Women who were part of a study in which polychlorinated biphenyls (PCBs) were measured in breast milk were exposed accidentally to a PCB spill. While the overall level of PCBs found in their milk was not different from background levels, the chromatograms showed unusual peaks that indicate the presence of heavily chlorinated PCBs of the kind that were spilled.
Rogan WJ, Gladen BC, McKinney JD, Albro PW. Chromatographic Evidence of Polychlorinated Biphenyl Exposure From a Spill. JAMA. 1983;249(8):1057-1058. doi:10.1001/jama.1983.03330320055033