United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/010 Apr. 1986
&EPA Project Summary
Toxic and Priority Organics in
Municipal Sludge Land Treatment
Systems
Michael R. Overcash, Jerome B. Weber, and William Tucker
Research was conducted to investi-
gate the fate of organic priority pol-
lutants applied to plant-soil systems at
rates characteristic of municipal sludge
land treatment. A single chemical was
applied at rates that were 0.1, 1.0, 10,
and 100 times the expected values re-
ceived during an annual application of
municipal sludge. The "C-chemicals
investigated were in the following
groups: polynuclear aromatics, phthalic
acid esters, and substituted aromatic
compounds. None of the organic priority
pollutants studied was entirely excluded
from all plant species at the rates of soil
application used. The ratio of chemical
concentration in the fresh plant to the
level loaded initially onto the soil (bio-
accumulation) was most typically less
than 0.01 and always less than 1.0. Of
the crops studied (fescue, corn, soy-
beans, and wheat), no vegetation type
routinely evidenced the highest uptake
of the organic chemicals used. Plant
uptake of organics appears to be largely
governed by chemical losses from the
soil over time and the water solubility
of a given chemical. The presence of
sludge did not appear to alter signifi-
cantly the crop uptake or soil loss of
these compounds. If corroborated,
these data would allow a large expan-
sion of design information for municipal
sludge land treatment systems.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
Is fully documented In a separate report
of the tame title (tee Project Report
ordering Information at back).
Introduction
Before publication of the specific list of
priority pollutants in 1976, attention to
organic chemicals in municipal wastes
was restricted by the lack of information
about what compounds were present or
of concern. Research was therefore
limited in scope. With publication of the
priority pollutant list, a program was
undertaken to measure these specific
organics in municipal wastes, effluents,
and sludges. For organic chemicals, the
priority pollutant list has stimulated
recognition of a substantial data base
that already exists on the behavior of
organic compounds in the terrestrial sys-
tem. This data base has been built by
research on pesticides and residues,
other agricultural chemicals, soil sterili-
zation, chemical spills, organic fertilizers,
and soil-plant behavior. This very large
data base is an excellent starting point
for evaluating the impacts of specific
organic compounds on applications of
municipal effluents and sludges. Though
significant transferable information exists
for estimating behavior, relative assimila-
tion capacities, and critical levels for
specific organics, further research is also
needed on the organic priority pollutants
present in the municipal sludge or
effluent.
Experimental Procedures
Selection of the organics (nonpesticides)
to be studied was based on data from the
U.S. Environmental Protection Agency
evaluations of municipal sludge. Since a
major disposal alternative for municipal
sludge is application to land, those or-
ganics in highest concentration were
chosen for these experiments. As an ex-
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perimental plan, chemicals were tested
in similar groups: phthlate esters [bis (2-
ethylhexyl), di-n-octyl, di-n-butyl, and
diethyl], polynuclear aromatics [naphtha-
lene, anthracene, phenanthrene, and
benz(a)anthracene], and chlorinated aro-
matics (chlorobenzene and p-dichloro-
benzene).
A rationale was established for the
loading rates of individual organic
chemicals used in these experiments. As
a reference loading rate (1X), the sludge
nitrogen loading of 500 kg/ha per year
was selected as an intensive-use design
criterion. From extensive municipal
sludge characterizations available, the
nitrogen content was taken as 5% on a
dry solids basis. From the available priority
pollutant data, the average total solids
concentration was 57,000 mg/L for pri-
mary sludge. The average concentration
in wet sludge was determined for each
organic compound. This organic com-
pound concentration was combined with
the dry solids concentration and nitrogen
loading rates to determine the reference
study rate for each chemical. Each in-
vestigation usually involved multiples of
the reference rate, typically 10X and
100X.
