The presence of toxic agents in aquatic environments has increased in recent years. Some of them that are released into the aquatic environment interfere with the endocrine system of organisms by affecting development time, causing reproductive abnormalities and reducing population growth rates in zooplankton including rotifers. Bisphenol A (BPA, 4,4¹-isopropylidine diphenol) is a commercially important chemical with an estimated worldwide production capacity of 3.7 million metric tons per year and demonstrates estrogenic activity. Many acute and chronic toxicity studies under controlled conditions have used either fish or the cladoceran Daphnia magna. However there is little information using rotifers with BPA. With short life spans and high reproductive abilities, rotifers such as Brachionus calyciflorus are particularly useful for environmental toxicology because of their higher sensitivities to most toxicants. Moreover, rotifers are important trophic components of aquatic food webs constituting a major food source for fish and invertebrate predators and thus play a vital role in transporting energy and nutrients in aquatic ecosystems. The aim of the present work was therefore to use B. calyciflorus to study the effect BPA on the life history characteristics and mixis.
Population of B.calyciflorus was (0-2 h old) obtained by hatching resting eggs in EPA medium. Resting eggs were endowed by professor T W. Snell. Test toxicant solutions were prepared by US EPA medium. The rotifers were fed using unicellular green algae Chlorella pyrenoidosa at 1.0×10⁶ cells/mL,the alga was cultured in a semi-continuous culture using HB-4 medium in 3 L transparent flasks under a light intensity of 4000 lux and photo period was 12∶12 (L∶D). The results showed that 24 h median lethal concentration (24 h LC₅₀) value of BPA for B. calyciflorus was 13.76 mg/L, and 95% limits was 10.97-17.10 mg/L. In the tested concentration range of 0.25-4.0 mg/L, BPA at 2.0 and 4.0 mg/L extended significantly the durations of juvenile development and total eggs production. At 2.0-4.0 mg/L BPA did not affect significantly the durations of embryonic development. BPA concentration at 0.5 mg/L increased markedly net reproductive rate (R₀), 2.0-4.0 mg/L decreased R₀. BPA concentration had no effect on generation time (T) except at 4.0 mg/L. BPA concentration from 1.0 to 4.0 mg/L decreased the intrinsic rate of population increase (r_m), 0.5, 1.0 mg/L increased significantly mixis rate of B.calyciflorus. The results showed that different endpoints of both development and reproduction had different sensitivity to BPA. R₀ and mixis rate endpoint of the rotifers appeared to be more sensitive than other endpoints.