Effect of culture conditions and mother’s age on the sensitivity of Daphnia magna Straus 1820 (Cladocera) neonates to hexavalent chromium

Abstract

Daphnia magna is a freshwater cladoceran used worldwide as test organism in aquatic toxicity assays. In Mexico there is a test protocol for this species; nevertheless, some aspects of the controlled neonate production, as well as the possible consequences of the reproducers' culture conditions on the response of neonates to the toxic substance, are not completely known. In the present study, we evaluated the effect of temperature and photoperiod on the acute toxicity of CrVI in D. magna neonates, aimed at providing useful information on the Median Lethal Concentration (LC50) to this heavy metal, which is used as reference toxicant in some laboratories. D. magna was cultured at 20 and 25 degrees C, in combination with two photoperiod values: 16:8 and 12:12 (light:dark) during 40 days; the green microalga Ankistrodesmus falcatus (4x10(5) cells ml(-1)) was supplied as food. Once the reproduction began, the neonates were removed and acute toxicity bioassays at 20 and 25 degrees C were performed, by exposing them to hexavalent chromium. We also determined changes in neonates' size at 20 and 25 degrees C. Chromium toxicity increased along with increasing temperatures, and LC50 values were slightly lower for the first and last clutches in the observed period, but these findings are not conclusive because of the large variability recorded. The average LC50's were 0.2076+/-0.0164 mg l(-1) (at 20 degrees C) and 0.1544+/-0.0175 mg l(-1) (at 25 degrees C). The reproducers' culture temperature had no effect on neonates' sensitivity to chromium, in spite of performing the tests at temperatures either lower or higher than those at which the neonates had been obtained. The length of neonates produced during the first two clutches (<1.25 mm) was significantly lower than that measured in neonates of following reproductions (>1.3 mm), and were smaller at 25 degrees C; however, this did not seem to affect their sensitivity to chromium.

Suitability of Daphnia similis as an alternative organism in ecotoxicological tests: implications for metal toxicity

“…Table 2 summarizes some results of 48 h-LC 50 values for metals to daphnid species, however, the different physical and chemical parameters of culture media (hardness, and pH), make comparisons difficult. We obtained 48 h-LC 50 values for cadmium and chromium to D. similis lower than those that have been obtained for other daphnid species by Fargasová (1994), Barata et al (1998), Taylor et al (1998), Dorn et al (1987, Diamantino et al (2000), Muyssen and Janssen (2004) and Martínez-Jerónimo et al (2006). We used soft reconstituted water (44 mg l -1 CaCO 3 ) with a pH value of 7.2 as zooplankton culture media in the toxicity tests, while the cited authors have used hard (160-180 mg l -1 CaCO 3 ) or very hard (280-320 mg l -1 CaCO 3 ) reconstituted water with pH higher than 7.6 in their experiments.…”

The influence of natural stressors on the toxicity of nickel to Daphnia magna

“…At higher temperatures, the antagonistic behaviour given by the interpretation of model parameters was not confirmed by the LC 50 values calculation, where the values decreased with an increase of temperatures (Table 3). Synergistic effects are usually associated to extreme environmental conditions, as HT, by directly and/or indirectly increase the toxicity of chemicals, as reported by several studies (Folt et al 1999, Heugens et al 2003, Heugens et al 2006, Lewis and Horning 1991, Martinez-Jeronimo et al 2006. The increase of nickel toxicity at high temperatures might also be related to an increase in metabolism and destabilisation of homeostasis (Lannig et al 2006).…”

Modification of the acute toxic response of Daphnia magna Straus 1820 to Cr(VI) by the effect of varying saline concentrations (NaCl)

“…Although other authors have reported higher values as, for example, 1.3 mg l -1 Enserink et al (1990), 0.64 mg l -1 (Van Leeuwen et al 1987), or 0.35 mg l -1 (Bulus and Ronco 1996). Martínez-Jerónimo et al (2006) determined LC 50 values of 0.2076 ± 0.0164 and 0.1544 ± 0.0175 mg l -1 at 20 and 25°C, respectively, which are similar to those obtained herein, confirming that D. magna is a species sensitive to Cr(VI).…”