Study area:
Barrackpore (22°76´N and 88°37′E) and Kalyani (22°58′N and 88°26′E), two sub-divisional metropolitan towns of respective districts of North 24Parganas and Nadia have major industrial and agricultural area. Nadia has 79.48% of agricultural area (Matirkatha 2016) whereas Barrackpore is one of the dense industrial areas of West Bengal. Both are situated at the bank of Hooghly River (Ganga River), the water of which is the source of water treatment plants for drinking, agriculture, industrial use and aquaculture (KMDA 2017). Diversified cropping pattern is found in these two areas throughout the year.
Sampling:
River water (RW), pond water (PW) and tubewell water (TW) samples were collected for consecutive 48 weeks to monitor the pesticide residues in the aquatic systems of study area. A total of 144 samples (48 each of river, pond and tube-well water) from each district were collected throughout the year covering winter (November to February), summer (March to June) and monsoon (July to October) seasons. Six different sampling points in river, six different ponds and six different tube-wells were chosen for sampling purposes (Fig. 2). Ponds and tube-wells chosen for sample collection are located within 2–3 km radius under domestic, agricultural and industrial activities. Amber glass bottles (2 liter) with stopper cap were washed with commercial detergent using hot water and rinsed with deionized water and acetone. Bottles were then dried in an oven at 100°C and stored until use for sampling. Samples were collected from a depth of 1 ft from the surface of river and pond water using Kemmerer water sampler and kept in ice box at 40C. A 2.0 % solution of Sodium azide (NaN3) was used for the protection of water samples from microbial growth. Samples were extracted immediately and processed subsequently.
Chemicals and Reagents:
A total of 36 pesticides covering different groups namely insecticides, herbicides, fungicides and acaricides were selected for the present study (Table 1). All certified reference materials (CRMs) were purchased from Dr. Ehrenstorfer GmbH, Augsburg, Germany with purity mostly of > 97%. LC-MS grade dichloromethane (DCM), hexane, acetone and ethylacetate (EA) were obtained from J.T. Baker, Avantor, USA. Analytical grade anhydrous magnesium sulphate, sodium chloride and sodium sulphate were obtained from Rankem, India. Anhydrous magnesium sulphate was heated at 4500C for 5 hours to remove phthalets and then cooled naturally and stored in a desiccator.
Table 1
Parameters recovery experiments of selected pesticides in GC-MS.
Sl. No.
|
Pesticides
|
RTa
|
m/z for confirmation with ion ratio
|
bR2
|
LOQc (ng/ml)
|
Recovery
|
RPDe
|
Target Ion
|
Q1
(% Q1/T)
|
Q2
(% Q2/T)
|
LOQ (SDd)
|
2x LOQ
|
5xLOQ
|
1
|
4-Br 2-Cl- phenol
|
9.01
|
208
|
172 (42.09%)
|
170 (32.58%)
|
0.996
|
0.044
|
110.52 (5.23)
|
91.3
|
92.9
|
4.16
|
2
|
Trifluralin
