Spatial characteristics of PAHs concentration in surface sediments
The total and individual concentrations of PAHs in surface sediments collected from the different locations of Taihu Lake were shown in Table 1. 16 kinds of PAH were detected in the surface sediments of Lake Taihu in this study, with concentrations ranging between 1381.48~4682.16 ng g−1. There were obvious differences in the concentration of 16 PAHs. The values of DahA and IcdP were below the detection limit in some samples, while the concentrations of BghiP in each sample were higher. Ace had the lowest contents in each sample. The concentrations of PAHs in ZB were higher than those in other regions, and the concentrations of pollutants in the central area of the lake were the lowest. Compared with those in 2000 and 2010, the concentrations of PAHs had a clear upward trend16,17.
Table 1
The concentration of PAHs at different sampling points in Taihu Lake
Sample points
|
Nap
|
Acy
|
Ace
|
Flu
|
Phe
|
Ant
|
Flua
|
Pyr
|
BaA
|
Chry
|
BbF
|
BkF
|
BaP
|
DahA
|
IcdP
|
BghiP
|
∑16PAHs
|
Rings
|
2
|
3
|
3
|
3
|
3
|
3
|
4
|
4
|
4
|
4
|
5
|
5
|
5
|
5
|
6
|
6
|
-
|
|
ng g−1 (dry weight)
|
LC
|
C1
|
9.01
|
26.16
|
7.02
|
53.60
|
100.23
|
120.97
|
171.92
|
174.31
|
271.24
|
208.48
|
271.96
|
313.52
|
161.60
|
ND
|
ND
|
385.14
|
2275.17
|
C2
|
0.00
|
39.41
|
2.73
|
77.40
|
138.22
|
179.25
|
234.03
|
242.45
|
399.80
|
295.11
|
390.23
|
ND
|
235.24
|
ND
|
ND
|
ND
|
2233.86
|
C3
|
0.00
|
38.76
|
ND
|
77.66
|
139.05
|
177.84
|
243.72
|
249.01
|
402.08
|
301.25
|
383.14
|
ND
|
237.29
|
ND
|
ND
|
570.52
|
2820.32
|
C4
|
0.00
|
27.24
|
1.45
|
55.67
|
106.26
|
118.00
|
177.71
|
174.67
|
272.19
|
209.09
|
273.82
|
ND
|
ND
|
ND
|
ND
|
380.90
|
1797.00
|
C5
|
0.00
|
26.80
|
0.68
|
55.12
|
106.58
|
122.71
|
174.78
|
173.25
|
272.95
|
207.19
|
ND
|
ND
|
154.25
|
ND
|
ND
|
380.64
|
1674.96
|
C6
|
0.00
|
38.97
|
1.61
|
79.44
|
145.34
|
178.66
|
245.42
|
247.66
|
403.89
|
304.31
|
387.51
|
463.70
|
ND
|
ND
|
ND
|
ND
|
2496.52
|
C7
|
0.00
|
25.92
|
0.00
|
52.16
|
93.48
|
120.74
|
157.06
|
160.91
|
266.33
|
198.53
|
ND
|
306.35
|
ND
|
ND
|
ND
|
ND
|
1381.48
|
C8
|
0.00
|
26.68
|
0.00
|
54.67
|
96.57
|
158.51
|
178.52
|
174.56
|
272.23
|
210.04
|
285.00
|
309.99
|
156.51
|
ND
|
ND
|
378.26
|
2301.53
|
C9
|
0.00
|
ND
|
0.03
|
77.18
|
138.89
|
184.07
|
239.46
|
248.21
|
406.00
|
299.65
|
ND
|
ND
|
233.75
|
ND
|
ND
|
567.37
|
2394.61
|
C10
|
69.74
|
28.90
|
1.37
|
56.58
|
103.12
|
130.86
|
177.26
|
176.21
|
274.86
|
210.62
|
267.49
|
ND
|
ND
|
ND
|
ND
|
384.20
|
1881.19
|
ETA
|
E1
|
0.00
|
26.30
|
6.54
|
54.13
|
98.60
|
187.68
|
181.79
|
176.67
|
276.72
|
211.70
|
277.20
|
309.48
|
164.10
|
ND
|
ND
|
393.96
|
2364.86
|
E2
|
0.00
|
25.99
|
ND
|
53.58
|
103.32
|
176.03
|
186.92
|
180.44
|
276.39
|
ND
|
272.36
|
ND
|
156.58
|
