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991.
Natural muds used as or in cosmetics may expose consumers to toxic metals and elements via absorption through the skin, inhalation
of the dried product, or ingestion (by children). Despite the extensive therapeutic and cosmetic use of the Dead Sea muds,
there apparently has been no assessment of the levels of such toxic elements as Pb, As, or Cd in the mud and mud-based products.
Inductively coupled plasma mass spectrometry analysis of eight toxic elements in samples collected from three black mud deposits
(Lisan Marl, Pleistocene age) on the eastern shore of the Dead Sea in Jordan revealed no special enrichment of toxic elements
in the mud. A similar analysis of 16 different commercial Dead Sea mud cosmetics, including packaged mud, likewise revealed
no toxic elements at elevated levels of concern. From a toxic element standpoint, the Dead Sea black muds and derivative products
appear to be safe for the consumer. Whatever the therapeutic benefits of the mud, our comparison of the elemental fingerprints
of the consumer products with those of the field samples revealed one disturbing aspect: Dead Sea black mud should not be
a significant component of such items as hand creams, body lotions, shampoo, and moisturizer. 相似文献
992.
To understand trace radionuclide (uranium) migration occurring in rocks, a granitic batholith located at the Korea Atomic
Energy Research Institute (KAERI) site was selected and investigated. The rock samples obtained from this site were examined
using mineralogical methods, including scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The changes
in the distribution pattern of uranium (U) and small amounts of trace elements, and the mineralogical textures affected by
weathering, were examined. Based on the element distribution analyses, it was found that Fe2+ released from fresh biotite is oxidized in short geological time, forming amorphous iron oxides, such as ferrihydrite, around
silicate minerals. In that case, the amorphous ferrihydrite does not show distinct adsorption for U. However, as it gradually
crystallizes to goethite or hematite, the most U-rich phases were found to be associated with the secondary iron oxides having
granular forms. This evidence suggests that the geological subsurface environment is favorable for the crystallized iron oxides
to keep their structures more stable for a long time as compared with the amorphous phases. There is a possibility that the
long residence of U which is in contact with the stable crystalline phases of iron may finally lead to the partial sequestration
of U in their structure. Consequently, it seems that Fe-oxide crystallization can be a dominating mechanism for U uptake and
controls long-term U transport in granites with low U contents. 相似文献
993.
Ocean acidification (OA) and the biological consequences of altered seawater chemistry have emerged as a significant environmental
threat to healthy marine ecosystems. Because a more acidic ocean interferes with fixation of calcium carbonate to form shells
or calcified skeletons, future ocean chemistry may significantly alter the physiology of calcifying marine organisms. These
alterations may manifest themselves directly in the calcification process, or have synergistic effects with other environmental
factors such as elevated temperatures. New tools permit us to explore subtle changes in gene expression patterns in response
to environmental conditions. We raised sea urchins (Strongylocentrotus franciscanus) under conditions simulating future atmospheric CO2 levels of 540 and 970 ppm. When larvae raised under elevated CO2 conditions were subjected to 1-h acute temperature stress, their ability to mount a physiological response (as measured by
expression of the molecular chaperone hsp70) was reduced relative to those raised under ambient CO2 conditions. These results represent the first use of gene expression assays to study the effects of OA on sea urchin development.
They highlight the importance of looking at multiple environmental factors simultaneously as this approach may reveal previously
unsuspected biological impacts of atmospheric changes. 相似文献
994.
Young green turtles (Chelonia mydas) spend their early lives as oceanic omnivores with a prevalence of animal prey. Once they settle into neritic habitats (recruitment),
they are thought to shift rapidly to an herbivorous diet, as revealed by studies in the Greater Caribbean. However, the precise
timing of the ontogenic dietary shift and the actual relevance of animal prey in the diet of neritic green turtles are poorly
known elsewhere. Stable isotopes of carbon, sulfur and nitrogen in the carapace scutes of 19 green turtles from Mauritania
(NW Africa), ranging from 26 to 102 cm in curved carapace length (CCLmin), were analyzed to test the hypothesis of a rapid
dietary shift after recruitment. Although the length of residence time in neritic habitats increased with turtle length, as
revealed by a significant correlation between turtle length and the δ13C and the δ34S of the scutes, comparison of the δ15N of the innermost and outermost layers of carapace scutes demonstrated that consumption of macrophytes did not always start
immediately after recruitment, and turtles often resumed an animal-based diet after starting to graze on seagrasses. As a
consequence, seagrass consumption did not increase gradually with turtle size and animal prey largely contributed to the diet
of turtles within the range 29–59 cm CCLmin (76–99% of assimilated nutrients). Seagrass consumption by turtles larger than
59 cm CCLmin was higher, but they still relied largely on animal prey (53–76% of assimilated nutrients). Thus, throughout
most of their neritic juvenile life, green turtles from NW Africa would be better classified as omnivores rather than herbivores.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
995.
