Effects of delay,truncations and density dependence in reproduction schedules on stability of nonlinear Leslie matrix models

Understanding effects of hypotheses about reproductive influences, reproductive schedules and the model mechanisms that lead to a loss of stability in a structured model population might provide information about the dynamics of natural population. To demonstrate characteristics of a discrete time, nonlinear, age structured population model, the transition from stability to instability is investigated. Questions about the stability, oscillations and delay processes within the model framework are posed. The relevant processes include delay of reproduction and truncation of lifetime, reproductive classes, and density dependent effects. We find that the effects of delaying reproduction is not stabilizing, but that the reproductive delay is a mechanism that acts to simplify the system dynamics. Density dependence in the reproduction schedule tends to lead to oscillations of large period and towards more unstable dynamics. The methods allow us to establish a conjecture of Levin and Goodyear about the form of the stability in discrete Leslie matrix models.This research was supported in part by the US Environmental Protection Agency under cooperation agreement CR-816081     

Isolation and long-term culture of rat,rabbit, and human nasal turbinate epithelial cells

Summary Nasal turbinate epithelial cells were isolated from rats, rabbits, and humans using either a surgical or an in situ enzyme incubation technique. The culture conditions that permit optimal cell attachment and selective growth of the nasal epithelial cells were determined. These conditions will permit the long-term culture of these cells where typically 20 to 30 population doublings were observed. Differences between rat and human nasal epithelial cells were seen in substrate requirements, colony-forming efficiency, and response to fetal bovine serum and bovine serum albumin. These methodology and results will permit mechanistic studies of normal and abnormal cellular function and comparative response studies between nasal epithelial cells from rats and humans. This work was supported under U.S. Environmental Protection Agency contract 68-02-4032.     

Survival in continuous structured populations models

The extended McKendrick-von Foerster structured population model is employed to derive a nonautonomous ordinary differential equation model of a population. The derivation assumes that the individual life history can be delineated into several physiological stages. We study the persistence of the population when the model is autonomous and base the nonautonomous survival analysis on the autonomous case and a comparison principle. A brief excursion into alternate life history strategies is presented.This work was supported in part by the U.S. Environmental Protection Agency under cooperative agreement CR 813353010     

Persistence in stochastic food web models

A sufficient condition is given for stochastic boundedness persistence of a top predator in generalized Lotka-Volterra-type stochastic food web models in arbitrary bounded regions of state space. The main result indicates that persistence in the corresponding deterministic system is preserved in the stochastic system if the intensities of the random fluctuations are not too large. This work was supported, in part, by the U. S. Environmental Protection Agency under Grant No. CR 807830.     

The threshold of survival for systems in a fluctuating environment

Thresholds for survival and extinction are important for assessing the risk of mortality in systems exposed to exogeneous stress. For generic, rudimentary population models and the classical resource-consumer models of Leslie and Gallopin, we demonstrate the existence of a survival threshold for situations where demographic parameters are fluctuating, generally, in a nonperiodic manner. The fluctuations are assumed, to be generated by exogenous, anthropogenic stresses such as toxic chemical exposures. In general, the survival threshold is determined by a relationship between mean stress measure in organisms to the ratio of the population intrinsic growth rate and stress response rate. Research supported by the fund of Chinese Natural Science. Research supported in part by the U.S. Enviromental Protection Agency under cooperative agreement CR-813353-01-0.     

Evaluation of Potential Exposure to Metals in Laundered Shop Towels

We reported in 2003 that exposure to metals on laundered shop towels (LSTs) could exceed toxicity criteria. New data from LSTs used by workers in North America document the continued presence of metals in freshly laundered towels. We assessed potential exposure to metals based on concentrations of metals on the LSTs, estimates of LST usage by employees, and the transfer of metals from LST-to-hand, hand-to-mouth, and LST-to-lip, under average- or high-exposure scenarios. Exposure estimates were compared to toxicity criteria. Under an average-exposure scenario (excluding metals’ data outliers), exceedances of the California Environmental Protection Agency, U.S. Environmental Protection Agency, and the Agency for Toxic Substances and Disease Registry toxicity criteria may occur for aluminum, cadmium, cobalt, copper, iron, and lead. Calculated intakes for these metals were up to more than 400-fold higher (lead) than their respective toxicity criterion. For the high-exposure scenario, additional exceedances may occur, and high-exposure intakes were up to 1,170-fold higher (lead) than their respective toxicity criterion. A sensitivity analysis indicated that alternate plausible assumptions could increase or decrease the magnitude of exceedances, but were unlikely to eliminate certain exceedances, particularly for lead.     

