Tritium uptake and elimination by tissue-bound and body-water components in crickets (Acheta domesticus)

Tritium concentration ratios of less than unity (0·19) were determined for adult crickets which were at equilibrium for that particular instar with a tritium tagged food source. This phenomenon is interpreted as meaning that simple diffusion-equilibrium assumptions are not adequate for describing tritium movement in food chains when true equilibrium conditions are not met. Additional factors, such as rates of tritium assimilation and turnover for tissue-bound and body-water fractions, food habits, and duration of developmental stages must be considered along with environmental tritium concentrations in determining food chain transfers of this radionuclide.     

The transfer of tritium-labeled organic material from grass into cow's milk

Two lactating cows were given tritiated hay containing organically bound tritium (OBT) only for about 4 weeks. Tritium activity was determined in milk fat, casein, lactose, milk water, and whole milk. In one cow, milk was sampled for approximately 450 days, covering two lactation periods. At steady state, specific tritium activities in casein, lactose, and milk water were 58, 10, and 11%, respectively, of those in milk fat. Some OBT was converted into THO during catabolism and entered the body water pool. This 3H source accounted for nearly 40% of tritium in lactose, but in casein and milk fat about 97% of tritium was derived from ingested OBT. Comparison of the specific activity of milk constituents with the specific activity of ingested hay showed the following values: 0.84 for milk fat, 0.49 for casein, 0.05 for lactose, 0.10 for milk water. About one-half of the tritium transferred to milk was found in organic milk constituents and the other half in milk water. Decrease of tritium activity with time could be represented by three components with different half-lives for the organic milk constituents. Those for milk fat and casein were quite similar, with a slow component of nearly 3 months.     

Material recycling in a closed aquatic ecosystem. II. Bifurcation analysis of a simple food-chain model

The present paper deals with the bifurcation analysis of a simple food chain model consisting of components like detritus, nutrients, microorganisms, phytoplankton and zooplankton in an aquatic environment. The food chain model is described by a system of differential equations. If the length of the food chain (LFCH) is equal to 3 or 4, then an asymptotically stable equilibrium exists. For LFCH=5 or 6 the non-trivial equilibrium is unstable and the food-chain model has periodic orbits.     

A metabolic derivation of tritium transfer coefficients in animal products

Tritium is a potentially important environmental contaminant originating from the nuclear industry, and its behaviour in the environment is controlled by that of hydrogen. Animal food products represent a potentially important source of tritium in the human diet and a number of transfer coefficient values for tritium transfer to a limited number of animal products are available. In this paper we present an approach for the derivation of tritium transfer coefficients which is based on the metabolism of hydrogen in animals. The derived transfer coefficients separately account for transfer to and from free (i.e. water) and organically bound tritium. A novel aspect of the approach is that tritium transfer can be predicted for any animal product for which the required metabolic input parameters are available. The predicted transfer coefficients are compared to available independent data. Agreement is good (R ²=0.97) with the exception of the transfer coefficient for transfer from tritiated water to organically bound tritium in ruminants. This may be attributable to the particular characteristics of ruminant digestion. We show that tritium transfer coefficients will vary in response to the metabolic status of an animal (e.g. stage of lactation, diet digestibility etc.) and that the use of a single transfer coefficient from diet to animal product is inappropriate. It is possible to derive concentration ratio values from the estimated transfer coefficients which relate the concentration of tritiated water and organically bound tritium in an animal product to their respective concentrations in the animals diet. These concentration ratios are shown to be less subject to metabolic variation and may be more useful radioecological parameters than transfer coefficients. For tritiated water the concentration ratio shows little variation between animal products ranging from 0.59 to 0.82. In the case of organically bound tritium the concentration ratios vary between animal products from 0.15 (goat milk) to 0.67 (eggs). Received: 28 May 2001 / Accepted: 20 August 2001     

Tritium in plants: A review of current knowledge

The aim of this paper is to provide an overview of the literature regarding the fate of tritium in plants. At first, some prerequisites about the sources, chemical and physical characteristics, biological effects and potential risks associated to tritium are presented. The general scheme of tritium transport and cycling in the environment, the different tritium fractions in biological organisms and the corresponding techniques for sampling and measurement are discussed. Then, the main processes of uptake, incorporation and conversion of tritium into plants are described, based on experimental data. As tritium incorporated into the organic fraction may be the major contributor to the dose of radiation received following its ingestion by man, the biological mechanisms and kinetics of organically bound tritium (OBT) production are a major focus. Some predictive models of short-term or chronic exposure are described. Finally, the pending questions, concerning the fate of tritium in plants, are tackled.     

