The Joint Effect Of Binary Mixtures Of Nano-ZnO And Cetyltrimethyl Ammonium Chloride On The Growth Of Chlorella Vulgaris

With the wild application of nano technology, the ecological effects and environmental behaviors of nano materials have been focused on by researchers. Algae, as primary producers in aquatic ecosystem, have been subjected to as model organisms in toxicological studies. However, due to the diversity of actual aquatic ecosystem, there are other pollutants coexist with nano materials and thus lead to combined pollution. Among these pollutants, surfactants, which are commonly used as promoters in the production of nano materials, have been widely applied in various products. Therefore, it is important to study the joint effect of nano materials and surfactants, and to obtain a comprehensive understanding of the ecotoxicity caused by nano materials. Nevertheless, there are still limited studies on the joint toxicity of nano materials and surfactants on algae.This paper selected a single-celled green alga Chlorella vulgaris as model organism, and selected nano-ZnO and cetyltrimethyl ammonium chloride (CTAC) as the representatives of nano materials and surfactants respectively. Based on the research of ecotoxicity of nano-ZnO or CTAC single pollution system, we investigated the joint effect of binary mixtures of nano-ZnO and CTAC (nano-ZnO/CTAC) on the algal growth. Furthermore, we explored the interaction between nano-ZnO and CTAC and its effect on the joint toxicity. The following results are obtained in this paper:(1) Both nano-ZnO and CTAC exhibited high toxic effects on the growth of C. vulgaris. The 96h-ECso of nano-ZnO and CTAC, which are calculated by probit method, was 0.016 mmol/L and 263.61 ?g/L respectively. Moreover, we used four typical methods, toxic unit method, additive index method, mixture toxic index, similar parameter method, to evaluate the joint toxicity of nano-ZnO/CTAC. The results indicate that the joint effect of nano-ZnO/CTAC showed antagonistic effect with the initial CTAC concentration of 100 or 200 ?g/L. However, when the initial concentration of CTAC was 300 ?g/L, the joint effect was antagonistic by the additive index method, whereas showed partial additive by the toxic unit method and the mixed toxic index method.(2) In nano-ZnO single pollution system, when the initial concentration of nano-ZnO was 0.02 mmol/L, the distribution ratio of Zn in the solution was 77.12%. However, when the nano-ZnO concentration increased to 0.05 or 0.12 mmol/L, the distribution ratio of Zn on the surface of C. vulgaris was 55.20% and 73.18%, respectively. It means with increasing nano-ZnO concentration, we observed the tendency that Zn enriched more on the algal surface. Compared with nano-ZnO single pollution system, the distribution ratio of Zn in the solution of nano-ZnO/CTAC (CCTAC=200 ?g/L; Cnano-Zno=0.02,0.05,0.12 mmol/L) from 77.12%,33.37%,12.58% dropped to 53.56%,17.38%,7.21%, respectively, which indicate it is easier for Zn to be enriched on the algal surface and intracellular.(3) Compared with in pure water, nano-ZnO released more Zn2+ in OECD culture medium (algal culture medium). With the initial concentration of 0.01 mmol/L nano-ZnO, the dissolution rate of nano-ZnO was 56.65% and 98.24% in pure water and in OECD culture medium, respectively. However, after the addition of 200 ?g/L CTAC, the dissolution rate of nano-ZnO decreased to 43.08% in OECD culture medium. Moreover, we observed that the concentration of PO43- in the OECD culture medium decreased with nano-ZnO, while CTAC can weaken this decrease. Meanwhile, CTAC can neutralize the surface zeta potential and reduce the hydrodynamic diameter of nano-ZnO. The concentration of PO43- in the OECD culture medium decreased for 12.15% with 0.04 mmol/L nano-ZnO compared with the control (without nano-ZnO), while just decreased for 2.05% with the addition of 200 ?g/L CTAC. Meanwhile, the surface zeta potential of nano-ZnO increased from-14.8mV to -13mV, and the hydrodynamic diameter reduced from 1338.5 nm to 1000 nm. According to above results, the antagonism of nano-ZnO/CTAC may due to the inhibition effect of CTAC on the release of Zn2+ fromnano-ZnO.(4) The X-Ray Diffraction pattern shows CTAC presented no significant effect on the crystalline structure of nano-ZnO. Meanwhile, by comparing the Fourier transform infrared spectroscopy, we obtained that CTAC had effect on nano-ZnO while CTAC remained stable in the combined pollution system. A phosphate group vibration peaks (1000-1100 cm-1) and structure stretching vibration peak related to CTAC, like -CH2 (1480 cm-1), C-H (2850-2900 cm-1) and C-N (900-950 cm-1) were observed on the surface of nano-ZnO in OECD culture medium. These results indicate that the dissolution behavior of nano-ZnO is influenced by the adsorption of CTAC on its surface.