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# Unveiling the transformation of 2,4,6-trihalophenols by active species in drinking water pipelines: The role of goethite

Feilong Dong, Jiani Zhu, Cong Li, Eric Lichtfouse, Wei Wang, Shuang Song

► To cite this version:

Feilong Dong, Jiani Zhu, Cong Li, Eric Lichtfouse, Wei Wang, et al.. Unveiling the transformation of 2,4,6-trihalophenols by active species in drinking water pipelines: The role of goethite. Chemical Engineering Journal, 2024, 492, pp.152390. 10.1016/j.cej.2024.152390. hal-04586301

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# Unveiling the transformation of 2,4,6-trihalophenols by active species in drinking water pipelines: The role of goethite

Feilong Dong<sup>a,e</sup>, Jiani Zhu<sup>a</sup>, Cong Li<sup>b</sup>, Eric Lichtfouse<sup>c</sup>, Wei Wang<sup>d,*</sup>, Shuang Song<sup>a,*</sup>

## ARTICLE INFO

**Keywords:**

Disinfection byproducts

Chlorination

Goethite

Free radicals

Transformation

## ABSTRACT

The long-term accumulated pipe scale in the water distribution system (WDS) is vital for ensuring the safety of drinking water delivery. This study revealed a novel positive role of pipe scale in triggering interface free radicals for aromatic substances degradation. The goethite (main constituents of pipe scale) converts from the trivalent state to the divalent state by withdraw electrons from aromatic phenolic compounds. Active free radicals such as hydroxyl radical (•OH), Cl•, and ClO• were subsequently formed via a cascade of chain reactions under WDS conditions, among which •OH was the dominate active species driving efficient transformation of 2,4,6-trichlorophenol (60.8%) and 2,4,6-tribromophenol (80.5%) and the corresponding toxicity attenuation. The goethite mediated chlorination is a surface reaction following Langmuir–Hinshelwood model. Our works revealed the presence of natural source of •OH for disinfection byproducts transformation. Given the ubiquitous existence of iron scales inside ductile iron pipe, the finding renewed the understanding of the impact of WDS on drinking water quality.

## 1. Introduction

Disinfection byproducts (DBPs) persistently exist in tap water, primarily originating from the final disinfection processes in water treatment and continuing to be generated throughout the water distribution system (WDS). To date, more than 700 aromatic and aliphatic byproducts have been identified in drinking water [1]. In comparison to aliphatic DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) with concentrations at the µg/L level in drinking water, aromatic DBPs detected are typically 1 to 2 orders of magnitude lower [2]. Nonetheless, among various aromatic DBPs, 2,4,6-trihalophenols have received much attention to date since their cytotoxicity, developmental toxicity, and growth-inhibiting properties are tens to hundreds of factors higher when compared to numerous aliphatic halogenated DBPs and several halo-phenolic DBPs (e.g., halogenated hydroxybenzaldehyde and halogenated hydroxybenzoic acid) [3]. In which, 2,4,6-trichlorophenol (TCP) and 2,4,6-tribromophenol (TBP) are often found in drinking waters in China (ranging from 2.9 to 31.6 ng/L) [4]. In special, the highest concentration of TCP in the county of Ostergotland in

Sweden reached up to 640 ng/L in a tap-water sample [5]. Because of the high toxicity, persistent property and adverse impacts on environment and human health [6], TCP and TBP have been designated as priority pollutants in the USA and China [7,8].

Iron pipes are one of the extensively used materials in the WDS, but they are prone to form corrosion scale as a result of long-term use. Goethite is the predominant component of iron corrosion scales, comprising over 50 % of the iron minerals formed through corrosion processes [9–11]. It is composed of octahedral structural units consisting of $FeO_3(OH)_3$. Goethite exhibits adsorption behavior towards chlorophenols by forming surface complexes. The hydroxyl groups present on the goethite surface can interact with the chlorophenols through hydrogen bonding or other electrostatic interactions [12,13]. This adsorption process allows goethite to effectively adsorb chlorophenols from aqueous solutions. Under pure and controlled conditions, it has been shown that adding synthetic goethite converts HClO into hydroxyl radicals (•OH) via surface-initiated chain reaction similar to the Haber-Weiss Fenton process [14]. A single electron transfer from Fe(II) to HClO favors the generation of hydroxyl and chlorine radicals [15]. Therefore,

<footnote><sup>a</sup> College of Environment, Zhejiang University of Technology, Hangzhou 310014, China</footnote>

<footnote><sup>b</sup> School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200433, China</footnote>

<footnote><sup>c</sup> State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China</footnote>

<footnote><sup>d</sup> Department of Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China</footnote>

<footnote><sup>e</sup> Shaoxing Research Institute, Zhejiang University of Technology, Shaoxing 312085, China</footnote>

<footnote>* Corresponding authors.</footnote>

<footnote>E-mail addresses: ww1@zju.edu.cn (W. Wang), ss@zjut.edu.cn (S. Song).</footnote>
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we hypothesized that radical formation could happen 'naturally' by
reaction of Fe-enriched scale with aromatic phenolics. The •OH radicals
are widely recognized as potent oxidizing agents, with sufficient power
to decompose 2,4,6-trihalophenols through oxidative degradation [16].

The conversion of phenyl DBPs can proceed via electrophilic/
nucleophilic substitution, oxidation-reduction reactions as well as
decarboxylation [2]. The decomposition of 2,4,6-trihalophenols can
generate small aliphatic DBPs (e.g., HAAs, THMs and haloacetonitriles)
through two pathways involving ring opening and cleavage of the side
chain [2]. Currently, research on the decomposition of aromatic DBPs
primarily focuses on the disinfectant oxidation such as chlorination and
chloramination. However, •OH radicals generated by goethite mediated
chlorination alter the reaction between halogenated phenols and re-
sidual chlorine, leading to the more complex transformation pathway.
Due to the presence of residual chlorine and goethite in the pipe
network, the concentrations of 2,4,6-trihalophenols may vary with dis-
tance, thereby altering their impact on small aliphatic DBPs during de-
livery [17]. Understanding the transformation pathways of 2,4,6-
trihalophenols based on goethite mediated •OH process can further
reveal the mechanism of occurrence and transformation of DBPs, facil-
itating the development of strategies to control DBP formation.

In this work, we have demonstrated that the free radical process
could spontaneously occur on goethite surface in the WDS. TCP and TBP
were chosen as representative 2,4,6-trihalophenols to simulate the
transformation of aromatic DBPs. The detailed mechanism of radical
formation was elucidated through the use of radical scavenger and
verified by instrumental analysis. The reaction kinetics was modeled
based on the effect of processing variables. The degradation in-
termediates, potential degradation pathways and corresponding cyto-
toxicity were proposed.

## 2. Materials and methods

### 2.1. *Chemicals and reagents*

Goethite was obtained from Alfa Aesar Inc. (Ward Hill, USA). The X-ray powder diffraction (XRD) patterns reveals characteristic peaks that correspond to the distinctive crystal planes of goethite, which are in accordance with the main peaks of the XRD pattern of the representative iron scale (Fig. S1) [18]. The used chemicals and reagents are listed in Text S1.

### 2.2. *Experimental processes*

The experimental pipe reactor was custom-built to match the struc-
tural characteristics of the water supply pipe network (Fig. S2). Before
the experiments, goethite was loaded onto the reactor. The experiments
used tap water with stirring for 300 rpm, and the water quality pa-
rameters were summarized in Table S1. The analysis methods for water
quality parameters were as described in Text S2. The initial concentra-
tions of TCP and TBP were 2.0 µmol/L, while free chlorine (HClO/ClO⁻) and goethite concentrations were 2.0 mg/L and 4.0 g/L, respectively.
The temperature and pH were controlled at 7.5 ± 0.1 and 25 °C in the
pipe reactor, which is close to the actual WDS conditions. Some pa-
rameters encompassed TCP/TBP concentrations (0.5 to 3.0 µmol/L),
goethite dosages (2.0 to 8.0 g/L), pH values (6.5, 7.5, and 8.5) and
HClO/ClO⁻ concentrations (0.5 to 3.0 mg/L) were chosen to assess the
effects on TCP and TBP removal. Samples were collected periodically at
predetermined time (0, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 6.0 and 8.0 min),
filtered through a 0.22 µm microporous membrane, and quenched with
freshly prepared sodium thiosulfate by adding 0.1 mL of Na₂S₂O₃ (the
molar concentration was 1.0 mol/L).

