Phytomonitoring and NOx pollution around silver refineries

Pergamon

Environment

International, Vol. 25, No. 4, pp. 403-410, 1999 Copyright 01999 Elsevier Science Ltd Printed in the USA. All rights reserved 0160-4120/99rS-see front matter

PI1SO160-4120(99)00004-5

PHYTOMONITORING AND NO, POLLUTION AROUND StLVER REFINERIES Anamika Tripathi*, D.S. Tripathi, and Vishnu Prakash Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi-221005,

India

EI 9603-12 7 A4 (Received I8 March 1996; accepted 13 Decent ber 1998)

In order to assess the study was undertaken purpose, the five most indica, Cassiafistula,

impact of NO, pollution on vegetation around silver refineries, the present in Varanasi, India, during the period January to December 1994. For this common plants at all sites, Ficus religeosa, Syziumjambolana, Azadirachta and Mangifera indica, were selected as test plants. Five study sites were

selected around silver refineries. A control site, BHU, was also selected outside the city in the northern direction at a distance of about 10 km. Responses to nitrogen oxides of plants, such as folk injury symptoms, changes in chlorophyll, carotenoids, sugar, ascorbic acid, protein, and nitrogen content were measured. The NO, concentrations were high in the immediate vicinity of the silver refineries. There also exists a positive and significant relationship between the concentrations ofNO, and foliar injury, protein, and nitrogen content in plants. The levels of folk injury, chlorophyll, carotenoid, sugar, and ascorbic acid were found to decrease, and the amounts of protein and nitrogen were found to increase in comparison to plants growing at a control site. The magnitude of such changes was greatest in F. religeosa. The study suggests that the differential sensitivity of plants to NO, may be used in evaluating the air pollution impact around emission sources, and M indica plants can be used as an indicator plant for quantifying the biological

changes. 01999

Elsevier Science Ltd

INTRODUCTION The quickly increasing demand for silver, which is next to gold, has led to the development of a series of silver refineries. These are stationary sources of pollution responsible for most nitrogen oxide pollution. These refineries make use of concentrated HNO, to dissolve old silver in making silver biscuits. In the past, large amounts of dark brown waste fumes were routinely released from short height stacks on the roofs of the residential buildings, until neighbors’ complaints forced the operators of these refineries to increase chimney heights and to scrub the gases.

Ambient air pollution measurements are often performed at sites where large populations (Ellegard 1997; Chattopadhyay et al. 1997) or agricultural crops (Pandey and Agrawal 1994) might be subject to air pollution damage. Lahdesmaki et al. (1990) reported on the impact of NO, on plants in the form of discoloration, loss of leaves, changes in nitrogen metabolisms, levels of NH4’, free amino acids, and total protein content of the plants. Zedler et al. (1986) also reported that nitrogenous air pollutants are additional environmental stress factors which alter protein metabolism and protein spectra in plants. Certain investigators have reported that the NO, gas increases the concentration of free amino acids

*Postal address: D 61/24 E-l K, Sidhgiri Bagh, Varanasi221010, India. 403

A. Tripathi et al.

404

(Van Dijk and Roelofs 1988; Massal et al. 1988; Bolsinger and Fluckiger 1989) or increases the protein concentrations (Lahdesmaki et al. 1990). The effect of NO, on proteins has been suggested to take place at the translational or post-translational level due to altered composition of the amino acid pools, rather than at the transcriptional level (Khan and Malhotra 1983). Zedlar et al. (1986) also reported that nitrogenous air pollutants are one additional environmental stress factor which alters protein metabolism and the protein spectra in plants. Furthermore, according to Kaji et al. (1980) after entering through the stomata, NO, produces NO,and thenNO, ions, the latter being more toxic to plants than NO,- ions. The air quality in Varanasi City is known to be poor, resulting in environmental damages (Tripathi et al. 1991; Pandey et al. 1992; Tripathi 1994), however, no attempt has been made to identify the impact ofNO, on vegetation in the Chowk area of the city, where five silver refineries are located. Therefore, the aim of the present study was to collect data on the concentrations of NO, around silver refineries and to examine the effects of NO, on some common plants grown in that area. MATERIALS

