Influence of humic substances and iron and aluminum ions on the sorption of acetamiprid to an arable soil.

Humic substances (HS) in soil and sediments, and surface water influence the behavior of organic xenobiotics in the environment. However, our knowledge of the effects of specific HS fractions, i.e., humic acids (HAs), fulvic acids (FAs), and humin (HM), on the sorption of organic xenobiotics is limited. The neonicotinoid insecticide acetamiprid is thought to contribute to the collapse of honeybee colonies. To understand the role that soil organic matter plays in the fate of acetamiprid, interactions between acetamiprid and the above HS fractions were examined. Batch experiments were conducted using various combinations of a field soil sample and the above 3 HS fractions prepared from the same soil, and differences in isotherm values for acetamiprid sorption were investigated based on the structural differences among the HS fractions. The sorption of acetamiprid to soil minerals associated with HM (MHM) (Freundlich isotherm constant, Kf: 6.100) was reduced when HAs or FAs were added (Kf: 4.179 and 4.756, respectively). This can be attributed to hydrophobic interactions between HM and HAs or FAs in which their dissociated carboxyl and phenolic groups become oriented to face the soil solution. The amount of acetamiprid that was adsorbed to (MHM+HA) or (MHM+FA) increased when aluminum ions were added (Kf: 6.933 and 10.48, respectively), or iron ions were added (Kf: 7.303 and 11.29, respectively). Since acetamiprid has no affinity for inorganic components in soil, the formation of HS-metal complexes by cation bridging may have oriented the hydrophobic moieties in the HAs or FAs to face the soil solution and may also have resulted in the formation of dense structures, resulting in an increase in the amount of acetamiprid that becomes adsorbed to these structures. These results highlight the importance of interactions among soil components in the pedospheric diffusion of acetamiprid.

Novel 4-methyl-2-oxopentanoate reductase involved in synthesis of the Japanese sake flavor, ethyl leucate.

Ethyl-2-hydroxy-4-methylpentanoate (ethyl leucate) contributes to a fruity flavor in Japanese sake. The mold Aspergillus oryzae synthesizes leucate from leucine and then the yeast Saccharomyces cerevisiae produces ethyl leucate from leucate during sake fermentation. Here, we investigated the enzyme involved in leucate synthesis by A. oryzae. The A. oryzae gene/cDNA encoding the enzyme involved in leucate synthesis was identified and expressed in E. coli and A. oryzae host cells. The purified recombinant enzyme belonged to a D-isomer-specific 2-hydroxyacid dehydrogenase family and it NADPH- or NADH-dependently reduced 4-methyl-2-oxopentanate (MOA), a possible intermediate in leucine synthesis, to D-leucate with a preference for NADPH. Thus, we designated this novel enzyme as MOA reductase A (MorA). Furthermore, an A. oryzae strain overexpressing morA produced 125-fold more leucate than the wild-type strain KBN8243. The strain overexpressing MorA produced 6.3-fold more ethyl leucate in the sake than the wild-type strain. These findings suggest that the strain overexpressing morA would help to ferment high-quality sake with an excellent flavor. This is the first study to identify the MOA reductase responsible for producing D-leucate in fungi.

Dieldrin uptake and translocation in plants growing in hydroponic medium.

It has been known that the Cucurbitaceae family takes up a large amount of persistent organic pollutants from soils and that the translocation of those compounds in cucurbits is higher than those in non-cucurbits. To understand the persistent organic pollutant uptake mechanisms of plant species, we compared the dieldrin absorption and transportation potentials of several plants in hydroponic medium. Sorghum (Sorghum vulgare Moench), sunflower (Helianthus annuus L.), soybean (Glycine max), komatsuna (Brassica rapa var. peruviridis), white-flowered gourd (Lagenaria siceraria var. hispida), cucumber (Cucumis sativus L.), and zucchini (Cucurbita pepo L.) were grown in a dieldrin-added hydroponic medium for 10 d, and then the amount of dieldrin in their shoots and roots was measured. All of the roots contained dieldrin, whereas only the cucurbits (white-flowered gourd, cucumber, and zucchini) contained considerable amounts of dieldrin in their shoots. The dieldrin uptake to the roots depended on the concentration of the n-hexane soluble components in the roots, regardless of whether the dieldrin in the roots was translocated to shoots or not. The dieldrin uptake from the solution to the roots was thought to be due to a passive response, such as adsorption on the roots. The translocation of dieldrin from the roots to the shoots was probably through the xylems. The amounts of dieldrin in the shoots per transpiration rates were higher for cucurbits than for non-cucurbits. It seems likely that cucurbits have uptake mechanisms for hydrophobic organic chemicals.

