Differences In Accumulation Rates Research Articles

An accelerated rate of Beta‐amyloid Measured with [C‐11]PiB in Down Syndrome compared to Neurotypical Populations

AbstractBackgroundDown syndrome (DS) is characterized by a higher risk and earlier onset of beta‐amyloid (Aβ) plaque accumulation and Alzheimer’s disease (AD). The triplication of chromosome 21 containing the amyloid precursor protein (APP) gene is implicated in this process and in this study we compare the accumulation rates of Aβ between DS and neurotypical (NT) populations quantified by longitudinal [C‐11]PiB imaged at the same site to minimize experimental variation.MethodsIndividuals with three or more [C‐11]PiB scans spanning eleven years our site with at least one Aβ+ (global SUVR>1.40) and Aβ‐ [C‐11]PiB scan were selected. 12 of 74 DS and 15 of 246 NT participants fit these criteria. An identical imaging procedure was conducted for all participants imaged on either an ECAT HR+ or Biograph mCT PET scanner 50‐70 minutes post‐injection. Reconstructed PET images were summed and spatially normalized into template space and converted into 50‐70min SUVR images using a cerebellar grey matter reference region. Global SUVR composed of grey matter regions from the AAL atlas was used as a metric for Aβ deposition. SUVR data were fit against age with a logistic growth curve (f(t) = NS+K/(1+e(‐r(t‐t50)))) to determine Aβ accumulation as subjects transitioned to Aβ+. The rate of accumulation was found using the slope of the curve at Aβ positivity threshold based on the model fit. Our model fixed NS = 1.12, the average baseline SUVR of all Aβ‐ subject scans (n = 491), and K = 1.28, the highest specific binding in any participant.ResultsPlotting [C‐11]PiB SUVR against age provides visual comparisons of cohorts (Fig 1) and transforming the x‐axis to amyloid chronicity (t = 0 at Aβ+) illustrates differences in accumulation rates between groups (Fig 2). The average rate of amyloid accumulation (ΔSUVR/yr) when becoming Aβ+ in the DS cohort is 0.071(0.021) versus 0.043(0.009) for NT (p = 4.31×10−4).ConclusionsAβ accumulation rate was higher in the DS cohort compared to NT. This is consistent with the additional APP gene copy in DS, and we observed an accumulation rate 65% faster in this cohort. There was a higher variability in the DS population requiring further investigation towards understanding the influence of genetic and lifestyle factors on Aβ deposition.

Leukemia risk and the pattern of dose accumulation. Part 1: Characteristics of the study group of the Mayak Production Association personnel

Results of development of the database “Leukemia in the cohort of workers of the Mayak Production Association employed in 1948-1958” that was developed in the Laboratory of Radiation Epidemiology of Southern Urals Biophysics Institute were presented. The database contains hematological, clinical and dosimetric information for the workers of main plants of the first production facility of Soviet atomic industry employed in the period of production development – 1948-1958. The computer database contains information for two groups of Mayak Production Association workers: main group of workers with leukemia as the main cause of death (n=84) and group of personnel without hematological cancer pathology for comparison (n=300). The comparison group was composed in such a way to allow 3-4 controls of corresponding gender, age of exposure start, accumulated dose of external gamma-exposure to red bone marrow for each leukemia case. Methods of data collection and sources of medical data were described. Characteristics of software developed for the database was presented. The database containing a total of 19593 results of blood tests reflects dynamics of hematological values in atomic facility personnel due to prolonged radiation exposure. The range of accumulated absorbed doses of external gamma-exposure to red bone marrow in the group of personnel with leukemia diagnoses was 0.001-4.96 Gy; average dose for males was 1.24 Gy and 0.61 Gy – for females. Similar range is observed in the group of personnel without leukemia outcomes. Alongside differences in accumulation rates of external radiation exposure doses is evident: in the group of workers with hematological cancer pathology the average period of radiation exposure at production facility was 14.3 years for males and 12.1 years for females; in the comparison group – 20.4 and 13.9 years, respectively. Most leukemia cases were diagnosed in the workers of radiochemical facility (54.8%). Myeloid leukemia prevailed (47.6%) in the leukemia structure; among them acute myeloid leukemia made more than a half of the cases; lymphoid leukemia was diagnosed in 14.3% cases with prevailing role of chronic lymphoid leukemia. Acute and chronic monocytic leukemia were the rarest types of malignant neoplasms of hematopoietic tissue. Possible correlation between hematological values with individual doses of external gamma- and internal alpha-exposure (incorporated Pu-239) distributed over time was stated. The database allows calculating integrated leukocytic indices reflecting response of hemopoietic system to radiation exposure, tracking changes in hemopoiesis in proportion to accumulated dose to red bone marrow, analyzing specific characteristics of rehabilitation of hematological alterations after occupational contact to ionizing radiation is terminated. Information on acute and chronic diseases available for the workers in the database allows excluding non-specific response of hemopoietic system caused by associated pathology. A revision of leukemia risk estimated in the relation to dose rate for personnel exposed to chronic radiation could be regarded as one of perspective trends in using the database.

