RISK ASSESSMENT FOR ORGANIC MICROPOLLUTANTS:
U.S. POINT OF VIEW
By
R.L. Chaney, Soil-Microbial Systems Laboratory,
USDA-Agricultural Research Service, Beltsville, MD;
J.A. Ryan, Risk Reduction Engineering Laboratory, U.S.
Environmental Protection Agency, Cincinnati, OH; and G.A.
O'Connor, Department of Soil Science, University of Florida,
Gainesville, FL
Presented at and to be published in the proceedings from the EEC
Symposium on the Treatment and Use of Sewage Sludge and Liquid
Agricultural Wastes (Athens, September 1990).
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268

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To be published in Proc. EEC Symp. Treatment and Use of Sewage Sludge and
Liquid Agricultural Wastes (Athens, Sept. 1990). In press.
RISK ASSESSMENT FOR ORGANIC MICROPOLLUTANTS: U.S. POINT OF VIEW.
R.L. CHANEY1, J.A. RYAN2, and G.A. O'CONNOR3
1Soi1-Microbial Systems Laboratory, USDA-Agricultural Research Service,
Beltsville, MD, USA; 2Risk Reduction Engineering Laboratory, US-
Environmental Protection Agency, Cincinnati, OH, USA; and Department of
Soil Science, University of Florida, Gainesville, FL, USA.
Summary
Basic research and monitoring of sludge utilization programs
have identified specific Pathways by which potentially toxic
constituents of sewage sludge can reach and cause toxicity to
livestock, humans, plants, soil biota, wildlife, etc. In the
process of preparing a new regulation for land application of
sewage sludge in the US, a Pathway approach to risk assessment was
undertaken. Two Pathways were found to comprise the greatest risk
from persistent lipophilic organic compounds such as PCBs: 1)
direct ingestion of sludge by children; and 2) adherence of sludge
to forage/pasture crops from surface application of fluid sludge,
followed by grazing and ingestion of sludge by livestock used as
human food. Each Pathway considers risk to Most Exposed
Individuals (MEIs) who have high exposure to sludge. Because 1990
sewage sludges contain very low levels of PCBs, the estimated risk
level to MEIs was «10"4; low sludge PCBs and low probability of
simultaneously meeting all the constraints of the MEI indicate that
MEIs are at <10"7 lifetime risk. We conclude that quantitative
risk assessment for potentially toxic constituents in sewage sludge
can be meaningfully conducted because research has provided
transfer coefficients from sludges and sludge-amended soils to
plants and animals needed for many organic compounds.
1. INTRODUCTION
U.S. approaches to sludge regulations have changed over the years as
scientific information about the fate and effects of potentially toxic
constituents has become more complete. Until the 1970s sludge was
regulated only as a source of infection or as a public nuisance due to
odors. Then, a program of constructing sewage treatment works which would
increase sludge production led to consideration of how sludge could be
handled safely. Research began to evaluate risks from toxic constituents
of sludge in different "ultimate disposal" environments (agricultural land,
incinerators, landfills, ocean). In 1979, the United States Environmental
Protection Agency (34) published a draft regulation on land application and
landfill disposal of sludge for public comment.
The 1970s were a period of intense research on land application of
sewage sludge. One of the most important areas of risk from sludge
utilization/disposal identified was from sludges sold or given to
individual citizens (Distributed or Marketed, D&M) without controls. Many
Publicly Owned Treatment Works (POTWs) dried sludge on sand beds during
part of the year, and dried sludge was often given to anyone who would take
it. As in Europe, research found examples of highly polluted sludges (Cd,
PCBs, etc.) being given away for use on lawns, gardens, and farms (5, 10,
24, 25). This information dramatized the need for regulation of sludge use
in situations other than farmland; either the practice should be controlled
or prohibited (14). In 1980, US-EPA started efforts to regulate D&M and to

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finalize the 1979 proposed regulations, but this effort was never
completed.
While reauthorizing the Clean Water Act in the mid-1980's, Congress
decided that further sludge regulations were needed, partly because the
first rule dealt with only a few pollutants, and partly because sludge D&M
had not been regulated and still continued in many cities. At the same
time, other Congressional and US-EPA actions have improved industrial
pretreatment regulations for many industries which discharged unwanted
pollutants to the sewers. Protection of the quality of sludge was judged
to be a valid reason to require pretreatment; if public acceptance of
sludge application, or meeting state regulations on sludge utilization
required better industrial pretreatment, states and cities now had the
power to protect sludge quality. Based on the recent National Sewage
Sludge Survey (39), sludge utilization in agriculture has increased since
1980 (Table 1), and concentrations of contaminants in most sludges are much
lower than found in previous surveys (Table 2). This survey (39) found
many "not detected", partly because solids content in sludge samples was
not considered in taking wet sludge sample weights. For those samples with
many "non detected" sludges, the Maximum Likelihood Estimation procedure
was used to provide a reasonable estimation of the geometric distribution
of a constituent in dry sludges.
Table 1. Methods of utilization and disposal of sewage sludge in the United States based on the
National Sewage Sludge Survey (39) of 479 POTWs in 1988-1989, and 208 POTWs in Analytical
Survey.
Information Survey Analytical Survey	Estimated US
US-EPA, 1989 (39) US-EPA. 1989 (39)	Distribution
Use/Disposal Method # POTWs Fraction # POTWs Fraction # POTWs Fraction


%

%

%
Land Application
161
33.61
78
37.50
3542
31.05
Distribution&Marketing
27
5.64
10
4.81
308
2.70
Municipal Landfills
76
15.87
51
14.90
1851
16.23
Monofills
28
5.85
6
2.88
203
1.78
Surface (e.g. lagoons)
59
12.32
13
6.25
3147
27.59
Incineration
63
13.15
23
11.06
294
2.58
Ocean
21
4.38
6
2.88
115
1.01
Other
24
5.01
25
12.02
1526
13.38

459
95.83




During the 1980s, it became clear that addition of equal amounts of a
pollutant in sludge or as a pure chemical caused different effects. Sludge
was found to add specific adsorption capacity for metals and organics to
the sludge-soil mixture (15). In the case of sludge metals, the plateau
response of plant metal concentrations to increasing application rates of a
sludge (13, 15) showed that the concentration of a pollutant in sludge did
affect potential for risk. Previously it had been believed that all
sludges had equal effect at equal cumulative applied amounts of a
constituent, and that limiting the cumulative amount of metals or organics
was the proper form of regulations. With this new information that the
concentration of a constituent in a sludge could strongly affect the
potential transfer to plants or animals, there was a scientific basis for
regulating sludge constituent concentrations. The final effect of these

