The objective of the present study was to evaluate the relative sensitivity of test organisms in exposures to dilutions of a highly toxic sediment contaminated with metals and organic compounds. One dilution series was prepared using control sand (low total organic carbon [TOC; <0.1%, low binding capacity for contaminants]) and a second dilution series was prepared using control sediment from West Bearskin Lake, Minnesota, USA (high TOC [$10% TOC, higher binding capacity for contaminants]). Test organisms included an amphipod (Hyalella azteca; 10-d and 28-d exposures), a midge (Chironomus dilutus; 20-d and 48-d exposures started with <1-h-old larvae, and 13-d and 48-d exposures started with 7-d-old larvae), and a unionid mussel (Lampsilis siliquoidea; 28-d exposures). Relative species sensitivity depended on the toxicity endpoint and the diluent. All 3 species were more sensitive in sand dilutions than in West Bearskin Lake sediment dilutions. The <1-h-old C. dilutus were more sensitive than 7-d-old C. dilutus, but replicate variability was high in exposures started with the younger midge larvae. Larval biomass and adult emergence endpoints of C. dilutus exhibited a similar sensitivity. Survival, weight, and biomass of H. azteca were more sensitive endpoints in 28-d exposures than in 10-d exposures. Weight and biomass of L. siliquoidea were sensitive endpoints in both sand and West Bearskin Lake sediment dilutions. Metals, ammonia, oil, and other organic contaminants may have contributed to the observed toxicity.
Standard laboratory sediment toxicity methods have been adapted for conducting toxicity tests with juvenile freshwater mussels. However, studies looking at juvenile mussel burrowing behavior at the water-sediment interface are limited. Juvenile mussels burrow in sediment for the first 0 to 4 yr of life but also may inhabit the sediment-water interface. The objective of this study was to evaluate burrowing behavior of various species and ages of juvenile freshwater mussels in three control sediments: West Bearskin Lake, Spring River, and coarse commercial sand. Species tested included (1) Fatmucket (Lampsilis siliquoidea), (2) Notched Rainbow (Villosa constricta), (3) Washboard (Megalonaias nervosa), (4) Rainbow (Villosa iris), (5) Arkansas Fatmucket (Lampsilis powellii), and (6) Oregon Floater (Anodonta oregonensis). Greater than 95% of the mussels burrowed into test sediment within 15 min. Across species, life stage, and substrate type, most mussels were recovered from the upper layers of sediment (91% at a sediment depth of 3.4 mm or less), and only 2% of the mussels were recovered at a depth .5.1 mm. No mussels were recovered from a depth .6.8 mm. There was no difference in mussel burrowing depth at 4 h versus 24 h across species, age, and sediment type. Two ages of Fatmucket burrowed to a significantly greater depth in the West Bearskin Lake sediment compared to the Spring River sediment or Coarse Sand. However, there was no significant difference in mean depth across sediment type with the other five species of mussels tested. Based on species and age of mussels tested, juvenile mussels up to an age of at least 20 wk and a length of at least 5 mm readily burrow into sediment and likely would be exposed to contaminants in whole sediment and associated pore water throughout a laboratory sediment toxicity test.
Fish hatcheries and other types of aquatic facilities are potential sources for the introduction of nonnative species of fish or aquatic invertebrates into watersheds. Chlorine has been suggested for use to kill organisms that might be released from the effluent of a facility. While acute LC50s (concentrations lethal to 50% of organisms exposed for up to 96 h) for chlorine are available for some species, short‐term LC100s for chlorine have not been determined. The objective of this study is to establish concentrations of chlorine that are lethal to 100% of organisms after brief (1‐, 5‐, or 15‐min) exposures. A total of 22 species were exposed to total residual chlorine concentrations (TRC) of 1, 10, or 25 mg TRC/L for 1, 5, or 15 min under static conditions followed by a 24‐h postexposure recovery period in water without the addition of chlorine. Concentrations of chlorine resulting in 100% lethality of organisms were established for all of the species tested except for four species of mollusks or for a beetle. Exposures for 5 to 15 min to 10–25 mg TRC/L were the lowest combined time–chlorine treatments under which all of the fish tested and the other invertebrates tested (17 species) exhibited 100% lethality by the end of the initial chlorine exposures or after the 24‐h recovery period.
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