The experiments were conducted in a
greenhouse with temperature and hu-
midity control. The study cf organic
priority pollutants was undertaken pri-
marily using 14C-labeled compounds. A
Norfolk fine, loamy, siliceous, thermic,
typic, paleudult soil was selected. The
vegetation species used were fescue,
corn, wheat, and soybeans. Most plants
were sampled after early growth of about
30 days, but the wheat and soybeans
were allowed to grow to maturity. These
latter species were then sampled, with
the plant and seeds being analyzed
separately for chemical uptake.
The primary determination of plant
uptake of an organic chemical was by 14C
analysis. This quantification after the
initial loading period was necessarily a
combination of metabolites and parent
compound. Thus such data represent
maximum uptake of parent compound. In
a number of situations, thin-layer chro-
matography (TLC) was used to verify the
percentage of 14C detected that was
actually parent compound. These data
were used to judge the overall behavior
of the parent compounds.
The loss of each chemical from the soil
system was determined to evaluate this
major pathway. Losses were a combina-
tion of microbial decomposition and
volatilization. Determination of the
chemical concentration in the soil at the
start and end of the plant growth cycle
was used to assess overall loss. The rate
of loss was thus a minimum measure,
since decomposition was often sub-
stantially achieved over shorter time
periods.
Results
PhthallcAdd
The phthalic acid loading rate to the
soil was 0.6, 6, 60, and 600 ppm; also, a
control sample received no phthalic acid.
Height and dry weight of corn (21 -day),
tall fescue (45-day), immature soybean
(21-day) plant, mature soybean plant,
soybean seeds, wheat seeds, and mature
wheat straw were not affected by the
phthalic acid applied to the soil. The
height of immature wheat (40-day) was
affected at the highest chemical loading
rate. The phthalic acid uptake ranged
from less than detectable to 23 ppm and
was significantly above the control for all
plants and plant materials except soybean
pods. Fescue and immature wheat plants
exhibited the highest concentration of
phthalic acid, and mature wheat plants
and wheat seeds exhibited the least. Most
of the phthalic acid was lost from the soil
by the end of the study, with an average
of only 5.7% recovered in plants and soil.
Phthalic Add Esters
The loss from soil and uptake by
vegetation was investigated at initial
loading rates of 0.022,0.22, and 2.2 ppm
for all the phthalate esters except di(2-
ethylhexyl), which was 0.44, 4.4, and 44
ppm. The height and dry weight of young
corn, fescue (30-day), mature wheat, and
mature soybeans were not affected phyto-
toxically at these chemical loading rates.
Plant uptake (14C basis) of phthalate esters
was typically at less than detectable limits
(LDL) — up to 1 ppb for the loading rates
corresponding with municipal sludge
practice, except for di(2-ethylhexyl), which
was between LDL and 28 ppb. Crop levels
increased with increasing soil loading
rate, but the bioaccumulation (ratio of
chemical concentration in the dry plant
to the level initially applied to the soil)
was always less than 0,1 and averaged
0.06 in plants and 0.03 in the seeds
harvested. The plant bioaccumulation
ratio is typically lower than the above
volume by a factor of 4.5 when the
chemical concentration of the fresh plant
is used. The percentage of UC that was
actually found to be phthalate ester (by
TLC method) in the plant ranged between
9% and 35%. After correcting for the TLC
results and the ratio of extraction to
plant-bound 14C, the bioaccumulation
factor (dry-weight basis) is about 0.04 for
plants and 0.07 for seeds. Loss of phtha-
late ester after incorporation in the sur-
face 15 cm of soil appears to be by first
order process (coefficient of loss about
0.3 days'1) followed by a much slower
rate of decrease. In an overall UC balance,
between 1% and 25% of the radiolabel
was still in the plants, roots, or soil at the
time of harvest.
Polynuclear Aromatics
For each chemical in this group, the
loading rate to the soil was 0.1, 1.0, and
10 ppm; also, a control sample received
no polynuclear aromatic compound.
