Uptake of perchlorate in terrestrial plants

Cucumber (Cucumis sativus L.), lettuce (Lactuca sativa L.), and soybean (Glycine max) were used to determine uptake of the perchlorate anion (100 ppb) from sand. Plants were watered with different ratios of Hydrosol (a diluted solution of Peters All-Purpose Plant Food) to Milli-Q water (18 MΩ) to determine if the presence of other nutrients (such as nitrate) influenced perchlorate uptake. Perchlorate concentrations in sand and plant tissues were determined weekly. Perchlorate uptake was observed in all three plant species. In most experiments, perchlorate was completely depleted from sand in which plants were growing. Perchlorate concentrations in lettuce were also significantly higher than those in cucumber and soybean (P<0.0001). Perchlorate concentrations in sand decreased at a higher rate at lower ratios of Hydrosol to Milli-Q, indicating that plant (cucumber) uptake of perchlorate is influenced by the presence of external nutrients. The results of an 8-week uptake study in cucumber and a 6-week uptake study in lettuce suggest that a threshold perchlorate concentration is reached: for cucumber, 150 ppm and for lettuce, 750 ppm. Although the presence of external nutrients decreases the rate of perchlorate uptake by plants, significant concentrations of perchlorate occur in aboveground plant tissues even after relatively short periods of growth. The potential for trophic transfer of perchlorate from soil to higher organisms through plants exists.