Clean Water Advocacy - Newsroom - AMSA in the News
No. 180
Tuesday, September 17, 2002 Page A-8
ISSN 1521-9402
News
Water Pollution
Cities Oppose Numeric Limits for Dioxins In Sludge; Environmental Groups
Disagree
New data from the Environmental Protection Agency demonstrate that numeric
limits for dioxins in treated sewage sludge applied to lands as fertilizer are
not needed in an upcoming final rule, municipal groups said in comments
submitted Sept. 10.
The groups said the data showed declining concentrations of dioxins in treated
sludge.
Environmental advocates disputed that position, calling dioxins "one of the most
toxic substances on Earth" and saying the risks posed by not restricting land
application of sludge are unacceptable. State officials also said numeric limits
were needed to help bolster public confidence in the use of treated sludge as
fertilizer.
The comments were submitted on a "notice of data availability" issued June 12,
which indicated that the average level of dioxins in land-applied sludge was
much lower than a threshold proposed by EPA in 1999 (114 DEN A-1, 6/13/02 ).
The agency proposed in 1999 to limit the land application of sewage sludge if it
contained more than 300 parts per trillion toxic equivalents (TEQ) of dioxins
(242 DEN A-8, 12/17/99). TEQs are an internationally recognized approach to
evaluating the toxicity of dioxins. Dioxins refer to
2,3,7,8-tetrachlorodibenzo-p-dioxin and some 28 dioxin-like compounds known as
congeners.
EPA expects to issue the final rule for sewage sludge usage, known as the Part
503 rule, in late 2003, officials have said. The rule will also contain
monitoring and recordkeeping requirements.
Proposed Limit Too High, Groups Say
The Natural Resources Defense Council said in its comments that the agency is
directed under Section 405 of the Clean Water Act to set minimum standards for
sludge management that "shall be adequate to protect public health and the
environment from any reasonably anticipated adverse effects of each pollutant."
NRDC and other public advocacy groups said the 300 ppt limit was too high and
posed unacceptable risks. Moreover, NRDC said, the agency understated the risks
when it calculated the incremental cancer risk to the highly exposed individual
from exposure to dioxins in land-applied sludge as high as 2.4 cases in 10,000
persons.
The agency based the upper end of its cancer risk on a hypothetical farm family
that consumes half its diet from home-produced crops and animal products raised
on their land to which sludge was applied.
Among other things, NRDC said the agency must also consider other chemicals that
may be present in sewage sludge and assess their risks, especially persistent
bioaccumulative toxics compounds. The agency also did not consider other
pathways by which dioxins may enter the body, NRDC said.
"Various exposure routes are not considered, including dermal exposure,
simultaneous inhalation and breast milk ingestion for infants, and fish
consumption from an on-farm pond," the comments said.
Restrictions Not Needed, Cities Say
Comments from the Association of Metropolitan Sewerage Agencies said recent
surveys both by the association and EPA show that concentrations of dioxins in
biosolids--the term used for sludge that has been treated before it is applied
to fields--"are low and do not present a significant risk to human health and
the environment."
AMSA pointed to EPA's 2001 Dioxin Update Survey, which showed an average or mean
concentration of dioxins in treated sludge of 31.6 ppt, not far from the
association's own survey showing average levels at around 48 ppt. No
quantifiable decrease in risk is seen when biosolids with dioxins concentrations
of 300 ppt are barred from being applied to fields, AMSA said.
"Because the concentrations of dioxins in biosolids are so low (i.e. there are
very few biosolids samples with levels above 100 ppt TEQ), a regulatory limit or
threshold that restricts the application of biosolids with dioxins
concentrations above these levels would have little or no impact on decreasing
the overall risks," the AMSA comments said.
Public Skeptical of Sludge Use
Some state officials said limiting the concentration of dioxins in biosolids
that will be applied to land is necessary to provide more assurance to the
public, which tends to be skeptical of the practice.
Without a standard, it would be legal to apply biosolids with concentrations far
greater than the 300 ppt proposed by EPA in 1999, according to officials with
the New England Interstate Water Pollution Control Commission.
"In the eyes of the public, this represents an unacceptable risk to public
health and the environment," the commission said.
