Fate of DTPA, EDTA, and EDDS in Hydroponic Media and Effects on Plant Mineral Nutrition

ABSTRACT

Synthetic chelators are commonly used in hydroponic media to solubilize iron (Fe); however, the fate of these chelators is unknown. This study examined the persistence of three synthetic chelators, ethylenediaminetetraacetate (EDTA), diethylenetriaminepentaacetate (DTPA), and ethylenediaminedisuccinate (EDDS) in a bench-scale lettuce production system. The EDDS concentration decreased rapidly within 7d, most likely due to biodegradation. The EDTA and DTPA concentrations stayed steady throughout the experiments despite additions to maintain a constant volume and loss of chelator may have been due to either plant uptake or photodegradation of the chelator. Despite large differences in solution chemistry, the final shoot concentrations of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) were similar among chelator treatments, whereas root concentrations of these same elements were highly variable. The concentration of DTPA in a commercial lettuce production system was measured and highly variable concentrations were found.

Keywords::

• DTPA
• EDDS
• EDTA
• hydroponics
• chelator
• nutrient solutions
• lettuce

Notes

∗Significantly different with P < 0.06.

¹Average from 1 experiment.

²Average from 3 experiments.

³Average from 4 experiments.

⁴Measured initial solution concentrations (μ M) from the final two EDTA experiments ranged from 15.5 to 15.9 for Fe, 1.49 to 2.24 for Mn, 1.99 to 2.69 for Cu, and 3.67 to 6.71 for Zn.

⁵Measured initial solution concentrations (μ M) from the final two DTPA experiments ranged from 15.7 to 17.1 for Fe, 2.13 to 2.26 for Mn, 0.66 to 3.98 for Cu, and 4.11 to 4.33 for Zn.

⁶Initial expected concentration based on nutrient solution composition.

∗n = 6, EDTA results from the third experiment were removed due to high solution contamination with Zn and Cu; if these values were included, the average root concentrations are 250 ± 230 ppm and 960 ± 900 for Cu and Zn, respectively.

^a Average values are not significantly different (P > 0.05).