Aquatic toxicity of waterpipe wastewater chemicals

Abstract

Introduction:

The recent increase in U.S. popularity and use prevalence of water pipe (WP) tobacco smoking raises concerns about the potential environmental impacts of WP waste disposal and the need for strategies to reduce such impacts. The U.S. Food and Drug Administration (FDA) is required to assess the environmental impacts of its tobacco regulatory actions per the U.S. National Environmental Policy Act (NEPA). The purpose of this study was to identify and quantify specific chemical constituents in WP wastewater and to determine their potential aquatic toxicity.

Methods:

Using a modified Beirut smoking regimen, five different WP charcoal brands (n = 70) and ten WP tobacco brands (n = 35) were smoked separately using a WP smoking machine in which smoke was passed through the WP base water. We analyzed and quantified specific chemical constituents in the WP bowl wastewater through standardized U.S. Environmental Protection Agency’s (EPA) Hazardous Waste Test Methods. We then characterized the ecological hazard for acute and chronic aquatic toxicity posed by the specific chemicals through compilations of Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and hazardous concentration values (concentration affecting 50% of the species).

Results:

Among the list of 31 specific chemicals analyzed, we detected 22 and 11 chemicals in wastewater from WP tobacco and WP charcoal smoking, respectively. Nearly half of the 22 WP wastewater chemicals were classified as “very toxic” or “toxic” for acute and chronic aquatic toxicity per GHS classification. The most hazardous compounds with acute and chronic toxicity in aquatic organisms include acrolein, acrylonitrile, and metals (cadmium, lead, chromium, nickel, cobalt) found in both WP tobacco and charcoal wastewater, and N-nitrosonornicotine, nicotine, crotonaldehyde and selenium were additionally found in WP tobacco wastewater. All the identified chemicals are considered harmful or potentially harmful constituents in tobacco products and tobacco smoke per FDA’s list, and seventeen of them represent hazardous waste per EPA’s list.

Conclusion:

Our study expands the identification and quantifies several WP wastewater chemical constituents. It characterizes the ecological hazard of these chemicals and identifies chemicals of concern, aiding our evaluation of the environmental impacts of WP waste products. Our results add to the existing evidence that WP wastewater is a source of toxins that could affect water quality and aquatic organisms, and bioaccumulate in the environment if disposed of into public sewers, on the ground, or in an onsite septic system. These findings highlight the importance of concerted efforts to raise awareness of appropriate WP waste disposal practices in both retail and residential settings, and applicable regulatory compliance requirements for WP retailer establishments, thereby limiting hazards from WP wastewater.

1. Introduction

The environmental impacts of tobacco product waste and its mitigation have lately received increased global attention with a predominant focus on cigarettes (Araújo and Costa, 2019; Novotny and Slaughter, 2014; Torkashvand et al., 2020; Venugopal et al., 2021; Wallbank et al., 2017; World Health Organization, 2017). In the past decade, waterpipe (WP) tobacco smoking has emerged as a global phenomenon with increasing use prevalence, particularly among youth, with potential adverse environmental impacts (Chaouachi, 2009; Maziak et al., 2015; Maziak and Sharma, 2020). A WP, also known as hookah, narghile, shisha, arguile, arghile, hubble-bubble, or goza, consists of a bowl that is partially filled with WP tobacco and heated with burning WP charcoal placed on top to produce smoke that passes through base water before inhalation by the user (Fig. 1) (Edwards et al., 2020).

Fig. 1.

Diagram of waterpipe (figure not drawn to scale).

In the U.S., nationally representative estimates of WP tobacco use by young adults document the increasing rates of use during 2009 through 2019 (see review by Cooper et al., 2019). Hookah bars, a likely contributing factor for the increased prevalence of WP tobacco use among youth, have proliferated around U.S. colleges, totaling 1700 as of 2015 (Kates et al., 2016). Concomitantly, U.S. imports of WP tobacco increased by 14%, from 738 metric tons in 2012 to 841 metric tons in 2019 (USDA - FAS, 2019). The increased popularity of WP tobacco smoking raises serious concerns about the potential environmental impacts from the WP waste disposal, and highlights the importance of developing strategies to reduce such impacts (Kassem et al., 2020; Maziak and Sharma, 2020).

