Biodegradation plays a key role in the environmental risk assessment of organic chemicals. The need to assess biodegradability of a chemical for regulatory purposes supports the development of a model for predicting the extent of biodegradation at different time frames, in particular the extent of ultimate biodegradation within a '10 day window' criterion as well as estimating biodegradation half-lives. Conceptually this implies expressing the rate of catabolic transformations as a function of time. An attempt to correlate the kinetics of biodegradation with molecular structure of chemicals is presented. A simplified biodegradation kinetic model was formulated by combining the probabilistic approach of the original formulation of the CATABOL model with the assumption of first order kinetics of catabolic transformations. Nonlinear regression analysis was used to fit the model parameters to OECD 301F biodegradation kinetic data for a set of 208 chemicals. The new model allows the prediction of biodegradation multi-pathways, primary and ultimate half-lives and simulation of related kinetic biodegradation parameters such as biological oxygen demand (BOD), carbon dioxide production, and the nature and amount of metabolites as a function of time. The model may also be used for evaluating the OECD ready biodegradability potential of a chemical within the '10-day window' criterion.
Large numbers of chemicals and products thereof are used in our daily routine to ensure a good quality of life. Substances may even serve as raw materials to produce daily life articles including electronic hardware, green houses, cars etc. Melamine is used for a great variety of products, such as wood panels, paints, coatings, foam seating’s and mattresses (as flame retardant), automotive brake tubes and hose. Based on the latest discussions, melamine has been concluded in the European Union to be classified as “carcinogenic to humans” (Carc. 2, H351) and “may cause damage to organs (urinary tract) through prolonged or repeated exposure” (STOT RE 2, H737). In addition, there is a self-classification of the European industry as suspect Repr. CAT2. Furthermore, the substance is considered a potential groundwater contaminant, due to a low log octanol carbon coefficient (Koc). However, the underlying data require further evaluation. Therefore, a review of available information related to the presence of melamine (M) and cyromazine (CM, of which M is a transformation product) in surface, ground and drinking water was conducted and the data were critically analysed for plausibility. Available monitoring data are scarce and investigated for the Netherlands and Germany mainly. Measurements in the catchment area of the river Rhine and Maas revealed, that both substances (M, CM) were not ubiquitously found in surface, ground and drinking water in these countries. All in all, it can be concluded that the available monitoring data are considered as conclusive, and thus requiring further investigation before a clear relationship between emission and occurrence of melamine in the environment can be drawn.
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