To explore the impact of free radicals on TCP and TBP degradation,
tert-butanol (TBA), benzoic acid (BA), and 1,4-dimethoxybenzene
(DMOB) at a concentration of 150.0 µmol/L were added to quench
•OH and reactive chlorine species (RCS, chlorine radical (Cl•)) and

oxychloride radical (ClO•)). The radicals competing experiments were
performed by using TBA as a strong scavenger for •OH, BA as a
quenching agent for both •OH and Cl•, and DMOB as a quenching agent
for •OH, Cl• and ClO•. To analyze the intermediate products during the
transformation, 30.0 mL samples were collected at a reaction of 1.0 h
and quenched by 0.5 mL of Na₂S₂O₃. Then the samples were extracted to
2.0 mL using liquid/liquid extraction with n-hexane.

The instruments and methods used for analysis and characterization
during the experimental process were displayed in Text S3.

## 3. Results and discussion

### 3.1. *Goethite-mediated transformation of 2,4,6-trihalophenols*

We hypothesized that goethite might influence the removal of organic compounds in water containing residual chlorine. To test this hypothesis, we firstly reacted TCP and TBP with goethite, a Fe-rich mineral, HClO/ClO⁻, or both. Results show 19.2 % TCP removal with goethite alone and 27.2 % TCP removal using HClO/ClO⁻ alone after 8 min (Fig. 1a). For TBP, 22.5 % and 37.3 % were respectively removed in the same conditions (Fig. 1b). Removal increased to 60.8 % for TCP and 80.5 % for TBP using both goethite and chlorine, with corresponding rise of rate contents by 2.4–4.0 (Table S2). These findings suggested that goethite mediated chlorination enhanced the removal of aromatic phenolics. This might be explained either by transformation of aromatic phenolics into degradation products, or by adsorption of the initial compounds and degradation products on solid surfaces, such as goethite and flask surfaces.

High performance liquid chromatography-mass spectrometry (HPLC-MS) analysis revealed that the main products of TBP transformation with HClO/ClO⁻ were 4,6-dibromo-1,2-benzenediol (OP9-267.86), 2,6-dibromo-1,4-benzoquinone (OP12-265.84) and 3,5-dibromo-2-hydroxy-1,4-benzoquinone (OP13-281.84) (Table S3). 2-chloro-6-bromo-1,4-benzenediol (OP16-223.91), 2-bromo-6-chloro-1,4-benzoquinone (OP17-221.89) and 3-bromo-5-chloro-2-hydroxy-1,4-benzoquinone (OP18-235.89) were chlorine-containing intermediates. This suggests that the bromine atom on the phenol ring is substituted by chlorine during chlorination, according to previous studies [19]. In our study, the chlorine atom from free chlorine replaces the bromine atom at the ortho- or para-position of the phenol ring through electrophilic substitution. This is confirmed by the presence of 2,3,4,6-tetrachlorophenol (OP1-231.88) bearing 4 substituted chlorines atoms. No intermediate without aromatic ring could be found using HClO/ClO⁻, suggesting that HClO/ClO⁻ does not possess sufficient energy to cleave the phenolic ring under our conditions.

By contrast, when both goethite and HClO/ClO⁻ were present, TCP
degradation resulted in the formation of ring-cleavage compounds,
including 2-chloro-4-oxohex-2-enedioic acid (OP4-194.00) and small
molecular hexanedioic acid (OP5-160.04) (Table S4). Compared to the
products from chlorination alone, the coexistence of goethite and HClO/
ClO⁻, resulted in the presence of ring-cleavage compounds during the
reaction process, indicating the presence of stronger oxidants in the
medium than HClO/OCl⁻. Similar observations were made during the
goethite mediated chlorination of TBP, thus strengthening this inter-
pretation. Since the redox potential of hypochlorous acid (HClO/Cl⁻,
0.89–1.48 V) is generally lower than that of •OH (2.80 V) [20], ClO•
(1.49 V) [21], Cl• (1.50 V) [22], and Cl₂• (2.00 V) [21,23], we presumed
that •OH could be the dominant species responsible for oxidation and
ring opening, as suggested by a previous study [24]. The higher removal
rates of TBP versus TCP is attributed to the lower C-Br bond energy in
TBP (276 kJ/mol), versus that of the C-Cl bond in TCP (327 kJ/mol)
[25].

### 3.2. *Identification of active species*

When goethite and HClO/ClO⁻ coexisted in aqueous media, a typical
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<figure><img src="image_2.png" /><figcaption>Fig. 1. The removal of (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: reaction time = 8.0 min, temperature = 25 ± 1C, initial pH = 7.5 ± 0.1, initial free chlorine = 2.0 mg/L, initial goethite dosage = 4.0 g/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>

four-line EPR signal characteristic with relative intensity of 1:2:2:1 corresponding to a DMPO-OH spin adduct were observed (Fig. 2a). The three peaks located at 3494, 3509, and 3524 G were ascribed to DMPO-Cl, and the other six peaks indicated the production of DMPO-OCI [26,27]. The EPR capture experiment provided evidence that the active species (e.g., •OH, ClO• and Cl•) are responsible for the TCP/TBP removal.

According to the Haber-Weiss mechanism, dissolved and surface-exposed bivalent iron is a key reactant contributing to free radical generation. To exprobraed the effect of dissolved and surface-exposed bivalent iron, we attempted to determine the concentrations of Fe²⁺ and Fe³⁺ in water and goethite using ortho phenanthroline spectro-photometry (Text S4). However, no Fe²⁺ and Fe³⁺ could be detected above the detection limit of the method. Subsequently, when 50.0 µg/L Fe²⁺ or 50.0 µg/L Fe³⁺ was added separately to the HClO/ClO⁻ solution, it was found that the removal of TCP and TBP could be neglected (Fig. S3). Hence, the goethite dissolution had neglected effect to the TCP/TBP elimination in our experiments. To elucidate the surface chemical process of goethite, reaction of TCP with goethite was conducted in a separate experiment in Text S5. At the end of 24.0 h reaction, 15 % of TCP was removed from the aqueous solution. Nonetheless, no intermediates could be detected in the reaction solution. After washing the used goethite with methanol, the TCP and 2,6-dichloro-p-quinone leached out from the goethite and were obviously detected (Fig. S4) [28–30]. According to literature [31–34], we concluded that Fe(III) in goethite could function as an electrophilic oxidant able to oxidize TCP towards 2,6-dichloro-p-quinone, accompanied with the generation of Fe

(II) (Eq. (1)). Together with the EPR results above, Fe(II) in turn induced the formation of a series of free radicals (Eqs. 2–10) [15,21,35–37].

$$2,4,6-\text{TCP} + \text{Fe(III)} + \text{H}_2\text{O} \rightarrow 2,6-\text{dichloro-p-quinone} + \text{Fe(II)} + \text{Cl} \cdot + \text{H}^+ \quad (1)$$

$$\text{HClO} + \text{Fe(II)} \rightarrow \text{Fe(III)} + \text{HO} \cdot + \text{Cl}^{-} \quad (2)$$

$$\text{HClO} + \text{HO} \cdot \rightarrow \text{ClO} \cdot + \text{H}_2\text{O} \quad k = 1.21 - 2.0 \times 10^9 \text{ M}^{-1}\text{s}^{-1} \quad (3)$$

$$\text{HO} \cdot + \text{Cl}^{-} \rightarrow \text{ClOH} \cdot^{-} \quad k = 4.3 \times 10^9 \text{ M}^{-1}\text{s}^{-1} \quad (4)$$

$$\text{ClOH} \cdot^{-} \rightarrow \text{Cl} \cdot + \text{HO} \cdot \quad k = 6.1 \times 10^9 \text{ M}^{-1}\text{s}^{-1} \quad (5)$$

$$\text{Cl} \cdot + \text{HO}^{-} \rightarrow \text{ClOH} \cdot^{-} \quad k = 1.8 \times 10^{10} \text{ M}^{-1}\text{s}^{-1} \quad (6)$$

$$\text{OCl}^{-} + \text{Cl} \cdot \rightarrow \text{ClO} \cdot + \text{Cl}^{-} \quad k = 8.2 - 8.3 \times 10^9 \text{ M}^{-1}\text{s}^{-1} \quad (7)$$

$$\text{HClO} + \text{Cl} \cdot \rightarrow \text{ClO} \cdot + \text{H}^+ + \text{Cl}^{-} \quad k = 3.0 - 4.3 \times 10^9 \text{ M}^{-1}\text{s}^{-1} \quad (8)$$

$$\text{OCl}^{-} + \text{HO} \cdot \rightarrow \text{ClO} \cdot + \text{OH}^{-} \quad k = 9.0 \times 10^9 \text{ M}^{-1}\text{s}^{-1} \quad (9)$$

To further assess the effects of various free radicals, the removal situations of 2,4,6-trihalophenols during goethite mediated chlorination was investigated in conditions with added a series of scavengers. According to the reaction rates of each scavengers with free radicals

