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New article on Great Lakes PCDD/PCDF Inputs/accumulation rates
The current (October 1997) issue of Environmental Science and Technology
has an interesting article by Pearson, Swackhamer, Eisenreich and Long
concerning chlorinated dibenzo-dioxin/furan
(PCDD/F) concentrations, accumulations and
inventories in Great Lakes sediments. ES&T 1997, 31, 2903-2909
The article indicates that PCDD/PCDF accumulation rates in sediments
peaked in 1970 ( plus or minus 10 years) and declined to present day
rates which are 30-70% of the maximum rates.
Highest accumulation rates are in Lake Ontario.
The article discusses accumulation rates as to sources by percentage...
.... regional air deposition
.... subregional air deposition (air parcels having higher concentrations
of PCDD/F than "remote air" due to local sources)
.... non-atmospheric inputs
For subregional air deposition and non-atmospheric inputs,
the article indicates that Lake Superior receives of the
order of 0% from these two sources, southern Lake
Michigan receives 20%, northern Lake Michigan
receives 60%, and Lake Ontario receives 90%.....
The authors conclude:
"Atmospheric deposition from suburban air can support
the accumulation of PCDD/F in southern Lake Michigan
but some non-atmospheric sources to northern
Lake Michigan are implicated. Lake Ontario may be
receiving greater than 70% of its current
inputs of PCDD/F from non-atmospheric sources."
Looks like there is still more work to do on
both PCDD/F air discharges and the
potential PCDD/F waste-water discharges, in-place river sediment
contributions and waste-site runoff issues as well.
One criticism of the Pearson article is that no sediment cores
were taken from northeastern Lake Superior, which
would be a location closer to some poorly controlled
bleached kraft pulp mills in that region, and that failure
would understate the non-atmospheric contributions
in that part of Lake Superior..
The same issue of ES&T also has a brief article
about joint US/Canada plans to study PCDD/F
emissions from iron and steel plants; as well as
a technical article on PCDD/F deposition rates
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