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The chlorocarbon mirex undergoes slow, successive loss of chlorine in the field to a series of related compounds that had lost one or more chlorine atoms. Soil samples were recovered 12 years after treatment at 1 part per million (ppm), and ant bait was recovered 5 years after an aircraft crash. As much as 50 percent of the original mirex was recovered at levels of about 0.5 and 640 ppm, respectively. Kepone was present at levels of 0.02 ppm in soil and 10 ppm in the bait or up to 10 percent of the recovered mirex, as determined by combined techniques of chromatography and mass spectrometry. This constitutes the first observation of the degradation of mirex in nature, and demonstrates a pathway for its eventual disappearance from the environment.

Fracture mechanics concepts, in terms of stress intensity factors, have been used in a study of the growth of cracks and crazes in Crystal Polystyrene in air at 293°K. Single edge notch tension specimens and tapered cleavage specimens have been tested over a wide range of strain rates and also at constant load.It was initially found that the critical stress intensity factor Kic (evaluated at crack instability) which should be a constant, independent of test method and specimen geometry, could apparently vary over a wide range. This phenomenon was shown to be caused by the presence of craze bunches at the crack tips; the size of these bunches being dependent upon the method of notching employed. A notching technique producing pure cracks was devised and as a result the lower bound value of Kic at instability for the material was shown to be 1.05 MN/m ~. A curve showing the relationship between crack speed and crack toughness Kc was also obtained and a lower value of Kc for crack initiation was extrapolated as being 0.78 MN/m ~.The role of inherent flaws in the fracture of unnotched tensile specimens and the consequences of crazing are discussed in terms of fracture stresses predicted from the notched tests using a Dugdale model.

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The nature of slow crack and craze propagation in polymers and crack propagation in inorganic glass has been considered in terms of time dependent processes. By using a fracture mechanics analysis together with time dependent material parameters, equations have been derived to describe crack and craze propagation in both inert and active environments. Experimental data from a range of materials suggest that a crack opening displacement (c. o. d. ) criterion governs the crack propagation behaviour. Incorporation of a simple fluid flow model into the c. o. d. analysis has allowed the failure processes in liquid environments to be described. The data on organic polymers and inorganic glass suggest that when there are no problems of maintaining the environmental supply, the crack growth behaviour is controlled by relaxation processes in the material. At high crack speeds a transition from relaxation to fluid flow control occurs when the time scale is too short for the liquid flow to be maintained. The flow of an environment in long crazes can be shown to influence their behaviour in a similar manner, while under other conditions relaxation controlled craze growth can occur.