Current methodologies for testing and interpretation are provided for aquatic toxicology and design of model aquatic ecosystems, wildlife toxicology, sediment toxicity, soil ecotoxicology, algal and plant toxicity, and the concept of landscape. Identification of biomonitoring programs and current use of biomarkers and bioindicators in aquatic and terrestrial monitoring are also important chapters in this section.
Chapter 2, by Adams and Rowland, provides a comprehensive overview of aquatic toxicology with an emphasis on test methods to meet the requirements of various regulatory guidelines. The chapter describes recent efforts to develop protocols and identify species that permit full-life cycle studies to be performed over shorter durations (e.g., 7-day Ceriodaphnia dubia life cycle tests, two-dimensional rotifer tests) and to establish protocols that use sensitive species and life stages that generate accurate estimates of chronic no-effect levels. There has been an increasing need to assess the toxicity of various types of suspect samples in minutes to hours instead of days. The use of rapid assays during on-site effluent biomonitoring allows for the collection of extensive data sets. The expanded use of biomarkers in natural environments, where organisms are exposed to multiple stressors (natural and anthropogenic) over time, will allow better detection of stress and provide an early indication of the potential for population-level effects. Model aquatic ecosystems, known as microcosms and mesocosms, were designed to simulate ecosystems or portions of ecosystems in order to study and evaluate the fate and effects of contaminants. Microcosms are defined by Giesy and Odum11 as artificially bounded subsets of naturally occurring environments that are replicable, contain several trophic levels, and exhibit system-level properties. Mesocosms are defined as larger, physically enclosed portions of natural ecosystems or man-made structures, such as ponds or stream channels, that may be self-sustaining for long durations. Chapter 3 by Kennedy et al. focuses on key factors in the experimental design of microcosm and mesocosm studies to increase their realism, reduce variability, and assess their ability to detect changes. The success in using such systems depends on the establishment of appropriate temporal and spatial scales of sampling. Emphasis is placed on the need to measure exposure as a function of life history using parameters of size, generation time, habitat, and food requirements. This chapter also addresses the utility of employing a suite of laboratory-to-field experiments and verification monitoring to more fully understand the consequences of single and multiple pollutants entering aquatic ecosystems.
With the advent of modern insecticides and the consequent wildlife losses, screening of pesticides for adverse effects has become an integral part of wildlife toxicology. Avian testing protocols developed by the U.S. Fish and Wildlife Service and other entities include protocols required for regulatory and other purposes. These are described with respect to acute, subacute, subchronic, chronic, developmental, field, and behavioral aspects of avian wildlife toxicity (Hoffman, Chapter 4). Several unique developmental toxicity tests assess the potential hazard of topical contaminant exposure to bird eggs and the sensitivity of "neonatal" nestlings to contaminants, including chemicals used for the control of aquatic weeds, mosquitoes, and wild fires. Coverage of toxicity testing for wild mammals, amphibians, and reptiles is provided as well, although in somewhat less detail since development of such tests has been more limited in scope and requirement.
Sediments serve as both a sink and a source of organic and inorganic materials in aquatic ecosystems, where cycling processes for organic matter and the critical elements occur. Since many potentially toxic chemicals of anthropogenic origin tend to sorb to sediments and organic materials, they become highly concentrated. Sediment toxicity testing (Burton et al., Chapter 5) is an expanding but still relatively new field in ecological assessments. The U.S. Environmental Protection Agency has initiated new efforts in managing contaminated sediments and method standardization that will result in an even greater degree of sediment toxicity testing, regulation, and research in the near future. A number of useful assays have been evaluated in freshwater and marine studies in which the importance of testing multiple species becomes apparent in order to protect the ecosystem. The assay methods described are sensitive to a wide variety of contaminants, discriminate differing levels of contamination, use relevant species, address critical levels of biological organization, and have been used successfully in sediment studies.