THE INCORPORATION OF TRITIUM FROM THYMIDINE INTO PROTEINS OF THE MOUSE

Tritium from methyl-H³-thymidine was found to be incorporated into proteins in mice. This incorporation in the mouse as a whole represented between 1 and 10% of the injected tritium. Tritiated water was not an intermediate. Transmethylation reactions are proposed as a means whereby certain amino acids might have acquired the tritium from thymidine at some stage of its catabolism. The initial (2 hr) ratios of DNA to protein tritium activities per milligram of wet tissue ranged from 5 in two tissues of low DNA synthetic activity (pancreas, liver) to 35 to 40 in two tissues of high DNA synthetic activity (spleen, small intestine). Labeled nuclear protein was coincident with labeled DNA in nuclei, where it constituted less than 2.5% of the total tritium. The significance of the findings is discussed.     

微塑料对湖泊生态系统初级生产者的影响

塑料的广泛应用导致大量微塑料进入环境,尤其是水环境,从而产生环境风险。浮游植物等自养生物是湖泊系统的主要初级生产者,是湖泊食物链的关键组成部分,为食物链的上游提供能量和物质基础。同时,浮游植物也是对微塑料响应最敏感的类群。了解湖泊浮游植物等初级生产者对微塑料的响应是探究微塑料对湖泊生态系统功能影响的重要基础。总结了全球湖泊生态系统微塑料的丰度、类型、尺寸、来源等分布特征,系统分析了微塑料暴露对浮游植物等初级生产者细胞结构、基因表达和生长,以及对浮游植物叶绿素a含量、光合活性的影响,并总结了其中的影响机制。总体而言,微塑料会降低初级生产者的叶绿素a含量,剂量越高、尺寸越小,这种抑制作用越强烈;同时,微塑料也会作用于初级生产者,造成细胞膜损伤、DNA损伤,调控其相关功能基因表达,抑制其生长和光合活性等。然而,湖泊生态系统微塑料的实际检出浓度远低于室内暴露实验中的添加剂量,微塑料结构和组分也更为复杂,野外观测结果与室内培养实验之间还不能建立直接的对应关系。因此,未来的相关研究应集中在如何有效联系野外观测结果与室内培养实验结果,进一步聚焦建立可靠的、可应用推广的微塑料浓度与初级生产者之间的剂量-效应关系模型,探究微塑料对湖泊初级生产者的作用机制,为刻画微塑料对湖泊生态系统初级生产者及其功能的作用机制提供科学支撑。     

Role of two toxin-producing plankton and their effect on phytoplankton-zooplankton system--a mathematical study supported by experimental findings

Plankton is the basis of the entire aquatic food chain. Phytoplankton, in particular, occupies the first trophic level. Plankton performs services for the Earth: it serves as food for marine life, gives off oxygen and also absorbs half of the carbon dioxide from the Earth's atmosphere. The dynamics of a rapid (or massive) increase or decrease of plankton populations is an important subject in marine plankton ecology and generally termed as a 'bloom'. Harmful algal blooms (HABs) have adverse effects on human health, fishery, tourism, and the environment. In recent years, considerable scientific attention has been given to HABs. Toxic substances released by harmful plankton play an important role in this context. In this paper, a mathematical model consisting of two harmful phytoplankton and zooplankton system will be discussed. The analytical findings will be verified through our experimental observations which were carried out on the eastern part of Bay of Bengal for the last three years.     

