Lead isotope ratios, determined by inductively coupled plasma quadropole mass spectrometry (ICPMS), have been used to assess environmental impacts from uranium and lead mining in northern Australia. The lead isotope composition of most environmental samples contained evidence of mixing of two or more end-member components; their characteristic lead isotope ratios allowed lead sources to be unambiguously identified. The isotopic characteristics and sources identified include highly radiogenic lead (low 207Pb/206Pb and 208Pb/206Pb ratios) in sediments from the Finniss River derived from the former Rum Jungle uranium mine; relatively non-radiogenic lead (high 207Pb/206Pb and 208Pb/206Pb ratios) in the livers of magpie geese from the Finniss River floodplains, originating from lead ores via ingested lead shot; and relatively non-radiogenic lead in seagrass leaves and oyster soft tissue from the Gulf of Carpentaria resulting from dispersion of small amounts of lead–zinc concentrate from a coastal loading facility.