Neither the chemical, the application rate,
nor the replication had significant effects
on total dry weight or height at harvest
for any of the crop plants studied. Thus
no phytotoxic response for these four
vegetative species was observed over the
range of chemical loading. The average
chemical uptake levels ranged from LDL
to 0.59 ppm for all plants and varied
directly with the loading rate applied to
the soil. Overall, immature wheat, corn,
and mature soybeans had the greatest
uptake, whereas soybean seed, mature
wheat plants, and wheat seed had the
least. Uptake also varied by chemical. For
all plants at all rates, the uptake was
ranked anthracene > benz(a)anthracene
> naphthalene > phenanthrene. Regres-
sion equations were produced to predict
plant uptake from soil loading rates.
Soil retention reflected chemical struc-
ture, water-solubility, and vapor pressure.
Benz(a)anthracene, with the largest struc-
ture, lowest water solubility, and lowest
vapor pressure, was most resistant to
loss. In contrast, naphthalene, with the
simplest structure, highest vapor pres-
sure, and highest water solubility, was
lost from the pots at the greatest rate.
Plant uptake accounted for very little of
the mass of applied radiolabel — less
than 0.5%.
Chlorinated Aromatics
The soil loading rate was 0.0094 ppm
for chlorobenzene and 0.2 ppm for p-di-
chlorobenzene, based on the projected
levels from cumulative annual municipal
sludge land treatment. In addition, a con-
trol sample received no added chemical.
No effect was observed in regard to
phytotoxicity at these soil loading rates of
chloro- and p-dichlorobenzene. The up-
take of chlorobenzene by plants was from
0 to 23 ppb, with the latter concentration
being achieved by fescue grass. For p-
dichlorobenzene, the uptake range was 0
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to 1 ppm, with immature wheat having
the highest concentration. This group of
chemicals was the only one to evidence a
14C bioaccumulation factor greater than
1.0 on a dry-plant basis. The factor for
green plants was less than 1.0. Verifica-
tion of the actual amount of parent
compound was not possible. The soil
concentrations after about 45 days were
8% of the initial loading for the chloro-
benzene and 4% for p-dichlorobenzene.
Thus losses from the soil system were
extensive.
Organic Chemicals In the
Presence of Municipal Sludge
A limited series of studies was con-
ducted in which organic compounds were
added to the soil in the absence of
municipal sludge and at two rates of
sludge addition (0.16 and 1.6 dry tons of
sludge per acre). The chemicals used in
separate pots were di-n-butyl phthalate
ester (0.22 ppm), chlorobenzene (0.0094
ppm), and p-dichlorobenzene (0.2 ppm).
For these three chemicals, plant uptake
by the four species used showed no
increase or decrease with the presence
of municipal sludge. That is, there was
no statistically significant dependence on
the presence or the rate of sludge addi-
tion. The exception to this was with di-n-
butyl phthalate, in which the uptake was
lowered by a factor of 2 to 3 when sludge
was also present. Over the duration of
one plant cycle, the loss of these organic
compounds from the soil was essentially
the same whether sludge was present or
not.
Summary and Conclusions
Important, previously unavailable,
quantitative data were obtained for each
separate chemical group studied. How-
ever, the aggregate behavior of all
chemicals leads to additional conclusions
about municipal sludge land treatment.
Two factors seemed to unify the experi-
ments: (1) The chemical concentration in
soil at the end of the experiment was a
measure of the chemical concentration
in soil over the duration of the experi-
ment, with higher concentrations indicat-
ing more compound available for uptake,
and (2) the water solubility of a chemical
was a measure of its availability in the
water phase, with lower solubility imply-
ing that any chemical present might be
bound to the soil (lipophilic phase).
An initial conclusion is that probably
all organic compounds have properties
that permit uptake by vegetation. Such
uptake occurs in natural soils and is
limited by the degree of solubility and by
the magnitude of competing mechanisms
(compound decomposition, volatilization,
absorption, etc.) occurring in the soil. All
compounds used in these experiments
were found in some vegetation, although
for many plants, no detectable concen-
trations were found. A similar conclusion
can be reached concerning all inorganics
(such as metals); and it simply reflects
the equilibrium distribution of all chemi-
cals between soil and water with the
subsequent dynamic processes by which
plants take up water from the soil.
