ABSTRACT
The ability to predict the environmental behavior of chemicals precisely is important for realizing more rational regulation. In this study, the bioaccumulation of nine chemicals of different molecular weights absorbed via the intestinal tract was evaluated in fish using the everted gut sac method. The amounts of chemicals that passed through the intestinal membrane after a 24-hr exposure were significantly decreased for chemicals with MW≥548 and Dmax min≥15.8 Å (or Dmax aver≥17.2 Å). These thresholds are consistent with those previously proposed in terms of MW (>800) and molecular size (Dmax min>15.6 Å or Dmax aver>17.1 Å) for the limit of permeable chemicals through the gill membrane. The results show that the same MW and Dmax criteria can be used to predict low bioaccumulation through both the gill membrane and the intestinal tract. These findings are helpful in reducing the need to conduct animal tests in environmental safety studies.
ABSTRACT
To evaluate the bioaccumulation potential of chemicals in fish, a molecular-size descriptor, Dmax aver, has been used as a weight of evidence under the EU REACH. The Dmax aver value, however, is estimated on the basis of 3-D structures of possible stable conformers in a vacuum using OASIS software that requires expertise upon parameter input. We developed a method to calculate the 3-D conformers in water, which is more suitable for bioaccumulation potential evaluation in an aquatic environment, by introducing MD simulation. By examining the relationship of the calculated molecular size of 1665 chemicals with their reported BCF values, we found that 17.1 Å of Dmax aver or 15.6 Å of Dmax min was a threshold of molecular size in water to predict the low bioaccumulation (i.e., BCF<5000) of a chemical. Setting this threshold as a new standard would reduce the number of animal tests without compromising the quality of safety evaluation.
ABSTRACT
Photoelectron spectroscopy (PES) of Na2- (H2O)n (n < or = 6) was investigated to examine the solvation of sodium aggregates in small water clusters. The PES bands for the transitions from the anion to the neutral ground and first excited states derived from Na2 (1(1)Sigmag+) and Na2 (1(3)Sigmau+) shifted gradually to the blue, and those to the higher-excited states correlated to the 3(2)S + 3(2)P asymptote dropped down rapidly to the red and almost degenerated on the 1(3)Sigmau+-type band at n = 4. Quantum chemical calculations for n up to 3 showed that the spectra can be ascribed to structures where one of the Na atoms is selectively hydrated. From the electron distributions, it is found that the Na- -Na+(H2O)n- -type electronic state grows with increasing cluster size, which can be regarded as a sign of the solvation of Na2- with ionization of the hydrated Na.
