The Roche Limit

The role of tides in deforming and possibly disrupting a secondary body orbiting about a primary body has been known for a considerable time. This was first inspired by the observations of ocean tides on Earth and then seen as playing an important role in the formation and evolution of the Earth–Moon system. Finally, in the beginning of the 20th century it was generally thought to have a significant role in the formation of the solar system through the tidal disruption of the Sun. Here, an overview of the historical developments of the ideas concerned with tidal disruption of a secondary body that can lead to mass loss is given. Some discussion of possible extensions to consider more realistic situations where the secondary body may not be moving on a circular orbit and may not rotate so as to maintain the phase-on configuration to the primary body is also given.     

Sediment–water interactions of natural oestrogens under estuarine conditions

The natural human female hormones oestrone and 17β-oestradiol have been implicated in the disruption of endocrine systems in some wildlife adjacent to sewage effluents. The sorption behaviour of these two compounds under estuarine conditions was studied by spiking either 2.55 μg of oestrone or 2.65 μg of 17β-oestradiol in kinetic experiments. In equilibrium experiments, 3 ng of oestrone or 3.2 ng of 17β-oestradiol was added in each of the centrifuge tubes. Sorption onto sediment particles was relatively slow, with sorption equilibrium being reached in about 70 and 170 h for oestrone and 17β-oestradiol, respectively. The effects of a variety of environmental parameters on sorption were studied including salinity, sediment concentration (SC), the presence of a third phase, particle size and, also, surfactant concentrations. Results show that although salinity did not induce any statistically significant effect on the sorption of 17β-oestradiol, it did statistically enhance the sorption of oestrone, and a salting constant of 0.3 l mol⁻¹ was derived. The partition coefficient for both compounds decreased with increasing sediment concentration, a phenomenon that has been widely reported and attributed to the presence of colloids (which could enhance dissolved concentrations). In this paper, the true partition coefficients for sediment particles (K_p^true) and colloidal particles (K_c^true) have been calculated, and a K_p^true value of 141 and 102 ml g⁻¹ was obtained for oestrone and 17β-oestradiol, respectively. In addition, K_c^true values for oestrone (222×10² ml g⁻¹) and 17β-oestradiol (135×10² ml g⁻¹) were two orders of magnitude higher than their respective K_p^true values, suggesting that the colloidal particles are significantly stronger sorbents for natural oestrogens than sediment particles. Particles of different sizes were found to have different partition coefficients due to the strong relationships between partition coefficients for the two compounds and particulate organic carbon (POC) contents and specific surface areas (SSAs). The presence of a surfactant was shown to reduce the partition coefficients for the two compounds, although its concentrations being used were higher than those normally found in the natural environment.     

华北克拉通破坏前的状态——对讨论华北克拉通破坏问题的一个建议

中生代华北克拉通破坏是目前引人关注的研究课题。鉴于目前一些文章在表达克拉通状态时引用的地质图件不准确,忽略了华北克拉通从古至今的不同阶段的演化,不能正确的表达克拉通在破坏之前或之后的状态,本文强调华北克拉通破坏前的状态是研究的重要基础。华北克拉通是经历过多期克拉通化形成的。     

Toxicity of tributyltin in the marine mollusc Mytilus edulis

Our previous studies have demonstrated that tributyltin (TBT) is genotoxic to the early life stages of marine mussels and worms. Here, the toxicity of TBT to adult organisms was determined using a suite of biomarkers designed to detect cytotoxic, immunotoxic and genotoxic effects. Exposure of adult mussels, Mytilus edulis, to environmentally realistic concentrations of TBTO for 7 days resulted in a statistically significant decrease in cell viability at concentrations of 0.5 μg/l and above. TBT had no effect on phagocytic activity or antioxidant capacity (FRAP assay). There was a statistically significant increase in DNA damage detected using the comet and micronucleus assays between the controls and 0.5, 1 and 5 μg/l of TBTO (P > 0.0005). Furthermore there was a strong correlation between DNA strand breaks (comet assay) and formation of micronuclei (P = 0.0005; R² = 61.5%). Possible mechanisms by which TBT could damage DNA either directly or indirectly are discussed including the possibility that TBT is genotoxic due to its ability to disrupt calcium homeostasis.     

