| Phenol, an important organic material, is considered as one of the most toxic pollutants and widespread both in terrestrial and aquatic ecosystems which causes a series of toxic effects in different organisms. Phenol and its derivatives are widely used in industries and they cause serious environment pollution. Moina macrocopa has a wide distribution in both tropical and temperate waterbody, and has been gaining importance as an alternative to Daphnia in ecotocicological evaluations. With a relatively thin-carapace, moina is sensitive to certain toxicants including heavy metals and is generally short-lived.The aim of this study is to investigate the responses of Cladoceran crustacean M. maocoropa to oxidative stress. We have analyzed the changes on body size, heart rate, reproduction capacity, the content of maglonydiadehyde (MDA), protein carbonyl derivates (PCO), DNA-protein crosslinks (DPC) and some biochemical parameters (including antioxidant enzyme activities, the key of enzyme on energy metabolism, and digestive enzyme activities, namely, SOD, CAT, GST, PK, LDH, SDH, GOP, GPT, Amylase, Lypase, Trypsinase and Protease), of waterfleas when exposed to different concentrations of phenol.The results demonstrated that:(1) 24-hour LC50 and 48-hour LC50 of phenol were 7.57 and 2.45 mg·L-1 respectively. According to the half lethal concentration (LC50), phenol concentrations were set in this study to range from 0.25 to 2.25 mg·L-1. The body size and heart rate gradually decreased with the increasing of phenol concentration. Under the life table parameters for M. macrocopa, progressively increased intrinsic rate of population growth (rm) and net reproductive rate (Ro) were observed when M. macrocopa were exposed to 0 mg/L to 1.25 mg·L-1 phenol, while mean generation time (T) showed a reverse trend. The further comparison showed that in the treated group the pre-breeding period, the productive period of waterflea are longer, and offspring numbers are larger than that in the control group. When exposed to 2.25 mg·L-1 phenol, it showed that the initial age of reproduction in M macrocopa was postponed.(2) SOD and CAT are considered the most important enzymes in the anti-oxidant system for invertebrate species. In this study, SOD activity was down-regulated at all exposure level compared to the control, while CAT activity showed a distinctly different pattern. CAT activity increased significantly when the exposure concentration is no more than 1.25 mg·L-1, and decreased when the exposure concentration is above that at 24 h post exposure. At 48h, however, CAT activity were down-regulated in all the treated groups. GST activity shows a similar trend to that of CAT. With the increasing of phenol concentration, MDA content, PCO content and DPC levels significantly decreased compared to the control.(3) To energy, after 24 and 48 h, glycogen, lipid reserves were significantly reduced compared to those of the controls from 0.75 to 2.25 mg·L-1. Protein content was increased at phenol concentrations more than 1.75 mg·L-1 treatment after 24 h. but after 48 h, the protein content was significantly higher than in the control in the 0.25 and 0.75 mg·L-1 treatment. Energy content decreased as phenol concentration increased, exposure to 2.25 mg·L-1. The activity of LDH gradually increased following the increase of the concentration of phenol and treatment duration. PK and SDH activities largely remained unchanged. After exposure, the activity of GOT showed an inverse "U" shape trend, and, to be specific, increased at 24h and decreased at 48 h. The activity of GPT was elevated, but there was no significant difference compared with controls. All these results indicated that phenol intoxication demands high level metabolic energy which leads to significant changes of the metabolic profiles of the daphnia, resulting in the shift to a certain extent of carbohydrate and protein catabolism. In gerneral, the LDH may be served as a biomarker to assess the biochemical toxicity of the phenolic contamination.(4) The activity of the four digestive enzymes in M. macrocopa varied across the different concentrations of phenol. Amylase activity had no significant changes compared with that of the control. Lipase activity level increased significantly in the groups treated with 0.25 mg·L-1 and 0.75 mg·L-1 phenol for 24 h. Trypsin content level increased significantly at 0.75 mg·L-1 for 48 h. Protease activity level decreased in all the treated groups at all the sampling time points except that 0.75 mg·L-1 group at 24 h post exporure. These results demonstrated that assimilation was inhibited in M. macrocopa under phenol stress. Results obtained by using light microscopy and transmission electron microscopy showed midgut cells exhibited distinct pathological changes and the microvilli of midgut cells were disordered and came off markedly. The data suggested that phenol is moderately toxic to M.macrocopa. But it seriously impairs the metabolic functions, resulting in alterations in biochemical constituents. |
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