Biodegradation and Ecotoxicity of HFCs and HCFCs
Abstract. 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.
Improved bacterial growth test for rapid water toxicity screening
Bacteria have several attributes which make them attractive as test organisms for the rapid screening of chemical pollution in natural waters. They have relatively short life cycles and, therefore, respond rapidly to environmental change. The degree of toxicity of chemicals to bacteria is normally established by measuring viability or growth. A very sensitive test has been described measuring cell multiplication inhibition of Pseudomonas putida, results being obtained after a 16 h incubation period. Because of their short generation time it is possible, however, that bacteria are capable of manifesting measurable growth within a shorter incubation period. In the present study P. putida was cultured under modified test conditions aiming at an equally sensitive but more rapid growth test. Subsequent to initial tests, using different growth media, a toxicity test procedure was developed which uses a medium with low complexing capacity, a standardized inoculum and a 6 h incubation period.
Impacts of climate and land use changes on flood risk management for the Schijn River, Belgium
Abstract Flooding is the most common natural disaster in Europe. Modern flood risk management relies not only infrastructure development but also on governmental and non-governmental actors applying legal, economic and communicative water management instruments. Within the European Union (EU), flood management closely relies on policy set at the EU and national levels. It is now recognized that a sound understanding of climate change is required in addition to current management by taking into account land use change and socio-political context, as climate and land use changes have major impacts on hydrological responses. This paper investigates the hydrological behavior due to urbanization under current and future climate scenarios of high summer and high winter rainfall for 20 sub-catchments of the Schijn River, located in the Flanders region near Antwerp, Belgium. As urbanization increases and existing rainfall-runoff models neglecting the specific behavior of urban runoff, a hydrological model was developed based on a basic reservoir concept and applied to the existing rainfall-runoff model (PDM) flow to examine the specific urban contribution. Results revealed that peak flow for urban runoff and the total peak flow (i.e. rural and urban runoff) were significantly higher (i.e. ranges from 200% to 500%) than the existing rainfall-runoff model (PDM) flows, because of faster and more peaked urban runoff response. The impact of climate change on current and future conditions was also assessed by estimating peak flows with respect to return periods from the flood frequency curve. The predicted peak flow of high summer future climate scenario was significantly higher (i.e. ranges from 200% to 250%) than that of the current climatic condition for this region. Furthermore, hourly peak flow and daily volume ratios of 100-year return period for the highest, lowest and average impervious area were projected for the time horizon of the year 2100. It is concluded that climate change impacts contribute the most in producing peak flow in coming years, while increased urbanization takes the second place for both hourly and daily values. Results on urbanization effect and climate change impact assessment are useful to the water managers for spatial planning, emergency planning and insurance industry.