Cytochrome c adducts with PCB quinoid metabolites

Polychlorinated biphenyls (PCBs) are a group of 209 individual congeners widely used as industrial chemicals. PCBs are found as by-products in dye and paint manufacture and are legacy, ubiquitous, and persistent as human and environmental contaminants. PCBs with fewer chlorine atoms may be metabolized to hydroxy- and dihydroxy-metabolites and further oxidized to quinoid metabolites both in vitro and in vivo. Specifically, quinoid metabolites may form adducts on nucleophilic sites within cells. We hypothesized that the PCB-quinones covalently bind to cytochrome c and, thereby, cause defects in the function of cytochrome c. In this study, synthetic PCB quinones, 2-(4′-chlorophenyl)-1,4-benzoquinone (PCB3-pQ), 4-4'-chlorophenyl)-1,2-benzoquinone (PCB3-oQ), 2-(3′, 5′-dichlorophenyl)-1,4-benzoquinone, 2-(3′,4′, 5′-trichlorophenyl)-1,4-benzoquinone, and 2-(4′-chlorophenyl)-3,6-dichloro-1,4-benzoquinone, were incubated with cytochrome c, and adducts were detected by liquid chromatography-mass spectrometry (LC-MS) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI TOF). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was employed to separate the adducted proteins, while trypsin digestion and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were applied to identify the amino acid binding sites on cytochrome c. Conformation change of cytochrome c after binding with PCB3-pQ was investigated by SYBYL-X simulation and cytochrome c function was examined. We found that more than one molecule of PCB-quinone may bind to one molecule of cytochrome c. Lysine and glutamic acid were identified as the predominant binding sites. Software simulation showed conformation changes of adducted cytochrome c. Additionally, cross-linking of cytochrome c was observed on the SDS-PAGE gel. Cytochrome c was found to lose its function as electron acceptor after incubation with PCB quinones. These data provide evidence that the covalent binding of PCB quinone metabolites to cytochrome c may be included among the toxic effects of PCBs.     

A combined model–observation approach to estimate historic gridded fields of PM2.5 mass and species concentrations

This paper introduces a methodology for estimating gridded fields of total and speciated fine particulate matter (PM_2.5) concentrations for time periods and regions not covered by observational data. The methodology is based on performing long-term regional scale meteorological and air quality simulations and then integrating these simulations with available observational data. To illustrate this methodology, we present an application in which year-round simulations with a meteorological model (the National Center for Atmospheric Research/Penn State Mesoscale Model, hereafter referred to as MM5) and a photochemical air quality model (the Community Multiscale Air Quality Model, hereafter referred to as CMAQ) have been performed over the northeastern United States for 1988–2005. Model evaluation results for total PM_2.5 mass and individual species for the time period from 2000 to 2005 show that model performance varies by species, season, and location. Therefore, an approach is developed to adjust CMAQ output with factors based on these three variables. The adjusted model values for total PM_2.5 mass for 2000–2005 are compared against independent measurements not utilized for the adjustment approach. This comparison reveals that the adjusted model values have a lower root mean square error (RMSE) and higher correlation coefficients than the original model values. Furthermore, the PM_2.5 estimates from these adjusted model values are compared against an alternate method for estimating historic PM_2.5 values that is based on PM_2.5/PM₁₀ ratios calculated at co-located monitors. Results reveal that both methods yield estimates of historic PM_2.5 mass that are broadly consistent; however, the adjusted CMAQ values provide greater spatial coverage and information for PM_2.5 species in addition to total PM_2.5 mass. Finally, strengths and limitations of the proposed approach are discussed in the context of potential uses of this method.     

WATER QUALITY IMPACTS OF CONSERVATION AGRICULTURAL PRACTICES IN THE MISSISSIPPI DELTA1

ABSTRACT: Nonpoint pollution in the form of runoff generated by conventional agricultural practices is one of the major sources of environmental degradation of surface water bodies. Agricultural conservation practices including no‐tillage operations have been introduced as alternatives to cope with such challenges. This study attempts to examine the economic and environmental impacts of no‐tillage as compared to conventional agricultural practices for cotton, soybeans and corn cultivated in the Mississippi Delta. Impacts in the form of sediment, nutrient and pesticide runoff at farm level are investigated, using the Erosion Productivity Impact Calculator (EPIC).     

Is Mutation Accumulation a Threat to the Survival of Endangered Populations?

