Environmental monitoring, as a prerequisite for environmental risk assessment, is crucial in developing nations from Africa, Latin America, South East Asia, or Melanesia, where conspicuously most of the World's mining activity concentrates. One of the most important environmental problems relates to the disposal of mine concentrates to river systems (e.g., Irian Jaya or Papua New Guinea). However, environmental monitoring is severely restricted in developing countries due to the chronic lack of funds. This paper explores the potential for a wider use of Field Portable X-Ray Fluorescence Spectroscopy instruments (FPXRFs) in fast, real-time, cost-effective environmental surveys for heavy metal dispersal in developing countries, where access to fully equipped geochemical labs is not usually a viable option. We simulated a scenario resembling conditions to be found in a remote region affected by mining-derived metal pollution where no proper laboratory facilities existed. We used an OXFORD X-MET 3000TX XRF analyzer under quasi-realistic conditions, relying solely on the instrument to allow geochemical characterization of a highly polluted Pb-Zn old mining district in the Alcudian Valley of central Spain. Our results for Pb, Zn, Cu, As, and Cd from 12 mine sites showed an excellent performance of the instrument, both under real-time and laboratory conditions. Furthermore, the instrument proved to be fit to endure a variety of field operational conditions and was able to deal with different types of samples, including tailings, soils, and stream sediments. Thus, taking into account the affordability of FPXRFs in relation to bench-top laboratory metal analyzers and their operational simplicity, we suggest that these portable instruments should become 'the equipment of choice' for environmental monitoring in developing countries. In this respect, FPXRFs satisfy the system-independence criterion for sustainable development, i.e., the instrument can stand alone and do its job with few or no other supporting facilities or devices. We go further on these matters providing some hints on how FPXRFs could become widely available via international cooperation, and the technical and social benefits that such equipments could bring to foreign aid recipient countries.