Chemosphere 207 (2018) 517e518
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Discussion
Reply to discussion by John Heinze on “occurrence, fate and
environmental risk of linear alkylbenzene sulfonate in the langat and
Selangor River basins, Malaysia”
Nobumitsu Sakai a, b, *, Junichi Shirasaka a, Yasuto Matsui a, Mohd Redzuan Ramli b,
Kousuke Yoshida c, Mustafa Ali Mohd b, Minoru Yoneda a
a
b
c
Division of Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 6158540, Japan
Shimadzu-UMMC Centre of Xenobiotic Studies, Department of Pharmacology, Faculty of Medicine, University of Malaya, Kuala Lumpur, 50603, Malaysia
Lion Corporation, 100 Tajima, Odawara-shi, Kanagawa, 256-0811, Japan
h i g h l i g h t s
We responded to Dr. Heinze's three discussion points.
LAS is not a primary determinant of WQ, but can be an indicator of untreated sewage.
LAS does not necessarily biodegrade faster than BOD.
Our monitoring results showed a moderate correlation between LAS and BOD.
Adsorption to suspended solids followed by settlement should be taken into account.
a r t i c l e i n f o
Article history:
Received 25 March 2018
Accepted 22 May 2018
Available online 22 May 2018
Handling Editor: Jian-Ying Hu
We thank Dr. Heinze for pointing out some questions in our
recent paper (Sakai et al., 2017). The comments from Heinze can be
summarized by the following three points: (1) linear alkylbenzene
sulfonate (LAS) concentration is not the primary determinant of
water quality in polluted river water and LAS concentrations should
not be the basis for prioritizing sewage treatment improvements;
(2) LAS biodegrades faster than biochemical oxygen demand (BOD),
which is based on the findings in the Balatuin River, the Philippines
(Dyer et al., 2003; McAvoy et al., 2003); (3) it is incorrect to
determine safety in river water based on LAS concentrations as
aquatic safety is determined by BOD, dissolved oxygen (DO) and
ammonia. The following is our responses to the three points.
In the first point, we do not suggest that LAS is the primary
determinant of water quality deterioration. There are numerous
* Corresponding author. Division of Environmental Engineering, Graduate School
of Engineering, Kyoto University, Kyoto, 6158540. Japan.
E-mail address: sakai@risk.env.kyoto-u.ac.jp (N. Sakai).
https://doi.org/10.1016/j.chemosphere.2018.05.126
0045-6535/© 2018 Elsevier Ltd. All rights reserved.
contaminants present in surface water which are derived from
various pollution sources, therefore general water quality parameters, including BOD, DO and ammonia which can indicate overall
water quality deterioration, are commonly used as a regulatory
basis. Because LAS has a unique characteristics in terms of the
specific pollution source that is mainly derived from households
due to the use of laundry detergent (Yamamoto et al., 2010) as well
as the almost complete elimination by sewage treatment (Matthijs
€der et al., 1999), we aimed to elucidate if LAS can
et al., 1999; Schro
be used as an indicator for the water quality deterioration by untreated sewage, particularly in a watershed scale. As present in our
paper (Sakai et al., 2017), the spatial distribution of LAS in the study
area was associated with population distribution, and the daily load
of LAS and the population density in each sub-basin showed a
strong logarithmic correlation (r ¼ 0.882). This fact clearly suggests
that LAS was originated from high population areas and sewage
treatment system around the areas was not covered enough.
Needless to say, BOD, DO and ammonia are primary determinants
of water quality affected by not only sewage but also effluents of
waste water treatment plants, industrial effluents and agricultural
runoff, however LAS can provide additional information for the
identification of untreated sewage which is hardly achieved by such
general water quality parameters.
In the second point, we cannot simply say that LAS biodegrades
faster than BOD. We analyzed the correlation between LAS and BOD
concentrations using the dataset of 28 monitoring points in our
study (Sakai et al., 2017). As shown in Fig. 1, there was a moderate
correlation between the parameters (r ¼ 0.668), indicating that the
518
N. Sakai et al. / Chemosphere 207 (2018) 517e518
Fig. 1. Positive linear correlation between LAS concentration and BOD (r ¼ 0.668) in
the surface water collected in the Langat and Selangor River basins (n ¼ 28).
pollution trend of LAS and BOD in the surface water was not
significantly different. Yamamoto et al. (2010) have reported that
there was a strong positive correlation between BOD geometric
mean values and 95th percentile of LAS concentrations in surface
water collected in Japan (r ¼ 0.993). In the two studies introduced
by Heinze (Dyer et al., 2003; McAvoy et al., 2003), LAS and BOD
values at 6 sites collected in the Balatuin River also show a strong
correlation (r ¼ 0.960), which we calculated based on the dataset
shown in the papers. These facts suggest that LAS did not necessarily biodegrade faster than BOD. However, the correlation in our
study (Fig. 1) may be overstated because the sample size (n ¼ 28)
was not enough to evaluate the correlation and there were a few
outliers between them, indicating that multiple factors would
affect their concentrations in surface water. The biodegradation of
LAS in surface water is thought to be subject to flow time vs. halflives, aerobic vs. anaerobic condition (Scott and Jones, 2000) and
contact to river bed with vs. without the existence of biofilm
(Takada et al., 1994). In other words, the influence of biodegradation on LAS concentrations in surface water would fluctuate
depending on geological condition, surface water quality and river
bed condition of study area. Our results showed that LAS was
considerably adsorbed to suspended solids particularly in polluted
sites (Fig. 3 of Sakai et al., 2017), and 70.2% of LAS in the most
polluted site of the Selangor River basin was adsorbed to suspended
solids which were larger than 11 mm (Table 2 of Sakai et al., 2017).
Therefore, the settlement due to the adsorption to suspended solids
might rather influence the LAS concentrations in the surface water.
It does not mean that biodegradation is negligible in aquatic
environment and could be a significant factor particularly in aerobic condition (Scott and Jones, 2000) as well as in shallow stream
enriched with biofilm (Takada et al., 1994). Nevertheless, the
reduction of LAS from surface water due to adsorption to suspended solids followed by settlement also should be taken into
account for elucidating the environmental fate of LAS.
In the third point, we do not generalize that the safety of river
water is determined by LAS. We aimed to assess the environmental
risks due to the LAS contamination based on its predicted no effect
concentration (PNEC), and found that 3 sub-basins exceeded their
PNEC values normalized by the average alkyl chain length (Sakai
et al., 2017). Nevertheless, it may be interesting to investigate if
LAS concentration could be correlated with toxicity of surface water
because the existence of LAS indicates the discharge of untreated
sewage which should contain various contaminants. Overall, the
main purpose of this study was to identify the occurrence and
distribution of LAS in a watershed scale using a novel combination
of spatial and quantitative analysis method, and we do not suggest
that LAS can be used as a primary determinant of water quality
deterioration as well as of aquatic safety.
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