Natural Exposure Conditions Research Articles

Towards the prediction of pinking of PVC profiles in mild climatic conditions

AbstractPinking of TiO2‐pigmented PVC can be observed for profiles exposed to the mild environmental conditions of Northern European countries. In this paper, the pinking phenomenon is accounted for at the molecular level by the formation of polyene sequences which are not completely photooxidatively bleached under conditions of oxygen starvation. Photoreduction of TiO2 to give Ti(III) species accounts for greying which cannot be converted into pinking under mild thermooxidative conditions (65°C). The polyenic sequences which account for an initial greying after brief exposure in the SEPAP 12.24 apparatus can be converted into shorter, modified polyene sequences which explain the pinking. From the basic understanding gained, a predictive test has been designed and validated by comparison with results obtained under natural exposure conditions.

Assessment of the Bioavailability of PAHs in Rats Exposed to a Polluted Soil by Natural Routes: Induction of EROD Activity and DNA Adducts and PAH Burden in Both Liver and Lung

In order to assess bioavailability of polycyclic aromatic hydrocarbons (PAHs) present in soils, male laboratory rats were exposed to litters of control and polluted soils. After 88±2 h of exposure, several biomarkers were measured in both liver and lung. When rats were exposed to SIV soil, contaminated by a mixture of at least 13 PAHs, (1) only 2 or 3 PAH compounds were detected in liver and lung; (2) cytochrome P450-dependent monooxygenase activity, followed by 7-ethoxyresorufin O-deethylase (EROD) activity measurement, was highly induced in liver (13-fold-induction) and lung (up to 78-fold); and (3) DNA adducts were significantly increased. For what concerns soil artificially contaminated by only one PAH (phenanthrene or B[a]P), EROD activity was not or fewly induced, respectively. These results demonstrate the occurrence of a high bioavailability of PAHs to mammals in natural conditions of exposure. First results concerning DNA adducts must be profounded, but they already show that a short exposure of mammals to PAH-polluted soils can lead to potential genotoxic effects. EROD activity can be used as a sensitive biomarker in both liver and lung of rats maintained on litters of soils in the laboratory, and such a test can be used routinely to contribute to risk assessment.

Influence of relative humidity and temperature on-site corrosion rates

When the steel rebar depassivates, the corrosion starts to develop at a rate which mainly depends upon the moisture content in the concrete pores. In natural outdoor exposure conditions, the moisture content will depend not only on the relative humidity of the atmosphere but also upon the temperature cycling occurring from day to night. In order to progress in the understanding of the influence of the climatic variables on the corrosion rate of real size structures, several experiments have been performed. Thus the corrosion is measured in solutions simulating the concrete pore solution and simultaneous measurement of oxygen content, Cl - /OH - ratio and conductivity were made. As well measurements in concrete specimens submitted to outdoor conditions was made. The results enable to deduce that the variation of temperature has a multiple simultaneous effect on different parameters which may counter-balance each-other. Thus the oxygen content and the pH decrease and the Cl - increase when temperature rises. The best fit of Icorr is found with resistivity.

A numerical kinetic model for bioaccumulation of organic chemicals in sediment-water systems

A numerical kinetic model was developed to simulate the bioaccumulation of toxic chemicals under natural exposure conditions where benthic sediment plays an important role in bioavailability. Based on a three compartment dynamic system, a set of simultaneous first-order ordinary differential equations was derived and numerically solved by employing the fourth order Runge-Kutta method. The model was validated against data obtained from the bioaccumulation of two chlordane isomers into goldfish in the presence of sediment. The model predictions agreed well with the experimental results. The experimental results indicate that sediment significantly lowers the amount of chlordane available to fish and acts as a reservoir of chlordane to water. The developed model was capable of simulating the role of sediment in bioavailability of chemicals to fish in sediment/water systems.

The effects of ambient ozone on lung function in children: a reanalysis of six summer camp studies.

