The environmental contamination problems caused by accelerated industrialization are becoming increasingly important issues. It is necessary to estimate the distributions of the contaminants and to recognize the risks to our environment. The behavior of volatile organic compounds (VOC) can be analyzed with the concept of fugacity. However, it is difficult to simulate the fate of heavy metals with this concept, because their vapor pressure is extremely small or unknown. Therefore, the aquivalence (from “equivalent aqueous”) theory, which was derived from the fugacity theory, is utilized to establish a mathematical model and to analyze the fate of heavy metals in an urban multimedia system. The target heavy metal is lead and the target region is around Jungrang stream in Seoul. The multimedia is composed of air, water, sediment, soil and vegetation. To verify the proposed mathematical model, the modeling results were compared with the measurement data obtained from the Korea Testing and Research Institute.