Kohji Hayase

Vertical distribution of fluorescent organic matter along with AOU and nutrients in the equatorial Central Pacific

Abstract The vertical profiles of fluorescent organic matter were studied at five stations in the equatorial Central Pacific. At every station, seawater fluorescence was low in the surface layer, indicating photochemical decomposition of fluorescent organic matter. Seawater fluorescence increased steeply with depth to a maximum at about 300 m depth and then decreased slightly, showing a minimum at 500–600 m depth, and then increased again slightly, exhibiting a broad maximum around 1000 m depth; thereafter it was almost constant or decreased slightly. This vertical distribution is similar to that of AOU, nitrate and phosphate. The observed linear correlations between fluorescence intensity and AOU, nitrate and phosphate in the middle layer (300–1000 m depth) are consistent with results in the North Pacific and the coastal seas of Japan. Among the parameters, the linear relation between AOU and fluorescence intensity is highest. Since AOU is a parameter of oxygen consumption, the high correlation between AOU and fluorescence confirms our previous observation that fluorescent organic matter is regenerated in the water column by oxidation and remineralization of organic substances on the sinking particles, as in the case of nutrients. On the other hand, a contribution of the fluorescent organic matter to the dissolved organic matter with regard to oxygen consumption in the water column is discussed in conjunction with “Redfield” ratios in the ocean.

Sedimentary humic acid and fulvic acid as surface active substances

Abstract Surface tension of sedimentary fulvic acid (FA) and humic acid (HA) with molecular weight from 300,000 was measured at 5°C and 25°C, over a wide range of concentrations (0.114-107.4 g/l) at pH 8. HA was in the form of sodium humate. Surface tension decreases with an increase in HA and FA concentration and both HA and FA were found to be surface active materials with FA exhibiting the lowest surface tension (31 dynes/cm). Plots of surface tension vs. log concentration gave two straight lines with a break at a certain concentration similar to surfactants. From the concentration at the break point, aggregation concentration (AGC) was determined. For HA with molecular weight above 10,000, the AGC decreased with an increase in molecular weight. The more hydrophobic the HA, the greater was the tendency to form aggregates. Surface excess (surface concentration) was determined (2.3 × 10−10−5.5 × 10−10mol/cn2) from the slope of the plot of surface tension vs. log concentration for concentrations lower than the AGC. Adsorption of HA into the surface layer increased with increasing molecular weight of HA.

Sedimentary humic acid and fulvic acid as fluorescent organic materials

Abstract Fluorescence and absorption spectra of sedimentary humic acid (HA) and fulvic acid (FA), with molecular weights ranging from 300,000, were measured at 20°C and pH 8. The maximum excitation and emission wavelengths of HA were longer than those of FA, being independent of molecular weight. The excitation and emission maxima can be utilized to differentiate between sedimentary HA and FA. It is suggested that the fluorophors in HA are of a higher molecular weight aromatic groups than those in FA. Smaller molecules were found to have a greater fluorescence than larger ones for sedimentary humic substances and this phenomenon is similar to those obtained for humic substances of terrestrial origin. The absorption coefficient (1/g/cm) of HA decreased, while that of FA increased with the increase in molecular weight. It was shown that fluorescence intensity per weight concentration unit of HA increases and that of FA decreases with increasing absorption coefficient.

Vertical distribution of fluorescent organic matter in the North Pacific

Abstract The vertical distributions of fluorescent organic matter were investigated at three stations in the North Pacific. Fluorescence intensity was low in the upper layer, and increased rapidly to a maximum at ∼ 1000-m depth. This vertical profile is similar to that of phosphate and nitrate; in the water column above the fluorescence maximum, fluorescence varies linearly with phosphate, nitrate and silicate. This is the same trend that has been reported for fluorescence and nutrients in the coastal seas of Japan. It is suggested that fluorescent organic matter is degraded in the euphotic zone and regenerated in the water column by degradation of organic matter on the settling particles as in the case of the nutrients. When deeper water was irradiated with UV light, the intensity of fluorescence decreased rapidly with time, implying that photodegradation may be primarily responsible for degradation of the fluorescent substances in the upper layers.

Behavior of natural fluorescence in Sagami Bay and Tokyo Bay, Japan — vertical and lateral distributions

Abstract The vertical distribution of natural fluorescence was investigated at one location in Sagami Bay, Japan. Natural fluorescence showed low values in surface seawater, increasing with depth. Linear relations were observed between natural fluorescence and nutrients, such as phosphate and nitrate. It is suggested that natural fluorescence resulting from marine humic substances can behave in a manner similar to phosphate and nitrate in the water column. Linear relations with negative slopes were found between salinity and natural fluorescence at several locations in Tokyo Bay, Japan. This indicates that natural fluorescence in this area results from terrestrial humic substances and is dispersed mainly by mixing of water masses. Fluorescence and absorption spectra of the seawater in Tokyo Bay showed spectra similar to sedimentary fulvic acid from Tokyo Bay. Fluorescence/absorbance ratios were nearly constant for the seawater samples in Tokyo Bay.

