Igor Linkov

The use of spatial modeling in an aquatic food web to estimate exposure and risk.

This paper quantitatively evaluates interactions among foraging behavior, habitat preferences, site characteristics and the spatial distribution of contaminants in estimating PCB exposure concentrations for winter flounder at a hypothetical open water dredged material disposal site in the coastal waters of New York and New Jersey (NY-NJ). The models implemented in this study include a spatial submodel to account for spatial and temporal characteristics of fish exposure and a probabilistic adaptation of the Gobas bioaccumulation model to account for temporal variation in concentrations of polychlorinated biphenyls (PCBs) in sediment and water. We estimated the geographic distribution of an offshore winter flounder subpopulation based on species biology, including such variables as foraging area, habitat size, disposal site size and migration characteristics. We incorporated these variables together with an estimate of differential attraction to a management site within a spatially explicit model to assess the range of expected PCB exposures to a winter flounder population. The output of this modeling effort, flounder PCB tissue concentrations, provides exposure point concentrations for estimates of human health risk through ingestion of locally caught flounder. The risks obtained for the spatially non-explicit case are as much as one order of magnitude higher than those obtained after incorporating spatial and temporal characteristics of winter flounder foraging and seasonal migration. Incorporating spatial and temporal variables in food chain models can help support sediment management decisions by providing a quantitative expression of the confidence in risk estimates.

Spatially explicit exposure models: application to military sites

As a result of defense-related activities, large areas of valuable habitats can be physically disturbed and/or contaminated by hazardous pollutants. It is, however, important to understand that the military impact on such areas may not be wholly detrimental to the environment: their closure to the public can result in environmental conservation of large portions of habitat. Many former military ranges have been converted for civil usage; others are still actively operated for military purposes. In both cases, a major task for environmental policy- and decision-makers is to determine scientifically justified reuse and/or operation scenarios that would not result in deterioration of site habitats and that would in fact be favorable to further development of biodiversity within the areas’ existing ecosystems. Ecological risk assessment is suggested as the key process to use in facilitating the assessment of the ecological value of contaminated and/or disturbed military sites and in the development of a reuse decision protocol. We are currently developing and integrating a number of risk and habitat assessment techniques into such a protocol. This paper presents our approach to one aspect of this system: the incorporation of spatial information into ecological risk assessment. We present a software prototype that calculates radionuclide accumulation by deer foraging in areas having specified contamination patterns.

Correlations among tumor types in mouse cancer bioassays: liver adenomas, liver carcinomas, leukemias and lymphomas

In an examination of rodent bioassays Young and Gries [Young S.S., and Gries C.L. Exploration of the negative correlation between proliferative hepatocellular lesions and lymphoma in rats and mice—establishment and implications. Fundam. Appl. Toxicol. 1984: 4: 632-640] and Haseman et al. [Haseman J.K., et al. Body weight-tumor incidence correlations in long-term rodent carcinogenicity studies. Toxicol. Pathol. 1997: 25: 256-263] noticed that there is a negative correlation (anticorrelation) between development of liver tumors and leukemia or lymphomas. If an animal has a lymphoma or leukemia it is less likely to develop liver tumors. These studies noted that this applies to several strains of animals. The anticorrelation appeared in control animals. In this paper we study this anticorrelation in the quarter of a million rodents exposed in the Carcinogenesis Bioassay Database System (CBDS) database of the National Toxicology program in both control and dosed animals. We failed to completely replicate Young and Gries or Haseman et al. However, when benign liver tumors (adenomas or nodules) and malignant liver tumors (carcinomas) are considered separately AND different leukemia and lymphoma types are considered, a strong anticorrelation appears. We identify survival and the time period (in years) during which the bioassay was completed as an important factor in interpreting correlations and anticorrelations. Differences between liver adenomas and carcinomas and lymphoma types contribute to a more general question of grouping of the individual tumor types. In our classification scheme (originally developed about 1986 by Dr. Bailar) an effort is made to distinguish benign and malignant neoplasms, while other investigators group all tumors at a specific site. For many analyses liver adenomas and carcinomas have been lumped together. This is because it is suspected that the diagnoses by pathologists may not distinguish, or ignore the (benign) adenoma when a (malignant) carcinoma is present. Possible biological differences in tumor mechanisms may require separate evaluation of these tumors with all the dangers of “pathologist bias” that this introduces.

Liver adenomas and carcinomas: correlations and relationship to body weight in long-term rodent cancer bioassays

The most common cancers induced in laboratory rodents are liver cancers—both adenomas and carcinomas. There has been a long argument about the relative merits of combining them or considering them separately in the interpretation of long-term bioassays for chemical carcinogenesis. In this paper, we examine various aspects of the liver adenomas and liver carcinomas as seen in the Carcinogenesis Bioassay Data System (CBDS) and Toxicology Database Management System (TDMS) databases of the National Toxicology Program (NTP). It appears that the data themselves demonstrate interesting differences between the behavior of these tumors that probably have biological origin. Specifically, we find a strong negative correlation between the appearance of adenomas and carcinomas in the same animal in both control and chemically treated groups. This relationship does not seem to result from differential survival but may be influenced by the animals body weight. Our analysis is generally consistent with either a progression of tumors from adenoma to carcinoma or a pathologist bias (that when a carcinoma is discovered, other tumors are ignored) as possible explanations for the negative correlation. However there are some differences between male and female mice that are puzzling. While we recognize the scientific and policy reasons for combination of adenomas and carcinomas for calculations of carcinogenic potency and risk we hope that toxicologists and pathologists will be encouraged to preserve the pathological distinctiveness of the two tumor types when analyzing rodent bioassays.

Pilot Elicitation of Expert Judgments on Model Parameters and Research Needs in Forest Radioecology

The high degree of uncertainty in modeling structure and input parameters used to describe radionuclide fate and transport in forest ecosystems has posed difficulties in accurately modeling radionuclide transport. Many dynamic parameters are required for modeling (such as radionuclide residence half-times in forest compartments) and these parameters are typically difficult to measure (e.g., half-lives vary over a wide range: from days to thousands of years). The NATO workshop brought together more than 70 experts in forest radioecology and ecosystem modeling encompassing a wide range of disciplines and backgrounds. It provided a unique opportunity to quantify the state of knowledge on processes and parameters used in forest ecosystem modeling.

Decision Evaluation for Complex Risk Networked Systems Development Progress

Environmental management requires decision support tools that are able to integrate heterogeneous technical information with decision maker values and judgment. Decision Evaluation in Complex Risk Networked Systems (DECERNS) is a software system under development that has the objective of providing a methodology, computer models, and software tools to facilitate decision making in the field of sustainable land use and related areas. DECERNS will integrate risk assessment and decision analysis tools from multiple disciplines (e.g., geographical information systems tools for mapping and data analysis, ecological and human health risk models, economic analysis tools for evaluating costs, and tools for incorporating social choices) into a single, user-friendly software package. This paper provides an overview of the approach used in DECERNS followed by a brief overview of multi-criteria decision analysis methods and tools used in the project. Future plans for development and testing of the software tool will be discussed.