Studies of children attending summer camps often have observed relationships between daily outdoor ozone (O3) concentrations and decreased lung function that are qualitatively similar to results seen in human chamber studies. The former studies, focusing on the pulmonary effects of O3 and associated pollutants on children under natural conditions of exposure, are potentially of great importance to understanding the public health impact of ambient O3. However, a thorough assessment of the results of these studies has been hampered by differences in the analysis and reporting of data across the various studies. We obtained data sets from six summer camp studies carried out by three separate investigative groups, including two New Jersey studies performed by New York University, two studies in Ontario carried out by Health and Welfare Canada, and two studies in southern California. The data consisted of sequential, daily measurements of forced expiratory volume in 1 sec (FEV1), peak expiratory flow rate (PEFR), and 1-hr O3 concentration in the hour preceding lung function measurements for each child. We analyzed the relationships between lung function and O3 using linear regression models that fit subject-specific intercepts and a single, pooled O3 slope. These models were fit for each of the six studies separately and for all studies combined. All of the study-specific slopes of FEV1 on O3 were negative (i.e., increased O3 associated with decreased FEV1); five of six were statistically significant. Analysis of the combined six-study data set yielded a slope of -0.50 ml FEV1/ppb O3 (p<0.0001). Addition of time-trend variables to the combined-data analysis diminished, but did not eliminate, the FEV1-O3 relationship. Study-specific slopes for PEFR on O3 were more variable. Combined over studies, no significant relationship was observed between PEFR and O3. However, this negative finding appeared to be partially confounded by time trends in PEFR. The results of this reanalysis provide strong evidence that children exposed to O3 under natural conditions experience decreases in FEV1 of the kind demonstrated in laboratory studies, and raise concern that other acute respiratory effects observed in those studies (e.g., pulmonary inflammation) may also occur in young people exposed to ambient O3.

A study of the vaccinal value of various extracts of concealed antigens and salivary gland extracts against Ornithodoros erraticus and Ornithodoros moubata

On pig farms, elimination of the argasid ticks acting as reservoirs and vectors for African swine fever greatly favours the eradication of this disease. The elimination of Ornithodoros erraticus involves many problems, most of which could be easily solved by the development of an anti- O. erraticus vaccine. With a view to developing this vaccine, we have tested the protective value of the immune response induced in swine by seven ‘concealed’ antigens and one soluble salivary gland extract. The latter extract was also prepared from Ornithodoros moubata specimens and tested against this tick. Our results indicate that the immune response elicited by the concealed antigens has no protective value against O. erraticus. The immune response induced by the salivary gland extracts against adults of O. erraticus and O. moubata was apparent in a reduced ingestion of blood (40–60%; P<0.01) (except in males of O. erraticus) and in a significant decrease (40–60%; P<0.01) in fecundity in 100% of the females of both species. The good results obtained with salivary antigens, which in situations of natural contact have no protective value, are attributed to the fact that when these antigens are injected with adjuvants, the immune system recognizes certain salivary components (probably those which enable the parasite to feed) which it does not recognize under natural conditions of exposure.

Chloride binding in concrete containing PFA, gbs or silica fume under sea water exposure

The paper reports an experimental investigation on different mix proportions of normal concrete and on concretes incorporating various fractions of cement replacement by pulverized fly ash (PFA), ground blastfurnace slag (gbs) or silica fume. The chloride binding capacity of each matrix was determined after immersion in sea water for up to 270 days, after exposure to laboratory marine cycles (up to 520 cycles) and after exposure to tidal cycles in the North Sea (up to 7.5 years). Extensive data on acid-soluble chloride concentration (total chloride), free chloride concentration in the pore fluid and the evaporable water content of hardened concrete were obtained in order to determine the chloride-binding capacity of the various concrete matrices. Corrosion of rebar electrodes embedded in these matrices was also monitored. The results show that the bound chloride and the chloride concentration decrease with increasing depth into concrete. Higher water-cement ratios or cement contents result in increased bound chloride. The chloride binding near the surface of concrete is not significantly affected by the incorporation of PFA or gbs. At greater depths, the use of PFA or gbs results in a reduction of Cl- bound in the cementitious binder. Replacement of cement with silica fume results in greatly reduced contents of bound chloride. Accelerated penetration of chloride in concrete results in lower binding than under natural exposure conditions. It is also shown that the free Cl- concentration of pore fluid correlates with the corrosion rates of reinforcement embedded in concretes made with various cementitious binders, while the Cl--OH- ratio has no correlation.

