Results from second part of contamination study show deadly levels in St. Louis robins
By Malachi Barrett, mbarrett@michigannewspapers.
Posted: 08/21/14, 4:41 PM EDT |
Michigan State University environmental toxicology professor Matt Zwiernik presented part two of the results from the 2013 dead bird collection in St. Louis to the Pine River Superfund Taskforce.
Zwiernik’s team monitored 60 active nests not only in the nine-block residential area surrounding the former Velsicol plant site but also 15 kilometers downstream. As was the case with the first batch of results, American robins eggs collected contained DDx levels far above those found to induce death in laboratory settings.
“Egg DDx levels in the nine-block residential area are some of the highest ever recorded,” Zwiernik said.
Tissue concentration in the residential area ranged from 57 parts-per-million to 770 ppm, averaging 153 ppm. The threshold for death is between 1-40 ppm, depending on the species, meaning even eggs collected with the least concentrations were far above safe levels.
“I can’t find anywhere in the literature where an egg had 770 ppm,” Zwiernik said. “It doesn’t appear to be possible, it is.”
DDx includes DDT, and the breakdown compounds of DDD and DDE.
The nests were monitored twice a week and one or more eggs were taken from 23 of the sixty nests.
The study found that no eggs survived from nests with DDx concentrations greater than 63 ppm. As expected, concentrations were higher in nests closer to the factory site but areas with the highest concentrations were in homes in the floodplain that recently mowed their lawns.
This is because these locations are nest foraging areas. Robins building their nests with contaminated grass exposed their eggs, resulting in hatching success, fledgling success and nest success rates being all significantly lower than species norms in watershed areas.
Results showed 0.5-2.3 ppm concentration of co-planar PBB’s in the residential area and from zero to one ppm downstream. No eggs hatched with concentrations higher than 0.87 ppm.
In the nine-block residential areas, hatching success ranged from 21 percent to 18 percent. Downstream this was between 44 percent to 33 percent.
For comparison, the hatching rate in the Chippewa Nature Park in Sanford ranges from 94 percent to 88 percent.
The study concluded that robins in residential areas are experiencing population adverse effects. In the floodplains, the birds are experiencing adverse effects, but there the sample size downstream was only 36 nests, not a sufficient enough amount to establish a cause.
At the taskforce technical committee meeting, Environmental Protection Agency Project Manager Tom Alcamo said about 200 trees will be removed from 60 properties, including trees in the parkway. Where trees are not removed, hand digging will be done only in the first six inches, regardless of how deep the contamination goes.
Zwiernick said cleaning up all of the contamination was more important in having a healthy ecosystem. He added the cleanup level of 5 ppm may be too high of a concentration in the soil to protect the health of the robins.
Alcamo said more sampling has taken place in the floodplains and expects results next month.
The next meeting is scheduled for.