vanishing ddt page 2 — Environmental Health News

(Continued fromPage 1.) 

Evolution of microbes?

Bay said perhaps there has been an “evolution or adaptation of the microbes” that break down DDT. Maybe something “revved them up” since 2004, after a decades-long lag, he said.

James Tiedje of Michigan State University said these types of chlorine-gobbling microbes “can have logarithmic growth.” The growth of their colonies starts out slowly, then reaches a point of exponential growth that transforms the entire environment.

“Some can grow up over night. There’s a number of examples where microbes in nature grow up and increase their numbers substantially and increase their rate of dechlorination,” said Tiedje, Distinguished Professor of microbiology and director of the university’s Center for Microbial Ecology.

Changes in carbon, for one, can cause an explosion of growth because it provides more food. “If more carbon is breaking down, especially when anaerobic, the microbes reach fatty acids and hydrogen and that’s what the dechlorinators like,” Tiedje said.

“DDTs don’t break down that quickly. I don’t see this as the bacteria all of a sudden eating up all this stuff. It’s a bit of a mystery.” -Steve Bay, Southern California Coastal Water Research Project There has been a major change in the conditions of that part of the ocean floor. Los Angeles County switched to full secondary sewage treatment in late 2002, which greatly reduced the volume of organic substances released into the ocean and increased the oxygen in the system. Tiedje, however, thought that might have the opposite effect, slowing the breakdown of the chlorinated chemicals.

Another possibility – one that alarms some experts – is that the chemicals diffused into the water so they are no longer on the ocean floor.

Gully of the county sanitation agency said that scenario is concerning because it means more fish in a wider area could be contaminated directly through the water, not just through the food web. Any cleanup would be virtually impossible. Water testing, however, has not detected any increase, he said.

Fish and birds are the real indicators

When the area’s bottom-dwelling fish were last tested in 2004, they remained highly contaminated, “and that’s the part people shouldn’t lose sight of," said Gold, who was executive director of the environmental group Heal the Bay before joining UCLA last year.

“Despite the dramatic drop in the sediment, we have not seen similar, commensurate drops in the fish. This recent result should lead to a much greater, more focused look at fish concentrations,” Gold said.

Tiedje said the fish – and consequently the eagles, seabirds and the rest of the food web – may remain contaminated for a long time, since fish are “good scavengers.”

“You have to have these sediments really cleaned up for it to have an effect on the fish,” he said.

Huang said the EPA now plans to do more sediment testing this fall to see what’s happened since 2009.

“We should go out and take another look because of the difference between 2009 and 2004,” she said. One lingering question: If it was 14 tons in 2009, what is it now? “We know it’s declining. It is getting smaller. How much smaller I do not know,” she said.

According to its 2000 plan, the EPA’s goal for capping the site was to “immediately bring” average DDT concentrations to 78 parts per million, down from the 150 ppm found in 2004. But the average is now calculated at 58 ppm. For PCBs, the goal was to reduce it to 7 ppm and the new data show it is now only 0.23 ppm.

“You have to have these sediments really cleaned up for it to have an effect on the fish.” - Jame Tiedje, Michigan State University"We’ve had concerns about capping it from day one,” Gully said. “The risks associated with putting a cap down are not insignificant. If it’s not done well, it can make a bad situation way worse.”

Nevertheless, at EPA, “capping is definitely still under consideration,” Huang said. But she added that other options now must be considered since it is so much smaller. One idea is to find ways to enrich the microbes so they work even faster.

More paralysis by analysis?

Gold worries that the shrinking deposit will lead to more paralysis at EPA. “The inaction of the last decade in a weird way is being rewarded,” he said. “But from my perspective, this project shouldn’t end.”

Sherwood said all eyes will be on the next round of sampling to see if it confirms the huge drop in contamination.

"If it does, there'd be reason to celebrate," he said. "But I'm not popping open the champagne yet."

For another EHN story on contamination off Southern California's coast, click here.

We welcome your feedback. Contact Editor in Chief Marla Cone at mcone@ehn.org

The above work, by Environmental Health News, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Follow us: