ReviewPhthalates in the environment: characteristics, fate and transport, and advanced wastewater treatment technologies
Graphical abstract
Introduction
Phthalate esters (PAEs) are synthesized by phthalic anhydride and alcohols, also known as phthalic acid esters (Kashyap & Agarwal, 2018). They are colorless, odorless, flavorless, exist as liquid types at a large temperature range (25 ℃ − 50 ℃), and are chemically stable (Tran et al., 2021). In the 1930 s, di(2-ethylhexyl)phthalate (DEHP) was added to plastic polyvinyl chloride (PVC) to improve flexibility and elasticity. According to Organization for Economic Cooperation and Development OECD (2018), PAEs were widely used in the global amounts up to approximately 5.5 million metric tons per year, through various sources, including household stuffs (furnishings, clothing, cosmetics, children's toys, nutritional supplements/food packaging, etc.), building and traffic materials, industrial fields (paints and varnishes, adhesives, lubricants, waxes, cleaning materials, electronics, inks), agricultural activities (insecticides, pesticides, fertilizers, mulch plastic) or others (e.g., pharmaceuticals, medical devices, etc.). As a result, PAEs are found in various environmental matrices, including the atmosphere, lithosphere (soil, sediment), and hydrosphere (surface water, and wastewater, etc.).
Human exposure to PAEs can happen through various pathways such as ingestion, inhalation, skin absorption/contact, and intravenous injection. For example, the human body can be easily exposed PAEs by oral exposure (i.e., the ingestion of food, or children’s toys); inhalation from air ambient mixed with PAEs; by skin contact with plastic products (i.e., personal care products, paints, clothes or cosmetics, etc.); and intravenous exposure related to medical equipment (Zhou et al., 2019a). Meanwhile, PAEs are a type of endocrine disruptive chemical (EDCs) that can cause substantial harm to the respiratory, reproductive, and endocrine systems of humans. So far, PAE exposure was linked to a variety of health problems, including abnormal reproductive system impacts, asthma, and allergies. For example, many studies showed that PAEs toxicity leads to reproductive failure related to the testicular cell functions (Wang et al., 2018). Besides, previous researches indicated that PAEs cause adverse health risks: increasing the hypertension risk, changing the thyroid hormone concentration, and even metabolic disorders (Zhang et al., 2021, Zhou et al., 2019a).
It could be seen that the PAEs presence at high concentrations in the environment is one of the global concerns. Phthalates can migrate from landfills to the groundwater and leach into the environment. In this situation, examining the fate and transport of PAEs not only can evaluate the exposure risks but also understand their trend in the environment. Furthermore, PAEs discharged from industrial and domestic wastewater treatment plants directly enter into the water or accumulated in sewage sludge that cause serious effects on the ecosystem and human health via the food chain. Fromme et al. (2002) reported that phthalates detected in surface water was 22.7 mg L-1, whereas, the highest concentration of 288 mg L-1 was found in the wastewater (Salaudeen et al., 2018). Thus, it is obligatory to remove PAEs from wastewater sources by applying various potential wastewater treatment technologies.
Particularly, various advanced treatment technologies have been successfully to remove PAEs from wastewater such as adsorption processes (e.g., biochar and activated carbon) (Yao et al., 2019), advanced oxidation process (e.g., photo-Fenton, photocatalysis, and ozonation) (Medellin-Castillo et al., 2013), and biological treatment (membrane bioreactor and activated sludge) (Boonnorat et al., 2014, Kanyatrakul et al., 2020, Ye et al., 2020). The performance, advantage, and limitation of each technology for PAEs treatment were reviewed and discussed in previous studies (Gani et al., 2017, Zolfaghari et al., 2014). Gani et al. (2017) conducted a critical review on the fate and transportation of phthalate in aquatic environments (surface water, groundwater, and wastewater). Also, advanced bioremediation technologies for phthalate treatment and degradation mechanisms were summarized. In addition, Zolfaghari et al. (2016) evaluate the combination of membrane bioreactor and electro-oxidation processes to degrade phthalates in the landfill leachate. The optimum operating condition with the highest removal efficiency and cost-feasibility for phthalates treatment were identified and discussed. However, key points and the optimal conditions of advanced wastewater treatment technologies significantly affect the removal has not been addressed yet. Therefore, this review aims (1) to examine the characteristics, fate, and transport of PAEs in the environmental matrices, (2) to assess cutting-edge wastewater treatment technology, and (3) to identify the key factors of each technology. In addition, the knowledge gap and recommendations for future studies were also emphasized.
Section snippets
Physico-chemical properties
Several PAEs compounds were detected in the environment, such as Diethyl phthalate (DEP), Dimethyl phthalate (DMP), Di(2-ethylhexyl)phthalate (DEHP), Dibutyl phthalate (DBP), Diisobutyl phthalate (DIBP), Butyl benzyl phthalate (BBP), Diisononyl phthalate (DINP), and Dinoctyl phthalate (DnOP). PAEs are grouped into: high-molecular-weight (HMW) PAEs with 7 to 13 carbon chains and low-molecular-weight (LMW) PAEs with 3 to 6 carbon chains. For example, DEHP (C24H38O4) belongs to the HMW whereas;
Fate and transport of phthalates in the environment
Phthalates leached out from plastic products during their lifetime (Prasad, 2021). The fate and transport of PAEs in the environment are illustrated in Fig. 2. PAEs are able to water, air, soil, sediment contamination through various processes such as leaching, evaporation or deposition, etc. The distribution and behavior of PAEs in the atmosphere is an important route in the environment. The main sources are anthropogenic activities including manufacturing, distribution, consumption, and
Adsorption process
To remove organic substances in wastewater, adsorption process is commonly applied in which biochar and activated carbon were used as adsorbents. The first candidate is activated carbon which is an effective adsorbent because of its large surface area and chemical structure. To achieve higher removal PAEs efficiency, several types of adsorbent employed innovative materials for removing phthalates, such as modified activated carbon, chitosan, activated sludge, seaweed, and microbial cultures.
Future recommendations
Aforementioned above, advanced technologies have exhibited very promising for phthalates treatment with removal efficiencies (70–95%) for each process. However, these technologies commonly required high-level operation and maintenance costs; therefore, these recommendations were provided for future research to maintain the optimal conditions and apply for practical conditions.
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The sorption efficiency of absorbents (e.g., activated carbon, biochar) is limited, significantly depending on their
Conclusions
This review discussed about the occurrence, fate, behavior and contamination of phthalates in the environment worldwide. Wastewater treatment technologies currently applied in PAEs removal had high efficiencies of 70 – 95% achieved by ozonation and/or photocatalysis, and membrane bioreactor. Membrane bioreactor is robust for phthalates treatment due to its high efficiency (>90%), environmentally friendly, and cost-feasible for different scales. In details, several key points contributing to
CRediT authorship contribution statement
Huu Tuan Tran: Conceptualization, Formal analysis, Writing – original draft. Chitsan Lin: Data curation, Supervision. Xuan-Thanh Bui: Data curation, Methodology. Minh Ky Nguyen: Methodology, Formal analysis, Writing – original draft. Ngoc Dan Thanh Cao: Methodology. Hussnain Mukhtar: . Hong Giang Hoang: . Sunita Varjani: . Huu Hao Ngo: . Long D. Nghiem: .
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 pa
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