Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publisher：Talanta Open  

The copper–cadmium reduction method has been applied to determine nitrogen compounds in heavily contaminated environmental water. However, there is an international demand to reduce the use of cadmium because it is harmful to humans and environment. Hence, a copper–zinc reduction continuous flow analysis system without using cadmium was developed for nitrogen-compound determination. However, the effects of seawater contaminants on this analytical method remains unknown. Therefore, in this study, the effects of contaminants on the developed method are investigated, and the applicability of the method to environmental water analysis is examined. Resultantly, interference due to magnesium precipitation is confirmed; however, this could be prevented by adjusting the concentration of the analytical reagent, i.e.,. ethylenediaminetetraacetic acid disodium. The measurement of certified reference materials under the new conditions, with precipitation countermeasures, show good results, with an accuracy of over 96 %. Additionally, a recovery study using actual environmental water afforded good results, with recovery of >95 % for all samples. These results indicate that the proposed method is an excellent, cadmium-free analytical method capable of analyzing environmental water as effectively as conventional methods.

DOI： 10.1016/j.talo.2024.100378

Scopus

Language：Japanese   Publisher：Society of Environmental Conservation Engineering  

<p>In order to establish a quick and simple analytical method for ammonium nitrogen without using phenol, which is a harmful substance, we developed a method involving continuous flow analysis （CFA）. To prevent interference by metal ions in the sample, ethylenediaminetetraacetic acid （EDTA） was added to the flow. A gas separator using a PTFE membrane filter was used to prevent EDTA interfering with the coloring mechanism and to avoid the effects of foreign substances on the measurement. Only ammonia in the sample is separated by the gas separator in the form of gaseous ammonia and is measured by the salicylic acid indophenol method; this enables analysis without using phenol, and with less susceptibility to inhibiting substances. Both this method and the conventional method using phenol were used to measure samples including seawater and industrial wastewater, and equivalent results were obtained. An evaluation of the method itself confirmed that there was no significant difference from the conventional method. These results suggest that our method offers the same measurement performance as the conventional method and can replace it.</p>

DOI： 10.5956/jriet.52.6_313

Language：Japanese   Publisher：Plants  

Most canopy-forming macroalgae have disappeared from temperate reefs in southern Japan, one of the ocean warming hotspots, but Sargassum nipponicum is surviving in this region. As this species’ annual shoots emerge from holdfasts during summer, both plant components may be highly tolerant to warm and nutrient-poor conditions in this season. The present study examined the effects of temperature and nutrient conditions on holdfast growth, shoot emergence from holdfasts, and shoot growth in S. nipponicum samples collected in Tanegashima Island, southern Japan. The summer temperature in this region (30 °C) allowed holdfast growth and shoot emergence but inhibited shoot growth. Nutrient-poor conditions had limited effects on the first two parameters but suppressed shoot growth. These results suggested that during warm summers and under nutrient-poor conditions in southern Japan, shoots can emerge from S. nipponicum holdfasts but cannot further grow. Additionally, nutrient loading from a nearby river was higher at the only site dominated by S. nipponicum, than at the other sites where this species was absent on Tanegashima Island. This was observed especially between autumn and winter, implying that such a nutrient-rich environment may contribute to shoot growth in S. nipponicum and to the persistence of its population in the area.

DOI： 10.3390/plants13121689

Scopus

PubMed

Language：Japanese   Publisher：Society of Environmental Conservation Engineering  

<p>Copper-cadmium reduced naphthylethylenediamine absorption spectrophotometry is one of the methods for analyzing nitrogen components in water, but it uses cadmium, a toxic substance, as a reducing agent. In this study, we developed a method to measure nitrogen components including nitrate nitrogen by reducing nitric acid and nitrite to ammonia using the copper-zinc reduction method with zinc instead of the copper-cadmium reduction method using continuous flow analysis（CFA）. Since the reagents used in the copper-zinc reduction inhibit the coloration of indophenol blue method, ammonia was separated from the inhibitors by an ammonia gas permeation method using a PTFE membrane filter to reduce the effect on the coloration. Comparison of the developed method with the conventional method showed that the lower detection limit of the instrument and the lower quantification limit of the developed method were equivalent to those of the conventional method. In addition, a good correlation was obtained by comparing the measurement results of actual samples such as seawater, environmental water, river water, and wastewater.</p>

