Mar 5, 2018 - Department of Civil and Environmental Engineering, National University of ... NUS Environmental Research Institute, National University of ...
Article Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
pubs.acs.org/est
Occurrence and Fate of Benzophenone-Type UV Filters in a Tropical Urban Watershed Feijian Mao,† Luhua You,† Martin Reinhard,‡ Yiliang He,*,§ and Karina Yew-Hoong Gin*,†,∥ †
Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, E1A 07-03, Singapore 117576, Singapore ‡ Department of Civil and Environmental Engineering, Yang & Yamasaki Environment & Energy Building, 473 Via Ortega, Stanford University, Stanford, California 94305, United States § School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China ∥ NUS Environmental Research Institute, National University of Singapore, 5A Engineering Drive 1, #02-01, Singapore 117411, Singapore S Supporting Information *
ABSTRACT: The study investigated the occurrence and fate of seven benzophenone-type UV filters (i.e., 2,4-dihydroxybenzophenone (2,4OH-BP), 2,2′,4,4′-tetrahydroxybenzophenone (2,2′,4,4′OH-BP), 2-hydroxy-4-methoxybenzophenone (2OH-4MeO-BP), 2,2′-Dihydroxy-4,4′-dimethoxybenzophenone (2,2′OH-4,4′MeO-BP), 2,2′-dihydroxy-4-methoxybenzophenone (2,2′OH-4MeO-BP), 4-hydroxybenzophenone (4OH-BP), and 4,4′-dihyroxybenzophenone (4DHB)) in a tropical urban watershed consisting of five major tributaries that discharge into a well-managed basin. Total benzophenone concentrations (∑CBPs) varied from 19−230.8 ng L−1 in overlying bulk water, 48−115 ng L−1 in pore water, 295−5813 ng g−1 dry weight (d.w.) in suspended solids, and 6−37 ng g−1 d.w. in surficial sediments, respectively. The tributaries (∑CBPs: 19−231 ng L−1) were the main source of benzophenone compounds entering the basin (∑CBPs: 20−81 ng L−1). In the water column, the vertical concentration profile in the aqueous phase was uniform while concentrations in the suspended solids decreased with depth. Different distribution profiles were also identified for benzophenones in suspended solids and sediments. A preliminary risk assessment suggested that the seven BPs were unlikely to pose ecotoxicological risks to local aquatic organisms except for 2OH-4MeO-BP in the case of an intermittent release.
1. INTRODUCTION
Various studies have demonstrated the estrogenic activity of BPs and thus they are currently regarded as potential endocrine disrupting chemicals.6,8,9 For example, studies have demonstrated the weak estrogenicity of 2OH-4MeO-BP, one of the most popular congeners.6 In addition, 2OH-4MeO-BP can form several metabolic byproducts with estrogenic activities, such as 2,2′OH-4MeO-BP and 2,4OH-BP.6 In addition, 2,4OH-BP is speculated to be associated with endometriosis, an estrogen-dependent disease.10 Other benzophenone derivatives, such as 4-hydroxybenzophenone (4OH-BP) and 2,2′,4,4′OH-BP, exhibited higher estrogenic activity than 2OH-4MeO-BP.11 Apart from endocrine disrupting properties, BPs can also cause coral bleaching and disrupt gene expression in zebrafish.12−14
A variety of benzophenone compounds (BPs) have been used as ultraviolet (UV) light absorbers in personal care products (e.g., sunscreens, shampoos, body lotions, and hair sprays) and synthetic products such as insecticides, plastic bags, and paints that are exposed to sunlight.1−3 In Australia, Europe, and China, 2-hyrdoxy-4-methoxybenzophenone (2OH-4MeO-BP) has been approved for use as an active ingredient in sunscreens at concentrations up to 10%.4 Other countries have permitted the use of 2,4-dihydroxybenzophenone (2,4OH-BP), 2,2′,4,4′tetrahydroxybenzophenone (2,2′,4,4′OH-BP), 2,2′-dihydroxy4,4′-dimethoxybenzophenone (2,2′OH-4,4′MeO-BP), and 2,2′-dihydroxy-4-methoxy-benzophenone (2,2′OH-4MeO-BP) in sunscreens.4,5 Due to extensive use, BP-type UV filters can enter water environments directly from recreational activities (e.g., bathing and swimming) and indirectly from sewage discharges (e.g., wastewater treatment plant effluent and domestic washing).2,6,7 © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
November 3, 2017 February 27, 2018 March 4, 2018 March 5, 2018 DOI: 10.1021/acs.est.7b05634 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
sample per tributary). Surficial benthic sediment samples were collected at the eight sampling sites from the top 10 cm with a stainless steel grabber. A total of five quarterly sampling events were conducted starting from December 2014 to December 2015. This was to capture the seasonal characteristics covering the northeast (NE) monsoon (December-early March), intermonsoon (late March−-May, October−November) and southwest (SW) monsoon (June−September) periods. All the samples were kept in an ice-packed container during transport to the laboratory. The samples were stored in a cold room (4 °C) in the dark. 2.3. Sample Pretreatment and Extraction. BPs in the aqueous phases (i.e., bulk water and pore water) and solid matrices (i.e., SS and sediments) were analyzed using a combination of solid phase extraction (SPE), ultrasoundassisted extraction and high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/ MS). Detailed description about the analytical procedures and method validation are described in the SI. 2.4. Evaluation of Distribution of Benzophenones in Dissolved and Solid Phases. The fraction of BPs associated with SS and sediments (ΦSS and ΦSed, %) was calculated with the following equations:
