Relative frequency histograms showing distribution of ∑PCB and ∑DDT levels for necropsied seals (n = 67). C. WilsonSusan M. EybatovTariel AmanoMasao JepsonPaul D. J. GoodmanSimon 2014 <p>Relative frequency histograms showing distribution of ∑PCB and ∑DDT levels for necropsied seals (n = 67).</p>