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Dioxins in Sludge Will Not Be Regulated Because of Low Cancer Risk, EPA Decides
Concentrations of dioxins in sewage sludge will not be regulated because the
potential risk of new cancer cases from exposure to the contaminant is low, the
Environmental Protection Agency announced Oct. 17.
The agency concluded that only 0.22 new cases of cancer would be expected for
the most exposed individuals over a lifetime, according to Geoffrey Grubbs,
director of science and technology in the EPA Office of Water. This was based on
an analysis that considered the potential exposure to dioxins of a "theoretical
farm family" that consumed meat and vegetables from its own land whose soil had
been "enhanced" by sewage sludge. Grubbs said the agency estimated that about
11,000 people "at the high end" fit the profile of this most-exposed theoretical
family.
The risk to the general population is even lower, with an incremental cancer
rate of about two cases per 100 million people over a lifetime, Grubbs said.
EPA proposed in 1999 to prohibit the land application of sludge with
concentrations of more than 300 parts per trillion toxic equivalents for dioxins
(64 Fed. Reg. 72,045; 242 DEN A-8, 12/17/99).
'Intensive Analysis and Evaluation.'
"After five years of intensive analysis and evaluation, we decided not to
regulate dioxin in sewage sludge applied to land," Grubbs told reporters. "The
reason is basically that the risk of new cancer cases is substantially smaller
than for the other chemicals we regulate."
Section 405 of the Clean Water Act directs EPA to assess the potential risks of
pollutants contained in sewage sludge and develop management standards. The
first round of regulations (40 CFR 503) were set in 1993 and addressed metals,
certain organics, and other pollutants for which the agency had adequate
information. The second round of regulations called on the agency to look at
other pollutants including dioxins.
The Oct. 17 final decision addresses dioxins and dioxin-like compounds including
seven polychlorinated dibenzo-p-dioxins, 10 polychlorinated dibenzofurans, and
12 dioxin-like coplanar polychlorinated biphenyls.
EPA's analysis was based on a peer-reviewed model that considered different
pathways for dioxin exposure, including inhalation.
Outrage From Environmental Groups
Environmental groups expressed outrage at the decision, saying dioxins are some
of the most potent carcinogens and that land-applied sludge is the second
leading source of the contaminant after backyard barrel burning, common in some
rural areas.
"Dioxins cause cancer and diabetes, as well as nervous system and hormonal
problems," Nancy Stoner, director of the Natural Resource Defense Council's
Clean Water Project, said. "EPA is required by law to protect the public from
toxic pollutants like dioxins. This decision shows the agency under this
administration has forgotten its mission."
Grubbs said EPA first began to study dioxins in sewage sludge in 1988 with a
review of about 188 sewage treatment plants. At the time, the data showed that
median concentrations of dioxins in sewage sludge was about 50 parts per
trillion, he said. This data was updated in EPA's 2001 Dioxin Update Survey,
which showed an average or mean concentration of dioxins in treated sludge of
31.6 ppt.
The Association of Metropolitan Sewerage Agencies, which represents the largest
wastewater treatment plants, issued its own 2000/2001 Survey of Dioxin-like
Compounds in Biosolids: A Statistical Analysis, showing average levels at around
48 ppt toxic equivalent or TEQ. The AMSA survey showed the median concentration
was 21.7 ppt-TEQ. The 200 samples showed a range of concentrations from 7.1
ppt-TEQ to 256 ppt-TEQ. One sample came in at about 3,590 ppt, the survey said.
Dioxins Down 90 Percent
Grubbs said dioxins in the environment have declined dramatically--about 90
percent--since the late 1980s largely because of EPA's regulatory efforts. For
example, the agency issued maximum achievable control technology standards under
the Clean Air Act for hazardous waste incinerators in 1999 that were expected to
cut dioxins emissions by about 70 percent. Another rule was published under the
Resource Conservation and Recovery Act to control cement kiln dust, also a
source of dioxins, Grubbs said.
Large municipal waste combustors reduced emissions of dioxins and furans by
about 99 percent because of MACT standards issued in 1995, EPA said in a June
2002 memo (122 DEN A-3, 6/25/02).
"The broad subject of dioxins is something the agency has been concerned about
for a long time," Grubbs said.
NRDC said that while the amount of dioxins in sewage sludge seems to have been
decreasing over time, its presence in the food supply has been relatively
constant because it has accumulated in the soil and in animal and human fat.
Moreover, the agency should also consider the non-cancer risks associated with
exposure to sludge with dioxins in it.
"The EPA itself has said the non-cancer risks of dioxins are so high that it
can't even calculate a 'safe' or acceptable level of exposure," Stoner said. "To
us that says EPA should keep dioxins out of our food, and that means, among
other things, regulating sewage sludge."
Grubbs said the agency considered "other possible effects" but that no
peer-reviewed methodology exists for quantifying the "non-cancer risks for this
set of contaminants."