Cellular responses to a 55-kilodalton recombinant Pneumocystis carinii antigen

The host-parasite interaction in Pneumocystis carinii pneumonia is poorly understood. In recent years, two major groups of P. carinii antigens have been identified. One class of antigens is characterized by a broad band of immunoreactivity between 45 and 55 kDa in P. carinii derived from rats. This antigen complex is the P. carinii antigen most commonly found in respiratory tract specimens and most frequently recognized by the host immune response. The availability of a recombinant antigen has permitted studies focusing on the cellular and humoral responses to a single antigen within this class, p55. In this study, we have demonstrated that the p55 antigen elicits a cell-mediated immune response in animals previously exposed to P. carinii. Under conditions of natural exposure, the 5' portion of the molecule, p55(1-200), appears immunologically silent, failing to elicit lymphocyte proliferation or cytokine secretion. Following active immunization, the 5' portion is capable of stimulating lymphocyte proliferation. The 3' portion, p55(268-414), has at least one immunodominant region which contains a 7-amino-acid repeat motif. The cells responding to p55 include a CD4+ T cell which secretes a Th1 cytokine pattern. A detailed understanding of the host-parasite interaction will facilitate the development of immunoprophylaxis and immunotherapy for P. carinii infection.

Assessment of the Protective Value of Antibodies to the Plasmodium falciparum Ring-infected Erythrocyte Surface Antigen (RESA): An Epidemiologic Study in Madagascar

The ring-infected erythrocyte surface antigen (RESA), a Plasmodium falciparum merozoite antigen, is a major vaccine candidate against falciparum malaria. To investigate the protective role of antibodies to RESA and its 4-mer, 8-mer, and 11-mer repeated amino acid sequences under conditions of natural exposure, a case-control and a cohort study were carried out in 1988 in a rural community in Madagascar where malaria reappeared recently. Fifty cases with greater than 1,000 P. falciparum per microliter of blood, and 45 controls with a negative blood smear were enrolled and sera were collected. Forty-one controls were followed for 20 weeks to identify malarial attacks. Protection against clinical malaria was assessed by the absence of malarial attacks requiring therapy. At enrollment, positivity rates and reactivity levels to RESA or repeats were similar in cases and controls. The 11-mer repeat antibody level was higher in the 26 controls who experienced at least one malarial attack during follow-up than in the 15 other controls (p less than 0.01). Thus, antibodies to the 11-mer repeat were predictors of the subsequent appearance of the disease. After adjustment for antibodies to the 11-mer repeat, antibodies to whole RESA had a negative predictive value on the occurrence of malarial attacks (p = 0.04). Different epitopes within the RESA molecule may elicit production of antibodies with different activities.