The National Environmental Policy Act (NEPA) requires U.S. federal agencies to assess the environmental impacts of their proposed actions. In accordance with NEPA, the U.S. Food and Drug Administration (FDA) evaluates the environmental impacts of its tobacco regulatory actions per rules described in 21 C.F.R. § 25 (Environmental impact considerations, 2019). Environmental impact assessments address the environmental effects of manufacture, use and disposal of FDA-regulated tobacco products.

Understanding the environmental impacts of WP waste is a crucial aspect of the environmental assessment of the disposal portion of the WP tobacco product lifecycle. With the various components involved in the WP assembly, environmental impacts from disposal after use of WP tobacco waste could occur from the used WP tobacco, burnt WP charcoal, used WP water (which is typically disposed after each smoking session), and packaging waste. Studies on WP tobacco disposal in residential and retail settings are scarce. Examination of the disposal habits of WP tobacco waste in U.S. home settings indicates that smoked WP tobacco was predominantly discarded in the trash that eventually reaches landfills. WP wastewater was mostly discarded in kitchen or bathroom sinks, flowing down the drain into public sewers or an onsite septic system, or discarded in backyard soils Kassem et al. (2020).

Available evidence from studies analyzing chemical constituents in WP wastewater indicates that many toxins may enter and accumulate in the soil and water systems through the disposal of WP wastewater. Qamar et al. (2015) reported the concentration of 18 metals, metalloids and radio toxins in WP wastewater, all considered environmental contaminants. Other harmful compounds in WP wastewater include carbonyls, phenols, furans, volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) (Al-Kazwini et al., 2015; Bagheri et al., 2017; Chaouachi, 2009; Maziak and Sharma, 2020; Schubert et al, 2011, 2012, 2015).

Aquatic systems and organisms may be the most vulnerable to potential impacts from toxins in WP wastewater that may ultimately reach water bodies through rainwater or onsite drainage systems, although wastewater treatment may curtail some of these contaminants (Neiheisel et al., 1988). Characterizing and quantifying the chemical constituents and hazard potential of WP wastewater informs the development of strategies to reduce its environmental impact on aquatic systems (Kassem et al., 2020). However, studies identifying the aquatic toxicity of specific chemicals in WP wastewater are currently not available. Therefore, the ecological risks to aquatic organisms from the chemical constituents of WP wastewater and their broader environmental effects remain poorly understood.

Additionally, calculating the chemical concentration at which a specified proportion of a species may be affected, through a probabilistic risk assessment paradigm using species sensitivity distributions (SSD), aids in risk analysis and environmental management (Belanger et al., 2017; Posthuma et al., 2019). European and U.S. regulatory agencies (e. g., European Union, U. S. Environmental Protection Agency (EPA)) utilize the hazardous concentration (HC) values for chronic and acute aquatic toxicity derived from SSDs for environmental protection, assessment, and management of aquatic ecosystems (Posthuma et al., 2019). However, HC values for the acute and chronic toxicity to aquatic organisms of specific chemical constituents in WP wastewater are not readily available.

In this study, we: (1) characterized and quantified the chemical composition of WP wastewater from machine smoked WP tobacco and WP charcoal; and (2) characterized the ecological hazard for acute and chronic toxicity to aquatic organisms posed by the specifically identified chemicals through (a) environmental hazard categorization per the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), and (b) HC values generated through SSDs from literature or based on predictions using quantitative structure-activity relationship (QSAR) (Blum and Speece, 1990).

