Subscriber access provided by READING UNIV
Article
Organophosphate Triesters and Diester Degradation Products in Municipal Sludge from Wastewater Treatment Plants in China: Spatial Patterns and Ecological Implications Lingfang Fu, Bibai Du, Fei Wang, James C.W. Lam, Lixi Zeng, and Eddy Y. Zeng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04106 • Publication Date (Web): 30 Oct 2017 Downloaded from http://pubs.acs.org on October 30, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 28
Environmental Science & Technology
Submitted for publication in Environmental Science & Technology
Organophosphate Triesters and Diester Degradation Products in Municipal Sludge from Wastewater Treatment Plants in China: Spatial Patterns and Ecological Implications
Lingfang Fu,
†
Bibai Du,
†
Fei Wang, † James C.W. Lam, ‡ Lixi Zeng, *,† and Eddy Y.
Zeng †
†
School of Environment, Guangzhou Key Laboratory of Environmental Exposure and Health, and Guangdong Key Laboratory of Environmental Pollution and Health, Jinan University, Guangzhou 510632, China
‡
Department of Science and Environmental Studies, The Education University of Hong Kong, Hong Kong SAR, China
*Corresponding author Dr. Lixi Zeng School of Environment, Jinan University 601 West Huangpu Avenue, Tianhe District Guangzhou 510632, China Tel: 8620-8522-6615 Fax: 8620-8522-6615 E-mail:
[email protected] ACS Paragon Plus Environment
Environmental Science & Technology
1
ABSTRACT:
2
Little is known about the occurrences, distributions, sources and potential risks of
3
organophosphate (OP) triesters and diester degradation products in municipal sludge from
4
wastewater treatment plants (WWTPs). In this study, we conducted the first nationwide
5
survey to simultaneously determine a suite of 11 OP triesters and six diester degradation
6
products in sludge from WWTPs across China. All OP triesters were detected and three
7
diesters were for the first time identified in sludge samples. Total concentrations of OP
8
triesters and diester degradation products were in the range of 43.9–2160 ng g-1 dw and
9
17.0–1300 ng g-1 dw, respectively, indicating relatively low pollution levels in China
10
compared with several developed countries. A distinct geographical variation of higher
11
concentrations of OP triesters and diesters in East China than in Central and West China was
12
observed, suggesting that regional levels of organophosphate esters are associated with the
13
magnitudes of regional economic development. Source analysis revealed nonchlorinated OP
14
diesters are mainly derived from degradation in WWTPs, while chlorinated OP diesters were
15
largely sourced from outside WWTPs. The estimated total emission fluxes of OP triesters and
16
diesters via land-application sludge in China were approximately 330 and 134 kg yr-1,
17
respectively. Further risk assessment based on risk quotient values in sludge-applied soils
18
indicated low to medium risks for most OP triesters and diesters except tris(methylphenyl)
19
phosphate. The significant accumulation of OP triesters and widespread occurrence of diester
20
degradation products in sludge raise environmental concerns about these contaminants.
21 22 23 24 25 26 27 28 29 30
ACS Paragon Plus Environment
Page 2 of 28
Page 3 of 28
31
Environmental Science & Technology
INTRODUCTION
32
Organophosphate esters (OPEs) have been extensively used as flame retarding chemicals
33
and as plasticizers and additives to plastics, lubricants, rubber products, electronic devices,
34
textiles, furniture, food packaging and hydraulic fluids.
35
polybrominated diphenyl ethers, OPEs have become one of the most frequently used
36
alternative flame retardants.
37
approximately 200 kilotons, 4 with more than 70 kilotons being produced in China. 5 Western
38
Europe, North America and China are three major consumers of flame retardants in recent
39
years, accounting for approximately 60% of global consumption.
40
OPEs produced and used worldwide have resulted in their widespread occurrence in various
41
environmental matrices,
42
linkage, OPEs can be categorized to aryl-, nonchlorinated alkyl-, chlorinated alkyl-, and
43
others.