The importance of soil ingestion in estimating exposure to environmental contaminants has been best documented in assessments of pesticides or wastes applied to land supporting farm animals. Soil ingestion tends to be most important for those environmental contaminants that are found at relatively high concentrations compared to concentrations in a soil-free diet. Chapter 6, by Beyer and Fries, is designed to relate the toxicological significance of soil ingestion by wild and domestic animals. Concepts covered include methods for determining soil intake, intentional geophagy in animals, soil ingestion by both domestic animals and wildlife, toxicity of environmental contaminants in soil or sediment to animals, relation of particle size of ingested soil to exposure to contaminants, bioavailability of organic and inorganic contaminants in soil, and applications to risk assessments.
Chapter 7, by Linder, Henderson, and Ingham, focuses on applications of ecological risk assessment (ERA) of contaminated soils on wildlife and habitat restoration, since at present there is little or no federal, state, or other guidance to derive soil cleanup values or ecological-based remedial goal options. Three components of this chapter include ERA tools used to characterize a lower bound, the role of bioavailability in critically evaluating these lower bound preliminary remedial goals, and remediation measures intended to address field conditions and modify soil in order to decrease a chemical's immediate bioavailability, while increasing the likelihood of recovery to habitats suitable for future use by fish and wildlife.
Evaluation of the phytotoxicity of a chemical is an essential component of the ecological risk assessment, since primary producers form an essential trophic level of any ecosystem. Since most chemicals introduced into the environment ultimately find their way into aquatic ecosystems, aquatic algal and plant toxicity evaluations are particularly critical. Klaine, Lewis, and Knuteson (Chapter 8) discuss the current state of phytotoxicity testing with particular attention to algal and vascular (both aquatic and terrestrial) plant bioassays. The algal bioassay section not only focuses on test methods developed over the relatively long history of algal toxicity testing, but also includes many adaptations to traditional laboratory methods to provide more realistic phytotoxicity estimates. The vascular plant section focuses on different species used for bioassays and the various endpoints used. Bioassay systems described include soil, hydroponics, foliar, petri dish, and tissue culture.
In recent years ecologists have established a need for studying natural processes not only at the individual, community, or ecosystem level, but over the entire landscape,12-14 since quite often ecological studies may be too small both spatially and temporally to detect certain important natural processes and the movement of pollutants across multiple ecosystems. Holl and Cairns (Chapter 9) discuss the concept of landscape ecology with a focus on (a) landscape structure, that is, spatial arrangement of ecosystems within landscapes; (b) landscape function, or the interaction among these ecosystems through flow of energy, materials, and organisms; and (c) alterations of this structure and function. Different types of landscape indicators in ecotoxicology are presented.
Biomonitoring data form the basis upon which most long-term stewardship decisions are made. These data often provide the critical linkage between field personnel and decision-makers. Data from biomonitoring programs have been very useful in identifying local, regional, and national ecotoxi-cological problems. Natural resource management decisions are being made that annually cost millions of dollars. These decisions should be supported by scientifically sound data. Chapter 10, by Breckenridge et al., discusses why monitoring programs are needed and how to design a program that is based on sound scientific principles and objectives. This chapter identifies many of the large-scale monitoring programs in the United States, how to access the information from the programs, and how this information can be used to improve long-term management of natural resources. Bioindicators are an important part of biomonitoring and reflect the bioavailability of contaminants, provide a rapid and inexpensive means for toxicity assessment, may serve as markers of specific classes of chemicals, and serve as an early warning of population and community stress. Melancon (Chapter 11) defines bioindicators as biomarkers (biochemical, physiological, or morphological responses) used to study the status of one or more species typical of a particular ecosystem. Systematically, the responses can range from minor biochemical or physiological homeostatic responses in individual organisms to major toxicity responses in an individual, a species, a community, or an ecosystem. Many currently used bioindicators of contaminant exposure/effect for environmental monitoring are discussed. Some of these bioindicators (e.g., inhibition of cholinesterase by pesticides, induction of hepatic microsomal cytochromes P450 by PAHs and polychlorinated biphenyls (PCBs), reproductive problems such as terata and eggshell thinning, aberrations of hemoglobin synthesis including the effects of lead on ALAD, and porphyria caused by chlorinated hydrocarbons) have been extensively field-validated. Other potentially valuable bioindicators undergoing further validation are discussed and include bile metabolite analysis, oxidative damage and immune competence, metallothioneins, stress proteins, gene arrays, and proteomics.
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