Given their wide ranging physicochemical properties, BPs can be accommodated in different environmental matrices (e.g., bulk water, suspended solids (SS), pore water, and sediments) in aquatic ecosystems.15−18 Previous studies have detected the concentrations of BPs in surface water and sediments, with levels typically ranging from ng L−1 to low μg L−1 for water samples and in the low ng g−1 range for sediments (dry weight).2,7,19,20 In contrast, studies on the detection of BPs in SS and pore water are limited.15,17 BPs associated with SS are expected to influence both the quality of the water column (via sorption and desorption) and benthic sediments (via sedimentation and resuspension).17,21 Sediment-pore water partitioning and diffusion across the sediment−water column boundary are important processes that govern the transport, fate and toxicity of BPs in aquatic systems.22,23 Since the fate of BPs in a surface water body is linked to the fate and transport of particles (SS and sediments), it is essential to study their occurrence concurrently in all relevant environmental compartments: bulk water, SS, surficial benthic sediments, and sediment pore water. Thus, the primary objectives of this investigation were to quantify the concentrations of seven targeted BP-type UV filters in a tropical urban watershed. BPs included were 2,4OHBP, 2,2′,4,4′OH-BP, 2OH-4MeO-BP, 2,2′OH-4,4′MeO-BP, 2,2′OH′4MeO-BP, 4OH-BP, and 4,4′-dihyroxybenzophenone (4DHB). BPs were quantified in the four environmental compartments (dissolved in bulk water and sorbed to SS in the water column and dissolved in pore water and sorbed to surficial sediments). The approach was to investigate the temporal and spatial variations of the target BPs and to evaluate the data with respect to sorption. Environmental risk assessment was performed to assess the ecotoxicological risks posed by these BP-type UV filters. Results are useful for assessing the environmental risk of BPs and elucidating their fate in aquatic environments.
ΦSS = mSS /(mSS + mBW ) × 100%
(1)
Φsed = mSed /(msed + mPW ) × 100%
(2)
where, mSS, mBW, msed, and mPW are the mass (in ng) of BPs in SS, bulk water, sediments, and pore water, respectively. Detailed derivations and calculation are provided in the SI. 2.5. Environmental Risk Assessment. Risk quotients (RQs) of BP-type UV filters were quantified with the ratio between the measured environmental concentrations (MECs) in the dissolved phase (bulk water and pore water) and the predicted no-effect concentrations (PNECs) (eq 3). The RQ of a water sample (i.e., RQtotal) was defined as the sum of RQs of each BPs (RQi) following the rule of concentration addition (eq 4).27,28
2. MATERIALS AND METHODS 2.1. Chemicals and Reagents. The seven targeted BPs (i.e., 2,4OH-BP, 2,2′,4,4′OH-BP, 2OH-4MeO-BP, 2,2′OH4,4′MeO-BP, 2,2′OH′4MeO-BP, 4OH-BP, and 4DHB) and benzophenone-d10 (BP-d10, internal standard) of high purity grade (>99.9%) were purchased from Sigma-Aldrich (SigmaAldrich, Singapore). Some environmentally important physicochemical properties are given in Supporting Information (SI) Table S1. Individual stock solutions (1000 mg L−1) were prepared in methanol from powder and stored in the dark at −20 °C. A mixture of all analytes was obtained by combining aliquots of the stock solutions. Other chemical reagents and solvents, such as HPLC grade methanol, were of high purity grade. Ultrapure water was produced by a Milli-Q system (Sartorius, Singapore). 2.2. Sampling Campaign. The watershed and sampling sites have been described elsewhere and are presented in SI Figure S1.24−26 Briefly, the study area (about 10 000 ha) is a tropical urban watershed located in Singapore, accounting for about one-sixth of Singapore’s land area. The watershed consists of a main water body (hereinafter “basin”), which receives the discharge of five major tributaries. Water samples were collected in 1 L amber water bottles at three sites (i.e., S1, S2, and S3) located in the basin: at 0.1 m (top), about 2.5 m (middle) and about 5 m below the water surface (near the bottom). At the five tributaries (identified as SR, SC, RC, KR, and GR), grab surface water samples were collected (one
RQ = MEC/PNEC n
RQ total =
(3) n
∑ RQ i = ∑ MECi /PNECi i=1
i=1
(4)
MEC values of BP-type UV filters were obtained from the present study. PNEC values were derived from available ecotoxicological data with an assessment factor (SI Table S2). The assessment factors were employed to compensate for the uncertainties in inter- and intraspecies variations, acute and chronic toxicity and the extrapolation of laboratory data to the field.3,29 They were calculated following the European Commission guidelines.30 To reflect the risk under the worst condition, the highest MEC and the lowest PNEC of each BPs were employed in the risk assessment.7,28,29 RQ based ranking criteria were applied to interpret the risk classification: “unlikely to pose risk” for QR < 0.01; “low risk” for 0.01 < RQ < 0.1; “medium risk” for 0.1 < RQ < 1; “high risk” for RQ >1.28 2.6. Statistical Analysis. Data were subjected to normality test (Shapiro-Wilk) before statistical analyses. A student’s t test (for normal distribution) or a Mann−Whitney U test (for not normal distribution) was employed to compare the differences in concentrations of BPs in samples collected from different locations. All statistical analyses were performed using OriginPro 2016 (OriginLab Corporation, Northampton, USA). B
DOI: 10.1021/acs.est.7b05634 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Table 1. Detection Frequency, Median and Range of BP Concentrations in Bulk Water and Suspended Solids from the Tributaries and the Basin tributary compounds
DF (%)
range
basin median
ratiob
20.4−81.0 1.4−5.2 1.6−12.3 4.5−56.1
