1
|
Dorheim K, Gough CM, Haber LT, Mathes KC, Shiklomanov AN, Bond‐Lamberty B. Climate Drives Modeled Forest Carbon Cycling Resistance and Resilience in the Upper Great Lakes Region, USA. J Geophys Res Biogeosci 2022; 127:e2021JG006587. [PMID: 35865142 PMCID: PMC9287023 DOI: 10.1029/2021jg006587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Revised: 11/02/2021] [Accepted: 11/29/2021] [Indexed: 06/15/2023]
Abstract
Forests dominate the global terrestrial carbon budget, but their ability to continue doing so in the face of a changing climate is uncertain. A key uncertainty is how forests will respond to (resistance) and recover from (resilience) rising levels of disturbance of varying intensities. This knowledge gap can optimally be addressed by integrating manipulative field experiments with ecophysiological modeling. We used the Ecosystem Demography-2.2 (ED-2.2) model to project carbon fluxes for a northern temperate deciduous forest subjected to a real-world disturbance severity manipulation experiment. ED-2.2 was run for 150 years, starting from near bare ground in 1900 (approximating the clear-cut conditions at the time), and subjected to three disturbance treatments under an ensemble of climate conditions. Both disturbance severity and climate strongly affected carbon fluxes such as gross primary production (GPP), and interacted with one another. We then calculated resistance and resilience, two dimensions of ecosystem stability. Modeled GPP exhibited a two-fold decrease in mean resistance across disturbance severities of 45%, 65%, and 85% mortality; conversely, resilience increased by a factor of two with increasing disturbance severity. This pattern held for net primary production and net ecosystem production, indicating a trade-off in which greater initial declines were followed by faster recovery. Notably, however, heterotrophic respiration responded more slowly to disturbance, and it's highly variable response was affected by different drivers. This work provides insight into how future conditions might affect the functional stability of mature forests in this region under ongoing climate change and changing disturbance regimes.
Collapse
Affiliation(s)
- Kalyn Dorheim
- Joint Global Change Research InstitutePacific Northwest National LaboratoryCollege ParkMDUSA
| | | | - Lisa T. Haber
- Department of BiologyVirginia Commonwealth UniversityRichmondVAUSA
| | - Kayla C. Mathes
- Department of BiologyVirginia Commonwealth UniversityRichmondVAUSA
| | | | - Ben Bond‐Lamberty
- Joint Global Change Research InstitutePacific Northwest National LaboratoryCollege ParkMDUSA
| |
Collapse
|
2
|
Woelmer WM, Bradley LM, Haber LT, Klinges DH, Lewis ASL, Mohr EJ, Torrens CL, Wheeler KI, Willson AM. Ten simple rules for training yourself in an emerging field. PLoS Comput Biol 2021; 17:e1009440. [PMID: 34710084 PMCID: PMC8553149 DOI: 10.1371/journal.pcbi.1009440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The opportunity to participate in and contribute to emerging fields is increasingly prevalent in science. However, simply thinking about stepping outside of your academic silo can leave many students reeling from the uncertainty. Here, we describe 10 simple rules to successfully train yourself in an emerging field, based on our experience as students in the emerging field of ecological forecasting. Our advice begins with setting and revisiting specific goals to achieve your academic and career objectives and includes several useful rules for engaging with and contributing to an emerging field.