Iteroparous reproduction strategies and population dynamics

Asymptotic relationships between a class of continuous partial differential equation population models and a class of discrete matrix equations are derived for iteroparous populations. First, the governing equations are presented for the dynamics of an individual with juvenile and adult life stages. The organisms reproduce after maturation, as determined by the juvenile period, and at specific equidistant ages, which are determined by the iteroparous reproductive period. A discrete population matrix model is constructed that utilizes the reproductive information and a density-dependent mortality function. Mortality in the period between two reproductive events is assumed to be a continuous process where the death rate for the adults is a function of the number of adults and environmental conditions. The asymptotic dynamic behaviour of the discrete population model is related to the steady-state solution of the continuous-time formulation. Conclusions include that there can be a lack of convergence to the steady-state age distribution in discrete event reproduction models. The iteroparous vital ratio (the ratio between the maximal age and the reproductive period) is fundamental to determining this convergence. When the vital ratio is rational, an equivalent discrete-time model for the population can be derived whose asymptotic dynamics are periodic and when there are a finite number of founder cohorts, the number of cohorts remains finite. When the ratio is an irrational number, effectively there is convergence to the steady-state age distribution. With a finite number of founder cohorts, the number of cohorts becomes countably infinite. The matrix model is useful to clarify numerical results for population models with continuous densities as well as delta measure age distribution. The applicability in ecotoxicology of the population matrix model formulation for iteroparous populations is discussed.     

Dynamics of games and genes: Discrete versus continuous time

It is shown that in the classical model of population genetics (Fisher-Wright-Haldane, discrete or continuous version) every solution p(t) converges to equilibrium for t → ∞. For related models of evolutionary games (with non-symmetric matrices) it is shown that the transformation that describes the dynamics is a diffeomorphism (in particular one-to-one).     

Round robin investigation of methods for recovering human enteric viruses from sludge.

To select a tentative standard method for detection of viruses in sludge the American Society for Testing and Materials D19:24:04:04 Subcommittee Task Group initiated round robin comparative testing of two procedures that, after initial screening of several methodologies, were found to meet the basic criteria considered essential by the task group. Eight task group member laboratories agreed to perform round robin testing of the two candidate methods, namely, The Environmental Protection Agency or low pH-AlCl3 method and the Glass or sonication-extraction method. Five different types of sludge were tested. For each particular type of sludge, a single laboratory was designated to collect the sludge in a single sampling, make samples, and ship it to the participating laboratories. In most cases, participating laboratories completed all the tests within 48 h of sample arrival. To establish the reproducibility of the methods, each laboratory tested each sludge sample in triplicate for the two candidate virus methods. Each processed sludge sample was quantitatively assayed for viruses by the procedures of each individual round robin laboratory. To attain a more uniform standard of comparison, a sample of each processed sample from all laboratories was reassayed with one cell line and passage number by a single laboratory (Environmental Protection Agency Environmental Monitoring and Support Laboratory, Cincinnati, Ohio). When the data were statistically analyzed, the Environmental Protection Agency method was found to yield slightly higher virus recoveries for all sludge types, except the dewatered sludge. The precisions of both methods were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)     

Round robin investigation of methods for recovering human enteric viruses from sludge

To select a tentative standard method for detection of viruses in sludge the American Society for Testing and Materials D19:24:04:04 Subcommittee Task Group initiated round robin comparative testing of two procedures that, after initial screening of several methodologies, were found to meet the basic criteria considered essential by the task group. Eight task group member laboratories agreed to perform round robin testing of the two candidate methods, namely, The Environmental Protection Agency or low pH-AlCl3 method and the Glass or sonication-extraction method. Five different types of sludge were tested. For each particular type of sludge, a single laboratory was designated to collect the sludge in a single sampling, make samples, and ship it to the participating laboratories. In most cases, participating laboratories completed all the tests within 48 h of sample arrival. To establish the reproducibility of the methods, each laboratory tested each sludge sample in triplicate for the two candidate virus methods. Each processed sludge sample was quantitatively assayed for viruses by the procedures of each individual round robin laboratory. To attain a more uniform standard of comparison, a sample of each processed sample from all laboratories was reassayed with one cell line and passage number by a single laboratory (Environmental Protection Agency Environmental Monitoring and Support Laboratory, Cincinnati, Ohio). When the data were statistically analyzed, the Environmental Protection Agency method was found to yield slightly higher virus recoveries for all sludge types, except the dewatered sludge. The precisions of both methods were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variables Affecting Two Electron Transport System Assays

