3.1 Quality control
Recovery rates, calculated by subtracting the concentration of the sample without the chemical from that of the sample with the chemicals added, was within the ranges of 71–143% (average: 98%) and 61–147% (average: 99%) for ultrapure water and the STP effluent, respectively.
3.2 Calculation of MDLs and MQLs
The MDLs and MQLs of the analyzed chemicals were calculated based on the results of the recovery tests conducted by adding the chemicals to ultrapure water and adjusting the concentration at the lowest calibration curve level. Eight extracted samples were analyzed with LC-MS/MS, and the respective t-values were calculated based on the standard deviation for each chemical. The MDLs and MQLs were calculated using the following formulas (Currie 1997): MDL = 2 × t (n-1, 0.05) × σn-1 × 2, and MQL = 10 × σn-1; where t (n-1, 0.05) indicates the t-value (one-sided) for the risk factor of 5% and the degree of freedom of n-1.
3.3 PNECs of PPCPs
The assessment factors were obtained from the “Guidelines for the Initial Environmental Risk Assessment of Chemicals,” published by the Ministry of Environment, Japan (2019). Following these guidelines, when chronic toxicity data were obtained for the three species (fish, algae, and crustacean), the assessment factor was 10; however, when chronic data were obtained for one or two species, the assessment factor was 100. Among the three methods used to calculate PNECs, TG-212 is considered an acute toxicity test, while the others are chronic toxicity tests. Therefore, the assessment factor for the six analyzed chemicals was set at 100.
Algae are highly susceptible to 14-hydroxyclarithromycin, compared to other species, with half (50%) maximal effective concentrations (EC50) > 2000 µg L-1 for fish and EC50 > 2000 µg L-1 for crustaceans; the concentration that results in 50% inhibition of growth rate (ErC50) of algae is 27.2 µg L-1 (Baumann et al. 2015). In this case, according to the guideline published by the Ministry of Environment, Japan (2019), the assessment factor can be assumed to be 10. Therefore, the PNEC of 14-hydroxyclarithromycin was set at 270 ng L-1, calculated by dividing the lowest NOEC (2.7 µg L-1) by the assessment factor of 10. Similarly, for tris(2-butoxyethyl) phosphate (TBOEP), the minimum PNEC was calculated by dividing 21 mg L-1 (96 h-lethal concentration for 50% of animals (LC50)) (obtained from the toxicity tests conducted by the Ministry of the Environment, Japan) by the assessment factor of 1000.
3.4 River water samples
Analyzed data for PPCP detected at a concentration more than the PNEC of each chemical or 1000 ng L-1, in at least one sampling point, are shown in Table 3, and the details of the data are shown in Tables S3 and S4. The names of the municipalities were indicated with letters (A to K), and the sampling points in each municipality were assigned identification numbers (e.g., "A-1" or "C-5”) based on the data obtained from the 11 institutes collaborating in this joint research.
Table 3
Concentrations of pharmaceuticals and personal care products (PPCPs) in water environment samples (ng L− 1)
Four institutes participating in this joint research project |
City or Prefecture | River name | Chemical Sampling point | clarithro mycin | 14-hydroxy clarithro mycin | erythro mycin | diclofenac | carbama zepine | sulpiride | fexo fenadine | diphenyl sulfone | telmisartan | valsartan | crotamiton | TBOEPd |
Osaka Ca. | Daini Neya gawa Rc. | Shigino-ohashi Bridge | 600 | 580 | 100 | 45 | 42 | 890 | 2500 | 1200 | 860 | 440 | 1300 | 660 |
