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Ocean Dumping of Containerized DDT Waste Was a Sloppy Process
Veronika Kivenson,
†,⊗
Karin L. Lemkau,
‡,⊗,∇
Oscar Pizarro,
§
Dana R. Yoerger,
∥
Carl Kaiser,
∥
Robert K. Nelson,
⊥
Catherine Carmichael,
⊥
Blair G. Paul,
‡
Christopher M. Reddy,
⊥
and David L. Valentine*
,‡,#
†
Interdepartmental Graduate Program in Marine Science, University of California, Santa Barbara, California 93106, United States
‡
Marine Science Institute, University of California, Santa Barbara, California 93106, United States
§
Australian Centre for Field Robotics, University of Sydney, Sydney 2006, Australia
∥
Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
02453, United States
⊥
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02453,
United States
#
Department of Earth Science, University of California, Santa Barbara, California 93106, United States
*
SSupporting Information
ABSTRACT: Industrial-scale dumping of organic waste to
the deep ocean was once common practice, leaving a legacy of
chemical pollution for which a paucity of information exists.
Using a nested approach with autonomous and remotely
operated underwater vehicles, a dumpsite offshore California
was surveyed and sampled. Discarded waste containers littered
the site and structured the suboxic benthic environment.
Dichlorodiphenyltrichloroethane (DDT) was reportedly
dumped in the area, and sediment analysis revealed substantial
variability in concentrations of p,p-DDT and its analogs, with a
peak concentration of 257 μgg
−1,∼40 times greater than the
highest level of surface sediment contamination at the nearby
DDT Superfund site. The occurrence of a conspicuous
hydrocarbon mixture suggests that multiple petroleum
distillates, potentially used in DDT manufacture, contributed to the waste stream. Application of a two end-member mixing
model with DDTs and polychlorinated biphenyls enabled source differentiation between shelf discharge versus containerized
waste. Ocean dumping was found to be the major source of DDT to more than 3000 km2of the region’s deep seafloor. These
results reveal that ocean dumping of containerized DDT waste was inherently sloppy, with the contents readily breaching
containment and leading to regional scale contamination of the deep benthos.
■INTRODUCTION
Deep ocean disposal of industrial, military, nuclear, and other
hazardous waste was a pervasive global practice in the 20th
century, the full magnitude of which remains unknown. In the
United States, records indicate that 50−97 million tons of
industrial waste were dumped at sea,
1−5
representing an
unknown fraction of the total quantity. This ambiguity is due
to sparse documentation as well as illegal and clandestine
disposal operations. The extent to which containerized waste
escaped containment, referred to here as “sloppy dumping”,
also remains uncertain. Abandoned industrial waste deep-sea
dump sites exist along all coastal states,
1−5
and one such site,
located in the Southern California Bight, is the focus of this
study (Figure 1A). According to a technical report by
Chartrand et al.,
6
this area may contain 336000−504000
barrels of acid sludge waste from the production of dichlor-
odiphenyltrichloroethane (DDT), in addition to various other
containerized waste streams.
7
Prior to this work, the
disposition of this waste and the status of its containment
was unknown.
DDT is an organohalide insecticide that was used
extensively in the 20th century, leading to a precipitous decline
in mosquito-borne malaria morbidity and mortality rates.
8,9
However, due to its indiscriminate use, recalcitrance, lipophilic
bioaccumulation, and adverse impacts on ecosystem and
human health, it was banned in 1972 for domestic use in the
US.
10
Montrose Chemical Corporation (MCC) was the largest
global supplier of DDT, manufacturing ∼800000 tons of the
compound at their Los Angeles County plant from 1947 to
Received: October 17, 2018
Revised: February 10, 2019
Accepted: February 18, 2019
Article
pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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1982; production following the US ban was exclusively for
export.
11
The sole product MCC manufactured, technical
grade DDT, was sold to other companies for formulation into
more dilute commercial insecticide products.
11
The composi-
tion of technical grade DDT was 65−80% p,p′-DDT (the main
insecticidal compound), 15−21% o,p-DDT, and small amounts
of other compounds, including impurities in the form of 1,1-
dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) and 1,1-
dichloro-2,2-bis(p-chlorophenyl)ethane (DDD).
12−14
Addi-
tionally, both DDE and DDD are common breakdown
products of DDT, and along with the DDE metabolite, 1-
chloro-2,2-bis(4-chlorophenyl)ethylene (DDMU), are fre-
quently detected in the environment. DDE, the result of
abiotic or aerobic degradation of DDT, is typically the most
abundant compound.
15−19
We use the shorthand notation
DDX to refer collectively to o,p′-DDT, p,p′-DDT, o,p′-DDE,
p,p′-DDE, o,p′-DDD, p,p′-DDD, and p,p′-DDMU and ∑DDX
as the summed concentration of DDT, DDD, DDE, and
DDMU (or DDX*for instances where DDMU was not
included). In cases where DDT or a metabolite is described
without a specified isomer, this refers to the sum of both
isomers (e.g., DDE = p,p′-DDE + o,p′-DDE).