Broad sampling and diverse biomarkers allow characterization of nearshore particulate organic matter

Suspended particulate organic matter (POM) is a primary food source for benthic and pelagic consumers in aquatic and marine ecosystems. POM is potentially composed of many sources including phytoplankton, bacteria, zooplankton and macrophyte (seaweed and seagrass) and terrestrial detritus. The relative importance of these sources to POM consumers is debated, in large part due to differing interpretations of stable isotope and fatty acid biomarkers. We investigated POM composition in a nearshore marine ecosystem using multiple methods including visual quantification of living and detrital components, multiple stable isotope (MSI) and fatty acid (FA) analyses. Sampling was conducted at multiple temporal and spatial scales to 1) determine the range of variability in POM biomarkers, 2) quantitatively evaluate δ¹³C, δ¹⁵N, δ³⁴S and FA biomarkers with proportional abundance of putative sources and 3) determine the availability of phytoplankton, macrophytes and terrestrial carbon in nearshore POM. Variation of total FA concentration and proportions, and δ¹³C and δ³⁴S were strongly correlated to phytoplankton abundance, at tidal and seasonal timescales. Using multivariate multiple regressions, MSI and FA explained 59.6% and 89.7% of the variation in POM composition, respectively. As phytoplankton abundance increased, total FA concentration increased concurrent to δ¹³C and δ³⁴S enrichment. In high detritus samples, bacterial FA and saturated FA were proportionally higher, corresponding to depletion of δ¹³C and δ³⁴S and enrichment of δ¹⁵N. We identify MSI and FA biomarkers that are good predictors of diatom, dinoflagellate and detrital contributions to the POM. The results of this multi‐scale study show that POM composition is highly dynamic and largely driven by phytoplankton abundance, with minor contributions from terrestrial or macrophyte subsidies. This quantitative approach provides novel and critical empirical information linking POM compositional dynamics to specific biomarkers that are commonly used for tracking energy subsidies and biogeochemical cycling in aquatic ecosystems.     

镉离子污染条件下微生物群落中细菌与藻类的相互作用

【背景】水体微生物有着丰富的多样性,不同种类的微生物之间的相互作用对水体生态系统的组成结构与功能具有重要影响。水体内的藻类与某些微生物可以发生多种相互作用,然而人们对逆境条件下的菌藻有益相互作用尚缺乏深入研究。【目的】为了研究镉对水体微生物群落的影响以及镉胁迫下菌藻之间可能的相互作用。【方法】本研究运用了基于16S rRNA基因的高通量测序技术,分析在不同Cd~(2+)条件下微生物群落结构的变化,利用微生物相互作用网络分析菌藻之间可能发生的相互作用。【结果】通过分离培养筛选出了与集胞藻PCC6803互作抗Cd~(2+)的关键细菌Y9菌株。【结论】研究结果表明Y9菌株属于Phyllobacteriaceae科,与微生物群落组成和微生物互作网络的分析结果相符。本研究为探索水体环境中微生物种间相互作用、菌藻互作抗Cd~(2+)的生态效应提供参考依据。     

Cascading effects of larval Crucian carp introduction on phytoplankton and microbial communities in a paddy field: top-down and bottom-up controls

Effects of fish predation propagate through aquatic food webs, where the classical grazing food chain and microbial loop are interwoven by trophic interactions. The overall impact on aquatic food webs is further complicated because fish may also exert bottom-up controls through nutrient regeneration. Yet, we still have limited information about cascading effects among fish, zooplankton, phytoplankton, and microbes. In this study, we performed a mesocosm experiment to evaluate effects of fish introduction on plankton communities. Six plots were set in factorial combination with fish introduction and rice straw plowing in a paddy field, and the experiment was continued for 4 weeks. Introduction of fish significantly increased chlorophyll a concentrations in smaller size fractions (<15 μm) and abundances of filamentous bacteria (>5 μm in length) and heterotrophic nanoflagellates in 3–15 μm fraction. Microbes in 0.8–3 μm fraction showed increasing but not significant trends in response to fish introduction. These results indicate cascading effects of fish predation operating via two pathways, one through grazing food chain and the other through microbial food web. Phytoplankton community compositions shifted in similar fashion in all plots until 1 week after fish introduction, and then diverged between plots with and without fish thereafter. Bottom-up effects of fish introduction were suggested by increases of total chlorophyll a and inedible phytoplankton species in response to fish introduction. This study provides an example of how fish predation regulates biomass and structure of phytoplankton and microbial communities.     

