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Biomedical subjects

J Blok

Publications and source records attributed to J Blok.

At least 19 recordsLinked to original sources
PubMed2005

Environmental exposure of road borders to zinc.

The emissions of zinc along roads originating from tyre wear, corrosion of safety fence and other traffic-related sources have been quantified and validated by measured long-term loads in road run-off and airborne solids (drift) for 29 published case studies. The distribution pattern over the road border at various distances from the edge of the paved surface is assessed on the basis of 38 published case studies with measured concentrations in soil. For the impact assessment, the road border is differentiated into a zone that is part of the "technosphere" and the "target zone" beyond that technosphere that can be considered as part of the receiving environment. The "technosphere" of the road includes the central reservation, the hard and the soft shoulder or, if one or both shoulders are not present, the so-called obstacle "free zone" that is defined by road engineers. Pollution within the technosphere may require appropriate management of solid disposal and isolation from groundwater to prevent further distribution of pollutants to the environment. In the target zone along regional roads, the zinc load is about 4 mg/m(2) year and this is of the same order of magnitude as that of atmospheric deposition in areas beyond the influence of roads (background). In the target zone along highways, the zinc load is increased in comparison to the background deposition. The average load of about 38 mg/m(2) year is similar to that in fertilised agricultural land. Because most of the emitted zinc stays in the technosphere, the total amount entering this target zone along highways is limited. From the 140 tons of zinc per year that is released from tyre wear in The Netherlands, 64 tons is emitted in the urban area, 6.5 tons reaches to the target zones of all roads and only 1.1 tons of zinc will enter the target zone along highways. This amount will be further decreased by the application of porous asphalt in the near future. The emission from safety fence corrosion does not enter the target zone. Only in special cases, such as bridges, crossings and squares the release of zinc from these sources may enter the aquatic environment by the discharge of run-off.

Environmental Monitoring↗
PubMed2001

A single model for mass transfer and growth for biodegradation rates in activated sludge.

In the scope of environmental risk assessment for new and existing chemicals a generic model is developed to predict the possible concentration of pollutants after passage of sewage treatment plants. The model combines Monod kinetics with mass transfer rates through an imaginary boundary layer between mixed liquor and active biomass. For each specific substance a combined rate constant can be calculated. This combined rate constant is dependent on the influent concentration of the substance and the maximum growth rate of the substance as the main inherent substance property. All other parameters are inherent for the activated sludge process and can be quantified on the basis of generic default values. Monod kinetics for bacterial growth are modified for a concentration gradient between the mixed liquor and the suspended solids. This gradient causes a difference between an apparent half-saturation value (K(S app)) and the real half-saturation value (K(S real)). Real half-saturation values are estimated by linear extrapolation of a plot of the apparent values against mass transfer rates, whereas the slope of this plot gives the specific diffusion limited mass transfer rate constant (K(diff)). From the available data it is concluded that values for K(S real) for water-soluble substances are below 100 microg COD/L, whereas the value for K(diff) varies between 100 and 500/day. Compared to the currently applied default values, which are based on a classification between ready and inherent biodegradability, the proposed method is more sophisticated.

Algorithms↗
PubMed2000

Probability of biodegradation, a novel concept for improving chemical classification and risk assessment.

In this article biodegradability is considered as a combination of an inherent substance property, defined as the maximum specific growth rate, mumax and a condition of the environment defined as a specific fraction (fs) of the total viable biomass. By proper analysis of test results it is possible to quantify both parameters by one single standard test. Calculations with literature data indicate that for the majority of the degradable substances, mumax may vary between 0.5 and 10 per day. The specific fractions, however, may vary 5 or 6 orders of magnitude and can be as low as 10(-8). This concept gives a valuable tool in environmental risk assessment. As the results will be less influenced by test conditions, data will be more reproducible and can be more predictive for a specific environment. The results allow predicting the time needed to achieve adaptation in a treatment plant and, in particular, the behavior under conditions with discontinuous discharge. By using threshold criteria for mumax, fs, and percentage mineralization, a new classification scheme with eight different classes for biodegradability is proposed. Compared to the currently used system with two classes, the prediction of biodegradation will be more sophisticated. The proposed system differentiates for six types of inherently degradable substances and identifies those substances with an abnormal growth curve, due to inhibition or toxicity, poor water solubility, or incomplete mineralization. For these classes the proposed equations are not directly applicable and more research will be required to predict their behavior.

Animals↗
PubMed1998

A simplified modeling approach using microbial growth kinetics for predicting exposure concentrations of organic chemicals in treated wastewater effluents.

