- Comments to US EPA regarding
- Dioxin Standards
for Land Applied Sewage Sludges
March 27, 2000
Comment Clerk, Water Docket MC-4101
Environmental Protection Agency
401 M Street SW, Washington, DC 20460
Re: Part 503 Sewage Sludge or Disposal Rule
Docket Number W-99-18
- Please contact Ellen Harrison, EZH1@cornell.edu,
607 255-8576, 100 Rice Hall, Ithaca, NY 14853 with any questions
- Submitted by the following Cornell
- Ellen Z Harrison, Director, Cornell Waste Management Institute,
Center for the Environment
- Murray McBride,
Professor, Department of Crop and Soil Science
James Gillett, Professor, Department of Natural Resources,
Lois Levitan, Program Leader, Environmental Risk Analysis
Program, Center for the Environment
Anthony Hay, Assistant Professor of Microbiology and Soil
Ecotoxicology, Department of Microbiology
Peter Woodbury, Senior Research Specialist, Boyce Thompson
Institute for Plant Research
David Bouldin, Professor Emeritus, Department of Crop
and Soil Science
- Table of contents:
Cancer is Not Most Sensitive End Point
if 10-5 Risk is Used
A wide range of non-cancer
effects are found (Brouwer, et al., 1998).
Non-cancer endpoints, especially developmental impacts through
fetal and nursing infant exposures, are more sensitive end points
than cancer where less than one-in-a-million cancer risk is used
as cancer end point (data in US Dept. of Health and Human Services,
ATSDR, 1998; WHO, 1998; Dr. Henry Anderson, Wisconsin Department
of Health and Social Services, personal communication).
- The immune system is a sensitive target
for toxicity (US Dept. of Health and Human Services, ATSDR, 1998).
- Developmental behavioral impacts were
found at a does of 0.12 ppt/kg bw/day in rhesus monkeys and developmental
effects are found to be among the most sensitive LOAEL in animals
leading to a chronic oral MRL based on these effects (US Dept.
of Health and Human Services, ATSDR, 1998).
to Wildlife and Soil Organisms Not Assessed
Shrews may be at risk from
TCDD and TCDF in land applied paper mill sludges (USEPA/Abt Assoc.
- Wildlife ingest significant quantities
of soil (17% of diet for nine banded armadillo, 10% for woodcock,
9% wild turkey) (Beyer, et al, 1994) Whether this represents
a risk due to sludge application is not clear.
- Risks to predators including raptors
higher on the food chain need to be assessed.
Protective of Farm Family
A dairy farm family in New
York that uses sludge may well obtain all or nearly all of its
meat and milk from animals exposed to sludge-amended pastures
and forages. Since these are the primary dietary sources of dioxins
and since diet is the primary non-occupational exposure route,
this is a critical issue for the farm family. The RA does not
take this potentially high level of exposure for the farm family
into consideration. Using a point value of 10% beef from sludged
sources is not protective of the family which raises its own
meat and milk.
- The farm family may also eat poultry
and eggs from birds which free-range on sludged lands. They are
also likely to inhale air that contains constituents volatilized
from sludge and may drink water that has received sludge-leached
inputs. Their diet may include vegetables grown on sludge-amended
soils. Thus analysis of simultaneous exposure to multiple pathways
- Land grant colleges and farm advisors
must be aware of the risks to farm families since they advise
- A revised risk assessment based on
farm family health including prenatal and nursing exposure to
infants of mothers residing on dairy farms is needed in which
higher values are used for the percent of diet from sludged sources
as well as simultaneous exposure from multiple pathways.
Protective of Children
Current levels of exposure
to nursing infants exceeds the 4 pg TEQ/kg level TDI recommended
by WHO (WHO, 1998) for nearly the entire population in Canada
(Hoover, 1999) and we would expect similar results for
infants in the US.
- Average daily intake of breast-fed
infants on a body weight basis may be almost 1-2 orders of magnitude
greater than that of an adult (WHO, 1998).