2. Materials and methods

We targeted a subset of chemicals included in FDA’s list of harmful and potentially harmful constituents (HPHC) in tobacco products and tobacco smoke (HPHC Established List, 2012; HPHC Established List – Proposed Addition, 2019). Among the HPHCs, 31 chemicals were targeted based on commonality in WP charcoal and WP tobacco smoke.

2.1. Chemical analysis of waterpipe wastewater

2.1.1. Wastewater sample preparation

A WP apparatus comprising a bowl, stem, and base was assembled, and approximately 1.5 L of 18 MΩ ultrapure water was added into the base covering 30 mm of the stem. A smoking machine (Hawktech FP2000 or Borgwaldt Shisha Smoker) operating under a modified Beirut smoking regimen (0.530 L puff volume, 2.6 s puff duration, 17 s puff interval) (Brinkman et al., 2015) was employed to smoke ten different flavored WP tobacco brands and five different WP charcoal brands. The WP charcoal and WP tobacco samples were purchased from online vendors and chosen for their random additives and flavors. For the WP tobacco samples, the smoking machine pulled air through 10 g of WP tobacco in the bowl, and WP tobacco was heated by an electric heater (no charcoal) (Edwards et al., 2020) with a targeted temperature of 360 °C until the smoking session was stopped after 171 puffs. For the WP charcoal samples, WP charcoal was first placed on an electric burner for 100 s to light it before placing it onto an 18-hole perforated foil. The smoking session was initiated (no WP tobacco), and at puff 99, the remaining WP charcoal (approximately half of one WP charcoal sample) was lit again and allowed to burn for an additional 100 s before being placed onto the aluminum foil at puff 105. The smoking session for the WP charcoal sample was also stopped after 171 puffs. All WP tobacco-smoking and WP charcoal-smoking wastewater samples were collected and stored in separate glass jars with lids in a refrigerator (temperature 2–8 °C).

2.1.2. Chemical analytical methods

Chemical constituents were analyzed (n = 70 for each analyte from tobacco products, and n = 35 for each analyte from charcoal products) using standardized EPA’s Hazardous Waste Test Methods (SW-846) (US Environmental Protection Agency, 2015). For VOC analysis, samples were analyzed via purge-and-trap gas chromatography/mass spectrometry (GC/MS) (EPA SW-846 Methods 5035 A, 5030C and 8260C) (US Environmental Protection Agency, 2015). The analytes of interest were separated via capillary GC (Agilent 6890 GC) and quantified using electron ionization MS (Agilent 5973 Mass Selective Detector) in full-scan mode. Deuterated benzene, deuterated toluene, and deuterated ethylbenzene were used as internal standards, and 1,4-difluorobenzene, deuterated chlorobenzene, and deuterated 1,4-dichlorobenzene were used as surrogate samples. The GC parameters were set as follows: valve oven temperature was set to 140 °C; column oven temperature of 30 °C was held for 10 min, and then ramped to 220 °C at a rate of 5 °C/min. The inlet and detector temperatures were set at 220 °C and 230 °C, respectively, and helium was used as the carrier gas at a column flow rate of 0.2 mL/min.

For aromatic amines analyses, samples were analyzed via a liquid chromatography-mass spectrometry/mass spectrometry instrument (LC-MS/MS, Waters ACQUITY Ultra-Performance Liquid Chromatography, Waters Quattro Premier with Z-spray source) (Schubert et al., 2011). Deuterated 4-aminobiphenyl (4-APB-d₉, CDN Isotopes Inc.) was used as an internal standard. A gradient consisting of 0.1% formic acid in water (solvent A) and 0.1% formic acid in 25/75 methanol and acetonitrile (solvent B) at a constant flow rate of 0.8 mL/min was used. The solvent gradient program was as follows: 0 min, 7% B; 2.0 min, 7% B; 8.0 min, 35% B; 13 min, 95% B; 15 min, 95% B; 16 min, 7% B; 21 min, 7% B. MS/MS transitions (m/z) for 1-amino-naphthalene, 2-amino-naphthalene, and 4-aminobiphenyl were as follows: 144 → 127, 77; 144 → 127, 77; 170 → 153, 152; 179 → 161, 162 (4-APB-d₉ internal standard).

