A comparative study of perchlorate uptake in terrestrial plants: Influence of plant type and soil nutrient concentration

Abstract

Cucumber {Cucumis sativus L.), lettuce {Lactuca sativa L.), and soybean {Glycine max) were used to determine uptake of perchlorate (100 ppb) in sand. Plants were watered with different ratios of Hydrosol (a commercial fertilizer) to Milli-Q water. Perchlorate concentrations in sand and plant tissues were determined weekly. In most experiments, perchlorate was completely depleted from the planted sand. Perchlorate uptake was observed in all three plant species. Perchlorate concentrations in leaves were significantly higher (p < 0.0001) at lower Hydrosol:Milli-Q ratios, which indicates that plant uptake of perchlorate is strongly influenced by the presence of external nutrients. Based on the results of the eight-week uptake study in cucumber and six-week uptake study in lettuce, there appears to be a perchlorate threshold concentration for cucumber at 150 ppm and for lettuce at 750 ppm before the plants begin to excrete perchlorate.

There was a significant difference (p ranged from <0.0001 to 0.0401) between planted and unplanted sand in each experiment with respect to perchlorate concentration. A significant difference (p <0.0001) was also observed among different ratios of Hydrosol and Milli-Q water in cucumber experiments and among plant species. Perchlorate concentrations in the leaves of plants grown in the presence of 100%, 50%, and 25% Hydrosol were significantly different from each other. Perchlorate concentrations in lettuce were also significantly different from cucumber and soybean. There was no significant difference between leaf concentrations in cucumber and soybean.

Results of these studies indicate the perchlorate is readily accumulated into plant tissues. Although the presence of external nutrients decreases the amount of perchlorate transported by plants, significant concentrations of perchlorate occur in above ground plant tissues. The potential for trophic transfer of perchlorate from soil to higher organisms through plants exists. Additional studies will help fill data gaps on the availability of perchlorate in plants to higher organisms.