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Table 2. Composition of U.S. Sewage Sludge based on 200 POTWs sampled
during 1988-1990 (8, 39).
Constituent	Geometric Median 90th 95th 98th Maximum Minimum
Mean-
	 mg/kg dry solids 	-
Comparison with the 1990
	Nat. Sewage Sludge Survey	
Pollutant	Normal Statistics	Maximum Liklihood'
Median 95th 98th	Median 98th
mg/kg dry sludge
As
6
43
62
5
33
Cd
7
21
25
4
19
Cr
40
635
1960
39
409
Cu
463
1940
2490
456
2180
Hg
4
17
43
2
19
Mo
11
42
56
5
32
Ni
29
223
438
18
159
Pb
106
296
444
76
373
Se
5
28
51
3
16
Zn
725
4100
4760
755
3270
PCB-1248
0.21
0.67
1.5
0.02
0
1	Adjusted downward for pretreatment considerations.
2	No adverse effects reported for any Cr level in municipal sludge.
3	Valid for all sludge uses except mushroom production.
4	Mo limit raised because Mo slowly leaches from alkaline soil.
5	Maximum Liklihood Estimation Procedure, assuming multicensored
lognormality.
changes is the development of the NOAEL (the No Observed Adverse Effect
Level) sludge approach in which sludge constituents are limited to
concentrations which comprise low risk to Most Exposed Individuals (MEIs)
under worst-case scenarios (27, 22, 8). Application of at least 1000 Mg of
a NOAEL sludge/ha has been found to comprise no risk to agriculture,
livestock, humans, or wildlife/ecosystems based on data from field studies
(27,8). The comprehensive risk analysis effort which allowed development
of the NOAEL sludge approach may be helpful to other nations which are
considering sludge regulations. Further, the detailed analyses identified
specific areas of needed research, research not yet conducted in the
agricultural or environmental research communities. Thus, this paper
summarizes the new US approach to sludge regulation and the general
conclusions reached. We conclude that if sludges can be beneficially used
in sustainable agriculture with so low risk to agriculture or environment,
that utilization of farmland should be the preferred method of "Ultimate
Disposal". Pretreatment of industrial and non-industrial sources of some
pollutants will often be required to achieve the NOAEL sludge quality.
Technology is presently available to achieve the needed pretreatment.
The details of the arguments and the data used for the risk analyses
have been described in several papers (30, 27, 8) and official documents

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(36). Details of the Cd risk analysis were recently described in Chaney
(8). We have also reviewed plant uptake of toxic organics, and discussed
at length the potential errors in research methods and methods of analysis
which have often caused over-estimation of the risk of toxic organics added
in sludges (26). After working on this reconsideration of the scientific
basis for sludge regulations for the US, we believe that a detailed example
of risk analysis for PCB transfer illustrates the efforts currently
underway in the United States. The paper shows the principles of the
Pathway Method of risk analysis. Data on PCBs are nearly as complete as
needed. Further, as with many of the persistent potentially toxic organics
in sludge, sludge concentrations have decreased with the prohibition of PCB
use or disposal in 1979. Based on these evaluations, we conclude that PCB
concentrations will not limit utilization of nearly any sludge in the US.
PATHWAY APPROACH FOR ANALYSIS OF THE RISKS TO HUMANS AND THE ENVIRONMENT
FROM TOXIC ORGANICS IN LAND-APPLIED MUNICIPAL SEWAGE SLUDGES.
In the ongoing effort to develop regulations to protect the environment
during land application of sewage sludge, EPA developed a "Methodology" to
assess the potential risk of toxic organic transfer to humans or the
environment from all identified pathways for this transfer (36). The EPA
Pathways (Table 3) were selected after consultation with the research
community (35). Under the Pathway Approach, risk assessment is conducted
in such a way as to protect the Most Exposed Individual (MEI) who ingests
sludge or sludge-grown foods as a high portion of his diet. The MEI can be
a human child eating sludge or soil-sludge mixture, a human adult consuming
foods grown on sludge-amended land for 70 years, livestock, earthworms,
soil bacteria and fungi, birds consuming large amounts of earthworms, etc.
Previous reviews have considered the possible transfer of toxic
organics from sludge to humans (e.g. 6, 9, 16, 19, 26, 28). These reviews
have focused on the direct ingestion of Distributed or Marketed (Pathway 2-
D&M) sludge products by children, and on human consumption of a large
fraction of ingested meats from livestock grazing sludge sprayed pastures
(Pathway 4-Surface) (19). It has become generally accepted that all other
Pathways transfer organics to humans at much lower levels than do Pathways
2-D&M and 4-Surface. However, a quantitative estimation of the allowed
applications of sludge PCBs under all the pathways should clearly
demonstrate why these two Pathways are so important. If these are the
critical pathways for all persistent TOs, then research on other TOs should
focus on the critical transfer coefficients involved in these Pathways.
Assessing Risk From Soil/Sludge Ingestion (Pathway 2-D&N; Sludge*Human).
Direct sludge ingestion by humans is the simplest Pathway for
pollutants in sludge to reach humans. Research on Pb risk from ingested
soil and dust (2, 32, 12) has shown the importance of hand-to-mouth play
and of pica (intentional ingestion of non-food items) on transfer of soi1 -
Pb and other strongly soil-adsorbed metals and TOs to children. Clearly,
soil Pb comprises much greater risk to children with pica than any other
way soil Pb can reach humans (e.g. plant uptake by garden food crops [12]).
Because of the concern about soil ingestion by children, information needed
to assess Pathway 2-D&M risks has been accumulated.
In the EPA Methodology, the algorithm for calculating Pathway 2 starts
by calculating the allowed daily ingestion of PCB so as to protect against
development of cancer in the exposed population. Cancer from excessive

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Table 3. Pathways for risk assessment of potential transfer of sludge-applied trace contaminants to humans, livestock, or the environment,
and the Most Exposed Individual to be protected by regulation to be based on the Pathway Analysis (36, 27).

PATHWAY
MOST EXPOSED INDIVIDUAL
1
Sludge-Soil-Plant-Human
General food chain; 2.5% of all food for lifetime.
1F
Sludge-Soil-Plant-Human
Home garden 5 yr after last sludge application; 50% of garden foods for lifetime.
1D&M
Sludge-Soil -Plant -Human
Home garden with annual sludge application; 50% of garden foods for lifetime.
2F
Sludge-Soil-Human Child
Residential soil, 5 yr after last sludge application; 200 mg soil/d.
2-D&M
Sludge-Human Child
Sludge product; 200 mg sludge/d.
3
Sludge-SoH-Plant -Animal -Human
Rural farm families; 40% of meat produced on sludge amended soil, for lifetime.
4-Surface
Sludge-Animal-Human
Rural farm families; 40% of meat produced on sludge sprayed pastures, for
lifetime.