- Sensitivity to toxicity of CDDs may
be greater during the fetal/neonatal period than for adults and
may have an impact on male reproductive system development (US
Dept. of Health and Human Services, ATSDR, 1998).
- Cognitive functioning in preschool
children is negatively impacted by in utero exposure to PCBs
and dioxins (Patandin, et al, 1999).
- Birth weight and postnatal growth until
3 months of age were impacted by in utero exposure to PCBs and
dioxins (Patandin, et al, 1998). Immune suppresive and delayed
reproductive effects are also a concern.
- A probabilistic risk evaluation of
organochlorine exposure through breast milk showed that for a
significant percentage of the population, PCBs and PCDD/PCDFs
provide the greatest concern for non-cancer health effects from
chemicals in breast milk (Hoover, 1999).
Animal Ingestion of Sludge
The pathways for animals
ingesting forage and for animals ingesting soil need to be summed
since a farmer using sludge would likely use it on pasture and
on field crops. The amount of sludge ingested due not to uptake
or soil ingestion but to ingestion of sludge adhering to plants
needs to be included in the assessment.
- The assumptions for amount of soil
ingested by grazing animals result in a low estimated soil intake
based on best management practices (1.5% of diet is value used
in RA). Grazing cattle ingest from 1-18% of their dry matter
intake as soils and sheep may ingest as much as 30% depending
upon management and the seasonal supply of grass (Fries, 1996;
Thornton and Abrahams, 1983). Other researchers use higher estimates
such as 6% of diet as soil and point out the critical importance
of assessing the amount of sludge ingested through material adhering
to vegetation and the lack of data on appropriate values
for that variable (Wild, et al, 1994). Use of a probabilistic
method for risk assessment would allow a more realistic range
of values to be used for these key parameters.
- Sludge applied to pastures is generally
not incorporated into soils yet the risk assessment appears to
assume that the sludge is tilled into the soil. This would have
a significant bearing on the concentration of sludge-borne contaminants
- The RA appears to assume zero dioxin
ingestion by animals in yrs 2 and 3 when no sludge is assumed
to be applied. It is not reasonable to assume that levels fall
to zero in pasture and that there is no residual in the years
- Free range poultry eat soil and would
bioaccumulate dioxins. Geese were found to consume 8% of their
diet as soil and wild turkey 9% (Beyer, et al, 1994). Free range
poultry might exhibit similar behavior. Chickens accumulate dioxins
animals foraging on soils containing low ppt PCDD/PCDF
levels may bioaccumulate these compounds to unacceptable levels
(Stephens et al, 1995). The risks to those consuming poultry
should be assessed.
The rationale for exempting
POTWs generating less than 1 MGD from testing is flawed. While
the total quantity of sludge these plants contribute may be low,
there is no reason to believe that the levels of dioxins in these
sludges would be low. (This is an issue that could be investigated.)
Since any particular farm may repeatedly apply sludge from a
single POTW, the farm family, the particular land and ground
and surface waters which flow from that land, and the meat and
milk produced from that land could be contaminated at levels
presenting a significant risk to those exposed. While the total
number of people exposed will be limited due to low sludge volumes,
the risk to those exposed, which may be substantially higher
than presumed in this rationale, will not be known if no testing
is done and that risk may be high. This is another example of
how the sludge rules rely on concepts of "average"
exposure which are not appropriate to protection of potentially
highly exposed individuals.
- The concept that monitoring frequency
be reduced if low concentrations of dioxins (less than 10% of
standard) are detected in sludge monitoring conducted in the
first two years has merit. We have reservations, however, about
the adequacy of the current level of knowledge regarding fluctuations
in dioxin concentrations from a particular POTW from sample to
sample and in knowledge about trends over time on which this
concept is based. The data were not presented in the EPA documentation
regarding the proposed rule. We believe that the amount of data
is very sparse and does not allow the stated conclusions to be
drawn. We would suggest that POTWs be required to collect data
for 3 years and that an analysis then be performed on those data
to assess the validity of the assumptions that there is little
fluctuation and that levels are decreasing.