ND
|
ND
|
381.25
|
1812.86
|
E3
|
0.05
|
26.08
|
ND
|
53.91
|
100.17
|
151.70
|
188.31
|
189.15
|
277.62
|
198.29
|
260.77
|
304.49
|
175.86
|
ND
|
ND
|
386.80
|
2313.22
|
E4
|
0.00
|
26.29
|
2.18
|
56.59
|
107.06
|
184.51
|
185.69
|
179.53
|
274.74
|
203.58
|
270.34
|
313.25
|
160.22
|
ND
|
ND
|
378.93
|
2342.93
|
E5
|
0.00
|
27.78
|
0.07
|
64.55
|
147.87
|
218.04
|
205.36
|
200.14
|
289.71
|
227.57
|
318.54
|
310.26
|
176.81
|
ND
|
648.89
|
413.54
|
2600.24
|
E6
|
0.00
|
27.07
|
ND
|
55.47
|
102.11
|
142.38
|
170.14
|
167.73
|
271.69
|
191.22
|
263.80
|
ND
|
ND
|
ND
|
ND
|
ND
|
1391.63
|
E7
|
10.98
|
32.81
|
5.17
|
65.62
|
140.49
|
174.12
|
247.72
|
239.08
|
314.24
|
264.44
|
345.82
|
302.68
|
262.66
|
549.66
|
646.07
|
478.18
|
4082.56
|
E8
|
0.00
|
40.86
|
1.82
|
85.31
|
163.16
|
245.64
|
266.84
|
264.57
|
413.63
|
306.67
|
396.91
|
452.88
|
259.32
|
ND
|
ND
|
573.25
|
3470.87
|
E9
|
48.99
|
31.02
|
3.14
|
69.25
|
175.53
|
222.23
|
289.06
|
255.16
|
305.16
|
277.12
|
307.12
|
320.41
|
197.01
|
ND
|
ND
|
436.08
|
3583.36
|
E10
|
0.00
|
25.66
|
ND
|
52.95
|
94.61
|
161.53
|
160.26
|
165.29
|
269.71
|
199.09
|
259.89
|
309.53
|
ND
|
ND
|
ND
|
ND
|
1698.52
|
E11
|
0.00
|
26.38
|
ND
|
52.61
|
93.90
|
145.41
|
176.78
|
173.06
|
273.78
|
198.93
|
281.31
|
315.80
|
158.90
|
ND
|
ND
|
382.49
|
2279.35
|
GB
|
G1
|
0.32
|
26.09
|
0.00
|
50.90
|
94.20
|
122.31
|
164.99
|
167.56
|
272.23
|
191.65
|
262.08
|
ND
|
158.39
|
ND
|
ND
|
378.04
|
1888.75
|
G2
|
0.00
|
25.67
|
0.00
|
53.28
|
117.15
|
125.16
|
183.29
|
181.58
|
276.82
|
209.93
|
270.96
|
305.16
|
157.18
|
ND
|
ND
|
384.10
|
2290.29
|
G3
|
25.74
|
27.63
|
3.69
|
57.67
|
115.80
|
128.13
|
221.14
|
207.84
|
288.55
|
233.93
|
300.87
|
314.77
|
169.85
|
ND
|
ND
|
425.43
|
2521.02
|
G4
|
11.38
|
41.99
|
2.67
|
81.26
|
152.52
|
189.97
|
299.67
|
292.49
|
427.29
|
334.47
|
418.40
|
456.97
|
238.74
|
ND
|
ND
|
600.29
|
3548.12
|
G5
|
0.00
|
25.88
|
0.86
|
53.46
|
106.83
|
123.81
|
165.50
|
166.17
|
269.50
|
200.80
|
270.20
|
ND
|
155.49
|
ND
|
ND
|
ND
|
1538.49
|
G6
|
0.00
|
38.60
|
ND
|
75.82
|
131.65
|
178.14
|
225.79
|
234.44
|
399.03
|
287.63
|
388.18
|
ND
|
230.13
|
ND
|
ND
|
ND
|
2189.40
|
MB
|
M1
|
42.47
|
ND
|
2.56
|
80.96
|
144.62
|
182.77
|
249.23
|
251.49
|
406.63
|
306.66
|
404.14
|
444.51
|
252.18
|
ND
|
622.55
|
570.21
|
3338.42
|
M2
|
71.41
|
ND
|
2.30
|
60.05
|
121.38
|
142.02
|
203.12
|
195.60
|
283.51
|
214.22
|
ND
|
319.36
|
162.39
|
ND
|
ND
|
392.40
|
2167.76
|
M3
|
69.78
|
31.20
|
4.67
|
64.22
|
187.56
|
156.75
|
365.56
|
335.70
|
375.83
|
324.39
|
328.47
|
338.64
|
257.65
|
550.53
|
ND
|
459.87
|
4473.36
|
M4
|
21.42
|
25.88
|
5.06
|
56.74
|
109.32
|
124.29
|
159.73
|
164.31
|
269.94
|
199.14
|
257.21
|
302.91
|
153.66
|
ND
|
ND
|
ND
|
1849.61
|
M5
|
7.27
|
41.05
|
0.16
|
81.07
|
149.12
|
184.10
