Toxicity of Fluoranthene and Its Biodegradation by Cyclotella caspia Alga

Fluoranthene Is one of the polynuclear aromatic hydrocarbons with four benzene rings. Because of Its toxicity, mutagenlclty, and carclnogenlclty, fluoranthene Is on the black lists of 129 and 68 priority pollutants established by US Environmental Protection Agency and the People＇s Republic of China, respectively. In recent years, the amount of fluoranthene In the aquatic environment has been Increasing with Increases In anthropogenlc discharge. Based on the biological investigation of tidal water In the Futlan mangrove, Cycioteila ~aspla was selected as the dominant algal species to determine the toxicity of fluoranthene towards C. caspla alga and to Investigate the blodegradatlon of fluoranthene by C. caspla under pure culture. The toxicity experiment showed that the 96-h EC50 value for fluoranthene was 0.2 mg/mL. Four parameters, namely C. caspla algal growth rate, chlorophyll （Chl） a content, cell morphology, and superoxlde dlsmutase （SOD） activity, were chosen as Indices of toxicity and were measured at 6 d （144 h）. The results showed that： （Ⅰ） the toxicity of fluoranthene towards C. caspla alga was obvious; （Ⅱ） C. caspla algal growth rate and Chl a content decreased with Increasing concentrations of fluoranthene; and （Ⅲ） the rate of cell deformation and SOD activity Increased with Increasing concentrations of fluoranthene. The blodegradatlon experiment showed that： （Ⅰ） the rate of physical degradation of fluoranthene was only 5.86%; （Ⅱ） the rate of blodegradatlon of fluoranthene on the 1st and 6th days （l.e. at 24 and 144 h） was approximately 35% and 85%, respectively; and （Ⅲ） the blodegradatlon capability of C. caspla alga towards fluoranthene was high. It is suggested that further Investigations on the toxicity of fluoranthene towards algae, as well as on algal blodegradatlon mechanisms, are of great Importance to use C. caspla as a biological treatment species In an organic wastewater treatment system.

Oral contrast agents lead to underestimation of dose calculation in volumetric-modulated arc therapy planning for pelvic irradiation

Background:The effects of oral contrast agents(OCAs)on dosimetry have not been studied in detail.Therefore,this study aimed to examine the influence of OCAs on dose calculation in volumetric-modulated arc therapy plans for rectal cancer.Methods:From 2008 to 2016,computed tomography(CT)images were obtained from 33 rectal cancer patients administered OCA with or without intravenous contrast agent(ICA)and 14 patients who received no contrast agent.CT numbers of organs at risk were recorded and converted to electronic densities.Volumetric-modulated arc therapy plans were designed before and after the original densities were replaced with non-enhanced densities.Doses to the planned target volume(PTV)and organs at risk were compared between the plans.Results:OCA significantly increased the mean and maximum densities of the bowels,while the effects of ICA on these parameters depended on the blood supply of the organs.With OCA,the actual doses for PTV were significantly higher than planned and doses to the bowel increased significantly although moderately.However,the increase in the volume receiving a high-range doses was substantial the absolute change of intestine volume receiving≥52 Gy:1.46[0.05-3.99,cubic centimeter range:-6.74 to 128.12],the absolute change of colon volume receiving≥50 Gy:0.34[0.01-1.53 cc,range:-0.08 to 3.80 cc].Dose changes due to ICA were insignificant.Pearson correlation showed that dose changes were significantly correlated with a high intestinal volume within or near the PTV(ρ>0.5,P<0.05)and with the density of enhanced intestine(ρ>0.3,P<0.05).Conclusions:Contrast agents applied in simulation cause underestimation of doses in actual treatment.The overdose due to ICA was slight,while that due to OCA was moderate.The bowel volume receiving≥50Gy was dramatically increased when OCA within the bowel was absent.Physicians should be aware of these issues if the original plan is barely within clinical tolerance or if a considerable volume of enhanced intestine is within or near the PTV.