Journal Pre-proof Using national sewage sludge data for chemical ranking and prioritization Arjun K. Venkatesan, Rolf U. Halden PII:
S2468-5844(19)30060-1
DOI:
https://doi.org/10.1016/j.coesh.2019.10.006
Reference:
COESH 146
To appear in:
Current Opinion in Environmental Science & Health
Received Date: 20 August 2019 Revised Date:
18 October 2019
Accepted Date: 25 October 2019
Please cite this article as: Venkatesan AK, Halden RU, Using national sewage sludge data for chemical ranking and prioritization, Current Opinion in Environmental Science & Health, https://doi.org/10.1016/ j.coesh.2019.10.006. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier B.V. All rights reserved.
1
Using national sewage sludge data for chemical ranking and prioritization
2
Arjun K. Venkatesan a,*, Rolf U. Halden b
3
a
4
Engineering, Stony Brook University, Stony Brook, New York, 11794
5
b
6
University, 1001 S McAllister Avenue, Tempe, AZ 85287-8101
7
*
Center for Clean Water Technology, Department of Civil Engineering, 250C Heavy
Biodesign Center for Environmental Health Engineering, The Biodesign Institute, Arizona State
Corresponding Author email:
[email protected]; phone: +1 (631) 632-1998
8 9
Abstract
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Treated sewage sludges (SS) or biosolids are rich in organic carbon, nutrients and, unfortunately,
11
chemical contaminants. Accumulation of chemicals in SS is influenced by the mass of chemical
12
produced and released into wastewater, resistance to (bio)degradation during treatment and the
13
chemicals’ propensity to sorb to particulates. Hence, accumulation of chemicals in SS is
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indicative of their persistent and bioaccumulative behavior: the two characteristics that are
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predominantly used for chemical prioritization. Thus, it is possible for risk assessors to use
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existing SS survey data to identify, rank and prioritize persistent and bioaccumulative chemicals
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present in the human society. In this review, we highlight unique papers that utilized this concept
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to help prioritizing chemical contaminants in SS and the environment. We additionally showcase
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a simple decision flowchart and scoring algorithm for prioritizing chemicals whose presence in
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SS warrants further investigation.
21 22
Keywords: Biosolids; Sewage sludge; PBT chemicals; Chemical prioritization; Chemical
23
ranking; Chemical risk
1
24 25
1. Introduction
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Municipal sewage sludge (SS) is an abundant byproduct of wastewater treatment. The SS matrix
27
is rich in organic carbon and nutrients, and hence >50% of the dry mass of municipal SS
28
produced in the United States currently is applied on land for inexpensive disposal and as soil
29
amendment (fertilizer) [1-3]. Research over several decades has shown that SS, unfortunately,
30
also is rich in pollutants such as toxic metals, pathogens, and organic contaminants [2,4-7].
31
Hence, land application of SS has been, and is, considered a controversial practice in the U.S.
32
and worldwide [8-12]. Looking at the presence of chemical contaminants in SS from a different
33
perspective, one could also say that SS is efficiently capturing and removing toxic, persistent and
34
highly bioaccumualtive chemicals present in reclaimed water during wastewater treatment,
35
which otherwise would be discharged into the environment along with treated effluent. The
36
presence of elevated levels of captured organic contaminants in SS, in essence, is evidence for
37
the effectiveness of wastewater treatment to remove pollutants from sewage and to prevent the
38
release of sewage-borne contaminants into the aquatic environment.
39 40
Chemicals accumulating in SS are the same chemicals used in every-day products for personal
41
care (shampoos, detergents, etc.), health care (prescription drugs), and other household purposes
42
(flame retardation, food preservation, etc.) [2, 13]. Although there are many variations of
43
wastewater treatment plants (WWTPs), a conventional treatment plant employs at a minimum
44
the following steps: pre-treatment (to remove large objects), primary treatment (sedimentation
45
tanks), secondary treatment (e. g., activated sludge system with secondary sedimentation step),
46
and handling of the solids generated (e. g., anaerobic digestion of SS). The secondary treatment
2
47
of municipal sewage consists of a biological treatment system that employs a highly complex
48
microbial community optimized to remove most of the organics present in the wastewater.