44
hydrophobic, while chlorinated alkyl-OPEs are generally more water soluble and resistant to
45
degradation.3 Chlorinated alkyl-OPEs, including tris(2-chloroethyl) phosphate (TCEP), tris(2-
46
chloroisopropyl) phosphate (TCIPP) and tris(1,3-dichloroisopropyl) phosphate (TDCIPP)
47
have attracted increasing attention because of their carcinogenicity and neurotoxicity. 13-15
48
12
3
1, 2
With the phase-out of
The annual global production of OPEs currently reaches
1-3, 5, 7-10
as well as in remote regions.
11
6
The large amounts of
Depending on the ester
Aryl- and nonchlorinated alkyl-OPEs with higher molecular weights are more
Organophosphate triesters can be rapidly enzyme-catalyzed and metabolized to diester
49
metabolites in humans and animals.
50
than triesters and are readily excreted in urine, which often function as biomarkers of
51
exposure to OPEs.
52
as
53
photodegradation
54
phosphate (DPHP), are more toxic than their parent compounds. 20 In cities, most released OP
55
triesters and diester degradation products are commonly collected in sewer systems and
56
accumulated in municipal wastewater treatment plants (WWTPs)
57
that OP triesters were detected in influents of WWTPs at µg L-1 levels 29-32, 34, 35. WWTPs are
58
therefore considered as major sinks and perhaps degradation sites. Studies on the behavior of
59
OPEs in WWTPs indicate that nonchlorinated alkyl- and aryl-OPEs can be partly degraded
60
by activated sludge treatment
microbial
17
3, 10, 16-26
These diester metabolites are more hydrophilic
OP diesters can also be generated via other degradation pathways such
metabolism/biotransformation,
base-catalyzed
hydrolysis
27
and
28
. It should be emphasized that some OP diesters, such as diphenyl
12, 29, 31, 32, 34, 36
29-33
. It has been reported
, while chlorinated alkyl-OPEs are poorly
ACS Paragon Plus Environment
Environmental Science & Technology
Page 4 of 28
61
removed even in the advanced oxidation processes
62
alkyl-OPEs, ultimately end up in sludge
63
wastewater-derived OPEs and their degradation products locally 37. However, up to now, only
64
limited studies have reported one or several selected OPEs in sludge at a regional level 12, 30,
65
33, 37-39
66
diesters in sludge 12, 33. Although OP triesters and diester as emerging global contaminants in
67
humans have been widely examined
68
and potential risks in abiotic matrices such as sludge at a large geographical scale still remain
69
unknown.
32
. Most OPEs, particularly chlorinated
31, 32, 36
. So sludge is an excellent medium to trace
. Among these studies, only two demonstrated the presence of both OP triesters and
3, 10, 17-19, 21-25
, their co-occurrence, distributions, sources
70
To fill the above-mentioned knowledge gap, we conducted the first nationwide survey to
71
simultaneously determine a suite of OP triesters and diester degradation products in sludge
72
from WWTPs in 36 cities across China. The aims were to (1) examine the geographical
73
distribution patterns and potential sources of currently used OP triesters and their diester
74
degradation products; (2) better understand the behavior and fate of the target compounds in
75
WWTPs and the ambient environment and (3) evaluate the environmental emissions and
76
potential ecological risks via land-application of sludge in China.