For aldehydes analyses, samples were diluted, adjusted for pH, derivatized, and purified using solid-phase extraction prior to analysis via high performance liquid chromatography (HPLC, Shimadzu Nexera system) (Al Rashidi et al., 2008; US Environmental Protection Agency, 2015). An isocratic gradient mode consisting of 70% acetonitrile and 30% water at a constant flow rate of 1.0 mL/min for 15 min was used, and the detector wavelength was monitored at 360 nm. For PAH analyses, samples were extracted and purified (EPA SW-846 methods 3640 A, 3610 B, and 8270D) (US Environmental Protection Agency, 2015). Each extract was spiked with internal standards (deuterated fluorene and deuterated chrysene), concentrated, analyzed via GC-MS (Agilent 6890 GC with an Agilent 5975 A MS), and operated in selected ion monitoring (SIM) mode. The GC parameters were as follows: column oven temperature of 40 °C was held for 1 min and then ramped to 300 °C at a rate of 6 °C/min and held constant for 20 min. The inlet and detector temperatures were set at 300 °C and 230 °C, respectively. Helium was used as the carrier gas at a column flow rate of 1 mL/min.

For nicotine and humectants analyses, samples were diluted with heavy water (deuterium oxide, D₂O, Sigma Aldrich) to a final volume of 3 mL (90:10 mixture of H₂O and D₂O) and analyzed via proton nuclear magnetic resonance (¹H NMR) spectroscopy (Bruker AVANCE 500 MHz NMR spectrometer). The water ZGESGP method was used for measurement and data collection, and sculpted excitation with a pulsed-field gradient was used for water suppression.

For phenols analyses, samples were analyzed via liquid chromatography with a fluorescence detector (Schubert et al., 2015). A gradient consisting of 1.0% acetic acid in water (solvent A) and 0.1% acetic acid in acetonitrile (solvent B) at a constant flow rate of 0.55 mL/min was used. The solvent gradient program was as follows: 0 min, 3% B; 3 min, 3% B; 5 min, 19% B; 15 min, 19% B; 17 min, 85% B; 19 min, 85% B; 21 min, 3% B; 24 min, 3% B. The excitation and emission wavelength used were 274 nm and 298 nm, respectively.

For trace metals analyses, samples were microwave digested (EPA SW-846 Method 3015 A) and analyzed via inductively coupled-plasma mass spectrometry (Perkin Elmer Elan with a Dynamic Reaction Cell [DRC-e]) (US Environmental Protection Agency, 2015, 1994). A solution containing scandium (Sc), indium (In), terbium (Tb), and yttrium (Y) in 1% nitric acid was used as an internal standard.

The pH of wastewater samples was determined as previously described (ASTM, 2014). The rearranged Henderson-Hasselbalch equation (Eq (1)) was used to calculate the free-base nicotine quantities:

$${\text{Nicotine}}_{\text{free}}=\frac{\left(\left[{10}^{\text{pH}-8.02}\right]{\text{Nicotine}}_{\text{total}}\right)}{\left(1+\left[{10}^{\text{pH}-8.02}\right]\right)}$$ Eq. 1