|
263.18
|
270.94
|
416.91
|
312.56
|
ND
|
ND
|
ND
|
ND
|
ND
|
569.36
|
2295.72
|
M6
|
0.00
|
38.53
|
4.15
|
78.29
|
139.17
|
177.86
|
240.92
|
251.80
|
410.17
|
299.46
|
ND
|
451.71
|
242.09
|
ND
|
ND
|
ND
|
2334.15
|
M7
|
49.39
|
29.59
|
4.15
|
64.29
|
144.29
|
142.51
|
236.37
|
223.03
|
302.92
|
242.52
|
317.38
|
308.15
|
183.74
|
ND
|
ND
|
419.88
|
2668.19
|
M8
|
0.00
|
38.85
|
ND
|
78.67
|
156.97
|
186.38
|
299.80
|
298.40
|
437.93
|
332.15
|
443.84
|
468.33
|
250.84
|
ND
|
ND
|
615.11
|
3607.27
|
M9
|
0.00
|
26.85
|
1.54
|
57.54
|
114.45
|
134.38
|
204.27
|
200.42
|
288.68
|
226.21
|
280.05
|
314.10
|
165.31
|
ND
|
ND
|
416.82
|
2430.63
|
M10
|
16.19
|
26.60
|
ND
|
54.53
|
102.36
|
127.17
|
177.27
|
174.80
|
274.88
|
205.07
|
262.19
|
ND
|
ND
|
ND
|
ND
|
384.85
|
1805.90
|
M11
|
0.00
|
38.92
|
8.44
|
77.20
|
136.29
|
181.26
|
242.95
|
247.37
|
406.50
|
299.80
|
ND
|
448.16
|
ND
|
ND
|
ND
|
ND
|
2086.90
|
STA
|
S1
|
0.00
|
27.28
|
3.40
|
53.30
|
97.36
|
163.02
|
167.68
|
169.49
|
270.00
|
205.80
|
264.17
|
306.54
|
ND
|
ND
|
ND
|
379.59
|
2107.63
|
S2
|
0.00
|
38.75
|
0.00
|
76.53
|
143.56
|
177.52
|
252.47
|
259.07
|
409.71
|
305.27
|
426.65
|
ND
|
ND
|
ND
|
ND
|
591.93
|
2681.47
|
S3
|
18.90
|
38.44
|
2.21
|
76.53
|
138.35
|
176.07
|
232.58
|
241.23
|
399.27
|
294.42
|
ND
|
ND
|
233.03
|
ND
|
621.3
|
ND
|
1851.03
|
S4
|
63.37
|
27.67
|
5.62
|
60.96
|
121.27
|
124.51
|
182.80
|
180.50
|
273.57
|
216.96
|
282.45
|
304.02
|
154.90
|
ND
|
ND
|
380.74
|
2379.35
|
WTA
|
W1
|
78.15
|
ND
|
6.57
|
65.42
|
146.75
|
141.95
|
248.17
|
234.96
|
305.03
|
247.55
|
289.74
|
326.22
|
-
|
ND
|
ND
|
449.36
|
3161.19
|
W2
|
0.00
|
29.14
|
4.23
|
62.77
|
133.21
|
152.42
|
209.60
|
210.30
|
290.97
|
224.43
|
289.14
|
308.11
|
199.40
|
ND
|
ND
|
419.14
|
2532.88
|
W3
|
49.50
|
27.76
|
1.95
|
58.77
|
110.91
|
123.05
|
174.66
|
168.76
|
272.97
|
186.93
|
285.68
|
301.34
|
-
|
ND
|
ND
|
378.61
|
2140.89
|
W4
|
31.27
|
25.72
|
3.20
|
62.90
|
114.37
|
130.26
|
174.95
|
177.06
|
274.52
|
206.78
|
ND
|
ND
|
-
|
ND
|
ND
|
388.30
|
1589.34
|
ZB
|
Z1
|
63.10
|
28.98
|
5.23
|
63.38
|
135.29
|
146.74
|
198.30
|
198.06
|
285.57
|
220.16
|
276.24
|
ND
|
183.60
|
ND
|
701.81
|
415.71
|
2220.36
|
Z2
|
41.89
|
42.18
|
0.00
|
93.48
|
184.75
|
204.60
|
280.61
|
289.34
|
419.03
|
317.72
|
412.27
|
463.39
|
240.43
|
ND
|
ND
|
611.22
|
3600.90
|
Z3
|
94.80
|
32.33
|
9.95
|
68.93
|
182.79
|
171.18
|
293.40
|
286.80
|
328.45
|
289.14
|
283.37
|
329.59
|
194.13
|
551.50
|
913.86
|
440.92
|
4259.07
|
Z4
|
44.42
|
46.39
|
6.40
|
92.44
|
212.31
|
237.40
|
328.17
|
349.91
|
439.20
|
355.34
|
ND
|
448.49
|
298.08
|
ND
|
ND
|
ND
|
2858.56
|
Z5
|
38.96
|
30.18
|
4.00
|
68.39
|
143.42
|
164.95
|
325.77
|
322.39
|
416.24
|
387.20
|
503.08
|
415.11
|
360.92
|
ND
|
ND
|
587.68
|
4682.16
|
Z6
|
1.35
|
41.34