海洋脊椎动物甲状腺系统的研究与应用

甲状腺（Glandula thyreoidea）是海洋脊椎动物体内重要的内分泌腺，从海洋脊椎动物开始，才有了独立的甲状腺结构。海洋脊椎动物的甲状腺一般为实质性的组织。实质由甲状腺滤泡组成，构成滤泡的上皮细胞合成、贮存和分泌的甲状腺激素是调节机体生长发育的关键激素。从海洋脊椎动物开始才有了独立的甲状腺结构。对于动物甲状腺的研究多集中在甲状腺形态及甲状腺与生长发育关系方面，而对海洋脊椎动物的甲状腺的研究则越来越多的集中于环境因素所引起的甲状腺病变方面，环境因素对甲状腺功能的影响也逐渐成为科学研究的重点。海洋水体污染导致的甲状腺机能受损，使海洋脊椎动物不能正常生长发育，数目与种类骤减之时，我们不得不重视对海洋脊椎动物甲状腺的研究。     

放养密度对大杂交鲟生长性能的影响及生理应答机制

为探讨放养密度对鱼类生长及生理应答机制的影响规律和作用,作者以大规格大杂交鲟(达氏鳇(Huso dauricus)♀×施氏鲟(Acipenser schrenckii)♂)为实验材料,研究了平均初始体质量约为243 g/尾,放养密度分别为6(SD1组)、9(SD2组)、12(SD3组)、15 kg/m3(SD4组)条件下,不同放养密度处理70 d后的实验鱼生长性能变化及生理应答机制。结果显示,放养密度对大杂交鲟肥满度影响不显著,SD2组鱼类具有最大的特定生长率和生长效率,随着放养密度增加,日增质量显著降低(P0.05),特定生长率和生长效率下降。测定了血液甲状腺素(T4)、三碘甲腺原氨酸(T3)和皮质醇水平变化,发现放养密度能引起大杂交鲟3个血液生理指标发生显著改变;随着养殖时间推移,T3和皮质醇浓度显著升高,T4浓度显著下降(P0.05)。这些结果说明神经内分泌活动的变化引起大杂交鲟血液生理指标变化,进而影响实验鱼生长性能。因此,在该养殖条件下推荐的养殖密度为9 kg/m3。     

Survey of estrogenic and androgenic disruption in Swedish coastal waters by the analysis of bile fluid from perch and biomarkers in the three-spined stickleback

The potential for endocrine disruption close to sewage treatment plant and pulp mill effluent discharge points along the Swedish Baltic Sea coast was explored using a dual survey strategy employing two stationary fish species. The levels of vitellogenin and spiggin as biomarkers of endocrine disruption were determined in juvenile three-spined sticklebacks (Gasterosteus aculeatus L.) together with the sex ratios and the presence of intersex. As an indication of exposure, estrogenic and androgenic substances were analysed by GC–MS in bile from perch (Perca fluviatilis L.). Spiggin and vitellogenin levels in juvenile three-spined sticklebacks were generally low, and, for most sampling sites no deviation in gonad type ratios were observed. No remarkable levels of natural or synthetic estrogens or androgens were observed in bile fluid from perch, while bisphenol A and 4-nonylphenol were detected in perch from both reference sites and exposed sites. Taken together, the results did not indicate estrogenic or androgenic disruption in the investigated waters.     

Sperm motility in the Pacific oyster (Crassostrea gigas) is affected by nonylphenol

Nonylphenol, a widespread aquatic pollutant with endocrine-disrupting potential has been found to affect sperm motility in the Pacific oyster, Crassostrea gigas (Thunberg). This marine invertebrate, a global aquaculture species, was exposed to nonylphenol at concentrations of 1 and 100 μg l⁻¹ for a duration of 72 h during the period of gametogenesis. Growth was monitored at regular intervals until sexual maturity when sperm motility was assessed. The growth rate of C. gigas remained unaffected by exposure to nonylphenol during gametogenesis. However, the number of individuals with motile sperm was significantly reduced.     