Shimoshiromi Bridge | 570 | 510 | 370 | 45 | 36 | 760 | 2200 | 970 | 810 | 420 | 1100 | 630 |
Hyogo Pb. | Inagawa R. | Inagawa Bridge | N.D.e | N.D. | 57 | N.D. | 4.8 | 4.1 | N.D. | (2.5) | (2.2) | N.D. | 7.8 | N.D. |
Tokura Bridge | 470 | 470 | 57 | 70 | 51 | 1000 | 3500 | 76 | 1300 | 180 | 1600 | 260 |
Nagoya C. | Hori kawa R. | Johoku Bridge | 340 | 330 | 23 | 17 | 22 | 400 | 2400 | 83 | 600 | 1100 | 750 | 660 |
Nakatsuchito Bridge | 400 | 390 | 25 | 27 | 26 | 470 | 2900 | 83 | 730 | 1100 | 890 | 530 |
Tokyo P. | Tama gawa R. | Nagata Bridge | N.D. | N.D. | N.D. | N.D. | (0.11) | N.D. | N.D. | N.D. | N.D. | N.D. | N.D. | N.D. |
Hino Bridge | 180 | 220 | 30 | 29 | 39 | 360 | 1700 | 47 | 620 | 130 | 510 | 170 |
11 institutes cooperating in this joint research project |
Institute | Chemical Sampling point | clarithro mycin | 14-hydroxy clarithro mycin | erythro mycin | diclofenac | carbama zepine | sulpiride | fexo fenadine | diphenyl sulfone | telmisartan | valsartan | crotamiton | TBOEP |
A | A-1 | 35 | 39 | 40 | (1.9) | 5.1 | 56 | 180 | 14 | 61 | 98 | 210 | 55 |
A-2 | 160 | 230 | 39 | 19 | 13 | 220 | 1600 | 63 | 270 | 78 | 460 | 110 |
B | B-1 | 21 | 24 | 57 | (1.7) | 3.7 | 42 | 82 | 19 | 69 | 66 | 190 | 91 |
B-3 | 200 | 240 | N.D. | 21 | 21 | 480 | 1100 | 62 | 670 | 370 | 650 | 410 |
C | C-3 | N.D. | N.D. | N.D. | N.D. | N.D. | N.D. | N.D. | (3.2) | N.D. | N.D. | N.D. | N.D. |
C-4 | 750 | 910 | 370 | 140 | 72 | 1200 | 3600 | 120 | 2300 | 3300 | 1500 | 1200 |
D | D-2 | 15 | 20 | (3.4) | 4.4 | 5.5 | 43 | 67 | 19 | 50 | 77 | 120 | 130 |
D-3 | 360 | 390 | 57 | 69 | 38 | 480 | 1300 | 56 | 820 | 260 | 1100 | 510 |
E | E-1 | 510 | 540 | 57 | 120 | 60 | 970 | 2100 | 74 | 1300 | 240 | 1700 | 240 |
E-2 | 58 | 59 | 9.8 | (2.8) | 10 | 100 | 230 | 26 | 200 | 100 | 290 | 71 |
F | F-1 | 79 | 88 | N.D. | 25 | 37 | 220 | 550 | 23 | 290 | 53 | 470 | 47 |
F-2 | 96 | 120 | 15 | 14 | 27 | 220 | 650 | 20 | 290 | 49 | 470 | 150 |
G | G-1 | 9.5 | 10 | N.D. | 5.6 | 5.7 | 19 | 44 | N.D. | 49 | 37 | 69 | 18 |
H | H-1 | 72 | 75 | (3.8) | 12 | 6.2 | 81 | 320 | 14 | 130 | 110 | 280 | 120 |
H-2 | 310 | 290 | 11 | 43 | 39 | 300 | 1200 | 41 | 490 | 180 | 680 | 130 |
I | I-1 | 9.1 | 12 | N.D. | 4.5 | 6.2 | 59 | 99 | 6.7 | 87 | (7.2) | 110 | 36 |
I-2 | 28 | 34 | (5.1) | 25 | 22 | 230 | 520 | 17 | 400 | 59 | 460 | 120 |
J | J-1 | 3.0 | 3.0 | N.D. | 4.9 | 5.0 | 43 | 48 | N.D. | 39 | 18 | 47 | 12 |
J-2 | 860 | 900 | 80 | 220 | 75 | 1400 | 3200 | 160 | 2200 | 3000 | 1500 | 1100 |
K | K-1 | 2.4 | 2.3 | N.D. | N.D. | 4.4 | 6.2 | 23 | (4.1) | (4.3) | 22 | 7.2 | 46 |
K-2 | 430 | 430 | 53 | 79 | 62 | 750 | 2300 | 57 | 810 | 280 | 1000 | 160 |
Method Detection Limit (MDL) | 0.8 | 0.2 | 3.3 | 1.2 | 0.1 | 1.2 | 1.7 | 1.9 | 2.1 | 3.1 | 2.5 | 2.6 |
Method Quantification Limit (MQL) | 2.2 | 0.7 | 8.7 | 3.3 | 0.2 | 3.3 | 4.6 | 5.0 | 5.6 | 8.1 | 6.7 | 6.8 |
Predicted no-effect concentration (PNEC) | 20 | 270 | 20 | 66 | 30 | > 100000 | 300000 | 3500 | 1600 | ― | 3500 | 21000 |
a: City, b: Prefecture, c: River, d: tris(2-butoxyethyl) phosphate, e: not detected |
The blank test value was subtracted from the raw measured values for N,N-diethyl-m-toluamide (DEET) and diphenyl sulfone because the blank test values were above the MDL for both chemicals. The gray cells shown in Table 3 indicate that the measured values exceeded the respective PNECs. The concentrations of clarithromycin, 14-hydroxyclarithromycin, erythromycin, carbamazepine, diclofenac, and telmisartan exceeded their respective PNECs at several sampling points, and almost all these points were in the downstream areas.