Calculation of radiation-induced DNA damage from photons and tritium beta-particles

Yields of DNA single- and double-strand breaks (SSB and DSB) in nucleosomal DNA were calculated for 137Cs, 70 keV photons and tritium beta-particles by Monte Carlo means. Monte Carlo-generated electron tracks for liquid water were used to model energy deposition. Chemical evolution of a track and interactions between species and DNA following water radiolysis were modelled in an encounter-controlled manner. The calculated relative biological effectiveness (RBE) for DSB production for tritium against 137Cs was 1.2 for the total DSB yield. Tritium beta-particles were slightly more efficient compared to 137Cs in producing complex DSB, defined as DSB accompanied by additional strand breaks. The RBE for complex DSB formation was 1.3. Most complex DSB exhibited associated base damage; the extent of the base damage was similar for all the radiation types considered. Correlated DSB conforming to nucleosome periodicity were observed. However, their frequency was low, of the order of 2% of total DSB. For all the DNA damage endpoints considered and their response to variation of the scavenging environment or DNA conformation no difference was observed between 70 keV photons and tritium beta-particles.     

The effects of flood pulse on multiple aquatic organisms in a seasonal shallow lake

Different aquatic organisms have different reactions to environmental variations due to their different ways of reaction traits. Understanding the effect of hydrological disturbance on lake from the perspective of multiple aquatic organisms is important for lake management. Poyang Lake (PYL) experiences severe hydrological disturbance under the effects of flood pulse during the rainy season. In this study, we analyzed the responses of phytoplankton, zooplankton, and macroinvertebrates to hydrological disturbance during the rainy season in PYL. Flood pulse determined the spatial variation in turbidity (Turb), transparency (Trans), dissolved oxygen (DO), total phosphorus (TP), and soluble reactive phosphorus. Physical factors (Turb, Trans, conductivity) explained phytoplankton (9.6%) and zooplankton (15%) community variation, and the combination of physical and nutrient factors explained macroinvertebrate (3.8%) community variation. Cyclotella sp., Attheya zachariasi, and Melosira ambigua were the keystone taxa of phytoplankton, and these taxa were driven by Turb and Trans. Brachionus angularia, Polyarthra vulgaris, Filinia longiseta, and Diffugia globulosa were the keystone taxa of zooplankton and entire aquatic organisms, which contributed a lot to maintain the biological community stability possibly through the food web. These keystone taxa were stimulated by high Trans, DO, dissolved organic carbon (DOC) and nitrate (NO₃^?). We found habitat conditions (Turb, Trans and DO) were the prominent factors influencing the aquatic organism structure in strong hydrological disturbance environment. For the keystone taxa, both habitat conditions (i.e., DO) and exogenous nutrient inputs (i.e., DOC and NO₃^?) caused significant effect. This study provides new insights into the holistic response of multiple aquatic communities to flood pulse as well as the role of keystone species in maintaining community stability, which could guide the conservation and management of seasonal lake ecosystems.

     

The Seasonal Dynamics and Trophic Relations of the Plankton Components in Lake Peipsi (Peipus)

The seasonal dynamics of the biomass and production of phyto-, zoo- and bacterioplankton was investigated during the vegetation periods (from May to November) in 1985 and 1986 in the pelagial of the large eutrophic lake Peipsi (Estonia). The average values of productions per vegetation period for the investigation years were as follows: phytoplanktion − 203.5 gC · m⁻²; bacterioplankton − 37.9 gC · m⁻²; filter-feeding zooplankton − 20.6 gC · m⁻² and predatory zooplankton − 1.5 gC · m⁻². The herbivorous zooplankton production constituted 10.1% of primary production. This ratio indicates a direct relationship between zoo- and phytoplankton in the food chain — filtrators are feeding mostly on living algae and the detrital food chain seems of little importance. The dominance of large forms (Melosira sp., Aphanothece saxicola), in the phytoplankton during the major part of the vegetation period is assumed to be a result of high grazing pressure on small algae. Zooplankton grazing was investigated in situ in a specially constructed twin bathometer. Experimental measurements revealed, that zooplanktion presence in the experimental vessel actually stimulated the phytoplankton growth in many cases — the negative grazing values have been registered. That could be caused by the stimulation effect of nutrients (N, P), excreted by the concentrated zooplankton in the grazing chamber, which led to an increase of the nongrazed phytoplankton production. Bacteria have satisfied the zooplankton food requirements on average by 11%. Grazing on bacteria increased, when grazing on phytoplankton was somehow disturbed.     