Collapse
Affiliation(s)
- Whitney M. Woelmer
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America
- * E-mail:
| | - L. M. Bradley
- Department of Biology, Emory University, Atlanta, Georgia, United States of America
| | - Lisa T. Haber
- Integrative Life Sciences, Virginia Commonwealth University, Richmond, Virginia, United States of America
| | - David H. Klinges
- School of Natural Resources and Environment, University of Florida, Gainesville, Florida, United States of America
| | - Abigail S. L. Lewis
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Elizabeth J. Mohr
- Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana, United States of America
| | - Christa L. Torrens
- Institute of Arctic and Alpine Research, University of Colorado at Boulder, Boulder, Colorado, United States of America
| | - Kathryn I. Wheeler
- Department of Earth and Environment, Boston University, Boston, Massachusetts, United States of America
| | - Alyssa M. Willson
- Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, United States of America
| |
Collapse
|
3
|
Gough CM, Bohrer G, Hardiman BS, Nave LE, Vogel CS, Atkins JW, Bond-Lamberty B, Fahey RT, Fotis AT, Grigri MS, Haber LT, Ju Y, Kleinke CL, Mathes KC, Nadelhoffer KJ, Stuart-Haëntjens E, Curtis PS. Disturbance-accelerated succession increases the production of a temperate forest. Ecol Appl 2021; 31:e02417. [PMID: 34278647 DOI: 10.1002/eap.2417] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 02/19/2021] [Accepted: 03/22/2021] [Indexed: 06/13/2023]
Abstract
Many secondary deciduous forests of eastern North America are approaching a transition in which mature early-successional trees are declining, resulting in an uncertain future for this century-long carbon (C) sink. We initiated the Forest Accelerated Succession Experiment (FASET) at the University of Michigan Biological Station to examine the patterns and mechanisms underlying forest C cycling following the stem girdling-induced mortality of >6,700 early-successional Populus spp. (aspen) and Betula papyrifera (paper birch). Meteorological flux tower-based C cycling observations from the 33-ha treatment forest have been paired with those from a nearby unmanipulated forest since 2008. Following over a decade of observations, we revisit our core hypothesis: that net ecosystem production (NEP) would increase following the transition to mid-late-successional species dominance due to increased canopy structural complexity. Supporting our hypothesis, NEP was stable, briefly declined, and then increased relative to the control in the decade following disturbance; however, increasing NEP was not associated with rising structural complexity but rather with a rapid 1-yr recovery of total leaf area index as mid-late-successional Acer, Quercus, and Pinus assumed canopy dominance. The transition to mid-late-successional species dominance improved carbon-use efficiency (CUE = NEP/gross primary production) as ecosystem respiration declined. Similar soil respiration rates in control and treatment forests, along with species differences in leaf physiology and the rising relative growth rates of mid-late-successional species in the treatment forest, suggest changes in aboveground plant respiration and growth were primarily responsible for increases in NEP. We conclude that deciduous forests transitioning from early to middle succession are capable of sustained or increased NEP, even when experiencing extensive tree mortality. This adds to mounting evidence that aging deciduous forests in the region will function as C sinks for decades to come.
Collapse
Affiliation(s)
- Christopher M Gough
- Department of Biology, Virginia Commonwealth University, Box 842012, 1000 West Cary Street, Richmond, Virginia, 23284, USA
| | - Gil Bohrer
- Department of Civil, Environmental and Geodetic Engineering, Ohio State University, 2070 Neil Avenue, Columbus, Ohio, 43210, USA
| | - Brady S Hardiman
- Forestry and Natural Resources and Environmental and Ecological Engineering, Purdue University, West Lafayette, Indiana, 47907, USA
| | - Lucas E Nave
- Biological Station and Department of Ecology and Evolutionary Biology, University of Michigan, Pellston, Michigan, 49769, USA
| | - Christoph S Vogel
- Biological Station and Department of Ecology and Evolutionary Biology, University of Michigan, Pellston, Michigan, 49769, USA
| | - Jeff W Atkins
- Department of Biology, Virginia Commonwealth University, Box 842012, 1000 West Cary Street, Richmond, Virginia, 23284, USA
| | - Ben Bond-Lamberty
- Joint Global Change Research Institute, Pacific Northwest National Laboratory, 5825 University Research Court, College Park, Maryland, 20740, USA
| | - Robert T Fahey
- Department of Natural Resources and the Environment, Center for Environmental Sciences and Engineering, University of Connecticut, 1376 Storrs Road, Storrs, Connecticut, 06269, USA
| | - Alexander T Fotis
- Department of Evolution, Ecology, and Organismal Biology, Ohio State University, 318 W 12th Avenue, Columbus, Ohio, 43210, USA
| | - Maxim S Grigri
- Department of Biology, Virginia Commonwealth University, Box 842012, 1000 West Cary Street, Richmond, Virginia, 23284, USA
| | - Lisa T Haber
