A number of field studies have shown that mayflies (Ephemeroptera) tend to be more sensitive than other benthic macroinvertebrate taxa to elevated levels of total dissolved solids in streams impacted by mining. Until relatively recently, difficulties with culturing have precluded the use of mayflies as laboratory toxicity testing organisms; however, other research groups have 1) found parthenogenic species that readily reproduce under laboratory conditions, and 2) developed laboratory cultured diets for mayflies that will help to move toward standardization of methods. The goal of the present study was to build on these efforts and develop a method for conducting full life-cycle toxicity tests with the mayfly Centroptilum triangulifer using a modification of the previously mentioned laboratory cultured diet. We used the USEPA Ceriodaphnia dubia chronic test as a model, with one < 24-h-old organism placed into each of ten replicate beakers per treatment. Organisms were fed scrapings of live biofilms consisting of two known diatom species cultured in the laboratory. Endpoints included survival to pre-emergent nymph (PEN) stage, number of days to PEN stage, percent emergence, pre-egg-laying live weight, and number of eggs produced. Initial tests were conducted with sodium salts of chloride, sulfate, and nitrate. In acute (96-h) exposures, LC50s for C. triangulifer were approximately one half to two thirds of those generated in our laboratory with Ceriodaphnia dubia. The full life-cycle test with sodium chloride had excellent control survival to PEN stage (100%), and robust weight (mean > 3 mg per adult) and reproduction (mean > 1400 eggs per adult) results. In this chloride test, the most sensitive endpoints were survival to PEN stage, and mean number of days to PEN stage, with a maximum allowable toxicant concentration (MATC) of 267 mg Cl-/L. Measured in terms of conductivity, the MATC was 1,178 μS/cm, which was surprisingly similar to the XC95 for this genus (1,092 μS/cm) documented in the USEPA conductivity benchmark despite the difference in ionic composition.
|Original language||English (US)|
|Title of host publication||Society of Environmental Toxicology and Chemistry North America 34th Annual Meeting, 17-21 November 2013, Nashville, Tennessee|
|State||Published - 2013|