4-Mixed
Sludge-Soil-Animal -Human
Rural farm families; 40% of meat produced on sludge amended soils, for lifetime.
5
Sludge-Soil-Plant -Animal
Livestock fed feed forages and grains, 100% of which are grown on sludged land.
6-Surface
Sludge-Animal
Grazing livestock on sludge sprayed pastures; 1.5% sludge in diet.
6-Mixed
Sludge-Soil-Animal
Grazing Livestock; 2.5% sludge-soil mixture in diet.
7
Sludge-Soil-Plant
"Crops"; vegetables in strongly acidic sludged soil.
8
Sludge-Soil-Solt Biota
Earthworms, slugs, bacteria, fungi in sludged soil.
9
Sludge-Soil-Soil Biota-Predator
Birds; 33% of bird diet earthworms affected by sludge.
10
Sludge-Soil-Airborne Dust-Human
Tractor operator.
11
Sludge-Soil-Surface Water-Human
Water Quality Criteria; fish bioaccumulation, lifetime.
12
Sludge-Soil-Air-Human
Farm households.
12W
SI udge -Soil -G roundwater-Human
Farm wells supply 100% of water used for lifetime.
D&M refers to sludge products distributed or marketed.

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ingested PCBs is the most sensitive risk endpoint for humans from chronic
ingestion of PCBs. The q,* is the cancer potency slope from the Cancer
Assessment Group of EPA. In this assessment of the cancer potency of a
compound based on lifetime feeding experiments with rats and other animals
at the maximum tolerated dose, the upper 95th percent confidence limit of
the slope is used as the limit to add further protection. This method of
estimating potential cancer incidence after lifetime exposure of humans is
generally agreed to lead to very conservative regulatory controls (1). The
q,* is used with other assumed parameters (RL, BW, RE) to calculate the
Adjusted Reference Intake (RIA). The RIA is the average daily intake of
PCBs that may not be exceeded if Risk Level is to be < 10"4.
RIA = | qRi~ REW j -1q3 = [ 10 7.*7 1.° 1^ J-103 = = 0.130 Mg/day
1
where RIA = Adjusted Reference Intake (/ig/day).
q.* = human cancer potency slope ([mg/kg BW/day]'1).
RL = risk level = 0.0001 of MEIs for EPA Proposed 503 Rule.
BW = body weight of 1-5 year old child = 10 kg.
RE = relative effectiveness, or bioavailability of pollutant in
ingested sludge compared to pure chemical form (used in
cancer potency slope assessment) added to diet.
The Reference Soil Concentration (RLC) which cannot be exceeded at the
selected risk level is then calculated from the RIA. In this case the
Pathway 2-D&M RLC is the maximum allowed sludge PCB concentration for a
sludge D&M product. Pathway 2F (ingestion of pollutants 5 years after
cessation of mixing sludge with soil) would provide appreciably less
exposure than Pathway 2-D&M.
The average soil ingestion by children has been estimated by several
researchers. The Calabrese et al. (7) paper shows the most reliable
published estimation at this time. The 95th percentile (log normal) of
soil/dust ingestion by 2 year old children was about 0.5 g/day, while the
geometric mean soil ingestion was < 50 mg soil/day. We believe that the
peak soil ingestion period by children is about 2 years long, and that use
of the 0.5 g sludge/day provides a conservative estimate of risk (27). As
it happens, use of either 0.2 g/day (the number used in the EPA Superfund
program [37]) for 5 years, or the 0.5 g/day for 2 years are the same amount
of sludge ingestion exposure.
The Duration Adjustment (DA) must be made when cancer risk slopes for
70 year lifetime exposure are used to estimate allowed exposures for
soil/sludge ingestion which lasts only a part of the lifetime. Thus, the
calculation can use 0.2 g/day for 5 years (DA = 0.0714) or 0.5 g/day for 2
years (DA = 0.0286). Values of RIA, Is, and DA are used to calculate the
RLC.
RLC =	= [(0.S.O^OzSsi'O^O143] * 9,09 PCB/g dry slud9e-
or [(0.2*0.0714)=0.0143]
RLC = Reference Soil/Sludge Concentration of the pollutant (/xg/g DW).
DA = Duration Adjustment for < 70 year: 5/70=0.0714; 2/70=0.0286.
Is = Soil Ingestion Rate (g DW per day).
Thus, for PCBs, the RLC =9.09 nq/q DW. The Pathway 2-D&M risk
assessment, in which children are assumed to ingest sludge directly for 2-5
6

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years, indicates that the required sludge PCB concentration limit is much
higher than present levels of PCBs in sludges (Table 2). Based on data
discussed below for bioconcentration of PCB from sludge ingested by cattle
compared to bioconcentration from pure PCB added to cattle diets, the
relative effectiveness of sludge PCB may be about 0.50, which would
increase the RLC estimate accordingly.
Assessing Risk From Sludge ingestion by Grazing Livestock Used as Food by
Humans (Pathway 4; SIudge*Soil *Animal¦~Human and Sludge-«Aniinal*Human)
Fat in the human diet which comes from livestock which graze in sludge-
amended pasture fields is the source of the human exposure calculated in
Pathway 4. Pathway 4 has two quite different kinds of exposure, and we
believe they should be considered separately. The first involves direct
ingestion of sludge by livestock, where sludge has been surface applied to
pasture crops. Livestock can ingest sludge adhering to the crops, or
sludge lying on the soil surface. Each year the grazing livestock are
presumed to be exposed to freshly applied sludge with no time for
dissipation of the organic chemicals (this is Pathway 4-Surface
Application). • Alternatively, sludge can be injected into the soil or mixed
with the plow layer soil, and the grazing livestock ingest the soil-sludge
mixture. Injected sludge is not at the soil surface, so injection
minimizes exposure until the plow layer soil is mixed. The highest
exposure under the Pathway 4-Mixed scenario would be livestock ingesting
soil while grazing a crop seeded immediately after mixing the applied
sludge into the plow layer soil.
Sludge ingestion by grazing livestock was expected after Chaney and
Lloyd (11) observed that sludge adhered to forages for a prolonged period
if the fluid sludge was not washed off the plants immediately after
application (23). If sludge is applied to standing forages, the rate of
application and solids content of the sludge affect sludge adherence. N-
fertilizer rate applications of typical fluid sludges containing 5% solids
to standing forage crops caused sludge to reach about 15% of the forage dry
matter. This evidence led to prohibition of sludge application on standing
forages (34), and thus reduced the potential for sludge ingestion by
livestock during sludge utilization on pastures.
Chaney et al. (9) reviewed several studies in which cattle grazed
pastures to which sludge was surface applied using good practices. In the
Decker et al. (17) study, fluid sludge was sprayed on the pastures after
mowing, and the crop grew for 21 days before cattle were allowed to graze;
the study used four "rotation paddocks" so that each 7 days the cattle were
moved to the next pasture which had grown for 21 days after sludge
application. By analysis of the cattle feces after 7 days grazing on the
treated pastures, they found that the animals ingested about 2.5% sludge in
their diets. Metals served as a label for sludge; concentration of metals
such as Fe, Pb, and Cu were much higher in treated forages and feces than
in control forages and feces of control treatment cattle. Similar results
were observed by Bertrand et al. (4). However, when sludge compost was
applied the previous grazing season rather than during each "rotation", the
cattle ingested only about 1.0% sludge (17).
Another possible consideration is the effect of having only part of a
farm treated with sludge each year. The EPA (36) Methodology considered
that for the rural farm family who consumed the greatest fraction of "home-
grown" livestock (the MEI in Pathway 4), all grazing fields were treated
with sludge each year for a 70 year lifetime. However, if sludge were
applied intermittently, the fraction of sludge in the chronic grazing