Energy metabolism used as a tool to model the transfer of 14C and 3H in animals

The transfer through the environment of ³H and ¹⁴C must be modelled differently than that of other radionuclides released from nuclear reactors because hydrogen and carbon enter straight into the life cycle. A solid understanding of the behaviour of ³H and ¹⁴C in the food chain is essential because ³H may be released in large quantities from future thermonuclear reactors, and ¹⁴C accumulates in the environment because of its long half-life. For the present study, the hypothesis that both ³H and ¹⁴C metabolism in mammals can be modelled based on the understanding of energy metabolism has been tested. Recently published results demonstrate that the loss rate of organically bound tritium and ¹⁴C from tissues of laboratory and farm animals can be assessed based upon their specific metabolic rates and enthalpy of combustion; the same is true for human beings. The improved model presented here relates the dynamics of organically bound tritium and ¹⁴C within organs to the whole body and has been expanded to account for the growth of ruminants. The improved model has been expanded and applied for ¹⁴C transfer in wild mammals and has been modified to apply to birds.     

基于稳定同位素技术的保安湖食物网结构特征研究

文章利用碳、氮稳定同位素技术对江湖阻隔典型湖泊-保安湖的食物网结构进行了研究。结果表明保安湖中鱼类消费者的主要营养级范围为2.1—3.3, 在调查到的16种鱼类中, 顶级肉食性鱼类种类很少, 杂食性鱼类的种类最多。保安湖食物网主要由两条营养传递途径构成, 即由POM、浮游植物为主要食物源的浮游牧食链与沉积物为主要食物源的底栖食物链。POM、浮游植物、浮游动物和底栖动物是保安湖水域食物网中鱼类的主要食物来源, 其次是沉积物中的碎屑和水生植物等。此外, 从基于理论食性数据的食物网与BIMM模型预测的食物网结构可以看出, 从POM、浮游植物、浮游动物到杂食性鱼类的浮游牧食链在整个食物网中具有主导性, 而从水生植物、沉积物和底栖动物到杂食性鱼类的底栖食物链相对重要性较低。     

Tritium NMR studies of the human carbonic anhydrase I–benzenesulfonamide complex

Tritium NMR spectroscopy has been used to examine the complexformed by [4-³H]benzenesulfon-amide and human carbonicanhydrase I. The results show that in solution the inhibitor forms a 1:1complex with the enzyme. A 100-spin computational model of the system,constructed with reference to crystallographic results, was used tointerpret tritium relaxation behavior and ³H{¹H}NOEs. The analysis shows that the rate of dissociation of theenzyme–sulfonamide complex is 0.35 s^–1 and thatthe aromatic ring of the inhibitor undergoes rapid rotation while complexed.     

Selenium in sediment and food webs of the Tapajós River basin (Brazilian Amazon) and its relation to mercury