|
13.69
|
306
|
43 (44.72%)
|
264 (40.28%)
|
0.998
|
0.041
|
97.44 (6.33)
|
85.6
|
101.43
|
4.92
|
3
|
Phorate
|
14.39
|
75
|
121 (50.28%)
|
260 (43.29%)
|
0.997
|
0.02
|
99.31 (9.37)
|
101.56
|
106.23
|
6.83
|
4
|
α-HCH
|
14.67
|
181
|
183 (93.37%)
|
219 (51.04%)
|
0.999
|
0.007
|
113.82 (2.7)
|
90.69
|
82.92
|
12.14
|
5
|
Atrazine
|
15.38
|
200
|
215 (97.23%)
|
58(76.68%)
|
0.998
|
0.048
|
107.43 (10.20)
|
100.64
|
99.54
|
15.09
|
6
|
β-HCH
|
15.6
|
181
|
183 (68.78%)
|
219 (95.78%)
|
0.998
|
0.012
|
83.57 (8.02)
|
105.11
|
99.17
|
18.15
|
7
|
Lindane
|
15.85
|
181
|
183 (96.48%)
|
219(54.23%)
|
0.999
|
0.011
|
77.84 (9.33)
|
106.58
|
107.27
|
14.14
|
8
|
Chlorothalonil
|
16.47
|
266
|
264 (76.28%)
|
268 (50.23%)
|
0.983
|
0.099
|
110.41 (7.02)
|
100.01
|
100.38
|
14.64
|
9
|
δ-HCH
|
16.98
|
181
|
183 (92.49%)
|
219(57.85%)
|
0.995
|
0.005
|
105.04 (5.2)
|
113.65
|
109.16
|
16.59
|
10
|
Dimethachlor
|
17.83
|
134
|
197 (40.23%)
|
77(52.91%)
|
0.993
|
0.056
|
92.12 (11.02)
|
102
|
98.45
|
1.93
|
11
|
Alachlor
|
18.28
|
45
|
160 (42.28%)
|
188 (26.22%)
|
0.999
|
0.05
|
92.57 (8.91)
|
105.35
|
103.43
|
8.93
|
12
|
Parathion-methyl
|
18.38
|
263
|
109 (42.21%)
|
125 (35.23%)
|
0.995
|
0.021
|
85.92 (7.19)
|
106.09
|
97.77
|
4.25
|
13
|
Heptachlor
|
18.79
|
100
|
272 (42.28%)
|
274 (30.56%)
|
0.998
|
0.015
|
111.7 (8.26)
|
113.44
|
101.39
|
8.73
|
14
|
Malathion
|
19.91
|
125
|
127 (65.59%)
|
93(47.54%)
|
0.996
|
0.036
|
86.17 (6.6)
|
109.4
|
104.87
|
15.47
|
15
|
Chlorpyriphos
|
20.23
|
97
|
197 (63.28%)
|
199 (41.56%)
|
0.997
|
0.022
|
96.35 (1.02)
|
109.84
|
105.52
|
13.55
|
16
|
Aldrin
|
20.46
|
66
|
263 (57.63%)
|
91(22.73%)
|
0.999
|
0.017
|
93.45 (5.81)
|
117.22
|
111.11
|
3.52
|
17
|
Pendimethylene
|
21.87
|
252
|
162 (18.93%)
|
181 (20.43%)
|
0.998
|
0.056
|
107.57 (7.19)
|
102.92
|
99.3
|
13.06
|
18
|
Quinalphos
|
22.77
|
146
|
118(65%)
|
156(61%)
|
0.999
|
0.031
|
87.66 (9.63)
|
109.33
|
101.39
|
10.75
|
19
|
Butachlor
|
23.72
|
57
|
176 (68.89%)
|
160 (76.31%)
|
0.999
|
0.014
|
112.24 (10.25)
|
107.75
|
99.62
|
10.98
|
20
|
α- Endosulfan
|
23.96
|
241
|
195 (80.25%)
|
159 (22.91%)
|
0.999
|
0.01
|
113.99 (7.29)
|
111.03
|
106.27
|
14.09
|
21
|
Profenophos
|
24.28
|
337
|
97(68.11%)
|
139 (66.97%)
|
0.998
|
0.016
|
92.47 (9.28)
|
98.43
|
94.16
|
4.04
|
22
|
p,p-DDE
|
25.85
|
246
|
318 (75.76%)
|
248 (54.81%)
|
0.962
|
0.023
|
98.28 (5.27)
|
102.56
|
96.05
|
14.58
|
23
|
o,p-DDD
|
25.85
|
235
|
165(76.43%)
|
237(53.85%)
|
0.993
|
0.018
|
86.67 (7.21)
|
102.47
|
98.51
|
4.33
|
24
|
Ethion
|
27.52
|
231
|
97(60.28%)
|
153 (50.78%)
|
0.997
|
0.017
|
90.2 (9.16)
|
102.7
|
98.72
|
12.62
|
25
|
p,p-DDD
|
27.74
|
235
|
165 (56.28%)
|
237 (32.50%)
|
0.999
|
0.021
|
91.94 (12.09)
|
92.59
|
93.63
|
14.54
|
26
|
Β-Endosulfan
|
27.86
|
241
|
195 (65.23%)
|
159 (40.21%)
|
0.997
|
0.014
|
89.809 (14.20)
|
99.04
|
95.21
|
9.65
|
27
|
p,p-DDT
|
27.87
|
235