A WHO panel recently completed
reevaluation of PCB/PCDD/PCDF and determined that existing background
exposures may be causing subtle effects at current intake levels
of 2-6 pg TEQ/kg bw/day (WHO, 1998). Thus current exposure from
background sources in an industrialized country like the US may
already put us at risk.
- This RA does not assume any background
exposure and is only an assessment of incremental exposure from
A revised risk assessment
using probabilistic methods which incorporates the various suggestions
in these comments and which then calculates a daily intake that
includes background intake from non-sludge sources is needed.
- Realistic data and scenarios incorporating
the variability and uncertainty should be used in a multi-media,
multi-exposure probabilistic analysis of rather than persisting
in use of out-dated point estimate risk assessment. EPA itself
recognizes need to represent variability and uncertainty in risk
assessments and the value of probabilistic tools such as Monte
Carlo analysis. (US EPA Office of Research and Development,
National Center for Environmental Assessment (NCEA). May 15,
1997. Policy for Use of Probabilistic Analysis in Risk Assessment
at the US Environmental Protection Agency. 4pp. Available
at: http://www.epa.gov/ncea/mcpolicy.htm. ;US EPA Risk Assessment
Forum. March 1997. Guiding Principles for Monte Carlo Analysis.
EPA/630/R-97/001. 35pp. http://www.epa.gov/oppefed1/ecorisk/backgrn.htm
links to a down-loadable PDF file; Report of the Workshop on
Selecting Input Distributions For Probabilistic Assessments.
EPA/630/R-98/004. January 1999. National Center for Environmental
- Using probabilistic methods to analyze
impact of breast-feeding, Hoover showed that fat content in breast
milk is a key variable. If an inappropriate single point value
was used, results are skewed. (Hoover, 1999).
- Uncertainty is great regarding dioxin
toxicity due to very different responses of different species.
- There are inadequate data on impacts
on humans during fetal development and infancy (Hoover, 1999)
(also inadequate data on wildlife for these same developmental
impacts). Milk, a food in which bioaccumulated dioxins are shed
and thus present in significant quantities is a primary food
for infants and children. Over 95% bioavailability of most PCB,
dioxin and furans from breast milk has been reported. (McLachlan,
1993; Hoover, 1999).
- Most standards are developed based
on adult models. Some research has tried to improve on this by
incorporating pharmacokinetic adjustments for infants. "The
breast-fed infant's intake of organochlorines has been found
in general to exceed guidance values, raising the possibility
that breast-feeding may pose health risks" (Hoover, 1999,
- Use of different assumptions in the
risk assessment process leads to different standards. Using a
risk assessment process, the state of Wisconsin evaluated dioxin
risks from paper sludge land application and derived a cancer-based
standard of 1.2ppt in soil associated with a one-in-a-million
risk and a value of 0.19ppt where grazing is allowed (Goldring,
1992). If the higher allowable cancer risk accepted by EPA in
the sludge rules of one-in-ten-thousand were used, acceptable
levels based on the Wisconsin assessment would be 19 ppt in soils
where grazing is allowed. Our understanding of the RA is that
30 ppt TEQ in soil might result from the application of sludges
containing 300 ppt under the assumptions used in the RA (Exhibit
3-7). Thus even based on cancer as an endpoint, using the Wisconsin
risk assessment assumptions and methods would result in a lower
standard, making the point that what assumptions are made is
critical to the RA results. As stated above, however, cancer
would not be the sensitive end point where risks greater that
one-in-a-million are accepted.
