Aquatic toxicology grew primarily out of two disciplines: water pollution biology and limnology. The development of these disciplines spanned about 130 years in Europe and the United States. Early studies included basic research to define and identify the biology and morphology of lakes, streams, and rivers. These studies included investigations on how plants, animals, and microorganisms interact to biologically treat sewage and thus reduce organic pollution. For example, the role of bacteria in the nitrification process was demonstrated in 1877 by Schoesing and Muntz. Stephen Forbes is generally credited as one of the earliest researchers of integrated biological communities (Forbes, 1887).1 Kolwitz and Marsson2,3 and Forbes and Richardson4 published approaches for classifying rivers into zones of pollution based on species tolerance and their presence or absence. It has become an accepted belief that the presence or absence of species (especially populations or communities) living in a given aquatic ecosystem provides a more sensitive and reliable indicator of the suitability of environmental conditions than do chemical and physical measurements. Thus, a great deal of effort has been expended over many years in the search for organisms that are sensitive to environmental factors and changes in these parameters. This effort has been paralleled by similar attempts to culture and test sensitive organisms in laboratory settings. The underlying belief has been that organisms tested under controlled laboratory conditions provide a means to evaluate observed effects in natural ecosystems and to predict possible future effects from humanmade and natural perturbations. The science of aquatic toxicology evolved out of these studies and has concentrated on studying the effects of toxic agents (chemicals, temperature, dissolved oxygen, pH, salinity, etc.) on aquatic life.
The historical development of aquatic toxicology up to 1970 has been summarized by Warren.5 Most early toxicity tests consisted of short-term exposure of chemicals or effluents to a limited number of species. Tests ranged from a few minutes to several hours and occasionally 2 to 4 days. There were no standardized procedures. Some of the earliest acute toxicity tests were performed by Penny and Adams (1863)6 and Weigelt, Saare, and Schwab (1885),7 who were concerned with toxic chemicals in industrial wastewaters. In 1924 Kathleen Carpenter published the first of her notable papers on the toxicity to fish of heavy metal ions from lead and zinc mines.8 This was expanded by the work of Jones (1939)9 and has been followed by thousands of publications over the years on the toxicity of various metals to a wide variety of organisms.
Much of the work conducted in the 1930s and 1940s was done to provide insight into the interpretation of chemical tests as a first step into the incorporation of biological effects testing into the wastewater treatment process or to expand the basic information available on species tolerances, metabolism, and energetics. In 1947 F.E.J. Fry published a classical paper entitled Effects of the Environment on Animal Activity.10 This study investigated the metabolic rate of fish as an integrated response of the whole organism and conceptualized how temperature and oxygen interact to control metabolic rate and hence the scope for activity and growth. Ellis (1937)11 conducted some of the earliest studies with Daphnia magna as a species for evaluating stream pollution. Anderson (1944, 1946)12,13 expanded this work and laid the groundwork for standardizing procedures for toxicity testing with Daphnia magna. Biologists became increasingly aware during this time that chemical analyses could not measure toxicity but only predict it. Hart, Doudoroff, and Greenbank (1945)14 and Doudoroff (1951)15 advocated using toxicity tests with fish to evaluate effluent toxicity and supported the development of standardized methods. Using aquatic organisms as reagents to assay effluents led to their description as aquatic bioassays. Doudoroff's 1951 publication15 led to the first standard procedures, which were eventually included in Standard Methods for the Examination of Water and Wastewater. 16 Efforts to standardize aquatic tests were renewed, and the Environmental
Protection Agency (EPA) sponsored a workshop that resulted in a document entitled Standard Methods for Acute Toxicity Test for Fish and Invertebrates.11 This important publication has been the primer for subsequent aquatic standards development and has been used worldwide.
The concept of water quality criteria (WQC) was formulated shortly after World War II. McKee (1952)18 published a report entitled Water Quality Criteria that provided guidance on chemical concentrations not to be exceeded for the protection of aquatic life for the State of California. A second well-known edition by McKee and Wolf (1963)19 expanded the list of chemicals and the toxicity database. WQC are defined as the scientific data used to judge what limits of variation or alteration of water will not have an adverse effect on the use of water by man or aquatic organisms.1 An aquatic water quality criterion is usually referred to as a chemical concentration in water derived from a set of toxicity data (criteria) that should not be exceeded (often for a specified period of time) to protect aquatic life. Water quality standards are enforceable limits (concentration in water) not to be exceeded that are adopted by states and approved by the U. S. federal government. Water quality standards consist of WQC in conjunction with plans for their implementation.
In 1916 the EPA published formal guidelines for establishing WQC for aquatic life that were subsequently revised in 1985.20 Prior to this time WQC were derived by assessing available acute and chronic aquatic toxicity data and selecting levels deemed to protect aquatic life based on the best available data and on good scientific judgment. These national WQC were published at various intervals in books termed the Green Book (1912),21 the Blue Book (1916),22 the Red Book (1911),23 and the Gold Book (1986).24 In some cases WQC were derived without chronic or partial life-cycle test data. Acute toxicity test results (LC50 — lethal concentration to 50% of the test organisms) were used to predict chronic no-effect levels by means of an application factor (AF). The acute value was typically divided by 10 to provide a margin of safety, and the resulting chronic estimate was used as the water quality criterion. It was not until the mid-1960s that chronic test methods were developed and the first full life-cycle chronic toxicity test (with fathead minnows) was performed.25
The AF concept emerged in the 1950s as an approach for estimating chronic toxicity from acute data.26 Stephan and Mount (1961)21 formalized this AF approach, which was revised by Stephan (1981)28 and termed the acute-to-chronic ratio (ACR). This approach provides a method for calculating a chronic-effects threshold for a given species when the LC50 for that species is known and the average acute-to-chronic ratio for two or more similar species is also available. Dividing the LC50 by the ACR provides an estimate of the chronic threshold for the additional species. The approach has generally been calculated as the LC50 GMCV, where GMCV = the geometric mean of the no-observed effect concentration (NOEC) and the lowest observed effect level (LOEC), termed the chronic value (CV). Before the ACR method was published, the AF concept was not used consistently. Arbitrary or "best judgment" values were often used as AFs to estimate chronic thresholds (CVs). Values in the range of 10 to 100 were most often used, but there was no consistent approach. The chronic value has also been alternatively referred to as the geometric mean maximum acceptable toxicant threshold (GM-MATC).
The passage of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA, 1912), the Toxic Substances Control Act (TSCA, 1916), and the Comprehensive Environmental Compensation Liabilities Act (CERCLA, 1980) as well as the incorporation of toxicity testing (termed biomonitoring) as part of the National Pollution Discharge Elimination System (NPDES, 1989)29 have increased the need for aquatic toxicological information. Standard methods now exist for numerous freshwater and marine species, including fishes, invertebrates, and algae, that occupy water and sediment environments.
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