Dieldrin-dissolving abilities of the xylem saps of several plant families, particularly Cucurbita pepo L.

The uptake ability of hydrophobic organic chemicals by plants and the nature of xylem sap of the plants were studied. The plants were grown in soil contaminated with dieldrin. High amounts of dieldrin were detected in the shoots of Cucurbita pepo and Cucumis sativus, but little was seen in the shoots of Brassica oleracea var. italica, Solanum lycopersicum, Glycine max, Zea mays, and Helianthus annuus. The xylem saps of C. pepo and C. sativus leached dieldrin adsorbed on C8 granules, but those of the other plants did not. The xylem saps of C. pepo and C. sativus eluted high amounts of dieldrin from the size-exclusion chromatography column near the fractions of RNase A (13.7 kDa) after Aprotinin (6.5 kDa), which has a larger molecular weight than dieldrin (381). The enhancement of dieldrin solubility by xylem sap was reduced by proteinase and heating. It was suspected that the protein-like materials in the xylem sap delivered dieldrin from the roots to the shoots.

Relationship between dieldrin uptake in cucumber and solvent-extractable residue in soil.

To prevent the distribution of cucumbers with dieldrin contamination exceeding the limit set by the Japanese Food Sanitation Law, the extraction solvent for dieldrin-contaminated soil was selected prior to cultivation so that the dieldrin residue level in cucumber could be predicted. The exhaustive extraction from soil could not explain the dieldrin uptake by cucumber plants. However, significant correlation (R(2) = 0.966, P < 0.001) was observed between dieldrin concentrations in cucumber and dieldrin concentrations extracted with 50% (v/v) methanol-water solution from soils. This was a result of the phytoavailability of dieldrin to the cucumber plants. The extractability of soil dieldrin with the methanol-water solution decreased as the organic carbon content in the soils increased. This suggested that a 50% (v/v) methanol-water solution is the optimal solution for predicting dieldrin concentrations in cucumbers by soil analysis.

Adsorption of herbicidally active degradate 2-(2,4-dichloro-3-methylphenoxy)propanoic acid on an andosol.

The adsorption of 2-(2,4-dichloro-3-methylphenoxy)propanoic acid (DMPA) on the surface horizon of a humus-rich Andosol was examined. To investigate the mechanisms of adsorption, chemically treated Andosols, such as organic matter removed Andosol, organic matter and active metals removed Andosol, and clay minerals of the Andosol, were prepared. Furthermore, humic acid was extracted from the Andosol. The mechanisms of the DMPA adsorption were identified by using those untreated and chemically treated Andosols and the humic acid. The amount of DMPA adsorbed increased with decreasing equilibrium pH value. Active surface hydroxyl groups were identified as the most important soil functional group in DMPA adsorption. The predominant mechanism of DMPA adsorption on the Andosol is a ligand-exchange reaction, in which an active surface hydroxyl on Al and/or Fe is replaced by a carboxylic group of DMPA. A comparative study revealed that the amount of DMPA adsorbed was slightly greater than that of (2,4-dichlorophenoxy)acetic acid (2,4-D), especially at equilibrium pH values below 5. This is because the octanol-water partition coefficient (log Kow) of DMPA in the equilibrium pH range is higher than that of 2,4-D, and SOM participates in the adsorption process through a hydrophobic interaction.