The effects of various chemical manipulations of test water on acute toxicity of silver to fathead minnows (Pimephales promelas) were investigated. Increases in hardness and organic carbon substantially reduced toxicity. Toxicity was also inversely related to pH and alkalinity when these parameters were jointly changed by addition of strong acid or base. The addition of 2 meq/L sodium sulfate had no significant effects, but the addition of 0.2 meq/L sodium chloride increased toxicity, perhaps related to the formation of the dissolved AgCl0 complex. We also evaluated the effects of static versus flow‐through test conditions, feeding during exposure, and aging of test solutions before exposure on the acute toxicity of silver to fathead minnows and Daphnia magna. Static conditions and feeding reduced toxicity, likely as a result of accretion of organic carbon. Aging of test solutions had little effect. For both juvenile fathead minnows and D. magna, silver was much less toxic in water from the St. Louis River than in our normal laboratory water, presumably because of the much higher organic carbon content of the river water. This study identified some aspects of test conditions that are important in assessing the risk of silver to aquatic biota, but improved assessments will require information for more conditions, species, and endpoints. More importantly, if toxicity test results are to be extrapolated among waters with different chemistries, adequate characterization of the chemical speciation of silver and a better understanding of the mechanisms of silver toxicity and its relationship to silver speciation and other chemical factors are needed.

Acid-volatile sulfide (AVS) has been proposed as the primary normalization phase for the development of sediment quality criteria for certain cationic metals. This study was designed to assist in this development by providing necessary field data on the relationships among season, AVS concentrations, and zinc bioavailability and toxicity in freshwater sediments. Zinc was spiked into uncontaminated sediments collected from a local pond, creating five simultaneously extracted metal (SEM) concentrations ranging from 0.8 to 12.0 mol/g dry weight. The spiked sediments were transferred to 4-L plastic trays, returned to the bottom of the pond, and sampled on five dates during 1993-1994. Results revealed a pronounced increase in AVS concentration with increasing zinc concentration. Acid-volatile sulfide concentrations in zinc-spiked sediments displayed only minor seasonal variation but were lowest in surficial (0-2 cm) sediments. Acid-volatile sulfide concentrations always exceeded SEM concentrations at Յ6.0 mol SEM/g; only at 12.0 mol SEM/g did SEM/AVS ratios exceed 1.0. Zinc was rarely detected in pore water at any treatment and never at concentrations which should have posed a hazard to benthic macroinvertebrates. No substantial effect on colonization of zinc-spiked sediments by benthic macroinvertebrates was observed. Only oligochaetes (Naididae) were significantly reduced in abundance at the high zinc treatment, although reductions were occasionally evident for other taxa. Lack of noteworthy pore-water zinc concentrations and lack of associated, ecologically meaningful effects were attributed to the increase in AVS levels observed with increasing SEM zinc sediment concentration. The increases in AVS theoretically resulted from a replacement of natural iron and manganese sulfides with the more stable zinc sulfide complex.

Abstract-The effects of various chemical manipulations of test water on acute toxicity of silver to fathead minnows (Pimephales promelas) were investigated. Increases in hardness and organic carbon substantially reduced toxicity. Toxicity was also inversely related to pH and alkalinity when these parameters were jointly changed by addition of strong acid or base. The addition of 2 meq/L sodium sulfate had no significant effects, but the addition of 0.2 meq/L sodium chloride increased toxicity, perhaps related to the formation of the dissolved AgCl 0 complex. We also evaluated the effects of static versus flow-through test conditions, feeding during exposure, and aging of test solutions before exposure on the acute toxicity of silver to fathead minnows and Daphnia magna. Static conditions and feeding reduced toxicity, likely as a result of accretion of organic carbon. Aging of test solutions had little effect. For both juvenile fathead minnows and D. magna, silver was much less toxic in water from the St. Louis River than in our normal laboratory water, presumably because of the much higher organic carbon content of the river water. This study identified some aspects of test conditions that are important in assessing the risk of silver to aquatic biota, but improved assessments will require information for more conditions, species, and endpoints. More importantly, if toxicity test results are to be extrapolated among waters with different chemistries, adequate characterization of the chemical speciation of silver and a better understanding of the mechanisms of silver toxicity and its relationship to silver speciation and other chemical factors are needed.

Abstract-Acid-volatile sulfide (AVS) has been proposed as the primary normalization phase for the development of sediment quality criteria for certain cationic metals. This study was designed to assist in this development by providing necessary field data on the relationships among season, AVS concentrations, and zinc bioavailability and toxicity in freshwater sediments. Zinc was spiked into uncontaminated sediments collected from a local pond, creating five simultaneously extracted metal (SEM) concentrations ranging from 0.8 to 12.0 mol/g dry weight. The spiked sediments were transferred to 4-L plastic trays, returned to the bottom of the pond, and sampled on five dates during 1993-1994. Results revealed a pronounced increase in AVS concentration with increasing zinc concentration. Acid-volatile sulfide concentrations in zinc-spiked sediments displayed only minor seasonal variation but were lowest in surficial (0-2 cm) sediments. Acid-volatile sulfide concentrations always exceeded SEM concentrations at Յ6.0 mol SEM/g; only at 12.0 mol SEM/g did SEM/AVS ratios exceed 1.0. Zinc was rarely detected in pore water at any treatment and never at concentrations which should have posed a hazard to benthic macroinvertebrates. No substantial effect on colonization of zinc-spiked sediments by benthic macroinvertebrates was observed. Only oligochaetes (Naididae) were significantly reduced in abundance at the high zinc treatment, although reductions were occasionally evident for other taxa. Lack of noteworthy pore-water zinc concentrations and lack of associated, ecologically meaningful effects were attributed to the increase in AVS levels observed with increasing SEM zinc sediment concentration. The increases in AVS theoretically resulted from a replacement of natural iron and manganese sulfides with the more stable zinc sulfide complex.

Tests were performed with the freshwater invertebrates Hyalella azteca, Chironomus tentans, and Lumbriculus variegatus to determine the acute toxicity of six phthalate esters, including dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBP), di-n-hexyl phthalate (DHP), and di-2-ethylhexyl phthalate (DEHP). It was possible to derive 10-d LC50 (lethal concentration for 50% of the population) values only for the four lower molecular weight esters (DMP, DEP, DBP, and BBP), for which toxicity increased with increasing octanol-water partition coefficient (Kow) and decreasing water solubility. The LC50 values for DMP, DEP, DBP, and BBP were 28.1, 4.21, 0.63, and 0.46 mg/L for H. azteca; 68.2, 31.0, 2.64, and > 1.76 mg/L for C. tentans; and 246, 102, 2.48, and 1.23 mg/L for L. variegatus, respectively. No significant survival reductions were observed when the three species were exposed to either DHP or DEHP at concentrations approximating their water solubilities.