- Why was the application scenario changed
from Round 1 TDS assumptions? The change in this and in other
parameters such as soil ingestion rates which are changed from
200 to 400 mg/day (and the concomitant change in the assumption
that what is ingested is not straight sludge but a sludge soil
mixture [the concentration of sludge vs. soil is not clear in
the RA and is important]) indicate that risk assessments are
based on many uncertain assumptions which critically alter the
outcomes. A number of the assumptions in the RA need to be more
- Much greater explanation and clarity
is needed regarding the assumptions used in the RA. A critical
example about which we would seek clarification has to do with
how soil concentrations were calculated. The algorithms in the
RA document do not permit the reader to assess the actual assumptions
made and values used. For example it is not clear how the many
fold reduction in concentration from sludge to soil is projected.
Various equations are displayed, but the justification for the
values used are not clear. It is not clear whether soil incorporation
into pasture is assumed, and if so to what depth. It is not clear
what assumption is made regarding residual levels in years between
applications and thus of cumulative soil levels. It is not clear
how much of the dioxins is projected to leach, volatilize and
degrade. It is not clear why 95th percentile was used for dairy
fat consumption and mean was used for beef and lamb fat (Exhibit
3-12). What is the assumed proportion of sludge in the sludge/soil
mixture used to calculate risks to children ingesting soil?
- Soil concentrations resulting from
application are a key variable. In fact soil concentration should
be the regulated end point. The large reduction in concentration
predicted in the risk assessment do not seem warranted nor do
they seem to agree with the projections in the USEPA/Abt Associates
document on risks to terrestrial wildlife from papermill sludges
(USEPA/Abt Associates, 1994). Various studies show little or
no loss of dioxins from soils (Orazio, et al. 1992; Hagenmaier,
et al., 1992 b). Half-life in soil is a critical parameter and
for TCDD estimates vary widely and are also very dependent on
whether the material is in the surface soil or subsurface (estimates
from 9 to 100 years in US Dept. of Health and Human Services,
- No information is included on potential
transformation to other toxic products.
- TEFs are continuing to evolve, so their
use is important but a source of uncertainty. The recent WHO
consultation reevaluted them and recommends revisions that would
result in an approximate 10% increase in TEQ calculations compared
to using I-TEFs (WHO, 1998).
- In regard to the groundwater pathway,
the role of facilitated transport of dioxins bound to organic
matter needs to be investigated. Sorption onto organic matter
may give rise to the facilitated transport of these compounds
into ground water (Nelson, et al 1998). This is a particular
concern as complexation of hydrophobic chemicals with organic
matter can also inhibit the ability of microorganisms to degrade
these compounds even though they may still be available and therefore
toxic to higher organisms (Rinella, 1993 #4).
- There is a need to assess multiple
simultaneous pathways for people ingesting soil, meat, dairy,
vegetables, inhalation, drinking water.
- Polybrominated biphenyls and dioxins
seem to pose similar risks to dioxins and PCBs (Hornung et al,
1996; Helleday, et al, 1999, Weber and Greim, 1997; Henck, et
al, 1994). They appear to be carcinogenic (Hoque, et al, 1998;
Henderson, et al, 1995). They are detected in sludges (Hagenmaier,
et al., 1992a). If they act in similar toxicologic or oncogenic
mode to dioxins, they need to be factored into the risk assessment.
- Many of the risk assessment assumptions
questioned in our analysis of Round 1 (Harrison, et al 1999)
also pertain to this assessment. For example, very low percent
of watershed assumed to receive sludge (0.006%); relatively high
cancer risk accepted; single point estimate of dietary intake
not appropriate for the range of consumption patterns. The revised
risk assessment should use a distribution rather than point estimates
for such highly variable inputs.
- Bioavailability is uncertain. While
dioxins in breast-milk are very bioavailable, the potential for
sludges to reduce bioavailability and the persistence of such
an effect need to be assessed.
A WHO panel recently completed
reevaluation of PCB/PCDD/PCDF and determined that: 1) a revised
TDI of 1 to 4 pg/km body weight is established with 4 considered
a maximum for long-term exposure on a provisional basis and 1
as a goal; 2) existing background exposures may be causing subtle
effects at current intake levels of 2-6 pg TEQ/kg bw/day; 3)
efforts should be made to limit environmental releases to the
extent feasible. (WHO, 1998; Brouwer, et al 1998). Thus in an
industrialized country like the US, current exposure from background
sources in an industrialized country like the US may already
put us at risk of unknown nature and extent.
