Toxic interactions among environmental pollutants: corroborating laboratory observations with human experience.

Combined exposures to multiple chemicals may result in interactions leading to a significant increase or decrease in the overall toxicity of the mixture compared to the summation of the toxicity of the components. A large number of chemical interactions have been described in animal studies by administering high doses of chemicals by routes and scenarios often different from anticipated human exposures. Though limited, there is some evidence for the occurrence of several supra-additive (the combined effects are greater than the simple summation of the individual effects) and infra-additive (the combined effects are smaller than the simple summation of the individual effects) chemical interactions in humans.

Fibre intake in elderly individuals with poor masticatory performance.

The effects of masticatory performance on food selection and nutrient intake in non-institutionalized elderly subjects wearing dental prostheses were investigated. A poor masticatory performance was associated with significantly lower intakes of insoluble and dietary fibre for both sexes (as compared to subjects with a good masticatory performance) and with lower intakes of vitamin A in women only. Further, 37 per cent of subjects with low masticatory performance were taking gastrointestinal drugs, as compared to 20 per cent of subjects with good performance.

[Research on factors determining health: role of the environment in the 21st century].

During the next few decades, actions on matters dealing with environmental pollution will have to be aimed at: 1) eliminating environmental contaminants at the source; 2) identifying biomarkers of exposure and/or adverse health effects; 3) improving our skills at assessing the probability of occurrence of adverse health effects in the community; and 4) informing the Canadian public in a responsible manner. Primary sources of pollution related to human activities should be our deep concern: utilization of energy sources, particularly fossil fuels; agricultural activities, such as deforestation and use of fertilizers and pesticides; and industrialization, responsible for the synthesis of numerous new molecules. Clinical investigators will be faced with rare disease entities characterized by low-level, long-term exposure via food, air, water and soil, and low-incidence responses (e.

Ethanol induced modification of m-xylene toxicokinetics in humans.

This study was undertaken to determine whether previous subacute treatment with ethanol could modify the kinetics of m-xylene in humans. A group of six volunteers was exposed twice to either 100 or 400 ppm of m-xylene during two hours (between 0800 and 1000). Ethanol was given orally in the early evening on each of two consecutive days before exposures (total ethanol intake of 137 g).

Nutrient intake and gastrointestinal disorders related to masticatory performance in the edentulous elderly.

The effects of chewing efficiency on nutrient intake and the prevalence of gastrointestinal disorders were determined in edentulous elderly subjects. Three hundred sixty-seven noninstitutionalized individuals aged 60 years and over were interviewed. Denture masticatory performance and the collection of dietary information were assessed with the "Swallowing Threshold Test Index" and a food-frequency questionnaire.

Physiologically based modeling of the toxicokinetic interaction between toluene and m-xylene in the rat.

The present study was undertaken to investigate the mechanism of toxicokinetic interaction between toluene (TOL) and m-xylene (XYL) in vivo in the male Sprague-Dawley rat by physiologically based toxicokinetic (PBTK) modeling. First, the metabolic constants (Vmax and Km) were determined for TOL and XYL individually by conducting a series of closed-chamber inhalation exposures of three rats to starting concentrations of 500 to 4000 ppm. The values of Km (TOL, 0.

A descriptive and mechanistic study of the interaction between toluene and xylene in humans.

This study was undertaken to characterize the mechanism of toxicokinetic interaction between toluene (TOL) and m-xylene (XYL) in the rat using physiologically-based toxicokinetic (PBTK) modeling approach. First, the metabolic rate constants were determined by conducting closed-chamber inhalation exposures with individual solvents (Vmax: TOL = 4.8, XYL = 8.

Effect of various exposure scenarios on the biological monitoring of organic solvents in alveolar air. I. Toluene and m-xylene.

The present study was undertaken to investigate the influence of different exposure scenarios on the elimination of toluene and m-xylene in alveolar air and other biological fluids in human volunteers. The study was also aimed at establishing the effectiveness of physiologically based toxicokinetic models in predicting the value of biological monitoring data after exposure to toluene and m-xylene. Two adult male and two adult female white volunteers were exposed by inhalation, in a dynamic, controlled-environment exposure chamber, to various concentrations of toluene (21-66 ppm) or m-xylene (25-50 ppm) in order to establish the influence of exposure concentration, duration of exposure, variation of concentration within day, and work load on respective biological exposure indices.

