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Persistent and mobile organic compounds (PMOCs) are highly soluble in water, thereby posing a threat to water resource quality. Currently, there are no methods that can accurately quantify guanidine derivative PMOCs, other than 1,3-diphenylguanidine (DPG) and cyanoguanidine (CG), in aqueous media. In this study, we developed a quantitation method that combines solid-phase extraction and liquid chromatography (LC)-tandem mass spectrometry to detect seven guanidine derivatives in aquatic environments and applied it to environmental water samples. Five LC columns were examined, and among them, a hydrophilic interaction liquid chromatography column was chosen owing to its suitable instrument detection limit and retention factor. Method precision was assessed using seven replicate analyses of river water. The corresponding analyte recoveries ranged from 73 to 137% (coefficient of variation = 2.1–5.8%). DPG and CG were detected in ultrapure water samples at levels up to 0.69 and 150 ng L−1, respectively; DPG and CG levels up to 44 and 2600 ng L−1, respectively, were detected in lake water, river water, sewage effluent, and tap water sampled in Western Japan. This is the first reported detection of DPG in the surface water of Japan, revealing that DPG and CG are ubiquitous compounds in aquatic environments. Moreover, this is the first study to detect 1-(o-tolyl)biguanide and N,N′′′-1,6-hexanediylbis(N′-cyanoguanidine) in water. This study provides a foundation for further research on the distribution, fate, and emission source of these pollutants, which is critical to maintain high water quality and to determine regulatory limits for these pollutants. Graphical Abstract

Water clarifier sludge was assessed as a capping material for preventing release of phosphorus from eutrophic pond sediments. Sediment incubation experiments were carried out over two months using five capping materials (sludge, sludge sintered respectively at 200, 400 and 600 degrees C, and sea sand) to evaluate the effect of sintering temperature. We also examined reduction in the nitrogen eluted from the sludge. Sludge, sludge sintered at 400 and 600 degrees C, and sea sand suppressed phosphorus release from sediments into the overlying water, whereas sludge and sludge sintered at 200 degrees C increased nitrogen release relative to that without capping. Sludge sintered at 600 degrees C was the most effective in reducing total nitrogen (TN) flux. Our experiments revealed that nitrogen and organic substances must be removed completely from sludge in order to avoid their release. The phosphate removal efficiency of sludge (including sintered sludge) was expressed in terms of Freundlich adsorption isotherms. The results showed that sludge sintered at 600 degrees C was suitable for use as a capping material since (1) its organic content (ignition loss) and TN were low (1.1% and 0.014 mg g(-1) dry, respectively), (2) its phosphorus adsorption capacity was 2.2 times higher than that ofunsintered sludge, and (3) it was effective in suppressing the diffusion of phosphorus and NH4+-N from sediments when used as a capping material.

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