A system (1) for monitoring the exposure of a plurality of individuals (5) to a physical or chemical property associated with an environment. The system includes a plurality of portable devices (9). Each portable device is arranged to be worn or carried by an individual in the environment. The system further includes a control unit (7) for communicating with each of the plurality of portable devices. Each of the portable device includes a detector arranged to measure a physical or chemical property that the individual wearing or carrying the device is exposed to in the environment; one or more physiological sensors each arranged to measure a physiological parameter of the individual; a geolocation module arranged to determine the location of the individual; and a communication module for communicating data collected by the portable device with other(s) of the plurality of the portable devices and with the control unit.