The acute and chronic toxicity of two xanthene dyes, fluorescein sodium salt and phloxine B, to Daphnia pulex

The toxicity of two xanthene dyes, fluorescein sodium salt and phloxine B, to Daphnia pulex was assessed using acute and chronic level toxicological e ndpoints. The 48-h LC50 (95% FL) of fluorescein and phloxine B to D. pulex neonates was 337 (278-403) mg/ liter and 0.423 (0.376-0.477) mg/liter, resp ectively. Statistical comparison of the lethal concentration regressions sh owed no significant difference between the slopes of the two curves. Acute exposure to combinations of these two dyes together resulted in a synergist ic increase in mortality compared to exposure to each dye separately. Follo wing 10-day chronic exposure under static conditions, fluorescein caused a concentration-dependent decline in the mean number of offspring produced by D. pulex. In contrast, chronic exposure to phloxine B did not appear to re sult in significant sublethal effects with respect to the reproductive pote ntial of exposed organisms. The mortality half-life of the more toxic compo und, phloxine B, was 20.4 h. Although we found both dyes to be toxic to D. pulex, the risk they would pose to wild populations following broad-based a pplications appears to be minimal. The rapid breakdown of both dyes followi ng exposure to sunlight suggests that concentrations likely to be encounter ed by these organisms in the field would be low. (C) 1999 Elsevier Science Ltd. All rights reserved.