For tobacco-specific nitrosamine analysis, N-Nitrosonornicotine (NNN) and 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were extracted from total particulate matter generated from waterpipe tobacco smoke and analyzed via LC-MS/MS (Waters ACQUITY HPLC and Waters Xevo TQ MS) (Lawler et al., 2013; US Environmental Protection Agency, 2015) using positive electrospray ion mode and multiple reaction monitoring mode. A gradient consisting of 0.1% acetic acid in water (solvent A) and 0.1% acetic acid in methanol (solvent B) at a constant flow rate of 100 μL/min was used. The solvent gradient program was as follows: 0 min, 40% B; 0.5 min, 40% B; 5.0 min, 65% B; 5.5 min, 100% B; 6.0 min, 100% B; 6.1 min, 30% B; 8.0 min, 30% B. MS/MS transitions (m/z) for NNN were as follows: 178 → 148 (quantitation); 178 → 120 (confirmation); 182 → 152 (NNN-d₄ internal standard). MS/MS transitions (m/z) for NNK were as follows: 208 → 122 (quantitation); 208 → 79 (confirmation); 212 → 126 (NNK-d₄ internal standard).

2.2. Aquatic toxicity of waterpipe wastewater chemicals

We used two complementary and internationally recognized methods to characterize the ecological hazards of WP wastewater chemicals - HC values generated through SSDs and the GHS.

2.2.1. Hazardous concentration values

Estimated HC values through SSDs, including extrapolations using QSAR, are particularly useful for screening and prioritizing chemicals for their aquatic toxicity potential (Hoondert et al., 2019; Posthuma et al., 2019). For the chemicals detected in WP wastewater, we collated the HC values (HC₅₀; hazardous concentration value at which 50% of species may be affected) for acute and chronic aquatic toxicity, as provided by Posthuma et al. (2019). HC values were originally derived by Posthuma et al. (2019) based on acute median effective concentration (e.g. LC₅₀, EC₅₀) or chronic no-effect (e.g. no-observed-effect concentration (NOEC)) or negligible-effect (EC₅, EC₁₀) data for multiple species and taxonomic groups.

2.2.2. Globally Harmonized System of Classification and Labelling of Chemicals (GHS) -Aquatic toxicity classification

We compiled the acute (H400, H401 and H402 - very toxic, toxic, and harmful to aquatic organisms, respectively) and chronic (H410, H411, H412, and H413 - very toxic, toxic, harmful, maybe harmful to aquatic life with long lasting effects, respectively) aquatic hazard categories per the GHS assessments (eChemPortal OECD, 2020; United Nations, 2019). Chemicals without GHS classification were grouped under “not available”, a category constituting chemicals with insufficient ecotoxicity data for GHS classification as well as those whose toxicity is considered to be insufficient to warrant classification (lethal concentration LC₅₀ or effective concentration EC₅₀ > 100 mg/l) (United Nations, 2019).

In addition to the ecological hazard characterization, we also identified the WP wastewater chemicals included in the EPA’s list of hazardous waste per 40 C.F.R. § 261 (Identification and Listing of Hazardous Waste, 2020).

2.2.3. Statistical analyses

For WP wastewater chemicals without available ecotoxicity data, we estimated the acute and chronic aquatic toxicity endpoints through QSARs with Ecological Structure Activity Relationships (ECOSAR) Predictive Model (V1.11) available in the Estimation Programs Interface Suite software (v4.11) (US Environmental Protection Agency, 2020). ECOSAR-based predictions for acute aquatic toxicity include LC₅₀ (fish; 96-hr) and EC₅₀ (daphnid, 48-hr; green algae, 96-hr) estimates, along with chronic endpoint values for these taxa. We derived the HC₅₀ values for acute and chronic toxicity from SSD extrapolations based on log-normal distributions with the QSAR predicted acute and chronic toxicity endpoints, respectively (Hoondert et al., 2019).

SSD extrapolations were performed in R program with package fitdistrplus v1.1–1(Delignette-Muller and Dutang, 2015) with 10,000 parametric bootstrap iterations and HC values were generated. Graphs were generated with packages “ggplot2” v3.3.0 (Wickham, 2016) and “ggrepel” v0.8.1 (Slowikowski et al., 2020) in R program v3.4.3.

