Multiphase OH Oxidation of Bisphenols: Chemical Transformation and Persistence in the Environment

Abstract

Bisphenol A (BPA) is a common endocrine disruptor widely found in commercial products. Despite negative human health effects, its usage is not fully banned worldwide with ongoing human exposure from sources including dust, aerosol particles, and surfaces. Although attention has been paid to the abundance of alternatives with similar structures that are replacing BPA, uncertainties remain with respect to their chemical transformations and products, toxicity, and environmental fate. We provide the first experimental and modeling assessment of gas-particle multiphase OH oxidation of BPA and six common bisphenol alternatives. We examine the transformation of condensed-phase BPA and its alternatives using an oxidation flow reactor with products monitored by online mass spectrometry. Fourteen products were identified and used to develop a generic mechanism applicable to all bisphenols and to provide inputs into an environmental fate model (PROduction-to-Exposure; PROTEX). Our modeling results highlight the role of heterogeneous surface reactions in determining the indoor retention of these chemicals and their relative environmental persistence indoors and outdoors. All investigated parent molecules yield transformation products predicted to accumulate indoors, with extended indoor persistence if a long chemical lifetime on surfaces (e.g., >100 weeks) is assumed. Evidence of phenoxy radical presence upon oxidation raises a human health risk concern.

Keywords: BPA alternatives; OH radical; environmental persistence; multiphase oxidation.

1

Time series of BPS and the observed transformation products during the control (O₃ only and UV only) and OH exposure periods. Decay and rise of ion signals were observed for BPS and products, respectively, only during OH exposure. The signal increase of parent BPS before OH exposure is due to the slight temperature variation of the heating tube for BPS. The OH exposure was not applied until the set temperature had been reached again and the BPS signal remained stable.

2

Differential positive ion EESI-TOFMS spectrum for BPS at OH exposure of 3.3 × 10¹¹ molecules s cm^–3. Based on the formula assignment, the main product peaks are labeled with the m/z ratio and gain or loss of C and O atoms with respect to the parent compound.

3

Proposed transformation pathways for bisphenols (BPX) upon OH oxidation, based on the observations for all the bisphenols assessed in this study. Followed by the production of intermediate resonance structures (R1 and R2) via OH addition, panel (A) involves pathways A and B that involve H atom abstraction and the formation of byproduct HO₂ with the presence of O₂, whereas panel (B) shows pathways C–F that are initiated by the formation of peroxy radicals (R3 and R4). Closed shell products observed by EESI-TOFMS are in solid boxes (P1–P14). Isomeric products are labeled as P X.X. Stable phenoxy radicals are in dashed boxes (PR1–PR4). Intermediate radical species are labeled as R1–R4. Note that structural isomers other than those indicated are possible. A summary of the proposed structures and associated pathways is provided in Tables S2b and S3a.

4

Indoor chemical mass distribution (C_m,%), defined as the percentage of steady-state chemical mass found indoors in all compartments across the defined totality of the regional environment, for BPA, BPS, and BPAF-related closed shell compounds included in the mechanism in Figure . The C_m results obtained under the assumption of 1, 10, and 100-week surface lifetimes are shown in black, blue, and red circles, respectively. The C_m values for the parent bisphenols are presented in solid circles, whereas the products are presented in hollow circles. A compound-specific figure that differentiates each individual compound is provided in Figure S3. The C_m results for other bisphenols (BPB, C, E, and F) are provided in Figure S5.

5

Indoor and outdoor (rural) overall persistence (P_ov,i and P_ov,o, hours), defined as the overall lifetime in the corresponding environment, for BPA, BPS, and BPAF-related compounds. For persistence indoors, the P_ov,i results obtained under the assumption of 1, 10, and 100-week surface lifetimes are shown in black, blue, and red circles, respectively. The P_ov,i values for bisphenols are presented as solid circles, whereas the products are presented as hollow circles. For persistence outdoors, the P_ov,o values for bisphenols and products are presented as solid and hollow green stars, respectively. A compound-specific figure differentiating each individual compound is provided in Figure S4. The P_ov results for other bisphenols (BPB, C, E, and F) are provided in Figure S6.