49
Chemicals that withstand the secondary biological treatment process have to be considered
50
notably resistant to biodegradation and thus have the potential to also persist in the environment
51
upon their release in reclaimed water or SS. Secondary treatment also may be viewed as a large-
52
scale biodegradability test for chemicals. Thus, if a chemical is not significantly attenuated
53
during treatment and still present in the two end products of wastewater treatment, namely
54
treated effluent (reclaimed water) and SS (biosolids), then it must be considered persistent and
55
potentially contaminating for the environment. This concept was introduced in the past, where
56
researchers recognized that WWTPs are observatories to study the environmental fate of
57
chemicals used in commerce [13]. The relative abundance of chemicals in these two end-
58
products of WWTP depends on the chemicals’ partitioning behavior; i.e., persistent hydrophilic
59
chemicals will be abundant in treated wastewater, whereas persistent hydrophobic chemicals will
60
accumulate in biosolids (Figure 1). Additionally, the levels at which they occur in these two
61
treatment process flows is related to the chemical’s production volume in commerce and to the
62
fraction that is disposed of into wastewater [13]. Wastewater-based epidemiology (WBE)
63
enables an estimation of the consumption volume of chemicals from their levels detected in raw
64
wastewater entering the treatment facility [14-18]. Thus, analogous to WBE, data on chemical
65
concentration in SS (e.g., national SS surveys) allow one to identify persistent and potentially
66
bioaccumulative compounds that may represent contaminants of emerging concern (CECs) in the
67
communities served by the respective WWTP.
3
Influent: Used for WBE approach to estimate chemical consumption irrespective of persistence
68
Wastewater Treatment Plant
Effluent: Captures persistent and hydrophilic chemicals used in commerce
Biosolids: Captures persistent and hydrophobic (bioaccumulative) chemicals used in commerce
69
Figure 1. Overview of how the major process streams of wastewater treatment may be used to
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prioritize chemicals with respect to their occurrence and threats posed.
71 72
2. Chemical prioritization in SS
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National SS surveys are a valuable data source for advancing the understanding of what is
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present in the treated SS and for evaluating the risks posed by sludge-borne, toxic pollutants. In
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the United States, the U.S. Environmental Protection Agency (U.S. EPA) thus far has conducted
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four national SS surveys to identify inorganic and organic contaminants of potential regulatory
77
concern [19,20]. The samples from the 2001 and 2007 (the most recent) surveys, now acquired
78
and archived by the National Sewage Sludge Repository (NSSR) within the Human Health
79
Observatory (HHO) at Arizona State University, have been tested for hundreds of organic CECs
80
providing nationwide chemical inventories [2]. A study conducted in 2014 [13], used the U.S.
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national SS monitoring data to conveniently identify and prioritize chemicals based on
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abundance and bioaccumulation potential. Results from the paper highlighted that (i) the
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chemicals detected in excess of 1 mg/kg in SS were all high production volume (HPV)
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chemicals, i.e., produced and used in commerce in excess of one million pounds per year; (ii) of
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the 55 chemicals identified as being potentially bioaccumulative [i.e., featuring an n-octanol
86
water partitioning coefficient (KOW) of greater than 105], 93% were halogenated; (iii) eight CECs
87
were identified as priority chemicals based on their abundance and bioaccumulation potential; 4
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these included penta-brominated diphenylether (BDE-99), deca-brominated diphenylether (BDE-
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209), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), nonylphenol (NP), nonylphenol
90
ethoxylates (NPEs, specifically NP-monoethoxylate, NP-diethoxylate), triclosan (TCS), and
91
triclocarban (TCC); and (iv) chemicals detected in the national SS survey samples, when
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compared with chemicals inventorized by biomonitoring as toxic pollutants in humans, revealed
93
an overlap of 70%, confirming the utility of using inexpensive and non-invasive monitoring of
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SS to estimate the type and average body burden of toxic pollutants present in local or national
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populations.
96 97
Methods for prioritizing organic contaminants typically use chemical properties to predict the
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likely occurrence and persistence of chemicals in SS [21]. A Canadian study used four
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physicochemical descriptors (volatility, organic carbon-partition coefficient, biodegradability,
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and hydrolysis) to rank chemicals on an overall scale from 2 (low priority) to 9 (high priority)
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[21]. The authors made use of the HPV chemical list to randomly select 34 chemicals that were
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not previously analyzed in their study, and applied this predictive approach using structure
103
activity relationship models. One chemical, BDE-209, received the maximum rank score of 9,
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and at that time (in year 1996) had not yet been analyzed in SS. However, later work showed that
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BDE-209 indeed was abundant in SS [13], and emerged in the investigation as a confirmed high-
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priority pollutant of SS. An important limitation of non-analytical approaches is that for many
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chemicals, reliable values of physical-chemical parameters needed for predicting partitioning in
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SS are not available.
