Biodegradation and ecotoxicity of HFCs and HCFCs.

Hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) are used or developed as substitutes for fully halogenated chlorofluorocarbons. Based on the results of closed-bottle tests, the biodegradation of HFC-32, HCFC-123, HCFC-124, HFC-125, HFC-134a, HCFC-141b, HCFC-225ca, and HCFC-225cb was less than 60% after 28 days and therefore these compounds are considered not readily biodegradable. Standard acute toxicity tests with HCFC-123, HCFC-141b, and HCFC-225ca using algae, water fleas, and fish revealed EC50 values in the range of 17-126 mg/L. EC50 values of HFC-134a ranged between 450-980 mg/L. Fish studies with HCFC-141b and HCFC-225ca revealed bioaccumulation factors of <3 and 15-64, respectively. A study with plants revealed no effect of HCFC-141b on seed germination and growth of wheat (Triticum aestivum), radish (Raphanus sativus), and cress (Lepidium sativum). In conclusion, HFCs and HCFCs are not very toxic to aquatic organisms and terrestrial plants. No evidence for any aerobic biodegradation for most of the HFCs and HCFCs was found.

Bioaccumulation and lack of toxicity of octachlorodibenzofuran (OCDF) and octachlorodibenzo-p-dioxin (OCDD) to early-life stages of zebra fish (Brachydanio rerio).

Previous studies with octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) in juvenile or adult fish exposed via water revealed no toxicity, despite significant bioaccumulation. With 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), the fish early-life stage study has been shown to be the most sensitive test system. Therefore, the effects of OCDD and OCDF on the early-life stages of zebra fish (Brachydanio rerio) were determined during a flow-through test based on a column generator method. No statistically significant effect of OCDD and OCDF on the survival and hatching time of the eggs was found. Furthermore, no effects on survival, weight, general appearance or behaviour of the larvae were observed at the end of the exposure period of 32 days. GC-MS analysis of test solution samples revealed geometric mean measured concentrations of 32 (OCDD) and 34 ng/l (OCDF), respectively. Concentrations in surviving larvae at the end of the study were 61 (OCDD) and 94 (OCDF) micrograms/kg, respectively. These concentrations in zebra fish larvae were several orders of magnitude higher than concentrations in fish collected from the wild. In a review of the available laboratory fish experiments, we found a lack of biomagnification of OCDD and OCDF. We do not expect to find adverse effects of these compounds on the aquatic environment.