Clean Water Advocacy - Newsroom - AMSA in the News
No. 114
Thursday, June 13, 2002 Page A-1
ISSN 1521-9402
News
Water Pollution
Average Dioxin Concentrations in Sludge Lower Than Limit EPA Proposed in 1999
New data from an Environmental Protection Agency survey on the concentrations
of dioxins in sewage sludge show the average levels to be much lower than a
threshold proposed in 1999, a notice of data availability published June 12 said
(67 Fed. Reg. 40,554).
The 1999 proposed rule would have limited the land application of sewage sludge
if it contained more than 300 parts per trillion toxic equivalents (TEQ) of
dioxins (64 Fed. Reg. 72,045; 242 DEN A-8, 12/17/99). TEQs are an
internationally recognized approach to evaluating the toxicity of dioxins.
EPA published a notice of data availability in the June 12 Federal Register with
new information it has obtained regarding the levels of dioxins in sewage sludge
and has revised an assessment of risks associated with the land application of
sludge.
A final rule governing the land application of sewage sludge was to have been
published April 1 but was delayed until late 2003 to give the agency and the
public time to consider the new data (63 DEN A-5, 4/1/02 ).
Smaller POTWs
The proposal would have excluded publicly owned treatment works that have a flow
rate of less than 1 million gallons per day from the 300 ppt limit and from
certain monitoring requirements.
Data from EPA's 2001 dioxin update survey showed "very small differences in the
median dioxin concentrations between small and large POTWs," which are those
with flows exceeding 1 million gallons per day. However, at the upper
percentiles, the differences were substantial between the large and small
facilities, EPA said.
The agency seeks comment on the significance of the differences of dioxin
concentrations in sludge from facilities with flow rates of less than 1 million
gallons per day and those with higher flows.
The values EPA obtained for facilities in the upper percentiles of the survey
were lower than those found in a similar survey conducted in 1988, the agency
said.
"On this basis, the concentration of dioxins in sewage sludge appears to have
declined since 1988," the notice said. The agency said it was uncertain about
the significance of this difference because of changes in the sampling
procedures and analytic methodology and asked for comment.
Nevertheless, the agency said the new data support its proposal to exclude from
the 300 ppt limit those POTWs with flow rates of less than 1 million gallons per
day. The highest observed level of dioxins from these smaller POTWs was 78.6 ppt
TEQ. This compares with the highest observed level of 718 ppt TEQ from
facilities with flows of greater than 1 million gallons per day.
AMSA Data
The notice also discusses survey data collected by the Association of
Metropolitan Sewerage Agencies in 2000 and 2001. The study showed that the mean
concentration of dioxins in biosolids, the term used for sludge that is treated
before it is applied to land, is much lower than a threshold level proposed by
EPA in 1999. That survey looked at information from 171 mostly large POTWs and
found the median concentration of dioxins and dioxin-like compounds was 21.7
ppt-TEQ with a range of concentrations from 7.1 ppt-TEQ to 256 ppt-TEQ (229 DEN
A-3, 11/30/01) .
EPA said it found AMSA's data to be "useful in describing dioxins in sewage
sludge from larger POTWs" and that the data tend to "corroborate the results"
from EPA's 2001 survey.
The AMSA data were not used to establish a national average of dioxins in sewage
sludge or to estimate risks of land-applied sludge because the facilities from
which the information came were not randomly selected, EPA said.
EPA is also in the process of revising a risk assessment used in the 1999
proposed rule, which focuses on cancer in humans. The notice discussed EPA's
draft Dioxin Reassessment, which has been in the works since 1991. Since the
draft reassessment is still preliminary, the agency said the cancer slope in it
is not used in the revised risk assessment.
However, the notice contains a discussion on how the draft reassessment "could
apply to the analysis of impacts of dioxins in land-applied sewage sludge,
including the revised cancer slope," EPA said. The agency said it seeks comment
on the implications of the information in the draft reassessment in the event
that policies in it become final before EPA issues the final rule on the land
application of sewage sludge.
Revised Scenario
The revised risk assessment discussed in the notice changed the scenario for
exposure to sewage sludge. It looked at a farm family that consumes half its
diet from home-produced crops and animal products raised on their land to which
sludge was applied. The agency seeks comment on the use of this scenario.
Among other things, calculations estimate the impact on the risk if sludge with
300 ppt TEQ dioxin and 100 ppt TEQ dioxin were restricted from being land
applied, EPA said. Eliminating the samples with higher concentrations of dioxins
did not change the estimated risk, EPA said.
"No quantifiable decrease in risk is calculated if sewage sludge with greater
than 300 ppt TEQ dioxins or greater than 100 ppt TEQ dioxins were restricted
from being land applied," EPA said in the notice.
The reason for this finding, the agency said, is that "there is so little sewage
sludge that contains dioxin at or above these concentrations."
EPA estimated the annual cost to implement the sludge rule would be about $4.5
million instead of the $18 million estimated in the 1999 proposal. The lower
cost results from the smaller percentage of sewage sludge that exceeds the 300
ppt TEQ limit based on the 2001 survey data.
"The estimated benefit of a 300 ppt limit would be very low, since such a limit
would not likely produce a detectable change in lifetime cancer, even to highly
exposed farm families and using conservative assumptions," EPA said.
Comments on the notice are due Sept. 10 and should be sent to W-99-18 NODA
Comment Clerk, Water Docket (MC-4101), EPA, 1200 Pennsylvania Ave. N.W.,
Washington, D.C. 20460. Comments can also be sent electronically to OW-Docket@epamail.epa.gov.
More information is available from Arleen Plunkett, EPA, Office of Water, Health
and Ecological Division at (202) 566-1119.
By Susan Bruninga