- Department of Biology, Virginia Commonwealth University, Box 842012, 1000 West Cary Street, Richmond, Virginia, 23284, USA
| | - Yang Ju
- Department of Civil, Environmental and Geodetic Engineering, Ohio State University, 2070 Neil Avenue, Columbus, Ohio, 43210, USA
| | - Callie L Kleinke
- Department of Civil, Environmental and Geodetic Engineering, Ohio State University, 2070 Neil Avenue, Columbus, Ohio, 43210, USA
| | - Kayla C Mathes
- Department of Biology, Virginia Commonwealth University, Box 842012, 1000 West Cary Street, Richmond, Virginia, 23284, USA
| | - Knute J Nadelhoffer
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, 48109, USA
| | - Ellen Stuart-Haëntjens
- Department of Biology, Virginia Commonwealth University, Box 842012, 1000 West Cary Street, Richmond, Virginia, 23284, USA
| | - Peter S Curtis
- Department of Evolution, Ecology, and Organismal Biology, Ohio State University, 318 W 12th Avenue, Columbus, Ohio, 43210, USA
| |
Collapse
|
4
|
Gough CM, Atkins JW, Bond-Lamberty B, Agee EA, Dorheim KR, Fahey RT, Grigri MS, Haber LT, Mathes KC, Pennington SC, Shiklomanov AN, Tallant JM. Forest Structural Complexity and Biomass Predict First-Year Carbon Cycling Responses to Disturbance. Ecosystems 2020. [DOI: 10.1007/s10021-020-00544-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
5
|
Atkins JW, Bond‐Lamberty B, Fahey RT, Haber LT, Stuart‐Haëntjens E, Hardiman BS, LaRue E, McNeil BE, Orwig DA, Stovall AEL, Tallant JM, Walter JA, Gough CM. Application of multidimensional structural characterization to detect and describe moderate forest disturbance. Ecosphere 2020. [DOI: 10.1002/ecs2.3156] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Affiliation(s)
- Jeff W. Atkins
- Department of Biology Virginia Commonwealth University Richmond Virginia 23284 USA
| | - Ben Bond‐Lamberty
- Joint Global Change Research Institute Pacific Northwest National Lab College Park Maryland USA
| | - Robert T. Fahey
- Department of Natural Resources and the Environment Center for Environmental Sciences and Engineering University of Connecticut Storrs Connecticut USA
| | - Lisa T. Haber
- Department of Biology Virginia Commonwealth University Richmond Virginia 23284 USA
| | - Ellen Stuart‐Haëntjens
- Department of Biology Virginia Commonwealth University Richmond Virginia 23284 USA
- United States Geological Survey Sacramento California 95819 USA
| | - Brady S. Hardiman
- Department of Forestry and Natural Resources Purdue University West Lafayette Indiana 47907 USA
- Department of Civil and Environmental Engineering Purdue University West Lafayette Indiana 47907 USA
| | - Elizabeth LaRue
- United States Geological Survey Sacramento California 95819 USA
| | - Brenden E. McNeil
- Department of Geology and Geography West Virginia University Morgantown West Virginia USA
| | - David A. Orwig
- Harvard University Harvard Forest Petersham Massachusetts USA
| | | | | | - Jonathan A. Walter
- Department of Environmental Sciences University of Virginia Charlottesville Virginia USA
| | - Christopher M. Gough
- Department of Biology Virginia Commonwealth University Richmond Virginia 23284 USA
| |
Collapse
|
6
|
Haber LT, Fahey RT, Wales SB, Correa Pascuas N, Currie WS, Hardiman BS, Gough CM. Forest structure, diversity, and primary production in relation to disturbance severity. Ecol Evol 2020; 10:4419-4430. [PMID: 32489607 PMCID: PMC7246213 DOI: 10.1002/ece3.6209] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 11/04/2019] [Accepted: 02/26/2020] [Indexed: 11/12/2022] Open
Abstract
Differential disturbance severity effects on forest vegetation structure, species diversity, and net primary production (NPP) have been long theorized and observed. Here, we examined these factors concurrently to explore the potential for a mechanistic pathway linking disturbance severity, changes in light environment, leaf functional response, and wood NPP in a temperate hardwood forest.Using a suite of measurements spanning an experimental gradient of tree mortality, we evaluated the direction and magnitude of change in vegetation structural and diversity indexes in relation to wood NPP. Informed by prior observations, we hypothesized that forest structural and species diversity changes and wood NPP would exhibit either a linear, unimodal, or threshold response in relation to disturbance severity. We expected increasing disturbance severity would progressively shift subcanopy light availability and leaf traits, thereby coupling structural and species diversity changes with primary production.Linear or unimodal changes in three of four vegetation structural indexes were observed across the gradient in disturbance severity. However, disturbance-related changes in vegetation structure were not consistently correlated with shifts in light environment, leaf traits, and wood NPP. Species diversity indexes did not change in response to rising disturbance severity.We conclude that, in our study system, the sensitivity of wood NPP to rising disturbance severity is generally tied to changing vegetation structure but not species diversity. Changes in vegetation structure are inconsistently coupled with light environment and leaf traits, resulting in mixed support for our hypothesized cascade linking disturbance severity to wood NPP.
