Chronic toxicity of chlordane to Daphnia magna and Ceriodaphnia dubia: a comparative study.

Chronic toxicity of chlordane, an organochlorine insecticide, was assessed on Ceriodaphnia dubia under standardized conditions of testing. Results were compared to Daphnia magna to determine the sensitivity of the two freshwater cladoceran species to this persistent organic pollutant (POP) and to explore the possibility of using the 7-day C. dubia test as an alternative to the 21-day D. magna test in chronic toxicity assessment of POPs. The NOEC-7d value of chlordane on reproduction of C. dubia (2.9 µg/L) was much higher than the NOEC-21d value of D. magna (0.18 µg/L), attesting that the 7-day test on C. dubia was less sensitive than the 21-day reproduction test on D. magna to chlordane. However, extending the period of exposure of C. dubia to chlordane from 7 to 14 days led to a NOEC-14d value similar to the NOEC-21d value in D. magna (0.18 µg/L). This study highlights the usefulness of prolonging the exposure time of the reproduction test in C. dubia from 7 to 14 days to increase the performances of the reproduction test on C. dubia for assessing chronic toxicity of POPs.

Ecotoxicity of cyanide complexes in industrially contaminated soils.

This study deals with acute and chronic ecotoxicity of leachates from industrially contaminated soils. Analyses focused on cyanides (complex and free forms) to study their possible involvement in leachates toxicity. No acute toxicity on the Microtox and 48 h-Daphnia magna tests was found in leachates collected over 18 months, but a high chronic toxicity was recorded on the reproduction of Ceriodaphnia dubia (EC50-7d=0.31±0.07%) and on the algal growth of Pseudokirchneriella subcapitata (EC50-72 h=0.27±0.09%). Ceriodaphnids were as sensitive to free cyanide as to complex forms (EC50-7d as CN(-)=98 µg/L, 194 µg/L and 216 µg/L for KCN, Fe(CN)(6)K(3) and Fe(CN)(6)K(4), respectively). The EC50-72 h of KCN to P. subcapitata (116 µg/L) as CN(-) was also of the same level as the EC50-72 h of potassium ferricyanide (127 µg/L) and ferrocyanide (267 µg/L). Complex cyanides explained a major part of the toxicity of leachates of the soil. On the other hand, cyanide complexes had no effect on survival of the earthworm Eisenia fetida up to 131 mg CN(-)/kg, while potassium cyanide was highly toxic [EC50-14 d as CN(-)=74 µg/kg soil]. Thermodesorption treatment eliminated a majority of cyanides from the soil and generated much less toxic leachates. Complex cyanides must be integrated into environmental studies to assess the impact of multi-contaminated soils.

Reproductive effects and bioaccumulation of chlordane in Daphnia magna.

Acute and chronic toxicity of high-grade chlordane (98%) and bioaccumulation were investigated in Daphnia magna at water soluble concentrations obtained without cosolvent. The measured effective concentrations immobilizing 50% of the microcrustacea (95% confidence interval) were 22.6 (19.7-26.1) microg/L at 24 h and 13.4 (11.3-15.8) microg/L at 48 h. This indicated an increase of chlordane toxicity with time of exposure as confirmed in chronic studies. After 21 d of exposure, significant effects on survival were recorded at a chlordane concentration greater than 2.9 microg/L, whereas reproduction (number of offspring per adult, brood size) and length of adults decreased at 0.7 microg/L or more in a concentration- and time-dependent manner. The production of male offspring and developmental abnormalities, consisting of underdeveloped second antennae and shell spines in live neonates, were recorded. The chlordane concentration tested with no significant adverse effect (NOEC) on reproduction of daphnids after 21 d compared with controls was 0.18 microg/L. The bioaccumulation factor of chlordane by daphnids exposed at a level of concentration close to the 21-d NOEC reached 10,600, wet weight, and 244,000, dry weight, after 40 d. The trans-chlordane bioaccumulated to a greater extent than the cis isomer in daphnids, whereas the cis isomer was predominant in the test medium. The results suggest a crucial role of the invertebrates in transfer of chlordane in aquatic food webs and can be used to derive a freshwater guideline for environmental protection accounting for bioaccumulation.