Among the chemicals investigated, the
ratio of chemical concentration in the
fresh plant to that in the soil at the
beginning of the experiment appears to
indicate low bioaccumulation. That is,
this ratio was always less than 1.0 and
most often than 0.1. In the majority of
cases, the ratio is less than 0.01. The
actual ratio is probably far lower since
14C — and not exclusively the parent
compound — are being measured at the
end of the experiment, whereas the initial
soil loading is clearly the parent
compound.
The factors affecting plant uptake are
complex and involve competing soil be-
havior for each specific organic com-
pound. If one qualitatively diagrammed
the factors of relative availability for a
chemical in a soil system and of relative
loss by competing mechanisms, the crop
uptake would appear to have certain
trends. For chemicals in which competing
losses are high (i.e., volatile or microbially
labile), the compound is not available for
uptake. Likewise, if a compound is pre-
sent but not easily dissolved in water, the
chemical will then be bound to the soil
(the organic phase) and will not be readily
available. Conversely, compounds that
are only slowly lost by competing path-
ways and are highly water soluble would
be predicted to have generally higher
rates of plant uptake. The compounds
studied in this project offer few, if any,
exceptions to this qualitative behavior.
The specific conclusions of this report
are:
1. Measurement of radiolabel (which
can be parent or metabolites) proved
to be an indication of the parent 14C
compound.
2. After a full growth cycle, a certain
fraction of 14C and possibly parent
compound remained unextractable
from the plants.
3. All organic compounds studied were
taken up by plants, but the bioac-
cumulation factors appear to be
significantly less than 1. This condi-
tion represents a major safety factor.
since with the losses of an organic
compound (e.g., decomposition),
uptake of successive crops will
approach the lowest level of
detection.
4. For the three organic chemical
groups studied, the bioaccumulation
factor (chemical concentration in the
fresh plant: chemical level applied
to the soil) was always less than
1.0; most often it was less than 0.1,
and in the majority of cases it was
less than 0.01.
5. No single crop (among corn, fescue,
soybean, and wheat) was routinely
the species with the highest uptake.
6. The competing phenomena of loss
from the soil and solubility (bioavail-
ability) appeared to control the levels
of an organic chemical taken up by
vegetation. These phenomena are
complex.
7. In experiments with three organic
compounds, the presence of
municipal sludge as a large organic
addition did not appear to signifi-
cantly alter the crop uptake or
decomposition of the organic chemi-
cals. Should these results prove
even qualitatively correct, large
amounts of available information
on organic compounds in terrestrial
systems could be used in estimating
the effects of specific organics on
land disposal of municipal sludges.
8. Organic compound studies in
municipal sludge land treatment
systems will remain complex, ex-
pensive, and time-consuming in-
vestigations for the near future.
The overall specific recommendations
for future research are as follows:
1. Investigations should be initiated to
expand the number of groups of
organic chemicals in which repre-
sentative compounds are evaluated
as to their behavior in soil-plant
systems.
2. Designers and evaluators of munici-
pal sludge land treatment systems
must maintain some perspective
about the effects of all the various
sludge constituents (e.g., pathogens,
metals, organics, anions) when
evaluating or designing municipal
sludge land treatment systems.
3. With the limited information avail-
able as a part of this report, and
with data more broadly available,
preliminary consideration of the risk
sequence probable with municipal
sludge and crops grown on such
systems should be undertaken.
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The full report was submitted in ful-
fillment of Grant No. CR806421 by North
Carolina State University under the
sponsorship of the U.S. Environmental
Protection Agency.
Michael R. Overcash, Jerome B. Weber, and William Tucker are with North
Carolina State University, Raleigh, NC.
James A. Ryan is the EPA Project Officer (see below).
The complete report, entitled "Toxic and Priority Organics in Municipal Sludge
Land Treatment Systems," (Order No. PB 86-150 208/AS; Cost: $16.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
4
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S2-86/010
QCQQ329
U S
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