- Schecter and Olson (1997) calculate
that current dietary exposure to PCDDs and PCDFs results in approximately
30-300 excess cancers per million pop and this does not
include dioxin-like chemicals such as PCBs which might further
increase the risk.
- These standards do nothing to move
towards the goal of minimizing exposure since more than 95% of
US sludges tested fall within the proposed standards (Exhibit
3-1). The RA should include a more complete description of the
distribution and pattern of dioxin levels in US sludges with
a goal of better understanding sources exposure routes, relation
to POTW processes, and especially how to reduce levels in sludges.
It would appear to be incumbent on the regulated industries and
regulatory community to move quickly to reduce the specific uncertainties
of exposure and response in a way which expedites risk management
of those sludges which may evoke adverse effects in non-cancer
areas (learning, endocrine development, immune function) in particular
segments of society and parts of potentially impacted ecosystems.
- Given many of the uncertainties and
concerns raised, it would be prudent to establish rules for exposure
to dioxins that minimize exposure from land application. The
current proposal not only does not accomplish that, but also
offers no incentive for reaching a better understanding of critical
processes, such as features of sludge and its uses which enhance
or reduce bioavailability. Consideration should be given not
only to setting a lower standard, but also to restricting uses
in order to minimize exposure. Since meat and milk are the primary
routes of significant exposure, consideration should be given
to restricting use of sludges with more than very minimal dioxin
levels on land used for grazing or growing forage crops.
EPA needs to continue to
examine the sludge rules to both consider regulating additional
contaminants and to reassess those already addressed. Additional
contaminants not presently characterized and which are present
at relatively high levels in sludges include surfactants (LAS
and nonylphenol polyethoxylates) (Klopffer, 1996). The degradation
of common nonionic surfactants such as nonylphenol polyethoxylates
in POTWs leads to the accumulation of estrogenic nonylphenols
in anaerobically digested sludge at levels as high as 4000mg/kg
(Bennie, 1999). Although recent evidence suggests that nonylphenols
spiked into uncontaminated sludge are degraded over several months,
a significant portion of the nonylphenols in aged sludges is
recalcitrant to biological transformation (Topp, 2000). In addition
to persistence in the soil, the sorption of nonylphenols onto
organic matter may give rise to the facilitated transport of
these compounds into ground water (Nelson, et al, 1998,). Sludges
were also found to contain potent polyaromatic EROD-induing compounds
not presently being analyzed (Engwall et al, 1999). Poly brominated
biphenyls used as flame retardants in the past need to be monitored
and their risks assessed.
- Changed assumptions in the dioxin RA
from those in the TSD for Round 1 suggest a need to reassess
the ingestion pathway for the round 1 pollutants since ingestion
was limiting pathway for a number of pollutants.
- Animal health risks posed by molybdenum
are of critical concern particularly in states like NY where
dairy is the major agricultural enterprise. Research in progress
at Cornell suggests that even single applications of sludges
can result in uptake of molybdenum into leguminous forages that
may present a significant risk to ruminant herd health. Standards
are needed to address this issue.
- As recommended by the National Research
Council, a new survey of sludge quality is needed with improved
analytic methods and additional parameters.
- There is a need for additional sludge
research to address outstanding questions. A separate list of
research needs follows:
Needs Pertaining to Land Application of Sewage Sludges
- These are some areas in which additional
research is needed. It is important to recognize that different
soils, crops, sludges and sludge products will respond differently
so that research results will vary depending on these and other
variables. Research should be supported through an entity that
is independent of the sludge stakeholders.
Quality and Variability
- - Survey US sludges for additional
contaminants (such as surfactants) and using improved analytic
methods (as recommended by National Research Council)
- Analyze the temporal variability of quality and nutrient content
of sludges from individual WWTPs. Quality varies significantly
from sample to sample. Farmers and their advisors apply based
on monitoring results not obtained from the particular sludge
load being delivered and may thus over or under apply nutrients.
