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of the chemicals were also tested when available. When purity of test chemicals was known, all calculated concentrations were based on percent active ingre- dients. Stock solutions were prepared immediately before each test, with commercial grade acetone as the carrier solvent. Occasionally, ethanol or dimethyl- formamide was substituted. Solvent concentrations did not exceed 0.5 mL/L in final dilution water. Test water (dilution water) was reconstituted from deionized water of at least 108 ohms resistivity by the addition of appropriate reagent grade chemicals (Marking 1969). Water was buffered to maintain a pH of 7.2 to 7.5, an alkalinity of 30 to 35 mg/L, and a hard- ness of 40 to 50 mg/L as CaCO.. Test water was mixed thoroughly and aerated before transfer into test chambers. Fish were acclimated to dilution water by gradually changing the water in acclimation tanks from 100% well water to 100% reconstituted water over a 1- to 3-day period at the desired testing tem- perature. Invertebrates were acclimated from well water to dilution water over a 4- to 6-h period. Toxicity tests were conducted under static conditions without aeration, and the organisms were not fed during accli- mation or testing. Temperature of test solutions was maintained within ± 1 °C of that required for a given test. Toxicity tests with fish were conducted in 18.9-liter (5-gal) wide-mouthed jars containing 15 liters of test solution. Fingerling fish weighing 0.2 to 1.5 g were tested at each concentration. Caution was taken not to exceed 0.8 g of test organisms per liter of solution. Duplicate test chambers were used to accommodate larger fish. Test chambers varied in size for inver- tebrates, depending on the species used; volume of test solution ranged from 0.25 to 4 liters. At least 10 organ- isms were exposed to each concentration for all defini- tive tests. At least six concentrations were used per toxicity test. The tests began upon initial exposure to the toxicant and continued for 96 h. Immobilization tests with invertebrates were conducted for only 48 h. The number of dead or affected organisms in each test chamber was recorded and the dead organisms were removed every g4 h; general observations on the condi- tion of test organisms were also recorded at these times. Toxicity data were analyzed by a statistical method described by Litchfield and Wilcoxon (1949) to deter- mine LC50 (theoretical estimate of the concentration lethal to 50% of the test animals) and 95% confidence intervals. This method is recommended by the Amer- ican Public Health Association (1971) and by Sprague (1969) for determining median lethal concentrations. The procedure is easily modified for computing a single LC50 when replicate tests are performed. Arrangement of Data In the section on toxicological data, acute tox- icity data are summarized separately for each of the 197 chemicals arranged alphabetically by common name in Table 3. Results of tests with an additional group of 74 chemicals, for which only limited data were available, are summarized in Table 4 (p. 81). The EC50 and LC50 values and their 95% confidence intervals are expressed as either mg/L (ppm) or µg/L (ppb). The standard 96-h LC50 is presented for fish and most invertebrates; 48-h EC50 values are given for daphnids and midges. Exceptions to this form of data presentation fall into one of three categories: (1) when confidence intervals could not be calculated, only the LC50 is reported; (2) when the LC50 could not be calcu- lated because of heterogeneity of the data, range values are presented, usually at 0.5 to 1.0 logarithmic interval; (3) when the LC50 was not calculated but was outside the limits of the test concentrations the values are expressed as "greater than" (>) or "less than" (<). For many of the chemicals tested, a NOTE section following the summary of acute toxicity highlights additional toxicity data, when available. Results are given for acute toxicity tests in which different pH's, temperatures, or hardnesses, or aged test solutions (chemical deactivation) were used. Also, variations in sensitivity due to size or developmental life stage of the test organisms are included. Time-independent LC50 (TILC50) values-mathematically derived toxi- cant concentrations at which 50% of the test animals would be expected to survive indefinitely-are sum- marized for some chemicals. Organisms are exposed to toxicants under flow-through conditions for up to 30 days, and the TILC50's are calculated by the method of Green (1965), as modified by the additional require- ments recommended by Johnson and Julin (1980). The cumulative action of a test chemical can be estimated by computing the ratio of the 96-h LC50 to the TILC50. This ratio or the "cumulative toxicity index" serves as an estimate of the cumulative action of a toxicant (Hayes 1967; Tucker and Crabtree 1970). Chemicals with an index of less than 11 are not consid- ered highly cumulative. We have also added sum- maries of the results from chronic toxicity studies con- cerning effects on survival, growth, reproduction, residue dynamics, physiology and biochemistry, or histopathology. A glossary of terms is given in Appendix I, a cross- index of chemical equivalent names in Appendix II, and a list of publications originating from the Colum- bia Laboratory that contain toxicity data on any chemicals covered in this Handbook, in Appendix III.