Influências de substâncias húmicas nas características bionômicas, toxicocidade e bioacumulação de cobre por Ceriodaphnia silvestrii Daday (Crustacea, Cladocera).
Santos, Maria Alice Penna Firme dos
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Effects of different food sources and culture medium on life history traits of Ceriodaphnia silvestrii were studied under controlled conditions. Animals were submitted to five different treatments: (1) autoclaved natural water filtered through plankton net of 20µm mesh size, supplied with Chlorella lacustris as food source; (2) autoclaved natural water filtered through plankton net of 20µm mesh size, supplied with Scenedesmus bijugus; (3) soft reconstituted water supplied with S. bijugus; (4) soft reconstituted water supplied with S. bijugus plus humic substances (20mg L-1); and (5) hard reconstituted water supplied with S. bijugus. Observations were performed at 12 hours intervals from organism birth until its natural death. All treatments were kept in a 25±1 ºC temperature. Instantaneous rate of population increase (r) was calculated for all treatments. Body length-dry weight relationship was also established. Results showed longer longevity in C. lacustris treatment, and better fecundity on treatment with natural water and S. bijugus. In the treatment with artificial medium, fecundity and growing parameters were lower than in natural water treatment. Increased hardness did not affect reproduction and growth values. Humic substances addition resulted in greater fecundity and survival values. Copper acute toxicity to Ceriodaphnia silvestrii (Cladocera, Daphnidae), was also studied in the absence and presence of humic substances (HS). Groups of 20 adult females of similar sizes were exposed to copper (total concentration range from 10-8 to 10-5 M) for a period of 24h. LC50 was estimated by the Trimmed Spearman-Karber method. It revealed that humic substances altered LC50 from 4.4 x 10-8 M without humic substances to 1.1x10-6 M with 20mg HS L-1 in the medium. Free copper ions were determined in test media and it showed that humic substances reduced Cu2+ concentration. LC50 values based on total copper concentration varied significantly between the two treatments. However, when lethality was estimated based on free ion concentrations, the values were similar: 3.3 x 10-8 M without humic substances, and 2.8 x 10-8 M when HS were present in the medium. Moreover, C. silvestrii is capable of regulating its body copper levels over a range of copper availabilities, as so many other crustaceans. As also reported, humic substances did not influence copper bioaccumulation by C. silvestrii.