residents who consume home grown produce. The levels of sodium and strontium exposure represent no apparent public health hazard to children or adults.


RECOMMENDATIONS

None


PREPARERS OF REPORT

Peter J. Kowalski, CIH
Environmental Health Scientist
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation

Reviewed by

Susan Moore
Chief, Consultation Section
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation


REFERENCES

  1. Chernobyl: Agriculture and Environmental Impacts-Chapter 6. International Nuclear Energy Agency.

  2. US Environmental Protection Agency, Integrated Risk Information System Report on Strontium, October 1,1992.

  3. Pennington J.A., Young B. Sodium, Potassium, Phosphorus and Magnesium in Foods from the United States Total Diet Study. Journal of Food Composition and Analysis 3, 145-165 (1990).

  4. US Environmental Protection Agency, Exposure Factors Handbook. August, 1997.

  5. Dietary Electrolytes and Blood Pressure. American Heart Association. April, 1998.

1. E-mail Communication from Jim Haklar, EPA to Peter Kowalski, ATSDR, dated June 23, 1999.
2. Personal Communication, Shaw Reid PhD, Cornell University, June 17, 1999.
3. Personal Communication, Rufus Chaney, USDA, June 29,1999.


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