The median tolerance limits (TLm) of Diquat (1:1‐ethylene‐2:2′ dipyridylium dibromide) and Dichlobenil (2,6‐dichlorobenzonitrile) to one amphipod and larvae of five species of aquatic insects were determined. Diquat was over 300 times more toxic to the amphipod (Hyalella azeteca) than to the mayfly (Callibaetis sp.) while the caddisfly (Limnephilus sp.), tendipedid (Tendipedidae), damselfly (Enallagma sp.), and dragonfly (Libellula sp.) in that order, were more resistant. The addition of pond mud to the test vessels changed the 96‐hour TLm of Diquat for the amphipod from 0.046 to 6.8 mg/liter. Dichlobenil was less toxic than Diquat to the amphipod but more toxic to the aquatic insects. Dichlobenil had a narcotizing effect that was recorded as an immobilization concentration (IC50). The addition of pond mud did not reduce the toxicity of Dichlobenil to the caddisfly. The 4% granular formulation of Dichlobenil had a 72‐hour “lag” before an effective concentration was obtained equivalent to the toxic effect of the 50% wettable powder. Dichlobenil formed a strong layer at the bottom of the test vessel and was more toxic with time to the invertebrates than to the fishes Micropterus salmoides and Lepomis macrochirus.

Ages, lengths, and weights were determined for 124 female shiner perch, Cymatogaster aggregata Gibbons, collected in Yaquina Bay, Oregon, from May 17 through June 29, 1968. Embryos (1005) were obtained from 111 gravid females either by dissection (737) or at parturition in the laboratory (268). Embryo lengths, weights, and numbers per female parent were determined.As females increased in age from 1 to 6 years, their mean fork length increased from 9.32 to 13.65 cm, their weight from 13.65 to 47.78 g, and the mean number of embryos per parent female increased from 5.83 to 20.00. The equations and their correlation coefficients (R) computed for the relationships of embryo number (Y) to parent female fork length, weight, and age are, respectively: log Y = −1.892 + 2.735 log X (R = 0.89); Y = 1.131 + 0.313 X (R = 0.70); and Y = 4.23 + 1.73 X (R = 0.51). Embryo size at birth was also directly related to female parent size. The equations computed for the relationships of total length of embryo at birth (Y) to parent female fork length and parent female weight are, respectively: Y = 24.211 + 1.620 X (R = 0.79); and Y = 0.384 + 0.015 X (R = 0.72). The equation computed for the relationship of embryo weight (Y) to embryo length at birth is Y = −2.266 + 0.712 X (R = 0.95).

Acid-mine discharges from the Spring Creek drainage contribute large quantities of toxic copper, zinc, and cadmium to anadromous chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Salmo gairdneri) fisheries below Keswick Dam after regulated release with the Sacramento River, California. Release criteria and water quality objectives for the protection of salmonids from the metals in the waste have been developed using laboratory toxicity tests and field monitoring studies. These metal criteria and objectives were evaluated by on-site toxicity tests and additional monitoring studies. Chinook salmon and steelhead trout fry were exposed to Spring Creek acid-mine waste in on-site toxicity tests. Acutely lethal concentrations of copper, zinc, and cadmium from the waste were similar to those from laboratory tests on metal sulfate mixtures, indicating that these metals are the major toxic components of the waste. Monitoring the waste in the Sacramento River after controlled dilution using criteria for copper and zinc indicated the following: (1) mean concentrations of the metals approached or exceeded incipient lethal levels (96-h LC10 values); (2) short-term (<5 out of 24 h) peak concentrations of copper, zinc, and cadmium in the Sacramento River exceeded median lethal levels (96-h LC50 values) under normal operating conditions; and (3) no measurable loss of copper from adsorption onto particulate matter and subsequent precipitation and deposition occurred when the waste was diluted to levels tolerable to fish. New criteria for zinc and new release schedules for the copper criteria that will protect against acutely lethal levels should be developed.

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