Nowadays, environmental pollution levels are a worldwide concern due to the risks for people's health. The demand for cutting-edge technologies to determine the sensible areas where pollutants are present in dangerous concentrations is ever increasing, along with the stringent requirements of avoiding the exposure of human operators to toxic substance. For this reason, the proposed work presents a novel method for the surveillance and monitoring of large areas by means of unmanned aerial vehicles. The work encompasses both hardware and software integration of a low-power multi-sensor platform hosted by the aerial vehicle. The platform comprises a multi-spectral camera, digital optics sensors and toxic/pollutant gas concentration detectors coupled with low-power computing and wireless communication capabilities. Furthermore, a base station platform is implemented to collect data and to provide the analytical tools that facilitate the responsible authorities in the decision of intervention.