<figure><img src="image_3.png" /><figcaption>Fig. 2. (a) EPR spectra of DMPO adducts formed with radicals generated during the goethite mediated chlorination. Red triangles indicate the •OH adduct; Blue hexagons indicate the Cl• adduct; and yellow circles indicate the ClO• adduct. The removal of (b) TCP and (c) TBP after addition of TBA, BA, and DMOB (150.0 µM) during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1C, initial pH = 7.5 ± 0.1, initial goethite dosage = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
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(Table S5), TBA was preferred as the scavenger of •OH (reaction rate = 3.9 × 10⁹ M⁻¹s⁻¹) [37], BA was selected as the scavenger of Cl• (reaction rate = 1.8 × 10¹⁰ M⁻¹s⁻¹) and •OH (reaction rate = 5.9 × 10⁹ M⁻¹s⁻¹) [38,39], and DMOB was acted as a scavenger of •OH (reaction rate = 7.0 × 10⁹ M⁻¹s⁻¹), Cl• (reaction rate = 1.8 × 10¹⁰ M⁻¹s⁻¹) and ClO• (reaction rate = 2.1 × 10⁹ M⁻¹s⁻¹) [38,40]. As depicted in Fig. 2b and 2c, the addition of TBA resulted in a significant decrease in TCP and TBP removal, from 60.8% to 27.8% and from 80.5% to 44.2%, respectively. When BA and DMOB were introduced, TCP removal rates decreased to 24.6% and 19.0%, while TBP removal rates descended to 39.2% and 33.6%, respectively. To facilitate meaningful comparisons, we normalized the contribution rates of all active species to 100%, as detailed in Table S6 and S7. This analysis elucidated that •OH predominantly influenced the removal rates of TCP and TBP, accounting for 87.44% and 84.07%, respectively (Fig. S5 and S6). This obviously inhibition effect implied that •OH was vital in the overall transformation of 2,4,6-trihalophenols. The relatively modest contribution of RCS was attributed to the fact that ClO• and Cl• had lower oxidation potential than that of •OH, as mentioned above [23,41]. Overall, our findings revealed the major contribution of •OH in the transformation of 2,4,6-trihalophenols when goethite and HClO/ClO⁻ were present simultaneously.

### 3.3. Kinetics of surface reactions

In the heterogeneous catalytic reaction, either the Eley–Rideal model (where only TCP/TBP or free chlorine adsorbs on the goethite surface and reacts with other un-adsorbed substances) (eq (10) [42] or the Langmuir–Hinshelwood model (where both reactants are adsorbed on the goethite surface and then react) (eq (11) [43,44] is followed. The removal process of TCP/TBP was investigated through these two models.

$$k_{\text{app}} = \frac{\text{KSk}_{\text{TCP/TBP}}^{n} \text{c}_{\text{TCP/TBP}}^{n-1} (k_{\text{HClO/ClO}^{-}} - c_{\text{HClO/ClO}^{-}})^{m}}{(1 + (k_{\text{TCP/TBP}}c_{\text{TCP/TBP}})^{n} + (k_{\text{HClO/ClO}^{-}} - c_{\text{HClO/ClO}^{-}})^{m})^{2}} \quad (10)$$

$$\frac{c_{\text{TCP}_0/\text{TBP}_0} c_{\text{HClO/ClO}^{-0}}}{k_{\text{app}}} = \frac{1}{K} + \left(\frac{K_A}{K}\right) c_{\text{HClO/ClO}^{-}} \quad (11)$$

where K was the molar rate constant of goethite per square meter; S was the surface area of goethite normalized by the volume of the reaction solution; K_A represented the adsorption equilibrium coefficient; k_TCP, k_TBP, and k_HClO/ClO represented the reaction coefficients of TCP, TBP and free chlorine (HClO/ClO⁻), respectively; c_TCP, c_TBP and c_HClO/ClO represented the concentrations of TCP, TBP and free chlorine (HClO/ClO⁻), respectively. Based on previous research, the adsorption of TCP and TBP were most accurately represented by assuming an exponent of n = 0.5, while the adsorption of free chlorine followed a model with m = 1

[43,44].

The data of the L-H model and E-R model were shown in Fig. 3, Fig. S7 and Table S8. For the L-H model, the correlation coefficients (R²) between TCP/TBP removal kinetics and different concentrations of TCP/TBP or free chlorine (HClO/ClO⁻) were all greater than 0.99, which was far more than that of the E-R model (R² < 0.75). Thus, the reaction between aromatic DBPs and free chlorine (HClO/ClO⁻) in the presence of goethite was more consistent with the L-H model. In other words, aromatic DBPs and free chlorine (HClO/ClO⁻) were both adsorbed on the surface of goethite to undergo complex reactions.

The adsorption of reactants on the adsorbent surface is crucial for heterogeneous reactions, as the reaction rate highly relies on the adsorption of reactant molecules. Based on the L-H model, the values of k_TCP, k_TBP and k_HClO/ClO are all around 10⁴, with little difference, indicating that TCP/TBP and free chlorine were both easy to be adsorbed on goethite surface. Hence, compared to the addition of goethite or HClO/ClO⁻ alone, aromatic DBPs and free chlorine (HClO/ClO⁻) were absorbed on the surface of goethite to increase the concentration of reactants, which accelerated the reaction rate of aromatic DBPs. According to previous literatures, the phenolic hydroxyl group could bond with the Fe (III) via H-bond [45], and the -OH in TCP/TBP binding with Fe in goethite to form Fe-O-C [34].

On the basis of the above analysis, the goethite mediated chlorination in the WDS was a surface reaction, rather than the traditional view of homogeneous reaction. (2),4,6-trihalophenols and free chlorine (HClO/ClO⁻) were both adsorbed on the surface of goethite. 2,4,6-trihalophenols reacted with HClO/ClO⁻ to produce electrons and haloquinones. Fe(III)-goethite obtained electrons to form Fe(II)-goethite. Subsequently, HClO/ClO⁻ reacted with Fe(II)-goethite to from free radicals (e.g., •OH, ClO•, and Cl•) via the Fenton-like reaction and oxidized Fe(II)-goethite to Fe(III)-goethite. Both free chlorine (HClO/ClO⁻) and free radicals simultaneously reacted with 2,4,6-trihalophenols to form intermediates and aliphatic DBPs.

### 3.4. Effects of complex reaction conditions

Ensuring water quality in the distribution system is a key factor that guarantees public health. To further elucidate the influence of water environment, a heatmap was employed to visualize the impact of reaction conditions on the removal of 2,4,6-trihalophenol in the coexistence of goethite and free chlorine system (Fig. 4). The activation of free radicals was significantly enhanced with increasing concentrations of goethite and free chlorine, thus leading to improved removal of 2,4,6-trihalophenol.

In the real WDS, as the age of the pipe prolongs, the amounts of goethite tend to increase due to the corrosion around the internal surface of the pipe. The content of pipe-scale in aged pipes of WDS ranged from

<figure><img src="image_4.png" /><figcaption>Fig. 3. L-H model fitting of different initial concentrations of (a) TCP and TBP and (b) free chlorine (HClO/ClO⁻) on aromatic DBPs removal during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite dosage = 4.0 g/L).</figcaption></figure>
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<figure><img src="image_5.png" /><figcaption>Fig. 4. The heatmap of the effect of free chlorine concentrations and goethite doses on the degradation of TCP (a) and TBP (b) during the goethite-mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>

0.2 to 8.0 g/L [46,47]. As shown in Fig. S8, when goethite varied from 2.0 to 8.0 g/L, the decay of TCP and TBP was enhanced 2.0-fold and 1.5-fold, respectively. Considering the presence of magnetite in corrosion pipe scale, we have included experiments involving magnetite in our study. We observed that as the ratio of goethite to magnetite increased, the removal of 2,4,6-trihalophenols also increased accordingly (Fig. S9). Because the irregular surface and pores of goethite typically offers more active sites for the formation of •OH radical, potentially leading to faster degradation of pollutants [48]. Therefore, from the viewpoint of hydroxyl radical process induced by goethite, the presence of scale accelerates the transformation of aromatic disinfection byproducts.

