Progress 12/15/01 to 12/31/04
Outputs
The overall objective of this study was to quantify the risks to livestock and/or humans from consumption of plants irrigated with perchlorate-contaminated water. To meet this objective, we examined factors affecting plant uptake of perchlorate and then toxicity of perchlorate-contaminated food in rodent models. We determined that perchlorate accumulates in many types of leafy, above-ground vegetation; however, uptake varies greatly by plant species. Based on field and laboratory data, perchlorate is taken up by cucumbers, soybeans, alfalfa, lettuce, and tomatoes. We saw no evidence to suggest that perchlorate is significantly toxic to plants. Perchlorate did not appear to accumulate in nuts and fruits as much as leaves. We determined that vegetative uptake is a function of both length of exposure and perchlorate concentration in the exposure media. In general, there is a fairly constant relationship between concentrations of perchlorate in leafy vegetation and
irrigation water. Perchlorate concentration in leafy vegetation (fresh weight) was over 100 times greater than the perchlorate concentration in the irrigation water. High concentrations of nutrients can decrease the rate of perchlorate uptake into plants, but have little effect on long-term plant uptake. Total perchlorate uptake into plants was largely unrelated to nitrogen source. High nitrate levels do not affect the overall uptake of perchlorate into vegetation. Finally, perchlorate uptake into plants was similar in both sand and soil experiments, indicating that perchlorate in the environment is readily available and does not sorb to soil. Field sampling generally supported laboratory results and included wheat, and alfalfa from commercial production facilities and garden vegetables from private residences. Perchlorate exposure through food items appeared to be slightly less toxic to rodents than exposure through drinking water. Minimal differences in thyroid function were
observed among prairie voles exposed to perchlorate via food versus water. Thyroid hormone concentrations provided little evidence that perchlorate, at high environmentally relevant doses, altered thyroid function. Although perchlorate exposure via water appeared to have a slightly greater effect on thyroid function, the results were equivocal due to the low number of affected individuals. Perchlorate residues were seldom detected in liver and kidney tissues, but detection may have been effected by analytical capabilities and rapid elimination of perchlorate. Individuals in perchlorate treatment groups had lower reproductive success rates than controls, but reproductive endpoints evaluated were not different among treatment groups. Body mass data and food consumption rates of individuals receiving perchlorate-contaminated food in this study suggest that metabolic rates and activity levels may have been affected by perchlorate.
Impacts
Concern over animal exposure to perchlorate has largely centered on drinking water. This research highlights the need to further consider plant ingestion as an exposure route for humans, livestock, and wildlife. These data demonstrate that food items should be considered a significant source of perchlorate exposure. However, our results indicate that exposure via vegetation may not produce the same degree of effect as exposure via drinking water. This study has begun to define the relationship between concentrations of perchlorate in vegetation when irrigated with perchlorate-contaminated water. Concentration factors derived from this research can be used to evaluate the overall exposure for populations from food which has been grown using irrigation water containing perchlorate. Finally, these data will be useful in determining the occurrence of perchlorate in the food supply of wildlife, livestock, and humans.
Publications
- Jackson, W. A., P. C. Joseph, L. B. Patil, K. Tan, P. N. Smith, L. Yu, and T. A. Anderson. 2005. Perchlorate accumulation in forage and edible vegetation. Journal of Agricultural and Food Chemistry. (In press).
- Severt, S. A., W. A. Jackson, T. A. Anderson, P. N. Smith. 2005. Food safety assessment of perchlorate-contaminated crops using deer mice. Journal of Toxicology and Environmental Health. (accepted).
- Tan, K., T. A. Anderson, M. W. Jones, P. N. Smith, and W. A. Jackson. 2004. Uptake of perchlorate in aquatic and terrestrial plants at field scale. Journal of Environmental Quality. 33:1638-1646.
- Yu, L., J. E. Canas, G. P. Cobb, W. A. Jackson, and T. A. Anderson. 2004. Uptake of perchlorate in terrestrial plants. Ecotoxicology and Environmental Safety. 58:44-49.
- Cheng, Q., L. Perlmutter, P. N. Smith, S. T. McMurry, W. A. Jackson, and T. A. Anderson. 2004. A study on perchlorate exposure and absorption in beef cattle. Journal of Agricultural and Food Chemistry. 52(11):3456-3461.
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Progress 10/01/02 to 09/30/03
Outputs
The overall objective of this study was to quantify the risks to livestock and/or humans from consumption of plants irrigated with perchlorate-contaminated water. To meet this objective, we examined factors affecting plant uptake of perchlorate and then toxicity of perchlorate-contaminated food in rodent models. We determined that perchlorate accumulates in many types of leafy, above-ground vegetation; however, uptake varies greatly by plant species. Based on field and laboratory data, perchlorate is taken up by cucumbers, soybeans, alfalfa, lettuce, and tomatoes. We saw no evidence to suggest that perchlorate is significantly toxic to plants. Perchlorate did not appear to accumulate in nuts and fruits as much as leaves based on limited data. We determined that vegetative uptake is a function of both length of exposure and perchlorate concentration in the exposure media. High concentrations of nutrients can decrease the rate of perchlorate uptake into plants, but have
little effect on long-term plant uptake. Total perchlorate uptake into plants was largely unrelated to nitrogen source. Finally, perchlorate uptake into plants was similar in both sand and soil experiments, indicating that perchlorate in the environment is readily available and does not sorb to soil. Perchlorate exposure through food items appeared to be slightly less toxic to rodents than exposure through drinking water. Minimal differences in thyroid function were observed among prairie voles exposed to perchlorate via food versus water. Thyroid hormone concentrations provided little evidence perchlorate at high environmentally relevant dose altered thyroid function. Histopathological changes were the most sensitive indicators of effect. Although perchlorate exposure via water appeared to have a slightly greater effect on thyroid function, the results were equivocal due to the low number of affected individuals. Perchlorate residues were seldom detected in liver and kidney tissues,
but detection may have been effected by analytical capabilities and rapid elimination of perchlorate. Individuals in perchlorate treatment groups had lower reproductive success rates than controls, but reproductive endpoints evaluated were not different between treatment groups. Body mass data and food consumption rates of individuals receiving perchlorate-contaminated food in this study suggest that metabolic rates or activity levels may have been affected by perchlorate.
