Organophosphate esters (OPEs) are increasingly used as flame retardants and plasticizers in various products. Most of them are physically mixed rather than chemical bonded to the polymeric products, leading to OPEs being readily released into the surrounding environment. Due to their relatively high solubility and mobility, OPEs are ubiquitous in the aquatic environment and may pose potential hazards to human health and aquatic organisms.
1. Water
As for mammals,
organophosphate esters (OPEs
) were detected in dolphins, seals, and polar bears. Aznar-Alemany et al.
[103][1] investigated the concentrations of OPEs in the muscles of Indian Ocean dolphins. The mean concentration of OPEs was 10,452 ± 11,301 ng/g lw, with TBOEP accounting for 82 ± 28% of the total OPE contamination. Sala et al. (2019) reported OPEs in the dolphin samples from the Alboran Sea
[104][2]. The concentrations of OPEs in the muscle tissue varied from 70 to 2939 ng/g lw, and were one order of magnitude lower than those detected in the Indian Ocean
[103][1]. According to Sutton et al. (2019), four types of OPEs were detected in harbor seal blubber: TDCPP (nd-56 ng/g lw), TCPP (nd-30 ng/g lw), TCEP (nd-8.3 ng/g lw), and TPhP (nd-27 ng/g lw)
[63][3]. Letche et al.
[105][4] collected tissue samples from the polar bears of various Hudson Bay subpopulations. Only TEHP could be quantified in the samples despite the presence of several types of OPEs, indicating limited intake and absorption due to the rapid metabolism in polar bears.
As some OPEs have a relatively large logK
ow through bioaccumulation, they can be transferred from low trophic organisms to high trophic organisms through the food web
[63,107,108][3][5][6]. The survival and reproduction of organisms may be threatened by the toxicity of OPEs, which mainly manifests as growth inhibition
[89[2][7][8],
104,109], developmental delay
[110[9][10],
111], reproduction toxicity
[13][11], neurotoxicity toxicity
[12], and apoptosis
[15][13].
2. Surface Water (Rivers, Lakes, and Coastal Seawater)
The concentrations of OPEs in rivers and lakes range widely, depending on local industrial distribution and human activities, especially in the manufacturing and construction industry
[42,68][14][15]. OPEs are usually observed near urban and industrial areas
[59,65][16][17]. For example, Lian et al. (2022) studied the Zijiang River, which has large mining operations occurring in its downstream
[51][18]. The results showed that TCEP, TCPP, TEP, TNBP, and TBOEP were detected in almost all samples, with TNBP and TBOEP accounting for 14.2% and 9.3% of the OPEs, respectively. TNBP and TBOEP are widely used in hydraulic fluids and lubricants, which may be released into the surrounding environment during mining. Human activity is a main factor in causing the different spatial distribution of OPEs
[54][19]. Zhang et al. (2018) used GC-MS to study eight OPEs of urban and rural surface water samples
[55][20]. The concentrations of the OPEs detected in urban rivers (340–1688.7 ng/L) were higher than those in rural rivers (185.4–321 ng/L). The concentrations of three Cl-OPEs in urban surface water were significantly higher than those in rural surface water, indicating that there may be more potential pollution sources in urban areas. The amount and type of OPEs in surface water also reflects the industrial development level between urban and rural areas
[55,65][17][20].
Significant differences in the level of OPEs were found in different seasons
[56,57,62][21][22][23]. Chen et al. (2019) sampled seawater and sediments in northwestern Bohai Bay from 2014 to 2017, and detected the concentrations of 12 OPEs using GC-MS/MS
[69][24]. The concentration of TEP in summer was the highest among the three seasons investigated, which may be caused by the high temperature and frequent rainfall in Tianjin in the summer. High temperature may lead to the release of OPEs from the materials, and the wet deposition utilizes the atmosphere to migrate OPEs from the air to the aquatic system. Among the OPEs studied, TEP has the highest water solubility among all the investigated OPEs, so it is more readily soluble in water. However, for TCEP and TBOEP, the trend is the complete opposite. The concentrations of TCEP and TBOEP were the lowest in summer, and this difference may be related to the physical and chemical characteristics of OPEs. Besides the impact of high temperature
[69[24][25],
70], floods can also affect the level of OPEs in rivers. Increased discharge during floods reduces the levels of OPEs in water and results in a relatively uniform distribution throughout the river
[19][26].
The coastal environment is an important sink of OPEs
[68][15]. The release of OPEs from the inland is accompanied by the flow of rivers into the sea. At the same time, the pollution from intensive fishery activities, aquaculture wastewater discharge, and even some ports and tourism activities, all lead to great environmental stress
[58][27]. The Bohai Sea, Yellow Sea, and East China Sea are important marginal sea areas for China. According to Zhong et al. (2020), Qi at al. (2021), and Lin et al. (2022), high concentrations of OPEs were detected in the Bohai Sea and the Yellow Sea. The total concentration of OPEs in the Bohai Sea (10.9–516.4 ng/L) was the highest, followed by the Yellow Sea (12.7–202.6 ng/L) and then the East China Sea
[53[28][29][30],
71,72], which was attributed to there being more pollution sources and poor seawater exchange around the Bohai Sea. Due to a low boiling point and semi-volatility, the OPEs in coastal seawater can be deposited into sediments and be volatilized into the atmosphere
[73][31]. The long-distance migration of the atmosphere and ocean currents transport OPEs from industrialized regions to the sea
[74,75][32][33]. Na et al. (2020) demonstrated the long-distance migration ability of OPEs
[76][34]. Ten OPEs were found in seawater samples from the northwestern Pacific and the Arctic, with the concentration varying from 8.5 to 143 ng/L. Xiao et al. (2021) collected surface seawater from the West Pacific Ocean
[60][35]. The total concentration of OPEs was 3.02–48.4 ng/L, which were comparable with those in the surface water of the largest High Arctic lake (mean: 12.9 ng/L)
[77][36]. In addition, Li et al. (2017) revealed there were OPEs (0.3–8.4 ng/L, mean: 2.9 ng/L) in the seawater of the northeast Atlantic and the Arctic Ocean
[74][32]. Compared with the open sea, the concentrations of OPEs in coastal waters were higher
[64][37].
Previous studies have shown that some OPEs can accumulate in sediments and persist in aquatic environments
[18,50,52,53,59,63,67,69][3][16][24][28][38][39][40][41]. OPEs may even produce more toxic transformation products through biotransformation, photodegradation, or hydrolysis. Rivers are the main vehicle for transporting and mobilizing OPEs from the mainland to the coastal marine environment. Monitoring and controlling the concentration of pollutants in rivers and lakes can effectively prevent marine pollution.
3. Drinking Water (Tap Water, Bottled Water, and Barreled Water)
Drinking water is regarded as one of the main ways for OPEs to come into contact with humans. In general, bottled water, tap water, and barreled water are the three common types of drinking water
[78][42]. At present, plenty of studies on the fate of OPEs in drinking water have been carried out in China
[20,56,79,80[21][43][44][45][46][47],
81,82], Pakistan
[83][48], South Korea
[84[49][50],
85], Canada
[86][51], USA
[64[37][52],
87], and in other countries and regions
[88][53]. The concentrations of OPEs in different types of drinking water are summarized in
Table 1.
Table 1.
Concentration of OPEs in several types of drinking water (ng/L).