Collapse
Affiliation(s)
- Lisa T. Haber
- Department of BiologyVirginia Commonwealth UniversityRichmondVAUSA
| | - Robert T. Fahey
- Department of Natural Resources and the Environment & Center for Environmental Sciences and EngineeringUniversity of ConnecticutStorrsCTUSA
| | - Shea B. Wales
- Department of BiologyVirginia Commonwealth UniversityRichmondVAUSA
| | | | - William S. Currie
- School for Environment and SustainabilityUniversity of MichiganAnn ArborMIUSA
| | - Brady S. Hardiman
- Department of Forestry and Natural ResourcesPurdue UniversityWest LafayetteINUSA
| | | |
Collapse
|
7
|
Fahey RT, Atkins JW, Gough CM, Hardiman BS, Nave LE, Tallant JM, Nadehoffer KJ, Vogel C, Scheuermann CM, Stuart‐Haëntjens E, Haber LT, Fotis AT, Ricart R, Curtis PS. Defining a spectrum of integrative trait‐based vegetation canopy structural types. Ecol Lett 2019; 22:2049-2059. [DOI: 10.1111/ele.13388] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 08/05/2019] [Accepted: 08/22/2019] [Indexed: 01/21/2023]
Affiliation(s)
- Robert T. Fahey
- Department of Natural Resources and the Environment and Center for Environmental Sciences and Engineering University of Connecticut Storrs CT USA
| | - Jeff W. Atkins
- Department of Biology Virginia Commonwealth University Richmond VA USA
| | | | - Brady S. Hardiman
- Department of Forestry and Natural Resources and Environmental and Ecological Engineering Purdue University West Lafayette IN USA
| | - Lucas E. Nave
- Department of Ecology and Evolutionary Biology and Biological Station, University of Michigan Ann Arbor and Pellston MI USA
| | - Jason M. Tallant
- Department of Ecology and Evolutionary Biology and Biological Station, University of Michigan Ann Arbor and Pellston MI USA
| | - Knute J. Nadehoffer
- Department of Ecology and Evolutionary Biology and Biological Station, University of Michigan Ann Arbor and Pellston MI USA
| | - Christoph Vogel
- Department of Ecology and Evolutionary Biology and Biological Station, University of Michigan Ann Arbor and Pellston MI USA
| | | | | | - Lisa T. Haber
- Department of Biology Virginia Commonwealth University Richmond VA USA
| | - Alexander T. Fotis
- Department of Evolution, Ecology and Organismal Biology Ohio State University Columbus OH USA
| | - Raleigh Ricart
- Department of Evolution, Ecology and Organismal Biology Ohio State University Columbus OH USA
| | - Peter S. Curtis
- Department of Evolution, Ecology and Organismal Biology Ohio State University Columbus OH USA
| |
Collapse
|
8
|
Abstract
A peer review panel made up of experts in toxicology, epidemiology, cancer mode of action (MOA), cancer mechanisms, carcinogenicity, genotoxicity, dose–response, US Environmental Protection Agency (EPA) cancer and noncancer methods, pharmacokinetic modeling and acrylonitrile, met on 22–23 September 2003 in Cincinnati, OH. The purpose of the meeting was to provide an independent review of a risk assessment of acrylonitrile that had been prepared by the Acrylonitrile Group (AN Group). Toxicology Excellence for Risk Assessment (TERA) organized the peer review and selected the panel. The panel discussed the toxicity and epidemiology literature of acrylonitrile and MOA information, and reached conclusions regarding its MOA, weight of evidence (WOE) for carcinogenicity, preferred approach for dose-response assessment and risk values. This paper summarizes the discussion and conclusions of the panel regarding the acrylonitrile assessment. Subsequent to the peer review, the authors of the acrylonitrile assessment revised their report and the panel reviewed the revised report. A manuscript of the revised assessment is being published in Regulatory Toxicology and Pharmacology.