For risk assessment, the concentrations of these chemicals were compared with their respective PNECs. Among the chemicals studied, carbamazepine and diclofenac are the most frequently researched in previous studies (Bendz et al. 2005; Kim et al. 2007; Kim et al. 2009; Agunbiade and Moodley 2014; Olaitan et al. 2014; Zhou and Broodbank 2014; Xie et al. 2015; Ma et al. 2016; Ma et al. 2017). The concentrations of these chemicals were nearly the same as or lower than those reported in previously published studies.
3.5 Removal efficiency of STPs
Table 4 shows the PPCP concentrations at each process step in the six investigated STPs. The removal rates of the macrolide antibiotics, i.e., clarithromycin, 14-hydroxyclarithromycin, and erythromycin, were approximately 24–53% (35% on average), 18–57% (36% on average), and − 59–84% (− 10% on average), respectively. The concentration of erythromycin in the effluent of F STP was below the MQL. As mentioned above, all effluent and influent STP samples analyzed in this study were composite samples used to determine the average variability of pollution load throughout the day. However, when preparing composite samples, sampling of both influent and effluent fractions starts simultaneously. In typical STPs, there is a time lag of 6–8 h even only for a reactor in which conventional activated-sludge treatment is conducted (Japan Sewage Works Association 2013). Therefore, even for composite samples, the gap due to time lag cannot be compensated totally.
Table 4
Concentrations of the pharmaceuticals and personal care products (PPCPs) at each process in the six sewage treatment plants (STPs).
Chemical STPs | clarithro mycin | 14-hydroxy clarithro mycin | erythro mycin | trimetho prim | diclo fenac | 5-hydroxy diclo fenac | sulpiride | carbama zepine | 2-hydroxy carbama zepine | 3-hydroxy carbama zepine | carbamazepine 10,11 epoxide | fexo fenadine | epina stine | ketotifen | diphen hydra mine | diphenyl sulfone |
A ozonized water | 5.4 | 8.2 | N.D.a | N.D. | N.D. | 39 | 140 | (0.23) | N.D. | 4.9 | 28 | 770 | 82 | N.D. | 18 | 77 |
A effluent | 540 | 540 | 59 | 120 | 180 | 110 | 1300 | 91 | 61 | 63 | 57 | 2700 | 210 | N.D. | 340 | 110 |
A influent | 730 | 850 | 40 | 210 | 250 | 220 | 1600 | 81 | 48 | 50 | 33 | 4000 | 310 | N.D. | 1000 | 130 |
Removal rate by ozone (%) | 99% | 98% | 100% | 100% | 100% | 64% | 89% | 100% | 100% | 92% | 50% | 71% | 61% | ― | 95% | 30% |
Removal rate (%) | 26% | 36% | -49% | 43% | 28% | 50% | 19% | -12% | -26% | -26% | -73% | 33% | 32% | ― | 66% | 15% |
B effluent | 740 | 840 | 31 | 150 | 210 | 190 | 1400 | 120 | 86 | 85 | 76 | 2900 | 290 | N.D. | 460 | 110 |
B influent | 980 | 1100 | 31 | 240 | 230 | 230 | 1600 | 97 | 67 | 62 | 50 | 3500 | 350 | 0.86 | 1000 | 110 |
Removal rate (%) | 24% | 24% | -1% | 38% | 9% | 17% | 13% | -24% | -28% | -38% | -51% | 17% | 17% | 100% | 54% | 0% |
C effluent | 620 | 770 | 67 | 120 | 160 | 160 | 1400 | 85 | 72 | 73 | 64 | 3900 | 220 | (0.38) | 270 | 120 |
C influent | 840 | 940 | 42 | 150 | 200 | 230 | 1400 | 84 | 66 | 64 | 51 | 4300 | 270 | 0.65 | 890 | 150 |
