Effects of CuO nanoparticles on Lemna minor

Abstract

Background: Copper dioxide nanoparticles (NPs), which is a kind of important and widely used metal oxide NP, eventually reaches a water body through wastewater and urban runoff. Ecotoxicological studies of this kind of NPs effects on hydrophyte are very limited at present. Lemna minor was exposed to media with different concentrations of CuO NPs, bulk CuO, and two times concentration of Cu²⁺ released from CuO NPs in culture media. The changes in plant growth, chlorophyll content, antioxidant defense enzyme activities [i.e., peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) activities], and malondialdehyde (MDA) content were measured in the present study. The particle size of CuO NPs and the zeta potential of CuO NPs and bulk CuO in the culture media were also analyzed to complementally evaluate their toxicity on duckweed.

Result: Results showed that CuO NPs inhibited the plant growth at lower concentration than bulk CuO. L. minor roots were easily broken in CuO NPs media under the experimental condition, and the inhibition occurred only partly because CuO NPs released Cu²⁺ in the culture media. The POD, SOD, and CAT activities of L. minor increased when the plants were exposed to CuO NPs, bulk CuO NPs and two times the concentration of Cu²⁺ released from CuO NPs in culture media, but the increase of these enzymes were the highest in CuO NPs media among the three kinds of materials. The MDA content was significantly increased compared with that of the control from 50 mg L^-1 CuO NP concentration in culture media.

Conclusion: CuO NPs has more toxicity on L. minor compared with that of bulk CuO, and the inhibition occurred only partly because released Cu²⁺ in the culture media. The plant accumulated more reactive oxygen species in the CuO NP media than in the same concentration of bulk CuO. The plant cell encountered serious damage when the CuO NP concentration reached 50 mg L^-1 in culture media. The toxicology of CuO NP on hydrophytes must be considered because that hydrophytes are the basic of aquatic ecosystem.

Fig. 1

TEM observation of CuO NPs (a) and size of CuO NPs aggregates in culture media (b)

Fig. 2

Changes in the zeta potentials of CuO NPs and bulk CuO in the culture media

Fig. 3

Cu²⁺ released from CuO NPs in culture media

Fig. 4

Frond number changes of L. minor in different culture media

Fig. 5

Root length of L. minor in different culture media

Fig. 6

Fresh weight of L. minor in different culture media

Fig. 7

Chlorophyll content of L. minor frond in different culture media

Fig. 8

SOD activity of L. minor in different culture media

Fig. 9

CAT activity of L. minor in different culture media

Fig. 10

POD activity of L. minor in different culture media

Fig. 11

MDA content of L. minor in different culture media