United States
Environmental Protection
Agency
Environmental Research
Laboratory
Gulf Breeze FL 32561
Research and Development
EPA-600/S3-83-021 June 1983
Project Summary
Effects of Drilling Fluids on
Embryo Development
Richard B. Crawford
Toxicity of used drilling fluids to
embryo development was investigated
to ascertain the limits of safe usage of
these fluids in marine environments.
Embryos used as test systems were of
theteleost Fundulus heteroclitus. and
four echinoderms Echinarachnius par-
ma. Strongylocentrotus purpuratus.
Lytechinus p/ctus, and Lytechinus
variegatus. Gametes were collected in
season and combined for fertilization;
the resultant embryos were reared in
various concentrations of the drilling
fluids. Any departure from normal
developmental patterns was noted and
the embryotoxicity for each flu id deter-
mined. The drilling fluids tested came
from various sources; 24 different sam-
ples were evaluated In addition, several
commercial drilling fluid components
were examined in the test systems
including a synthetic reference mud.
These studies demonstrated that no
single drilling fluid is "typical" and that
the quantitative effects on embryos
vary considerably from one fluid to
another. Some drilling fluids are quite
toxic to one or more of the embryo
systems, requiring dilutions of over
10s to become "safe." Others are
relatively innocuous, requiring very little
dilution to achieve a concentration in
which embryo development can pro-
ceed normally. Also, the effects on
development show variation from one
fluid to another, thus indicating that a
variety of components or compounds
are responsible for toxic manifestations.
Identification of the components re-
sponsible fortoxicity must await chemi-
cal analysis of these fluids.
This Project Summary was developed
by EPA's Environmental Research La-
boratory, Gulf Breeze. FL, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
As a result of offshore petroleum drilling,
large quantities of drilling fluids (muds)
are introduced into the marine environ-
ment These drilling fluids are aqueous
suspensions of a variety of components
pumped down the center of the drill bit.
The composition of such fluids varies with
the needs of the drilling operation, such as
lubrication, cooling, prevention of intrusion
of seawater into the bore hole, antibacterial
action, suspension of drill cuttings, and
capture of H2S. The drilling fluid may be
partially or wholly discharged into the
surrounding waters during drilling, espec-
ially at its completion. This discharge can
amount to significantly large quantities in
the vicinity of a drilling platform.
The impact of drilling fluids on marine
and estuarine environments has been
largely unknown due to the paucity of
toxicological studies. Recently, a few
studies on biological parameters affected
by drilling fluids have been reported. Ef-
fects on the chemosensory neurons in the
walking legs of the lobster have been
examined. The impact of drilling fluids on
the distribution of organisms in benthic
communities has been measured. Several
marine invertebrates, as well as some
teleosts, have been tested for their survival
in dilutions of drilling fluids. In each case,
some drilling fluids at appropriate concen-
trations have been shown to have adverse
effects on the biological model.
The studies reported here were carried •
out to examine in some detail the effect of
several representative drilling fluids on
fertilization and embryo development For
model systems, embryos of an estuarine
teleost Fundulus heteroclitus, were chosen
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as well as embryos of four echinoderms,
Echinarachnius parma, Strongylocentrotus
purpuratus, Lytechinus pictus, and Lyte-
chinus variegatus. These models rep-
resent a variety of habitats and embryo
types which would be found in the vicinity
of petroleum drilling operations. In addition,
each of these species represents an im-
portant member of food chains. Conditions
which might interfere with the reproductive
capacity of the species would have effects
more far reaching than simply on the
species alone.
Design of Experiments
Models for the study of effects on em-
bryogenesis must be easily obtained and
easily reared in the laboratory. Also, they
should represent species found in the
locale of interest Furthermore, it is helpful
if the species has been extensively studied
so that conditions for its use may be
anticipated. All these criteria were met by
the species used in these studies.
Because Fundulus eggs and sperm were
obtained in season, the time of fertilization
could be controlled. Within one minute of
fertilization, the zygotes were placed in
various seawater dilutions of the drilling
fluids. The embryos developed in those
fluids until a few days past hatching (35
days) and the various aspects of develop-
ment were observed daily. Any departure
from observed normal development was
considered a measure of the toxicity of the
drilling fluid.