|
0.00
|
83.01
|
159.48
|
212.66
|
281.45
|
285.59
|
426.33
|
331.13
|
406.85
|
476.68
|
259.13
|
ND
|
ND
|
613.56
|
3578.55
|
Note: ND expresses the sample concentration below the detection limit; LC, ETA, GB, MB, STA, WTA, and ZB represents the different lake areas i.e., Lake Center, East Taihu area, Gonghu Bay, Meiliang Bay, South Taihu area, West Taihu area and Zhushan Bay, respectively. |
In the past 5 years, related researches on the average concentrations of ∑16PAHs worldwide had been aggregated in this study (Fig. 2). Many studies compared the concentration of ∑16PAHs in the surface sediments in China25,27−29. The values of ∑16PAHs in Mediterranean Ports30, Maba River31, Indian Sundarbans32, Forcados Rivers, and Niger Rivers33 were higher than 10000 ng g−1. It was worth pointing out that average values in the sediments from Douro River estuary and Porto Atlantic coast (Portugal) were as high as 65500 ng g−134, which could induce aquatic metabolism disorders and promote unpredictable effects on humans healthy. The concentration of ∑16PAHs in Taihu Lake was at an upper-middle level in this study. |
Occurrence and compositions of PAHs in different lake areas
The values of ∑16PAHs in different regions were calculated, and the proportions of different monomers of PAHs were analyzed. Figure 3 showed that the concentration of ∑16PAHs in the ZB lake area was much higher than in the other regions, and the same research results have appeared many times in previous studies35,36. The sources of agricultural, industrial, and domestic sewage in the surrounding watershed of ZB were higher than the other locations37, resulting in higher PAHs concentrations than other areas. The concentration in the north of Taihu Lake was higher than that in the south, and the surrounding concentration was higher than the central region, which mainly depended on the anthropogenic activities, i.e., industrial and agricultural development around the area38. The 4-ring PAHs were dominant, accounting for 35.69%~45.02%. A previous Suzhou Industrial Park study pointed out that medium-molecular-weight PAHs (4-ring) were predominant in stream sediments39, but in this study, the top 4 regions with higher average PAHs concentrations (ZB, MB, ETA, WTA) showed high-molecular-weight PAHs (5~6-ring) were dominant. The low-molecular-weight (2~3-ring) PAHs were mainly derived from the release and combustion of petroleum emissions, and medium to high-molecular-weight (4~6 rings) PAHs were mainly derived from pyrolysis40, of which 5 and 6 rings were sources from anthropogenic pyrolysis41,42, which preliminarily proved the main source of the study area in Taihu La
Source appointment of PAHs in the sediments and influencing factors