The accumulation of new deleterious mutations has been predicted to constitute a significant threat to the survival of finite sexually reproducing populations. Three measures of genetic load were made on populations of Drosophila melanogaster maintained at effective population sizes of 25, 50, 100, 250, and 500 for 45 or 50 generations and their outbred base population and a new sample from the same wild population. Genetic loads were measured as fitness differentials between inbred and non-inbred lines derived from each population under both benign ( productivity of single pairs) and competitive (competitive index) conditions. No trend of smaller populations exhibiting greater genetic loads than larger ones was observed under either benign or competitive conditions. Further, genetic loads were similar in captive and wild populations. Frequencies of deleterious and lethal alleles on chromosome II were measured by making the chromosome (approximately 40% of the genome) homozygous using a marked balancer stock. Neither deleterious nor lethal allele frequencies exhibited a relationship with population size. The accumulation of detrimental mutations does not appear to pose a significant threat to finite sexual populations with effective sizes of 25 or more over the 100–200 year time frames considered in most wildlife conservation programs.     

Assuming a 50% cell occupancy of the lorica overestimates tintinnine ciliate biomass

To estimate biomass and production, the cell volume of tintinnine ciliates has been assumed to be 50% of lorica volume. This assumption was tested using a high-precision digitizing system which measured individuals of 17 tintinnine species in samples taken in two annual studies of biomass and production in both tropical (Kingston, Jamaica in 1986) and temperate (Passamaquoddy Bay, Canada in 1983–1984) regions. Using this assumption, percent occupancies and hence, biovolume estimates, were overestimated by as much as 317% for tropical species and 178% for temperate species. Daily production estimates of the tropical tintinnine assemblage were overestimated by as much as 147%. In studies attempting to estimate biomass and production accurately, it is concluded that cell volume of tintinnines should be measured directly rather than assumed to be 50% of lorica volume.This research was financed by an NSERC Canada operating grant awarded to Dr D. H. Lynn     

A reliability index for models

Since the prediction of environmental changes depends heavily on mathematical models, environmental planners have a definite need for a general test that can be easily applied to determine the reliability of a model or to choose between available models. In this paper a ‘reliability index’ for a model is defined. This index is a number k ? 1 which is determined from a set x₁,x₂,…,x_n of model predictions and a corresponding set y₁,y₂,…,y_n of observations. One interpretation of the index k is that the model predictions agree with observations, in some sense, within a factor of k. The index k is defined using an intuitive, geometric approach and is justified through agreement with another index developed using statistical techniques. Examples are given for a model which predicts the atmospheric movement of radon-222 originating from a concentrated source of radium-226, such as a uranium tailings pile.     

THE OPPORTUNITY COST OF TIME AND AVERTING EXPENDITURES FOR SAFE DRINKING WATER1

ABSTRACT: A survey of individuals during a Giardia contamination incident provided data to calculate the cost of boiling, hauling, or purchasing water to avoid infection. Three different approaches to the valuation of time were used to assess the implications of the opportunity cost of time for the measurement of averting costs. Mean monthly household averting costs were $33.47 using family income to value time, $13.07 using the minimum wage to value time, and $5.60 using zero opportunity cost of time. Comparisons of the mean costs for different sources and household characteristics indicated the value of time from family income was too high and that the other methods of valuing time were superior.     

Questions and answers. TQEM performance indicators—how do you measure up?

I have seen a number of corporations accept the philosophy of TQEM and start the process of total quality environmental management with great enthusiasm. I believe that many organizations are attracted because TQM principles demand measurements of success and results that are definable for the environment. It reduces the emotionalism that frequently tends to surround environmental issues. Emotionalism has perhaps been the bane and boon of efforts by corporations and advocacy groups to incorporate environmental issues into the day-to-day functions of organizations. Abt Associates, a well-known research-based consulting firm, recently completed a study of U.S. Fortune 250 firms' environmental management programs. Abt found evidence that environmental performance is a competitive issue. Benchmarking is hotly pursued to develop firm-wide indices of performance. One third of the benchmarking is against competition, another third is against worldwide firms. There is a race to develop “Best in Class” standards now. E2M and Abt Associates have combined resources to study corporate Canada's environmental management programs and compare these with those of the United States. This research will help companies benchmark activities and will build a strong North American data base. Unfortunately it will not be ready in time to answer TQEM's question for this issue. (The study results will be released to participating companies in Fall 1992.)