Environmental tracers, as isotopes, have been used to reveal origin, movement and dispersion of compounds because they behave the same as environmental processes. These isotopes are useful tools for understanding dynamics of natural systems, providing a unique tool to trace the biogeochemical cycles within ecosystems. The hydrological complex of Babitonga Bay (Brazil) forms a vast environmental system; hosting the last great expanse of mangrove forests in the southern hemisphere. Mangroves are among the most productive ecosystems on earth. Effects of an oil spill on mangrove ecosystems were studied in Babitonga Bay using lead and carbon isotopes. Samples of the spilled oil, as well as sediment and water samples, were obtained nine months after the accident, at the time of the salvage operation. Isotopic composition of the oil was utilized to trace the extent of the environmental pollution. In addition, isotopes of lead and carbon allowed for the identification of areas where oil was present. Contaminated sediments exhibited an isotopic composition (206Pb/207Pb and 208Pb/206Pb) close to that of the oil spilled. δ13C data confirmed these results. The results of this investigation suggest that lead isotope ratios can be very useful in the field of environmental forensics