Given the fact of the residual chlorine ($HClO/ClO^{-}$) remaining from 0.05 to 2.0 mg/L in WDS, we investigated the TCP/TBP conversion as a function of $HClO/ClO^{-}$. The gradual increase in TCP/TBP removal efficiency is evident with the increasing concentration of $HClO/ClO^{-}$, as demonstrated in Fig. S10. This enhancement was expected since higher residual chlorine ($HClO/ClO^{-}$) concentrations facilitated the formation of active species for the effective degradation of TCP/TBP (Eq. (3)). The results indicated that the destruction of aromatic components mainly occurred in the initial stage of WDS because the chlorine ($HClO/ClO^{-}$) concentration usually decays while the water flows through pipelines [49]. In addition, pH value is an important factor affecting aromatic DBPs transformation in the WDS. As evidenced above, degradation of TCP/PBP followed L-H model, indicating that the significance of organic compound and $HClO$ adsorption on the goethite surface. As displayed in Fig. S10, weak alkaline condition is not conducive to TCP/TBP conversion. At pH higher than 7.5, the surface of the goethite bears a negative charge [50–52] due to its pHpzc of 6.99 [53]. Free chlorine at the pH above 8.0 tends to exist in the major form of $OCl^{-}$ [54,55]. Moreover, $TCP^{-}$ and $TBP^{-}$ are present in negatively ionized form rather than molecular form as a consequence of $pKa$ 5.99 for TCP and 5.94 for TBP, respectively [56,57]. Thus, weak alkaline condition in the WDS is unfavorable to the adsorption of both free chlorine and halogenated phenol via electrostatic attraction. The conversion of phenolic pollutants is inhibited accordingly.

### 3.5. Degradation products

The major intermediates of TCP and TBP treated with the goethite mediated chlorination were identified (Fig. S12–17). The DFT calculation was used to validate the degradation pathways. According to the frontier molecular orbital theory, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and the corresponding related energies were calculated. Atoms with higher values of $FED_{HOMO}^{2}$ + $FED_{LUMO}^{2}$ were easily attacked by free radicals to undergo hydroxyl substitution reactions (Fig. S18 and Table S9) [58,59].

Based on the identified intermediates and theoretical calculations, the $2FED_{HOMO}^{2}$ of C(1), C(2), C(3), C(4), C(6) on the benzene ring were relatively high, hence, three reaction pathways on TCP transformation were proposed (Fig. 5a). On pathway I, within the bulk containing chloride ions, a potential reaction occurs between $ClO^{-}$/Cl$^{-}$ and 2,4,6-TCP, resulting in the formation of OP1-231.88 [7]. On pathway II, the reaction mechanism of 2,4,6-TCP is influenced by the selective elimination of Cl from the ortho- or para- positions, followed by the attack of •OH radical, ultimately leading to the formation of OP2-177.96 [60]. Furthermore, the fragments were degraded into OP3-159.99 through the attack of •OH and removal of Cl atom. Due to the low bond energy of C-Cl [61], electrophilic substitution reactions were easy to be occurred in C-Cl under the attack of •OH [62,63]. The presence of three hydroxyl groups in the phenol activated the ring, and hence, facilitating the ring cleavage process. Since OP3-159.99 had a strong negative potential region, OP4-194.00 and OP5-160.04 were produced from the cleavage of the benzene ring [64]. In particular, the open-chain compounds were only detected in goethite mediated chlorination but not in the chlorination-only process. It was deduced that the ring cleavage was attributed to the radical mediated reaction [65–67].

On pathway III, the C(4) attached to the phenolic hydroxyl group on TCP underwent a one-electron oxidation step with the attack of •OH, resulting in the formation of a carbon-centered radical [68–70]. Through a subsequent one-electron oxidation step under the attack of radicals, 2,4,6-TCP could be transformed into the carbon-centered radical cation, leading to the generation of OP6-175.94 following deprotonation and elimination of HCl [7]. Additionally, it is observed that free radicals preferentially target the para- and ortho-positions of the phenolic hydroxyl [60]. Two sub-pathways were derived from OP6-175.94, one of which involved the reaction between OP6-175.94 and •OH (formed during the goethite mediated redox reaction between Fe (II)-goethite and $HClO/ClO^{-}$) to form OP7-191.94 [71]. And the other sub-pathway was formation of OP2-177.96 and OP8-161.96 via hydrolysis, addition and elimination reaction [7].

The transformation pathway of TBP degradation during the goethite-mediated chlorination was proposed in Fig. 5b. According to the DFT analysis, the C(6), C(7), C(10) site connecting bromine on the TBP structure presented a higher value of $FED_{HOMO}^{2}$ + $FED_{LUMO}^{2}$, which was more vulnerable for free radical attack. TBP transformation also had three possible pathways. The pathway I and II were similar to the TCP conversion pathways. In stark contrast, on pathway III, the three bromine atoms in the benzene ring were seen to be easily replaced by chlorine to generate bromochlorophenol because of the high electron cloud density [19]. In the presence of •OH, the Cl on OP15-241.87 was attacked and replaced by •OH, leading to the conversion of OP15-241.87 into OP16-223.91, and then further transformed to OP17-221.89 and OP18-235.892. Compared with TCP transformation, TBP reacted with
<figure><img src="image_6.png" /><figcaption>Fig. 5. The proposed pathways of (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite dosage = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>

chlorine-containing disinfectants to generate chlorinated aromatic DBPs and brominated aromatic DBPs. Furthermore, the intermediate products were also analyzed by adding TBA (Fig. S19 and S20). During the reaction, only chlorine-substituted products were detected, and hydroxyl radical oxidation products and ring-opening products were not detected. Therefore, free radicals triggered by goethite mediated chlorination exhibited greater efficacy in ring cleavage for the complete degradation

of TCP and TBP compared to chlorination alone.

### 3.6. Formation of aliphatic DBPs during goethite-mediated chlorination

The concentrations of aliphatic DBP formation were further confirmed in the transformation of aromatic DBPs, including four trihalomethanes (THMs, chloroform (TCM), tribromomethane (TBM),

<figure><img src="image_7.png" /><figcaption>Fig. 6. The formation of trihalomethanes (THMs), haloacetaldehyde (HALs) and trichloroacetone (TCA) from (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 10.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite dosage = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>
bromodichloromethane (BDCM), and chlorodibromomethane (DBCM)), three haloacetaldehyde (HALs, trichloroacetaldehyde (TCAL), dichloroacetaldehyde (DCAL), and tribromoacetaldehyde (TBAL)) and trichloroacetone (TCA).

Fig. 6a illustrates that TCM, TCAL, DCAL and TCA were the main byproducts during the chlorination of TCP. The concentration of THMs kept increasing over time in the chlorination of TCP, supporting the assumption that the transformation products such as ring-cleavage compounds (OP4-194.00) and small molecular hexanedioic acid (OP5-160.04) acted as intermediates and further decomposed to form aliphatic halogenated DBPs. The formation of TCAL initially increased to 27.7 µg/L and then decreased to 17.9 µg/L during the reaction. The trends of DCAL and TCA formation were similar with TCAL. Due to sufficient free chlorine at the beginning of the reaction, TCP was rapidly degraded to form aliphatic DBPs. After 1 h of reaction, the decrease of free chlorine and TCP resulted the lower formation rate of TCA and HALs than that of conversion rate. Moreover, the change in TCAL and DCAL concentration may be related to α, β-unsaturated C4-dialdehydes [72]. Several current studies have reported the formation of α, β-unsaturated C4-dialdehydes as more toxic DBPs during chlorination of TCP [73]. Based on the detection of ring-opening products and haloacetaldehyde (e.g., TCAL and DCAL) during the reaction process, we infer the potential formation of α, β-unsaturated C4-dialdehydes during goethite-mediated chlorination. Fig. 6b shows the formation of TBM, BDCM,

DBCM, and TBAL during the conversion of TBP. TBM and TBAL exhibited a gradual increase over the course of the reaction, while BDCM and DBCM displayed an initial increase followed by a decrease. After stopping the reaction, TBM and TBAL emerged as the predominant DBPs, constituting 31.6 % and 61.1 % respectively. Previous research has suggested that BDCM and DBCM could be oxidized and converted into TBM and TBAL in the presence of free chlorine [48].

