Effect of High-Voltage Atmospheric Cold Plasma Treatment on Germination and Heavy Metal Uptake by Soybeans (Glycine max)

Abstract

The need to feed 9.9 billion people by 2050 will require the coordination of farming practices and water utilization by nutrient-dense plants and crops. High levels of lead (Pb), a toxic element that can accumulate in plants, can lead to toxicity in humans. With the development of novel treatment technologies, such as atmospheric cold plasma (ACP) and engineered nanoparticles (NPs), the time to germination and levels of heavy metals in food and feed commodities can be reduced. This study provides insight into the impact of plasma-activated water (PAW) on the germination rates and effects of soybean seeds, and the resultant combination effects of zinc oxide uptake in the presence of lead. Soybean seedlings were watered with PAW (treated for 3, 5, and 7 min at 30, 50, and 70 kV), and the germination and growth rate were monitored for 10 days. The germinated seedlings were then grown hydroponically in a nutrient solution, and the biomass of each example was measured. The PAW treatment that resulted in the best growth of soybean seeds was then exposed to Pb and zinc-oxide nanoparticles (ZnONPs) to investigate heavy metal uptake in the presence of nanoparticles. After acid digestion, the rate of heavy metal uptake by the soybean plants was evaluated using inductively coupled plasma-mass spectrometry. The PAW seeds grew and germinated more quickly, demonstrating that the plasma therapy had an effect. The rate of heavy metal uptake by the plants was also shown to be 5x lower in the presence of ZnONP.

Keywords: atmospheric cold plasma; germination; plasma activated water; soybean; zinc oxide nanoparticles.

Figure 1

(a) Growth in the size of the seedlings on the 10th day at different treatment conditions. (b) Number of seeds germinated on different selected days under different treatment conditions. After 10 days of sowing, about 60% to 93.3% of seeds were germinated. The maximum germination of seeds was 93.3%, observed in the 50 kV 3 min- and 50 kV 5 min-treated PAW and tap-water-applied group (b) which was 7% higher than the control group.

Figure 1

(a) Growth in the size of the seedlings on the 10th day at different treatment conditions. (b) Number of seeds germinated on different selected days under different treatment conditions. After 10 days of sowing, about 60% to 93.3% of seeds were germinated. The maximum germination of seeds was 93.3%, observed in the 50 kV 3 min- and 50 kV 5 min-treated PAW and tap-water-applied group (b) which was 7% higher than the control group.

Figure 2

Mean radicle growth changes in the seeds with PAW from the control group (error bars represent standard deviation from the mean).

Figure 3

Day 7, when radicle growth was >2 cm. Left to right: PAW daily treatment, initial PAW treatment and control.

Figure 4

Dry biomass of Glycine max (L.); combinations of 100 mg/L Pb and/or 100 mg/L ZnO-NPs. (a) Control samples with different treatment. (b) Plasma-treated samples with different treatments. The values in the columns represent mean values of the samples and error bars.

Figure 5

Daily mean growth of seeds after 10 days with 70 kV, 7 min PAW. The growth/shrinkage pattern of the seeds is also shown.

Figure 6

Germination percentage and the growth pattern of seeds treated with PAW at 50 KV for 3 min and PAW + TW at 50 KV for 3 min.

Figure 7

Changes in the seeds’ structure after treatment with PAW (left) compared to the PAW + TW (right)-treated seeds on 6th day of germination.

Figure 8

Schematic diagram of a high-voltage atmospheric cold plasma system. Note that image is not to scale.