Alteration of immune function following dietary mycotoxin exposure

Mycotoxins are a group of structurally diverse fungal secondary metabolites that elicit a wide spectrum of toxicologic effects. Of particular interest is the capacity of some mycotoxins to alter normal immune function when present in foods at levels below observable overt toxicity. Aflatoxin, patulin, citrinin, and zearalenone experimentally alter immunity, and recent evidence suggests that the immunologic effects of ochratoxin A and trichothecenes may have particular significance to human and animal health. For example, the capacity of ochratoxin A to inhibit natural killer cell activity and increase growth of transplantable tumour cells has been associated with renal and hepatic carcinomas in mice and might similarly contribute to human cancer. Impaired resistance to pathogenic microorganisms occurs after exposure to the trichothecenes T-2 toxin and vomitoxin. This may predispose food animals to infectious disease and could result in decreased productivity as well as increased animal-to-human transmission of pathogens such as Salmonella and Listeria. Vomitoxin also alters normal mucosal immune function, specifically at the level of regulation of development, differentiation, and homing of IgA-producing plasma cells. Interestingly, vomitoxin-induced enhancement of IgA production in the systemic compartment contributes to manifestations in the mouse that are highly analogous to human IgA nephropathy, the most common form of human glomerulonephritis worldwide. Over the long term, the extrapolation of mycotoxin-induced immunologic effects observed in inbred mice to actual disease in livestock and humans will require investigations that both simulate natural exposure conditions as well as improve understanding of the cellular and molecular bases for these effects among different species.

Antibodies to the ring-infected erythrocyte surface antigen and the circumsporozoite protein of Plasmodium falciparum in a rural community from Burkina Faso

A population-based study in Burkina Faso was conducted to determine, under conditions of natural exposure to malaria parasites, the prevalence rate and seasonal variation of antibodies to the repeated amino acid sequences of the Plasmodium falciparum ring-infected erythrocyte antigen (RESA) and the circumsporozoite (CS) protein, and the relationship of the presence of malaria parasites in the blood with the level of these antibodies. A random sample of households was selected and visited twice during 1988, in April just before the rainy season and in September at the end of the rainy season. Serological testing included an immunofluorescent assay for total anti-blood stage antibodies; a modified immunofluorescent assay on glutaraldehyde-fixed parasitized erythrocytes to detect antibodies to RESA; and an enzyme-linked immunosorbent assay (ELISA) using synthetic peptides representing repeat amino acid sequences of RESA [(EENV) 5, (EENVEHDA) 4, and (DDEHVEEPTVA) 2] and CS protein [(PNAN 5]. In April, at the end of the dry season, 98% of the individuals had total P. falciparum antibodies, and 39% had anti-RESA antibodies. 32%, 82%, 80%, and 41% of the individuals had antibodies to the respective peptides. All prevalence rates increased with age. After the rains, in September, prevalence rates and levels of reactivity increased in each serological assay, except in the ELISA with (DDEHVEEPTVA) 2. Presence of P. falciparum parasitaemia was inversely related to antibody response to the CS protein (PNAN) 5 peptide but not to any other assay.

Randomized blind trial of a commercial FeLV vaccine

Summary A randomized blind trial of a commercial FeLV vaccine was conducted to evaluate its performance in cats under conditions of long-term natural exposure. Seventy-nine nonviremic, seronegative cats were randomized into 2 groups. Cats were given 3 doses of either FeLV vaccine or placebo (killed rabies virus vaccine) sc at weeks 0, 3, and 9 of the trial. Six weeks later, 44 known-viremic cats were added to the colony. Cats were housed in a single large room and food dishes and litter pans were used in common. Blood samples were collected at 4, 8, and 12 months after the addition of the viremic cats and were assayed for viremia by use of elisa. Twelve-month samples were also assayed independently by use of indirect fluorescent antibody testing. Investigators conducted assays on coded samples without knowledge of the cat's vaccination status; neither the investigators nor colony personnel knew which cats had been given the FeLV vaccine and which had been given the placebo until the twelfth month of exposure. After 12 months of cohabitation with infected cats, vaccinated cats had a significantly (P ≤ 0.02) lower incidence of persistent viremia (defined as 2 positive elisa test results at least 8 weeks apart or 1 positive indirect fluorescent antibody test result), compared with the placebo-inoculated cats. The incidence of persistent viremia was approximately 3 times greater among the placebo-inoculated cats than among vaccinates.