109
5
110
In another recent study conducted in Finland, multi-criteria decision analysis (MCDA) was used
111
to build a decision support tool (DST) for selecting the optimal SS treatment [22]. In
112
constructing the DST, the authors used the occurrence of specific organic contaminants
113
considered to be risky as an important decision criterion. Similar to the Canadian study [21], the
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authors scored the chemical based on toxicity, accumulation (in soil, plants and animals), and
115
risk to groundwater and surface water on a scale from 0 (low priority) to 11 (high priority).
116
Perfluorooctanoic acid (PFOS) was ranked the highest (value 9), followed by polychlorinated
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dibenzodioxins and furans (PCDD/F) and polychlorinated biphenyls (PCBs). In contrast to the
118
U.S. [13] and Canadian [21] studies, the authors scored polybrominated diphenyl ethers (PBDEs)
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and nonylphenols and their ethoxylates (NP & NPE) with lower scores of 7 and 3, respectively.
120
This was because the latter study used occurrence only, but not abundance (or concentration), for
121
assessing risks of SS-borne contaminants. Whereas PBDE and NP/NPEs feature toxicity values
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that are lower when compared to dioxins and PCBs, they occur at quantities several orders of
123
magnitude higher than PCDD/F and PCB, thereby driving the risk from land application [2].
124
The importance of considering contaminant abundance was highlighted in a study where
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researchers developed a quantitative risk ranking model to evaluate human exposure to CECs by
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utilizing predicted environmental concentrations in soil, surface runoff, groundwater and from
127
the ingestion of contaminated drinking water [23]. The predicted concentrations used in the
128
model were calculated from average concentration of the chemicals in SS, thus incorporating the
129
abundance of the chemical as an important parameter for risk determination. Similar to the U.S.
130
study, the authors ranked NP as posing the largest threat among all contaminants to human
131
health. The model also highlighted TCS and TCC as CECs requiring further investigation,
132
cementing a conclusion previously drawn by others [6,24]. Noteworthy, both TCS and TCC later
6
133
were banned in consumer products in the U.S. [25] by the Food and Drug Administration,
134
thereby validating the utility of risk prioritization approaches using SS as a diagnostic matrix.
135 136
3. Decision flowchart for chemical ranking and prioritization using SS data
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From the models discussed in the previous section, some common characteristics of chemicals
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were used for ranking and prioritization: persistence (P), bioaccumulation (B), toxicity (T) and/or
139
long-range transportation potential (LRTP) [26]. These characteristics, especially P & B, are
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commonly employed in risk assessment framework by the U.S. EPA [27], and by other countries
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[28-30]. As shown in multiple studies [13,21,23], SS is a useful matrix for identifying chemicals
142
of the P and B category, and for estimating the mass of CECs released in reclaimed water and
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land-applied SS [31-33]. Hence, one could use the SS monitoring data to prioritize P and B
144
contaminants, and also to identify contaminants likely to leach into groundwater or surface water
145
after land application. A decision flowchart was developed based on this concept (Figure 2) to
146
score and rank CECs based on concentration in SS, and the chemical’s octanol-water partitioning
147
coefficient (KOW).
148 149
Since persistence has been shown to be inherent to chemicals detected in SS [13], only the
150
concentration in SS (indirectly representing chemical abundance in commerce and disposal into
151
wastewater), and bioaccumulation potential are scored on a scale from 1 to 3 (i.e., low to high
152
concern). These scores are then added up to provide a single score (2 to 6), which can be used to
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compare chemicals and prioritize them for further investigation (toxicity and risk assessment).
154
As opposed to making use of only physical-chemical properties to prioritize CECs as performed
155
by non-analytical methods, the proposed tool additionally incorporates the true abundance of the
7
156
compound in the environment. In order to validate the applicability of the proposed ranking
157
technique, we compared the scores obtained from SS analysis with the traditional scoring
158
calculated using only P and B characteristics of chemicals (Table 1, Figure 3). National SS Analysis Abundance >1000 µg/kg dry wt.
Y
High (Score = 3)
N 1-1000 µg/kg dry wt.