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animal diet is lower because adhering sludge exceeded sludge ingested from
the soil surface in season-long grazing studies with sludge (see 9). Based
upon our experience and discussion with regulatory officials in several
states, we estimate that in any one year, the normal maximum fraction of a
farm treated with sludge may be 33% rather than 100%. If one presumes the
cattle are rotated among several pasture fields, the actual fraction of the
diet which is sludge will be lower than the 2.5% measured with continual
exposure (this lifetime approach is necessary because the cancer endpoint
protected against requires that exposure appropriate for a chronic lifetime
model be estimated). To take this into account, the allowed RFC for
sludge-treated forage should be adjusted for the fraction of livestock diet
affected by sludge application. Using 1% sludge ingestion during non-
application periods (2/3 of time), and 2.5% ingestion during sludge
application periods (1/3 of time), the long term average would be 1.5%
sludge in diet.
To estimate sludge PCB transfer from grazing livestock to humans, the
lifetime average amounts of fat of meat and dairy products from grazing
livestock ingested per day are needed. The US-EPA (36) "Methodology"
estimated the amounts of fat in the human diet from each class of
livestock, for a range of age and sex groups of the US population. The
original data were described by Pennington (31). One can calculate a
lifetime diet composition by assuming the number of years each age range of
consumption covers. Table 4 shows the estimated average lifetime daily
consumption of fat from meats from different livestock. Other foods
considered in this paper are also included in Table 4.
The MEI for Pathway 4 is believed to be members of a rural farm family
ingesting much of their lifetime meat consumption from home grown livestock
(which consume sludge on forages or soil-sludge mixture) for their 70 year
lifetime exposure. The calculation starts with estimation of the maximum
allowed daily PCB intake to limit 70 year lifetime cancer risk:
RIA = ! qL*Bre I*103 = | 10 7 7 7.° | * 1q3 = °-909 M PCB/day
RIA = adjusted reference intake (/xg/day)
q.* = human cancer potency ([mg/kg/day]"1)
RL = risk level = 0.0001 for TSD
BW = body weight = 70 kg
RL = Relative Effectiveness or bioavailability.
After calculating the RIA, one calculates the maximum allowed feed
concentration of PCBs (RFC) for Pathway 4 (see Table 5):
RFC	—	
2 (UAf-DAf-FA,.)
RFC = reference feed concentration of the pollutant (/xg/g DW)
RIA = adjusted reference intake (/ig/day)
UAj = uptake response slope of pollutant in the animal tissue food group i
for organics, on a fat basis, = 2 (/xg PCB/g fat)• (/xg PCB/g feed DW)*1
for sludge-borne PCBs added to test diets.
DAf = Daily dietary consumption of animal food/fat group i, g dry wt.
FA,- = fraction of the food group i assumed to be derived from amended soil
(in this case, from fat in tissues of or milk from cattle consuming
1.5% sludge averaged over their lives). Assumes that a high fraction
of the diet came from cattle raised on the sludge-treated pastures
(44% for meat fat, and 40% for dairy fat for a 70 year lifetime).

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Table 4. Human consumption of selected foods (fat from meats derived from
several classes of livestock; garden crops) (g dry weight/day) for
different age groups, and estimated lifetime average food intakes for 70 kg
US adult citizens. The child age group (not reported by Pennington [31])
was assumed to consume the average of that consumed by toddlers and teen-
agers. Meats in mixed foods assigned to source by US-EPA (36).
Food		Age Grouping
Group Baby
Toddler
Child
Teen-
Adult
Older
Estimated



Agers

Adult
Li fetime
Age: 0-1
1-6
6-14
14-20
20-45
45-70
0-70
Grazing Livestock:






Beef Fat 2.45
6.48
11.34
16.22
20.40
14.07
15.50
Beef Liver Fat 0.05
0.07
0.08
0.10
0.29
0.33
0.25
Lamb Fat 0.14
0.08
0.07
0.06
0.31
0.22
0.21
Dairy Fat 38.99
16.48
20.46
24.43
18.97
14.51
18.13
Non-Grazing Livestock:






PorkFat 2.01
8.19
10.47
12.75
14.48
13.04
12.73
PoultFat 1.10
0.83
1.12
1.41
1.54
1.31
1.34
EggFat





