Environmental Factor, December 2007, National Institute of Environmental Health Sciences
Superfund Grantee Shares "Lessons from the Wild"
By Eddy Ball
In his work as director of the Superfund Basic Research Program at Duke University, Toxicologist Richard Di Giulio, Ph.D., combines evolutionary theory, ecology, basic biology and toxicology into a research approach he describes as "evolutionary toxicology." During his November 2 Frontiers of Environmental Sciences lecture in Rodbell Auditorium, Di Giulio reported on his lab's investigations into the adaptive phenotype and the resulting fitness costs of a fish species living in a heavily polluted Superfund site on the Elizabeth River in southern Virginia.
Di Giulio's talk was titled "Environmental Health Lessons from the Wild: Studies of Fish Coping with Pollution" and hosted by NIEHS Associate Director of the Office of Risk Assessment Research Chris Portier, Ph.D. At the beginning of his talk, Di Giulio articulated the motivation for his work in the wild. "What goes on in the outside world can give some interesting insights into the mechanisms of toxicity... [and help] inform what you do in the lab," he said.
The 47.5-acre site of his research along the Chesapeake Bay tributary is the location of a former wood-treatment facility, Atlantic Wood Industries, Inc. From 1926 to 1991, when the plant ceased operation, its treated-wood storage and waste disposal practices resulted in elevated concentrations of creosote constituents, known as polycyclic aromatic hydrocarbons (PAHs) in sediments adjacent to the site. The PAHs produce a poisonous soup that causes high rates of liver cancer among the fish there.
Di Giulio and his team focused their research on the PAH-resistant Atlantic killifish, which he described as "the darling of adaptation" and "a great lab model" due to its wide distribution, limited home range, and size and behavior. Gene sequencing of the killifish is also well underway, giving the researchers substantial genetic data.
The team used nearby King's Creek, a pristine tributary of the York River just off the Williamsburg Parkway, as a reference site in their experiments. The researchers bred and interbred fish from both sites to determine the effect of genetics on adaptation to PAHs. They found that resistance to the embryonic anomalies of the cardiovascular system resulting from exposure to sediments was at least partially due to evolutionary adaptation. This resistance carried with it a significant fitness cost - a loss of resilience when exposed as larvae to a very important environmental stressor, oxygen depletion.
"When we started this work," Di Giulio observed, "we really had no idea what toxicity the Elizabeth River fish were avoiding." Because single PAH compounds do not produce the congenital deformities observed in King's Creek fish exposed to the Elizabeth River sediment, the team experimented with several combinations of PAHs to see what if any additive effects a mixture might have. Mixtures containing PAHs that both blocked the CYP1A detoxification enzyme and up-regulated the Aryl Hydrocarbon Receptor-Signaling Pathway produced as much as a three order-of-magnitude increase in toxicity over individual PAHs.
"It's going to be much more difficult to ferret out this connection in rodent models and so forth," Di Giulio conceded. Among the "beauties" of working with the killifish, he noted, "is that we can study the heart [of the living killifish] as it develops," something researchers cannot do as easily with mammals.
In spite of the difficulties involved in establishing biological connections between pollution's effects on fish and people, Di Giulio remains concerned "that the health of systems pervades into the health of humans in very subtle ways" that do not lend themselves as well to experimentation. Di Giulio closed his lecture as the famous words attributed to Chief Seattle appeared behind him on the final slide of the presentation: "All things are connected. Whatever befalls the earth befalls the children of the earth."