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Two different test methods for assessing the toxicity of aminotriazole to Selenastrum capricornutum are compared. Growth medium composition is demonstrated to have a significant effect on the toxicity of aminotriazole. 相似文献
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The octachlorodibenzo-p-dioxin (OCDD) concentrations have been determined in aged samples of commercial pentachlorophenol (PCP), in wood protection formulations containing PCP and in wood treated with PCP as a preservative or as an anti-sapstain treatment. The concentrations of OCDD found in the various samples are within the range expected from the amount of commercial PCP initially present in the samples. In view of the known stability of OCDD the results are interpreted as indicating that the formulation, treatment and ageing processes have not led to any substantial conversion of PCP to OCDD; although one result indicates that outdoor exposure of treated samples increased the OCDD concentration by a factor of approximately 2 after years. Analysis of aged samples of treated wood indicate that OCDD is lost much less rapidly from the wood than PCP. 相似文献
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The TiO2-catalyzed photooxidation of arsenite (As(III)) to arsenate (As(V)) was studied in aqueous TiO2 suspensions using a solar simulator which emitted ultraviolet and visible radiations. The concentration of As(III) was varied between 50 microg l(-1) and 10 mg l(-1), and the concentration of TiO2 between 1 mg l(-1) and 50 mg l(-1). Total oxidation of As(III) to As(V) occurred within minutes. The concentration of As(III) declined exponentially which indicates first-order kinetics. In the pH range between 5 and 9 there was no significant influence of the pH of the suspension on the reaction rate. Batch experiments without irradiation showed that part of the arsenic was adsorbed on the TiO2 surface. When using 100 microg l(-1) As and between 1 mg l(-1) and 50 mg l(-1) TiO2, 8-39% of As(III) and up to 73% of As(V) were adsorbed by TiO2. As(III) was also oxidized by UV radiation in the absence of TiO2, but the reaction was slower than in the presence of TiO2 resulting in an irradiation time too long for practical use. In addition, oxidation of As(III) in the presence of TiO2 was also observed under solar irradiation within a few minutes. 相似文献
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Andreas J. Schindelin Fritz H. Frimmel 《Environmental science and pollution research international》2000,7(4):205-210
By means of simulated sunlight, the influence of natural organic matter (NOM) on the photochemical degradation of halogenated
pesticides in the absence and presence of nitrate as a precursor of the highly reactive OH radicals in aqueous solutions and
freshwater was investigated. Solutions of dichlorprop or terbutylazine (a) in phosphate-buffered demineralized water containing
nitrate and/or NOM and (b) in natural freshwaters were irradiated by a 1000-W Xe short-arc lamp. The collimated beam was filtered
using a combination of optical filters (WG 320 and WG 295) to simulate the solar spectrum under summer midday conditions.
In the absence of nitrate and NOM, the pesticides were degraded photolytically by simulated sunlight. The degradation rates
depended on the absorption spectrum in the UVB range and the quantum yield of the degradation. The photochemical degradation
of the pesticides was faster in the presence of nitrate due to the sunlight-induced formation of OH radicals. In the absence
of nitrate, low concentrations of NOM of a brownwater lake accelerated the degradation due to the formation of reactive species
by NOM. At higher concentrations of NOM, the inner filter effect of NOM lowered the degradation rates. In the presence of
50 mg l−1 nitrate, NOM decreased the degradation rate significantly. In case the natural water samples were used as a matrix
for the experiments (nitrate concentrations between 2 mg l−1 and 15 mg l−1, DOC concentrations below 2.3 mg l−1), NOM acted
mainly as a radiation filter and as a scavenger of OH radicals. As a consequence, in most freshwater systems, the accelerating
effect of NOM by the formation of reactive species is of minor importance compared to the inner filter effect and to radical
scavenging. 相似文献
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The results of analyses for polychlorodibenzofuran (PCDF) content in two samples of polychlorobiphenyl (PCB) from used electrical transformers are presented and discussed. In neither sample was there evidence for enhanced PCDF concentrations even though one of them had been subjected to overheating while in service. 相似文献
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Results of analyses of eight samples of technical pentachlorophenol conducted by three different analytical methods are presented and discussed. 相似文献
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The activity of a chemical in solution determines its tendency to move into other media. At low concentrations (<0.01M) it is generally considered to be linearly related to concentration. A hypothetical model based on the structure of liquid water is discussed which could cause deviations from this linearity in the ppb region, a concentration much lower than that normally investigated thermodynamically, but one of great importance environmentally. Headspace experiments are reported with carbon tetrachloride and chloroform in water at concentrations down to ~10?3 ppb but no such deviations were discerned. 相似文献
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Wood samples treated with technical pentachlorophenol (PCP), technical sodium pentachlorophenoxide (NaPCP) and octachlorodibenzo-p-dioxin have been exposed outdoors for periods up to years. Analysis of extracts from the samples show that photolytic reductive dechlorination of highly chlorinated dibenzo-p-dioxins to less chlorinated isomers occurs. However there is no discernible increase in polychlorodibenzo-p-dioxin concentrations in the technical PCP treated wood presumably because further photolytic reactions and volatilisation compete effectively with the photolytic formation. There is no evidence for formation of octachlorodibenzo-p-dioxin (OCDD) in technical PCP treated wood in this study, probably because photolytic destruction and volatilisation compete effectively with formation reactions when the initial OCDD concentration is relatively high. 相似文献
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