Y
N
Low (Score = 1)
Y
KOW> 105
Highly Bioaccumulative (Score =3)
Non- to Moderately Bioaccumulative (Score = 1-2)
N
Persistent CEC likely to bioaccumulate Sum of scores = 2-6
Persistent CEC with moderate to high leachability from SS Sum of scores = 1-5
159
Medium (Score = 2)
Priority chemicals with score 5: Antimicrobials = TCS, TCC Antibiotics = Ciprofloxacin, Ofloxacin, Azithromycin
Priority chemicals with score 6: Surfactants = NP & NPEs Flame retardants = BDE-99, BDE-209; BTBPE
160
Figure 2. Decision flowchart for pre-screening priority contaminants of emerging concern
161
(CECs) using data from the national SS survey. 8
162 163
Table 1. Scoring criteria based on P and B characteristics of chemicals. Characteristics Persistence
Bioaccumulation
Criteriaa Half-life, days <60 60 to 180 >180 Bioconcentration factor <1000 1000 to 5000 >=5000
Interpretationb
Low (1) Medium (2) High (3) Low (1) Medium (2) High (3)
a
Source: [34] The U.S. EPA does not provide numerical scores as shown within parentheses; these were included in this study for comparison purposes only.
b
164 165
The comparison of P + B scores and the SS scores for 73 chemicals detected with varying
166
abundances in national SS data is shown in Figure 3 (see supplemental Table S1). These 73
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chemicals were selected based on the availability of P and B data in the U.S. EPA’s PBT Profiler
168
and SciFinder® (Chemical Abstract Services) software packages. About 42% of the chemicals
169
had the same scores from both approaches and ~48% of the chemicals had a P + B score within a
170
range of ±1 of the SS scores (15% underestimated (P + B score -1) and 33% overestimated (P +
171
B score + 1) by the SS analysis approach.) These results suggest that the proposed SS scoring
172
technique is valuable and accurate in capturing P and B chemicals in the environment.
173
Interestingly, ~10% of the chemicals’ SS scores were greater than a value of 2 compared to the
174
calculated P + B score. These include three surfactants (NP and NPEs), one flame retardant
175
(BDE-209), and three pharmaceuticals and personal care products (TCS, TCC, and ibuprofen).
176
9
8 (NP)
Proposed SS Score
(NPEs)
2
6
1
1
1
2
8
1
1
8
5
3
7
25
5
(TCS, TCC)
4
(Ibuprofen)
(BDE-209)
3
2 n = 73
0 0
2
4 P + B Score
6
8
177 178
Figure 3. Comparison of scores obtained for 73 chemicals from the proposed SS analysis
179
approach and P + B approach. P- persistence; B- bioaccumulation. P + B scores are based on
180
values in Table 1 and are scored out of a total score of 6 (1-3 for each P and B). SS scores were
181
obtained as shown in the decision flow chart in Figure 2. The center line represents equal scores
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in both approaches, while the dotted line represents ±1 deviation from equal scores. The number
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next to the point corresponds to the number of chemicals satisfying that score value. The
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chemicals with significantly different scores (≥ 2) are named next to the point in parenthesis.
185 186
The difference in scores observed for these chemicals between the two approaches is due to the
187
incorporation of chemical abundance information in SS scoring approach. For example, NP has a
188
half-life of 140 days in the environment and a BCF of 120 leading to a P+B score of only 3. NP
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is a HPV chemical and significant amounts of this chemical have been detected in environmental
190
matrices [35]. The U.S. national SS data from 2001 samples showed a mean concentration of
191
534.2 mg/kg for NP, resulting in a score of 3 for “abundance” and a score of 3 for its
192
bioaccumulative property (KOW>105) [13]. For this reason, the SS approach scores this chemical 10
193
as a high priority chemical with a maximum score of 6. The same reasoning holds true for the
194
other five chemicals that were underestimated by the P + B scoring technique. In addition to
195
identifying P & B chemicals, the proposed scoring tool can also identify chemicals that is likely
196
to leach from land-applied SS based on the lower KOW value (Figure 2). It must be noted that
197
many of the chemicals detected in SS are ionizable [36], and hence the mobility of the
198
compounds is determined by the pH of the SS and soil environment [37]. A better representation
199
of their leachability would be to use the pH-adjusted KOW values (DOW) as highlighted in past
200
studies [33,36].
