Figure 8. Residues of chlorinated hydrocarbons. Eggs of herring gull (Larus argentatus) were sampled at breeding sites on two islands in Lake Ontario. The insecticide DDT accumulates in organisms as DDE, a slightly modified chemical, while PCBs are industrial chemicals. The use of these organochlorines was banned in North America in the 1970s, partly because of ecotoxicological damage they were causing to wildlife. Source: Freedman et al. (2014), using data of Ryckman et al. (2005).