Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2012
Publication Date: 1/18/2013
Publication URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2390.pdf
Citation: Ha, W., Suarez, D.L., Lesch, S.M. 2013. Predicting perchlorate uptake in greenhouse lettuce from perchlorate, nitrate and chloride irrigation water concentrations. Journal of Environmental Quality. 42:208-218. Interpretive Summary: There has been concern about the detection of perchlorate in edible leafy vegetables, primarily lettuce, in various areas in the world, but especially from irrigated regions in the southwestern U.S. The human health concern is that perchlorate can substitute for iodine and thus interrupt thyroid iodine uptake contributing hormone disruption and potential disruption of metabolic activities. There have been a number of studies on perchlorate uptake but the interactive effect of other ions in soil water on perchlorate uptake is not known in detail. We conducted a greenhouse experiment using two varieties of lettuce to investigate the interaction of perchlorate, chloride and nitrate uptake under controlled conditions. Perchlorate uptake was suppressed by the presence nitrate and chloride in the irrigation water. In general, the outer leaves of lettuce contained more perchlorate than did the inner leaves. The results indicate that perchlorate is not taken up passively with the water but that specific uptake mechanisms exist related to uptake of chloride and nitrate. A predictive model was developed to describe the perchlorate concentration in lettuce as related to the chloride, nitrate and perchlorate concentrations in the irrigation water. Research results can be utilized by extension specialists and growers who can either reduce perchlorate uptake, by controlling chloride and nitrate in the irrigation water, or by removing the outer lettuce leaves during harvest.
Technical Abstract: Perchlorate (ClO4-) has been detected in edible leafy vegetables irrigated with Colorado River water. The primary concern has been the ClO4- concentration in lettuce. There has been a limited number of studies on ClO4- uptake but the interactive effect of other anions on ClO4- uptake is not known in detail. We conducted a greenhouse ClO4- uptake experiment using two varieties of lettuce (iceberg and butterhead) to investigate the interaction of uptake of ClO4-, chloride (Cl-) and nitrate (NO3-) on ClO4- uptake under controlled conditions. We examined three concentrations of ClO4-, 40, 220, and 400 nmolc/L, Cl- at 2.5, 13.75, and 25 mmolc/L, and NO3- at 2, 11, and 20 mmolc/L. Perchlorate was taken up the most in lettuce when ClO4- was the greatest and NO3- and Cl- were lowest in concentration in the irrigation water. More ClO4- was detected in leafy material than that in root tissue. In general, the outer leaves of iceberg and butterhead lettuce contained more ClO4- than did the inner leaves. The results indicate that selective ClO4- uptake occurs for green leaf lettuce. A predictive model was developed to describe the ClO4- concentration in lettuce as related to the Cl-, NO3-, and ClO4- concentration in the irrigation water. Research results can be utilized to elucidate the effect of salts on the accumulation and uptake of ClO4- by edible leafy vegetables.