Total versus inhalable sampler comparison study for the determination of asphalt fume exposures within the road paving industry

Exposure to asphalt fumes has a threshold limit value (TLV of 0.5 mg m(-3) (benzene extractable inhalable particulate) as recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). This reflects a recent change (2000) whereby two variables are different from the previous recommendation. First is a 10-fold reduction in quantity from 5 mg m(-3) to 0.5 mg m(-3). Secondly, the new TLV specifies the "inhalable" fraction as compared to what is presumed to be total particulate. To assess the impact of these changes, this study compares the differences between measurements of paving asphalt fume exposure in the field using an "inhalable" instrument versus the historically used 'total' sampler. Particle size is also examined to assist in the understanding of the aerodynamic collection differences as related to asphalt fumes and confounders. Results show that when exposures are limited to asphalt fumes, a 1:1 relationship exists between samplers, showing no statistically significant differences in benzene soluble matter (BSM). This means that for the asphalt fume ACGIH TLV, the 'total' 37-mm sampler is an equivalent method to the "inhalable" method, referred to as IOM (Institute of Occupational Medicine), and should be acceptable for use against the TLV. However, the study found that when confounders (dust or old asphalt millings) are present in the workplace, there can be significant differences between the two samplers' reported exposure. The ratio of IOM/Total was 1.37 for milling asphalt sites, 1.41 for asphalt paving over granular base, and 1.02 for asphalt over asphalt pavements.     

Utility of dynamics as indicators of stress in population models

The relationships between the dynamics of environmentally and chemically stressed populations and indicators of the effects of the stressor are explored in a model framework. The physiologically structured population, represented by a system of McKendrick–von Foerster hyperbolic partial differential equations, includes the dynamics of numerous individuals distinguished by ecotype. Chemical uptake of nonpolar narcotics is modeled by first order kinetics. Classical methodologies, frequency analysis and phase space reconstruction, are explored in a search for indicators of magnitude of stress. When these techniques proved generally unsuccessful for the objective of indicator selection in our model setting, summary statistics, as related to bifurcation diagrams, were constructed and appear more useful as indicators. It is concluded that physiological structures generally lead to more feasible measurable indicators of magnitude of stress than do specifics of population dynamics.     

Risk assessment of water pollutants

The sources of toxic xenobiotics and different factors such as ecological diversity, differences in comparative anatomy, physiology and biochemistry, food chain variation, interrelationship within species and life span, etc., are considered during risk assessment of pollutants, and their impact on aquatic ecotoxicology is identified. A fugacity and multimedia compartment model is suggested, based on toxicodynamic (toxicity of the chemical) and toxicokinetic (metabolism of the chemical) considerations to predict and screen the behaviour of pollutants quantitatively in the aquatic environment. The significance of the risk analysis approach in anticipatory actions and regulation of pollution levels is discussed.     

Application of remote sensing to exposure monitoring

Although exposure assessments cannot be completed remotely, remote sensing techniques provide an invaluable adjunct in exposure monitoring programs. Exposure can be defined as the summation over time, in all media, of the amount of a pollutant available at the exchange boundaries of the receptor during a specified period. This paper describes a few remote monitoring techniques that provide direct measurement input into an exposure assessment and several that furnish quantitative or qualitative information leading to decisions regarding how to monitor, such that the source-exposure-dose relationships can be fully defined. Two general classes of remote sensing systems are included in this discussion-passive and active. Passive systems depend on a measurement of the energy reflected or emitted by a target and active systems use an energy source, e.g., a laser to perform the environmental interrogation. Airborne as well as ground-based remote monitoring measurements or systems are also considered in this paper.     

Genetic population structure of the recently introduced Asian clam,Potamocorbula amurensis,in San Francisco Bay

The genetic population structure of the recently introduced Asian clam, Potamocorbula amurensis, in San Francisco Bay was described using starch gel electrophoresis at eight presumptive loci. Specimens were taken from five environmentally distinct sites located throughout the bay. The population maintains a high degree of genetic variation, with a mean heterozygosity of 0.295, a mean polymorphism of 0.75, and an average of 3.70 alleles per locus. The population is genetically homogeneous, as evidenced from genetic distance values and F-statistics. However, heterogeneity of populations was indicated from a contingency chi-square test. Significant deviations from Hardy-Weinberg equilibrium and heterozygote deficiencies were found at the Lap-1 locus for all populations and at the Lap-2 locus for a single population. High levels of variability could represent a universal characteristic of invading species, the levels of variability in the source population(s), and/or the dynamics of the introduction. Lack of differentiation between subpopulations may be due to the immaturity of the San Francisco Bay population, the general purpose phenotype genetic strategy of the species, high rates of gene flow in the population, and/or the selective neutrality of the loci investigated.     

Immunity in children with exposure to environmental lead: II. Effects on humoral immunity

Lead has been found to depress the immune system in animal studies at levels far below those responsible for overt toxicity. Literature studies in animal systems most clearly showed an effect of lead on response to a specific immunogenic stimulus. Data are sparse concerning the effects of lead on the immune system in the human population at greatest risk for exposure-children up to six years of age. This portion of the Phase I study reports concentrations of IgG, IgM, IgA, and IgE, as well as antibody titers to the specific antigenic stimuli provided by the vaccines against diphtheria, tetanus, and Rubella. The study population consisted of a group of 193 children, ages 9 months to 6 years, who participate in the WIC (Women, Infants and Children) and Lead Poisoning Prevention Programs in the urban area of Springfield-Greene County Missouri. Blood lead levels ranged from 1 to 50 g dL^–1. Total Ig levels were determined and the data were analysed. No consistent significant differences were observed among the risk categories in the five age groups examined. A single Ig class in each of three age groups showed apparent significant differences among the various risk categories, but these differences were not correlated with blood lead. An analysis of specific antibody titers to diphtheria, tetanus, and Rubella was performed. Regression analyses of current data in Phase I of this study suggest a detrimental effect of lead on the antibody titres to diphtheria and Rubella.     

Rapid prediction of disinfection by-product formation potential by fluorescence

Recent drinking water regulations have lowered the disinfection by-product standards as well as added new disinfection by-products for regulation. Natural organic matter (NOM) plays a major role in the formation of undesirable organic by-products following disinfection/oxidation of drinking water. It is suspected that most precursors to disinfection by-products are humic, although nonhumic substances are also suspected of contributing to these by-products. Many of the disinfection by-products have adverse health effects in humans (i.e., carcinogenic or mutagenic effects). The primary chlorinated disinfection by-products of concern include trihalomethanes, haloacetic acids, and haloacetonitrile. Fluorescence spectroscopy was used to study humic and fulvic acids. The two fractions of humic substances, humic and fulvic acids, were characterized by a double-peak phenomena in an overlapping fluorescing region. Disinfection by-product formation potentials of humic and fulvic acids have been correlated with total organic carbon, UV absorbance at 254 nm, specific absorbance and fluorescence. River humic and fulvic acid was found to have the highest reactivity to disinfection by-product formation as compared to soil and peat humic and fulvic acid. Fluorescence spectroscopy has shown to be a rapid and predictive tool for disinfection by-products formation potential of humic and fulvic acids.