77
MATERIALS AND METHOD
78
Chemicals and Materials
79
Eleven target OP triesters,
40
i.e., tris(propyl) phosphate (TPP), tris(butyl) phosphate
80
(TNBP),
81
tris(2-ethylhexyl) phosphate (TEHP), TCEP, TCIPP, TDCIPP, tris(phenyl) phosphate
82
(TPHP), tris(methylphenyl) phosphate (TMPP) and 2-ethylhexyl diphenyl phosphate
83
(EHDPP) were purchased from Dr. Ehrenstorfer (Augsburg, Germany). Six OP diesters,
84
including di-n-butyl phosphate (DNBP) for parent TNBP, bis(2-butoxyethyl) phosphate
85
(BBOEP) for parent TBOEP, bis(2-chloroethyl) phosphate (BCEP) for parent TCEP,
86
bis(2-chloroisopropyl) phosphate (BCIPP) for parent TCIPP, bis(1,3-dichloroisopropyl)
87
phosphate (BDCIPP) for parent TDCIPP and diphenyl phosphate (DPHP) for parent TPHP
88
were studied. DNBP, BBOEP, BCEP, BCIPP and BDCIPP were purchased from Toronto
89
Research Chemicals (North York, Canada), and DPHP was purchased from Tokyo Chemical
tris(isobutyl)
phosphate
(TIBP),
tris(2-butoxyethyl)
ACS Paragon Plus Environment
phosphate
(TBOEP),
Page 5 of 28
Environmental Science & Technology
90
Industry (Tokyo, Japan). Detailed information on their molecular formula/weight and
91
physicochemical parameters is listed in Table S1. Internal standards: TNBP-d27, TDCIPP-d15,
92
TPHP-d15 and DPHP-d10 were obtained from Cambridge Isotope Laboratories (Andover, MA,
93
USA). Stock solutions of the target analytes were prepared in acetonitrile and stored at -20 °C.
94
Methanol, acetonitrile, ethyl acetate and cyclohexane of high-performance liquid
95
chromatography grade were acquired from Oceanpak (Gothenburg, Sweden).
96
Field Sampling
97
A total of 64 sewage sludge samples from WWTPs in 36 cities across China (Figure S1)
98
were collected from October 2010 to May 2011. Details about the secondary treatment
99
technologies, sewage sources and treatment capacities for the WWTPs have been published
100
previously 41, as well as presented in Table S2. Freshly digested sludge 0.5–1.0 kg wet weight
101
from secondary clarifier in each WWTPs was collected after the dewatering process. Wet
102
sludge samples were packed in aluminum foil, sealed in ziplock bags, and transported
103
immediately to laboratory, where they were freeze-dried, homogenized, sieved through 100
104
mesh sieve and then stored at -20 °C before extraction.
105
Sample Extraction and Cleanup
106
Sample extraction procedure for OP triesters was adopted from previous studies with
107
moderate modifications.
108
different from that for triesters. Detailed sample extraction and cleanup procedures are
109
presented in the Supporting Information (SI).
110
UPLC-MS/MS Analysis
32, 42
The procedure used to extract samples for OP diesters was
111
Analyte concentrations were measured using an ultra-performance liquid chromatography
112
(Nexera X2, Shimadzu) coupled to a tandem mass spectrometer (Triple Quad™ 5500 System,
113
AB SCIEX) based on previously reported methods with some optimizations.
114
information with regard to UPLC and MS/MS parameters (Table S3) is given in the SI.
115
Quality Assurance and Quality Control
43-46
Detailed
116
Strict quality controls were implemented to ensure accurate quantification of these target
117
compounds. All glassware was soaked in a phosphate-free cleaning agent (decon90) for 12 h
118
and then rinsed thoroughly with deionized water. After drying carefully, the glassware was
119
solvent rinsed, then heated at 450 °C overnight prior to use. For the evaluation of extraction
ACS Paragon Plus Environment
Environmental Science & Technology
Page 6 of 28
120
efficiency, sludge samples were randomly chosen for the fourth extraction after the first three
121
extraction cycles, and the target compounds were undetected in the fourth extraction, which
122
indicated high efficiencies of the first three extractions for sludge samples. One procedure
123
blank sample was included in every batch of 10 samples to monitor the blank contamination.
124
Most analytes in the blanks were under the limit of detection except TIBP and TPHP (Table
125
S4), and therefore the two OP triester concentrations were corrected by the blank.
126
Randomly selected sludge samples (n = 6) were fortified with known concentrations of
127
OPEs (5–25 ng) for determination of matrix effect (for details see SI).
128
was within 91–107%, and thus the potential over/underestimation of concentrations could be
129
excluded. Matrix spike recovery was examined in matrix spike sample and matrix spike
130
duplicate according to U.S. EPA method.
131
analytes and internal standards (IS) were between 67-99% and 74-104%, respectively.