201 202
4. Conclusions and future directions
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It is estimated that about 2,500 new chemicals are introduced each year in the U.S., equivalent to
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a rate of seven new chemicals per day [38]. Identifying problematic chemicals is a time-
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consuming process and thus developing interventions through policies and laws may take several
206
decades to address risks to humans and the environment. The SS scoring approach proposed
207
here, that makes use of available national SS monitoring data, promises to provide an inventory
208
of priority CECs for future assessment. Along with other tools, it may serve as valuable tool
209
helpful in speeding up the data mining process for identifying priority chemicals of concern. This
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list of chemicals can be further expanded by applying non-target screening in SS samples; this
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was demonstrated in one study [39], where the researchers identified several siloxanes and
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organophosphate flame retardants as emerging contaminants in the Artic region. These two
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groups of chemicals represented 68% of the suspect chemicals detected in the SS samples
214
analyzed in the study [39], further supporting the notion of using SS as an indicator matrix to
215
identify P & B chemicals in the environment. However, this approach also has limitations in that
11
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it does not inform on the toxicity of chemicals. It is possible that chemicals ranked lower via this
217
approach are highly toxic (e.g., PCBs, dioxins etc.), and hence a more comprehensive approach
218
would be to integrate a toxicity score with the SS score. Also, this tool is applicable only to
219
sludge-borne chemicals; but if one could analyze WWTP effluent, a much wider range of
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chemicals also could be screened in a similar way, including hydrophilic CECs. A recent study
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[40] utilized a similar approach to identify CECs relevant for reclaimed water reuse (managed
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aquifer recharge) by considering usage volumes, ecological and health effects, and
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concentrations of CECs in wastewater effluents. The researchers identified eight potential CECs
224
that required further treatment for potable water reuse applications, namely: PFOS,
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perfluorooctanoate (PFOA), ibuprofen, carbamazepine, diclofenac, erythromycin,
226
sulfamethoxazole, and NP. All these chemicals were also detected in national SS samples at
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varying abundance (Table S1), and additionally ibuprofen and NP were also ranked as high
228
priority chemicals in SS via the proposed ranking approach in this study. Hence, this ranking tool
229
using existing SS monitoring data can be useful for risk assessors as a pre-screening approach to
230
conveniently identify and prioritize chemicals for further investigations.
231 232
Acknowledgments
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This study was supported in part by Award Number R01ES020889 from the National Institute of
234
Environmental Health Sciences (NIEHS) and by award LTR 05/01/12 of the Virginia G. Piper
235
Charitable Trust. The content is solely the responsibility of the authors and does not necessarily
236
represent the official views of the sponsors.
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31. Chari BP, Halden RU: Predicting the concentration range of unmonitored chemicals in
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contaminants to improve the quality of municipal sewage sludge destined for land
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37. Lachassagne D, Soubrand M, Casellas M, Gonzalez-Ospina A, Dagot C: Impact of sludge
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39. Lee S, Kim K, Jeon J, Moon H-B: Optimization of suspect and non-target analytical
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methods using GC/TOF for prioritization of emerging contaminants in the Arctic
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In this study, the researchers applied non-target screening in various environmental matrices to
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identify contaminants of emerging concern for the Arctic environment. The analysis included
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sewage sludge samples, which showed high detections of priority contaminants identified in the
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study. This is the first study to employ suspect and non-target analysis using GC-TOF for
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prioritizing contaminants in the Arctic region.
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40. Yuan J, Van Dyke MI, Huck PM: Identification of critical contaminants in wastewater
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effluent for managed aquifer recharge. Chemosphere 2017, 172:294-301.**
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In this study the authors make use of a multi-criteria approach to identify priority contaminants
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in wastewater effluent for managed aquifer recharge. The study showcased that a statistical
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analysis of WWTP effluent monitoring data can facilitate the selection of critical and priority
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contaminants. The approach is very similar to what is proposed in the present study for sewage
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sludge and helps to identify persistent, hydrophilic contaminants not detected in sewage sludge
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matrix.
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Highlights • • • •
Sewage sludge (SS) is abundant with persistent (P) and bioaccumulative (B) chemicals National SS survey data has been used by researchers to prioritize P & B chemicals A decision flowchart and scoring algorithm was developed to rank contaminants SS can be used as diagnostic matrix by risk assessors for chemical prioritization
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Competing interests: The authors declare no competing interests.
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