RACIAL-ETHNIC DIFFERENCES IN MULTIMORBIDITY PROGRESSION ACCORDING TO BODY-WEIGHT STATUS AMONG OLDER U.S. ADULTS

Obesity and multimorbidity are more prevalent among underrepresented U.S. racial/ethnic minority groups. Evaluating whether racial/ethnic disparities in multimorbidity accumulation vary according to body-mass index (BMI) may guide interventions aimed at reducing multimorbidity burden in vulnerable racial/ethnic groups. We used 1998-2014 data from the Health & Retirement Study (N=8,635 participants, age 51-55 years old at baseline) and negative binomial models stratified by BMI category to evaluate differences in rates of accumulation of seven chronic conditions (arthritis, cancer, diabetes, heart disease, hypertension, lung disease, and stroke), focusing on differences between racial/ethnic groups [White (reference; 64.7%), Black (21.5%), Hispanic (13.8%)]. Overweight and obesity were more prevalent in Black (80.9%) and Hispanic (78.6%) than White (69.9%) participants at baseline; in all BMI categories, Black participants had higher rates of multimorbidity compared with White participants (normal BMI:β=0.304, p<0.001; overweight:β=0.243,p<0.001; and obese:β=0.135,p=0.013); initial burden of disease was similar between Whites and Hispanics in the normal and overweight categories, but significantly lower among Hispanics (vs. Whites) in the obese category (β= -0.180,p=0.017). We found no significant differences in rates of disease accumulation between the racial/ethnic groups in any of the BMI categories. There are substantial differences in initial disease burden between Black and White middle-aged/older adults, but not in the rate of accumulation of disease between the race/ethnic groups in the 3 main BMI categories. These findings suggest an opportunity to reduce racial disparities in multimorbidity by intervening early in the lifecourse to reduce the burden of chronic disease among vulnerable racial minorities prior to entering middle-age.

Evaluating the historical sedimentation patterns in two different Mediterranean deep environments (Sardinia and Sicily Channels)

The sediment accumulation rate in the Sardinia and Sicily channels in the central part of the Mediterranean Sea was studied by using short-lived radionuclides (210Pb and 137Cs) in two deep sediment cores. Different sedimentation regimes were identified indicating substantial differences in accumulation rates and historical patterns. The 210Pb-derived mean accumulation rate found in the Strait of Sardinia was 0.05 g.cm-2.y-1, lower than that in Sicily Channel (0.1 g.cm-2.y-1) suggesting an inverse correlation with water depth. Excess 210Pb inventories were 24 ± 1 and 6.0 ± 0.4 kBq.m-2, while the fluxes to the sediment were 745 ± 31 and 188 ± 11 Bq.m-2.y-1 in Sicily and Sardinia channels, respectively. 137Cs failed to use for the validation of the established chronologies, while its inventories found 450 Bq.m-2 and 355 Bq.m-2 in the Sicily and Sardinia channel, respectively.