Various mathematical relationships have been used to assess exposure concentrations of organic chemicals when emissions occur via wastewater treatment. These relationships range from a simple removal factor calculation to more sophisticated approaches using kinetic based mathematical models. While these existing approaches have been used by decision makers to screen new chemicals for exposure assessments, they all have limitations in the predictive capabilities. Thus, a simplified modeling approach grounded in sound scientific fundamentals that utilizes relatively easy to obtain input parameters is needed. In this paper a simplified modeling approach that utilizes microbial growth kinetics was developed for predicting effluent concentrations in secondary biological wastewater treatment systems. Receiving water predicted exposure concentrations (PEC) are assessed by using a dilution factor. One advantage of this approach is that it allows for wastewater treatment plant effluent concentrations, and therefore receiving water exposure levels, to be predicted with a minimum amount of experimental data. It also provides quantitative data that can be used to assess the relative biodegradability of different chemicals for use in regulatory and risk assessment activities.

Bacteria↗
PubMed1996

Measurement and validation of kinetic parameter values for prediction of biodegradation rates in sewage treatment.

Analysis of about 140 oxygen uptake curves from standard biodegradation tests with the electrolytic respirometer yielded growth kinetic parameter values. The maximum observed growth rate, mumax, on the 52 different substances varied between 1 and 6/day. The measurement of the half-saturation constant Ks at the depletion phase of the oxygen uptake curves appeared problematic. For 24 substances the values were below 1 mg ThOD/liter. Apparently high Ks values of several tenth mg ThOD/liter for the other 28 substances are explained by retarded mineralization of intermediates due to the relatively high initial test concentrations of up to 300 mg ThOD/liter. At lower test concentrations (down to 15 mg ThOD/liter) the measured Ks values for these substances were also typically below or around 1 mg ThOD/liter. Based on the above-mentioned maximum growth rates and the low values for Ks, the predicted steady-state residual concentration of these substances in the effluent of completely mixed sewage treatment plants is between 10 and 100 micrograms/liter. This level is in accordance with the range of measured values taken from literature. Based on this research and additional data from literature, the separation between readily and inherently degradable can be made at the critical values of mumax approximately 1.5/day and Ks approximately 1 mg ThOD/liter.

Amines↗
PubMed1994

Classification of biodegradability by growth kinetic parameters.

On the basis of classical Monod equations for microbial growth, kinetic parameter values are assessed to enable the characterization of biodegradability as a substance property. Although growth is a microbial property, the substance selects those species from a mixed inoculum that can profit at most under the prevailing conditions. Hence it is concluded that the combination of observed cell yield Y approximately 0.5 g solids/g COD, maximum growth rate mu max > 0.3/day, and half-saturation constant Ks < 0.6 mg COD/liter provides a suitable set of borderline criteria for classification of chemicals as readily biodegradable. Of these parameters mu max is suitable for differentiating chemicals, whereas Y seems more or less equal for all readily degradable substances and Ks is not easily measurable with existing standard test methods. In this approach the density of specific microbes in the inoculum or during the test is excluded from the substance characterization and thus adaptation phenomena have no influence. From correlation studies and model calculations it can be expected that if the above parameters are estimated on the basis of standard tests for ready biodegradability, these tests will not produce false positives. Provided that the above parameters can be estimated, any other method than just the standard methods can be used to classify a substance as readily biodegradable.

Biodegradation, Environmental↗
PubMed1994

Extrapolation of biodegradability test data by use of growth kinetic parameters.

Formulas for extrapolation of test data on biodegradability to percentage removal in treatment plants and biological half-life time in surface water are derived from growth kinetics. A pseudo-first-order rate constant can be used provided that substance properties and microbial density in the environment are assessed independently. For comparison of kinetics at different concentration levels an extrapolation factor can be used that is based on the ratio between maximum growth rate and sludge age in a treatment plant. The specific microbial density is estimated on the basis of proportional growth on all degradable substances in a state of equilibrium after adaptation. As a consequence the percentage removal can be predicted on the basis of sludge age and influent concentration in combination with the substance properties. The formulas predict that the combination of sewage treatment and surface water gives an almost equal biological half-life time for all readily biodegradable substances in the surface water. The predicted removal percentages and biological half-life times are in agreement with observations.

Biodegradation, Environmental↗
PubMed1993

Conservation of gene structure and arrangement between vaccinia virus and orf virus.