132
Accuracy and precision were evaluated by fortification of samples (n = 6) with native and
133
internal standards, and analysis of those samples through the entire procedure. 12 For accuracy,
134
the deviations of IS-corrected quantitative results from the known values were ≤ 15%. For
135
precision, the relative standard deviations (RSDs) in duplicate sample tests were ≤ 10%.
136
Recoveries of TNBP-d27, TDCIPP-d15, TPHP-d15 and DPHP-d10 in all field samples (n = 64)
137
were 73 ± 6%, 84 ± 17%, 101 ± 10% and 78 ± 13%. The method quantification limits (MQLs)
138
of the analytes were calculated as a signal-to-noise ratio of 10, which were from 0.09 (DPHP)
139
to 3.76 ng g-1 (TCIPP). Detailed data are presented in Table S4. Concentrations below MQLs
140
were replaced by half of the MQLs, and all data were log-transformed for statistical analysis
141
using IBM SPSS Statistics 20.0 (IBM Corp, 1989−2011). Eight-point calibration curves were
142
established at the range of 0.50–500 ng mL-1 with regression coefficient r2 > 0.995.
143
Ecological Risk Assessment
144 145
146
47
12
The matrix effect
Average matrix spike recoveries (n = 6) of target
The risk assessment in sludge-applied soils was performed using risk quotient (RQ) values, which are expressed as: RQ =
PEC soil PNEC soil
147
where PNECsoil is defined as the predicted no effect concentration on organisms and often
148
derived from no observed effect concentration (NOEC) in the laboratory. PECsoil was
ACS Paragon Plus Environment
Page 7 of 28
Environmental Science & Technology
149
estimated as the concentration of contaminant in agricultural soil from one year after
150
sludge-dose application
151
based on the commonly recommended criteria: high risk (RQ ≥ 1.0), medium risk (0.1 ≤ RQ
152
< 1.0) and low risk (0.01 ≤ RQ < 0.1) 48, 49.
153
48
. The maximum probable risk of ecological effects was evaluated
In this study, the PNECsoil values for TCEP, TCIPP, TDCIPP, TPHP, TMPP and EHDPP
154
refer to the data from European Commission
155
triesters and diesters were estimated as a quotient of toxicological relevant concentration
156
LC50 and an assessment factor (f) using the formula: PNECsoil = LC50 / f, where f was 1000 51,
157
52
158
TEHP, DNBP, BBOEP, BCEP and DPHP was used for PNECsoil calculation 53.
159 160
50
, while the PNECsoil values for other OP
. For this purpose, the LC50 for earthworm associated with TPP, TNBP, TIBP, TBOEP,
The PECsoil values in sludge-applied soils were determined according to the European Commission Technical Guidance Document (TGD) on Risk Assessment 48, 51: PEC soil =
161
Csludge × APPLsludge DEPTH soil × RHO soil
162
where Csludge (g/kg dw) is the measured concentration of target compound in sludge;
163
APPLsludge is the application rate of dry sludge into agricultural soils (usually 0.50 kg m-2 yr-1);
164
DEPTHsoil is the mixing depth (usually 0.20 m for agricultural soils); and RHOsoil is the bulk
165
density of wet soil (usually 1.5 × 103 kg m-3 for agricultural soils).
166
RESULTS AND DISCUSSION
167
Concentrations, Spatial Distribution and Composition Profiles of OP Triesters in
168
Nationwide Sludge
169
All the target OPEs (triesters) were detected in most sludge samples (Table 1). The total
170
concentration of 11 OPEs (sum of which is designated as ∑11OPE thereafter) ranged from
171
43.9 to 2160 ng g-1 dry weight (dw) with an average value of 303 ng g-1 dw, indicating
172
considerable variability among the WWTPs. The maximum and minimum concentrations of
173
OPEs were found at WWTPs located in Zhejiang province of East China and Yunnan
174
province of West China, respectively. The WWTPs under investigation mainly treat domestic
175
wastewater or mixed domestic/industrial wastewater (Table S2). The highest ∑11OPE
176
concentration from East China may be attributed to the high industrial output in this region as
ACS Paragon Plus Environment
Environmental Science & Technology
177
corroborated by a large portion (70%) of industrial wastewater in the WWTP influents.
