Principles of concentration addition and independent action have been used as effective tools to predict mixture toxicity based on individual component toxicity. The authors investigated the toxicity of a pharmaceutical mixture composed of the top 10 detected active pharmaceutical ingredients (APIs) in the Tama River (Tokyo, Japan) in a relevant concentration ratio. Both individual and mixture toxicities of the 10 APIs were evaluated by 3 short-term chronic toxicity tests using the alga Pseudokirchneriella subcapitata, the daphnid Ceriodaphnia dubia, and the zebrafish Danio rerio. With the exception of clarithromycin toxicity to alga, the no-observed-effect concentration of individual APIs for each test species was dramatically higher than the highest concentration of APIs found in the environment. The mixture of 10 APIs resulted in toxicity to alga, daphnid, and fish at 6.25 times, 100 times, and 15,000 times higher concentrations, respectively, than the environmental concentrations of individual APIs. Predictions by concentration addition and independent action were nearly identical for alga, as clarithromycin was the predominant toxicant in the mixture. Both predictions described the observed mixture toxicity to alga fairly well, whereas they slightly underestimated the observed mixture toxicity in the daphnid test. In the fish embryo test, the observed toxicity fell between the predicted toxicity by concentration addition and independent action. These results suggested that the toxicity of environmentally relevant pharmaceutical mixtures could be predicted by individual toxicity using either concentration addition or independent action.

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Chemicals released into the environment have the potential to affect various species and it is important to evaluate such chemical effect on ecosystems, including aquatic organisms. Among aquatic organisms, Daphnia magna has been used extensively for acute toxicity or reproductive toxicity tests. Although these types of tests can provide information on hazardous concentrations of chemicals, they provide no information on their mode of action. Recent advances in toxicogenomics, the integration of genomics with toxicology, have the potential to afford a better understanding of the responses of aquatic organisms to pollutants. In a previous study, we developed an oligonucleotide-based DNA microarray with high reproducibility using a Daphnia expressed sequence tag (EST) database. In this study, we increased the number of genes on the array and used it for a careful ecotoxicogenomic assessment of Daphnia magna. The DNA microarray was used to evaluate gene expression profiles of neonate daphnids exposed to beta-naphthoflavone (bNF). Exposure to this chemical resulted in a characteristic gene expression pattern. As the number of the genes on an array was increased, the number of genes that were found to respond to the chemicals was also increased, which made the classification of the toxic chemicals easier and more accurate. This newly developed DNA microarray can be useful for a obtaining a better mechanistic understanding of chemical toxicity effects on a common freshwater organism.

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The Ward linkage method in agglomerative hierarchical clustering is sometimes used for non-Euclidean similarity, i.e., non-positive definite matrix of similarity, which is not an adequate use of this method, since the square Euclidean distance should be its basis. Nevertheless, this paper shows that the Ward method for non positive-definite similarity can partly be justified. It is shown that the result from the Ward method to a non positive-definite and normalized similarity is almost the same as another result from the Ward method to a positive-definite matrix obtained from the original similarity by adding a positive constant to the diagonal elements. More precisely, the same clusters are generated by the same order from the both data. Only the levels of their generations are different.

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Watching competitive games is a pervasive entertainment in humans and likely to be facilitated by our social cognitive abilities. We investigated the brain activity during observation of a competitive game by using near-infrared spectroscopy. The result showed that activity in the motor area was significantly greater when the individual's favored player won, compared with when the same player lost. The motor area was also activated when the individuals themselves performed the same action, showing the mirror neuron system property. Our results first showed that the motor area activity during observation of competitive games was modulated by the outcome of the game. We suggest that the observer's brain is more likely to share the winner's internal motor representation than that of the loser.

Azolla (Azolla filiculoides) is a common aquatic fern that has been used successfully as a dual crop with lowland rice. It grows rapidly and has the ability to fix N 2 for rice paddy. However, its ecological significance especially on greenhouse gases emissions remains unclear. To investigate the effect of azolla cover on methane (CH 4 ) and nitrous oxide (N 2 O) emissions from rice paddy, a pot experiment with two treatments, control (rice plant only) and azolla cover (rice plus azolla covering on the flooding water), was carried out in Tsuruoka, Yamagata, Japan, in 2016. The results showed that the rice growth parameters, like shoot height, maximum and productive tiller numbers, and plant biomass were not significantly different between the two treatments. Dual cropping of azolla with rice significantly suppressed CH 4 emissions, likely due to an increase in dissolved oxygen concentration and redox potential at the soil-water interface between flooding water and soil surface. There were significant (P < 0.05) positive correlations between CH 4 flux and night respiration (CO 2 emissions) between the two treatments. The cumulated CH 4 emissions during the growth period until 106 days after transplanting (DAT) was significantly lower at 36.2 g C m −2 from azolla cover treatment than that from control treatment pot at 55.4 g C m −2 . A prolonged nonsignificant N 2 O emission under the azolla cover treatment after the initial highest peak at 15 DAT was recorded due to denitrification of the nitrate in initial soil. No further N 2 O emissions were recorded thereafter from both treatments. Azolla cover did not affect N 2 O emissions from both treatments. ARTICLE HISTORY