Waste-management practices at MCC included discharge of
DDT-laden waste products into storm drains and the sewer
Figure 1. (A) Map of the study region. (B) Multibeam bathymetry from AUV Sentry dive 208. (C) Close-up view of selected area from panel B,
highlighting topographic anomalies consistent with barrels. (D) Sidescan sonar from AUV Sentry dive 208 highlighting anomalies consistent with
barrels. (E−H) Images of waste containers from AUV and ROV photo-surveys (I-P).
Environmental Science & Technology Article
DOI: 10.1021/acs.est.8b05859
Environ. Sci. Technol. XXXX, XXX, XXX−XXX
B
system from 1950 to 1971,
6,20
leading to contamination of the
Palos Verdes Shelf (PVS) with 870−1450 tons of DDT.
15,20,21
Because of this and other waste, the PVS was added to the US
National Priorities List for uncontrolled hazardous contami-
nation, otherwise known as Superfund site designation, and at
the time of this publication, remediation is ongoing.
MCC also engaged in another form of DDT waste discharge
not accounted for in the creation of the Superfund site:
permitted ocean dumping of containerized solid waste. The
ocean disposal of these manufacturing byproducts resulted in
at-sea dumping of an estimated 2000−3000 barrels per month,
equal to ∼1 million gallons of waste per year, from 1947 to
1961.
6
Ocean dumping practices were prescribed by the
California Department of Fish and Game, US Coast Guard,
and Los Angeles Harbor Department, specifying that waste-
hauling companies dump barrels at designated locations in the
basins offthe coast of Southern California, ∼16 km offshore;
however, short-dumping at locations closer to shore was
common practice.
6,22,23
Dumping of other containerized waste,
including caustic and acid waste produced by petroleum
refineries, also occurred in these areas.
6,7,24
The DDT contents of MCC’s waste barrels was substantially
lower than the composition of the product they sold. While not
explicitly documented, it has been estimated to contain 0.5−
1% DDT, totaling 384−767 tons of DDT; the remainder was a
mixture of sulfuric acid, organic substances, and water.
6
However, a patent on DDT acid waste treatment describes
this mixture as about 2% DDT, 72% sulfuric acid, 25% p-
chlorobenzene-sulfonic acid, with traces of water and hydro-
chloric acid.
25
Thus, we surmise that the total DDT content of
waste in ocean-dumped barrels may have been as high as 2%,
resulting in the revised range of 0.5−2%, and a total discharge
of 384−1535 tons. The upper limit of this revised estimate is
comparable to DDT released at the White Point outfalls, on
the nearby PVS Superfund site (870−1450 tons of DDT).
15,21
In addition to the ambiguity about the total amount of DDT
dumped into the deep ocean as containerized waste, several
other factors contribute to the complexity of understanding the
fate and impact of these materials. First, minimal record
keeping was performed as to what, where, when, and how
waste was dumped. Second, site access is limited and costly
due to the ∼900 m site depth, which requires substantial
resources (e.g., the use of specialized submersibles for
identifying relatively small seafloor anomalies and for benthic
sampling, as well as the cost of the associated vessel). Third,
potential shelf sources
16,26,27
complicate interpretation of DDT
origin. Fourth, decades of overprinting from environmental
processes such as burial, suspension, redistribution, and
biodegradation have undoubtedly altered the site’s chemical
inventory.
15,17,28,29
Fifth, the hydrophobic nature of DDT
30
and its potential association with organic matter, including
sorption to hydrocarbons, has previously been found to
influence localized concentrations
31
and may affect DDX
distributions in basin sediment. Sixth, spatial variability related
to the location of dumping provides for an expectation of
heterogeneity. Finally, the integrity of waste containers is
unknown, precluding an accurate assessment for the spatial
distribution of contamination. Given these ambiguities, the
scale of ecological effects is uncertain and the long-term fate of
the disposed material remains unknown.
In this work, we describe a nested approach to the
exploration of deep ocean waste dumpsites as applied to the
suboxic San Pedro Basin (SPB), located offthe coast of
southern California (Figure 1A). We first apply autonomous
underwater vehicle (AUV) technology to identify sea floor
anomalies consistent with containers and to collect associated
images of the sea floor. We then use a remotely operated
vehicle (ROV) to collect sediment cores for analysis of
chlorinated hydrocarbon and hydrocarbon distributions, to
generate insights into the industrial processes that gave rise to
the contamination, as well as the weathering and biogeochem-
ical processes that occurred since deposition. Finally, we apply
these findings to provide a framework for differentiating the
major sources of DDT contamination at the regional scale.
This nested approach has considerable potential for other areas
of seafloor exploration, in addition to exploration of deep-sea
waste disposal sites.