Human Studies of Human Health Hazards: Comparison of Epidemiology and Toxicology

The two principal methods of evaluating environmental health risks are observational epidemiologic studies of exposed populations and laboratory studies of the effects of agents on experimental animals. The principal advantages of the laboratory approach are random exposure assignment and precise exposure assessment. Epidemiologic studies have the virtue of studying the species of ultimate interest (humans) under natural exposure conditions. Given these characteristics, a strategy is offered for resolving contradictory results from these approaches. Epidemiologic evidence of a hazard with contradictory laboratory data may indicate confounding of the human data from other risk factors or bias due to systematically erroneous data. Animal studies might have erred in selecting an inappropriate species or exposure conditions. Where animal studies suggest a hazard but human studies do not, the human studies may be in error due to random exposure misclassification. Animal studies may have overstated risks due to high exposure levels or selection of an unusually sensitive species for study. Studies of electromagnetic fields suggest an effect on cancer risk based on epidemiologic data with negative results from the laboratory, possibly reflecting confounding or bias in the human research or poor selection of the species or exposure conditions in the laboratory. Improved coordination across these disciplines would benefit those who must reconcile these lines of research in assessing risks to human populations.

A critical evaluation of acute ozone epidemiology results.

Evidence from controlled human exposure studies demonstrates transient pulmonary functional responses to ozone exposure concentrations near the U.S. primary air quality standard of 0.120 ppm. There have been several recent efforts to document low concentration ozone effects in the epidemiological setting. Quantification of ozone effects under natural conditions of exposure can provide valuable information for risk assessment. However, results of epidemiological studies on acute ozone effects have had a limited role in decisions for air quality standards. This reflects difficulties in the quantitative interpretation of results that are to some extent inherent in the epidemiological approach, such as the difficulty of assessing individual exposures, failure to account for varying activity levels, and confounding by temporal covariates, e.g., temperature and pollen. However, in spite of the limitations of individual studies, when viewed as a group the epidemiological studies are consistent among themselves and with results from chamber studies.

Bis(tributyltin) oxide as a wood preservative: Its chemical nature in timber

AbstractTributyltin compounds have been used for many years as wood preservatives. This study has provided, for the first time, an explanation for the previously reported dealkylation and/or volatilization of the tributyltin species in, and from, timber. Thus 119Sn NMR studies have shown that, on impregnation into timber, bis(tributyltin) oxide, (Bu3Sn)2O, is rapidly converted to other tributyltin species, Bu3SnOX, and that these subsequently undergo disproportionation to Bu4Sn and Bu2Sn(OX)2 compounds. We have additionally demonstrated that Bu4Sn, so produced, is not persistent in timber and is lost by volatilization. Since the rate of disproportionation of the Bu3SnOX species should be dependent upon the nature of the X group, it should be possible to affect significantly, if not to stop, this process by the use of alternative tributyltin fungicides, e.g. tributyltin methanesulphonate. However, tributyltin fungicides have been used successfully in wood preservation for at least 25 years. Therefore, it must be concluded that, even after disproportionation in timber, in service, sufficient preservative action is retained to prevent decay of wood under the conditions of natural exposure.

The development and stability of surface layers on concrete exposed to sea-water

Concrete exposed to sea-water may develop a surface skin causing a marked reduction in permeability. The skin typically consists of a layer of brucite (magnesium hydroxide) of aroun 30 μm thickness, overlain by a thicker, but more slowly developing, layer of aragonite (calcium carbonate). The aragonite may convert to calcite in an aqueous environment free from magnesium ion. The degree of saturation of sea-water with aragonite or brucite is primarily a function of its pH value. Uncontaminated sea-water has a pH within the range 7.8 to 8.3 and is supersaturated with aragonite at pH values greater than around 8.1. For good correlation of laboratory tests with natural exposure conditions appreciable increases in pH should therefore be prevented. Temperature variations may have a significant effect on layer precipitation, but the range of pressures encountered by offshore structures has negligible effect. Organic compounds present in sea-water may inhibit precipitation.

