Osamu Hayashi

Bioaccumulation and Metabolism of [14C]Bisphenol A in the Brackish Water Bivalve Corbicula japonica

The brackish water bivalve mollusk Corbicula japonica was exposed to brackish water containing approximately 9 μg/l [14C]bisphenol A (BPA) for 168 h (the uptake phase), and subsequently transferred to clean brackish water for 144 h (the depuration phase) under semi-static conditions. Mono and disulfate conjugates of BPA were detected in the bivalves as major metabolites. At the end of the uptake phase, the visceral mass contained the highest 14C-concentration, and the monosulfate conjugate of BPA was a major metabolite in the visceral mass. These data suggest that the visceral mass is the major tissue/organ to take up and metabolize BPA in these bivalves. The BPA concentration in the bivalves readily reached steady state during the uptake phase and immediately decreased in the depuration phase. The accumulation and elimination rates of the mono and disulfate conjugates of BPA were slower than those of BPA.

Bioconcentration and biotransformation of [14C]methoxychlor in the brackish water bivalve Corbicula japonica

To obtain basic information on the metabolic fate of xenobiotics in the brackish water, bivalve Corbicula japonica, bioconcentration and biotransformation experiments were performed using methoxychlor (MXC) as a model compound. Bivalves were exposed to [ring-U-14C]MXC (10 µg L−1) for 28 days under semi-static conditions followed by a 14-day depuration phase. The 14C concentration in the bivalves rapidly increased and reached a steady state after exposure for 7 days (BCFss = 2010); however, it rapidly decreased with a half-life of 2.2 days in the depuration phase. Mono- and bis-demethylated MXC, and their corresponding sulphate conjugates, were identified as minor metabolites. No glycoside conjugates (including glucuronide and glucoside) were detected. Despite this biotransformation system, bivalves were found to excrete retained MXC mostly unchanged although its relatively hydrophobic nature.

Differences in Concentrations of Acetyl-CoA and Malonyl-CoA in Shoots and Roots of Zea mays

We measured the concentrations of acetyl-CoA and malonyl-CoA in shoots and roots of corn (Zea mays, L., cv. “Peter Corn”). Acetyl-CoA and malonyl-CoA concentrations were found to be relatively constant in shoots and in roots under a light-dark cycle. Acetyl-CoA concentrations were lower in shoots than in roots, whereas malonyl-CoA concentrations were higher in shoots than in roots.

Degradation of the persistent organic pollutant [14C]heptachlor in Japanese field soils.

The fate of [14C]heptachlor in Saitama soil and the degradation of [14C]heptachlor in four Japanese field soils over 112 d after application were investigated. Heptachlor was degraded mainly to cis-heptachlor epoxide by a biotic process and to 1-hydroxychlordene by an abiotic process in the field soils. Volatilization of heptachlor and cis-heptachlor epoxide from the soil was observed over the experimental period. The amount of 1-hydroxychlordene produced in the soils appeared to be related to the soil water contents. Because heptachlor and heptachlor epoxides are predicted to volatilize to the atmosphere and to persist in soils, these compounds are thought to spread among Japanese environmental compartments even after a ban on their use.

Transformation of Herbicide Pentoxazone by Soil Microorganisms

The metabolism of herbicide pentoxazone, 3-(4-chloro-5-cyclopentyloxy-2-fluorophenyl)-5-isopropylidene-1,3-oxazolidine-2,4-dione, was investigated by soil microorganisms with a liquid medium applied with radiolabeled pentoxazone. Four different types of Japanese agricultural soils were inoculated as the sources of microorganisms There was no marked difference in the degradation profiles among the four soils. Pentoxazone decreased rapidly, and N-(4-chloro-5-cyclopentyloxy.-2-fluorophenyl)-3-methyl-2-oxobutanamide (A-0505, a hydrolysate at the carbonyl group of C2 in 1,3-oxazolidine-2,4-dione ring followed by decarboxylation) increased up to about 57% of applied dosage. After transient accumulation of A-0505, N-(4-chloro-5-cyclopentyloxy-2-fluorophenyl)-2-hydroxy-3-methylbutanamide (A-1374, a reduction product of A-0505) increased up to about 71%. The other metabolites, 4-chloro-5-(cyclopentyloxy)-2-fluoroaniline (A-0480, an aniline derivative), hydrated-pentoxazone (another hydrolysate at the carbonyl group of C4 in 1,3-oxazolidine-2,4-dione ring) and one unidentified compound were detected over 10% of applied dosage. Pentoxazone is likely to be readily transformed by ubiquitous soil microorganisms. These microbes which can proliferate in soil/water environment would play an important role in the progress of the degradation of pentoxazone.