■MATERIALS AND METHODS
Mapping and Sampling. These sites were accessed using
the AUV Sentry and the ROV Jason. The AUV Sentry was
deployed to collect high-resolution multibeam echosounder
(MBES) bathymetry,
32
which was processed shipboard to
identify positive elevation anomalies consistent with barrels.
The ROV Jason was deployed to enable closer inspection of
the observed features and sampling of the sediments.
Following ROV retrieval, sediment cores were sectioned at
2 cm intervals and samples stored at −20 °C for chemical
analysis. Further description of the mapping and sampling
information is provided in the SI Methods.
Analytical Methods. Extensive chemical analysis by means
of one-dimensional and comprehensive two-dimensonal gas
chromatography (GC and GC ×GC) with mass spectrometry
(MS), flame ionization detection (FID) and high resolution
time of flight mass spectrometery (HR-ToF-MS) were
conducted to analyze chlorinated and other hydrocarbons as
described previously,
33−37
and the methods used in this study
are described in full in the SI Methods.
DDX Mass Balance. DDX source attribution for each core-
top sample
38
was calculated assuming a mass balance of two
end-members: sediment near to the White Point sewage
outfalls (∑DDX:∑PCB = 13.8) and dumped barrels that
contain DDX but no PCBs (∑DDX:∑PCB = ∞). The
following mass balance results:
=−
f
RR1/
dPVS s (1)
where fdis the fraction of ∑DDX attributed to deep-sea
disposal for a given sample; RPVS is the ∑DDX:∑PCB ratio
assumed for the PVS endmember (13.8); and Rsis the
∑DDX:∑PCB ratio for a given sample. The full list of
compounds, concentrations, method detection limits and other
relevant information about data processing for figure plots is
included in the SI Methods.
■RESULTS AND DISCUSSION
Discovery and Observations. According to a 1985
technical report by Chartrand et al.,
6
practices for industrial
waste dumping at specific locations in the SPB and Santa
Monica Basin (SMB) were established in 1947 by the
California Department of Fish and Game, US Coast Guard,
and Los Angeles Harbor Department. However, dumping at
unassigned locations was known to be common practice.
23
One of the assigned dumpsites (Figure 1A) is located near an
existing methane hydrate study site, and we were twice
afforded the opportunity to use robotic marine technology to
Environmental Science & Technology Article
DOI: 10.1021/acs.est.8b05859
Environ. Sci. Technol. XXXX, XXX, XXX−XXX
C
explore the seafloor in this area. Samples for the current study
were collected from two adjacent locations (J2-603 and J2-
746) within the study site (Figure 1A and Figure S37).
In 2011 and 2013, we developed and applied a nested
approach to investigate seafloor features near the assigned
dumpsite in the SPB. This approach included use of AUV
Sentry for identification of seafloor anomalies by multibeam
echosounder (Figure 1B,C), side scan sonar (Figure 1D), and
stereopaired imaging (Figure 1E−H), followed by the use
of ROV Jason for detailed visual surveys (Figure 1I−P) and
sample collection. We focused on the landward side of the
assigned dump area, with logic dictating that shorter trips
would be desirable for those who conducted dumping
operations. About 60 waste barrels were visually located at a
water depth of ∼900 m. All barrels were partially buried in the
sediment, though it was not possible to differentiate initial
emplacement versus subsequent sedimentation. Some of the
barrels were clearly not intact (Figures 1L and S4,S6),
including barrels with apparent puncture marks (Figures
1E,N and S22), while the presence of gas inside other barrels,
observed during sampling, suggests that they were at least
partially intact. Different barrel and cylinder types were present
at the site (Figures 1E−P and S1−S35), implying multiple
waste origins, consistent with the report of Chartrand et al.
6
The stereopair imaging from AUV Sentry was used to estimate
the volume for several of the barrels and cylinders (Figure
S36). Some barrels had dimensions consistent with standard
110-gallon and smaller drums, while others were consistent
with XL-type gas cylinders. There is evidence to suggest that
the waste was dumped purposefully. Many barrels occurred in
groups of identical appearance (Figures 1M and S18−S21).
Concrete footings for barrels and cylinders chained at the neck
to a footing around their base suggest intentional ballasting.
Additionally, the distribution of barrels on the seafloor
corresponds to an imprecise line, as would occur if barrels
were offloaded from a moving barge (Figures 1C and S37−
S42).
The biota associated with barrels at this low-oxygen (<10
μM) site
39,40
is fundamentally different from other settings
where barrels serve as artificial substrate for the growth of
sessile organisms, including sponges, anemones, and tunicates,
and provide habitat for crabs, starfish, and brittle stars.
41−43
In
those settings, sessile organisms sometimes form distinct
structures on barrels, resembling bioherms.