Sand dollar and sea urchin gametes
were obtained in season by intracoelomic
injection of KC1. Within 15 minutes after
fertilization, the embryos were placed in
the drilling fluid solutions and develop-
ment was observed. Rearing these em-
bryos through the pluteus stage takes
about four days and therefore an assay
may be accomplished quite quickly. In
addition, the gametes may be pre-incu-
bated in drilling fluid solutions to test the
effects of these substances on fertilization.
Drilling fluids of various types and from
scattered regions were obtained from the
Environmental Research Laboratory of the
United States Environmental Protection
Agency, Gulf Breeze, Florida. These fluids
were stored at 4°C and, when dilutions
were made for testing, were kept at the
temperature used for rearing the em-
bryos. Commercial components of drilling
fluids were also obtained from the U.S.
EPA and were tested for their toxicity.
Drilling fluid test solutions were stan-
dardized according to dry weight Since
the dry weights of the fluids showed great
variation (from 1 300 mg/ml to 135 mg/
ml) different amounts of dilution were
required to achieve the standard stock
suspension of 10 parts per thousand
(ppt). This suspension was stirred for 1
hour and then filtered through Whatman
#1 paper. Further dilutions were made by
diluting the 10 ppt stock with filtered sea-
water.
Results
Fundulus development was not affected
by any of the drilling fluids during early
stages. At the onset of organogenesis,
some fluids caused a diminution of heart
beat rate at 10 ppt The most significant
effect was on hatching and on coordination
of swimming of the fry. Adverse effects on
these activities could be achieved at con-
centrations of 1 ppt with some fluids.
Echinoderm egg fertilization was pre-
vented by most drilling fluids at concentra-
tions of 10 ppt Many of the fluids also
significantly reduced the fertilization rate
at 1 ppt Some of the components were
effective against fertilization at 10 parts
per million (ppm), especially those contain-
ing lignosulfonates or detergents.
Development of the echinoderm em-
bryo was the most sensitive test with
these drilling fluids; adverse effects were
observed in some cases at 100 ppm and
10 ppm. Developmental arrest or distor-
tions occurred at a variety of stages, de-
pending on the fluid tested. Also, the
commercial drilling fluid components, es-
pecially those containing lignosulfonates
or detergents, inhibited development at
low concentrations.
From the data it is clear that drilling
fluids vary to a considerable extent regard-
ing their toxicity. By calculating actual
dilutions of the fluids required to achieve
toxic manifestations, "safe" dilutions, or
concentrations of the drilling fluids which
yield no adverse effects in these assay
systems, can be determined. Such "safe"
dilutions range from 135 to 1,132,000
(least toxic to most toxic). That is, one of
the fluids must be diluted about one-
million-fold to allow normal development
of one of the sea urchins. On the other
hand, another fluid is "safe" by diluting it
slightly more than one-hundred-fold.
Conclusions
Clearly, drilling fluids contain toxic ma-
terials, substances which interfere with
fertilization and normal development It is
also clear that no one fluid is typical. Since
the range of toxicity varies greatly from
one fluid to another, it is not always
possible to prejudge the effect on marine
life of a large discharge of drilling fluids
from a drilling rig; each fluid must be
tested, or an accurate log kept of the
makeup of the fluid compared with log
data from previously tested fluids. Even
with such logs, the effects of cuttings from
the bore hole on the toxicity of the fluid
would not be known.
Further, accurate determinations of the
actual dilutions of discharges from rigs
must be known. If a dilution of one million
fold were easily obtained a short distance
from a rig, it would seem that the most
toxic drilling fluid is harmless to the animal
systems tested in these studies. Also,
more data are needed about chemical or
physical changes in the drilling fluid that
might render it more or less toxic in
seawater over a given period of time.
Comparison of chemical analyses of
these drilling fluids with their toxicities
may yield interesting and useful conclu-
sions regarding those components which
are harmful.
Richard B. Crawford is with Trinity College, Hartford. CT061O6.
Thomas W. Duke is the EPA Project Officer (see below).
The complete report, entitled "Effects of Drilling Fluids on Embryo Development,"
(Order No. PB 83-190 983; Cost: $8.50, 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:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Sabine Island
Gulf Breeze, FL 32561
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