Two-phase flow insights into open-channel flows with suspended particles of different densities 总被引:1,自引:0,他引:1
The effect of particle density on the turbulent open-channel flow carrying dilute particle suspensions is investigated using
two specific gravities and three concentrations of solid particles. The particles, identical in size and similar in shape,
were natural sand and a neutrally buoyant plastic. The particles were fully suspended, and formed no particle streaks on the
channel’s bed. Accordingly, the changes in the flow are attributed to the interactions between suspended particles and flow
turbulence structures. Measurements were obtained by means of image velocimetry enabling simultaneous, but distinct, measurement
of liquid and particle velocities. The experimental results show that, irrespective of particle specific gravity, particle
suspension influences bulk velocity of flow and the Kármán coefficient, while friction velocity essentially remains constant.
The results also show that particles in suspension modify local water turbulence over the flow depth, but in ways not accurately
predicted using the customary parameters for characterizing turbulence modification. 相似文献
996.
Transmissible spongiform encephalopathies (TSEs) are a group of fatal neurological conditions affecting a number of mammals,
including sheep and goats (scrapie), cows (BSE), and humans (Creutzfeldt-Jakob disease). The diseases are widely believed
to be caused by the misfolding of the normal prion protein to a pathological isoform, which is thought to act as an infectious
agent. Outbreaks of the disease are commonly attributed to contaminated feed and genetic susceptibility. However, the implication
of copper and manganese in the pathology of the disease, and its apparent geographical clustering, have prompted suggestions
of a link with trace elements in the environment. Nevertheless, studies of soils at regional scales have failed to provide
evidence of an environmental risk factor. This study uses geostatistical techniques to investigate the correlations between
the distribution of TSE prevalence and soil geochemical variables across the UK according to different spatial scales. A similar
spatial pattern in scrapie and BSE occurrence is identified, which may be linked with increasing pH and total organic carbon,
and decreasing iodine concentration. However, the pattern also resembles that of the density of dairy farming. Nevertheless,
despite the low spatial resolution of the TSE data available for this study, the fact that significant correlations are detected
indicates there is a possibility of a link between soil geochemistry, scrapie, and BSE. It is suggested that further investigations
of the prevalence of TSE and environmental exposure to trace metals should take into account the factors affecting their bioavailability. 相似文献
997.
Arsenite [As(III)]-oxidizing bacteria play important roles in reducing arsenic [As] toxicity and mobility in As-contaminated
areas. As-resistant bacteria were isolated from the soils of two abandoned mines in the Republic of Korea. The isolated bacteria
showed relatively high resistances to As(III) up to 26 mM. The PCR-based 16S rRNA analysis revealed that the isolated As-resistant
bacteria were close relatives to Serratia marcescensa, Pseudomonas putida, Pantoea agglomerans, and Alcaligenes sp. Among the five As-resistant bacterial isolates, Alcaligenes sp. strain RS-19 showed the highest As(III)-oxidizing activity in batch tests, completely oxidizing 1 mM of As(III) to As(V)
within 40 h during heterotrophic growth. This study suggests that the indigenous bacteria have evolved to retain the ability
to resist toxic As in the As-contaminated environments and moreover to convert the species to a less toxic form [e.g., from
As(III) to As(V)] and also contribute the biogeochemical cycling of As by being involved in speciation of As. 相似文献
998.
We investigated the constraints on sulfide uptake by bacterial ectosymbionts on the marine peritrich ciliate Zoothamnium niveum by a combination of experimental and numerical methods. Protists with symbionts were collected on large blocks of mangrove-peat.