Comments from the Rhode Island Department of Health agreed that the limits
should be set and questioned whether the 300 ppt concentration would be
protective enough, given that other contaminants could be present that combined
with the dioxins could increase the risk of exposure to land applied biosolids.
"By not considering risks contributed by other constituents present in sludge or
setting the limit at a more protective risk level, the potential exists for
cumulative risks to exceed the acceptable risk range," Rhode Island officials
said.
The officials also questioned EPA's methodology in its approach to assessing the
risk of biosolids applied as fertilizer.
Probabilistic Approach
For one thing, using a probabilistic approach and a range of national data make
it difficult to ascertain the relevancy of a 300 ppt concentration at the local
level where environmental factors may vary, Rhode Island officials said.
Municipal groups said the probabilistic approach, as opposed to a deterministic
approach, was better. A deterministic approach involves plugging single point
values into a model, instead of carrying over data to actual distribution inputs
over a range of values such as occurs with the probabilistic approach, EPA
officials have said.
The Chlorine Chemistry Council, an industry group representing manufacturers and
users of chlorine, said EPA was too conservative in its position on the
potential cancer risk of individuals exposed to dioxin. The council said EPA
should incorporate in its notice of data availability "the world-wide
convergence" on an acceptable dioxin exposure of 1 to 4 picograms per kilograms
per day (pg/kg/day) and "fully consider the impact of dramatically decreasing
emissions and exposures to dioxin on the need for regulating biosolids."
The agency relies on a "linear default model" that the council said does not
accurately estimate the cancer risk. The council cited comments by the Agency
for Toxic Substances and Disease Registry on EPA's draft dioxin reassessment
released this summer, in supporting its views on setting numeric limits for
land-applied sludge.
"ATSDR observed that EPA's dioxin reassessment 'may place too much confidence in
the ability to accurately predict cancer risks at low doses. This approach
dramatically increases cancer risk estimates that are not based on compelling
new data but rather on the application of statistical models ... [that] are not
yet fully validated,' " the comments said.
Methodology Supported
The Northwest Biosolids Management Association, a consortium of publicly owned
treatment works and private companies in several Northwestern states and British
Columbia, was supportive of the agency's findings and methodology.
"We commend the agency for conducting a screening ecological risk analysis to
assess potential adverse impacts the 29 dioxin congeners would have on mammal
and bird receptors, particularly with respect to the effect land-applied
biosolids activities would have where solids are topically distributed over
pasture," the NBMA comments said. "Screening results strongly suggest biosolids
land-application actions will not adversely impact targeted wildlife species
considered."
Lynn Willet, professor and toxicologist in the Department of Animal Sciences at
Ohio State University, said the proposed 300 ppt limit for dioxins in sewage
sludge is too high.
"My concern is not of risk of toxic or carcinogenic responses to humans that
consume animal products but the potential concern for actionable residues
occurring particularly in milk and meat products," Willet said, adding that she
would recommend a dioxin level for land-applied biosolids of 10 ppt.
Background Soil Concentrations
Willet added that background soil concentrations of dioxins, when factored in
with dioxins that could be added through the land application of sludge, could
result in total concentrations that exceed tolerances adopted by the European
Union in 2001 for dioxins and dioxin-like compounds in food products of animal
origin.
The EU concentrations range from 1 ppt to 6 ppt, depending on the product,
Willet said. No concentrations have been adopted in the United States, she said.
"If standards similar to those adopted in Europe are imposed in the United
States, it will be imperative that 'background' exposure to livestock forage
feeds be reduced from those that already exist in many sections of the country,"
Willet said.
"Sewage sludge that contains between 10 and 300 ppt would significantly increase
exposure to forage crops and increase the probability that livestock and
livestock products would be excluded from commerce," she said.
AMSA said that if the agency decides to adopt numeric limits, it should also
require that publicly owned treatment works establish baseline dioxin
concentrations. If the baseline level is lower than the limit adopted by the
federal government, the POTW should have to monitor for dioxin concentrations
every five years, AMSA said.
If the baseline levels exceed what EPA adopts, AMSA recommended a two-step
approach. The first would involve more testing to confirm elevated levels and
then to determine the source. If the source of the higher dioxin levels cannot
be identified and concentrations controlled, AMSA said POTWs then should not be
allowed to apply biosolids to land.
By Susan Bruninga