Collapse
|
9
|
Haber LT, Maier A, Gentry PR, Clewell HJ, Dourson ML. Genetic polymorphisms in assessing interindividual variability in delivered dose. Regul Toxicol Pharmacol 2002; 35:177-97. [PMID: 12052003 DOI: 10.1006/rtph.2001.1517] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Increasing sophistication in methods used to account for human variability in susceptibility to toxicants has been one of the success stories in the continuing evolution of risk assessment science. Genetic polymorphisms have been suggested as an important contributor to overall human variability. Recently, data on polymorphisms in metabolic enzymes have been integrated with physiologically based pharmacokinetic (PBPK) modeling as an approach to determining the resulting overall variability. We present an analysis of the potential contribution of polymorphisms in enzymes modulating the disposition of four diverse compounds: methylene chloride, warfarin, parathion, and dichloroacetic acid. Through these case studies, we identify key uncertainties likely to be encountered in the use of polymorphism data and highlight potential simplifying assumptions that might be required to test the hypothesis that genetic factors are a substantive source of human variability in susceptibility to environmental toxicants. These uncertainties include (1) the relative contribution of multiple enzyme systems, (2) the extent of induction/inhibition through coexposure, (3) allelic frequencies of major ethnic groups, (4) the absence of chemical-specific data on the kinetic parameters for the different allelic forms of key enzymes, (5) large numbers of low-frequency alleles, and (6) uncertainty regarding differences between in vitro and in vivo kinetic data. Our effort sets the stage for the acquisition of critical data and further integration of polymorphism data with PBPK modeling as a means to quantitate population variability.
Collapse
Affiliation(s)
- L T Haber
- Toxicology Excellence for Risk Assessment, 1757 Chase Avenue, Cincinnati, OH 45223, USA.
| | | | | | | | | |
Collapse
|
10
|
Haber LT, Maier A, Zhao Q, Dollarhide JS, Savage RE, Dourson ML. Applications of mechanistic data in risk assessment: the past, present, and future. Toxicol Sci 2001; 61:32-9. [PMID: 11294971 DOI: 10.1093/toxsci/61.1.32] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Mechanistic data, when available, have long been considered in risk assessment, such as in the development of the nitrate RfD based on effects in a sensitive group (infants). Recent advances in biology and risk assessment methods have led to a tremendous increase in the use of mechanistic data in risk assessment. Toxicokinetic data can improve extrapolation from animals to humans and characterization of human variability. This is done by the development of improved tissue dosimetry, by the use of uncertainty factors based on chemical-specific data, and in the development of physiologically based pharmacokinetic (PBPK) models. The development of the boron RfD illustrates the use of chemical-specific data in the improved choice of uncertainty factors. The draft cancer guidelines of the U.S. Environmental Protection Agency emphasize the use of mode of action data. The first choice under the guidelines is to use a chemical-specific, biologically based dose-response (BBDR) model. In the absence of a BBDR model, mode of action data are used to determine whether low-dose extrapolation is done using a linear or nonlinear (margin of exposure) approach. Considerations involved in evaluating a hypothesized mode of action are illustrated using 1,3-dichloropropene, and use of a BBDR model is illustrated using formaldehyde. Recent developments in molecular biology, including transgenic animals, microarrays, and the characterization of genetic polymorphisms, have significant potential for improving risk assessments, although further methods development is needed. Overall, use of mechanistic data has significant potential for reducing the uncertainty in assessments, while at the same time highlighting the areas of uncertainty.