The blocks were placed in a flow cell with flow adjusted to in situ velocity. The water motion around the colonies was then
characterized by particle tracking velocimetry. This shows that the feather-shaped colony of Z. niveum generates a unidirectional flow of seawater through the colony with no recirculation. The source of the feeding current was
the free-flowing water although the size of the colonies suggests that they live partly submerged in the diffusive boundary
layer. We showed that the filtered volume allows Z. niveum to assimilate sufficient sulfide to sustain the symbiosis at a few micromoles per liter in ambient concentration. Numerical
modeling shows that sulfide oxidizing bacteria on the surfaces of Z. niveum can sustain 100-times higher sulfide uptake than bacteria on flat surfaces, such as microbial mats. The study demonstrates
that the filter feeding zooids of Z. niveum are preadapted to be prime habitats for sulfide oxidizing bacteria due to Z. niveum’s habitat preference and due to the feeding current. Z. niveum is capable of exploiting low concentrations of sulfide in near norm-oxic seawater. This links its otherwise dissimilar habitats
and makes it functionally similar to invertebrates with thiotrophic symbionts in filtering organs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
999.
Giovanni A. P. dos Santos Sofie Derycke Verônica G. F. Genevois Luana C. B. B. Coelho Maria T. S. Correia Tom Moens 《Marine Biology》2009,156(4):629-640
Accurate prediction of the biodiversity–ecosystem functioning relationship requires adequate understanding of the interactions
among species in a community. Effects of species diversity on ecosystem functioning are usually considered more pronounced
with increasing functional dissimilarity, although species within functional groups may also perform non-identical functions
and interact with each other. Here we present results of a laboratory experimental study aimed at elucidating whether interspecific
interactions among species within a single nematode trophic group, bacterivores, (1) affect population development and community
structure, and (2) depend on food availability. We studied the population growth of Rhabditis (Pellioditis) marina, a rhabditid nematode known to favour very high food densities when in monoculture, and of Diplolaimelloides meyli and D. oschei, congeneric Monhysteridae known to perform better in monocultures at intermediate food availability. Both Diplolaimelloides species showed significantly different patterns of food-density dependence in combination culture compared to monoculture.
At very high food availability, the rhabditid nematode facilitated growth of both monhysterid species, probably as a result
of down-regulation of bacterial density. At the lowest food availabilities, the presence of even low numbers of monhysterid
nematodes lead to exclusion of the rhabditid, which at such low food availability has a very inefficient food uptake. At intermediate
food availabilities, abundances of both Diplolaimelloides species were strongly depressed in the combination culture, as a result of food depletion by the rhabditid, indirect inhibitory
interactions between the two congeneric species, or both. The complexity of the species interactions render predictions on
the outcome and functional consequences of changes in within-trophic-group diversity highly problematic. 相似文献
1000.
Pedro Daleo Tomás Luppi Agustina Mendez Casariego Mauricio Escapa Pablo Ribeiro Paola Silva Oscar Iribarne 《Marine Biology》2009,156(3):269-275
Size advantage in male–male competition over mates, combined with male preference over large females, is a common feature
that can drive to size assortative mating and, eventually, sexual selection. In crabs, appendage autotomy can affect assortative
mating and opportunity for sexual selection by affecting size advantage in mating contests. In this work, we evaluate the
effect of size and appendage autotomy in generating assortative mating in the mud crab Cyrtograpsus angulatus. Field observations of guarding pairs in two different populations show a positive correlation between carapace width of
males and females in both the populations. In one of the populations, incidence of appendage autotomy was low and the variability
in the size of reproductive males was lower than the variability in the size of randomly collected males (i.e. only larger
males were successful in getting a female), whereas there was no differences in the other population (i.e. most male sizes
were successful) where the incidence of appendage autotomy was very high, indicating that the importance of size is higher
when the incidence of autotomy is low. In this context, experiments (in both populations) show that, in contests for a female,
larger males outcompete smaller ones only when they had intact appendages. When males had missing chelipeds, winning or loosing
against smaller males was random. This may lead to a decrease in the importance of male size in populations with high incidence
of cheliped autotomy, affecting assortative mating and opportunity for selection and, thus, affecting selective pressures. 相似文献