Determinants of mercury contamination in viperine snakes, Natrix maura, in Western Europe

The effects of Hg contamination are presumably widespread across the components of aquatic ecosystems, but investigations have been mainly focused on freshwater fish, because this biota represents a major source of Hg for human populations. Yet, the possible bioaccumulation of Hg on other freshwater meso- and apex-predators (e.g., amphibians, reptiles) has been largely overlooked, especially in Western Europe. In this study, the determinants of Hg concentrations were assessed for the viperine snake (Natrix maura) across 6 populations (>130 individuals sampled in 2016 and 2017) in France and Spain. Specifically, body size, sex, and diet were compared with Hg concentrations measured in ventral scales. Overall, N. maura accumulated Hg in their scales. Sex did not seem to influence Hg concentrations in this species. Significant differences in Hg concentrations were observed between study sites, and these differences were likely to be mediated by site-specific diet. Frog-eating individuals were characterized not only by lower mean values of Hg (0.194±0.018μg·g−1 versus 0.386±0.032μg·g−1 for piscivorous individuals), but also by weaker slopes of the body size-Hg relationship as compared to fish-eating snakes, suggesting strong differences in accumulation rates due to food resources. Importantly, the highest slope of the body size-Hg relationship and the highest values of Hg were found in individuals foraging on trout raised by a fish farm, suggesting that fish farming may contribute to Hg contamination in inland freshwater systems. Finally, our results are compared with data on Hg concentrations in other species of aquatic snakes, in order to provide a comparative point for future studies.

Uranium isotope geochemistry in modern coastal sediments: Insights from Toulon Bay, France

Abstract By assessing U geochemistry in marine sediments of Toulon Bay (NW Mediterranean Sea), authigenic U accumulation was found to be tightly linked to that of Mo and V with slight differences in accumulation rate depending on sediment redox conditions. In sediments collected on a transect along a river plume, the authigenic accumulation of these redox-sensitive elements appears to be linked to sediment grain size which probably drives the redox status of the sediments. A typical U loss in re-oxidized sediments was observed in sediments that had been previously disturbed. However, the dissolved U profiles do not show a simple and typical depletion trend but rather a depletion in the top 10 cm followed by release in deeper pore waters that could be linked to a potential reoxidation/mobilization of authigenic U(IV). The released U could be further scavenged as a U-P precipitate. The U isotopic data (δ238U), which are the first reported for the coastal hypoxic sediments of Toulon Bay, average −0.12 ± 0.12‰ in surface sediments. However, sediments situated in front of river mouths show higher values of δ238U (up to +0.75‰); these high values are reported for the first time in sediments below an oxic water column.

Rapid Increase in Genome Size as a Consequence of Transposable Element Hyperactivity in Wood-White (Leptidea) Butterflies.

Characterizing and quantifying genome size variation among organisms and understanding if genome size evolves as a consequence of adaptive or stochastic processes have been long-standing goals in evolutionary biology. Here, we investigate genome size variation and association with transposable elements (TEs) across lepidopteran lineages using a novel genome assembly of the common wood-white (Leptidea sinapis) and population re-sequencing data from both L. sinapis and the closely related L. reali and L. juvernica together with 12 previously available lepidopteran genome assemblies. A phylogenetic analysis confirms established relationships among species, but identifies previously unknown intraspecific structure within Leptidea lineages. The genome assembly of L. sinapis is one of the largest of any lepidopteran taxon so far (643 Mb) and genome size is correlated with abundance of TEs, both in Lepidoptera in general and within Leptidea where L. juvernica from Kazakhstan has considerably larger genome size than any other Leptidea population. Specific TE subclasses have been active in different Lepidoptera lineages with a pronounced expansion of predominantly LINEs, DNA elements, and unclassified TEs in the Leptidea lineage after the split from other Pieridae. The rate of genome expansion in Leptidea in general has been in the range of four Mb/Million year (My), with an increase in a particular L. juvernica population to 72 Mb/My. The considerable differences in accumulation rates of specific TE classes in different lineages indicate that TE activity plays a major role in genome size evolution in butterflies and moths.

Spatial and temporal variations and controlling factors of sediment accumulation in the Yangtze River estuary and its adjacent sea area in the Holocene, especially in the Early Holocene