### 3.7. Cytotoxicity assay during transformation of aromatic DBPs

TCP and TBP were transformed to form some intermediates and aliphatic DBPs during the goethite mediated *OH oxidation, it is essential to assess the toxicity of the reaction system. As shown in Fig. 7a and 7c, the relative viability of CHO cells exposed to TCP and TBP in chlorination alone and goethite mediated chlorination was compared. The relative viability of TCP and TBP in chlorination alone (97.75 % and 95.76 %) was approximately 1.28 and 1.21 times higher than that in goethite mediated chlorination (76.47 % and 79.35 %), respectively. Since TCP could produce more toxic α, β-unsaturated C4-dialdehydes during chlorination alone, these α, β-unsaturated C4-dialdehydes could be further oxidized by free radicals in the goethite mediated chlorination process, thus reducing the toxicity of TCP in the goethite system [72,73]. Thus, the transformation process of aromatic DBPs in the presence of residual chlorine and goethite was beneficial to weaken

<figure><img src="image_8.png" /><figcaption>Fig. 7. The relative viability of CHO cells exposed to (a) TCP and (c) TBP in different reaction systems at different reaction times during the goethite mediated chlorination in batch-scale pipe reactor; predicting the acute/chronic toxicity of various intermediates of (b) TCP and (d) TBP to fish, daphnia, and green algae using ECOSAR software. (Experimental conditions: Reaction time = 10.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite dosage = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
the toxicity of water quality. According to toxicity software calculations (Fig. 7b and 7d and Table S10), the toxicity of aliphatic compounds (such as trihalomethanes, haloacetaldehyde, and trichloroacetone) was found to be lower than that of 2,4,6-trihalophenol and aromatic intermediates. The previous researches have certified that halogenated compounds with aromatic ring exhibited higher toxicity than aliphatic compounds [74,75]. The potential contribution of the aromatic ring was contributed to the higher toxicity of 2,4,6-trihalophenols. Furthermore, some of the ring-opened products were also toxic, which was related to the unsaturated C-C or C-O double bonds [76]. When aromatic structures were gradually transformed into aliphatic structures by hydroxyl radicals, the toxicity of 2,4,6-trihalophenols-containing water decreases accordingly. Therefore, hydroxyl radical with high oxidation capacity produced in goethite mediated chlorination system contributed to the effective detoxification of organic pollutants.

## 4. Conclusions

In conclusion, this research focused on the decomposition of 2,4,6-trihalophenols (e.g., TCP and TBP) by the interface free radicals triggered by goethite mediated chlorination. It was found that various free radicals (e.g., •OH, ClO• and Cl•) were generated by transferring electrons from 2,4,6-trihalophenols to goethite for activating residual chlorine. The •OH served as dominant active species responsible for organic compounds degradation. Higher concentrations of goethite and free chlorine promoted the decomposing of 2,4,6-trihalophenols, and the process followed the L-H model. The degradation process involved ring opening, oxidation, substitution, addition, hydrolysis, accompanied by effective detoxification. Notably, in contrast to the traditional negative understanding of pipe scales on DBP formation and transformation, we proposed a positive effect of free radical process induced by goethite. This work reveals novel insights into the risk assessment of pipe scale in the WDS.

### CRediT authorship contribution statement

**Feilong Dong:** Writing – original draft, Funding acquisition, Formal analysis, Data curation, Conceptualization.
**Jiani Zhu:** Writing – original draft, Methodology, Formal analysis, Data curation.
**Cong Li:** Writing – review & editing, Methodology.
**Eric Lichtfouse:** Wei Wang: Writing – review & editing, Project administration, Conceptualization.
**Shuang Song:** Writing – review & editing, Project administration, Formal analysis, Conceptualization.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Data availability

Data will be made available on request.

### Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (No. 52100015), the Zhejiang Provincial Natural Science Foundation of China (Grants LQ22E080018) and the China Postdoctoral Science Foundation (2021M692860).

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cej.2024.152390.

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# Unveiling the transformation of 2,4,6-trihalophenols by active species in drinking water pipelines: the role of goethite

Feilong Dong<sup>a,e</sup>, Jiani Zhu<sup>a</sup>, Cong Li<sup>b</sup>, Eric Lichtfouse<sup>c</sup>, Wei Wang<sup>d*</sup>, Shuang Song<sup>a*</sup>

## Text S1 Chemicals and materials

2,4,6-trichlorophenol (TCP) and 2,4,6-tribromophenol (TBP) were purchased from Sigma-Aldrich. 5% of hypochlorous acid solution was purchased from Aladdin Industrial Corporation (Shanghai, China), which was diluted with ultrapure water to obtain the 500 mg/L of hypochlorous acid stock solution. 2, 6-Dichloro-p-quinone was purchased from Tokyo Chemical Industry (Shanghai, China). 90% Dulbecco's modified Eagle medium (DMEM) was prepared using 10% fetal bovine serum (Sabakang) and 1% double antibody. Phosphate buffered saline (PBS) was purchased from Procell (Hubei, China). 3-(4,5)-Dimethylthiahiazo(-Z-Y1)-3,5-di-phenytetrazoliumromide (MTT) was purchased from Beijing Solebao Technology Co., LTD. Dimethyl sulfoxide (DMSO) was purchased from Tianjin Fuyu Fine Chemical Co., Ltd. Hexane, acetonitrile and methyl tert-butyl ether (MTBE) of chromatography grade were purchased from Sigma-Aldrich. All other chemicals such as sodium thiosulfate ($Na_2S_2O_3$), tert-butanol (TBA), benzoic acid (BA), and 1,4-dimethoxybenzene (DMOB) were purchased from Sinopharm Chemical Reagent (Shanghai, China). Ultrapure water was obtained from a Milli-Q system with resistivity > 18 MΩ·cm at 25 °C.

## Text S2 The determination of water quality parameters

DO and pH were measured by a portable multi-parameter meter (HACH HQ 40d). Turbidity was measured using a turbidimeter (HACH 2100Q). The concentrations of TCP and TBP were determined using high performance liquid chromatography (HPLC; Waters Corporation, USA) equipped with Waters 2489 UV/Vis detector and XDB-C18 chromatographic column (150 mm × 4.6 mm, 5 µm, Agilent Zorbax).

<footnote><sup>a</sup>College of Environment, Zhejiang University of Technology, Hangzhou, 310014, China.</footnote>

<footnote><sup>b</sup>School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai, 200433, China.</footnote>

<footnote><sup>c</sup>State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China.</footnote>

<footnote><sup>d</sup>Department of Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China</footnote>

<footnote><sup>e</sup>Shaoxing Research Institute, Zhejiang University of Technology, Shaoxing, 312085, China.</footnote>

<footnote>*Corresponding author.</footnote>

<footnote>Email addresses: ss@zjut.edu.cn</footnote>

<footnote>ww1@zju.edu.cn</footnote>
Text S3 Analytical methods

The concentrations of TCP and TBP were determined using high performance liquid chromatography (HPLC; Waters Corporation, USA) equipped with Waters 2489 UV/Vis detector and XDB-C18 chromatographic column (150 mm × 4.6 mm, 5 µm, Agilent Zorbax). The mobile phases for TCP analysis were acetonitrile and an ultrapure aqueous solution (pH=3.0) with phosphoric acid at a ratio of 80:20 (v/v), the detector wavelength was set at 295 nm, the column temperature was maintained at 30 °C, and the flow rate was 0.6 mL/min. The mobile phases for TBP analysis were acetonitrile and ultrapure aqueous solution containing 0.1% perchloric acid at a ratio of 65:35 (v/v), the detector wavelength was at 230 nm, the column temperature was maintained at 30 °C, and the flow rate was 0.8 mL/min.

The intermediate products of TCP and TBP were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS, Agilent qtof6550). The mobile phase was acetonitrile: water (90:10, v/v) spiked with 0.1% formic acid at a flow rate of 0.3 mL/min. The MS system was operated in ESI+ mode with a capillary voltage of 4 kV and a gas temperature of 150 °C. The drying gas was 15 L/min, the temperature of the jacket gas was 350 °C, and the flow rate of the jacket gas was 12 L/min. The m/z range was from 100 to 500, and the scan time was 0.1 s.

The concentrations of the aliphatic DBPs were analyzed using gas chromatography equipped with an electron capture detector (GC-ECD) (GC-450, Varian, Palo Alto, CA, USA) and a DB-5 capillary column (30 m×0.25 mm×0.25 µm) [1,2]. The initial temperature of the oven was held at 35 °C for 10 min, then warming up to 80 °C at 10 °C/min, thereby warming up to 150 °C at 20 °C/min [2,3]. The temperatures of the spitless injector and detector were 210 and 290°C, respectively.

In addition, the chlorine concentration was determined by N,N-diethyl-p-phenylenediamine (DPD) colorimetric method with a free chlorine kit (HACH DR300). An electron paramagnetic resonance (EPR) spectrometer (Bruker EMX PLUS, Germany) was employed to determine the species of free radicals generated by chlorination. DMPO was used as a trapping agent for •OH, ClO• and Cl•. The goethite was characterized using XRD (XPert Pro MPD; PANalytical B.V., Netherlands) analysis with Cu Kα radiation (λ = 0.154 nm) and X-ray photoelectron spectroscopy (XPS, PHI 5000C ESCA, Perkin-Elmer, USA) with an Al Kα X-ray source (hv = 1486.6 eV).