41−43
In this study,
sponges were observed on some barrels, for example, Figure
1E,G,O, and one of the barrels apparently hosted dozens of
snails (Figure S4C). However, rather than promoting
substantial macrofaunal growth, the barrels in this oxygen-
limited environment primarily host microbial communities,
including apparent mats of filamentous sulfur bacteria atop
some barrels and ring-structured microbial mats on the
sediment surface surrounding some barrels (Figures 1F,H−K
and S2−S35). In some instances, the bordering microbial ring
formation differentiates the appearance of the sediment surface
inside versus outside the ring (Figures 1F,J,K and S7, S25,
S27−S29, and S35).
Disposition of Chlorinated Hydrocarbons in Sedi-
ments. Sampling was conducted under the presumption that
many of the barrels contained DDT, based on the report of
prolific dumping at or near the study site.
6
Using the ROV
Jason, 19 sediment cores were collected (four in 2011 and 15
in 2013) (Tables S1−S6) to reconstruct the chronology,
magnitude, and spatial distribution of contamination, including
an association with barrels and their microbial ring features.
Target analytes included isomers of DDT and its degradation
products, DDD, DDE, and DDMU. While these compounds
have been monitored extensively at the PVS, few analyses have
been conducted in the SPB, despite reported waste disposal
operations in the region.
38,44−46
DDT and its degradation
products were present in all cores, and the concentrations were
highly variable (Tables S1−S6). Notably, proximity to barrels
does not appear to control ∑DDX (Figures S37 and S43−S45
and Table S7); sediment with the highest ∑DDX was
collected away from barrels, including one core with high
∑DDX concentrations (core 11-1A) taken at a conspicuous
mound. These findings indicate the disposal process was
inherently sloppy, which we define here as intentional disposal
of containerized waste wherein the waste ultimately escapes
the container.
The DDX chemical data set consists of 386 concentrations,
comprised of four metabolites across five depth horizons (at 2
cm resolution to a depth of 10 cm) for 19 cores (two of which
were subsampled, see Methods) and is summarized in Table
S8. Here, we consider the findings in terms of three discrete
sediment intervals (Table S1−S3) representing different eras
based on the assumption of uniform sedimentation at a rate of
∼1mmy
−1:
47
postdisposal (core-top 0−2 cm; after domestic
DDT use and disposal ended), peak disposal corresponding to
dumping operations (midcore 4−6 cm), and predisposal
(down-core 8−10 cm; preceding widespread DDT use or
disposal). Depth profiles of ∑DDX for representative cores
from the sampling sites (J2-603 and J2-746) are shown in
Figure 2 along with the metabolite distribution by depth
horizon.
The postdisposal (core top) ∑DDX concentrations are
variable (Table S1), with a maximum of ∼800 ng g−1and a
mean of 106 and 201 ng g−1at the J2-603 and J2-746 sites,
respectively (Figure S46A). Postdisposal sediment overlying
high DDT intervals is not systematically enriched in ∑DDX
compared to other samples. DDE was dominant in many
samples.TheprevalenceofDDEmaybeduetothe
combination of DDE originating from waste in barrels, and
an additional input of DDE from the PVS, where DDE is an
abundant contaminant.
15
Data from another study reveals a
similar trend of relatively low ∑DDX surface concentrations
(dominated by DDE) overlying very high ∑DDX intervals in
the SPB.
24
These observations are consistent with ongoing
burial of DDX and only minor amounts of vertical
redistribution post deposition.
However, substantial DDT concentrations were also
observed in surface sediment not associated with underlying
intervals of high DDT, indicating that a recent or ongoing
source is also present. This is consistent with two samples
collected for a study by the Southern California Coastal Water
Research Project (SCCWRP), which also found elevated
surface concentrations of ∑DDX.
38
Importantly, one of our
samples and one of the SCCWRP samples from the SPB have
elevated concentrations of DDT, in excess of that measured for
the highest ∑DDX sample at the PVS,
38
suggesting a
contemporary, nonshelf source of DDT to the SPB. These
observations are consistent with the possibility that the
contents of the barrels are slowly leaking or that DDT
remobilization from buried sediment is occurring with spatial
heterogeneity, as might be caused by limited burrowing activity
of infauna.
Environmental Science & Technology Article
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D
The 4−6 cm depth interval corresponds to the recorded
period of disposal. Measured ∑DDX concentrations from the
J2-603 samples are low in two of four cores, while the other
two cores have elevated concentrations, one with ∑DDX of
257 μgg
−1, the highest of our data set (Table S5). For the
samples collected at J2-746, both the highest ∑DDX
concentration (1520 ng g−1) and the mean (370 ng
g−1) were substantially lower than the concentrations meas-
ured at J2-603 (257 000 ng g−1and 64 600 ng g−1, respectively;
Table S8). Again, this is suggestive of a nonuniform
distribution of discarded waste, demonstrating the occurrence
of hotspot contamination including elevated proportions of
DDT.