The sub-bottom and collected borehole data provide insight into the transport and accumulation processes of the Yangtze-derived sediment in the study area since ~11kyr BP. Five seismic units were identified according to six major acoustic surfaces. The sedimentary strata consist of fluvial, estuarine and deltaic systems from the bottom up, characterized by two different trends in sediment accumulation rates, i.e., low-high-low, and high-low-high. On the inner shelf of the East China Sea, the terrain with trough and ridge was formed by the Early Holocene transgression strata (formed in ~10 to 12kyr BP) scoured by the later rectilinear tidal current due to postglacial sea-level transgression, and the sharply protruding seismic units are interpreted to be bedrocks outcropping on the seafloor. An analysis of the sedimentary characteristics in the boreholes and such factors as difference in accumulation rates, and tectonic subsidence led us to conclude that the paleo-coastline was located not far away from and to the east of Core ZK09 at ~9kyr BP, and the southern bank of the Yangtze River estuary was located to the south of Core ZK09. At ~9kyrBP, the Yangtze-derived sediments were transported eastwards along the southern bank of the Yangtze River and the barrier due to the influence of the paleo-coastal current from the north, the direction of the Yangtze-derived sediment transport was split on the northeast of the Zhoushan archipelago, and the sediments covered the terrain with trough and ridge. During the high sea level period (7kyr BP–present), the eastward migration of paleo-coastline had resulted in the increase in accumulation rate. We also conclude that the sharp increase in accumulation rate near the Yangtze River estuary after ~2kyr BP was not primarily caused by human activities. The position shifts of the estuary caused by the paleo-coastline migration and sea level oscillations since the Holocene is the main cause controlling the Yangtze-derived sediment distribution, and the difference in accumulation rate at different locations in the study area.

Particle Accumulation Rate of Drinking Water Distribution Systems Determined by Incoming Turbidity

Particulate material accumulates in drinking water distribution systems (DWDS) and this can cause discolouration. To minimize customer complaints it is required to understand the influencing factors and determine an appropriate flushing frequency. The accumulation rates of two comparable DWDS were examined. Area A with a constant incoming water quality experiences a steady accumulation rate; area B with a more variable incoming water quality has a variable accumulation rate. The difference in accumulation rate is proportionate to the difference in the particle loading of the two areas and is thus largely determined by the difference in incoming water quality. The water quality into a DWDS is not only determined by the treatment works, but also by the material accumulation and resupsension in the trunk mains supplying it. Monitoring the particle loading of a DWDS part can help in determining the required flushing frequency.

Observations, theory, and modeling of the differential accumulation of Antarctic megadunes

Antarctic megadunes are characterized by significant spatial differences in accumulation rate, with higher accumulation on the windward side and near-zero accumulation on the lee side. This leads to spatial differences in physical properties of snow and surface roughness, as well as to the upwind migration of the megadunes. While previous studies agree that megadunes are a result of complex interactions between wind, topography, and snow, it is not clear how they form or why they accumulate on the windward side. Here we use ICESat observations, dimensional analysis, and atmospheric flow modeling to investigate what conditions are responsible for the accumulation patterns and upwind migration of the megadunes. First, we use ICESat data to quantify the pattern of differential surface elevation change across the megadunes. We then use dimensional analysis based on supercritical-flow theory and atmospheric flow modeling to show that the megadunes topography and a stable atmosphere will always lead to upwind dune migration. We show that a combination of persistent katabatic winds, strong stability, and spatial variability in surface roughness is responsible for the accumulation on the upwind slope and hence the upwind migration of the megadunes. We further show that spatial differences in surface roughness are the primary control on accumulation magnitudes and hence dune migration velocity. The dune migration velocity in turn influences the degree of snow-metamorphism and the physical properties of snow that are relevant for paleoclimate records. Our findings pertain to the ongoing evolution of the megadunes, but their genesis remains an open question.

Microstructural evolution of fine-grained layers through the firn column at Summit, Greenland

AbstractWe present a microstructural characterization of fine-grained layers from the top 90 m of firn from Summit, Greenland, performed using a combination of scanning electron microscopy techniques including secondary electron imaging, energy-dispersive spectroscopy and electron backscattered patterns, and X-ray microcomputed tomography. The impurities in the firn, both soluble impurities and dust particles, were found largely in the grain interiors. Both c- and a-axis pole figures do not show strong evidence of a preferred orientation of the grains even at the bottom of the firn column. The firn structure became increasingly anisotropic with vertical alignment in the top 3 m, probably due to vapor transport associated with dry-snow metamorphism. The anisotropy decreases below this level until at ∼50 m the average firn structure is close to isotropic. In the near surface, the level of anisotropy is weaker than at Hercules Dome, Antarctica, confirming that differences in accumulation rates and temperatures leave enduring evidence in the structure of the firn. The fraction of closed-off pores is relatively low until ∼65 m; below that it rises through the end of our sampling at 90 m. Our microstructure measurements on the microscale are consistent with in situ firn-air sampling measurements on a decimeter scale, both indicating the existence of the lock-in zone starting near 69 m depth, and pore close-off at 81 m at this site.