0.96
Garden Food CroDs:






Potatoes 5.67
10.03
14.72
19.40
17.28
14.79
15.60
Leafy Veg. 0.84
0.49
0.85
1.22
2.16
2.65
1.97
Legume Veg. 3.81
4.56
6.51
8.45
9.81
9.50
8.75
Root Veg. 3.04
0.67
1.20
1.73
1.77
1.64
1.60
Garden Fruit 0.66
1.67
2.57
3.47
4.75
4.86
4.15
For Teen, Adult, and Older Adult categories, FDA (31) intakes of females
and males were averaged; for other groups, no separation of data by sex was
reported. Child intake was set equal to the average of Toddler and Teen.
The best value for UA for PCB transfer from feed to fat has been
discussed by Fries (19). Based on his own and other research, Fries
concluded that the UA was 4 for beef fat and 4.8 for dairy products.
However, this was for pure PCB added to cattle diets or provided in corn
oil. Baxter et al. (3) tested the bioaccumulation ratio for PCB in a dried
anaerobically digested sludge containing 24 mg PCBs/kg DW. Because sludge
adsorbs PCBs strongly, the UA for sludge-borne PCB was only 1.9. This
value was the average for beef cows and steers fed 10% sludge in their
complete diet for 270 days. It should not be unexpected that sludge PCB
adsorption properties and oils could reduce the bioavailability of sludge
PCBs. Rozman et al. (33) found adding mineral oils to feeds increased the
excretion of hexachlorobenzene from cattle. Fairbanks and O'Connor (16)
found soil organic matter strongly adsorbed PCBs, and the adsorbed PCBs
showed strong hysterisis (limited release) of PCBs in sludge.
RFC = 2(UAi^DA)«FAj) = or RFC = 27.9139 = °-0335 M/9 DW
The fraction of sludge in the diet enters into the calculation so the
maximum amount of PCB allowed in the sludge can be estimated for Pathway
4-Surface Application. Reference Sludge Concentration (RSC) can be
calculated as specified in the Methodology:

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Table 5. Calculation of 2(UAj.DAj«FA)) needed to estimate human exposure
to PCB in fat of meat from grazing livestock. UA value from Baxter et al.
(3), based on feeding cattle 10% sludge for 270 days at which time
equilibrium of PCB in fat with the diet would have been reached according
to Fries (19). DA is the lifetime daily average intake of fat from grazing
livestock. FA is the fraction of total lifetime ingestion of these meats
by the MEIs (members of a rural farm family.
Sludge PCB in Diet of Grazing Livestock
Food Group
DA
g/day
UA
FA
(UA-DAj.FAJ
Estimated Lifetime
Beef fat
15.50
1.9
0.44
12.96
Beef 1 iver fat
0.25
1.9
0.44
0.21
Lamb fat
0.21
1.9
0.44
0.18
Dairy fat
18.13
1.9
0.40
13.78
ZFat from grazing
livestock 34.09


27.13
RSC = RFC/FS
RSC = Reference Sludge Concentration
RFC = Reference Feed Concentration
FS = Fraction of livestock diet comprised of sludge (chronic lifetime
exposure = 0.015 according to discussion above.)
RSC = RFC/FS = 0.0335/0.015 = 2.23 /xg PCB/g DW in applied sludge.
This same number is used for estimating allowed sludge PCB applications
under Pathway 4-Mixed With Soil, only now it is 2.23 /xg PCB/g dry soil-
sludge mixture which is chronically ingested by the grazing livestock at
1.5% of diet (annual average basis; see also [9, 19, 21]). In the case of
sludge mixed into soils, however, the regulatory approach is quite
different because PCBs can volatilize or be biodegraded over time after
application. The 2.23 nq PCB/g dry soil-sludge mixture which must not be
exceeded is considered to be the equilibrium reached when PCB dissipation
during one year equals the annual PCB application. Persistent higher
chlorinated PCBs have about a 6-10 year half-life; for these calculations,
the T0 5 is presumed to be 10 yr (k = 0.693/Tp 5 = 0.0693/yr).
An'equil ibrium PCB concentration is reached after about 5.6/k = 81
years (36), and the formula used to calculate the annual PCB application
mixed into the soil (RPa) needed to reach this equilibrium RSC after 81
continuous annual applications is:
RPa = RLC« (2000 Mg soi 1/ha) • 10"3. [le0*0-0693+le"1'°-0693+...+ le"81*0-0693]"1
= 2.23 • 2 • [14.9]"1 = 0.299 kg PCB/ha/yr.
This could be applied by 10 Mg/ha/yr of a sludge containing 29.9 mg PCB/kg:
0.299 kq PCB . 	1 ha,Vr	 = 0-0299 kq PCB _ 2g g mg pcB/kg siU(jge DW.
ha»yr	10 Mg sludge DW Mg sludge
Thus, Pathway 4-Surface Application comprises significantly greater

-------
potential for PCB transfer to humans than does Pathway 4-Mixed. Pathway 4
risk assessment remains a very conservative estimation of allowable toxic
organic concentrations in sewage sludge. The exposure scenario, a rural
farm family ingesting, for a 70 year lifetime, a high proportion of home
grown meat and dairy products from livestock which often graze sludge-
amended pastures, is conservative. In Pathway 4-Surface Application, the
sludge is assumed to remain on the surface of pastures continuously for 70
years in contrast with known agronomic practices which require that the
surface be intermittently tilled with the plow layer soil to incorporate
pH-modifying agents, fertilizers, and organic matter into the surface soil.
The MEI is conservatively assumed to consume 44% of meat of grazing
livestock and 40% of dairy products from livestock raised on sludge-using
farms, but few farms raise both lamb and beef, and dairy cattle are fed
feed supplements to improve production efficiency (21). Further, it is
likely that current data on food consumption by rural farm families would
show that a lower fraction of locally grown livestock is consumed by the
highest consuming families.
The alternatives to surface application of sludge on pastures include
use of sludge injection, and mixing sludge with the soil before forage
crops are established. These would all lead to much lower estimations of
risk than found with Surface Application. Pathway 4-Mixed With Soil
calculations indicate that much greater protection of humans from sludge-
applied PCBs can be achieved by avoiding surface application of sludge on
pastures. The use of sludge injection minimizes sludge ingestion by
grazing livestock, conserves sludge nutrients, and prevents malodors and
unsightliness of surface applied sludge. In any case, the MEI is well
protected against chronic health effects of sludge PCBs by limitations
appropriate for the method of application.
Assessing Risk From Uptake of Soil PCB Residues by Forage and Feed Crops
For Livestock Used as Food by Humans (Pathway 3; Sludge*Soil*Plant*Animal*
Human)
For Pathway 3, sludge is presumed to be uniformly mixed with the plow
layer soil, and forage and feed crops are grown on the sludge-treated soil.
As in Pathway 4, the ME Is are rural farm families assumed to consume a high
proportion of their lifetime meat and dairy products from livestock which
eat only crops grown on sludge-treated soils. This Pathway is similar in
approach to Pathway 4-Mixed, but all meats and dairy products are
considered. Fat from non-grazing livestock classes (poultry, swine) are
included in Pathway 3 because feed grains can be harvested from sludge-
amended soils in addition to hay and silage harvested for ruminant
livestock. Transfer of PCBs from sludge-amended soil to edible parts of
crops is quite low (28, 40) and annual sludge applications are limited by
the N fertilizer supplied by the sludge, resulting in the steady state
concentration of PCB in soil being quite low compared sludge lying on the
soil surface in Pathway 4. Pathway 3 therefore, would always be expected
to provide lower transfer of persistent PCBs to humans via animal fat.
For Pathway 3 (uptake of PCBs by forage/feed plants, or contamination
with PCB independent of sludge or soil ingestion), the EPA (36) Methodology
presumed that the PCB uptake slope for forage crops was the appropriate
transfer slope to feeds for all livestock. However, in calculating the
estimate of toxic organic compound transfer to humans by this Pathway, we
believe it is important to also discriminate between grain crops fed to
some classes of livestock and forage crops fed to ruminant livestock.
Further, milk cows are supplied grains and other "concentrates" to provide
11