A 3.3-kb BamHI fragment from the center of the orf virus (OV) NZ2 genome has been sequenced, revealing three major open reading frames (ORFs) with homology to vaccinia virus (VAC) genes. These ORFs have been designated F2L, F3R, and F4R and the proteins they encode were found to be homologous to VAC genes H4L (RNA polymerase-associated protein RAP94), H5R (35-kDa virion envelope antigen) and H6R (topoisomerase), respectively. The OV ORFs are arranged on the genome in an almost identical manner to their VAC counterparts revealing the common evolutionary origin of the two viruses despite the extreme difference in their G+C content. Like its VAC counterpart, F3R was shown to be transcribed early and late during infection. S1 and primer extension analysis located the 5' ends of F3R early transcripts to a position 15-16 nt and 5-10 nt, respectively, downstream from an AT-rich sequence resembling a VAC early promoter. The 5' ends of F3R late transcripts were located to an A within the sequence 5'-TAAAG, 41 nt downstream from the early promoter and 17 nt upstream from the initiation codon. S1 analysis of F2L, which is transcribed only late in infection, revealed transcripts initiating from within the sequence 5'-TAAATG. No transcriptional start point could be detected for F4R but the VAC late transcriptional initiation sequence TAAAT was found close to the predicted translational start point. Another late promoter-like sequence, 5'-TAAATG, was found at the 3' end of F2L. This preceded a short ORF tentatively designated as F1L and predicted to be the beginning of a homologue of VAC H3L.

Amino Acid Sequence↗
PubMed1992

Comparison of a dengue-2 virus and its candidate vaccine derivative: sequence relationships with the flaviviruses and other viruses.

A comparison of the sequence of the dengue-2 16681 virus with that of the candidate vaccine strain (16681-PDK53) derived from it identified 53 of the 10,723 nucleotides which differed between the strains. Nucleotide changes occurred in genes coding for all virion and nonvirion proteins, and in the 5' and 3' untranslated regions. Twenty-seven of the nucleotide changes resulted in amino acid alterations. The greatest amino acid sequence differences in the virion proteins occurred in prM (2.20%; 2/91 amino acids) followed by the M protein (1.33%; 1/75 amino acids), the C protein (0.88%; 1/114 amino acid), and the E protein (0.61%; 3/495 amino acids). Differences in the amino acid sequence of nonvirion proteins ranged from 1.51% (6/398 amino acids) in NS4 to 0.33% (3/900 amino acids) in NS5. The encoded protein sequences of 16681-PDK53 were also compared with the published sequences of other flaviviruses to obtain a detailed classification of 17 flaviviruses using the neighbor-joining tree method. The analyses of the sequence data produced dendrograms which supported the traditional groupings based on serological evidence, and they suggested that the flaviviruses have evolved by divergent mutational change and there was no evidence of genetic recombination between members of the group. Comparisons of the sequences of the flavivirus polymerase and helicase-like proteins (NS5 and NS3, respectively) with those from other viruses yielded a classification of the flaviviruses indicating that the primary division of the flaviviruses was between those transmitted by mosquitoes and those transmitted by ticks.

Amino Acid Sequence↗
PubMed1991

NS 1 gene sequences from eight dengue-2 viruses and their evolutionary relationships with other dengue-2 viruses.

The nucleotide sequences of the NS 1 genes from five Thai and three Sri Lankan dengue-2 viruses were determined by sequencing the viral RNA using synthetic oligonucleotide primers. The results were shown to be similar to four published dengue-2 NS 1 sequences and the classification of these genes was compared with the one obtained for the envelope genes of the same viruses. The classification was similar and showed that the Thai isolates could be divided into two separate groups and that the Sri Lankan isolates were distinct. We found no correlation between disease severity, serological response (1 degree or 2 degrees), or year of isolation and various aspects of NS 1 protein sequence variation; and no particular amino acid changes were correlated with virulence. The sequences were combined with those published and classified elsewhere to provide a comprehensive E/NS 1 gene taxonomy of dengue-2 virus isolates.

Adolescent↗
PubMed1989

Variation of the nucleotide and encoded amino acid sequences of the envelope gene from eight dengue-2 viruses.

The nucleotide sequences of the envelope genes from five Thai and three Sri Lankan dengue-2 viruses were determined by sequencing the viral RNA using synthetic oligonucleotide primers. The results were compared with the four published dengue-2 envelope sequences to obtain a classification of these viruses, which showed that the Thai isolates could be divided into two separate groups while the Sri Lankan isolates were distinct. There was no correlation between disease severity and envelope protein sequence, or between year of isolation and sequence. No particular amino acid changes were associated with virulence or a change in hydrophilic region which could perhaps act as an epitope.