Removal rate (%) | 26% | 18% | -59% | 20% | 20% | 30% | 0% | -1% | -10% | -14% | -25% | 9% | 19% | 41% | 70% | 20% |
D effluent | 390 | 420 | 23 | 75 | 180 | 140 | 1200 | 89 | 66 | 77 | 64 | 1800 | 240 | N.D. | 280 | 140 |
D influent | 750 | 970 | 23 | 210 | 210 | 220 | 1200 | 69 | 64 | 62 | 54 | 3700 | 340 | 2.2 | 970 | 160 |
Removal rate (%) | 48% | 57% | -1% | 64% | 14% | 37% | 0% | -30% | -3% | -24% | -18% | 51% | 29% | 100% | 71% | 13% |
E effluent | 510 | 630 | 76 | 110 | 150 | 140 | 1100 | 78 | 53 | 55 | 47 | 2800 | 220 | 1.6 | 220 | 120 |
E influent | 790 | 910 | 58 | 170 | 170 | 180 | 1200 | 77 | 53 | 44 | 33 | 3600 | 310 | 1.2 | 860 | 150 |
Removal rate (%) | 35% | 31% | -31% | 35% | 12% | 22% | 8% | -2% | 0% | -25% | -45% | 22% | 29% | -38% | 74% | 20% |
F effluent | 520 | 670 | (7.6) | 100 | 84 | 180 | 1100 | 71 | 57 | 60 | 47 | 5700 | 480 | 1.2 | 220 | 160 |
F influent | 1100 | 1300 | 46 | 170 | 200 | 230 | 1100 | 56 | 47 | 47 | 32 | 9500 | 800 | N.D. | 280 | 180 |
Removal rate (%) | 53% | 48% | 84% | 41% | 58% | 22% | 0% | -27% | -20% | -28% | -49% | 40% | 40% | ― | 21% | 11% |
Method Detection Limit (MDL) | 0.8 | 0.2 | 3.3 | 3.1 | 1.2 | 2.0 | 1.2 | 0.1 | 0.4 | 0.2 | 1.1 | 1.7 | 1.3 | 0.20 | 1.9 | 1.9 |
Method Quantification Limit (MQL) | 2.2 | 0.7 | 8.7 | 8.2 | 3.3 | 5.2 | 3.3 | 0.2 | 0.9 | 0.6 | 3.0 | 4.6 | 3.3 | 0.53 | 5.1 | 5.0 |
Average removal rate (%) | 35% | 36% | -10% | 40% | 24% | 30% | 7% | -16% | -15% | -26% | -43% | 29% | 28% | 51% | 59% | 13% |
LogKow | 3.18 | 1.64 | 2.48 | 0.73 | 4.51 | 3.18 | 0.65 | 2.25 | 1.42 | 1.42 | 0.95 | 2.81 | 2.54 | 3.85 | 3.11 | 2.61 |
Max removal rate (%) | 53% | 57% | 84% | 64% | 58% | 50% | 19% | -1% | 0% | -14% | -18% | 51% | 40% | 100% | 74% | 20% |
Min removal rate (%) | 24% | 18% | -59% | 20% | 9% | 17% | 0% | -30% | -28% | -38% | -73% | 9% | 17% | -38% | 21% | 0% |
Chemical STPs | telmi sartan | irbesartan | olme sartan | valsartan | losartan | cande sartan | crotami ton | DEETb | TEPc | TCEPd | TCPPe | TDCPPf | TPhPg | TBP | TBOEP | TCP |
A ozonized water | 530 | 210 | (1.8) | 130 | N.D. | 110 | (4.0) | 44 | 21 | 230 | 630 | 130 | 15 | 53 | 200 | 2.1 |
A effluent | 1800 | 470 | 670 | 330 | 76 | 380 | 2000 | 63 | 23 | 230 | 590 | 120 | 14 | 43 | 320 | 2.6 |
A influent | 2100 | 580 | 780 | 2600 | 230 | 340 | 1600 | 300 | 28 | 180 | 870 | 200 | 46 | 69 | 1200 | 13 |
Removal rate by ozone (%) | 71% | 55% | 100% | 61% | 100% | 71% | 100% | 30% | 5% | 0% | -7% | -8% | -6% | -23% | 38% | 18% |
Removal rate (%) | 14% | 19% | 14% | 87% | 67% | -12% | -25% | 79% | 21% | -27% | 32% | 40% | 69% | 38% | 73% | 80% |
B effluent | 1900 | 680 | 780 | 870 | 170 | 350 | 1800 | 51 | 22 | 160 | 620 | 120 | 12 | 35 | 490 | 2.6 |
B influent | 2600 | 700 | 740 | 3300 | 260 | 300 | 1600 | 670 | 24 | 150 | 680 | 130 | 39 | 54 | 1200 | 11 |
Removal rate (%) | 27% | 3% | -5% | 74% | 35% | -17% | -13% | 92% | 6% | -7% | 9% | 8% | 100% | 35% | 59% | 76% |
C effluent | 2000 | 600 | 530 | 180 | 160 | 410 | 2000 | 50 | 23 | 140 | 690 | 120 | 29 | 53 | 200 | 2.5 |