Comparison of dental caries and oral hygiene indices for 13- to 14-year-old Quebec children between 1977 and 1989-1990.

A comparison of the principal dental health indices of 13- to 14-year-old Quebec school children between 1977 and 1989-1990 is reported. Data derive from a dental health survey of 1,093 Quebec school children in 1977 and from a province-wide probability sample of 1,342 children in 1989-1990. The most interesting conclusions are: the DMFT index for 13- to 14-year-old children dropped from 9.

Prevalence of non-cavitated and cavitated carious lesions in a random sample of 7-9-year-old schoolchildren in Montreal, Quebec.

This report describes the prevalence of non-cavitated and cavitated carious lesions in 911 randomly selected children in grades one through three on the Island of Montreal, Quebec, Canada. The criteria for diagnosis were developed for a longitudinal epidemiological study of restorative treatment decisions by dentists practising under a provincial dental insurance program for children. The intra- and inter-examiner reliability correlation coefficients of the two examiners were excellent (Kappa > or = 0.

A multivariate model to predict caries increment in Montreal children aged 5 years.

A study was carried out in Montreal (Canada) to predict caries development over the period of one year in primary teeth of kindergarten children (mean age 5 years 8 months +/- 4 months) living in a non-fluoridated area. The 302 children were examined at school on two occasions, one year apart. At the first examination selected predictors were collected: caries experience, salivary S.

Nutritional deficiencies and gastrointestinal disorders in the edentulous elderly: a literature review.

Many factors influence the food selection and nutritional status of elderly individuals. In this brief review, it is hypothesized that the functional status of dental prostheses is a prime determinant in the food selection, dietary fibre intake and prevalence of gastrointestinal disorders in edentulous elderly subjects.

Modulation of hexachlorobenzene-induced hepatic porphyria by methyl isobutyl ketone in the rat.

Potential toxic interaction between hexachlorobenzene (HCB) and methyl isobutyl ketone (MiBK) was investigated using two different schedules of toxicant administration. The first schedule involved simultaneous administration of HCB (50 mg/kg/d, p.o.

Assessment of occupational health risk during unusual workshifts: review of the needs and solutions for modifying environmental and biological limit values for volatile organic solvents.

Aspects of occupational health risk assessment for unusual workshifts are discussed in relation to the question of: 1) using a suitable model for adjusting occupational exposure limits, and 2) assessing the influence of altered work schedules on biological exposure limits. The relative importance of two separate approaches, i.e.

Influence of various mixtures of inhaled toluene and xylene on the biological monitoring of exposure to these solvents in rats.

The present study was undertaken to describe the influence of simultaneous exposure by inhalation to toluene and xylene on some aspects of their respective metabolic disposition. Adult male rats were exposed acutely (5 h) to 75, 150, and 225 ppm of toluene or xylene and to various mixtures of these solvents: toluene (75 ppm) and xylene (225 ppm), toluene (150 ppm) and xylene (150 ppm), toluene (225 ppm) and xylene (75 ppm). Compared with single exposure, simultaneous exposure resulted in lower amounts of excreted hippuric acid (20-30%) and methylhippuric acids (4-40%) in urine over a period of 24 h, even though significant differences were seen only with the toluene (150 ppm) and xylene (150 ppm) combination.

Efficacy of APF treatments without prior toothcleaning targeted to high-risk children.

A clinical field trial was conducted, over a 2-yr period, to evaluate the efficacy of bi-annual APF gel topical applications without previous prophylaxis in reducing dental caries among high-risk children living in non-fluoridated communities. 488 children 6 yr old, presenting at least three cavities on proximal surfaces of their primary teeth, were randomly assigned to two groups. The experimental group received bi-annual topical APF gel applications and the control group received a placebo.

Assessment of occupational health risk from multiple exposure: review of industrial solvent interaction and implication for biological monitoring of exposure.