Mechanism of the desmutagenic effect of humic acid

The mechanism of an apparent desmutagenic effect of humic acid was investigated. Firstly, components of humic acid (resorcinol, vanillin, vanillic acid, ferulic acid, protochatechuic acid and benzoic acid) were tested and were not found to show a desmutagenic effect. By contrast, lignin did show a desmutagenic effect. The desmutagenic effect of humic acid was decreased by ozone treatment, and the degree of decrease corresponded with a decrease in KMnO4 consumption. Benzo[a]pyrene and humic acid were incubated at 37 degrees C for 1 h and extracted by ethyl acetate and the extract was investigated by gas chromatography (GC). The peak of the decomposition product did not appear, but the amount of benzo[a]pyrene was decreased. This suggests that the desmutagenic effect of humic acid was caused by adsorption of benzo[a]pyrene by humic acid rather than by decomposition of benzo[a]pyrene. Humic acid had the largest adsorption activity at its critical micelle concentration (CMC), while adsorbed benzo[a]pyrene could be released by ultrasonication. Fulvic acid and water-soluble humic substance showed a slight inhibitory effect on the mutagenicity of benzo[a]pyrene.

Effects of temperature on the distribution of 1-alcohols in aqueous SDS micellar solutions and ISA (Interaction of Surfactant and Additive) Coefficients

Abstract The distribution coefficients (K) of alcohols (1-butanol, 1-pentanol, 1-hexanol, and 1-heptanol) between the aqueous and sodium dodecyl sulfate (SDS) micellar phases at 40 and 55°C were determined in addition to that at 25°C. The standard free energy change (ΔG°p) of penetration of the alcohol from the aqueous to the micellar phase was obtained using the equation ΔG°p = -RT ln(K). There is a linear relation between ΔG°p and the carbon number of the alcohols, and the increment in ΔG°p per methylene group slightly decreases with increasing temperature. The standard enthalpy change (ΔH°p) and entropy change (ΔS°p) of penetration of the alcohol were estimated at 10, 25, 40, and 55°C by the use of temperature variation of the K and the Gibbs-Helmholtz equation. The fact that both ΔH°p and ΔS°p become less positive with the increase in temperature indicates that at lower temperature the penetration of the alcohol into micelle exhibits a greater entropy dependence. Estimated values of ΔH°p were compared with calorimetrical values. At 40 and 55°C, similar to that at 25°C, linear relations are observed between K and critical micelle concentration (CMC) decrease upon the addition of the alcohols. From the linear relations, ISA (interaction of surfactant and additive) coefficients defined as d ln(CMC)/dYa = (ISA)K were obtained to be −0.95 and −0.56 at 40 and 55°C, respectively, where Ya is the mole fraction of the alcohol in the aqueous phase, d ln(Q)/dXa was estimated from ISA, where Q is the degree of ionization of ionic micelles, and Xa is the mole fraction of the alcohol in the micellar phase. The theoretical value of d ln(Q)/dXa from ISA was compared with the experimental one, and a good agreement was obtained between them.

Adsorption of mutagens by humic acid.

Humic acid inhibited the mutagenicity of various mutagens. The inhibitory effect was desmutagenic, heat-resistant and increased with an increase of the humic acid molecular weight. Typical monomeric components of humic acids had no desmutagenic effect. The desmutagenic effect of humic acid was caused by adsorption of mutagen, not by decomposition of mutagen. The adsorption activity was largest at its critical micelle concentration and the adsorbed mutagen was released by ultrasonication. Humic acids exist in natural environment in large amounts and may play an important role for natural purification by adsorption of mutagens.

Determination of organically-associated trace metals in estuarine sea-water by solvent extraction and atomic-absorption spectrometry.

Chloroform extraction of trace metals (Ni, Cu, Mo, Mn, Cd and Pb) in estuarine sea-water was studied at pH 8 and pH 3, on the basis that the metals would be associated with dissolved organic matter (DOM), which has recently been characterized by reversed-phase liquid chromatography. Ni, Cu, Mo and Mn were extracted more at pH 8 than at pH 3. Cd and Pb were not associated with the DOM at either pH 8 or 3. The percentage of the total dissolved trace metals in sea-water associated with DOM varied from 0 to 14%. The metals extracted into chloroform at pH 8 were assumed to be associated with neutral or weakly basic DOM while at pH 3 they could be associated with either the neutral (or weakly basic) DOM or two types of acidic DOM.

Monolayer properties of sedimentary humic acid at the air—water interface

Abstract Pressure-area measurements were carried out at 25°C of sedimentary humic acid (HA), which was fractionated into five molecular weight ranges, at an air—water interface. Surface pressure—area curves of the HA exhibited a typical monolayer characteristic at the air—water interface. The limiting specific area of the HA decreased with the increase in molecular weight. Carbon numbers for the thickness of the monolayers were calculated as 23–67 for the molecular weight fractionated HA. HA appears to be linear rather than spherical. Compressibility decreased with increasing molecular weight. Collapse pressure increased and collapse specific area decreased with the increase in molecular weight. The four monolayer properties of unfractionated sedimentary HA exhibited values similar to those of the calculated average HA, which were computed from the molecular weight fractionated HA and their weight percentages. Pressure-area measurements can be employed as a new effective method for the study of physicochemical properties of HA.