The Monitoring and Assessment Research Centre (MARC) has been developing and applying the exposure commitment method to the assessment of pollutant transport in the regional and global environment. Exposure commitments give a basis for comparing contributions to exposure from various pathways and for estimating equilibrium concentrations resulting from continuing releases. As an illustration of the method, environmental aspects of arsenic are summarised and relationships are formulated between environmental sources and concentrations of arsenic in the body. Arsenic is present in the environment primarily in inorganic form; however, relatively higher concentrations of arsenic in organic forms occur in fish. Ingestion intake by man is variable, dependent on seafood consumption and also on geography, determining for example the levels which may be present in drinking water. Based on measured absorption and retention of arsenic in man, it is estimated that an ingestion intake rate of arsenic in terrestrial foods of 1 mg y-1 contributes a concentration of arsenic in the body of 0.28 microgram kg-1. The relationship is 0.14 microgram kg-1 per mg y-1 intake of organic arsenic in seafood. The body burden of arsenic is estimated to be about 1 mg from reported tissue measurements and from representative intake estimates. Harmful effects from arsenic in the body could be expected at levels perhaps 5 to 80 times the current background levels. Uncertainties are recognized. Improved estimates of the transfer fractions can be made as additional data are acquired.