3. Results

3.1. Chemical constituents in waterpipe wastewater

Using a modified Beirut smoking regimen, we identified 22 and 11 HPHCs in wastewater from WP tobacco and WP charcoal smoking, respectively (Table 1). All the chemicals detected in wastewater from WP charcoal smoking were also detected in wastewater from WP tobacco smoking. For wastewater from WP tobacco and WP charcoal smoking, nine and seven other chemicals, respectively, were below levels of detection. Glycerol, propylene glycol, nicotine, formaldehyde and acrolein were the major chemical constituents in wastewater from WP tobacco smoking (Table 1). Formaldehyde and lead were the main chemical constituents from wastewater from WP charcoal smoking (Table 1). In both WP tobacco and WP charcoal wastewater, cadmium, chromium, cobalt, lead, and nickel were detected, with selenium additionally being detected only in WP tobacco wastewater (Table 1). Concentrations of benzene and total PAHs were higher with WP charcoal wastewater than tobacco wastewater.

Table 1.

Chemical constituents and concentrations in wastewater from waterpipe tobacco and charcoal smoking.

Serial Number	Chemical	Chemical Abstracts Service Number	Limit of Detection μg/L	Mean Concentration from Tobacco Smoking ±SDa (μg/L)	Mean Concentration from Charcoal Smoking ±SDa (μg/L)
1	1,3-Butadiene	106-99-0	0.41	*	*
2	1-Aminonaphthalene	134-32-7	0.6	*	NA
3	2-Aminonaphthalene	91-59-8	0.6	*	NA
4	4-Aminobiphenyl	92-67-1	0.6	*	NA
5	Acetaldehyde	75-07-0	4	1950.84 ± 814.58	17.93 ± 10.22
6	Acrolein	107-02-8	6.2	610.81 ± 249.39	12.11 ± 12.59
7	Acrylonitrile	107-13-1	0.62	0.84 ± 0.14	0.77 ± 0.17
8	Arsenic	7440-38-2	0.085	*	*
9	Benzene	71-43-2	0.51	0.58 ± 0.06	7.35 ± 4.84
10	Benzo(a)pyrene	50-32-8	0.003	*	*
11	Cadmium	7440-43-9	0.011	0.020 ± 0.014	0.047 ± 0.038
12	Catechol	120-80-9	14	143.91 ± 83.00	NA
13	Chromium	7440-47-3	0.726	2.72 ± 1.73	1.41 ± 0.50
14	Cobalt	7440-48-4	0.0049	0.14 ± 0.12	0.15 ± 0.09
15	Crotonaldehyde	4170-30-3	3.2	36.40 ± 18.34	*
16	Formaldehyde	50-00-0	12.9	935.59 ± 402.67	106.31 ± 70.62
17	Glycerol	56-81-5	410	253,530 ± 167,030	NA
18	Isoprene	78-79-5	0.13	*	*
19	Lead	7439-92-1	0.015	211.74 ± 152.60	76.46 ± 100.06
20	m_p-Cresol	108-39-4/106-44-5	4	17.29 ± 6.28	NA
21	Mercury	7439-97-6	0.055	*	*
22	Nickel	7440-02-0	0.05	3.87 ± 4.11	2.11 ± 2.32
23	Nicotine (free-base)	NA	NA	*	NA
24	Nicotine (total)	54-11-5	350	1220 ± 1240	NA
25	NNK	16543-55-8	7.5	106.55 ± 165.38	NA
26	NNN	64091-91-4	7.5	250.95 ± 262.80	NA
27	o-Cresol	95-48-7	6	17.93 ± 6.00	NA
28	Phenol	108-95-2	2	188.01 ± 63.90	NA
29	Propylene glycol	57-55-6	300	82,860 ± 141,250	NA
30	Selenium	7782-49-2	1.04	1.53 ± 0.20	*
31	Total PAHs	NA	0.001– 0.003	0.251 ± 0.111	4.04 ± 3.73

The pH of charcoal-smoked and tobacco-smoked wastewater samples was 6.94 (± 0.30) and 4.02 (± 0.88), respectively.