Impacts
Concern over animal exposure to perchlorate has largely centered on drinking water. This research highlights the need to further consider plant ingestion as an exposure route. In addition, other plant tissues besides green leafy vegetation may also contribute to total perchlorate exposure among humans and livestock. These data demonstrate that food items may be a significant source of perchlorate exposure in humans and livestock, but exposure via food may not produce the same degree of effect as exposure via drinking water.
Publications
- Yu, L., Canas, J. E., Cobb, G. P., Jackson, W. A., and Anderson T. A. 2004. Uptake of perchlorate in terrestrial plants. Ecotoxicol. Environ. Saf. (In press).
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Progress 10/01/01 to 09/30/02
Outputs
The objective of this study is to quantify the risks of consuming plants irrigated with perchlorate-contaminated water. To that end, the following studies have been conducted: Sorption Study: Sorption studies were conducted to determine if anion exchange or non-specific sorption would occur. Kaolinite, montmorillonite, and quartz sand (control) were examined over a 30 day period. Five grams of each mineral sample were placed in a flask with deionized sterilized water spiked with 100 ppb sodium CLO4. The kaolinite and montmorillonite samples had average peak sorptions of 0.2 and 0.16 mg CLO4/kg, respectively. Between days 5-31, CLO4 seemed to be desorbing back into solution. Plant Uptake: Role of Nitrogen Source: Alfalfa was grown in "cone-tainers" using pre-washed sterilized sand for 3 months under 4 different nitrogen concentrations delivered every 1-2 days as a weighed mass of nutrient solution. Sodium CLO4 was maintained at a concentration of 500 ppb in the
nutrient solution. Every 2 weeks 4 cone-tainers were examined. Plants were analyzed for CLO4 as well as total uptake. Sand was extracted and analyzed for CLO4, nitrate, and TDS. The experiment is complete but data are not yet available. Hydroponic Test 1: A 68 day CLO4 uptake study was conducted in a recirculating hydroponic system. Germinated plants in Rockwool blocks were placed in gutters at varying concentrations of CLO4: 0, 20, 100, and 500 ppb with plant food solution. Each portion of the plant was weighed, rinsed, and allowed to dry prior to extraction and analysis by ion chromatography. CLO4 (500 ppb) significantly inhibited growth of soybeans. There was a decrease of leaf mass in the 500 ppb group compared to others. Significant differences were observed in seed production among treatments. There was little change in seed mass in the 20 ppb group compared to controls, but there was an observable difference in 100 ppb group. A significant decrease in seed mass occurred in the
500 ppb group. No CLO4 was detected in soybean seeds. Little CLO4 was detected in roots and stems. There was significant CLO4 uptake in leaves and seed covers. The highest CLO4 mass in leaves occurred in the 100 ppb treatment group. Rodent Dosing Study: A 3 generation prairie vole feeding study was conducted to evaluate exposure to CLO4 through forage. CLO4 concentrations in hydroponically grown plants were determined and an environmentally relevant (2.1 ppm in feed) dose was prepared by adding 12 grams of CLO4 laden plant matter to 50 kg of rabbit chow at Purina Special Blends Laboratory. Final concentration of CLO4 was 2111 ng/g. Three dosing groups were established: CLO4-contaminated forage, CLO4-contaminated water (700 ppb in water), and control. Study treatments began in August 2002 with a 21 day feeding trial with individually housed prairie voles (N = 120). On day 22, 30 breeding pairs were established and those not paired were euthanized and necropsied. Analysis of tissues for
CLO4, T3 and T4 hormone analysis, and thyroid histology is ongoing to assess food-related exposure and effects.
Impacts
Perchlorate has emerged as a contaminant of national interest. Analytical advances have permitted detection of perchlorate in groundwater used for human consumption, watering livestock, and irrigation of food crops. Moreover, perchlorate has been shown to accumulate to elevated concentrations in plant tissues and can be detected in wild animals inhabiting contaminated sites. Recent media reports in the western United States have documented elevated concentrations of perchlorate in lettuce and other crops intended for consumption. Therefore, it is critical to elucidate the biotic and abiotic characteristics that regulate perchlorate uptake into plants, and the potential adverse effects caused by consuming food crops grown with perchlorate-contaminated irrigation water. This research project will help us understand the factors that influence perchlorate uptake into plants intended for human or livestock consumption and identify subsequent health risks.
Publications
- No publications reported this period
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