|
165(52.28%)
|
237(61.12%)
|
0.996
|
0.015
|
118.15 (6.37)
|
110.78
|
101.28
|
1.85
|
28
|
Endosulfan sulphate
|
29.7
|
272
|
274(53.37%)
|
239(50.21%)
|
0.998
|
0.017
|
84.92 (4.28)
|
100.26
|
96.56
|
14.94
|
29
|
Spiromesifen
|
31.85
|
272
|
99(52.23%)
|
273(36.16%)
|
0.972
|
0.053
|
80.38 (2.98)
|
103.32
|
98.26
|
17.04
|
30
|
Bifenthrin
|
32.97
|
181
|
166(53.27%)
|
165(62.74%)
|
0.986
|
0.039
|
97.25 (7.23)
|
95.94
|
98.42
|
3.15
|
31
|
Fenpropathrin
|
33.53
|
97
|
181 (96.97%)
|
265 (35.12%)
|
0.994
|
0.05
|
83.49 (8.29)
|
102.94
|
103.04
|
13.55
|
32
|
Lamda-cyhalothrin
|
36.22
|
181
|
197(95.70%)
|
208(58.77%)
|
0.996
|
0.087
|
82.47 (7.08)
|
98.43
|
70.67
|
4.53
|
33
|
β-Cyfluthrin
|
41.27
|
163
|
206 (65.23%)
|
226 (54.15%)
|
0.999
|
0.025
|
82.4 (4.09)
|
102.56
|
112.24
|
18.65
|
34
|
Cypermethrin
|
42.22
|
181
|
163 (75.86%)
|
127 (47.59%)
|
0.968
|
0.035
|
111.44 (4.45)
|
102.47
|
113.99
|
7.53
|
35
|
Fenvalerate
|
44.76
|
125
|
167 (57.88%)
|
225 (44.54%)
|
0.994
|
0.044
|
97.75 (5.23)
|
102.7
|
92.48
|
1.46
|
36
|
Deltamethrin
|
47.82
|
181
|
253 (72.62%)
|
77(69.84%)
|
0.996
|
0.041
|
111.37 (6.37)
|
85.36
|
98.29
|
13.43
|
aRT- Retention Time (min.); bR2: Coefficient of regression equation; c LOQ: Limit Of Quantification; dSD: Standard Deviation; eRPD: Relative Percentage Difference.
|
Glassware and Equipments:
Separating Funnel shaker (Yamato Scientific, Japan), vortex mixer (Spinix, Tarson, India), Rotary vacuum evaporator with temperature controlled water bath (HS 2001 NS, Germany), Turbo Vap evaporator (Caliper Life Sciences, Hopkinton, Massachusetts, USA) and 100–1000µL and 1-10mL micropipettes (Eppendorf Research, Germany) were also used for sample preparation. The electronic analytical balance Sartorius GD603 (Sartorius, Germany) with readability = 0.001ct/0.2 mg was used for weighing. All the equipments were calibrated externally with certified agencies. All the glassware viz. conical flask (1000 mL), separating funnel (1000 mL), measuring cylinder (500 ml and 1000 ml) and volumetric flasks (100 mL), graduated tubes (25 mL) were calibrated and purchased from Borosil Glass Works Ltd., Gujarat, India. Membrane filter paper, Ultipor N66, Nylon 6,6 membrane, 13 mm (Pall Life Sciences, USA) and syringe filter (SGE Analytical Science, Australia) were used for filtration process.
Preparation of stock and working standards:
Stock solutions of each CRM were prepared into a 100 ml volumetric flask with hexane:toluene (1:1) solvent mixture. Working standards of different concentration (1,00,000 ngml− 1, 10,000 ngml− 1, 5,000 ngml− 1, 2,500 ngml− 1, 1,000 ngml− 1, 500 ngml− 1, 250 ngml− 1, 100 ngml− 1, 50 ngml− 1, 20 ngml− 1 and 10 ngml− 1) were prepared from the stock solution using dilution technique. All the stock and working solutions of 36 pesticide standards were stored under refrigerated condition (-4oC), protected from sun light.