^*Below limits of detection.

PAH: Polycyclic aromatic hydrocarbons.

NA - Not applicable.

^{a -}Mean value from ten WP tobacco products (n = 70 for each analyte) and five WP charcoal products (n = 35 for each analyte).

3.2. Aquatic toxicity of waterpipe wastewater chemicals

The acute aquatic toxicity hazard characterization of WP wastewater chemicals per HC₅₀ values and GHC classifications are provided in Fig. 2. Acrolein, nicotine and metals (cadmium, lead, chromium, nickel, selenium, cobalt) represent the most hazardous chemical constituents for acute aquatic toxicity per HC₅₀ values (Fig. 2). Nearly half of the WP wastewater chemicals were very toxic or toxic for acute aquatic toxicity per GHS classification, while classification was not available for the remaining chemicals (Fig. 2).

Fig. 2.

Acute aquatic toxicity of chemicals in wastewater from waterpipe tobacco and charcoal smoking. The hazardous concentration values (HC₅₀; concentration affecting 50% of the species) and the categorization per the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) for acute aquatic toxicity are depicted. Low HC₅₀ values indicate high aquatic toxicity hazard.

The chronic aquatic toxicity hazard characterization of WP wastewater chemicals per HC₅₀ values and GHC classifications are provided in Fig. 3. Acrolein, NNN, nicotine, acrylonitrile, crotonaldehyde and metals (cadmium, lead, chromium, nickel, selenium, cobalt) represent the chemicals with chronic aquatic toxicity potential per HC₅₀ values. Nearly half of the WP wastewater chemicals were very toxic or toxic per GHS classification for acute aquatic toxicity, while GHS classification was not available for the remaining chemicals.

Fig. 3.

Chronic aquatic toxicity of chemicals in wastewater from waterpipe tobacco and charcoal smoking. The hazardous concentration values (HC₅₀; concentration affecting 50% of the species) and the categorization per the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) for chronic aquatic toxicity are depicted. Low HC₅₀ values indicate high aquatic toxicity hazard.

Among the 22 chemicals detected in the WP wastewater, 17 are considered to be hazardous waste per the EPA identified list. This includes acrolein and nicotine listed as acute hazardous waste; acetaldehyde, acrylonitrile, benzene, cadmium, chromium, cobalt, crotonaldehyde, formaldehyde, lead, nickel, o-Cresol, m-cresol, p-Cresol, phenol and selenium listed as toxic hazardous waste.

4. Discussion

The recent increase in popularity and use prevalence of WP tobacco smoking raises concerns about the potential environmental impacts of WP waste disposal (Kassem et al., 2020; Maziak and Sharma, 2020; Qamar et al., 2015). We identified and quantified the chemical composition of WP wastewater, and characterized chemicals’ aquatic toxicity potential. Our study represents the first effort characterizing the ecological hazard for aquatic organisms across trophic levels posed by WP wastewater chemicals. The study also represents the first effort to document the unique contribution of WP tobacco and WP charcoal for specific chemicals in WP wastewater. The results identify WP tobacco as the primary sources of toxic chemicals in WP wastewater.

Our analytical results document aliphatic amines, nitriles, and other organic compounds, in addition to previously reported phenols, PAHs, VOCs, carbonyls, metals and metalloids (Al-Kazwini et al., 2015; Bagheri et al., 2017; Chaouachi, 2009; Maziak and Sharma, 2020; Qamar et al., 2015; Schubert et al, 2011, 2012, 2015). Among metals, the hookah assembly unit may also act as a source of lead and chromium, although our analytical techniques quantified overall concentrations. Available research studies, including ours, utilized targeted chemical analytical techniques to identify certain chemical constituents in WP wastewater. These reported chemicals constituents were chosen as being more commonly detected in waterpipe tobacco and charcoal smoke. They represent a minor fraction of those found in WP tobacco and charcoal smoke, and tobacco and charcoal waste in general (Chaouachi, 2009; World Health Organization, 2017). This highlights the need for non-targeted chemical analyses that more broadly detect the wide spectrum of chemicals in WP wastewater.