The sources of PAHs could be identified based on the molecular diagnostic ratio of PAH in the samples43,44. The proportion of PAH monomer was calculated in this study (Fig. 4). The ratios of Ant/(Ant+Phe) in most sediment samples from Lake Taihu were greater than 0.10, while in ZB was less than 0.10. The same phenomenon appeared in the BaA/(BaA+Chr) ratios, in addition to ZB, ratios were greater than 0.35, indicating that except for ZB, where was the petroleum source, the main sources of PAHs in other regions from Taihu Lake were combustion. The values of Flua/(Flua+Pyr) were mainly greater than 0.50, and the values of LC and STA were between 0.40 and 0.50, which represented the PAHs in LC and STA came from liquid fossil fuels (vehicles and crude oil). IcdP/(IcdP+BghiP) of ETA and WTA between 0.20 and 0.50, which meant the burning of liquid fossil fuels43,45. Based on the above results, it was further derived the PAHs in ZB mainly were the petroleum source, the main sources of GB and MB were the burning of grass, wood and coal, while PAHs in other areas of Taihu Lake were the combustion of liquid fossil fuels, which was consistent with the previous studies46,47.
To further determine the source of PAHs, PCA was selected as an effective identification tool. Figure 5 illustrated the score plot of the first two components (PC) of PAHs in surface sediments of Taihu Lake, accounting for 96.8% of the variance. PC1 was responsible for 92.5% of the total variance and exhibited high loading for BghiP, BaA, BbF, Chry, BkF, Flua, and Pyr (4.43, 3.85, 2.30, 2.06, 1.66, 1.41, and 1.40). PC2 was responsible for 4.3% of the total variance, and mostly due to IcdP, BghiP, and DahA (1.56, 0.47, and 0.15). It has been proved in previous studies, BghiP, BkF, and IcdP were derived from vehicle exhaust, BaA and Chry were the products of petroleum combustion, BbF was a product of the high-temperature combustion, and Flua and Pyr came from coal-burning48–50. To further derive, the main sources of PAHs in the surface sediments from Taihu Lake were the man-made sources, including vehicle exhaust and combustion, which was consistent with the results of PAH molecular diagnostic ratio.
Risk assessment and ecological suggestions
The biological toxicity assessment of PAHs in different sediments from Taihu Lake was compared. It was shown (Table 2) that the concentrations of Nap, Ace, Phe, Flua, Pyr, and BaP in all sampling sites were lower than those of ERL value, which would not cause adverse effects on the environment. The concentrations of Chry, BkF, BbF, and BghiP at some sampling points were higher than ERL value but lower than ERM value, which had little impact on the environment, which was the same as Acy, Flu, Ant, BaA. It was worth noting that both DahA and IcdP were much higher than ERM values, influencing greatly on the ecological community.