Sample preparation:
The conventional liquid-liquid extraction (LLE) method was used for water samples using three different solvent mixtures namely S1 (EA:DCM 8:2), S2 (Hexane:DCM 8:2) and S3 (100% DCM) to check and compare the % recovery (Fig. 3). Collected water samples were filtered through whatman glass fibre filter (GF/F, 0.45 mm) to remove suspended particles before extraction. Sample (750 ml) was taken in separatory funnel (1 litre), NaCl (150 g) was added to separatory funnel and mixed properly, extracted thrice with 70, 40 and 40 mL of each solvent mixture (S1, S2 and S3) using separating funnel shaker @ 210 rpm and allowed 15 min to settle down for clear solvent phase separation. Altogether 150 ml (= 70 + 40 + 40) of organic solvent layer was collected in a conical flask after passing over anhydrous Na2SO4. The collected solvent was evaporated to dryness in a rotary vacuum evaporator at 400C and the volume was made up with 5 mL hexane. It was taken in tarbo-vap tube for evaporation to dryness using Turbo Vap LV. The volume was reconstituted in 1 mL acetone. After vortexing for 30s and sonication for 5 min., the acetone was transferred to 2ml vial for Gas Chromatography-Mass Spectrometric (GC-MS) analysis with proper filtration using syringe filter.
Instrumental analysis:
The final extracts were analyzed using GC-MS, QP 2010 Plus (Shimadzu Corp., Kyoto, Japan), with a mass selective detector (MSD).The oven conditions were: initial temperature of 40°C (hold for 1 min), raised @ 25°C/min to 130°C, then @ 12°C/min to180°C, and finally @ 3°C/min to 280°C, with a hold time of 7 min. The injector temperature was 250°C. Helium was used as a carrier gas with purity-99.999%. The ion source temperature was 250°C. The interface temperature was 280°C. The instrument was operated in the spit mode with split ratio of 1:10. The injection volume was 2 µL. The MS conditions include solvent delay of 6 min; scan rate of 0.50/s and scanned mass range of 50–500 m/z. All samples were analyzed in the Selected Ion Monitoring (SIM) mode (Fig. 4).Data were acquired and processed by GC-MS Lab Solution Software (version 4.45). The compound specific retention times, m/z ions and molecular mass for the identification, confirmation and quantification are represented in (Table 1). Pesticides were identified based on their retention times, quantification and identification transitions.
Method validation:
The method was validated following SANTE/11813/2017 guidelines with linearity, limit of detection (LOD), limit of quantification (LOQ), specificity, accuracy (% recovery) and precision (% RSD) (SANTE 2017). LOD was determined based on signal to noise ratio (S/N) 3:1 whereas S/N ratio of 10:1 was used to determine the LOQ. The five-point (10, 20, 50, 100 and 250 ng ml− 1) calibration curve of mix-standard solution was prepared for checking linearity with the regression coefficient (R2). A comparative recovery experiment in three replicates was carried out spiking blank water sample with the working mix-standard solution at fortification levels of LOQ, 2×LOQ, and 5×LOQ. The precision and trueness of the results, expressed as %RPD was also calculated using RPD=(M/N)*100 where M = A + B and N=(A-B)/2, A = Inter assay recovery and B = Intra assay recovery (Tripathy et al. 2019).
Risk assessment:
Risk Quotient (RQ) was assessed and curtained following EPA's Level of Concern (LOC) for aquatic animals (e.g., fish and invertebrates), for presuming the potential risk associated with the presence of pesticide residues in the aquatic environment (USEPA 2017a). RQ was calculated as follows: RQ = EEC/LC50 or EEC/EC50 or EEC/NOAEC where, EEC = Estimated Environmental Concentration (i.e. detected pesticide level in environmental water); LC50 and EC50 = Median Lethal and Effective Concentration, respectively (for estimation of acute toxicity) and NOAEC = No Observed Adverse Effect Concentration (for estimation of chronic toxicity). Pesticide Properties Data Base (PPDB 2020) was used for the collection of all eco-toxicological (LC50 or, EC50 or NOAEC) data (Table 2).