All the chemicals reported in WP wastewater are included in FDA’s established HPHC list or proposed additions, and 17 are considered hazardous per EPA’s identified list. These results add to growing evidence of the toxicity potential of WP wastewater. Acrolein, NNN, nicotine, acrylonitrile, crotonaldehyde and metals (cadmium, lead, chromium, nickel, selenium, cobalt) represent the most hazardous compounds for acute and chronic toxicity for aquatic organisms based on the ecological hazard characterization per GHS classification and HC₅₀ values. These findings add to the existing evidence that WP wastewater is a source of toxins that could bioaccumulate in the environment if disposed of into public sewers or on the ground, or in onsite septic systems (Kassem et al., 2020; Maziak and Sharma, 2020; Qamar et al., 2015). This raises potential environmental impact concerns given the high toxicity and hazard potential in relation to the concentrations found in WP wastewater. Our results highlight the importance of research on WP wastewater disposal practices in commercial WP establishments such as hookah bars.

Disposal of WP wastewater “down the drain” into public sewers or an onsite septic system by retail establishments, similar to disposal habits in residential settings (Kassem et al., 2020), could be important sources of toxins affecting water quality and aquatic organisms. Our findings on the concentrations of EPA-listed hazardous waste in WP wastewater such as acrolein, acetaldehyde, acrylonitrile, benzene, crotonaldehyde, formaldehyde, metals (cadmium, lead, chromium, nickel, selenium, cobalt), nicotine and phenol are relevant for regulatory requirements and permitting processes for hookah bars in the U.S. given the disposal practices. Hazardous wastes are regulated in the U.S. under the Resource Conservation and Recovery Act (RCRA), and hazardous waste generators are regulated based on the monthly amount of waste generated (US Environmental Protection Agency, 2014a). The multiple steps involved in complying with regulations for hazardous wastes per RCRA requirements are applicable to WP retail establishments (US Environmental Protection Agency, 2014b). Hence, there is an urgent need for concerted efforts to raise awareness of appropriate WP wastewater disposal practices in both retail and residential settings, and applicable RCRA compliance requirements for WP retailer establishments, thereby limiting hazards from WP wastewater.

5. Conclusions

Overall, our study helps characterize the ecological hazard posed by WP wastewater chemicals and identify chemicals of concern for ecotoxicity risk potential. Our study furthers the evaluation of the environmental impacts of WP products. The finding that all the reported chemicals are in FDA’s established HPHC list or proposed additions and many are included in EPA’s hazardous chemicals list highlights the importance of research addressing potential human health impact. The HPHCs and EPA-listed hazardous compounds we measured in WP wastewater include nicotine, NNN, metals, PAHs and volatile organic compounds, which are also very toxic to aquatic organisms. To characterize ecological risk of these chemicals, exposure concentration estimates based on environmental fate and transport models along with the hazard characterization information will help support risk assessment for aquatic organisms potentially impacted from exposure to WP wastewater chemicals.

Abbreviations:

ECOSAR

Ecological Structure Activity Relationships

EPA

U.S. Environmental Protection Agency

FDA

U.S. Food and Drug Administration

GC

Gas chromatography

GHS

Globally Harmonized System of Classification and Labelling of Chemicals

HC

Hazardous concentration

HPHC

Harmful and Potentially Harmful Constituents in Tobacco Products and Tobacco Smoke

HPLC

High performance liquid chromatography

MS

Mass spectrometry

NEPA

U.S. National Environmental Policy Act

NNK

Nicotine-derived nitrosamine ketone

NNN

N-Nitrosonornicotine

QSAR

Quantitative Structure-Activity Relationship

RCRA

Resource Conservation and Recovery Act

SSD

Species sensitivity distributions

WP

Waterpipe