ARS | Publication request: Perchlorate uptake in spinach as related to perchlorate, nitrate and chloride concentrations in irrigation water

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 22, 2011
Publication Date: September 22, 2011
Citation: Ha, W., Suarez, D.L., Lesch, S.M. 2011. Perchlorate uptake in spinach as related to perchlorate, nitrate and chloride concentrations in irrigation water. Journal of Environmental Science and Technology. 45(21):9363-9371.

Interpretive Summary: The main health concern of perchlorate ion is that perchlorate can substitute for iodine and thus interrupt the thyroid iodine uptake in human beings, resulting in subsequent hormone disruption and potential perturbations of metabolic activities. Elevated perchlorate concentrations have been reported in the Colorado River and in ground water used for irrigation. Elevated concentrations are attributed to perchlorate salt manufacturing and industrial uses. The fresh vegetable industry relies on Colorado River water for irrigation in the lower Colorado River regions of California and Arizona. Use of Colorado River water has thus caused elevated perchlorate concentrations in vegetables. The objectives were to: (1) investigate the influence of chloride and nitrate salt on the uptake of perchlorate by spinach. (2) to examine the physiological effect of perchlorate uptake and determine the pattern of translocation of perchlorate from roots to leaves. (3) to develop predictive equations to represent perchlorate uptake in spinach as related to perchlorate, nitrate, and chloride in the irrigation water. The results revealed that spinach accumulates perchlorate in the plant tissue at much higher levels than reported for lettuce. Increased concentrations of nitrate greatly decreased perchlorate uptake while increased chloride concentrations only slightly reduced perchlorate in spinach leaves. The results also provide evidence that selective perchlorate uptake occurs for spinach from irrigation waters containing perchlorate. Results are of interest to regulatory agencies and irrigation specialists and growers developing management practices to control perchlorate accumulation in vegetables.

Technical Abstract: Several studies have reported on the detection of perchlorate in edible leafy vegetables irrigated with Colorado River water. However, there is no information on spinach as related to perchlorate in irrigation water nor on the effect of other anions on perchlorate uptake. A greenhouse perchlorate uptake experiment using spinach was conducted to investigate the impact of presence of chloride and nitrate on perchlorate uptake under controlled conditions. We examined three concentrations of perchlorate, 40, 220, and 400 nmol/L, three concentrations of chloride 2.5, 13.75, and 25 mmol/L, and nitrate at 2, 11, and 20 mmol/L. The results revealed that perchlorate was taken up the most when nitrate and chloride were lowest in concentration in the irrigation water. More perchlorate was detected in spinach leafy material than that in root tissue. Relative to other green leaf vegetables, spinach hyper-accumulates perchlorate in the plant tissue. Perchlorate was accumulated in spinach leaves approximately 10 times more than reported for outer leaves of lettuce at 40 nmol/L of perchlorate. The results also provide evidence that spinach selectively takes up perchlorate relative to chloride. We developed a predictive model to describe the perchlorate concentration in spinach as related to the chloride, nitrate, and perchlorate concentration in the irrigation water.