Table 2
The biological toxicity assessment form of PAHs in different sediments of Taihu Lake (ng g−1 dw)
PAHs
|
ERL
|
ERM
|
Average concentration in different lake areas
|
Concentration range
|
ZB
|
MB
|
GB
|
ETA
|
STA
|
WTA
|
LC
|
Nap
|
160.00
|
2100.00
|
47.42
|
25.27
|
6.24
|
5.46
|
20.57
|
39.73
|
7.87
|
0.00~94.80
|
Acy
|
16.00
|
500.00
|
36.90
|
27.04
|
30.98
|
28.75
|
33.04
|
20.66
|
27.88
|
NA~46.39
|
Ace
|
44.00
|
640.00
|
4.26
|
3.00
|
1.20
|
1.72
|
2.80
|
3.99
|
1.49
|
NA~9.95
|
Flu
|
19.00
|
540.00
|
78.27
|
68.51
|
62.07
|
60.36
|
66.83
|
62.47
|
63.95
|
50.90~93.48
|
Phe
|
240.00
|
1500.00
|
169.67
|
136.87
|
119.69
|
120.62
|
125.14
|
126.31
|
116.77
|
93.48~212.31
|
Ant
|
85.30
|
1100.00
|
189.59
|
158.14
|
144.59
|
182.66
|
160.28
|
136.92
|
149.16
|
118.00~245.64
|
Flua
|
600.00
|
5100.00
|
284.62
|
240.21
|
210.06
|
205.35
|
208.88
|
201.85
|
199.99
|
157.06~365.56
|
Pyr
|
665.00
|
2500.00
|
288.68
|
237.62
|
208.35
|
199.17
|
212.57
|
197.99
|
202.12
|
160.91~349.91
|
BaA
|
261.00
|
1600.00
|
385.80
|
352.17
|
322.24
|
294.85
|
338.14
|
285.87
|
324.16
|
266.33~439.20
|
Chry
|
384.00
|
2800.00
|
316.78
|
269.29
|
243.06
|
207.15
|
255.61
|
216.42
|
244.43
|
NA~387.20
|
BkF
|
280.00
|
1620.00
|
355.54
|
308.72
|
179.48
|
267.16
|
152.64
|
233.92
|
139.36
|
NA~503.08
|
BbF
|
320.00
|
1880.00
|
313.63
|
208.48
|
318.45
|
295.82
|
243.31
|
216.14
|
225.91
|
NA~ 476.68
|
BaP
|
430.00
|
1600.00
|
256.05
|
151.62
|
184.96
|
155.59
|
96.98
|
49.85
|
117.86
|
NA~ 360.92
|
DahA
|
63.40
|
260.00
|
91.92
|
50.05
|
NA
|
19.97
|
NA
|
NA
|
NA
|
NA~ 551.50
|
IcdP
|
-
|
-
|
269.28
|
56.60
|
NA
|
117.72
|
NA
|
155.32
|
NA
|
NA~ 913.86
|
BghiP
|
430.00
|
1600.00
|
444.85
|
348.05
|
297.97
|
347.68
|
338.07
|
408.85
|
304.70
|
NA~ 615.11
|
Note: ZB, MB, ETA, WTA, GB, STA, and LC represent the Zhushan Bay, Meiliang Bay, East Taihu area, West Taihu area Gonghu Bay, South Taihu area, and Lake Center, respectively. |
Due to the high carcinogenicity of DahA and IcdP51,52, the carcinogenic risk of DahA and IcdP had been further studied in this study. The BaPE was a useful indicator for quantitative assess the potential carcinogenic risks of PAHs53,54.
The BaPE in this study was calculated through the data of Table 1, and the calculation results were shown in Fig. 6. It could be seen from Fig. 6 that BaPE values for 52 surface sediments samples of Taihu Lake varied from 16.47 to 708.62 ng g−1 dw. The high BaPE levels were noticed at sites E7, M3, Z3, and Z5 indicating that PAHs in these sites showed relatively high toxicity compared to other sites. The PAHs in ZB, MB, and southeast area of Taihu Lake had higher carcinogenic risks, compared with 2012, the risk of PAHs had increased obviously37.