Urban transportation systems are major sources of environmental contamination, generating complex mixtures of airborne particles, heavy metals, and organic pollutants that accumulate along roadways and in surrounding areas. These pollutants originate primarily from vehicular emissions, mechanical wear of vehicle components, and atmospheric deposition associated with urban industrial activities. Occupational groups working directly in these environments may therefore experience greater exposure to environmental contaminants than the general population. The purpose of this paper is to develop a theoretical model of the biological effects of environmental contaminants and health risks in street cleaners and road workers based on a detailed review of the existing literature. The results for occupational health outcomes show that exposure to particulate matter generated by sweeping and waste collection is an important determinant of respiratory risk among sanitation workers. Environmental monitoring studies have demonstrated elevated airborne particulate concentrations during manual sweeping operations, particularly under dry conditions when accumulated road dust is easily re-suspended into the breathing zone of workers. Furthermore, repeated exposure to these airborne particles may therefore contribute to chronic respiratory irritation and the development of respiratory disorders among street cleaners. Cardiopulmonary health effects have also been reported in association with exposure to particulate air pollution, while epidemiological and toxicological studies have demonstrated that inhalation of fine and ultrafine particulate matter can trigger systemic inflammatory responses and oxidative stress that extend beyond the respiratory tract. These biological responses may contribute to alterations in vascular function, increased blood pressure, and disturbances in autonomic regulation of the cardiovascular system. Street cleaners and road maintenance workers experience re