Although research regarding antibiotic resistance genes (ARGs) in aquaculture environments has gained increasing scientific interest, further studies are required to understand the abundances and removal mechanisms of ARGs during the entire rearing period of shrimp aquaculture. Thus, in this study, abundances, distributions and removal rates of ARGs in different environmental compartments of intensive shrimp farms in South China were investigated during the entire rearing period. The results indicated that sul1 and cmlA were the predominant ARGs in the water and sediment samples. Additionally, the total abundance of ARGs was higher in shrimp pond water than in the source water and farm effluent. Moreover, sediment samples indicated significantly higher ARG abundances than water samples from the shrimp ponds (P?<?0.05). Environmental factors were found to significantly affect the distribution of ARGs in shrimp rearing environments. Furthermore, stable ponds aided the removal of ARGs from shrimp pond water. This study accounted for temporal variations in ARG abundances as well as removal of ARGs in different environmental compartments during the entire shrimp rearing period. However, additional research is required to optimize the water treatment process for removal of ARGs from the aquaculture. 相似文献
Spatial variations of Cr, Cu, Hg, Ni, Pb, and Zn in the surface sediments from 34 stations of the Kaohsiung coastal zone southwestern Taiwan were studied to address the current pollution status, sediment quality, and potential ecological risk. The study revealed that the concentrations of sediment metals in Kaohsiung Harbor were alarmingly high compared to the other region of Kaohsiung coast. The concentrations of Cr, Cu, Hg, Ni, Pb, and Zn in the harbor sediments were as high as 351, 247, 1.93, 61.8, 60.9, and 940 mg kg−1, respectively. The current situation of metal pollution was assessed by different pollution indices and results showed moderate to severe enrichment of Cu, Hg, and Zn in the harbor sediments. According to the degree of contamination, pollution load index, and contamination severity index, the sediments from the inner Kaohsiung Harbor show high degree and high severity of metal contamination, while the rest of Kaohsiung coastal areas show uncontaminated or low-level pollution. Results of mean ERM quotient and potential ecological risk index also indicated that the harbor sediments posed a 49% probability of biological toxicity and very high ecological risk. The toxic units indicated that the negative biological effects of the six metals in the harbor sediments were Zn > Cu > Cr > Ni > Hg > Pb. In contrast to Kaohsiung Harbor as a trap where considerable amount of anthropogenic metal loadings accumulated in sediments, low metal concentrations were observed in most Kaohsiung coastal sediments. It probably resulted from the limited fine-grained sediment deposition. In the wave-dominated Kaohsiung coastal zone, fine-grained sediments associated with polluted metals tend to be easily resuspended and transported offshore via waves and wave-induced currents. The results of this study can provide valuable information for river and coastal zone management.
In order to give an effective and rapid analysis of the photochemical pollution and information for emission control strategies, a photochemical box model (PBM) was applied to one moderate summer episode, 11 July 1996, and one typical winter episode, 3 December 1996, in the center of Tokyo, Japan. The box model gave a good prediction of the photochemical pollution with minimal investment. As expected, the peak ozone in summer is higher than in winter. The NOx concentrations in winter are higher than those in summer. In summer, NO and NO2 have one peak in the morning. In winter, NO and NO2 show two peaks during the day. Three model runs including no reactions, a zero ozone boundary condition and dark reactions were conducted to understand the photochemical processes. The effects of emission reduction on the formation of the photochemical pollution in the center of Tokyo have been studied. The results show that the reduction of NMHC emission can decrease the ozone, however, the reduction of NOx emission can increase the ozone. It can be concluded that if the NOx emission are reduced, the reduction of NMHC should be more emphasized in order to decrease the ozone concentration in the center of Tokyo, Japan, especially the reduction of the NMHC from stationary source emission. 相似文献
A kinetic model is developed for de novo synthesis of PCDD/F from carbon in incinerator fly ash. The main mechanistic steps considered in the model are carbon gasification, PCDD/F formation, desorption and degradation. Rate equations are derived which can relate PCDD/F formation with process variables including carbon concentration of fly ash, partial pressure of oxygen, reaction temperature and time. The kinetic model has been verified using laboratory de novo synthesis data reported in the literature. When the model is applied to industrial incinerator conditions, PCDD/F formation levels of 0.1-0.5 microg/N m3 in the gas phase and 0.1-1.2 microg/g in the solid phase are calculated, and both are in good agreement with incinerator measurements. 相似文献
Heavy metal-contaminated sediments posed a serious threat to both human beings and environment. A biosurfactant, rhamnolipid, was employed as the washing agent to remove heavy metals in river sediment. Batch experiments were conducted to test the removal capability. The effects of rhamnolipid concentration, washing time, solution pH, and liquid/solid ratio were investigated. The speciation of heavy metals before and after washing in sediment was also analyzed. Heavy metal washing was favored at high concentration, long washing time, and high pH. In addition, the efficiency of washing was closely related to the original speciation of heavy metals in sediment. Rhamnolipid mainly targeted metals in exchangeable, carbonate-bound or Fe-Mn oxide-bound fractions. Overall, rhamnolipid biosurfactant as a washing agent could effectively remove heavy metals from sediment.