AND METHODS

Study site

Varanasi is located at latitude 25 o 18’N and longitude 83” 01’ E, with a population of 928 000. It is located at an average height of about 76.19 m above sea level, in the eastern gangetic plain of the Indian subcontinent. The climate of this city is tropical with a marked monsoonal effect. Due to marked variation in temperature and rainfall, the year was divided into three distinct seasons: rainy (July-October), winter (November-February), and summer (March-June). An annual average temperature of 25°C was recorded, with a relative humidity of 60% and 1000 mm of annual precipitation. Project design

The five silver refineries in the Chowk area are located at about 100-150 m distance from each other, with stack heights ranging from 22 fi (6.6 m) to 35 ft (10.5 m). Some stacks were open on the roof of the residential buildings. These refineries have no pollution treatment plant and are processing 5.5 Tg ton of silver annually. The location is one of the busiest commercial areas of the city, with the associated high

traffic. In order to study the effect of NO, emission in and around the Chowk area, five study sites (site 1 (sl), site 2 (Q, site 3 (s&, site 4 (s4), and site 5 (s&) were selected in the prevailing wind direction of the five refineries. As shown in Fig. 1, a control site (BHU), located about 10 km in direction of the emission source (Fig. 2), was selected. The air quality study was carried out four times a month at 8-h intervals during the period January 1994 to December 1994. Air samples were analysed by the Jacobs and Hochheiser (1958) method. For NO, analysis, quality control measures were taken to assess the reliability of data due to any type of contamination during calorimetric analysis. Blanks were run for each determination to eliminate the contaminants. The coefficient of variation (r) was determined between the replicate analysis and was found to be less than 10%. The five plants, Ficus religeosa, Syzium jambolana, Azadirachta indica, Cassia Jistula, and Mangifera indica, were used as biomonitors. The plants were present in five study sites and in the control site. For the purpose of the study, they were grown in pots and placed on the roof of the building near the stack. Seeds were provided by the BHU Nursery and plants raised from them were screened for NO, susceptibility by exposure to 150 pg m3 for two successive 7-h period. Susceptible individuals (those that developed the most symptoms) were used to raise a seed stock, and they were tested over a range of concentrations. Plants were raised on a standard compost and transferred into 30 cm self-watering pots before field exposure. Plants were kept in a clean-air greenhouse as long as possible before exposure to avoid any lesions caused by the pollutants. Five groups of plants (five plants in each) were placed on each site for 15 d in December 1994. From each species the 3rd to 5th leaves were collected at the end of 15 d to measure leaf area injury, chlorophyll, carotenoid, sugar, ascorbic acid, protein, and nitrogen content. The leaf area injury was measured with a portable leaf area meter (Licor, USS.) and expressed as a percentage of the total area. The total chlorophyll content was determined using the method of Maclachlan and Zalik (1963). Extraction and analysis of ascorbic acid in fresh leaves were performed using the method of Keller and Schwager (1977). Sugar, protein, and nitrogen content were determined by the phenol reagent method (Dubois et al. 1956; Horwitz 1970) and the microkjeldahl method (Misra 1968).

Phytomonitoring

7

and NO, pollution around silver refineries

,I

II

405

I

I

Fig. 1. Study site map of Varanasi.

Fig. 2. Locations of sampling sites.

PLAN SCAL E

KEY NOT 10

n

Phytomonitoring and NO, pollution around silver refineries

407

Table 1. Summary of annual statistics on monthly average NO, concentrations (pg m”) at five different sites, 1994. Percentiles Sites

n

Min.

20

sl

70

80

98

Max.

AM*

f

SD

48 82 48 98 48 168 48 246

92 149 238 297

178 483 672 760

200 563 680 780

217 572 685 783

217 572 685 783

48 338 454 560 561 682 759 783 786 791 * Annual arithmetic mean f standard deviation. * * Annual geometric mean f geometric standard deviation.