Text S4 The methods of DFT calculation

All quantum chemical calculations were performed on a Gaussian 03 package based on
density functional theory (DFT) [4]. The structure of 2,4,6-tirhalophenols (e.g., 2,4,6-
Trichlorophenol and 2,4,6-Tribromophenol) were optimized using the hybrid B3LYP/6-
311++G (d,p) method. Besides, this study calculated the 2FED<sup>2</sup><sub>HOMO</sub> of each atom on 2,4,6-
tirhalophenols molecule. The high values of highest occupied molecular orbital (HOMO) are
considered to be the most prone to electrophilic reactions [5]. The calculation considered the
effect of reaction solvent (i.e., water) by using "pop = reg".
**Text S5 The methods of cytotoxicity analysis**

The Chinese hamster ovary (CHO) cells was employed to evaluate the cytotoxicity variation in the degradation process of TCP and TBP, since the cell line has been widely used in comparison of the toxicity of DBPs and abundant relevant data were available. The water sampled during the experiments of TCP and TBP was used to detect the relative viabilities. Before toxicity analysis, the samples and consumables were autoclaved in an autoclave to avoid the interference of microorganisms. The CHO cells were taken and counted in the logarithmic growth phase. The cells were seeded into 96-well plates at 8×10³ /well, and cultured in a 5% CO₂ incubator at 37 °C until the cells adhered. After culturing for 72 h, the medium containing the sample was removed. Each well was washed three times using PBS, and 100 µL of medium containing 0.5 mg/mL MTT was added to each well. Then 96-well plates were incubated in 5% CO₂ and 37°C incubators for 4.0 h. Finally, 100 µL of DMSO was added to each well after discarding the supernatant. After 10 min of gentle shaking, the absorbance at 570 nm was detected using a microplate reader (TECAN, model: SPARK 10 M), and the cell viability was determined.

**Text S6 The identification of iron species.**

To identify Fe species produced by goethite dissolution, we firstly determined the concentrations of Fe²⁺ and Fe³⁺ in water and goethite. The removal of TCP/TBP was conducted in darkness with headspace-free glass bottles, the initial concentrations of TCP and TBP were 2 µmol/L, free chlorine (HClO/ClO⁻) and goethite were 2.0 mg/L and 4.0 g/L, respectively. Results shown that Fe²⁺ and Fe³⁺ were not observed above the detection limitation of 50.0 µg/L. As a consequence, 50.0 µg/L of Fe²⁺ and 50.0 µg/L of Fe³⁺ were used to activate HClO/ClO⁻ in additional experiments. As show in Fig. S2, negligible removal of TCP/TBP was found after 8 min of reaction. The results demonstrated that the goethite dissolution had neglected effect to the TCP/TBP elimination in our experiments.

**Text S7 The intermediates of TCP during the direct oxidation with goethite.**

To elucidate the surface chemical process of goethite, direct oxidation of TCP with goethite was conducted in a separate experiment. The removal of TCP in the presence of goethite was performed at pH 7.5 ± 0.1 and 25 °C. TCP was conducted in batch-scale pipe reactor, the initial goethite concentration was 4.0 g/L and initial TCP concentration was 2.0 µmol/L. At the reaction of 24 h, the removal of TCP and intermediates were detected in the reaction solution. Subsequently, the goethite used in the experiment was washed with methanol, and the leached components were detected, as illustrated in Fig. S4.
<figure><img src="image_9.png" /><figcaption>Fig. S1. The XRD patterns of the goethite and corrosion scales on iron pipe. The peak of corrosion scale was referred from Wang et al [6].</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. S2.** Schematic diagram of batch-scale pipe reactor used for goethite mediated chlorination. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>**Fig. S3.** The degradation of (a) TCP and (b) TBP during chlorination with the existence of goethite, free chlorine, and iron ion in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L, initial iron ion concentration = 50.0 µg/L).</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Fig. S4.** The HPLC spectra of (a) TCP and (b) 2,6-dichloro-p-quinone with the existence of goethite in batch-scale pipe reactor. (Experimental conditions: Reaction time = 24.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial TCP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_13.png" /></figure>

**Fig. S5.** The rate constants for degradation of TCP (columns, primary y-axis); contribution of active species for TCP (symbols, secondary y-axis) removal during the goethite-mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP concentration = 2.0 µmol/L)

<figure><img src="image_14.png" /></figure>

**Fig. S6.** The rate constants for degradation of TBP (columns, primary y-axis); contribution of active species for TBP (symbols, secondary y-axis) removal during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TBP concentration = 2.0 µmol/L)
<figure><img src="image_15.png" /><figcaption>Fig. S7. E-R model fit diagram for initial chlorine concentration changes of (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Fig. S8. Effect of goethite on the degradation of (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Fig. S9. Effect of the ratio of goethite to magnetite on the degradation of (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /><figcaption>Fig. S10. Effect of free chlorine on the degradation of (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /><figcaption>Fig. S11. Effect of pH on the degradation of (a) TCP and (b) TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</figcaption></figure>

<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /></figure>

<figure><img src="image_24.png" /><figcaption>Fig. S12. The intermediates were generated by TCP degradation during chlorination alone in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial free chlorine concentration = 2.0 mg/L, initial TCP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_25.png" /><figcaption>**Fig. S13.** The intermediates were generated by TBP degradation during chlorination alone in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial free chlorine concentration = 2.0 mg/L, initial TBP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_26.png" /><figcaption>**Fig. S14.** The LC-MS chromatogram spectra of TCP intermediates during the goethite mediated chlorination in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_27.png" /></figure>

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /><figcaption>**Fig. S15.** The intermediates were generated by TCP degradation during the goethite mediated chlorination in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_34.png" /><figcaption>**Fig. S16.** The LC-MS chromatogram spectra of TBP intermediates during the goethite mediated chlorination in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TBP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /></figure>