C influent | 1700 | 490 | 530 | 3000 | 250 | 360 | 2100 | 410 | 34 | 330 | 650 | 87 | 46 | 59 | 1100 | 7.9 |
Removal rate (%) | -18% | -22% | 0% | 94% | 36% | -14% | 5% | 88% | 33% | 58% | -6% | -38% | 36% | 10% | 82% | 68% |
D effluent | 1800 | 700 | 600 | 140 | 35 | 370 | 1800 | 48 | 27 | 150 | 570 | 100 | 9.3 | 19 | 200 | 2.9 |
D influent | 1900 | 710 | 590 | 4700 | 180 | 310 | 1400 | 400 | 22 | 120 | 410 | 120 | 32 | 54 | 1600 | 16 |
Removal rate (%) | 5% | 1% | -2% | 97% | 81% | -19% | -29% | 88% | -22% | -25% | -39% | 17% | 71% | 64% | 88% | 81% |
E effluent | 1400 | 410 | 560 | 210 | 130 | 300 | 1400 | 36 | 18 | 140 | 420 | 94 | 14 | 38 | 320 | 2.5 |
E influent | 1600 | 450 | 530 | 2300 | 220 | 250 | 1500 | 430 | 23 | 110 | 430 | 92 | 39 | 48 | 2000 | 17 |
Removal rate (%) | 13% | 9% | -6% | 91% | 41% | -20% | 7% | 92% | 23% | -27% | 2% | -2% | 63% | 22% | 84% | 86% |
F effluent | 1400 | 600 | 730 | 73 | 71 | 220 | 1900 | 25 | 22 | 230 | 500 | 94 | 33 | 24 | 550 | 4.3 |
F influent | 1800 | 590 | 730 | 2100 | 250 | 220 | 2000 | 240 | 27 | 120 | 570 | 130 | 44 | 54 | 1200 | 11 |
Removal rate (%) | 22% | -2% | 0% | 97% | 71% | 0% | 5% | 90% | 19% | -92% | 12% | 27% | 25% | 56% | 54% | 61% |
Method Detection Limit (MDL) | 2.1 | 0.19 | 1.4 | 3.1 | 0.15 | 2.5 | 2.5 | 2.2 | 0.42 | 5.4 | 4.1 | 0.89 | 0.86 | 0.23 | 2.6 | 0.27 |
Method Quantification Limit (MQL) | 5.6 | 0.51 | 3.7 | 8.1 | 0.40 | 6.6 | 6.7 | 5.9 | 1.1 | 14 | 11 | 2.4 | 2.3 | 0.61 | 6.8 | 0.71 |
Average removal rate (%) | 11% | 1% | 0% | 90% | 55% | -14% | -8% | 88% | 13% | -20% | 2% | 9% | 61% | 38% | 73% | 75% |
LogKow | 8.42 | 5.31 | 3.63 | 3.65 | 4.01 | 4.79 | 2.73 | 2.26 | 0.87 | 1.63 | 2.89 | 3.65 | 4.7 | 3.82 | 3.0 | 6.34 |
Max removal rate (%) | 27% | 19% | 14% | 97% | 81% | 0% | 7% | 92% | 33% | 58% | 32% | 40% | 100% | 64% | 88% | 86% |
Min removal rate (%) | -18% | -22% | -6% | 74% | 35% | -20% | -29% | 79% | -22% | -92% | -39% | -38% | 25% | 10% | 54% | 61% |
a: not detected, b: N,N-diethyl-m-toluamide, c: triethyl phosphate, d: tris(2-chloroethyl) phosphate, e: tris(2-chloroisopropyl) phosphate, f: tris(1,3-dichloro-2-propyl) phosphate, g: triphenyl phosphate. |
Anti-hypertensive agents (telmisartan, irbesartan, olmesartan, valsartan, losartan, and candesartan) presented a wide range of average removal rates (from − 14% for candesartan to 90% for valsartan). High removal rates for valsartan have been reported in multiple studies; for example, the removal rate was reported to be 90% by Archer et al. (2017) and approximately 75% by Kasprzyk-Hordern et al. (2009). Carbamazepine and its metabolites (2-hydroxycarbamazepine, 3-hydroxycarbamazepine, and carbamazepine-10,11-epoxide) were scarcely removed, and this trend was also reported by Jelić et al. (2011). The overall concentrations of chemicals were greatly reduced by ozone treatment in STP A. In terms of PFRs, triphenyl phosphate (TPhP), TBOEP, and tricresyl phosphate (TCP) were relatively well removed (average removal rates of 61%, 73%, and 75%, respectively). In addition, the ratio of PFRs subjected to biodegradation removal by sewage treatment was almost