791

143 344 461 529 629

f f f f f

52 184 202 217 172

S2 s3 s4

30

40

50

60

96 102 138 162 246 249 309 479 249 353 506 559 369 387 514 652

S<

Statistical analysis of the data was done and the correlation coefficient (r) values were determined between the biological parameters and NO, concentrations. RESULTS

The emission of nitrogen oxides from the stacks of silver refineries is quite significant up to 5 km downwind of the emission source in the Chowk area of the city. The maximum NO, concentration was recorded in July at site 5 (Table 1). A pronounced seasonal variation was observed in the concentration of NO,. The winter season revealed the maximum concentrations of 217, 572, 685, 783, and 791 ug mm3as s,, s2, s3, s,, and s,, respectively. The levels of NO, were found to exceed the limit prescribed by IS1 (1969). At the control site, BHU, NO, concentration was 35 ug m”. The plant species growing around the silver refmeries showed visible leaf injury in the form of chlorotic patches, usually in the mid-laminar region. However, in all plant species, leaf injury was increased in the prevailing wind direction towards the east. Chlorophyll, carotenoid, sugar, and ascorbic acid were low in plant species nearer to emission sources, and these values gradually increased at increasing distances from the source. The leaves of plant species growing at five polluted sites contained a reduced amount of chlorophyll. The maximum decrease was recorded in M indica followed by S. jambolana, A. indica, C.$stula, and F. religiosa at all the sites. The maximum percent decreases in chlorophyll a, chlorophyll b, carotenoid, sugar, and ascorbic acid content for the above plants is illustrated in Table 2 with respect to the control. Analysis of protein and nitrogen content in plants growing at differently polluted and control sites revealed that these values in all the plant species were higher at polluted sites than the control site (Table 3).

GM** f 134 290 414 484 603

f f f f f

SD 1.5 1.9 1.7 1.6 1.4

The foliar injury level showed a significant and positive correlation with NO, concentration (Table 4). The M. indica, S. jambolana, and A. indica plants showed injury symptoms at all the sites, while F. religeosa showed injury symptoms only at two sites, i.e., 2.90% at site s, and 5.6 1% at site s5. The maximum leaf area injury was observed at site s5, the values being 5.61% in F. religeosa, 7.62% in C. jistula, 11.52% in A. indica, 13.92% in S. jambolana, and 16.67% in M indica. Chlorophyll, carotenoid, sugar, and ascorbic acid showed a negative and significant correlation with the NO, concentration (Table 4). The protein content showed significant and positive correlation (r-0.92; ~~0.01) (Table 4) with NO, concentration. There also exists a positive correlation between the concentration of NO, and the amount of N in leaves (1=0.96; p < 0.01) (Table 4). The maximum N accumulation was observed in F. rehgeosa followed by C.Jistula, A. indica, S. jambolana, and M. indica at site s5. At site s,, there was no percent increase reported in A. indica and M indica plants (Table 3). The maximum nitrogen accumulation of 1.28 mg g-l was found in F. religiosa at site s5. DISCUSSION The results of this study indicate that the emission pattern of the pollutants from silver refineries is governed by the west and north-west prevailing winds, which usually disperse the stack plume mainly in the east and south-east direction, where the NO, concentrations were higher than in any other direction. As the prevailing wind direction is towards sites s2, s,, sq, and sg, visible injury is seen on these sites in M indica, S. jambolana, and A. indica in the form of chlorotic patches on the leaves. The leaves of M indica are affected most, and the plants grown at site s, are affected

A. Tripathiet al.

408

Table 2. Chlorophyll, carotenoid, end sugar content at various study sites(mean+- SD). Plants/sites