For the two cores with the highest ∑DDX in the 4−6cm
interval (cores 11-1A and 11-1B; Table S5,S6), the sediment
from this interval was split (see the Methods), and the
concentrations for each split were found to differ by an order
of magnitude. The ∑DDX*for core 11-1B and its split (S-
core 11-1B) were 256 μgg
−1and 26 μgg
−1, respectively while
core 11-1A and its split (S-core 11-1A) had concentrations of
96 μgg
−1and 7.9 μgg
−1. These data highlight substantial
heterogeneity in chemical concentrations across different
spatial scales: between the two adjacent sites, within a single
site (e.g., between different cores collected during a single
dive), as well as within a 2-cm core section. Large differences in
DDX concentration have recently been noted on the
centimeter scale for PVS sediment pore water,
31
and the
patchy concentrations of DDX may be influenced by the
hydrophobicity of DDT
30
and its sorption to hydrocarbons or
organic matter present in sediment.
31
In the predisposal sediment horizon (8−10 cm), most of the
∑DDX concentrations, as well as the mean and median
∑DDX, are substantially lower compared to those of
the overlying intervals (Table S3). Nonetheless, measurable
concentrations are apparent in our samples as well as in a core
previously collected near this site for another study (NOAA
core V),
24
consistent with slight downward redistribution in
the sediment. Notably, DDMU in the 8−10 cm depth horizon
from the J2-746 cores is common and accompanied by little or
no other DDX compounds, indicating this is not an artifact of
coring (Figure S46C). The presence of DDMU to the
exclusion of other metabolites in this depth horizon suggests
downward transport and subsequent degradation are occurring
in situ. For example, DDE can anaerobically degrade to
DDMU.
18
Distinguishing Contamination from Shelf and Deep
Basin sources. The PVS Superfund site is among the most
Figure 2. ∑DDX depth distribution for two representative cores, one
from each expedition: (A) J2-603 in 2011 and (B) J2-746 in 2013.
Concentrations are shown on a log scale (note different axes). Shown
at right is the distribution of DDX compounds corresponding to each
depth interval shown at left.
Figure 3. (A) Bathymetric map showing SCCWRP core-top sampling locations used for comparison in this study. Note that leftmost station is NW
of the PVS. Also shown are Dumpsites 1 and 2 (in the SMB and SPB, respectively). (B) Ratio of the ∑DDX:∑PCB by station type with median
(line) and the interquartile range (box) shown; the green dashed line shows the end-member ratio for the PVS reference site. (C) Percent of
∑DDX attributed to deep-sea disposal by location, as determined by the mixing curve, derived from eq 1 (see DDX Mass Balance). The detailed
(color) legend is as follows: red outline, white fill: SPB; light red fill: SMB north; dark red fill: SMB south; black diamond: Core 11-1B; grey
diamond: minimum estimate determined using method detection limits for ∑PCB for Core 11-1A; green box: PVS reference site. For data from
this study, ∑DDX*and ∑PCB*were used.
Environmental Science & Technology Article
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Environ. Sci. Technol. XXXX, XXX, XXX−XXX
E
contaminated sites globally for chlorinated hydrocarbons, with
a surface sediment ∑DDX concentration of up to 6.5 μgg
−1
measured recently near the White Point outfalls.
38
The PVS is
commonly considered the primary source of DDT contami-
nation to the Southern California Bight, for which 71% of
surface sediments are enriched in ∑DDX.
45
We asked what contribution deep ocean dumping could
have on the DDX inventory of the two offshore basins in this
region, an area comprising over 3000 km2. To make this
estimate, we developed a mass balance using the proportion of
∑DDX to polychlorinated biphenyls (∑PCB), an approach
similar to that suggested by Venkatesan.
24
PCBs are similar to
DDTs in terms of hydrophobicity, recalcitrance, and years of
disposal, but were neither manufactured in California nor
present in MCC waste barrels.
30,39,47−49
Importantly, PCBs
were commingled with DDT in the Los Angeles County
Sanitation District outfalls at White Point.
46
We chose the
most heavily ∑DDX-contaminated core sample at the White
Point outfalls (∑DDX:∑PCB = 13.8) (Figure 3A,B) as an
endmember representative of the Palos Verdes Shelf.
38
An analysis of core-top ∑DDX:∑PCB from a recent
monitoring campaign by SCCWRP
38
reveals that the deep SPB
(n= 4) and adjacent Santa Monica Basin (SMB) (n=7)
(Figure 3A) contain ratios of 48.2−54.1 and 24.3−65.8,
respectively, substantially greater than for the PVS and other
shallower environments (Figure 3BandTable S10).
Application of mass balance to these deep basin samples and
cores from this study (using ∑DDX*) yields a ∑DDX
fractional contribution for deep sea disposal ranging from 71 to
80% for the SPB and 43−79% for SMB (Figure 3C), with
some percentages as minimum estimates (the method
detection limit values were used when ∑PCB was below
detection limits).