Amino Acid Sequence↗
PubMed1989

The value of MLA 144 culture fluid for the isolation of human immunodeficiency virus.

Human immunodeficiency virus (HIV) was readily isolated by co-cultivation of patients' cells with phytohaemagglutinin-stimulated mononuclear cells from umbilical cord blood in 2 ml cultures in 24-well plates. Fluids from cultures of the MLA 144 cell line acted as an excellent source of interleukin-2, and promoted early replication of HIV in the primary cultures. Reverse transcriptase activity was commonly present at significant levels by 4-7 days. In contrast, recombinant IL-2 (recIL-2) did not promote early replication under these conditions. Adequate washing of the phytohaemagglutinin blasts was critical in this system, although others have reported it to be less important under other culture conditions. Cell concentrations and HIV: target cell ratios appeared not to play a major role in early outgrowth of virus. The particular sheep anti-alpha interferon tested resulted in a two-fold reduction in RT activity. Virus was readily transmitted in this simplified cheaper culture system.

Cell Line↗
PubMed1988

Isolation and characterization of dengue viruses serotype 1 from an epidemic in northern Queensland, Australia.

Thirteen strains of dengue type 1 were isolated from the lymphocyte fractions of 69 acute phase blood samples collected at Thursday Island Hospital during 1981 and 1982. One further strain of type 1 was isolated from 7 blood samples despatched by air from Cairns Base Hospital during 1982. Four of these Australian isolates representing the beginning, middle, and end of the epidemic were examined by restriction enzyme mapping and were found to be identical for the nine restriction enzymes used. The maps differed from those derived from two Malaysian dengue type 1 strains isolated during the epidemic of 1981-82 in that country. This suggests reliance on serological typing to establish global circulation patterns of epidemic dengue is insufficient and that more specific methods such as genome mapping are useful.

Adolescent↗
PubMed1988

Insulin-induced translocation of glucose transporters from post-Golgi compartments to the plasma membrane of 3T3-L1 adipocytes.

A semiquantitative method using immunocytochemistry on ultrathin cryosections and the protein A-gold technique was performed to study the effect of insulin on the cellular distribution of the glucose transporters in cultured 3T3-L1 adipocytes. In basal cells a substantial portion of the label was present in a tubulovesicular structure at the trans side of the Golgi apparatus, likely to represent the trans-Golgi reticulum, and in small vesicles present in the cytoplasm. Treatment with insulin induced a rapid translocation of transporters from the tubulovesicular structure to the plasma membrane. The transporter labeling of the plasma membrane increased three-fold and that of the tubulovesicular structure decreased by half. There was no effect of insulin on the degree of label in the small cytoplasmic vesicles. Removal of insulin from stimulated cells rapidly reversed the distribution of transporters to that seen in basal cells. This study thus provides the first morphological evidence for the occurrence of transporter translocation in insulin action and identifies for the first time the intracellular location of the responsive transporters.

Adipose Tissue↗
PubMed1988

Variation in dengue type 2 viruses isolated in Bangkok during 1980.

Dengue type-2 viruses isolated in metropolitan Bangkok during 1980 (Bangkok/80) were characterized by oligonucleotide fingerprinting, restriction enzyme (RE) mapping and antigenic analysis using monoclonal antibody probes. Of 10 isolates analysed by oligonucleotide fingerprinting, nine were very closely related, showing 72.5% to 91.4% oligonucleotide homology. One isolate (D80-141) produced a distinctly different fingerprint (55.7% to 58.0% homology) and was less related to other Bangkok/80 dengue-2 virus isolates than to a 1964 Bangkok isolate (16681). RE mapping conducted on complementary dsDNA prepared from three Bangkok/80 isolates, strain 16681 and the prototype New Guinea C strain confirmed that D80-141 was genetically distinct. On antigenic analysis, only one of 22 monoclonal antibody probes produced against representative 1980 Bangkok dengue-2 isolates, D80-100 and D80-141, was able to distinguish between these virus strains. Monoclonal antibody 47-10/10, prepared using D80-100 virus and directed at the NS1 non-structural glycoprotein, had a significantly lower (100-fold) solid phase radioimmune assay endpoint titre for D80-141 antigen than for D80-100 antigen. By the indirect immunofluorescence assay, 47-10/10 had lower antibody endpoint titres against D80-141, the NGC strain and 13 (12%) of 110 Bangkok/80 isolates than to a control antibody preparation. These results suggest that strain D80-141 represents a second minor topotype of dengue-2 which was circulating concurrently with the major endemic topotype in Bangkok in early 1980.

Antibodies, Monoclonal↗