Metal accumulation and metallothionein induction in the spotted dogfish Scyliorhinus canicula

Recent studies indicate that elasmobranch fish respond differently to metal exposure than marine teleosts. Accumulation rates can be high, which despite the fact that normal background levels for metals in the marine environment are low, is worrying due to the long life span and late fecundity of most shark. The goals of the present study were to examine differences in accumulation rates and toxicity of a range of metals at equimolar concentrations (10 µM) in the Mediterranean or spotted dogfish, Scyliorhinus canicula. For this purpose, we exposed the dogfish to Ni (587 µg/L), Cd (1124 µg/L), Pb (2072 µg/L), Cu (635 µg/L), and Ag (1079 µg/L and two additional exposures at 10 µg/L and 1 µg/L) for one week and measured total metal accumulation, metallothionein induction, and parameters related to osmoregulation. Our study confirms the high toxicity and accumulation rates of Ag for elasmobranch fish, even at levels 100 to 1000 times lower than exposure levels of other metals. Also Pb accumulated readily in all organs, but did not cause any osmoregulatory disturbance at the exposure levels used. Ni and Cd seem to accumulate primarily in the kidney while Cu mainly accumulated in liver. In contrast to Ni and Cd, the three other metals Ag, Cu and Pb accumulated in the rectal gland, an important organ for osmoregulation and possible target organ for metal toxicity. Only Cu succeeded in initiating a protective response by inducing MT synthesis in liver and gills.

Metal accumulation and metallothionein induction in the spotted dogfish Scyliorhinus canicula

article i nfo Keywords: Elasmobranch Chondrichthyes Shark Nickel Cadmium Lead Silver Copper Urea Recent studies indicate that elasmobranch fish respond differently to metal exposure than marine teleosts. Accumulation rates can be high, which despite the fact that normal background levels for metals in the marine environment are low, is worrying due to the long life span and late fecundity of most shark. The goals of the present study were to examine differences in accumulation rates and toxicity of a range of metals at equimolar concentrations (10 µM) in the Mediterranean or spotted dogfish, Scyliorhinus canicula. For this purpose, we exposed the dogfish to Ni (587 µg/L), Cd (1124 µg/L), Pb (2072 µg/L), Cu (635 µg/L), and Ag (1079 µg/L and two additional exposures at 10 µg/L and 1 µg/L) for one week and measured total metal accumulation, metallothionein induction, and parameters related to osmoregulation. Our study confirms the high toxicity and accumulation rates of Ag for elasmobranch fish, even at levels 100 to 1000 times lower than exposure levels of other metals. Also Pb accumulated readily in all organs, but did not cause any osmoregulatory disturbance at the exposure levels used. Ni and Cd seem to accumulate primarily in the kidney while Cu mainly accumulated in liver. In contrast to Ni and Cd, the three other metals Ag, Cu and Pb accumulated in the rectal gland, an important organ for osmoregulation and possible target organ for metal toxicity. Only Cu succeeded in initiating a protective response by inducing MT synthesis in liver and gills.

Near‐zero recent carbon accumulation in a bog with high nitrogen deposition in SW Sweden

AbstractWe present data on the accumulation of carbon and nitrogen into an open oceanic ombrotrophic bog, SW Sweden, with high levels of anthropogenic nitrogen deposition. The aim was to investigate if this peatland currently acts as a sink for atmospheric carbon. Peat cores were sampled from the top peat layer in five different vegetation types. Small pines were used to date the cores. The cores bulk density and carbon and nitrogen content were determined. A vegetation‐classified satellite image was used to estimate the areal extent of the vegetation types and to scale up these results to bog level. The rate of current carbon input into the upper oxic acrotelm was 290 g m−2 yr−1, and there were no significant differences in accumulation rates among the vegetation types. This organic matter input to the acrotelm was almost completely decomposed before it was deposited for storage in the deeper peat layers (the catotelm) and only a small fraction (≪1%) or 0.012 g m−2 yr−1 of the carbon would be left, assuming a residence time of 100 years in the acrotelm. Nitrogen accumulation rates differed between the vegetation classes, and the average input via primary production varied from 5.33 to 16.8 g m−2 yr−1. Current nitrogen input rates into the catotelm are much lower, 0–0.059 g m−2 yr−1, with the highest accumulation rates in lawn‐dominated communities. We suggest that one of the main causes of the low carbon input rates is the high level of nitrogen deposition, which enhances decomposition and changes the vegetation from peat‐forming Sphagnum‐dominance to dominance by dwarf shrubs and graminoids.