Evaluation of .5% and 1% Iodophor Teat Dips on Commercial Dairies

Two postmilking teat dips containing .5 and 1% iodine were evaluated for approximately 8 mo under conditions of natural exposure to mastitis pathogens on four commercial dairy farms. In the two herds using .5% iodophor, incidence of intramammary infection with Staphylococcus aureus and Streptococcus agalactiae was reduced 68.3 and 46.2%, respectively. When numbers of new infections with both pathogens were combined, efficacy for the .5% iodophor was 62.3%. In the two herds using 1% iodophor, incidence of intramammary infection with Staph. aureus and Strep. agalactiae was reduced 52.4 and 70.7%, respectively. When numbers of new infections with both pathogens were combined, effacacy for the 1% idophor was 64.3%. Efficacy of teat dips was variable against coagulase-negative staphylococci and Corynebacterium bovis.

Simultaneous administration of TCDD and TDCF at different ratios induces different effects

2.3.7.8-Tetrachlorodibenzo-p-dioxin (TCDD) is among the most potent mixed-function oxidase (MFO) inducing agents and is also a very potent immunosuppressant in animals (1,2). Generally, 2.3.7.8-Tetrachlorodibenzofuran (TCDF) induces similar toxic effects at amounts 10-30 times larger (3). The toxic effects of both compounds are considered to depend upon binding to the cytosolic receptor regulated by the Ah locus (I). It is now known that incineration of solid urban waste produces emissions in which polychlorinated dibenzo-dioxins (PCDD) and dibenzofurans (PCDF) are measurable components (4). The ratio between the two classes of compounds and the amounts of the different isomers may vary greatly because of the composition of the waste burned and the burning temperature (4). However, in spite of the potential hazard of these emissions, there is only fragmentary information on the bioavailability of the toxins present in the mixtures and even less data on their effects when mixtures with known amounts of different toxins are studied in controlled experimental conditions. Since TCDD is such a potent ~0 inducer and TCDF is qualitatively similar, there are grounds for carefully evaluating the effects of combined exposure, alterations in the metabolism and bioavailability of both being a realistic possibility. Among the toxic effects induced by TCDD, alteration of primary antibody production and induction of hepatic aryl hydrocarbon hydroxylase (AHH) are the most sensitive parameters, even at very low doses, at least in Ah b mice (1,2). In an attempt to investigate the potential toxicological properties of mixtures of TCDD and TCDF, their effects were studied on immune response and enzyme inducibility. The two toxins were used at different ratios in order to cover different natural conditions of exposure and to find out whether the relative concentrations influenced the final results differently.

A method for the experimental exclusion ofLittorina littoreaL. (Gastropoda) and the establishment of fucoid germlings in the field

Abstract A new method for the exclusion of Littorina littorea L. and methods for the establishment and growing of fucoids on experimental granite plates and on the rocky shore are described. The equipment used requires regular attention, but provides more natural conditions of light, wave exposure, and recruitment of flora and fauna, compared with the use of wire cages. The grazing activity of Littorina littorea was highest from April to September, and significantly less during October–March in the inner Oslofjord, Norway.

Electrochemical Sensors for Atmospheric Corrosion Rates: A New Design

A description is given of a modified electrochemical atmospheric corrosion monitor(EACM), having a built-in reference electrode which makes it possible to apply the 3-electrode technique in plotting polarisation curves with thin electrolyte layers, such as those responsible for the atmospheric corrosion phenomenon.In order to determine the possibilities of the new EACM's, some examples are given of their response under laboratory conditions: (1) with 400 μm thick water and Na Cl solution layers, and (2) with invisible adsorbed moisture layers. The EACM's were also tested under natural exposure conditions on CENIM's flat-roof.