negligible. For example, the removal rate of triethyl phosphate (TEP) calculated by the EPI suite and attributed to biodegradation was 0.09%, while the total removal rate was 1.87%. Similarly, a TPhP removal rate of 0.56% was attributed to biodegradation, while the total removal rate was 60.71%. The correlation factor between removal rates and octanol-water partition coefficient (log Kow) of PFRs was 0.6989. In contrast, the removal rates obtained by ozonation ranged from − 23% for tributyl phosphate (TBP) to 38% for TBOEP, with an overall low value for PFRs. The removal of hydrophobic chemicals, such as TBOEP and TBP, was nearly negligible, including that by ozonation. Among PFRs, tris(2-chloroethyl) phosphate (TCEP), tris(1,3-dichloro-2-propyl) phosphate (TDCPP), and tris(2-chloroisopropyl) phosphate (TCPP) were particularly unsusceptible to ozonation (removal rates < 5%); however, their concentrations were found to be reduced by advanced oxidation processes (AOPs; UV/H2O2 treatment) (Yuan et al. 2015). Watts and Linden (2009) determined the second-order rates of reactions of four PFRs (TBOEP, TBP, TCEP, and TCPP) with ultraviolet and ozone-generated •OH in water. Among them, TBOEP was the fastest to react with •OH (kOH = 1.03 × 1010 M− 1 s− 1), followed by TCPP, TCEP, and TBP (6.40 × 109, 5.60 × 108, and 1.98 × 108 M− 1 s− 1, respectively). Yuan et al. (2015) reported the energy consumption for the degradation of PFRs from municipal secondary effluents by ozone and UV/H2O2 treatment. They estimated the total cost of the ozone and UV/H2O2 treatments (reaction time: 10 min) to be 0.344 and 0.279 € m-3, respectively. Therefore, the AOP method can be used to regulate PFR emissions effectively.
3.6 Mass balance of chemicals in the Tamagawa River in Tokyo
Figure 2 shows the PPCP loads measured at each sampling point along the Tamagawa River. Six PPCPs exceeded their PNEC at one sampling point at least, and their respective loads were calculated. The load of each sampling point was calculated by multiplying the concentration and the flow rate at that point, whereas the cumulative load indicates the accumulated load of the tributary streams and STPs, starting from Nagata Bridge, which is the most upstream point in this study. When the load of a chemical at a point on the Tamagawa River (Hino, Sekido, or Tamagawara bridges) coincided with the cumulative one, the chemical was considered to flow downstream without degrading, volatilizing, or getting adsorbed on the riverbed. For all chemicals, except diclofenac, the measured load at each point on the Tamagawa River coincided with the cumulative one to a certain extent. The measured loads of diclofenac at Hino, Sekido, and Tamagawara bridges were significantly lower than its cumulative load at each point; the ratios of the measured and cumulative loads at Hino, Sekido, and Tamagawara bridges were 0.33, 0.48, and 0.42, respectively. Since diclofenac is reported to photodegrade in water environments (Buser et al. 1998; Bartels and Tümpling Jr. 2007), we assumed that it photodegraded while flowing down the river.