-------
nutrients and energy for high production rates, and it is inappropriate to
presume 100% forage diet for dairy products (21). A modified approach to
calculating this limitation is shown below which allows correction of this
error in the risk assessment Pathways.
For 70 year lifetime exposure, the EPA (36) algorithm to calculate RIA
for Pathway 3 is the same as in Pathway 4). After calculating the RIA, one
calculates the RFC for the feed as under Pathway 4, but adds the fat from
other foods as shown in Table 6:
RFC = 	—	
2 (UAj«DAi«FAi)
RFC = reference feed concentration of the pollutant {ng/g DW)
RIA = adjusted reference intake (/zg/day.)
UAj = uptake response slope of pollutant in the animal tissue food group i
for organics, on a fat basis, = 4 for PCB mixtures added to test
diets; does not use the data from Baxter et al. used for Pathway 4
because sludge is not present to adsorb PCB during transit through
the gut.
DA,- = Daily dietary consumption of the animal tissue food group i
FA, = fraction of the food group i assumed to be derived from amended soil
(in this case, from fat in tissues of or milk from cattle consuming
feeds which were all grown on soils which received sludge annually.
The RLC is calculated from the RFC by dividing by the uptake slope for the
compound for the crop used to estimate uptake (UC):
RLC = (RFC + UC) + BS
where:
RLC = Reference Soil Concentration (/zg/g DW)
UC = linear response slope of forage crop [fig/g crop DW (/zg/g soil DW)*1]
BS = background soil concentration of pollutant (jig/g DW) (assumed to be 0
since the cancer risk to be estimated is the incremental risk, not
the absolute risk.
Our method of calculation sums a new product of UC( and DFS (Diet
Fraction) times the old product (Table 6) to directly calculate RLC from
RIA:
RIA	0 909
RLC = z((uc..DFf.UA1.DAj.FAj) = 0.04954 = 18,3 mg/kg s0ll"slud9e mixture DW
The Methodology calculation then estimates an annual sludge PCB
application rate taking into account the rate of dissipation
(volatilization or degradation) of PCBs (T05 = 10 yr) so that the RLC is
reached at steady state between application' and dissipation.
The formula was introduced above.
RPa = RLC-(2000/1000).(14.9)"1 = 2.46 kg PCB/ha/yr.

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Table 6. New approach to estimate PCB limitation for Pathway 3;
I(UC1«UAi«DAi»FAj) is calculated to allow discrimination between PCB
transfer to livestock which consume grain and those consuming forage.
Animal
Group
Tissue Diet
Feed Type Fraction
Uptake(UCj)
Slope
UA
DA
FA
2
Beef Fat
Forage
1.00
0.001
4.0
15.50
0.44
0.02728
Beef Liver
Fat Forage
1.00
0.001
4.0
0.25
0.44
0.00044
Lamb Fat
Forage
1.00
0.001
4.0
0.21
0.44
0.00036
Pork Fat
Grain
1.00
0.0001
4.0
12.73
0.44
0.00224
Poultry Fat
Grain
1.00
0.0001
4.0
1.34
0.34
0.00018
Dairy Fat
Forage
0.50
0.001
4.8
18.13
0.40
0.01740
Dairy Fat
Grain
0.50
0.0001
4.8
18.13
0.40
0.00146
Eggs Fat
Grain
1.00
0.0001
4.0
0.96
0.48
0.00018
Total



-
-
-
0.04954
Uptake slopes (UCJ from [28].
At an annual application rate of 10 Mg dry sludge/ha, the sludge could
contain as much as 246 mg PCBs/kg.
2.46 ka PCBs # 1 ha-vr _ 0.246 ka PCBs _ 246 ma PCBs .
ha»yr ' 10 Mg sludge DW ~ Mg sludge DW ~ kg sludge DW
This high allowed annual application of sludge PCBs will not
practically limit sludge application because modern sludges contain low
levels of PCBs, with median levels < 0.1 mg/kg DW.
Another way to view this high annual allowed PCB application and
equilibrium soil PCB concentration under Pathway 3 is that Pathway 4 would
estimate unacceptable risk levels for the same soils. During periods of
sludge use on pastures, the limitations of Pathway 4 must limit sludge PCB
application. These considerations confirm the summary of relative risk
from Pathways 3 and 4 noted in the introduction.
Calculations for Pathway 3 also remain very protective for the presumed
MEIs. Sources of protection include: 1) the assumption that the rural
farm family consumes a large portion of "home-grown meats" for their 70
year lifetime exposure; and 2) that sludge is applied annually to 100% of
the farmland used to produce forage and grain crops used as animal feed.
Assessing Risk From Food Crops (Pathway IF; S1udge*So11«P1ant*Human):
The production of food crops for humans on sludge-amended soils will
transfer some sludge constituents into human diets. The MEI for this
Pathway is the home gardener who grows a large fraction of his diet on
sludge amended soil, for 70 years. Sludge is presumed to be applied and
mixed into the soil annually until the PCB concentration reaches an
equilibrium with PCB loss (81 years as noted above). The exposure is
assumed to be at the equilibrium level for the whole 70 year consumption of
garden crops grown on the treated soil. Pathway 1F-D&M could be estimated
by assuming a D&M product is applied annually, so no waiting period is
allowed. In the Agricultural Use Pathway IF, a five year waiting period is
assumed before crops are grown on the treated soil, presuming a waiting
period followed by conversion of the site to residential use. Because