DOI： 10.5956/jriet.53.3_157

Language：Japanese   Publisher：Ecological Modelling  

Phytoplankton growth can cause red tide, lowering water quality and damaging fisheries. The simple Lotka–Volterra model (LV model), estimating the population changes in different species, is often used to analyze the growth and competition of causative species. However, the LV model has not been sufficiently applied to examining the actual occurrence and development of red tides in the field. Therefore, the mechanism of seasonal dominant species replacement and applicability of the LV model were studied to analyze the competition between the harmful raphidophytes Chattonella marina and Heterosigma akashiwo. Sensitivity analysis was performed, and optimization method of competition coefficient (α) was discussed by comparison with measured data from culture experiments. We found that it is crucial to evaluate in advance the initial cell density conditions under which the population size changes concerning α (the order of root mean squared logarithmic error ≥ 10−2). Using this as a reference, we pointed that the initial cell density difference between the two species in co-culture experiments should be as large as possible. In addition, simulation analysis using the model revealed that growth rate (r) and carrying capacity (K) determine H. akashiwo dominance in spring, and the increase in α due to rising temperatures causes C. marina dominance in summer. Comparing α of C. marina with α of C. antiqua cited from a previous study found that the formation of red tides of C. marina less than that of C. antiqua can be explained by α that is 0.42 times smaller than α of C. antiqua. Moreover, the increase in α with increasing temperature is related to the physiological and ecological characteristics of C. marina, which is more likely to dominate the space suitable for growth with temperature rise. We consider that investigations of α, in particular, contributes to modeling various competition and more improving accuracy in analyses. These results provide valuable scientific findings on the occurrence and development of red tide flagellates and their analytical method.

DOI： 10.1016/j.ecolmodel.2024.110660

Scopus

Language：Japanese   Publisher：Japan Society on Water Environment  

<p>We developed an analysis method for total nitrogen using a copper-zinc reduction coil without cadmium by continuous flow analysis. In this study, we attempted to realize a total nitrogen analysis method without using harmful substances by combining the previously reported nitric acid analysis method using a copper-zinc reduction coil and by decomposition using potassium peroxodisulfate. The coefficient of determination was 0.9996, and the instrument limit of detection and the method limit of quantification were lower than the limit of quantification required for the measurement of environmental water and wastewater. In the analysis of environmental water and wastewater samples by this method, we were able to obtain results equivalent to those obtained by the conventional method. In addition, we conducted measurements at three facilities. Repeatability relative standard deviation was lower than 10%, suggesting the validity of this method.</p>

DOI： 10.2965/jswe.47.163

Language：Japanese   Publisher：Plants  

Ocean warming and the associated changes in fish herbivory have caused polarward distributional shifts in the majority of canopy-forming macroalgae that are dominant in temperate Japan, but have little effect on the alga Sargassum fusiforme. The regeneration ability of new shoots from holdfasts in this species may be advantageous in highly grazed environments. However, little is known about the factors regulating this in Sargassum species. Moreover, holdfast tolerance to high-temperature and nutrient-poor conditions during summer has rarely been evaluated. In the present study, S. fusiforme holdfast responses to the combined effects of temperature and nutrient availability were compared to those of sexually reproduced propagules. The combined effects of holdfast fragmentation and irradiance on regeneration were also evaluated. Propagule growth rate values changed from positive to negative under the combination of elevated temperature (20◦C–30◦C) and reduced nutrient availability, whereas holdfasts exhibited a positive growth rate even at 32◦C in nutrient-poor conditions. The regeneration rate increased with holdfast fragmentation (1 mm segments), but was unaffected by decreased irradiance. These results suggest that S. fusiforme holdfasts have a higher tolerance to high-temperature and nutrient-poor conditions during summer than propagules, and regenerate new shoots even if 1-mm segments remain in shaded refuges for fish herbivory avoidance.

DOI： 10.3390/plants10081522

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Society For Microbiology  

DOI： 10.1128/MRA.00608-20

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本防菌防黴学会  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Publisher：Microbiology Resource Announcements  

DOI： 10.1128/MRA.01666-18

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Publisher：(公社)におい・かおり環境協会  

充填塔型生物脱臭装置を適切に維持・運転するためには、装置の充填層に適切な水分と栄養塩類が維持されている必要がある。本研究では、ガス状VOC(揮発性有機化合物)を処理対象とする生物脱臭装置で供給される栄養塩成分として窒素源に着目し、栄養塩溶液を多孔性PVF(Polyvinyl formal)担体充填層に浸漬供給する装置での塩化アンモニウムの物質移動過程を、モデル浸漬実験により推定した。また、実際の生物脱臭装置における最適な浸漬条件の検索、また浸漬方式と通常装置で適用される散布方式との間での装置性能の比較を目的に、VOCガスの処理実験を行った。その結果、浸漬方式での栄養塩供給は、散布方式と比較して疎水性ガスであるトルエンの除去に有効であった。また、栄養塩溶液から充填担体への物質移動については、含水率75%を境に、高含水率側では分子拡散が、低含水率側では水分移動に伴う移流が、それぞれ主要な物質移動推進力となっていた。ただし、低含水率の充填層に対する実際の栄養塩移動量は、水分移動量から推定される移動量よりも低くなる傾向にあった。浸漬頻度を上げると充填層に過剰な菌体増殖が生じる傾向にあり、その原因は窒素源よりも水分の過剰な存在にあると推察された。過剰な菌体増殖を抑制するためには、充填層の含水率が75%を下回る程度まで乾燥してから浸漬操作を実施すべきと考えられた。(著者抄録)

