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.     

Immunity in children with exposure to environmental lead: I. Effects on cell numbers and cell-mediated immunity

Studies conducted in animal systems have shown that lead is an immunosuppressive agent at levels far below those causing overt toxicity. Children less than six years of age are the population at highest risk for exposure to environmental lead; however little data were available to assess effects on the developing immune system in this age group. Reported here is the completed Phase I study on 193 children, ages 9 months to 6 years, with blood lead levels from 1 to 50 (g dL^–1, recruited from the urban population of Springfield-Greene County, Missouri, through their participation in the WIC (Women, Infants, and Children) and Lead Poisoning Prevention Programs. This portion of the study dealt with enumeration of cells involved with the immune response andin vitro mitogenic stimulation of lymphocytes. The percent lymphocytes, monocytes, granulocytes, T cells (total), B cells, CD4+T's and CD8+T's and CD4+/CD8+ ratios were determined and the data were analysed. No consistent significant differences were seen among the various risk categories currently identified by the CDC. Though two age groups showed some possible effect of lead, none of the various cellular parameters within these age groups showed significant correlation with blood lead. The lymphocyte response toin vitro mitogenic stimulus was studied on 42 children (including 17 in risk classifications IIA and higher) using the mitogens phytohemagglutinin (PHA), Concanavalin A (Con A), and Pokeweed mitogen (PWM). No consistent statistically significant differences were seen among the various risk categories; the effects of lead, if present, are most likely subtle and obscured by the interindividual and time-dependent variation inherent in this type of study.     

ESTIMATING MEAN AND VARIANCE FOR ENVIRONMENTAL SAMPLES WITH BELOW DETECTION LIMIT OBSERVATIONS1

ABSTRACT: Left-censoring of data sets complicates subsequent statistical analyses. Generally, substitution or deletion methods provide poor estimates of the mean and variance of censored samples. These substitution and deletion methods include the use of values above the detection limit (DL) only, or substitution of 0, DL/2 or the DL for the below DL values during the calculation of mean and variance. A variety of statistical methods provides better estimators for different types of distributions and censoring. Maximum likelihood and order statistics methods compare favorably to the substitution or deletion methods. Selected statistical methods applicable to left-censoring of environmental data sets are reviewed with the purpose of demonstrating the use of these statistical methods for coping with Type I (and Type II) left-censoring of normally and log-normally distributed environmental data sets. A PC program (UNCENSOR) is presented that implements these statistical methods. Problems associated with data sets with multiple DLs are discussed relative to censoring methods for life and fatigue tests as recently applied to water quality data sets.     

Closing the mass balance at chlorinated solvent sites: Sources and attenuation processes

Using detailed mass balance and simple analytical models, a spreadsheet‐based application (BioBalance) was developed to equip decision makers with a predictive tool that can provide a semiquantitative projection of source‐zone concentrations and provide insight into the long‐term behavior of the associated chlorinated solvent plume. The various models were linked in a toolkit in order to predict the composite impacts of alternative source‐zone remediation technologies and downgradient attenuation processes. Key outputs of BioBalance include estimates of maximum plume size, the time frame for plume stabilization, and an assessment of the sustainability of anaerobic natural attenuation processes. The toolkit also provides spatial and temporal projections of integrated contaminant flux and plume centerline concentrations. Results from model runs of the toolkit indicate that, for sites trying to meet traditional, “final” remedial objectives (e.g., two to three orders of magnitude reduction in concentration with restoration to potable limits), “dispersive” mechanisms (e.g., heterogeneous flow and matrix diffusion) can extend remedial time frames and limit the benefits of source remediation in reducing plume sizes. In these cases, the removal of source mass does not result in a corresponding reduction in the time frame for source remediation or plume stabilization. However, this should not discourage practitioners from implementing source‐depletion technologies, since results from the toolkit demonstrate a variety of measurable benefits of source remediation. Model runs suggest that alternative, “intermediate” performance metrics can improve and clarify source remediation objectives and better monitor and evaluate effectiveness. Suggested intermediate performance metrics include reduction in overall concentrations or mass within the plume, reduction of flux moving within a plume, and reduction in the potential for risk to a receptor or migration of a target concentration of contaminant beyond a site boundary. This article describes the development of two key modules of the toolkit as well as illustrates the value of using intermediate performance metrics to evaluate the performance of a source‐remediation technology. © 2010 Wiley Periodicals, Inc.     