Control

s1

s2

s3

S4

s5

6.00 f 0.52

5.80 f 0.42

5.30 f 0.65

4.60 f 0.62

Chlorophyll (mg g-‘) F. religeosa

6.90 f 0.52

6.60 f 0.72

C. jistula

4.90 f 0.58

4.20 f 0.36

3.50 f 0.21

3.50 f 0.26

3.40 f 0.37

3.30 f 0.21

A. indica

4.10 f 0.11

3.70 f 0.42

3.10 f 0.37

3.00 f 0.56

2.80 f 0.91

2.60 f 0.56

S. jambolana

4.00 f 0.37

3.50 f 0.08

2.80 f 0.76

2.70 f 0.07

2.40 f 0.09

2.30 f 0.07

M. indica

1.80 f 0.22

1.40 f 0.32

1.10 f 0.92

0.90 f 0.43

0.80 f 0.81

0.50 f 0.43

Carotenoid (mg g-r) F. religeosa

3.70 f 0.92

3.30 f 0.08

3.10 f 0.09

2.80 f 0.18

2.60 f 0.10

2.50 f 0.19 1.70 f 0.09

C. fistula

2.90 f 0.86

2.10 f 0.04

2.00 f 0.01

1.90 f 0.09

1.80 f 0.08

A. indica

2.80 f 0.85

2.60 f 0.19

1.60 f 0.08

1.50 f 0.04

1.30 f 0.07

1.20 f 0.08

S. jambolana

1.50 f 0.03

1.oo f 0.09

0.80 f 0.07

0.70 f 0.01

0.70 f 0.08

0.60 f 0.06

M. indica

1.00 f 0.01

0.50 f 0.02

0.40 f 0.06

0.30 f 0.05

0.20 f 0.01

0.10 f 0.06

F. religeosa

Sugar (mg g-‘) 24.90 f 0.84 24.70 f 0.27

23.80 f 1.47

23.60 f 125

22.50 f 1.38

22.1 f 1.75

C. fistula

23.80 f 0.08

23.70 f 1.34

23.60 f 0.32

23.80 f 0.46

22.4 Ozk0.26

22.20 f 0.61

A. indica

22.50 f 0.65

21.60 f 0.71

21.00 f 0.18

19.70 f 0.19

19.50 i 0.15

19.10 f 0.27

S. jambolana

22.00 f 1.14

21.50 f 0.28

19.80 f 0.35

19.20 f 0.31

18.50 f 0.25

17.30 f 0.42

M. indica

18.50 f 1.09

18.00 f 0.16

17.70 f 0.24

17.20 f 0.21

16.80 f 1.11

15.30 f 0.30

Table 3. Ascorbic acid, protein, and nitrogen content in various plants at various study sites (mean f SD). Plants/sites