Impacts of an accumulation hiatus on the physical properties of firn at a low‐accumulation polar site

Recent field investigations of a megadune region of East Antarctica provide evidence that differences in grain size, thermal conductivity, and permeability across a megadune profile are due to spatial accumulation variability in the absence of significant microclimate variations. The megadunes are low‐amplitude (2–8 m), long‐wavelength (2–5 km) bands with perceptible but low accumulation (less than 40 mm water equivalent (weq) yr−1) and accumulation hiatus within several kilometers proximity, as determined by remote sensing, surface feature classification, and ground‐penetrating radar profiling. Our hypothesis that accumulation rate impacts the extent of temperature gradient–driven metamorphic growth in low accumulation rate sites is supported by measurements of various firn physical properties. Relatively small differences in accumulation rate (less than 40 mm weq yr−1) result in large differences in physical properties, including grain size, thermal conductivity, and permeability, which are apparent in satellite‐based microwave data from both passive and active sensors. The differences in physical snow structure between low‐accumulation areas and accumulation hiatus areas in the near surface are sufficiently distinct that evidence of past accumulation hiatus should be observable in the physical and chemical properties of an ice core record.

Physico-chemical and toxicological characterization of the historic estuarine sediments: A multidisciplinary approach

The accumulation rates, the geochronology of metals and PAH contamination, and the Microtox ® toxicity are studied in five sediment cores (50 cm length) covering different areas of the Santander Bay, Northern Spain. Chronology given by 210Pb and 137Cs reveals significant differences in accumulation rates between sites (0.2–1.1 cm/year), as well as a variable degree of anthropogenic enrichment factors for Fe, Mn, Cu, Pb, Zn, Ni (from 1 to 15) and concentrations of ∑16PAHs (from 0.01 to 23.84 mg/kg dw) in sediments over the last 90 years. The results indicate the increasing contamination pressure from industrial and urban activities along the Bay. No toxic results from the Microtox ® test are obtained either with pore water or with normalised sediment aqueous extracts (European Norm EN 12457), suggesting low water solubility and low availability of contaminants in the studied sediments. However, the EC50 values from the Microtox ® Basic Solid Phase Test (BSPT) ranged from 0.03% to 2.35%, showing vertical toxicity profiles in accordance with metal and PAHs behaviour. The correlation degrees of Microtox ® BSPT toxicity to chemical concentration in sediment profiles are widely variable showing a high site-dependent toxicity. The oligochaete Limnodrilus hoffmeisteri has been used as a chronic bioassay over surface sediments of two of the studied sites, showing results coherent with the Microtox ® BSPT acute test results. Global results of the present work provide regional geochemical baselines for metals and PAHs and toxicological data now make it possible to obtain a preliminary quality assessment of the Santander Bay sediment profiles.

Biomonitoring of selected freshwater macrophytes to assess lake trace element contamination: a case study of Nal Sarovar Bird Sanctuary, Gujarat, India

