UV Light Combined with Nitrate Remove Bisphenol A: Kinetics, Transformation Pathways, and Acute Toxicity Assessment

As a powerful endocrine disruptor, bisphenol A (BPA) is a serious threat to human 26 health. In this study, low-pressure UV lamp (LP-UV) photolysis nitrate was used to 27 degrade BPA in different aqueous solutions. Results showed that BPA could be 28 decomposed efficiently in the UV/nitrate process. ·OH played a significant role in the 29 UV/nitrate process, and the steady-state concentration of ·OH ([·OH] ss ) was calculated 30 to be 5.26×10 -15 M under control conditions. Moreover, the contributions of UV 31 irradiation (4.1%), ·OH (52.7%), and reactive nitrogen species (43.2%) were obtained. The observed rate constant of BPA degradation ( k obs ) increased with nitrate concentration since more activity species were generated in high nitrate concentration. degradation rate significantly accelerated pH value absorption obs concentration of BPA was slightly enhanced then decayed in the UV/nitrate process.


Introduction 48
Various man-made chemicals, such as pesticides, flame retardants, plastic additives, that the BPA degradation increased in UV-C/SPS oxidation system as a result of the 79 BPA molecules attacked by the SO4 ·radicals. Over recent years, the UV/nitrate system 80 has received growing attention because nitrate (NO3 -) is a naturally occurring ion 81 involved in the nitrogen cycle in the environment and it can effectively decompose 82 EDCs (e.g., estrone, and 17α-ethynylestradiol) ( Therefore, this work aims to achieve the following objectives: (ⅰ) to assess the 104 proportions of direct UV, RNS, and ·OH to BPA decomposition in UV/nitrate system, 105 (ⅱ) to analyze the effect of NO3concentration, initial BPA dosage, pH values, common 106 anions (including bicarbonate/carbonate (HCO3 -/CO3 2-) and chloride ions (Cl -)), and 5 natural organic matter (NOM) on BPA decomposition in the UV/nitrate process, (ⅲ) to 108 analyze intermediate products and explore the possible transformation pathways, (ⅳ) 109 to assess the acute toxicity and evaluate application significant of UV and was from Tedia Company. Groundwater and surface water were obtained from 119 Baotu Spring and Xiaoqing River in Jinan, China. Drinking water was taken from the 120 municipal tap and left for two days before use. De-ionized water was obtained from the 121 Milli-Q Biocel water system. 122

Analytical methods 123
The concentrations of BPA, NB were detected using high-performance liquid 124 chromatography (HPLC, Waters 2695) reported in the previous study (Gao et al. 2020b).

Experimental methods 137
The photochemical experiment was conducted using four 10 W low-pressure Hg UV 138 lamps (peak wavelength output at 254 nm, Heraeus, GPH212T5L/4) in a closed box. 139 The UV light intensity was 0.172 mW·cm -2 after preheating for an hour. In order to As illustrated in Fig. 1, the NO3concentration did not decrease significantly after 7 the 3600 s process, and a very small amount of nitrite produced was detected. (9) 163 Because of the following relationship (Eq. (10)), the contribution ratios of UV, ·OH, 164 and RNS for BPA decomposition in the UV/nitrate process can be calculated, 165 respectively. 166 Where k UV, NB and k UV, BPA represent apparent rate constant of NB and BPA in the 168 direct UV process, respectively, and k •OH, NB , k •OH, BPA , and k RNS, BPA are the second-169 order rate constants of ·OH with NB, ·OH with BPA, and RNS with BPA, respectively. In the work, BPA degradation efficiencies in direct UV and UV/nitrate processes 177 were quite different. Fig. S1 demonstrates that 30 µM BPA was efficiently degraded in 178 the UV/nitrate process while direct UV had a little effect and the degradation of BPA in 179 sole NO3was negligible. In reality, the root cause of this phenomenon is that UV254 180 irradiation of NO3generates reactive oxygen radicals (e.g., ·OH, O ·-, O( 3 P)) and 181 reactive nitrogen radicals (e.g., ·NO2, ·NO, ONOO -) (Mack &Bolton 1999). What is 182 more important, the second-order rate constant of ·OH with BPA is 1.02 × 10 10 M -1 s -1 183 and ·OH plays a crucial part in the UV/nitrate process (Rosenfeldt &Linden 2004). 184 The NB degradation in different dosages of NO3is shown in Fig. 2. And the 185 Table S1 shows the increase of [·OH]ss with the concentration of 186 NO3 -, i.e., 5.64  10 -16 M, 1.15 10 -15 M, 5.26 10 -15 M, and 7.45 10 -15 M at 10, 20, 30, 187 50mM NO3 -, respectively. 188