Several methodological variables were critical in two commonly used electron transport activity assays. The dehydrogenase assay based on triphenyl formazan production exhibited a nonlinear relationship between formazan production (dehydrogenase activity) and sediment dilution, and linear formazan production occurred for 1 h in sediment slurries. Activity decreased with increased time of sediment storage at 4°C. Extraction efficiencies of formazan from sediment varied with alcohol type; methanol was unsatisfactory. Phosphate buffer (0.06 M) produced higher activity than did either U.S. Environmental Protection Agency reconstituted hard water or Tris buffer sediment diluents. Intracellular formazan crystals were dissolved within minutes when in contact with immersion oil. Greater crystal production (respiration) detected by a tetrazolium salt assay occurred at increased substrate concentrations. Test diluents containing macrophyte exudates produced greater activity than did phosphate buffer, U.S. Environmental Protection Agency water, or ultrapure water diluents. Both assays showed decreases in sediment or bacterial activity through time.     

Evaluation of physical coverings used to control Escherichia coli O157:H7 at the compost heap surface

Throughout four field trials, compost heaps covered with finished compost maintained temperatures under the physical covering that were ca. 7 to 15.5°C higher, resulting in rapid Escherichia coli O157:H7 reduction, than those of the heaps covered with fresh straw or left uncovered. Our results validated recommendations made by the U.S. Environmental Protection Agency for covering fresh compost.     

Examining the Links between Biodiversity and Human Health: An Interdisciplinary Research Initiative at the U.S. Environmental Protection Agency

Under the U.S. Environmental Protection Agency’s mission to protect human health and the environment, the agency seeks to conduct research on the structure and function of ecosystems and to improve our understanding of the processes that contribute to the sustained health of the nation’s ecosystems and the well-being of human populations. Changes in biodiversity can profoundly impact the ability of ecosystems to provide clean water, energy, food, recreation, and other services that contribute to human well-being. In addition, changes in biodiversity can affect the transmission of infectious disease to humans, particularly vectorborne diseases such as malaria and Lyme disease. The Environmental Protection Agency’s new initiative supports interdisciplinary research to characterize the mechanisms that link biodiversity and human health and to use this knowledge to develop integrative tools and approaches for quantifying and predicting these relationships. Research on these links can have an important impact on our view of biodiversity and how we manage resources to protect human and ecosystem health. Disclaimer: This work was funded in part under Grant #CX3-832328 with the American Association for the Advance of Science (AAAS). The views expressed do not necessarily reflect the views of the Environmental Protection Agency.     

The FQPA 10X Safety Factor: How Much is Science? How Much is Sociology?

On August 3, 1996, the Food Quality Protection Act of 1996 (FQPA) was signed into law. The FQPA instructed the U.S. Environmental Protection Agency, in making its “reasonable certainty of no harm” finding, that in “the case of threshold effects,…an additional tenfold margin of safety…shall be applied for infants and children to take into account potential pre- and postnatal toxicity and completeness of data with respect to exposure and toxicity to infants and children.” The law further states that “the Administrator may use a different margin of safety……only if, on the basis of reliable data, such margin will be safe for infants and children.” This paper describes how the Office of Pesticide Programs of the U.S. Environmental Protection Agency proposes to implement this legislative mandate in its 1999 draft.     

Confirmation of the safety of Lagenidium giganteum (Oomycetes: Lagenidiales) to mammals

Lagenidium giganteum Couch, a fungal parasite of mosquito larvae, is considered a promising agent for operational control. Quantitative reisolation of the fungus from rodent blood and tissue is easily accomplished because the cell walls are much more persistent than those of mammalian cells. The mycelium forms discrete, septate cells very early in its development, in marked contrast to filamentous fungi. The fungus is rapidly cleared from mice following intraperitoneal injection of large quantities of mycelium and oospores. More than 95% of viable cells are cleared within 24 h. Mortality following intravenous injection of mycelium in tail veins of mice is caused solely by embolism of heart and lung tissue. Recently revised U.S. Environmental Protection Agency protocols for testing of microbial pest control agents may have to be altered further to accommodate physically large microbial agents such as L. giganteum.     