To further validate the assumptions inherent to this
approach, diagnostic characteristics of DDX originating from
deep disposal were identified and assessed. Here, we examine
high-concentration DDX cores from this study as well as from
a core collected in the SPB in 1989, reported in a NOAA
technical document
24
(Table S9). First, the ratios of
∑DDX*:∑PCB are consistent with the premise that deep
ocean waste disposal is the source of persistent DDX
contamination in the SPB. Second, ocean-dumped barrels
contained waste from technical-grade DDT, which has
approximately a 4:1 ratio of p,p′-DDT to o,p′-DDT.
14,50
The
cores from this study yield ratios of 4.05 and 4.50; NOAA core
data are also in agreement. Third, high ∑DDX*was also
measured in these samples and is dominated by DDT or DDD
(>50%), inconsistent with material transported from the PVS
which is dominated by DDE and DDMU.
15,26,38
Finally,
sediment strata containing high ∑DDX correspond to the
timing for containerized waste dumping.
6
Although the spatial resolution of sampling is overly coarse,
these results are consistent with a scenario in which a majority
of DDX in the two borderland basins adjacent Los Angeles
derive primarily from deep ocean disposal, rather than the
highly publicized disposal to the PVS.
Chemical Complexity of Discarded Waste. To better
understand the provenance of waste dumped at the site, we
conducted additional chemical analysis including GC-FID on
J2-603 sediment (Figures S47−S49) and additional analyses
on the sediments with the highest concentrations of DDT (2−
4 and 4−6 cm depth horizons of core 11-1A and 4−6cmof
core 11-1B). The occurrence of multiple distinct petroleum
fractions was identified by GC−FID and GC−MS in the form
of a multimodal distribution of the unresolved complex
mixture (Figure 4B), triggering subsequent analysis by GC ×
GC−FID, GC ×GC−ToF−MS and GC ×GC−HR−ToF−
MS (Figure 4 and SI part 2 and part 3).
Using comprehensive two-dimensional chromatography,
these modes were resolved into five mass islands in
chromatographic space (Figure 4), four of which we attribute
to industrial petroleum distillates, based on the pattern of mass
distribution. The first eluting mixture comprises a minor
fraction of the total mass, and contains branched and cyclic
hydrocarbons containing ∼9−15 carbons. The compounds in
this mass island are primarily branched, isoprenoidal, and
straight-chain alkanes along with C0−C4decahydronaphtha-
lenes (decalins) with the C2-decalins as the most abundant
members of this suite of compounds. The second eluting
mixture contains aromatic and cyclic hydrocarbons with ∼12−
20 carbons, likely representing a light distillate cut similar to
diesel fuel. Compounds of note in this mixture include a
distinctive family of m-xylenes substituted with tertiary butyl or
other tertiary alkyls (Figure 4D). The abundance of these
unusual compounds suggests formulation by a second
industrial process, beyond simple distillation. This moderately
polar mixture has a lower boiling point than for DDT, making
it a candidate solvent for extraction and purification following
DDT synthesis. The third mass island contains compounds
commonly found in petroleum: tricyclic terpanoids (cheilan-
thanes), a tetracyclic terpanoid, and two steranes with
prominent m/z218 ions (diginane and 20-methyldiginane).
The fourth mixture is a petroleum residue that is dissimilar in
its biomarker distribution to regional oil seeps of the Monterey
Formation
51
(Figure 4E). This fourth mixture appears to be
consistent with a “tank bottom”residue left behind after
distillation, based on the presence of 2-methylanthracene and a
tentatively identified (by GC ×GC retention position) hopene
structural analog to 17α(H)-22,29,30-trinorhopaneboth
indicators of petroleum refining.
52
Collectively, the presence
of four apparent petroleum distillate cuts suggests complex
petrochemical use during DDT manufacture, potentially
overprinted by mixing of waste streams.
6,7,23
The mass resolving power of GC ×GC−HR−ToF−MS
enabled a search for organo-chlorine ions across the full GC ×
GC chromatogram (Figure 4A, SI Part 2), capitalizing on the
mass difference between chlorine isotopes. A complex mixture
of mainly chlorophenyl-containing compounds was identified
(Figure 4A) using the identification criteria indicated,
described in full in SI part 2 and part 3. In addition to DDT
and common degradation products (DDE, DDD, and
DDMU), several notable compounds were detected, including
dicofol isomers (peak 15), tris(4-chlorophenyl)methane
isomers (TCPMe, peaks 16 and 17), dichlorodiphenylmethane
isomers (DDM, peaks 3 and 4), and dichlorobenzophenone
isomers (DBP, peaks 5 and 6) in addition to a variety of related
compounds for which mass spectra did not match known
compounds (SI part 2 and part 3). Dicofol, synthesized from
DDT, is an acaricide that is currently in use in the United
States and was recently classified as a candidate persistent
organic pollutant in the Stockholm Convention.