BackgroundWe investigated Se levels along the Tapajós River basin - which is an important tributary of the Amazon River - and the possible antagonistic effect of Se in Hg availability. This is the first study to investigate Se transfer from abiotic to biotic compartments and along the food chain in aquatic ecosystems of the Amazon basin.MethodsSe concentrations were measured in superficial sediment (n = 29), plankton (n = 28) and fishes (n = 121) along two stretches of the Tapajós River basin (Tap_up/mi and Tap_low), comprising approximately 500 km with different hydrological characteristics.ResultsSe concentrations in sediment were significantly higher in the Tap_low (345−664 μg kg⁻¹) than in the Tap_up/mi (60−424 μg kg⁻¹). The seasonal flooding of the Amazon River probably helps to carry selenium-rich sediment to the Tapajós mouth (Tap_low stretch). We suggest that Se in sediment could decrease the bioavailability of Hg resulting in lower MeHg concentrations in fish, as observed in the Tap_low (45−934 μg kg⁻¹). Sediment and plankton were positively correlated in relation to their Se concentrations (r = 0.62; p = 0.001) suggesting that sediment can possibly be the main source of Se to plankton. Our data indicate Se uptake by primary consumers, as noted in phytoplankton levels. The decrease of Se concentrations along the food chain was also noteworthy.ConclusionThis work elucidates some aspects of Se biogeochemistry in the Amazon basin and shows its importance regarding Hg cycles in aquatic ecosystems.     

Partitioning the Relative Importance of Phylogeny and Environmental Conditions on Phytoplankton Fatty Acids

Essential fatty acids (EFA), which are primarily generated by phytoplankton, limit growth and reproduction in diverse heterotrophs. The biochemical composition of phytoplankton is well-known to be governed both by phylogeny and environmental conditions. Nutrients, light, salinity, and temperature all affect both phytoplankton growth and fatty acid composition. However, the relative importance of taxonomy and environment on algal fatty acid content has yet to be comparatively quantified, thus inhibiting predictions of changes to phytoplankton food quality in response to global environmental change. We compiled 1145 published marine and freshwater phytoplankton fatty acid profiles, consisting of 208 species from six major taxonomic groups, cultured in a wide range of environmental conditions, and used a multivariate distance-based linear model to quantify the total variation explained by each variable. Our results show that taxonomic group accounts for 3-4 times more variation in phytoplankton fatty acids than the most important growth condition variables. The results underscore that environmental conditions clearly affect phytoplankton fatty acid profiles, but also show that conditions account for relatively low variation compared to phylogeny. This suggests that the underlying mechanism determining basal food quality in aquatic habitats is primarily phytoplankton community composition, and allows for prediction of environmental-scale EFA dynamics based on phytoplankton community data. We used the compiled dataset to calculate seasonal dynamics of long-chain EFA (LCEFA; ≥C₂₀ ɷ-3 and ɷ-6 polyunsaturated fatty acid) concentrations and ɷ-3:ɷ-6 EFA ratios in Lake Washington using a multi-decadal phytoplankton community time series. These analyses quantify temporal dynamics of algal-derived LCEFA and food quality in a freshwater ecosystem that has undergone large community changes as a result of shifting resource management practices, highlighting diatoms, cryptophytes and dinoflagellates as key sources of LCEFA. Moreover, the analyses indicate that future shifts towards cyanobacteria-dominated communities will result in lower LCEFA content in aquatic ecosystems.     

Phytoplankton and its contribution to primary productivity in two coral reef areas of French Polynesia

A study of phytoplankton productivity and related parameters was carried out in two fringing and barrier reef systems around Moorea island (Tiahura lagoon) and Tahiti (Vairao lagoon), Society Islands, during July–August 1974.In Tiahura lagoon, which is the narrower and the shallower, phytoplankton standing crop and production are extremely low; photosynthetic assimilation, as measured in situ by the ¹⁴C method, ranges from 4 to 27 mg C m^?2 day^?1, presumably less than in the impoverished open ocean, but it is surprisingly high at a station just outside the barrier reef (645 mg C m^?2 day^?1) as the result of some island mass effect. As compared to the latter station, the lagoon shows a ten-times increase in particle content and glucose uptake, and a higher percentage of decomposition products of plant pigments. These data support the concept that, in such environments where benthic primary producers prevail, phytoplankton may have lost its ‘usual’ rôle in the aquatic food web.Vairao lagoon, a deeper and wider one, subjected to a greater extent to land fertilization, is more productive (103–420 mg C m^?2 day^?1). Considering this difference, as well as the considerable range of phytoplankton production in coral reef areas of the world, the need for a trophic classification of such ecosystems is emphasized.