- At what rate does the
N in selected sludges and sludge products become available as
a plant nutrient?
- How variable over time is the N and P content and availability
of N in sludge from particular treatment plants?
- What are the relationships between P availability and sewage
- How much of trace metals
applied in sludges and sludge products leaches through soils?
- What is the role in the movement of contaminants to groundwater
of preferential flow through macropores?
- What is the role in the movement of contaminants to groundwater
of facilitated transport by complexation of contaminants with
- How much nitrogen applied in sludges, fertilizers and manures
leaches through soils?
- Do pathogens applied in sludges leach through soils? Particularly
viruses leaching from Class B sludges.
- What groundwater flow model will predict mobility of contaminants?
Yield and Quality
- What are the yield responses
of sensitive crops (like alfalfa) to sludge applied metals in
long-term applications to acidic agricultural soils?
- What is the concentration of molybdenum and the Cu:Mo ratio
in forage crops and pasture grown on agricultural soils in to
which sludges have been added (both short and long term)? And
what are the implications for dairy farms?
Although nonylphenol based
surfactants have been phased out in Europe they are still widely
used in the United States. A preliminary analysis of sludge from
two upstate New York STPs shows nonylphenols to be present at
concentrations of more than 1000mg/kg. These values can be compared
to the temporary permissible limit of 50mg/kg nonylphenol allowed
in land-applied sewage sludges in Denmark (Cavalli, 1999). At
present there is neither monitoring nor regulation of nonylphenol
concentrations in sludges in the United States. As application
of nonylphenol contaminated sludges is a possible source of ground
and surface water contamination as well as through direct exposure
from soil ingestion, more work is needed to understand the fate
of these compounds in agricultural settings.
- Direct land application is not the
only fate of nonylphenol contaminated sludges however. In New
York state 57% of beneficial biosolids are either composted or
heat dried (Rowland, 1998) before further use. Nonylphenols are
volatile and significant atmospheric concentrations have recently
been detected above STPs and rivers receiving nonylphenol inputs
(Dachs, 1999). To date no work has been reported characterizing
the fate of nonylphenols in high-temperature composting environments
or during heat treatment. However, the elevated temperatures
in these procedures, combined with the volatile nature of nonylphenols
suggest a potential for localized atmospheric contamination during
the treatment of contaminated sludge. More work therefore needs
to be done to assess the fate of nonylphenols during processing
- - At what levels are surfactants and
their metabolites present in sludges and in soils to which sludges
have been applied?
- What is their fate when land applied?
- Are they volatilized during sludge composting and other treatment
- To what chemicals and
pathogens are people exposed from aerosols and volatile emissions
from land applications and sludge processing sites and what are
the health risks associated with those exposures?
- - What
are the sources that are responsible for concentrations of particular
contaminants of concern in sludges?
- What can be done to reduce or eliminate the discharge of those
pollutants into WWTP?
- What analytic methods
will detect and quantify (if necessary) infective viruses and
- What analytic methods are appropriate for monitoring movement
- What analytic methods are appropriate for monitoring soils
contaminants and their bioavailability?
- What is the impact on
soil microbial system of long term sludge additions?
- What is the impact on wildlife exposed to sludge-treated systems?
- What are the likely exposures and impact of those exposures
to the dairy farm family.
- Need to address multiple exposure pathways being experienced
simultaneously (drinking water, breathing air, eating dairy,
meat and vegetables, ingesting soil).
- Need to reassess direct ingestion risk since dioxin risk assessment
uses 400mg/day ingestion rate and TSD used 200mg/day and since
direct ingestion was the most limiting pathway for a number of
the contaminants. Also need to evaluate the potential for acute
toxicity from one-time high ingestion days.
- Need to apply probabilistic vs. deterministic methods of risk
- What other uses might
be made of sludges that would pose fewer risks?
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