This review is a critical survey and evaluation of recent literature on solvent interactions for the assessment of health risk. It addresses the implications of multiple solvent exposures 1) by examining the influence of solvent-solvent and ethanol-solvent interactions on the biological indices of chemical exposure, and 2) by indicating how the eventual modifying effects can be considered in the biological monitoring of mixed exposure. Reviewed studies reveal the effects of toxicokinetic interactions on the biological parameters, and the gaps in our knowledge.

Factors affecting the ingestion of fluoride dentifrice by children.

Several factors affecting the amount of fluoride ingested during toothbrushing by 2- to 7-year-old children were investigated. The specific purpose of this study was to determine the contribution of age, the amount of dentifrice used, and rinsing after brushing to the variation in the ingestion of fluoride dentifrice. Four hundred and five children brushed their teeth in front of a portable sink.

Influence of acetone on the severity of the liver injury induced by haloalkane mixtures.

Acetone potentiation of haloalkane-induced liver injury is a well-known phenomenon. Acetone-treated rats challenged with a trichloroethylene-CCl4 mixture exhibit a more sever liver injury than that predicted by the addition of the single potentiating effects of each. The purpose of the present study was to determine if acetone exerted similar interactions with other haloalkane mixtures.

Synovial fluid levels of complement SC5b-9 and fragment Bb are elevated in patients with rheumatoid arthritis.

To determine whether complement turnover in synovial fluids of patients with rheumatoid arthritis (RA) reflects activation by the classical or alternative pathway, we used novel immunoassays to measure products of complement activation (the membrane attack complex SC5b-9 and the cleavage fragments Bb and C4d). Mean synovial fluid levels of SC5b-9 were more than 8 times higher in RA than in crystal-induced arthritis (gout and pseudogout) and over 16 times higher than in degenerative joint disease (DJD). Similarly, Bb levels were more than 3 times higher in RA synovial fluids than in crystal-induced arthritis and over 7 times higher than in DJD.

Ingestion of fluoride from dentifrices by children aged 12 to 24 months.

The increase of dental fluorosis is largely imputable to the ingestion of dietary fluoride supplements and fluoride toothpastes. However, the toothbrushing habits of very young children is poorly documented. The purpose of this pilot study was to determine the toothbrushing habits of 12- to 24-month-old children and to estimate the quantity of fluoride ingested during toothbrushing.

Development of an experimental model for the study of hexachlorobenzene-induced hepatic porphyria in the rat.

Hexachlorobenzene (HCB) induces hepatic porphyria in rats. Various protocols of repeated cumulative and daily doses of HCB administered for several weeks until porphyria develops have been traditionally used. In order to undertake studies on early biochemical events occurring in HCB-induced porphyria, we have designed an experimental model involving the administration of a minimal amount of HCB inducing a fully developed porphyria in a well defined and predictable time frame.

Male rat specific nephrotoxicity resulting from subchronic administration of hexachlorobenzene.

Male rats are more sensitive to the nephrocarcinogenic effect of hexachlorobenzene (HCB) than are female rats. The purpose of this study was to shed light on this phenomenon by investigating mechanisms of subchronic nephrotoxicity of HCB. Groups of rats were administered HCB in corn oil (po) at 100 mg/kg, 5 days per week for 15 days or at 50 mg/kg, 5 days per week for 50 days.

[Adolescents' fear of dental treatment: development and evaluation of a cognitive inventory].

Morin et al.'s Inventaire cognitif de la peur des traitements dentaires pour adolescent(e)s [Adolescents' Fear of Dental Treatment Cognitive Inventory] was administered to 343 subjects. Factor analysis revealed a single general factor that accounted for 33.

Effect of simultaneous exposure to toluene and xylene on their respective biological exposure indices in humans.

Studies that specifically address the influence of controlled human exposure to a combination of solvents on the biological monitoring of exposure are limited in number. The present study was undertaken to investigate whether simultaneous exposure of human volunteers to toluene and xylene could modify the respective metabolic disposition of these solvents. Five adult Caucasian men were exposed for 7 consecutive h/day over 3 consecutive days to 50 ppm toluene and 40 ppm xylene either separately or in combination in a dynamic, controlled exposure chamber (low-level exposure).