Partition of biocides between water and inorganic phases of renders with organic binder

Equilibria of semi-volatile isothiazolinones between air and glass surfaces measured by gas chromatography and Raman spectroscopy

Trace amounts of semi-volatile organic compounds (SVOCs) of the two isothiazolinones of 2-methylisothiazol-3(2H)-one (MIT) and 2-octyl-4-isothiazolin-3-one (OIT) were detected both in the air and on glass surfaces. Equilibria of SVOCs between air and glass were examined by solid phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS). Surface to air distribution ratios of K_sa for MIT and OIT were determined to be 5.10 m and 281.74 m, respectively, suggesting more abundant MIT in the gas phase by a factor of ∼55. In addition, a facile method of silver nanocube (AgNC)-assisted surface-enhanced Raman scattering (SERS) has been developed for the rapid and sensitive detection of MIT and OIT on glass surfaces. According to MIT and OIT concentration-correlated SERS intensities of Raman peaks at ∼1585 cm^-1 and ∼1125 cm^-1, respectively. Their calibration curves have been obtained in the concentration ranges between 10^-3 to 10^-10 M and 10^-3 to 10^-11 M with their linearity of 0.9986 and 0.9989 for MIT and OIT, respectively. The limits of detection (LODs) of the two isothiazolinones were estimated at 10^-10 M, and 10^-11 M for MIT and OIT, respectively. Our results indicate that AgNC-assisted SERS spectra are a rapid and high-ultrasensitive method for the quantification of MIT and OIT in practical applications. The development of analytical methods and determination of the Ksa value obtained in this study can be applied to the prediction of the exposure to MIT and OIT from various chemical products and dynamic behaviors to assess human health risks in indoor environments.

Photochemical fate of medetomidine in coastal and marine environments

Medetomidine has been authorized in ship hull paints as an antifouling biocide under the biocidal product regulation in Europe since 2016. Its release into marine systems causes concerns over persistence and toxicity. However, the environmental fate of medetomidine has not been fully investigated. In this study, the photodegradation of medetomidine under natural sunlight conditions was investigated using collected coastal and sea waters. In addition, the phototransformation of medetomidine with reactive species (i.e., singlet oxygen, excited triplet state organic matter, and hydroxyl radicals) under UVA light was examined. Photoproducts were isolated by high-performance liquid chromatography (HPLC), identified by a combination of nuclear magnetic resonance (NMR) spectroscopy and time-of-flight mass spectrometry (qTOF), and reaction mechanisms were proposed. The results show that medetomidine is a neutral base (pKa of protonated form = 7.2) that leads to two different protonation states in the aquatic environment. Photodegradation of neutral medetomidine was dominated by reaction with singlet oxygen, while protonated medetomidine was relatively photostable. The contribution of reactive species to the overall photodegradation of neutral medetomidine was calculated to provide an assessment of phototransformation of medetomidine. The half-live of medetomidine was < 1.5 days in natural waters (pH_coastal = 8.3; pH_sea = 8.1) under sunlit near-surface conditions, suggesting that it is not persistent in the aquatic environment. Because medetomidine has a relatively short half-life in sunlit aquatic ecosystems, a number of products, such as 2-(2,3-dimethylphenyl)propanamide, can be formed by photochemical reactions of medetomidine, with unknown consequences for marine and coastal waters.

Adsorption–desorption behavior of carbendazim by sewage sludge-derived biochar and its possible mechanism

Biochar application in agricultural soil for environmental remediation has received increasing attention, however, few studies are focused on sewage sludge based biochar. The present study evaluated the effect of raw sewage sludge and sewage sludge based biochars produced at different pyrolysis temperatures (100–700 °C) on the adsorption–desorption of carbendazim in soil. Sewage sludge derived biochar significantly enhanced the sorption affinity and limited the desorption capacity of the soil for carbendazim. A maximum removal efficiency of 98.9% and a greatest value of 144.05 ± 0.32 μg g⁻¹ sorption capacity occurred in soil amended with biochar pyrolyzed at 700 °C (BC700). As the pyrolysis temperature and the amendment rate of biochars increased, the sorption of carbendazim was promoted and desorption was further inhibited. The adsorption–desorption hysteresis index of carbendazim was consistently higher in soils amended with biochars (>0.85) than in the unamended soil (0.42–0.68), implying that carbendazim could be immobilized in soil amended with sewage sludge derived biochars. The partition effect was dominant in the sorption process for carbendazim in the biochar–soil mixtures. This study will be helpful for the disposal of sewage sludge and its utilization, and it is the first report for the study the sorption–desorption process of carbendazim in soil amended with sewage sludge derived biochar. Furthermore, these findings may be also useful for understanding the distribution and transport of carbendazim in the environment and will be of great significance in remediation strategies for contaminated soil.

Biochar application in agricultural soil for environmental remediation has received increasing attention, however, few studies are focused on sewage sludge based biochar.