Widespread apathy and the public's reaction to information concerning the health effects of indoor air radon concentrations

The thoughts and ideas expressed in this paper are those of the author and are not necessarily those of the U.S. Environmental Protection Agency.     

Availability and uptake of inorganic nitrogen in a mixed old-growth coniferous forest

Old-growth forest stands of mixed species composition provide the opportunity to study species-specific influences on soil properties. We monitored rates of nitrogen mineralization, nitrification and an index of ammonium and nitrate uptake in a mixed old-growth stand of Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla) and western redcedar (Thuja plicata) over a two-year period. Litter and mineral soil (0–10-cm depth) were sampled adjacent to ten large trees of each species. After initial characterization of litter and soil, buried bags were incubated in both layers for ca. 2-month intervals. Soil and litter pH was lowest near western hemlocks. Nitrification, nitrate concentrations, and percent uptake as nitrate differed among the tree species; rates were highest near western redcedars. For all species, percent nitrification and nitrate uptake rate were higher in soil than in litter. The results indicate species-specific effects on ammonium and nitrate production and uptake within this forest type.The research described in this article has been funded in part by the US Environmental Protection Agency. This document has been prepared at the EPA Environmental Research Laboratory in Corvallis, Oregon, through Contract No. 68-C8-0006 to ManTech Environmental Technology, Inc. It has been subjected to the Agency's peer and administrative review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.The research described in this article has been funded in part by the US Environmental Protection Agency. This document has been prepared at the EPA Environmental Research Laboratory in Corvallis, Oregon, through Contract No. 68-C8-0006 to ManTech Environmental Technology, Inc. It has been subjected to the Agency's peer and administrative review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

Fate of polycyclic aromatic hydrocarbons during composting of activated sewage sludge with green waste

The level and fate of 16 polycyclic aromatic hydrocarbons (PAHs), targeted by the US Environmental Protection Agency (USEPA), has been studied over 90 days of composting of activated sludge with green waste, under a semi-arid climate. The total PAH calculated from the sum of the amounts of the 16 PAHs in the initial mixture of activated sludge and green waste, was lower than accepted European Union cut-off limits by about 0.48mgkg(-1). The treatment by composting led to a decrease of all PAHs mainly in the stabilization phase, but some differences could be observed between PAHs with three or fewer aromatic rings (N3) and those with four or more (N4). The former (except phenanthrene) exhibited a continuous decrease, while the latter PAHs with N of four or more and phenanthrene showed increases in the intermediate stages (30-60 days). This indicates the high potential sorption mainly of PAH with high molecular weight (N4) plus phenanthrene, their tight adsorption makes them inaccessible for microbial attack. The high molecular weight PAHs showed a greater reduction of their bioavailability than those of low molecular weight. Naphthalene, with the lowest molecular weight, showed the smallest decrease (about 67.8%) compared to other PAHs of higher molecular weight (decrease reaching 100%). This is in agreement with the fact that the adsorption is less reversible with increased numbers of fused aromatic rings or an increase of their hydrophobicity.     

Reproductive and developmental responses in the self-fertilizing fish,Rivulus marmoratus,induced by the plasticizer,di-n-butylphthalate

Synopsis Specialized life-history attributes of the cyprinodontiform fish, Rivulus marmoratus, allow continuous life cycle testing to reveal effects of chemicals or environmental stresses upon fertilization, fecundity, egg viability, embryonic development, sex ratios, frequency of growth or skeletal anomalies, as well as other biological markers. This study reports responses in fecundity, viability of embryos, and skeletal anomalies during and after exposure of parental fish to the plasticizer, di-n-butylphthalate (DBP). Skeletal anomalies among offspring were classified as mild, moderate, or severe compared with non-deformed normal offspring. The frequency of skeletal anomalies increased from 4% (all categories combined) in controls, to 10% and 19% of the offspring from adults exposed to 1 and 2 mg I^-1 DBP, respectively. DBP treatment was conducted over a 21 week interval, followed by a 9 week post-treatment observation interval. During post-treatment, frequency of skeletal anomalies decreased to less than 5% in all groups. Contributions No. 610, Environmental Research Laboratory, Gulf Breeze, Florida 32561 U.S.A. The information in this document has been funded wholly by the U.S. Environmental Protection Agency, and has been subjected to the Agency's peer and administrative review. Mention of commercial products or trade names does not constitute the Agency's endorsement or recommendation for use.