Elevated concentrations of selenium (Se) have been previously measured in biota sampled from the Kesterson National Wildlife Refuge (KNWR) in the San Joaquin Valley of central California. We conducted acute and chronic toxicity tests with the cladoceran Daphnia magna and the midge Chironomus riparius to determine the toxicity or bioaccumulation of waterborne Se in a reconstituted water sinilar to the San Joaquin River. Daphnids were more acutely sensitive than midges to the toxic effects of inorganic Se. An organic form of Se (seleno-[L]-methionine) was extremely toxic to daphnids, but was relatively nontoxic to midges. In long-term exposure to a 6:l mixture of selenate to selenite (a mixture representative of KNWR), the emergence time of adult midges was delayed at Se concentrations 2 837 pg/L. Daphnid reproduction and intrinsic rate of natural increase ( r ) were reduced at Se concentrations 2 348 pg/L and growth of adults was reduced at 2156 pg/L. Whole body Mg, K and Na concentrations in daphnids were not affected by chronic Se exposure; however, whole body Ca concentration increased at intermediate Se exposure concentrations. In addition, whole body C1 concentration was reduced at 71 1 pg Se/L. Daphnids accumulated potentially toxic concentrations of Se from water that may adversely affect fish or waterfowl through the food chain.

Irrigation drain waters entering Stillwater Wildlife Management Area (SWMA) in south‐western Nevada contain elevated levels of salinity and several inorganic contaminants (As, B, Cu, Li, Mo, and Sr). Mortalities of fish and waterfowl at the management area are believed to be associated with the poor water quality of the drains. The objective of the present study was to use fresh‐water and saltwater animals to distinguish between the toxic effects of salinity and contaminants in effluent samples collected from irrigation drain waters. Static acute effluent tests were conducted with water collected from four sites at SWMA. Animals acclimated or cultured in fresh water (fathead minnows, Pimephales promelas; amphipods, Hyalella azteca; cladocerans, Daphnia magna) and salt water (striped bass, Morone saxatilis; amphipods, Hyalella azteca; and cladocerans, Daphnia magna) were used to separate toxic effects of salinity from the effects of inorganic contaminants in the drain water. One drain water (TJ drain, salinity 19 parts per thousand (grams per liter), osmolality 503 mmol/kg, hardness 3,780 mg/L as CaCO3) was toxic only to freshwater animals and saltwater cultured daphnids; water from a receiving pond (Pintail Bay, salinity 23 g/L, osmolality 542 mmol/kg, hardness 830 mg/L as CaCO3) was toxic to both freshwater and saltwater animals. Acute tests conducted with reconstituted waters representative of the Pintail Bay sample indicated that atypical ion ratios were toxic to striped bass and amphipods, even without the addition of inorganic contaminants. However, the addition of inorganic contaminants representative of the Pintail Bay sample increased the toxicity of this reconstituted water. These findings indicate that the toxicity of the TJ drain sample was related mainly to elevated salinity and that the toxicity of the Pintail Bay sample was a function of inorganic contamination and atypical ion ratios in combination with elevated salinity.

Acute toxicity tests with reconstituted water were conducted to investigate the relationship between water hardness, salinity, and a mixture of trace elements found in irrigation drain waters entering Stillwater Wildlife Management Area (SWMA), near Fallon, Nevada. The SWMA has been the site of many fish kills in recent years, and previous toxicity studies indicated that one drain water, Pintail Bay, was acutely toxic to organisms acclimated or cultured in fresh water or salt water. This toxicity could reflect both the ionic composition of this saline water and the presence of trace elements. The lowest water salinity tested with Daphnia magna was near the upper salinity tolerance of these organisms; therefore, we were unable to differentiate between the toxic effects of ion composition and those of trace elements. In toxicity tests conducted with striped bass (Morone saxatilis), we found that the extent to which salinity was lethal to striped bass depended on the ion composition of that salinity. Survival of striped bass increased as hardness increased. In addition, a trace element mixture was toxic to striped bass, even though the concentrations of individual elements were below expected acutely lethal concentrations. Although salinity is an important water quality characteristic, the ionic composition of the water must be considered when one assesses the hazard of irrigation drain waters to aquatic organisms.

Methods for testing the toxicity of whole sediments are described for the amphipod Hyalella azteca and the midge Chironomus riparius. Amphipod tests (static and flow-through) start with juvenile animals (≤ third instar) and continue up to 29 d until reproductive maturation. Flow-through tests with the midge start with first instar larvae (<24 h old) and continue up to 29 d through adult emergence. Data obtained from these laboratory exposures can be used to assess the effects of contaminants in sediments on survival, growth, or emergence of amphipods and midges. The methods were used to assess the potential toxicity of field-collected contaminated sediment from two sites in Waukegan Harbor, Illinois, an inlet of Lake Michigan contaminated with polychlorinated biphenyls (PCBs), polycyclic aromatic compounds (PACs), and metals; and a single site at Homer Lake, a small recreational lake in the agricultural region of central Illinois. Survival of both species was reduced after short-term (10-to 13-d) and long-term (29-d) exposure to contaminated sediment. In addition, sublethal effects were indicated by reduced growth of amphipods and a delay in emergence of adult midges.