-------
Pathway l-D&M estimates the highest possible exposure under Pathway 1, it
is used for an example. Exposure from Pathway 1F-D&M is much lower than
from Pathway 2-D&M or Pathway 4-Surface. Pathway 1F-D&M will not
practically limit utilization of sludges with low PCB concentrations
presently available.
The method of calculation of food chain transfer of toxic organics
according to the Methodology (36) (home garden scenario) uses several steps
to complete the calculation. The first step is the calculation of daily
allowed TO intake (RIA) based on the cancer potency value. One then sums
the amount of each food group consumed times the slope of plant uptake for
the compound times the fraction of food group grown on sludge amended soil.
This value is divided into the RIA to produce the RLC, the soil PCB
concentration which sludge application may not be allowed to exceed.
From calculations above, we know the RIA is 0.909 jig PCB/day. The next
step sums the amount of PCB ingested if FC (fraction of the diet) were
grown on sludge amended soil, if DC (g DW of foods) were consumed daily on
average for 70 years, and if UC were the transfer coefficient from soil to
each food group (ng PCB/g dry crop per ng PCB/g dry soil) grown in the
garden.
Calculation of the 2(UC,-• DCf• FC,-) for PCBs relies on the values in
Table 7. The DC for garden vegetables lifetime ingestion estimates were
shown in Table 4. Table 7 combines the new food intakes, corrected crop
PCB uptake slopes, and fraction of diet from the US-EPA Proposed 503 Rule
(US-EPA, 1990a) to calculate the ^(UCj• DC,-• FC,-) for PCBs. Carrot accounts
for 53% of the dry matter of the root vegetable grouping according to
Chaney et al. (9). Thus, the overall root vegetable group is shown as
equal to 53% of the uptake slope of carrot. Although most people peel
carrots before consuming them, there is no assurance that carrots will be
peeled. Therefore, the uptake slope for unpeeled carrots was used.
O'Connor et al. (29) found little PCB entry to carrot deeper than the
normal peel depth.
Table 7. Using corrected UC slopes, food intakes (DC), etc., for the
calculations for Pathway IF home garden analysis for PCBs. The absolute
slope used for unpeeled carrot was (0.075 ng/g DW carrot), [^ig PCB/g soil
DW]"1; from O'Connor et al. (29), after review of PCB uptake by carrot and
lettuce from sludge-PCB treated soil. Other data are best judgement values
because slopes are not generally available from properly conducted field
experiments with sludge-applied PCBs.
Food
Food Intakes
; UDtake SloDe
Fraction
(UC1 'DC,- • FCj)
Group


home-grown.
ua/dav

DC
UC
FC
fig/g soil DW

g DW/day
jig/g^g/g)"'

%Total
Potatoes
15.60
0.025Carrot=0.00188
0.45
0.0132 24.9
Leafy Veg.
1.97
<0.0010
0.60
0.00118 2.2
Legume Veg
. 8.752
0.001Carrot=0.000075
0.29*
0.00019 0.4
Root Veg.
1.60
0.53Carrot =0.03975
0.60
0.03816 72.1
Garden Fruit 4.15
0.001Carrot=0.000075
0.60
0.00019 0.4



2
= 0.05292 100.0
*0.17 for dried legume vegetables (8.412 g DW/day) and 0.60 for fresh
legume vegetables (3.340 g DW/day) gives 0.29 for weighted total legume
vegetables.

-------
Using the corrected (UC,• DC• FC,-), the estimated RLC is:
RLC =	0.909 /xq PCB/day	 . 17 2 pcB/ d il
0.05292 fig PCB/day (/xg PCB/g soil DW) 1
This is the maximum allowed concentration of PCB in soil at any time
that garden vegetables are grown on the soil. This can be converted to an
annual sludge-PCB application as done above in Pathway 4-Mixed With Soil,
and Pathway 3. The RPa would be 17.2 • 2 + 14.9 = 2.31 kg PCB/ha/yr. A
sludge applied at 10 Mg/ha/yr could contain 231 mg PCB/kg DW.
Table 8 compares the original calculated limitations for the Proposed
503 Regulation (38), and the estimated limitations if the appropriate
algorithms and transfer coefficients shown in this paper were used (28, 8).
Table 8. Comparison of PCB application limits for each pathway for data from the 503 Proposed
Rule and the corrected versions reported in this document. The last column lists concentrations
of PCBs which could exist in sludges applied as N fertilizer annually at 10 Mg/ha.
Original EPA Estimate	Corrected Approach	Sludge Limit,
mg/kg
Pathway	Limit Units Limit value Limit Units Limit value @ 10 Mg/ha/yr
1
kg/ha^r
4.1



1 D&M
kg/ha^r
0.264
mg/kg Soil Max.
17.2

1 D&M
kg/ha/yr
2.31

231.

2D&M
kg/ha^r
7.3
mg/kg sludge DW
9.09
9.09
3
kg/ha^r
0.0056
mg/kg Soil Max.
18.3




kg/ha/yr
2.46
246.
4-Surface Application
kg/ha^r
0.019
mg/kg sludge DW
2.23
2.23
4-Mixed With Soil
kg/ha/yr
0.019
mg/kg Soil Max.
2.23

4-Mixed With Soil
kg/ha/yr
0.019
kg/ha/yr
0.299
299.
FUTURE
The effort to complete development of the Clean Water Act 503
Regulations for sewage sludge is continuing. Final regulations are
expected to be issued in 1992, and all 28 contaminants being considered in
the present regulation will undergo risk assessment for all Pathways.
LITERATURE CITED
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Housworth, and P.J. Landrigan. 1977. Lead poisoning In children of lead workers. Home
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3.
Baxter, J.C., D. Johnson, E. Kienholz, W.D. Burge, and W.N. Cramer. 1983. "Effects on Cattle