Methodological considerations in forecasting Saudi Arabian economic growth

The author surveys a number of factors responsible for Saudi Arabian economic growth and concludes that, contrary to popular belief, the petroleum sectors have had more than just a short-run transitory stimulating impact on the domestic economy. It appears that changes in the level of exports (and resulting government expenditures) have a number of impacts on the non-oil sector of the economy which take some time for their full effect to be felt. Government expenditures have become somewhat independent of current oil exports, so the current oil glut and falling revenues for Saudi Arabia are not likely to be translated into slower non-oil income growth.     

PCBQ: Computerized quantification of total PCB and congeners in environmental samples

Computerized methodologies for the quantification of total PCBs, PCB in Aroclor mixtures and individual PCB congeners in environmental samples are presented. The method for total PCBs is based on a multiple-linear regression analysis using data from capillary gas chromatography of Arocolor standards. PCB congeners were identified and their weight percentages determined in Aroclor mixtures by GC/MS. PCB congeners and total PCBs were accurately quantified in predetermined test data and environmental samples.     

Detecting and quantifying reductive dechlorination under monitored natural attenuation conditions

Field sampling and testing were used to investigate the relationship between baseline geochemical and microbial community data and in situ reductive dechlorination rates at a site contaminated with trichloroethene (TCE) and carbon tetrachloride (CTET). Ten monitoring wells were selected to represent conditions along groundwater flow paths from the contaminant source zone to a wetlands groundwater discharge zone. Groundwater samples were analyzed for a suite of geochemical and microbial parameters; then push‐pull tests with fluorinated reactive tracers were conducted in each well to measure in situ reductive dechlorination rates. No exogenous electron donors were added in these tests, as the goal was to assess in situ reductive dechlorination rates under natural attenuation conditions. Geochemical data provided preliminary evidence that reductive dechlorination of TCE and CTET was occurring at the site, and microbial data confirmed the presence of known dechlorinating organisms in groundwater. Push‐pull tests were conducted using trichlorofluoroethene (TCFE) as a reactive tracer for TCE and, in one well, trichlorofluoromethane (TCFM) as a reactive tracer for CTET. Injected TCFE was transformed to cis‐ and trans‐dichlorofluoroethene and chlorofluoroethene, and, in one test, injected TCFE was completely dechlorinated to fluoroethene (FE). In situ TCFE transformation rates ranged from less than 0.005 to 0.004/day. In the single well tested, injected TCFM was transformed in situ to dichlorofluoromethane and chlorofluoromethane; the TCFM transformation rate was estimated as 0.001/day. The results indicate that it is possible to use push‐pull tests with reactive tracers to directly detect and quantify reductive dechlorination of chlorinated ethenes and ethanes under monitored natural attenuation conditions, which has not previously been demonstrated. Transformation rate estimates obtained with these techniques should improve the accuracy of contaminant transport modeling. © 2012 Wiley Periodicals, Inc.     

Historical analysis of monitored natural attenuation: A survey of 191 chlorinated solvent sites and 45 solvent plumes

A survey of experts in the application of natural attenuation was conducted to better understand how monitored natural attenuation (MNA) is being applied at chlorinated solvent sites. Thirty‐four remediation professionals provided general information for 191 sites where MNA was evaluated, and site‐specific data for 45 chlorinated solvent plumes being remediated by MNA. Respondents indicated that MNA was precluded as a remedy at only 23 percent of all sites where evaluated as a remedial option. Leading factors excluding MNA as a remedial approach were the presence of an expanding plume and an unreasonably long estimated remediation time frame. MNA is being used as the sole remedy at about 30 percent of the sites, and 33 percent are implementing MNA in conjunction with source zone remediation. The remaining sites are implementing MNA with plume remediation (13 percent), source containment (9 percent), or some other strategy (16 percent). © 2004 Wiley Periodicals, Inc.     

“New” DDT inputs to North America: Atmospheric deposition

Measurement of untransformed (p,p'- and o,p'-) DDT in rain, snow, and peat indicates that input of “new” DDT continues over a large portion of eastern North America. Peat cores obtained from ombrotrophic bogs indicate that current atmospherically derived fluxes are about 10–20% of those which occurred during peak DDT usage (～1960). Since DDT has been banned in North America and considering the magnitude of present fluxes, these residues must result from atmospheric transboundary transport. It is suggested that “new” DDT is being transported from neighboring areas where current use is substantial, Mexico and Central America.