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 endpoints. 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, respectively. Statistical comparison of the lethal concentration regressions showed no significant difference between the slopes of the two curves. Acute exposure to combinations of these two dyes together resulted in a synergistic increase in mortality compared to exposure to each dye separately. Following 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 result in significant sublethal effects with respect to the reproductive potential of exposed organisms. The mortality half-life of the more toxic compound, 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 applications appears to be minimal. The rapid breakdown of both dyes following exposure to sunlight suggests that concentrations likely to be encountered by these organisms in the field would be low.