calculated [·OH]ss in
As demonstrated in Fig. S2, after 3600 s of irradiation, the removal ratio of BPA in 189 UV/nitrate control experiment system was 30.39%. Obviously, RNS played a 190 significant role and UV, ·OH, and RNS accounted for 4.1%, 52.7%, and 43.2% (Fig. 3) 9 of the total removal ratio, respectively. Therefore, although the [·OH]ss was low in the 192 control experiment, the contribution of ·OH to BPA was larger than that of RNS can 193 attribute to their superhigh second-order reaction rate constant. 194

Effect of the initial BPA concentration 214
The influence of the initial BPA concentration (5~50 μM) was also examined in the 215 UV/nitrate process. According to the results of   However, when solution pH higher than or equal to 10, kobs rapidly grow, and the kobs 252 at pH 10 was almost twice times as high as that at pH 9. It seems that only the change 253 . What is more, this result also can be ascribed to ·NO2. From Eq. (6), it is not 277 hard to conclude that the equilibrium shifted to the right side due to ·OH scavenged by 278 HCO3and CO3 2-. Thereby, BPA degradation was facilitated owing to 279 accumulative ·NO2. 280

Effect of Cl -281
As a common anion in the environment, the effect of Clin UV/nitrate was also 282 explored. Fig. 9 represented the result that Clhad not outstanding inhibition or 283 acceleration BPA degradation (i.e., kobs=9~10×10 -5 s -1 , Clconcentration varies from 0 284 to 10 mM). In general, some chlorine species, like Cl·, Cl 2 -• , and ClOH ·-, may be 285 generated due to Clreacting with ·OH (Eq. 2014). Therefore, the ability of nitrate to absorb photons was reduced extremely, which 313 led to the decrease of the reaction efficiency of producing ·OH. 314

Intermediate products and proposed transformation pathways 315
The changes of TOC of BPA before and after reaction in the UV/nitrate process are 316 depicted in Fig. S3, indicating that mineralization was little in this study. BPA predominantly transformed small organic compounds. Based on the results of 318 LC/MS/MS, the possible transformation pathways of BPA in the UV/nitrate process are 319 elucidated in Fig. 11. Intermediate products and detailed information are supplied in 320 Table.  (m/z=131.16) and B136 (m/z=136.14) were generated. Besides, with the aromatic ring 332 of B151 H-abstraction and further oxidation, a benzoquinone derivative (i.e., B181, 333 m/z=181.17) formed. All the above products were further oxidated and occurred ring 334 cleavage, some small-molecule organic compounds (e.g., B97 (m/z=97.14), B79 335 (m/z=79.13), and B92 (m/z=92.09)) formed. Besides, the mineralization of partial 336 organic compounds could produce inorganic compounds such as CO2, H2O, and NO3 -. To investigate the application of the UV/nitrate system in the real environment, BPA 352 degradation experiments were also conducted in several actual waters. As is 353 demonstrated in Fig. 13, compared with de-ionized water, BPA degradation in surface 354 water was inhibited. From Table. S3, the possible reason for this phenomenon is the 355 relatively high concentration of NOM (TOC=4.115mg-C/L). Although the total 356 alkalinity was as high as 230.63 mg CaCO3/L (i.e., 2.3mM CO3 2-) and the NO3 -357 concentration was 10.418mg-N/L (i.e., 0.744mM), the inhibition effect can not be offset. 358 In contrast, BPA decomposition rates in groundwater and drinking water were accelerated. The results can be ascribed to their high total alkalinity and low TOC (Table.  360 S3). Consequently, the decomposition of BPA and other EDCs in the UV/nitrate process 361 could become a reality theoretically. But the strict condition (e.g., needing a relatively 362 high concentration of NO3 -) limits the scope of its application. Numerous studies have 363 shown that high concentration NO3and generated NO2can harm human health (e.g.,

Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download.