| Combined pollution of xenobiotics in aquatic ecosystems represents an emerging environmental issue since the reciprocal interactions between chemicals and their toxic mechanisms remain insufficient. Therefore, understanding the joint effects of multi-pollutants is crucial for ecological risk assessment of contaminations in aquatic systems.The paper focused on the toxicity of combined pollution system of cetyltrimethylammonium chloride (CTAC) and Fluoranthene (Flu) on fresh-water algae and its mechanism. Using environmentally sensitive aquatic biology, Chlorella vulgaris, Scenedesmus obliquus, Microcystis aerugina and Spirulina platens is as the testing algae, we investigated the effect of CTAC and Flu signal pollutant system and combined pollutant system on the biomass of the four fresh-water algae, repectively. Then, the effect of the combined pollution system on the pigment, dissolvable protein, absorption of nutritive element by Chlorella vulgaris was studied. Furthermore, the anti-oxidation protection of Chlorella vulgari, which contained the detoxification effect of malondialdehyde (MAD), enzyme activity, the activity of O2-and the role of external NO, was explored in this paper. The main results were as follows:(1) The resistance ability of the four fresh-water algae to CTAC is as follows: Scenedesmus obliquus> Chlorella vulgaris> Microcystis aerugina> Spirulina platensis. Regressing the logarithmic of concentration (x) and probability unit(y), the96h-ECso of Chlorella vulgaris, Scenedesmus obliquus, Microcystis aerugina and Spirulina platensis was caculated to be0.18mg/L,0.23mg/L,0.13mg/L and0.05mg/L, respectively.The96h restraining effect of Flu to the four fresh water algae have not arrived at the half to extension of Flu concentration. And the restraining effect of Flu to the four fresh water alga was as follows:Scenedesmus obliquus≈Chlorella vulgaris> Spirulina platensis> Microcystis aerugina. The96h restraining rate of Flu to Chlorella vulgaris, Scenedesmus obliquus, Microcystis aerugina and Spirulina platensis is6.7%,7.2%、35.0%and29.5%, respectively. The toxicity of combined pollutant system of CTAC and Flu on two green algae(Chlorella vulgaris, Scenedesmus obliquus) displayed an increase (Flu:0～2.5μg/L)and then a decrease (Flu:2.5～200μg/L) with the the increase of Flu concentration, which achieved at a maximum value at2.5μg/L Flu. And combined pollutant system was characterized by antagonism effect (RI<1) when the concentration of Flu was between50μg/L and200μg/L. However, the toxicity of the combined pollutant system on the two blue algae(Microcystis aerugina and Spirulina platensis) exhibited synergistic effect when the concentration of Flu was less than200μg/L. The RI of multiple system to Microcystis aerugina and Spirulina platensis are1.42and1.22, respectively.(2) The effect of combined pollution system of CTAC and Flu on the pigment and dissolvable protein of Chlorella vulgaris first decreased (Flu:0～2.5μg/L) and then increased with the increase of Flu (Flu:2.5～200μg/L), which achieved a minimun value at2.5μg/L Flu. Fhurthermore, carotenoids,chlorophyll-a, chlorophyll-b and dissolvable protein decreased from0.91mg/L,5mg/L,2.91mg/L for the reference to80.65μg/mg to0.52mg/L,2.57mg/L,1.8mg/L and50.36μg/mg repectively.The absorption quantity of nitrogen and iron first decreased (Flu:0～2.5μg/L) and then increased (Flu:2.5～200μg/L) with the increase of Flu, which was in accord with the change fo biomass. However, the absorbption quantity of phosphorus is impregnability.In addition, the residual CTAC exhibited a decrease(Flu;0～2.5μg/L) and ac increase (Flu:2.5～200μg/L), which descended from54μg/L to41.5μg/L. On the other hand, the absorption percentage of Flu increaseed along with the Flu concentration. When the concentration of Flu changed from2.5μg/L to200μg/L, the absorption percentageof Flu by Chlorella vulgaris rised from13.1%to88.8%.(3) The effect of the combined pollutant system of CTAC and Flu on the quantity of MAD showed an increase(Flu:0～2.5μg/L)and then a decrease (Flu:2.5～200μg/L) with the increase of Flu. The content of MDA rised from0.88ng/mL to1.45ng/mL (1.65times of the reference) when the concentration of Flu declined to2.5μg/L Furthermore, in the combined pollution system containing100μg/L CTAC and2.5μg/L Flu, the superoxide dismutase (SOD) first increased and then decrease. And the SOD activity was only0.082U/mg at24h, and then reached a maximum value of0.288U/mg at48h, finally dropped to0.216U/mg at96h. The change of peroxidase (POD) activity is similar to that of SOD activity. The catalase (CAT) activity decreased gradually from0.535U/mg at24h to0.051U/mg at96h. Meanwhile, content of O2-represented a trend of first decrease and then increase, which was442.75U/g at24h (144.50U/g more than vacant experiment),340.25U/g least at48h(102.50U/g less than24h), finally increased to980.15U/g at96h (3times of vacant experiment). The external NO reacted protective function to the antioxidant. The quantity of algal cell in the combined pollution system of100μg/L CTAC and2.5μg/L Flu increased from7.1×105cells/mL to21.6×105cells/mL (3times of initialization) when added with2μM sodium nitroprusside (SNP). |
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