Several approaches to the environmental safety assessment of chemicals have been reported. The basic principles involved in predicting environmental behavior combine degradation kinetics and the partitioning/distribution of chemicals in the environment. The transport mechanisms within the environment can be modeled as partitioning/distribution which are essentially functions of the physico-chemical properties of the chemical. Phthalazine (2,3-Benzodiazine, C8H6N2) is a component of a specialized paper product. The major route for environmental entry of phthalazine is through land disposal of waste paper. Information available on phthalazine chemistry is consistent with behavior of heterocyclic aromatic hydrocarbons. Several laboratory test methods and QSAR estimation procedures were used to measure key environmental properties of phthalazine. This assessment examines the environmental release of phthalazine, and its partitioning and distribution in the environment. It predicts the probable fate and possible biological effects of phthalazine.