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Environmental DNA (eDNA) is a useful tool for biological monitoring of a target species by detecting DNA contained in environmental samples. However, the suppression of eDNA degradation after sample collection is a major issue when estimating the presence of a target species. Recently, benzalkonium chloride (BAC) was shown to dramatically suppress the degradation of eDNA in fish species from freshwater environments. However, the effect of this inexpensive reagent has not yet been tested in the other fish and shellfish species. We examined changes in eDNA concentrations for three target species (Corbicula japonica, Lateolabrax japonicus, and Anguilla japonica). eDNA was measured in samples containing added BAC. The effects of storage temperature (25 C, 4 C, and −30 C) and storage periods (periods up to 21 d) were also measured to determine how sample degradation was affected. We observed that BAC addition was effective in suppressing eDNA degradation, and its influence was similar among species but not storage temperatures. The concentrations of eDNA with BAC for all three species did not decrease with storage period, except for L. japonicus at 25 C and 4 C. Our results suggest that BAC affects eDNA degradation universally for a variety of species inhabiting both freshwater and brackish water.

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The removal of NO by absorption in manganese zirconium oxide (Mn–Zr oxide) was investigated in both the presence and absence of gaseous O2. The Mn–Zr oxide at Mn/Zr = 1 exhibited a high NO absorption rate and capacity at 200 °C. The absorption was promoted in the presence of O2. The absorption capacity was not strongly affected by the NO concentration (75—900 ppm) and W/F (0.125—1 g s cm−3). An infrared analysis of the absorbed species indicated that the absorption proceeds as the formation of nitrate in the bulk solid. The absorption and desorption were reversible, and the oxide solid was recovered upon heating a preabsorbed sample at 400 °C. Although the amorphous phase of the Mn–Zr oxide which is formed after heating at 450 °C is effective for NO absorption, due to good mixing of manganese oxide and zirconium oxide, heating at higher temperatures (≥550 °C), leading to a decrease in the surface area and crystallization of single oxides, resulted in a decrease in the absorption capacity. NO removal appears to proceed by the oxidation of NO on the Mn sites, and a subsequent absorption at the Zr sites as (NO3)− species.