To collect heron eggs she enlisted the help of some professional tree climbers and a couple of biologists trained to climb trees. She also collected some herself. During the two field seasons Thomas collected 140 eggs. About half of the eggs ended up in the incubator at a U.S. Fish and Wildlife Service lab, labeled and cataloged by site. Hatching rates varied from site to site.
Similar enzymes are present in birds, mammals and fish.
Thomas wondered if dioxin concentrations detected in eggs were inducing or elevating CYP450 levels in Columbia and Willamette River heron embryos. While other studies have shown a relationship, her findings did not. A laboratory working on contract performed chemical analyses on the other half of the egg collection. OCs are pesticides. PCBs are compounds found in electric transformers, some plastics, lubricants and flame retardants.