Collapse
Affiliation(s)
- L T Haber
- Toxicology Excellence for Risk Assessment, 1757 Chase Avenue, Cincinnati, Ohio 45223, USA.
| | | | | | | | | | | |
Collapse
|
11
|
Haber LT, Erdreicht L, Diamond GL, Maier AM, Ratney R, Zhao Q, Dourson ML. Hazard identification and dose response of inhaled nickel-soluble salts. Regul Toxicol Pharmacol 2000; 31:210-30. [PMID: 10854127 DOI: 10.1006/rtph.2000.1377] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A substantial body of occupational epidemiology data has shown that exposure to mixed soluble and insoluble nickel causes the development of lung and nasal cancer. However, due to coexposure of these populations to soluble and insoluble forms of nickel, and limitations in exposure measurements, the contribution of soluble nickel is difficult to determine. Soluble nickel was negative in an NTP inhalation bioassay, while there was some evidence for tumorigenicity in rats for less soluble nickel oxide, and there was clear evidence for tumorigenicity of insoluble nickel subsulfide in rats. Results of parenteral assays follow a similar pattern, but provide evidence of weak carcinogenicity of soluble nickel. Kinetic factors also indicate that exposure to soluble nickel alone has a low carcinogenic potential. Overall, we conclude that the carcinogenic activity of insoluble nickel compounds should not be used to predict the carcinogenic potential of water-soluble nickel salts. The overall data suggest a nonlinear dose-response relationship for carcinogenicity, but the data are insufficient to determine the doses at which such nonlinearities occur. Under the U.S. EPA's 1996 proposed "Guidelines for Carcinogen Risk Assessment," inhaled soluble nickel compounds would be classified as "cannot be determined," because the existing evidence is composed of conflicting data. A reference concentration of 2 x 10(-4) mg Ni/cu x m was calculated, based on lung fibrosis in male rats observed in the NTP study.
Collapse
Affiliation(s)
- L T Haber
- Toxicology Excellence for Risk Assessment, Cincinnati, Ohio 45223, USA
| | | | | | | | | | | | | |
Collapse
|
12
|
Abstract
People can ingest soluble nickel compounds as a normal constituent of food or as a contaminant in drinking water. This paper presents an assessment of the noncancer and cancer human health risks from ingestion of soluble nickel compounds. A reference dose (RfD) of 8 x 10(-3) mg Ni/kg/day in addition to the amount in food was calculated, based on albuminuria in female rats exposed to nickel sulfate in drinking water for 6 months (A. Vyskocil et al., 1994, Hum. Exp. Toxicol. 13, 689-693). This RfD is comparable to the current RfD based on decreased body weight in a chronic feeding study in rats (A. M. Ambrose et al., 1976, J. Food Sci. Technol. 13, 181-187). The potential for nickel-induced reproductive toxicity was also taken into account in the derivation of the RfD. There are a number of negative animal bioassays with soluble nickel salts, but all of them have deficiencies that preclude a definitive conclusion. According to EPA's 1996 draft cancer guidelines, the carcinogenic potential of oral exposure to soluble nickel "cannot be determined because there are inadequate data to perform an assessment."
Collapse
Affiliation(s)
- L T Haber
- Toxicology Excellence for Risk Assessment, Cincinnati, Ohio 45223, USA
| | | | | | | | | |
Collapse
|
13
|
Haber LT, Allen BC, Kimmel CA. Non-cancer risk assessment for nickel compounds: issues associated with dose-response modeling of inhalation and oral exposures. Toxicol Sci 1998; 43:213-29. [PMID: 9710963 DOI: 10.1006/toxs.1998.2430] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This report presents the results of noncancer dose-response modeling for inhalation and oral exposures to nickel compounds using the NOAEL/LOAEL and benchmark dose (BMD) approaches. Several key issues associated with the implementation of the BMD approach were examined. Primary among them are difficulties associated with use of data for which the dose-response shape is poorly defined: nonuniqueness of maximum likelihood estimates and lower bounds equal to zero. In addition, several generalizable properties of the "hybrid approach" for modeling continuous endpoints were identified. A hybrid modeling approach allows one to consider "biological significance" on an individual (rather than group) basis; differences between individual- and group-based biological significance in the definition of benchmark response (BMR) levels are elucidated. In particular, it is shown that BMDs defined using group-based BMRs may be more like LOAELs than NOAELs. Application of cross-chemical and cross-endpoint comparisons suggest that, for chronic inhalation exposure, nickel sulfate appears to be as toxic or more toxic than nickel subsulfide and nickel oxide, although the high response rates for the latter two compounds at the lowest chronically administered concentration make such conclusions problematic. A nickel reference concentration could be derived based on the most sensitive benchmark concentration for chronic inhalation exposure to nickel sulfate, 1.7 x 10(-3) mg Ni/m3 for lung fibrosis in male rats. Analyses of oral studies of nickel sulfate and nickel chloride suggest that an appropriate basis for the nickel oral reference dose would be a BMD of 4-5 mg Ni/kg/day, based on increased prenatal mortality. (Uncertainty factors were not determined and neither an RfD nor an RfC was derived in this paper.) The BMD approach provides appropriate quantitative support for toxicological judgment; this paper addresses specific issues associated with the role of the BMD approach in noncancer risk assessment. Resolution of these and other issues may require the accumulation of a number of case studies such as the one presented here.
