The effects of various water chemistry parameters on the toxicity of copper to larval fathead minnows were investigated. Increased pH, hardness, sodium, dissolved organic matter, and suspended solids each caused toxicity to decrease on the basis of total copper concentrations. In contrast, added potassium resulted in increased toxicity. Alkalinity had no observed effect on total copper LC50s, but its effects might have been masked by those of the cations added with it. In most cases, the effects of water chemistry were found to be similar for different endpoints (growth, survival at different durations), but there were differences in the relative magnitude of some effects across these endpoints. Over all experimental treatments, 96-h total copper LC50s varied 60-fold. Every water chemistry parameter also caused toxicity to vary significantly when expressed on the basis of cupric ion selective electrode measurements, sometimes more so than on the basis of total copper. Therefore, this study does not support attributing to cupric ion a singular importance in regulating toxicity to this test organism. A variety of copper species might be contributing to toxicity and it is evident that toxicity is also affected by water chemistry in ways not related to copper speciation.

Abstract-The effects of various water chemistry parameters on the toxicity of copper to larval fathead minnows were investigated. Increased pH, hardness, sodium, dissolved organic matter, and suspended solids each caused toxicity to decrease on the basis of total copper concentrations. In contrast, added potassium resulted in increased toxicity. Alkalinity had no observed effect on total copper LC50s, but its effects might have been masked by those of the cations added with it. In most cases, the effects of water chemistry were found to be similar for different endpoints (growth, survival at different durations), but there were differences in the relative magnitude of some effects across these endpoints. Over all experimental treatments, 96-h total copper LC50s varied 60-fold. Every water chemistry parameter also caused toxicity to vary significantly when expressed on the basis of cupric ion selective electrode measurements, sometimes more so than on the basis of total copper. Therefore, this study does not support attributing to cupric ion a singular importance in regulating toxicity to this test organism. A variety of copper species might be contributing to toxicity and it is evident that toxicity is also affected by water chemistry in ways not related to copper speciation.

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Juvenile amphipods (Gammarus pseudolimnaeus and Crangonyx pseudogracilis) and fathead minnows (Pimephales promelas) were exposed to pentachlorophenol (PCP) at pH values of 6.5, 7.5, 8.0 and 8.5 for 96 h, and early life stages of fathead minnows were exposed for 32 d at the same pH values to determine the relationship between test pH and the acute and chronic toxicity of PCP. Residue analyses were performed on fathead minnows after 32 d to determine the relationship between test pH and PCP bioaccumulation. Technical‐grade PCP (88% active ingredient; Dowicide EC7) was used as the toxicant source. Acute exposures with all three species showed that PCP toxicity was decreased with increased test pH. The slopes of this relationship were similar for the amphipods, but were different from that observed for fathead minnows. Early life stage exposures of fathead minnows showed that chronic PCP toxicity and bioaccumulation were similarly decreased when pH values were increased. The decrease in chronic PCP toxicity appeared to be due to the reduction in PCP accumulation as a direct result of the increased ionization of PCP at higher pH values, indicating that the ionized form was less toxic per unit concentration than was the un‐ionized form. However, these studies suggest that chronic as well as acute toxicity may be caused by both forms of PCP when significant concentrations are present in solution.

Comparative acute toxicity values for Ceriodaphnia dubia, Scapholeberis sp. and Pimephalespromelas exposed to copper were used to calculate water effect ratios (e.g., site water LC50 valueheference water LC50 value), which reflect the difference in the biological availability and/or toxicity of copper between water from the Naugatuck River, Connecticut and Lake Superior reference water. These ratios were used to modify U.S. Environmental Protection Agency (EPA) ambient aquatic life criteria for copper to site-and station-specific criteria, using the indicator procedure of the U.S. EPA guidelines for deriving site-specific water quality criteria. A water effect ratio of 1 . O was established using unpolluted upstream water, resulting in a site-specific criterion maximum concentration (CMC) and criterion continuous concentration (CCC) of 8.7 and 6.2 pg/L copper, respectively. Mean water effect ratios of 3.9 to 7.0, reflective of reduced biological availability and/or toxicity of copper, were determined for four successive downstream stations where the water contained copper and other industrial and domestic wastes. The resulting station-specific CMCs and CCCs ranged from 32 to 57 and 22 to 39 pg/L copper, respectively. These copper criteria were compared with effluent-contributed ambient copper concentrations and ecological survey data from each downstream station to ascertain impact on aquatic life. It was concluded that the national and site-specific criteria derived for copper would be protective of the river's aquatic life because a relatively healthy aquatic community existed where these criteria were exceeded slightly. Whether or not the station-specific criteria were protective could not be determined because these criteria were not exceeded at stations with healthy communities; however, where they were exceeded, impaired aquatic communities were evident.Generally, C. dubia survival and young production data from receiving water tests and copper addition tests, conducted just prior to the acute toxicity tests, were also indicative of reduced copper biological availability and/or toxicity in the Naugatuck River at downstream stations.