Fundamentally distinct outcomes of asteroid collisional evolution and catastrophic disruption

The outcomes of asteroid collisional evolution are presently unclear: are most asteroids larger than 1 km size gravitational aggregates reaccreted from fragments of a parent body that was collisionally disrupted, while much smaller asteroids are collisional shards that were never completely disrupted? The 16 km mean diameter S-type asteroid 433 Eros, visited by the NEAR mission, has surface geology consistent with being a fractured shard. A ubiquitous fabric of linear structural features is found on the surface of Eros and probably indicates a globally consolidated structure beneath its regolith cover. Despite the differences in absolute scale and in lighting conditions for NEAR and Hayabusa, similar features should have been found on 25143 Itokawa if present. This much smaller, 320 m diameter S-asteroid was visited by the Hayabusa spacecraft. Comparative analyses of Itokawa and Eros geology reveal fundamental differences, and interpretation of Eros geology is illuminated by comparison with Itokawa. Itokawa lacks a global lineament fabric, and its blocks, craters, and regolith may be inconsistent with formation and evolution as a fractured shard, unlike Eros. An object as small as Itokawa can form as a rubble pile, while much larger Eros formed as a fractured shard. Itokawa is not a scaled-down Eros, but formed by catastrophic disruption and reaccumulation.     

Dust production from the hypervelocity impact disruption of the Murchison hydrous CM2 meteorite: Implications for the disruption of hydrous asteroids and the production of interplanetary dust

More than half of the C-type asteroids, the dominant type of asteroid in the outer half of the main-belt, show evidence of hydration in their reflectance spectra. In order to understand the collisional evolution of asteroids and the production of interplanetary dust and to model the infrared signature of small particles in the Solar System it is important to characterize the dust production from primary impact disruption events, and compare the disruption of hydrous and anhydrous targets. We performed a hypervelocity impact disruption experiment on an ∼30 g target of the Murchison CM2 hydrated carbonaceous chondrite meteorite, and compared the results with our previous disruption experiments on anhydrous meteorites including Allende, a CV3 carbonaceous chondrite, and nine ordinary chondrites. Murchison is significantly more friable than the ordinary chondrites or Allende. Nonetheless, on a plot of mass of the largest fragment versus specific impact energy, the Murchison disruption plots within the field of the anhydrous meteorites points, suggesting that Murchison is at least as resistant to impact disruption as the anhydrous meteorites, which require about twice the energy for disruption as terrestrial anhydrous basalt targets. We determined the mass-frequency distribution of the debris from the Murchison disruption over a nine order-of-magnitude mass range, from ∼10⁻⁹ g to the mass of the largest fragment produced in the disruption. The cumulative mass-frequency distribution from the Murchison disruption is fit by three power-law segments. For masses >10⁻² g the slope is only slightly steeper than that of the corresponding segment from the disruption of most anhydrous meteorites. Over the range from ∼10⁻⁶ to 10⁻² g the slope is significantly steeper than that for the anhydrous meteorites. For masses <10⁻⁶ g the slopes of both the Murchison and the anhydrous meteorites are almost flat. Thus the Murchison disruption significantly over-produced small fragments (10⁻⁶-10⁻³ g) compared to anhydrous meteorite targets. If the Murchison results are representative of hydrous asteroids, the hydrous asteroids may dominate over anhydrous asteroids in the production of interplanetary dust >100 μm in size, the size of micrometeorites recovered from the polar ices, while both types of asteroids might produce comparable amounts of ∼10 μm interplanetary dust. This would explain the puzzle that polar micrometeorites (>100 μm in size) are similar to hydrous meteorites, while the majority of the ∼10 μm interplanetary dust particles are anhydrous.