Collapse
Affiliation(s)
- L T Haber
- ICF Consulting Group, ICF Kaiser International, Fairfax, Virginia 22043, USA
| | | | | |
Collapse
|
14
|
Haber LT, Walker GC. Altering the conserved nucleotide binding motif in the Salmonella typhimurium MutS mismatch repair protein affects both its ATPase and mismatch binding activities. EMBO J 1991; 10:2707-15. [PMID: 1651234 PMCID: PMC452974 DOI: 10.1002/j.1460-2075.1991.tb07815.x] [Citation(s) in RCA: 116] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The Salmonella typhimurium and Escherichia coli MutS protein is one of several methyl-directed mismatch repair proteins that act together to correct replication errors. MutS is homologous to the Streptococcus pneumoniae HexA mismatch repair protein and to the Duc1 and Rep1 proteins of human and mouse. Homology between the deduced amino acid sequence of both MutS and HexA, and the type A nucleotide binding site consensus sequence, suggested that ATP binding and hydrolysis play a role in their mismatch repair functions. We found that MutS does indeed weakly hydrolyze ATP to ADP and Pi, with a Km of 6 microM and kcat of 0.26. To show that this activity is intrinsic to MutS, we made a site-directed mutation, which resulted in the invariant lysine of the nucleotide binding consensus sequence being changed to an alanine. The mutant MutS allele was unable to complement a mutS::Tn10 mutation in vivo, and was dominant over wild type when present in high copy number. The purified mutant protein had reduced ATPase activity, with the Km affected more severely than the kcat. Like the wild type MutS protein, the mutant protein is able to bind heteroduplex DNA specifically, but the mutant protein does so with a reduced affinity.
Collapse
Affiliation(s)
- L T Haber
- Biology Department, Massachusetts Institute of Technology, Cambridge 02139
| | | |
Collapse
|
15
|
Haber LT, Pang PP, Sobell DI, Mankovich JA, Walker GC. Nucleotide sequence of the Salmonella typhimurium mutS gene required for mismatch repair: homology of MutS and HexA of Streptococcus pneumoniae. J Bacteriol 1988; 170:197-202. [PMID: 3275609 PMCID: PMC210626 DOI: 10.1128/jb.170.1.197-202.1988] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The mutS gene product of Escherichia coli and Salmonella typhimurium is one of at least four proteins required for methyl-directed mismatch repair in these organisms. A functionally similar repair system in Streptococcus pneumoniae requires the hex genes. We have sequenced the S. typhimurium mutS gene, showing that it encodes a 96-kilodalton protein. Amino-terminal amino acid sequencing of purified S. typhimurium MutS protein confirmed the initial portion of the deduced amino acid sequence. The S. typhimurium MutS protein is homologous to the S. pneumoniae HexA protein, suggesting that they arose from a common ancestor before the gram-negative and gram-positive bacteria diverged. Overall, approximately 36% of the amino acids of the two proteins are identical when the sequences are optimally aligned, including regions of stronger homology which are of particular interest. One such region is close to the amino terminus. Another, located closer to the carboxy terminus, includes homology to a consensus sequence thought to be diagnostic of nucleotide-binding sites. A third one, adjacent to the second, is homologous to the consensus sequence for the helix-turn-helix motif found in many DNA-binding proteins. We found that the S. typhimurium MutS protein can substitute for the E. coli MutS protein in vitro as it can in vivo, but we have not yet been able to demonstrate a similar in vitro complementation by the S. pneumoniae HexA protein.
Collapse
Affiliation(s)
- L T Haber
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139
| | | | | | | | | |
Collapse
|