53−55
Atmos-
pheric and current-driven transport has been previously noted
for dicofol, and this compound was detected in low
concentrations (<15 ng g−1) in sediment at 10 SCCWRP
stations, primarily in Los Angeles/Long Beach bays and
ports.
38,54−55,56
Since dicofol is currently in use, it is difficult to
Environmental Science & Technology Article
DOI: 10.1021/acs.est.8b05859
Environ. Sci. Technol. XXXX, XXX, XXX−XXX
F
determine its long-term fate in the environment, due to a lack
of temporal resolution for monitoring data (e.g., nonsurface
sediment). The presence of dicofol in buried strata observed
here hints at its persistence in the environment. TCPMe has
been described as an inadvertent byproduct of DDT
manufacturing
12
and has been detected globally in birds and
mammals,
57,58
including in Southern California dolphins and
pinnipeds.
59,60
Concentrations of DDX compounds in these
dolphins were greater than 1 order of magnitude higher than in
dolphins from other locations around the world, and TCPMe
(an unmonitored compound) was second only to DDE.
59
Under environmental conditions, TCPMe may be much more
persistent than DDT and its analogs; however, despite
evidence of its persistence and bioaccumulation, TCPMe is
rarely studied in marine sediments.
61
DDM and DBP are
anaerobic degradation products from dehalorespiration of
DDT,
17
and recent work suggests that DBP may be a main end
product of DDT degradation.
62
The presence of DDM and
DBP at low relative abundance suggests the trace occurrence of
this anaerobic microbial process is associated with these
wastes.
Biogeochemical Processes. Several lines of evidence
indicate that dumped wastes structure benthic biogeochemical
processes, including the occurrence of microbial mats on the
barrels, the microbial ring structures that surround some
barrels, and the presence of putative metabolic products from
Figure 4. Chemical composition of DDT waste from core 11-1A, color coded by chromatographic island. (A) Chlorine-containing compounds
identified by unique mass assignment with GC ×GC−HR−ToF−MS. Peaks labeled 1−17 are each chlorinated, with a subset of structures
identified as described in the matching identification criteria. Compound identities are as follows: (1)(2) Trichloroethenyl benzene (3)
Bis(chlorophenyl)-methane isomer A (4) Bis(chlorophenyl)-methane Isomer B (5) 2,4'-Dichlorobenzophenone (6) 4,4'-Dichlorobenzophenone
(7) o,p'-DDMU (8) p,p'-DDMU (9) o,p'-DDE (10) p,p'-DDE (11) o,p'-DDD (12) p,p'-DDD (13) o,p'-DDT (14) p,p'-DDT (15) Dicofol Isomers
(16) 2,3',4"-TCPMe (17) 4,4',4"-TCPMe. Inset shows the relationship between ring double bond equivalents (RDBE) and carbon number,
highlighting prevalence of chlorinated aromatics. (B) GC ×GC−ToF−MS chromatogram shown in mountain view, with the total signal collapsed
in white at rear to simulate a one-dimensional chromatogram. (C) GC ×GC−ToF−MS chromatogram shown in plan view, color coded to
highlight five mass islands. (D) Partial GC ×GC−ToF−MS chromatogram illustrating a putative family of m-xylenes substituted with tertiary
alkyl groups. (E) Partial GC ×GC−ToF−MS chromatogram annotated to identify common petroleum biomarkers.
Environmental Science & Technology Article
DOI: 10.1021/acs.est.8b05859
Environ. Sci. Technol. XXXX, XXX, XXX−XXX
G
dehalorespiration. Based on their filamentous appearance, the
mats likely comprise dominant populations of sulfide-oxidizing
bacteria. Sulfide sources from underlying sediment may include
sulfate-reducing bacteria, coupled to the organic components
spilled from the waste containers, or driven directly by reduced
metal surfaces of the barrels.
63
Core collection also revealed that sediment near some
barrels was supersaturated with gas, which began bubbling
rapidly upon core removal, despite the ambient pressure of 91
bar. Gas ebullition provides one possible explanation for the
distinct appearance of the sediment surface immediately
surrounding some barrels as seen in Figure 1F,K,L, though
the process of gas generation remains unknown. Initially, we
suspected active methanogenesis, facilitated by the deposited
waste, caused gas buildup. However, measurements of
interstitial methane concentrations from cores (Table S11)
within 1 m of gas release yield a maximum concentration ∼19
μmoles per liter of bulk sediment, which is orders of magnitude
too low to support a free gas phase. Nonetheless, in one core,
the methane concentration increased with depth more than is
typical
64
and thus, the source of the observed gas remains
uncertain; we therefore consider other possible sourcing
mechanisms. One potential source of the gas is from the
barrels themselves, some of which were also observed during
sampling to contain a gas charge. While possible, it is difficult
to envision how the gas would migrate downward into the
sediment and laterally away from the barrel. A second potential
source is nonmethane microbial gases produced through
respiration (CO2), denitrification/anammox (N2,N
2O), or
fermentation (CO2,H
2). Still, it remains difficult to envision
how these gases would accumulate to the point of ebullition at
91 bar ambient pressure. A third potential source is cathodic
H2derived from electrochemical reactions
65,66
involving
corrosion of metallic components of the barrels. A fourth
potential source is from acidification of bicarbonate and
carbonate to CO2, driven by highly acid material in the barrel.
