Micro- and nanoplastics derived from environmental degradation of larger plastic debris can be ingested and accumulate in aquatic organisms, raising growing global ecological concerns. Toxicology studies of aquatic organisms predominantly use commercial formulations of micro- and nanosized polystyrene particles as model plastics. However, many of these commercially available formulations contain different preservatives, antimicrobials, or surfactants such as sodium azide, Tween 20, and sodium dodecyl sulfate, which may introduce artifacts in toxicity assessments. In this study, we carried out acute toxicity tests on Daphnia magna, using commercial 20 and 200 nm polystyrene nanoparticles (PS-NPs) containing 2 mM sodium azide as an antimicrobial preservative. The acute toxicities of nondialyzed PS-NPs, dialyzed PS-NPs, and sodium azide alone were compared. The results reveal that the acute toxicity of the complete commercial formulation of PS-NPs was mainly associated with sodium azide and not the particles themselves. The dialyzed PS-NPs did not cause mortality but significantly disrupted the swimming behavior of D. magna. As commercial PS-NPs are commonly and increasingly used in plastic toxicity assessments, these results highlight the importance of considering the impacts of the suspension matrix.

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The rate of nitrification within a laboratory-scale Biological Aerated Filtration treatment system at 48C was investigated during an exposure time of approximately four months (acclimatized experiments). In addition, shock experiments from 208C to 48C and from 48C to 208C were performed. The acclimatized experiments demonstrated that the exposure time the system remained at low temperature strongly affects the rates of nitrification. Nevertheless, the experiments showed that significant nitrification rates are maintained for up to 115 days at 48C.The rate of ammonia removal after an exposure time of 115 days at 48C was shown to be as high as 16% of the rate of removal observed at 208C. The 208C to 48C shock experiment demonstrated a 56% decrease in the rate of ammonia removal. On the other hand, the 48C to 208C shock experiment demonstrated an increase in the relative rates of ammonia removal of up to 300% when compared to rates of removal measured after 115 days at 48C. Thus, although the rates of nitrification have been shown to decrease significantly as a function of exposure time at 48C, the process has demonstrated important rates of ammonia removal at 48C for the approximate span of the North American winter.

In this study, photolytic and photocatalytic removal of the antibiotic sulfamethoxazole (SMX) under UVC radiation (λ=254 nm) was investigated. The light intensity distribution inside the batch photoreactor was characterized by azoxybenzene actinometry. The intensity of incident radiation was found to be a strong function of position inside the reactor. 12 mg L(-1) of SMX was completely removed within 10 min of irradiation under UVC photolysis, compared to 30 min under TiO(2) photocatalysis. COD measurement was used as an indication of the mineralization efficiency of both processes and higher COD removal with photocatalysis was shown. After 6h of reaction with photolysis and photocatalysis, 24% and 87% removal of COD was observed, respectively. Two of the intermediate photo-products were identified as sulfanilic acid and 3-amino-5-methylisoxazole by direct comparison of the HPLC chromatograms of standards to those of treated solutions. Ecotoxicity of treated and untreated solutions of SMX towards Daphnia magna was also investigated. It was found that a 3:1 ratio of sample to standard freshwater and a high initial concentration of 60 mg L(-1) of SMX were used to obtain reliable and reproducible results. The photo-products formed during photocatalytic and photolytic processes were shown to be generally more toxic than the parent compound.

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GaAs, a compound semiconductor commonly used in optoelectronic devices, is often subjected to wet-etching techniques during microelectronic device manufacture. In this work we investigated the wet etching of GaAs by H2O2−NH4OH−H2O solutions using a batch stirred-tank reactor and determined the intrinsic kinetics of the dissolution reaction. Increasing the NH4OH content produced a constant rate above a minimum concentration. The reaction rate was found, in the presence of excess NH4OH, to fit a rate equation r = k[H2O2]0.75 at 15, 25, and 40 °C with an activation energy of 33.7 kJ/mol. Using NaOH instead of NH4OH resulted in greatly reduced reaction rates, and it was concluded that the presence of the ammonium ion increases the rate by forming soluble compounds with oxidized species of Ga and As. Analysis of the surface by X-ray photon spectroscopy confirmed that samples etched in solutions containing NH4OH had considerably less oxide content on the surface than that etched in H2O2−H2O only. NH4OH does not directly react with GaAs but incorporates a second step into the overall etch reaction, facilitating the oxidation by H2O2 and the formation of soluble compounds.

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