A biomonitoring study was carried out at Nal Sarovar Bird Sanctuary, a proposed Ramsar site, Gujarat State, India, to ascertain the degree of trace element contamination. The study focused on assessment of trace element contamination in certain aquatic macrophytes to be used as biomonitors, in comparison with the sediments (abiotic monitor) for heavy metal pollution. Good information was provided by analyzing roots, stems and leaves of native aquatic plants (biomonitors) represented by eight species: Bergia odorata, Hydrilla verticillata, Ipomoea aquatica, Najas graminea, Nelumbo nucifera, Phragmites karka, Typha angustata and Vellisnaria spiralis, alongwith surface sediments and water, were analyzed for Cd, Co, Cu, Cu, Ni, Pb and Zn contamination. The highest concentrations of the trace elements were measured in Ipomoea aquatica and the lowest in Bergia odorata. Based on the concentration and toxicity status observed in the lake's vegetation, the six metals are arranged in the following decreasing order: Zn > Cu > Ni > Co > Pb > Cd. Compared with the standard, normal and critical toxicity range in plants, the detected values of Cd and Pb falls within normal range, while that of Co, Ni and Cu were within the critical range. However, Zn showed the highest concentration and alarming toxicity levels, which is considered as one of the most hazardous pollutants in Nal Sarovar Bird Sanctuary. Certain aquatic macrophytes species are also proposed as biomonitors for the investigated heavy metal pollutants. Such result was significant in the plant species such as Ipomoea aquatica and Phragmites karka, which are the two most useful species in biomonitoring studies due to their ability to accumulate elements in high concentration in the roots and their availability throughout the year. The results showed the significant difference in accumulation rate of some metals like Zn, Cu and Ni in different plant organs, which showed more accumulation in root than that of stem and leaves. Also, there is a high positive correlation between combinations of different metal-pairs in either plant's root, stem or leaf system.

Roles of uptake, biotransformation, and target site sensitivity in determining the differential toxicity of chlorpyrifos to second to fourth instar Chironomous riparius (Meigen)

Early life stages of aquatic organisms tend to be more sensitive to various chemical contaminants than later life stages. This research attempted to identify the key biological factors that determined sensitivity differences among life stages of the aquatic insect Chironomous riparius. Specifically, second to fourth instar larvae were exposed in vivo to both low and high waterborne concentrations of chlorpyrifos to examine differences in accumulation rates, chlorpyrifos biotransformation, and overall sensitivity among instars. In vitro acetylcholinesterase (AChE) assays were performed with chlorpyrifos and the metabolite, chlorpyrifos-oxon, to investigate potential target site sensitivity differences among instars. Earlier instars accumulated chlorpyrifos more rapidly than later instars. There were no major differences among instars in the biotransformation rates of chlorpyrifos to the more polar metabolites, chlorpyrifos-oxon, and chlorpyridinol (TCP). Homogenate AChE activities from second to fourth instar larvae were refractory to chlorpyrifos, even at high concentrations. In contrast, homogenate AChE activities were responsive in a dose-dependent manner to chlorpyrifos-oxon. In general, it appeared that chlorpyrifos sensitivity differences among second to fourth instar C. riparius were largely determined by differences in uptake rates. In terms of AChE depression, fourth instar homogenates were more sensitive to chlorpyrifos and chlorpyrifos-oxon than earlier instars. However, basal AChE activity in fourth instar larvae was significantly higher than basal AChE activity in second to third instar larvae, which could potentially offset the apparent increased sensitivity to the oxon.

Productivity Dynamics in a Large Sample of Countries: A Panel Study

Recent research shows that productivity differences are more important than differences in accumulation rates in explaining per capita income differences across countries. So far static differences in productivity have been mainly computed and analyzed in large samples of countries. This paper extends the research by focusing on productivity dynamics. It uses the panel approach to compute productivity indices for a large sample of countries for two time periods, namely an initial period of 1960–75 and a subsequent period of 1975–90. This allows computation of ordinal and cardinal changes in productivity between the two periods. The results show considerable variation in productivity dynamics across countries. The task ahead is to find out what accounts for the observed dynamics.

Responses of Niphargus montellianus and Gammarus balcanicus (Crustacea, Amphipoda) from karst waters to heavy metal exposure

The response to some heavy metals (Cd, Cu, and Zn) was examined in two amphipods, Niphargus montellianus and Gammarus balcanicus, living in karst waters and endowed with different ecological characteristics. Exposure experiments were made, in the controlled conditions of a biospeleology laboratory, to increasing concentrations of metals in the range 0.1-10 μg ml -1 for up to 10 days. Hypogean and epigean amphipods differed in their responses, G. balcanicus being more sensitive to the toxic effects of heavy metals than the hypogean N. montellionus. The degree of tolerance was Cu<Cd<Zn in both organisms. Metal contents were checked in amphipods in natural conditions and after metal exposure; differences in accumulation rates suggest the potential use of Niphargus as a biological indicator for monitoring groundwater heavy metal pollution.