<figure><img src="image_42.png" /><figcaption>**Fig. S17.** The intermediates were generated by TBP degradation during the goethite mediated chlorination in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TBP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_43.png" /><figcaption>**Fig. S18.** The LUMO (a) and HOMO (b) orbitals of TCP; The LUMO (c) and HOMO (d) orbitals of TBP.</figcaption></figure>
<figure><img src="image_44.png" /><figcaption>**Fig. S19.** The intermediates were generated by TCP degradation after addition of TBA during the goethite mediated chlorination in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP concentration = 2.0 µmol/L, initial TBA concentration = 150.0 µmol/L).</figcaption></figure>
<figure><img src="image_45.png" /><figcaption>**Fig. S20.** The intermediates were generated by TBP degradation after addition of TBA during the goethite mediated chlorination in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TBP concentration = 2.0 µmol/L, initial TBA concentration = 150.0 µmol/L).</figcaption></figure>
<figure><img src="image_46.png" /><figcaption>**Fig. S21.** The proposed pathways of TCP chlorination alone in batch-scale pipe reactor. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial free chlorine concentration = 2.0 mg/L, initial TCP concentration = 2.0 µmol/L).</figcaption></figure>
<figure><img src="image_47.png" /><figcaption>**Fig. S22.** The proposed pathways of TBP chlorination alone in batch-scale pipe reactor. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial free chlorine concentration = 2.0 mg/L, initial TBP concentration = 2.0 µmol/L).</figcaption></figure>
<table><caption>**Table S1.** The water quality parameters of the tap water.</caption><thead><tr><th>Water quality parameters</th><th>Content</th></tr></thead><tbody><tr><td>residual chlorine (as Cl<sub>2</sub>)</td><td>0.3 ± 0.1 mg/L</td></tr><tr><td>pH value</td><td>7.5 ± 0.1</td></tr><tr><td>DO</td><td>9.2 ± 0.4 mg/L</td></tr><tr><td>TCP</td><td>Not detected</td></tr><tr><td>TBP</td><td>Not detected</td></tr></tbody></table>
<table><caption>**Table S2.** The Kapp of TCP and TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1).</caption><thead><tr><th></th><th>TCP</th><th>TBP</th></tr></thead><tbody><tr><td>C<sub>HCIO/CIO</sub> (mg/L)</td><td>K<sub>APP</sub> (Min<sup>-1</sup>)</td><td>K<sub>APP</sub> (Min<sup>-1</sup>)</td></tr><tr><td>0.0</td><td>0.14127 ± 0.04979</td><td>0.18149 ± 0.01336</td></tr><tr><td>0.5</td><td>0.12225 ± 0.00157</td><td>0.25752 ± 0.00465</td></tr><tr><td>1.0</td><td>0.23420 ± 0.00050</td><td>0.37766 ± 0.00425</td></tr><tr><td>2.0</td><td>0.33996 ± 0.00145</td><td>0.47673 ± 0.00361</td></tr><tr><td>3.0</td><td>0.41672 ± 0.00025</td><td>0.53444 ± 0.00238</td></tr><tr><td>C<sub>TCP/TBP</sub> (µmol/L)</td><td>K<sub>APP</sub> (Min<sup>-1</sup>)</td><td>K<sub>APP</sub> (Min<sup>-1</sup>)</td></tr><tr><td>0.5</td><td>0.06975 ± 0.00385</td><td>0.17650 ± 0.00484</td></tr><tr><td>1.0</td><td>0.18306 ± 0.00117</td><td>0.32359 ± 0.00168</td></tr><tr><td>2.0</td><td>0.33996 ± 0.00145</td><td>0.47673 ± 0.00361</td></tr><tr><td>3.0</td><td>0.41672 ± 0.00600</td><td>0.56110 ± 0.00345</td></tr><tr><td>C<sub>goethite</sub> (g/L)</td><td>K<sub>APP</sub> (Min<sup>-1</sup>)</td><td>K<sub>APP</sub> (Min<sup>-1</sup>)</td></tr><tr><td>0.0</td><td>0.08448 ± 0.02104</td><td>0.14712 ± 0.00603</td></tr><tr><td>2.0</td><td>0.18370 ± 0.00242</td><td>0.37155 ± 0.00710</td></tr><tr><td>4.0</td><td>0.33996 ± 0.00145</td><td>0.47673 ± 0.00361</td></tr><tr><td>6.0</td><td>0.43910 ± 0.00181</td><td>0.73165 ± 0.00163</td></tr><tr><td>8.0</td><td>0.51522 ± 0.00094</td><td>0.81905 ± 0.00158</td></tr></tbody></table>
<table><caption>**Table S3.** The intermediate product of TBP produced in during the goethite mediated chlorination in darkness with headspace-free glass bottles with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TBP concentration = 2.0 µmol/L).</caption><thead><tr><th>Compounds</th><th>M/Z</th><th>Chemical formula</th><th>Structural formula</th></tr></thead><tbody><tr><td>TBP</td><td>328.80</td><td>C<sub>6</sub>H<sub>3</sub>Br<sub>3</sub>O</td><td><img src="tbp Structural formula.png" alt="Chemical structure of t-butyl 3-bromophenyl acetate"></td></tr><tr><td>OP5-160.04</td><td>160.04/205.04</td><td>C<sub>6</sub>H<sub>8</sub>O<sub>5</sub></td><td><img src="OP5-160.04 Structural formula.png" alt="Chemical structure of 160.04/205.04"></td></tr><tr><td>OP9-267.86</td><td>266.84</td><td>C<sub>6</sub>H<sub>4</sub>O<sub>2</sub>Br<sub>2</sub></td><td><img src="OP9-267.86 Structural formula.png" alt="Chemical structure of 267.86"></td></tr><tr><td>OP12-265.84</td><td>265.83</td><td>C<sub>6</sub>H<sub>2</sub>O<sub>2</sub>Br<sub>2</sub></td><td><img src="OP12-265.84 Structural formula.png" alt="Chemical structure of 265.83"></td></tr><tr><td>OP13-281.84</td><td>280.83</td><td>C<sub>6</sub>H<sub>2</sub>O<sub>3</sub>Br<sub>2</sub></td><td><img src="OP13-281.84 Structural formula.png" alt="Chemical structure of 281.84"></td></tr><tr><td>OP14-281.86</td><td>250.85</td><td>C<sub>6</sub>H<sub>4</sub>OBr<sub>2</sub></td><td><img src="OP14-281.86 Structural formula.png" alt="Chemical structure of 281.86"></td></tr><tr><td>OP16-223.91</td><td>223.91</td><td>C<sub>6</sub>H<sub>4</sub>ClBrO<sub>2</sub></td><td><img src="OP16-223.91 Structural formula.png" alt="Chemical structure of 223.91"></td></tr><tr><td>OP17-221.89</td><td>221.89/266.90</td><td>C<sub>6</sub>H<sub>2</sub>ClBrO<sub>2</sub></td><td><img src="OP17-221.89 Structural formula.png" alt="Chemical structure of 221.89"></td></tr><tr><td>OP18-235.89</td><td>237.86/282.89</td><td>C<sub>6</sub>H<sub>2</sub>ClBrO<sub>3</sub></td><td><img src="OP18-235.89 Structural formula.png" alt="Chemical structure of 235.89"></td></tr></tbody></table>
<table><caption>**Table S4.** The intermediate product of TCP produced during the goethite mediated chlorination in batch-scale pipe reactor with the help of LC-MS. (Experimental conditions: Reaction time = 1.0 h, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP concentration = 2.0 µmol/L).</caption><thead><tr><th>Compounds</th><th>M/Z</th><th>Chemical formula</th><th>Structural formula</th></tr></thead><tbody><tr><td>TCP</td><td>197.40</td><td>C<sub>6</sub>H<sub>3</sub>Cl<sub>3</sub>O</td><td><img src="image_0_0_0.png" alt="Chemical structure of TCP"></td></tr><tr><td>OP1-231.88</td><td>230.87/276.88</td><td>C<sub>6</sub>H<sub>2</sub>OCl<sub>4</sub></td><td><img src="image_0_0_1.png" alt="Chemical structure of OP1-231.88"></td></tr><tr><td>OP2-177.96</td><td>176.95/222.96</td><td>C<sub>6</sub>H<sub>4</sub>O<sub>2</sub>Cl<sub>2</sub></td><td><img src="image_0_0_2.png" alt="Chemical structure of OP2-177.96"></td></tr><tr><td>OP4-194.00</td><td>192.99</td><td>C<sub>6</sub>H<sub>7</sub>O<sub>5</sub>Cl</td><td><img src="image_0_0_3.png" alt="Chemical structure of OP4-194.00"></td></tr><tr><td>OP5-160.04</td><td>159.03</td><td>C<sub>6</sub>H<sub>8</sub>O<sub>5</sub></td><td><img src="image_0_0_4.png" alt="Chemical structure of OP5-160.04"></td></tr><tr><td>OP6-175.94</td><td>174.94</td><td>C<sub>6</sub>H<sub>2</sub>O<sub>2</sub>Cl<sub>2</sub></td><td><img src="image_0_0_5.png" alt="Chemical structure of OP6-175.94"></td></tr><tr><td>OP7-191.94</td><td>190.93</td><td>C<sub>6</sub>H<sub>2</sub>O<sub>3</sub>Cl<sub>2</sub></td><td><img src="image_0_0_6.png" alt="Chemical structure of OP7-191.94"></td></tr><tr><td>OP8-161.96</td><td>160.95/206.96</td><td>C<sub>6</sub>H<sub>4</sub>OCl<sub>2</sub></td><td><img src="image_0_0_7.png" alt="Chemical structure of OP8-161.96"></td></tr></tbody></table>
