Probabilistic ecological risk assessment of polycyclic aromatic hydrocarbons in
southwestern catchments of the Bohai Sea, China
Submitted to the journal Ecotoxicology
Lin Zeng*, Siyu Zeng, Xin Dong, Tianzhu Zhang, Jining Chen
School of Environment, Tsinghua University, Beijing 100084, P. R. China
*Corresponding author.
Postal address: School of Environment, Tsinghua University, Beijing 100084, China
E-mail: zenglin09@gmail.com (L. Zeng)
Tel: + 86 10 6279 4144
Fax: + 86 10 6279 6956
Table Captions
Table S1 Summary statistics of Bap’s concentrations in 22 sampling sites
Table S2 Descriptive statistics of estimated risk quotients of Bap and comparison to
other PAHs
Table S3 Formulas to obtain PNECs in sediment based on the equilibrium partitioning
method
S1
1. Explanation of the PAH Selection
Actually, all 16 U.S. EPA priority PAHs were measured in both surface water
and sediment samples. In our study, data availability was one important aspect for
selecting
the
PAH
compounds
to
assess
related
risks.
For
example,
Dibenz(a,h)anthracene is proved to be a carcinogenic PAH compound (USEPA 1993).
However, it was detected at only one sampling site for surface water and relevant
toxicity data were very limited. As a result, Dibenz(a,h)anthracene was not assessed in
the paper.
As for Benzo(a)pyrene (Bap), it was quite tricky but reasonable why the paper
did not include its assessment. Apparently, availability of toxicity data was not a
problem. Nevertheless, Bap was only detected at 4 and 9 sampling sites for surface
water and sediment, respectively. The statistical data of Bap’s concentration are
shown in Table R1 as follows:
Table S1 Summary statistics of Bap’s concentrations at 22 sampling sites
Water (µg/L)
Sediment (µg/kg)
Range
Mean
SDa
Detection rate (%)
NDb–0.0518
ND–1210
0.00254
105.5
0.0110
287.0
18.2
40.9
Samples where
was detectable
12, 13, 16, 17
1-6,18-20
Bap
a: SD: standard deviation
b: ND: no detection
Due to the scarcity of data, we could not find a known probabilistic distribution
that could well fit Bap’s exposure data (observations below the detection limit were
assigned a value of half the detection limit). In order to estimate the related ecological
risks roughly, the distribution type of Bap’s exposure data was then assumed as
uniform and lognormal distribution, respectively. Toxicity data were obtained from
USEPA ECOTOX database and literatures, including 18 species across the trophic
levels (Oh et al. 2010; USEPA 2012). Method to derive the risk quotients of Bap was
the same as the 6 PAHs in the manuscript (2000 times of Monte Carlo simulation was
applied). Descriptive statistics of estimated risk quotients of Bap are shown in Table
R2. Compared with 6 PAHs studied in the manuscript, risk levels of Bap under two
distribution scenarios were quite low in the study area. To make the paper more
S2
concise, the whole analysis on Bap was not reported. Since the reviewers asked, the
explanation above was provided in Online Resource 1.
Table S2 Descriptive statistics of estimated risk quotients of Bap and comparison to other PAHs
Benzo(a)pyrene
water
Fluorene
sediment
-5
lognormal
Median
5.04×10
distribution
p (RQ>1)
2.00×10-3
5.75×10-2
uniform
Median
5.05×10-2
3.71×10-1
-2
-1
distribution
p (RQ>1)
9.00×10
4.74×10
3.07×10
water
-5
3.58×10
sediment
-5
8.63×10-3
–
–
Pyrene
2.15×10
-4
5.04×10-2
–
–
water
2.42×10
sediment
-1
3.42×10-1
–
–
1.30×100
5.22×10-1
–
–
2. Formulas to obtain PNECs in sediment based on equilibrium
partitioning theory
S3
Table S3 Formulas to obtain PNECs in sediment based on equilibrium partitioning theory
Formula
PNECsed 
K susp  water
RHOsusp
Parameter specification
PNECwater: Predicted No Effect Concentration in water (ug/L)
 PNECwater 1000
References
EC (2002)
PNECsed: Predicted No Effect Concentration in sediment (ug/kg)
Ksusp-water: partition coefficient suspended matter-water (L/L)
RHOsusp: bulk density of wet suspended matter (1,150 kg/m3) a
K susp  water  Fwatersusp  Fsolid susp 
Kpsusp
1000
 RHOsolid
Fwatersusp: volume fraction water in suspended matter (0.9 m3/m3) b
EC (2002)
Fsolidsusp: volume fraction solids in suspended matter (0.1 m3/m3) c
Kpsusp: partition coefficient solid-water in suspended matter (l/kg)
RHOsolid: density of the solid phase (2500 kg/m3)
Kpsusp  Focsusp  Koc
Focsusp: weight fraction organic carbon in suspended solids (0.1 kg/kg) d
EC (2002)
Koc: partition coefficient organic carbon-water (l/kg)
log Koc  0.81 log Kow  0.10
Kow: partition coefficient octanol-water
a,b,c,d: Standard environmental characteristics applied in this study proposed by EC (2002).
S4
Sabljic et al. (1995)
References
EC (2002) Technical guidance document on risk assessment. Institute for Health and Consumer
Protection, European Chemicals Bureau，European Commission, Ispra, VA, Italy
Oh JH, Moon H-B, Choe ES (2010) Alterations in Differentially Expressed Genes in the Head of
Oryzias latipes Following Benzo a pyrene Exposure. Bulletin of Environmental
Contamination and Toxicology 84 (6):682-686
Sabljic A, Gusten H, Verhaar H, Hermens J (1995) QSAR modelling of soil sorption Improvements and systematics of log KOC vs. log KOW correlations. Chemosphere 31
(11-12):4489-4514
USEPA (1993) Provisional guidance for quantitative risk assessment of polycyclic aromatic
hydrocarbons. Office of reseach and development, Washington, DC
USEPA (2012) ECOTOX database. Office of Research and Development and the National Health
and Environmental Effects Research Laboratory's Mid-Continent Ecology Division
http://cfpubepagov/ecotox/indexhtml
S5