Control

sl

sr

s3

s4

s5

Ascorbic acid (mg g-r) F. religeosa

1.oo f 0.07

1.10 f 0.07

1.12 f 0.02

1.06 f 0.18

1.18 f 0.05

1.28 f 0.24

C. fistula

0.98 f 0.09

0.99 f 0.09

1.oo f 0.01

1.11 f 0.13

1.13 f 0.01

1.22 f 0.29

A. indica

0.96 f 0.08

0.98 f 0.08

0.00 f 0.04

1.01 f 0.17

1.17 f 0.07

1.20 f 0.16

S. jambolana

0.79 f 0.02

0.82 f 0.02

0.85 f 0.03

0.87 f 0.09

0.89 f 0.01

0.91 f 0.08

M. indica

0.60 f 0.03

0.63 f 0.03

0.68 f 0.01

0.69 f 0.05

0.71 f 0.02

0.73 f 0.06

Protein (mg g-‘) F. religeosa

5.82 f 0.49

5.99 f 0.27

6.07 f 0.58

6.11 f 0.62

6.34 f 0.52

7.22 f 0.87

C. fistula

6.05 f 0.78

5.70 f 0.32

5.60 f 0.52

5.42 f 0.21

7.02 f 0.38

6.92 f 0.65

A. indica

5.55 f q.37

5.41 f 0.48

5.56 f 0.11

5.63 f 0.56

6.41 f 0.20

6.73 f 0.37

S. jambolana

4.47 f 0.76

4.52 f 0.07

5.56 f 0.37

5.21 f 0.07

5.35 f 0.54

5.45 f 0.91

M. indica

3.53 f 0.92

3.63 f 0.31

5.01 f 0.21

3.95 f 0.43

4.11 f 0.63

4.24 f 0.09

Nitrogen (mg g-l) F. religeosa

1.oo f 0.07

1.10 f 0.07

1.14 f 0.02

1.16 f 0.18

1.18 f 0.05

1.28 f 0.24

C. j&da

0.98 f 0.90

0.99 f 0.09

1.oo f 0.01

1.11 f 0.13

1.13 f 0.01

1.22 f 0.29

A. indica

0.96 f 0.80

0.98 f 0.08

0.90 f 0.04

1.01 f 0.17

1.17 f 0.07

1.20 f 0.16

S. jambolana

0.79 f 0.02

0.82 f 0.02

0.85 f 0.03

0.87 f 0.09

0.89 f 0.01

0.91 + 0.08

M. indica

0.60 f 0.03

0.63 f 0.03

0.68 f 0.01

0.69 f 0.05

0.71 f 0.02

0.73 f 0.06

least. The development of visible foliar injury symptoms was positively correlated with NO, concentration at the sites leading to more absorption of NO, on foliar surfaces through stomata. As a consequence of higher NO, on foliar surfaces, chlorophyll and carotenoid

pigments decreased in plants compared to those growing at the control site. The sugar concentration was low in plant species growing at different sites with respect to the control site. As site s5 is under heavy pollution stress, all plant

Phytomonitoring

and NO, pollution around silver refineries

species showed the lowest sugar levels. Dugger et al. (1962) reported the development of injury symptoms in NO,-exposed plants only after reduction of sugar below a certain level. This decrease in sugar level is attributed to inhibition of the photosynthetic process. The acidity produced by NO, could also influence electron flow and photophosphorylation. The ascorbic acid content was found to be maximum at the control site, and then in descending order at sites s,, s,, sj, s,, and s,. Ascorbic acid provides resistance to plants against pollution as it regulates various biochemical and physiological processes in plants. Among all the five plants, the maximum foliar injury was observed in M. indica plants, which also had the lowest ascorbic acid content of 0.47 mg g“. According to Lewin (1976), ascorbic acid is a strong reducing agent and its reducing capacity depends upon its concentration in leaves. A decrease in its concentration would diminish the pollutant detoxifying capacity of plants and thereby increase their vulnerability to pollution stress. Ascorbic acid was found to be significantly negatively correlated with foliar injury (I=-0.92; pcO.01). The protein content was found higher in all plant species grown at site s,, which is under maximum pollution stress. A significant and positive correlation (Table 2) between the protein and NO, concentration suggests that, with the increase in NO, concentration, the protein concentration increased gradually. The highest protein content was recorded in F. religeosa (Table 4). The leaves of different plant species showed higher levels of nitrogen in comparison to the control area, which gives evidence that absorbed NO, has been metabolized by plants and accumulated in foliar systems as NO,. The nitrogen accumulation in different plant species may provide a reliable measure of NO, pollution in the air environment around silver refineries. Moreover, as there are no ancillary industries nearby, the effect at present is primarily due to the refinery emissions. Phytomonitoring of air pollution is a relatively simple and low-cost technique and provides a reasonable picture of the distribution of the pollution effect and load in a place and time. This study suggests that differential sensitivity of plants to NO, may be conveniently used for detection and monitoring pollution, and M. indica plants can be used as an indicator plant for monitoring emission effects around silver refineries. The measurement of foliar injury, chlorophyll, carotenoid, sugar, ascorbic acid, protein, and nitrogen

409

Table 4. Correlation coefficient (r) between NO, concentrations (AM) and different biological parameters. Parameters

r

Foliar injury

0.96**

Chlorophyll

‘a’

Chlorophyll

‘b’

0.97*** -0.95**

Carotenoid

-0.94**

sugar

-0.98***

Ascorbic acid

-0.97**

Protein

0.92**

Nitrogen

0.96**

Level of significance * p < 0.05 ** p < 0.01 *** p < 0.001

content in plants at different sites in the Chowk area provides a pattern of changes in pollutant emission induced by silver refineries. Acknowledgment-The authors are thankful to Prof. H.R. Sant, Dr. B.D. Tripathi, and Dr. Madhoolika Agrawal for valuable suggestions and to the Council for Scientific and Industrial Research (CSIR) New Delhi, for financial assistance.

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