TERATOGENESIS, TOXICITY, AND BIOCONCENTRATION IN FROGS EXPOSED TO DIELDRIN

Teratogenesis, acute and chronic toxicity, growth and bioconcentration were investigated in various life stages (embroys, tadpoles, juveniles, adults) of the frogs Xenopus laevis (African clawed frog), Rana catesbeiana (bullfrog) and Rana pipiens (leopard frog) exposed to aqueous dieldrin in static-renewal and flow-through systems in a study on the development of wildlife-based water quality criteria. R. catesbeiana was the most sensitive tadpole in acute tests; X. laevis was the most sensitive in embryo-larval and chronic tadpole tests. Tadpole 96-h LC50s ranged from 40.4 to 49.5-mu-g/L dieldrin for X. laevis, from 8.7 to 30.3-mu-g/L for R. catesbeiana and was 71.3-mu-g/L for R. pipiens. The 24-day LC50 for X. laevis tadpoles was 5.5-mu-g/L dieldrin; the 28-day LC50 for R. pipiens tadpoles was 8.3-mu-g/L. Adult R. pipiens had a 28-day LC50 of 53.4-mu-g/L dieldrin. Gross spinal deformities in embryo-larval tests were observed at dieldrin concentrations as low as 1.3-mu-g/L after 10-days exposure to X. laevis and at 25.4-mu-g/L for a 21-day exposure to R. catesbeiana. Mean X. laevis 14 to 21-day LOAEL (Lowest Observed Adverse Effect Level) and NOAEL (No Observed Adverse Effect Level) values for embryo-larval tests (25.5 and 11.0-mu-g/L dieldrin, respectively) were virtually the same as the 21-day single test values obtained for R. catesbeiana (25.1 and 11.0-mu-g/L dieldrin). Mean 14 to 24-day X. laevis LOAEL and NOAEL values for tadpole chronic tests (1.6 and < 1.4-mu-g/L dieldrin, respectively) were lower than the 28-day single test values obtained for R. pipiens (4.1 and 1.9-mu-g/L, respectively). Tissue dieldrin levels at the LC50, LOAEL and NOAEL in the tadpole acute tests were fairly similar between X. laevis (11, 24 and 7-mu-g/g, respectively) and R. catesbeiana (means of 8.6, 12.0 and 1.2-mu-g/g, respectively). In the tadpole chronic tests, dieldrin tissue concentrations were even closer for these parameters for X. laevis (1.8, 1.5 and 0.8-mu-g/g, respectively) and R. pipiens (1.7, 0.6 and 0.4-mu-g/g, respectively). Mean steady-state bioconcentration factors (BCF) for tadpoles (whole body) ranged from 430 for X. laevis, and from 540 to 1,130 for R. pipiens. Mean steady-state BCFs for adult R. pipiens skin, muscle and liver ranged from 40 to 310. The relative similarity of response to dieldrin between X. laevis and the two ranid species in this study demonstrates its usefulness in assessing potential environmental hazards. The current dieldrin water quality criterion of 0.0019-mu-g/L appears protective of frogs.