178
Sludge with predominant industrial inputs generally contained higher OPE levels than
179
domestic sludge
180
lower than that previously reported in two relatively more economically developed regions of
181
China, i.e., 699 ng g-1 dw with a range of 204–4100 ng g-1 dw in Beijing 33 and 420 ng g-1 dw
182
with a range of 96.7–1313 ng g-1 dw in the Pearl River Delta (PRD), 37 but higher than that
183
found in Henan Province (mean: 170 ng g-1 dw and range: 38.6–508 ng g-1 dw), where is a
184
less developed region. 38
185
37
. The national average concentration of sludge OP triesters in China was
Sludge ∑11OPE
concentrations in China were at least ten times lower than those in
186
Sweden (mean: 4239 ng g-1 dw and range: 620–6900 ng g-1 dw), 31 Spain (mean: 4476 ng g-1
187
dw and range: 1185–13370 ng g-1 dw)
188
1000–20000 ng g-1 dw)
189
dw).
190
consumptions of OPEs in China compared with these developed countries. According to a
191
report,
192
production in 2008, while Europe and the United States took up 40% and 35%, respectively.
193
These results implied that elevated sludge levels of ∑11OPE in developed countries were
194
likely associated with more frequently industrial activity together with larger consumption of
195
OPEs, but population density of WWTP location was another potential factor. 55
12
30
32
, Germany (only TCIPP detected over a range of
and U.S. (mean: 11800 ng g-1 dw and range: 4110–20200 ng g-1
The relatively low levels of ∑11OPE in China were consistent with the relatively low
54
the amount of OPEs consumed in China accounted for only 7% of the global
196
Of all target OP triesters, TNBP, TIBP, TCEP, TPHP and TMPP were detected in all
197
sludge samples, whereas TBOEP (98.4%), TCIPP (95.3%), EHDPP (93.8%), TDCIPP
198
(90.6%), TEHP (81.2%) and TMPP (76.6%) were partially detectable. In Sweden, Germany
199
and Spain 30-32, EHDPP, TCIPP, TBOEP and TEHP were the abundant compounds in sludge.
200
Some previous studies in China indicated that the predominant compounds of OP triesters
201
were TEHP and TMPP in Beijing 33, TBOEP and TPHP in the Pearl River Delta 37, and TCEP,
202
TBOEP and TCIPP in Henan province 38. In the present study, TIBP, TBOEP, TCEP, TCIPP
203
and TMPP contributed comparably (11.1−14.4%) to ∑11OPE (Table 1), which were identified
204
as the dominant compounds. Generally, sludge samples from the same province/municipality
205
were similar in the composition profile of OPEs, but variations among different regions were
206
observed (Figure S2). Differences in composition profiles of sludge OPEs between different
ACS Paragon Plus Environment
Page 8 of 28
Page 9 of 28
Environmental Science & Technology
207
regions in China and between China and other countries may be attributed to varying use
208
pattern.
209
There is still a lack of environmental data for OPEs in sludge among different countries
210
worldwide. We compared individual OP triester concentration with the reported data from
211
Sweden, Spain, Canada, U.S. and Germany (Table S5). In the present study, TPP was
212
detected in 49 of 64 samples with the concentration of < MQL–8.77 ng g-1 dw. The lowest
213
concentration and percentage composition for TPP (Table 1) could be partly attributed to its
214
low logKow and preferential partitioning in the aqueous phase, while production volume,
215
usage period, and stability were also related to sludge TPP level. The concentrations of TNBP
216
and TIBP in nationwide sludge samples from China were 2.97–430 and 6.25–387 ng g-1 dw,
217
respectively, comparable to those previously reported in Beijing and Henan Province
218
but lower than those detected in sludge from Sweden 31, Spain
219
Similarly, two other alkyl-OPEs, TBOEP (