<table><caption>**Table S5.** Second-order rate constants (M⁻¹s⁻¹) of radicals toward probe compounds.</caption><thead><tr><th></th><th>k<sub>HO•</sub></th><th>k<sub>Cl•</sub></th><th>k<sub>ClO•</sub></th><th>References</th></tr></thead><tbody><tr><td>NB</td><td>3.9 × 10<sup>9</sup></td><td></td><td></td><td>[7,8]</td></tr><tr><td>BA</td><td>5.9 × 10<sup>9</sup></td><td>1.8 × 10<sup>10</sup></td><td>&lt; 10<sup>7</sup></td><td>[8-11]</td></tr><tr><td>DMOB</td><td>7.0 × 10<sup>9</sup></td><td>1.8 × 10<sup>10</sup></td><td>2.1 × 10<sup>9</sup></td><td>[11,12]</td></tr></tbody></table>
<table><caption>**Table S6.** The Kapp of TCP and TBP during the goethite mediated chlorination in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial TCP and TBP concentration = 2.0 µmol/L).</caption><thead><tr><th rowspan="2">Condition</th><th>TCP</th><th>TBP</th></tr><tr><th><i>K</i><sub>APP</sub> (Min<sup>-1</sup>)</th><th><i>K</i><sub>APP</sub> (Min<sup>-1</sup>)</th></tr></thead><tbody><tr><td>No scavenger</td><td>0.33996 ±0.00145</td><td>0.47673 ±0.00361</td></tr><tr><td>TBA (150 µM)</td><td>0.12782 ±0.05793</td><td>0.20713 ±0.05793</td></tr><tr><td>BA (150 µM)</td><td>0.10680 ±0.04896</td><td>0.18842 ±0.04896</td></tr><tr><td>DMOB (150 µM)</td><td>0.09770 ±0.05771</td><td>0.15732 ±0.05771</td></tr></tbody></table>
<table><caption>**Table S7.** The relative contribution rates of active species. (The sum of all relative contribution rates is 100%)</caption><thead><tr><th>Contribution (%)</th><th>TCP</th><th>TBP</th></tr></thead><tbody><tr><td>•OH</td><td>87.4421</td><td>84.0740</td></tr><tr><td>Cl•</td><td>8.76381</td><td>5.98222</td></tr><tr><td>ClO•</td><td>3.79404</td><td>9.94373</td></tr></tbody></table>
<table><caption>**Table S8.** Calculation of *K* of TCP and TBP in reaction system by L-H model during the goethite mediated chlorination i in batch-scale pipe reactor. (Experimental conditions: Reaction time = 8.0 min, temperature = 25 ± 1°C, initial pH = 7.5 ± 0.1, initial goethite concentration = 4.0 g/L, initial free chlorine concentration = 2.0 mg/L, initial TCP and TBP concentration = 2.0 µmol/L).</caption><thead><tr><th></th><th>TCP</th><th>TBP</th></tr></thead><tbody><tr><td><i>K</i> (mol · L<sup>-1</sup> · S<sup>-1</sup>)</td><td>4.2046 × 10<sup>-5</sup></td><td>3.0885 × 10<sup>-4</sup></td></tr><tr><td><i>K</i><sub>TCP/TBP</sub> (L · mol<sup>-1</sup>)</td><td>4.7130 × 10<sup>5</sup></td><td>1.9848 × 10<sup>5</sup></td></tr><tr><td><i>K</i><sub>HCIO/ClO</sub> (L · mol<sup>-1</sup>)</td><td>7.3856 × 10<sup>4</sup></td><td>9.3572 × 10<sup>4</sup></td></tr></tbody></table>
<table><caption>**Table S9.** The DFT calculation of Frontier electron densities on the atoms in TCP and TBP, calculated using the UB3LYP/6-311++G (d, p) method.</caption><thead><tr><th colspan="4">TCP</th><th colspan="4">TBP</th></tr><tr><th>No.</th><th>Atom</th><th>Charge</th><th>2FED<sup>2</sup><sub>HOMO</sub></th><th>2FED<sup>2</sup><sub>LUMO</sub></th><th>No.</th><th>Atom</th><th>Charge</th><th>2FED<sup>2</sup><sub>HOMO</sub></th><th>2FED<sup>2</sup><sub>LUMO</sub></th></tr></thead><tbody><tr><td>1</td><td>C</td><td>-1.379</td><td>6.065</td><td>1177</td><td>1</td><td>Br</td><td>-0.109</td><td>0.002</td><td>3.611</td></tr><tr><td>2</td><td>C</td><td>1.444</td><td>2.229</td><td>1924</td><td>2</td><td>Br</td><td>-0.055</td><td>0.239</td><td>2.605</td></tr><tr><td>3</td><td>C</td><td>0.761</td><td>0.287</td><td>1563</td><td>3</td><td>Br</td><td>-0.116</td><td>0.027</td><td>15.82</td></tr><tr><td>4</td><td>C</td><td>-2.214</td><td>0.077</td><td>1247</td><td>4</td><td>O</td><td>-0.086</td><td>0.168</td><td>0.002</td></tr><tr><td>5</td><td>Cl</td><td>0.287</td><td>0.717</td><td>38.42</td><td>5</td><td>C</td><td>-1.786</td><td>0.020</td><td>206.4</td></tr><tr><td>6</td><td>C</td><td>1.445</td><td>0.027</td><td>1527</td><td>6</td><td>C</td><td>1.393</td><td>0.074</td><td>216.1</td></tr><tr><td>7</td><td>O</td><td>-0.227</td><td>1.072</td><td>3.069</td><td>7</td><td>C</td><td>1.395</td><td>0.005</td><td>40.54</td></tr><tr><td>8</td><td>C</td><td>-1.379</td><td>3.290</td><td>658.4</td><td>8</td><td>C</td><td>-1.052</td><td>0.002</td><td>30.81</td></tr><tr><td>9</td><td>Cl</td><td>0.287</td><td>0.042</td><td>13.40</td><td>9</td><td>C</td><td>-1.086</td><td>0.441</td><td>37.86</td></tr><tr><td>10</td><td>Cl</td><td>0.336</td><td>0.105</td><td>37.58</td><td>10</td><td>C</td><td>0.935</td><td>0.022</td><td>5.714</td></tr><tr><td>11</td><td>H</td><td>0.177</td><td>0.020</td><td>0.278</td><td>11</td><td>H</td><td>0.159</td><td>0.001</td><td>0.066</td></tr><tr><td>12</td><td>H</td><td>0.285</td><td>0.024</td><td>0.006</td><td>12</td><td>H</td><td>0.162</td><td>0.000</td><td>0.050</td></tr><tr><td>13</td><td>H</td><td>0.177</td><td>0.017</td><td>0.292</td><td>13</td><td>H</td><td>0.247</td><td>0.000</td><td>0.079</td></tr></tbody></table>
<table><caption>**Table S10.** The acute toxicity, chlorination toxicity and CHO cell cytotoxicity of TCP and TBP and some of their transformation products during chlorination with the presence of goethite, the acute toxicity, chlorination toxicity dates were calculated by ECOSAR software.</caption><thead><tr><th rowspan="2">Compounds</th><th colspan="3">Acute toxicity (mg/L)</th><th colspan="3">Chronic toxicity (mg/L)</th><th rowspan="2">CHO cytotoxicity (LC<sub>50</sub>) (mol/L)</th><th rowspan="2">References</th></tr><tr><th>Fish (LC<sub>50</sub>)</th><th>Daphnid (LC<sub>50</sub>)</th><th>Algae (EC<sub>50</sub>)</th><th>Fish</th><th>Daphnid</th><th>Algae</th></tr></thead><tbody><tr><td>2,4,6-TCP</td><td>2.728</td><td>1.564</td><td>6.252</td><td>0.340</td><td>0.297</td><td>2.844</td><td>2.44×10<sup>-4</sup></td><td>[13,14]</td></tr><tr><td>2,4,6-TBP</td><td>1.260</td><td>1.002</td><td>3.730</td><td>0.175</td><td>0.190</td><td>1.784</td><td>9.99×10<sup>-5</sup></td><td>[13,14]</td></tr><tr><td>OP6-175.94</td><td>172.0</td><td>131.8</td><td>153.7</td><td>124.0</td><td>0.306</td><td>23.68</td><td>1.12×10<sup>-5</sup></td><td>[14,15]</td></tr><tr><td>OP7-191.94</td><td>1198</td><td>846.1</td><td>783.5</td><td>1572</td><td>0.650</td><td>80.79</td><td>9.06×10<sup>-5</sup></td><td>[16]</td></tr><tr><td>OP12-265.84</td><td>391.1</td><td>295.7</td><td>326.0</td><td>322.4</td><td>0.533</td><td>45.91</td><td>1.44×10<sup>-5</sup></td><td>[16]</td></tr><tr><td>OP14-281.84</td><td>2649</td><td>1885</td><td>1615</td><td>3976</td><td>1.102</td><td>152.2</td><td>5.04×10<sup>-5</sup></td><td>[13,14,17,18]</td></tr><tr><td>OP15-241.87</td><td>2.175</td><td>1.391</td><td>5.429</td><td>0.281</td><td>0.264</td><td>2.496</td><td>1.75×10<sup>-4</sup></td><td>[13]</td></tr><tr><td>TCM</td><td>264.1</td><td>143.4</td><td>89.00</td><td>24.50</td><td>12.37</td><td>21.12</td><td>9.62×10<sup>-3</sup></td><td>[14]</td></tr><tr><td>TCAL</td><td>22.37</td><td>54.08</td><td>68.69</td><td>4.660</td><td>6.771</td><td>20.78</td><td>1.16×10<sup>-3</sup></td><td>[14,19]</td></tr><tr><td>DCAL</td><td>52.05</td><td>199.1</td><td>205.3</td><td>15.58</td><td>20.95</td><td>50.76</td><td>2.92×10<sup>-5</sup></td><td>[14,19]</td></tr><tr><td>TCA</td><td>22.37</td><td>54.08</td><td>68.69</td><td>4.660</td><td>6.771</td><td>20.78</td><td></td><td></td></tr><tr><td>TBM</td><td>320.8</td><td>178.6</td><td>122.8</td><td>30.65</td><td>16.51</td><td>30.80</td><td>3.96×10<sup>-3</sup></td><td>[14]</td></tr><tr><td>BDCM</td><td>318.1</td><td>175.7</td><td>116.7</td><td>30.10</td><td>15.86</td><td>28.74</td><td>1.15×10<sup>-2</sup></td><td>[14]</td></tr><tr><td>DBCM</td><td>301.2</td><td>165.0</td><td>106.0</td><td>28.21</td><td>14.55</td><td>25.60</td><td>5.36×10<sup>-3</sup></td><td>[14]</td></tr><tr><td>TBAL</td><td>30.83</td><td>65.19</td><td>87.99</td><td>5.778</td><td>8.585</td><td>28.24</td><td>3.58×10<sup>-6</sup></td><td>[14,19]</td></tr></tbody></table>
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