For any of these mechanisms, it remains unclear how the gas
phase is sustained near to the sediment surface for extended
periods of time, given dissolution and diffusion.
Environmental Impacts. Pervasive disposal of wastes to
the coastal ocean in the mid-20th century was ill-conceived
insofar as the potential for oceanic impacts was all but ignored.
From the chemical plants of Southern California, barrels of
chlorinated (and other) wastes were dumped into a low
energy, low-oxygen benthic environment that is typically
incapable of supporting respiratory demands for large macro-
fauna. Contrasting with the potential of this site for long-term
sediment burial, the disposal process was inherently sloppy,
with the discarded waste escaping containment and entering
the sedimentary system. The resulting legacy includes a
striking persistence of the discarded xenobiotic wastes,
including DDT and other chlorinated organics, as well as
petroleum-derived residues.
Despite typically low oxygen concentrations, the San Pedro
and Santa Monica basins host some infauna and experience
occasional flushing events that allow for additional benthic
macrofauna.
39,40
To understand the potential toxicity of
sediments, we compared our results with the NOAA sediment
quality guidelines for the effects range median (ERM), above
which adverse effects are likely.
67
For ∑DDX*, the ERM is
46.1 ng g−1
67
(note that in this study the o,p′- isomers are
included for assessing ∑DDX*values). Across samples from
the top 6 cm of sediment cores in this study, 86% exceed the
ERM value for ∑DDX*, and the median concentration is 4.8-
fold greater than the ERM. Hotspot contamination exceeds the
ERM by >160-fold. As suggested in previous studies, effects
range values should be referenced with caution: the relevant
sediment quality guidelines have been criticized for low
accuracy (overestimating toxicity), relatively high variability
(in regard to observed incidence of adverse effects), and not
accounting for the effects of bioaccumulation
38,67−69
and may
also further underestimate sediment toxicity due to the
exclusion of known DDT metabolites such as DDMU.
Nonetheless, sediment quality guidelines provide a well-
recognized metric that is commonly used for the context of
sediment toxicity and clearly demonstrate a potential for toxic
effects in the majority of sediments sampled.
Stemming from our observations, several questions remain,
including our contrasting findings of regional scale DDT
mobilization versus local preservation and sediment burial as
well as the underlying biogeochemical processes active or relict
around the wastes. The variability that accompanied waste
disposal practices undoubtedly contributes to these uncertain-
ties and also to the potential impacts on the broader
ecosystem. Despite the uncertainties, these findings serve as
a cautionary tale for the disposal and dispersal of containerized
industrial waste from even a quiescent benthic environment.
■ASSOCIATED CONTENT
*
SSupporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.est.8b05859.
Detailed description of the mapping and sampling,
analytical, and DDX mass balance data and methods,
images of additional barrels, maps of dumpsite location,
and chemical concentrations for each depth horizon and
metabolite analyzed (PDF)
Identification of compounds in sediment-core extracts
(PDF)
Compound identification criteria and comparison
(PDF)
■AUTHOR INFORMATION
Corresponding Author
*E-mail: valentine@ucsb.edu.
ORCID
Veronika Kivenson: 0000-0002-5715-3126
David L. Valentine: 0000-0001-5914-9107
Present Address
∇
(K.L.L.) Western Washington University, Bellingham, WA
98225.
Author Contributions
⊗
V.K. and K.L.L. contributed equally.
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
This material is based upon work supported by the National
Science Foundation Graduate Research Fellowship for V.K.
under Grant No. 1650114. Expeditions AT-18-11 and AT-26-
06 were funded by the NSF (OCE-0961725 and OCE-
1046144). Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the
author(s) and do not necessarily reflect the views of the
Environmental Science & Technology Article
DOI: 10.1021/acs.est.8b05859
Environ. Sci. Technol. XXXX, XXX, XXX−XXX
H
National Science Foundation. We thank the captain and crew
of the RV Atlantis, the pilots and crew of the ROV Jason, the
crew of the AUV Sentry, the scientific party of the AT-18-11
and AT-26-06 expeditions, Justin Tran for assistance with the
preparation of multibeam data, M. Indira Venkatesan for a
helpful discussion of the NOAA datasets, and Nathan Dodder
for advice on the procedure for compound identification.
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Environmental Science & Technology Article
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