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From Exposure to Sewage Sludge. PB83-170589." (EPA-600/2-83-012)
4.	Bertrand, J.E., M.C. Lutrlck, G.T. Edds, and R.L West. 1981. Metal residues in tissues, animal
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Lasztlty, and P.T. Kostecki. 1989. How much sou do young children ingest: An epidemiologic
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application research. BioCycle 31(9):54-59. 2) Public health and sludge utilization. BioCycle
31 (10):68-73.
9.	Chaney, R.L., R.J.F. Bruins, D.E. Baker, R.F. Korcak, J.E. Smith, Jr., and D.W. Cole. 1987.
Transfer of sludge-applied trace elements to the food-chain, pp. 67-99. [n A.L. Page,
T.J. Logan and J.A. Ryan (eds.) Land Application of Sludge — Food Chain Implications. Lewis
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utilization of sewage sludge in the Northeast, pp. 283-314. in R.C. Loehr (ed.). Land as a
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fescue. J. Environ. Qual. 8:407-411.
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13.	Chaney, R.L, S.B. Sterrett, M.C. Morella, and C.A. Uoyd. 1982. Effect of sludge quality and
rate, soil pH, and time on heavy metal residues in leafy vegetables, pp 444-458. in Proc. Fifth
Annu. Madison Conf. Appl. Res. Pract. Municipal and Industrial Waste. Univ. Wisconsin-
Extension, Madison, Wisconsin.
14.	Comptroller General. 1978. Sewage sludge: How do we cope with it? 38pp. USGAO Report
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of sludge properties on accumulation of trace elements by crops, pp. 25-51. in A.L Page
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Ml.
16.	Davis RD, Howell K, Oake RJ, Wilcox P (1984) Significance of organic contaminants in
sewage sludges used on agricultural land. In: Proceedings of the International Conference on
Environmental Contamination. CEP Consultants Lid, Edinburgh, Scottland, pp 73-79.
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1980. Animal performance on pastures topdressed with liquid sewage sludge and sludge
compost, p. 37-41. in Proc. Natl. Conf. Municipal and Industrial Sludge Utilization and
Disposal. Information Transfer, Inc., Silver Spring, MD.
16

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18.	Fairbanks, B.C. and G.A. O'Connor. 1964. Effect of sewage sludge on the adsorption of
polychiorinated biphenyls by three New Mexico soils. J. Environ. Qual. 13:297-300.
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21.	Fries, G.F. and D.J. Paustenbach. 1990. Evaluation of potential transmission of 2,3,7,8-
tetrachlorodibenzo-p-dioxin-contaminated incinerator emissions to humans via foods. J.
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Weber, and J. Werner. 1989. Distribution and Marketing, pp. 103-122. In A.L Page, T.J.
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Dowdy, P.R. Fitzgerald, T.D. Hlnesly. 1989. Land Application — Agricultural Land. pp. 27-83.
in A.L Page, T.J. Logan, and J.A. Ryan (eds.) W-170 Peer Review Committee analysis of the
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Riverside.
28.	O'Connor, G.A., R.L Chaney, and J.A. Ryan. 1991. Bioavailability to plants of sludge-borne
toxic organics. Rev. Environ. Contam. Toxicol. In press.
29.	O'Connor, G.A., D. Klehl, G.A. Eiceman, and J.A. Ryan. 1990. Plant uptake of sludge-borne
PCBs. J. Environ. Qual. 19:113-118.
30.	Page, A.L, T.J. Logan, and J.A. Ryan (eds.) W-170 Peer Review Committee analysis of the
Proposed 503 Rule on sewage sludge. CSRS Technical Committee W-170, Univ. California-
Riverside.
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Assoc. 82:166-173.
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Verduyn. 1980. Exposure to lead by the oral and the pulmonary routes of children living in the
vicinity of a primary lead smelter. Environ. Res. 22:81-94.
33.	Rozman, K., T. Rozman, H. Greim, I.J. Nieman, and G.S. Smith. 1982. Use of aliphatic
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hydrocarbons in feed to decrease body burdens of lipophilic toxicants in livestock. J. Agr.
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facilities and practices. Federal Register 44(l79):53438-53464.
35.	U.S. Environmental Protection Agency. 1985. Summary of environmental profiles and hazard
indices for constituents of municipal sludge: Methods and results. US-EPA, Off. Water Reg.
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for land application and distribution and marketing of municipal sludge. EPA/600/6-89/001.
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OSWER Directive 9850.4; Jan. 27, 1989.
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proposed rule. Federal Register 54(23):5746-5902.
39.	U.S. Environmental Protection Agency. 1990. National Sewage Sludge Survey; Availability of
information and data, and anticipated impacts on proposed regulations; proposed rule.
Federal Register 55(218) :47210-47283.
40.	Witte H, Langenohl T, Offenbacher G (1988) Investigation of the entry of organic pollutants
into soils and plants through the use of sewage sludge in agriculture. Part A. Organic
pollutant load in sewage sludge. Part B. Impact of the application of sewage sludge on
organic matter contents in soils and plants. Korresportdenz Abwasser 13:118-125, 126-136.

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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completi
1. REPORT NO. 2.
FPA/finn/n-9i/nfi?
3
4. TITLE AND SUBTITLE
Risk Assessment for Organic Micropol lutants: U.S.
Point of View
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R.L. Chaney, J.A. Ryan, and G.A. O'Connor
8. PERFORMING ORGANIZATION REPORT NO.
9 PERFORMING ORGANIZATION NAME AND ADDRESS
RREL/WMDDRD/MSWRMB/SRS
5995 Center Hill Road
Cincinnati, OH 45224
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Risk Reduction Engineering Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Complete
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: James A. Ryan (513) 569-7653 or FTS 684-7653
Proc. EEC Symp. Treatment & Use of Sewage Sludge & Liquid Agricultural Wastes, 9/90.
16. ABSTRACT
Basic research and monitoring of sludge utilization programs have identified
specific Pathways by which potentially toxic constituents of sewage sludge can
reach and cause toxicity to livestock, humans, plants, soil biota, wildlife, etc.
In the process of preparing a new regulation for land application of sewage sludge
in the US, a Pathway approach to risk assessment was undertaken. Two Pathways
were found to comprise the greatest risk from persistent lipophilic organic compounds
such as PCBs: 1) direct ingestion of sludge by chiTdren; and 2) adherence of sludge
to forage/pasture crops from surface application of fluid sludge, followed by
grazing and ingestion of sludge by livestock used as human food. Each Pathway
considers risk to Most Exposed Individuals (MEIs) who have high exposure to sludge.
Because 1990 sewage sludges contain very low levels of PCBs, the estimated risk
level to MEIs was less^QjO low sludge PCBs and low probability of sinju-H-aneously
meeting all the constraints\of the MEI indicate that MEIs are at lesfHO^M-ifetime
risk. We conclude that quantitative risk assessment for potentially "toxic
constituents in sewage sludge can be meaningfully conducted because research hasx
provided transfer coefficient's from sludges and sludge-amended soils to plants^an'd
animals needed for many organise compounds. 	—	
'• ••"> n /*> >
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS /
b.lDEN'TIFIERS/OPEN ENDED TERMS
c. COSATi Kield/Group
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18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS 'This Report?
Unclassified
21 . NO. OF PAGES
20
20. SECURITY class (This page/
Unclassified
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EPA Form 2220-1 (Rev. 4-77) previous edition is obsolete

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