Publisher：日本防菌防黴学会  

<p>　A marine raphidophyte <i>Heterosigma akashiwo</i> is a causative agent of harmful microalgal blooms, which often cause the massive mortality of aquacultured finfish. In the present study, the Pacific oyster <i>Crassostrea gigas</i> was reared with <i>H. akashiwo</i>, and effect of the microalga on filter-feeding behavior and microflora of the gastrointestinal tract was investigated. The intake of the raphidophyte cells inhibited the molluscan filter-feeding activities, suggesting the negative physiological effect of the microalgal cell contents. However, the bivalves ingested the <i>H. akashiwo</i> cells to the same extent as the diatom <i>Chaetoceros calcitrans</i>, a non-harmful indicator to estimate the filtration rate, showing a continuation of their non-selective ingestion of the phytoplankton. Microflora of the oyster soft tissue was dominated by bacteria affiliated with the family <i>Rhodobacteraceae</i>, some of which are associated with microalgae. In addition, the Bacteroidetes species, in which algicidal bacteria are included, were also found in the bivalve individuals exposed to <i>H. akashiwo</i>. These results suggested that the ingested phytoplankton affected the microbial flora in the gastrointestinal tracts, some constituents of which helped the mollusc assimilate the ingested red tide phytoplankton. This study will provide beneficial information to clarify mechanisms by which the oyster evades the ichthyotoxicity of harmful microalgae and the participation of the intestinal microorganisms in these processes.</p>

DOI： 10.4265/bio.22.79

Scopus

PubMed

Publisher：Japan Association on Odor Environment  

<p>In biofiltration systems for gaseous pollutants control, appropriate range of moisture and nutritious ingredients have to be maintained in a packed bed to obtain a stable performance. In this study, mass-transfer mechanisms of ammonium chloride in the biofiltration, which treats gaseous VOCs (volatile organic compounds) and which has the packed bed of porous PVF (polyvinyl formal) irrigated by soaking, were evaluated through a simplified soaking experiment focused on nitrogen source as the key constituent. And a series of experiments on biofiltration of gaseous VOCs was carried out for the following two purposes : to specify an optimal condition of soaking-irrigation, and to compare the performance between the system with soaking-irrigation and that with trickling-irrigation which is commonly applied. Results showed that soaking-irrigation was more effective than trickling-irrigation in removal of gaseous toluene, a hydrophobic component. With regarding 75% of moisture content of packed bed as the boundary value, molecular diffusion and irrigating-water advection were dominant mass-transfer mechanisms of nutritious materials in higher and lower moisture content, respectively. However, the amount of mass-transfer of nutritious material in lower moisture content tended to be lower than that is expected by the estimation under the amount of advection with water transfer. Excess frequency of soaking-irrigation led to excess biomass growth in the packed bed, and this is possibly derived not from excess nitrogen source but from water accumulation. Soaking-irrigation had better be conducted after that moisture content of packed bed is confirmed to be below 75%.</p>

DOI： 10.2171/jao.48.25

Publisher：日本防菌防黴学会  

<p>　Natural biodegradation of heavy oil in the marine environment can be accelerated by the addition of nutrients or seeding of pre-selected microorganisms. In this study, a microcosm experiment was conducted to investigate the effects of inorganic nutrient supplementation (biostimulation) and bacterial consortium amendment (bioaugmentation) on the natural degradative processes of artificially contaminated sediment. Our results revealed that the addition of nutrients had greater effect on remediation than the addition of bacterial cells. Supplementation of inorganic nutrients promoted and sustained the growth of oil-degrading and heterotrophic bacteria throughout the experimental period. Highest reduction in the total petroleum hydrocarbons, and of their components, <i>n</i>-alkanes, polycylic aromatic hydrocarbons (PAHs) and alkyl PAHs, were obtained in the biostimulated microcosms. Changes in the bacterial community were monitored by the PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) method targeting the 16S rDNA gene. Results revealed different responses of the bacterial community to the addition of heavy oil and remediation agents. Shifts in the bacterial communities in the seawater were more dynamic than in the sediment. Results of this study showed that addition of remediation agents significantly enhanced the natural biodegradation of heavy oil in a sediment-seawater microcosm trial.</p>

DOI： 10.4265/bio.22.187

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)