This paper presents an estimate of the quantities of cadmium, lead, mercury and arsenic entering the U.K. environment from human activities. Discharges are divided into three source categories: the production and use of the elements, inadvertent sources and various waste disposal practices. The major atmospheric sources of cadmium and mercury include refuse incineration, nonferrous metal production, iron and steel production, fossil fuel combustion and, for mercury alone, the chlor-alkali industry. In contrast, lead and arsenic each have only one major atmospheric source: petrol and coal combustion, respectively. The largest inputs of cadmium, lead and mercury to landfill arise from the disposal of municipal wastes; for arsenic, ash disposal from coal combustion is more important. Industrial activities represent the major sources of trace element input to the U.K. sewage system but domestic sources are important for lead and cadmium, while road run-off makes a considerable lead input. In U.K. coastal waters the major sources of cadmium are the direct discharge of sewage and industrial effluents. For the other elements, the dumping of solid wastes is of more significance. The largest inputs of lead, mercury and arsenic to U.K. agricultural land arise from atmospheric deposition; for cadmium the application of phosphate fertilizers is a more important source, while sewage sludge can be of local significance.