Table 2
Risk presumption in water ecosystem of river and pond.
Aquatic animals
|
Pesticides
|
River Water
|
Pond Water
|
EECa
|
LC50
|
NOAEC
|
RQ
|
EEC
|
LC50
|
NOAEC
|
RQ
|
Acute
|
Chronic
|
Acute
|
Chronic
|
T-HCH
|
1.26
|
2.9
|
2900
|
0.43448
|
0.0004344
|
0.11
|
2.9
|
2900
|
0.0379
|
0.000037
|
T-DDT
|
1.11
|
2510
|
130
|
0.0005
|
0.0085384
|
0.18
|
2510
|
130
|
0.000071
|
0.000062
|
T-Endosulfan
|
0.59
|
2
|
0.0001
|
0.295
|
5900
|
0.03
|
2
|
0.0001
|
0.015
|
0.000017
|
Phorate
|
0.005
|
13
|
-
|
0.000384
|
-
|
0.005
|
13
|
-
|
0.000385
|
-
|
Parathion-methyl
|
0.031
|
2700
|
-
|
0.000011
|
-
|
0.031
|
2700
|
-
|
0.000011
|
-
|
Malathion
|
0.015
|
18
|
91
|
0.00083
|
0.00016483
|
-
|
-
|
-
|
-
|
-
|
Chlorpyriphos
|
0.075
|
25
|
0.14
|
0.00301
|
0.53571428
|
0.13
|
25
|
0.14
|
0.0052
|
0.928571
|
Quinalphos
|
0.023
|
5
|
-
|
0.0046
|
-
|
0.083
|
0.005
|
-
|
16.6
|
-
|
Profenophos
|
0.015
|
0.08
|
0.002
|
0.1875
|
7.5
|
-
|
-
|
-
|
-
|
-
|
Butachlor
|
0.025
|
441
|
-
|
0.000056
|
-
|
0.047
|
441
|
-
|
0.000107
|
-
|
Semi-aquatic plants
|
|
EEC
|
EC50
|
NOAEC
|
RQ
|
EEC
|
EC50
|
NOAEC
|
RQ
|
Acute
|
Chronic
|
Acute
|
Chronic
|
T-HCH
|
1.26
|
2500
|
1900
|
0.000504
|
0.0006631
|
0.11
|
2500
|
1900
|
0.000044
|
0.000057
|
T-DDT
|
1.11
|
-
|
-
|
-
|
-
|
0.18
|
-
|
-
|
-
|
-
|
T-Endosulfan
|
0.59
|
2150
|
-
|
0.0002744
|
-
|
0.03
|
2150
|
-
|
0.0000139
|
-
|
Phorate
|
0.005
|
1300
|
-
|
0.0000038
|
-
|
0.005
|
1300
|
-
|
0.0000038
|
-
|
Parathion-methyl
|
0.031
|
1300
|
-
|
0.0000238
|
-
|
0.031
|
1300
|
-
|
0.0000238
|
-
|
Malathion
|
0.015
|
13000
|
-
|
0.0000011
|
-
|
-
|
13000
|
-
|
-
|
-
|
Chlorpyriphos
|
0.075
|
480
|
43
|
0.0001562
|
0.0017441
|
0.13
|
480
|
43
|
0.000271
|
0.003023
|
Quinalphos
|
0.023
|
-
|
-
|
-
|
-
|
0.083
|
-
|
-
|
-
|
-
|
Profenophos
|
0.015
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
Butachlor
|
0.025
|
210
|
-
|
0.00011904
|
-
|
0.047
|
210
|
-
|
0.000224
|
-
|
aEEC: Estimated Environmental Concentration; LC50 or EC50 or NOAEC represent ecotoxicological data; - (dash) represents that the data have not been found in PPDB, 2021 |
Meteorological Parameters:
Meteorological data (temperature, relative humidity and rain fall) were also collected from Department of Agricultural Meteorology and Physics, BCKV, Kalyani, for entire study period (Fig. 1). These data was used to correlate and discuss on the seasonal variation of occurrence of pesticide residues in environmental water samples.