lead decline in the indian environment resulting from the petrol-lead phase-out programme

ent 368 (2006) 686–694www.elsevier.com/locate/scitotenv

Science of the Total Environm

Lead decline in the Indian environment resulting from the petrol-leadphase-out programme

Amit Kumar Singh a, Munendra Singh b,⁎

a Department of Environmental Sciences, University of Lucknow, Lucknow 226 007, Indiab Department of Geology, University of Lucknow, Lucknow 226 007, India

Received 16 December 2005; received in revised form 3 April 2006; accepted 11 April 2006Available online 9 June 2006

Abstract

Recently, the lead content of various environmental components has decreased in response to replacement of leaded petrol byunleaded petrol. In India, 15 research studies are here assessed with respect to lead concentrations in various environmentalcomponents during the leaded petrol phase (before 1996), the transitional phase (1996–2000) and the unleaded petrol phase (2000onwards). The Ganga River Water exhibited a decrease in lead concentration from 18.0 μg/l in 1988 to 3.1 μg/l in 2001. InLucknow urban centre, mean lead concentrations in the urban air decreased from 1.6 μg/m3 in 1994 to 0.2 μg/m3 in 2002. Leadconcentrations in Dalbergia sissoo tree leaves also decreased from 18.7 μg/g dry wt. in 1994 to 8.3 μg/g dry wt. in 2004. Meanblood-lead levels of children from Mumbai, Chennai, Bangalore, Amritsar and Lucknow urban centres have fallen from 18.1 μg/dlin the leaded petrol phase to 12.1 μg/dl in the unleaded petrol phase. The petrol-lead phase-out effort in India has reduced leadconcentrations in the various environmental components after 2000. It will help to reduce the exposure of millions of people toenvironmental lead.© 2006 Elsevier B.V. All rights reserved.

Keywords: Lead; Unleaded petrol; Ganga River; Dalbergia sissoo; Children blood-lead; India

1. Introduction

The interactions between the environment andhuman activities are complex, important and poorlyunderstood. However, human activities are continuouslymodifying the physical, chemical and biological com-position of the environment. It is, therefore, essential tounderstand them as the existence, quality and survival ofhuman beings depend upon the appropriate interactions

⁎ Corresponding author. Tel.: +91 0522 2740015; fax: +91 05222740037.

E-mail address: [email protected] (M. Singh).

0048-9697/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.scitotenv.2006.04.013

with the environment (UNESCO, 1995; Butler et al.,2005).

Lead is a widely distributed and non-biodegradabletoxic metal in the environment. It has been added topetrol since the 1920s as an anti-knocking agent, toimprove fuel efficiency and to reduce wear on vehicleengines. Leaded petrol has caused more environmentallead exposure than any other source (Landrigan, 2002).At low levels, haem synthesis as well as psychologicaland neuro-behavioural functions is impaired. A highlevel of lead exposure damages almost all organs andorgan systems, most importantly the central nervoussystem, kidneys and blood, culminating in death atexcessive levels. It is of special concern to pregnant

http://dx.doi.org/10.1016/j.scitotenv.2006.04.013

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Table 1Petrol-lead phase-out programme in India (after Ghose, 2002)

Phase Implementationdate

Petrol type(Lead content)

Area covered

Before June,1994

Leaded petrol(0.56 g/l)

Entire country

Phase I June, 1994 Low-leaded petrol(0.15 g/l)

Delhi, Mumbai,Kolkata, Chennai

Phase II April, 1995 Low-leaded petrol and unleaded petrol(0.013 g/l)

Delhi, Mumbai, Kolkata, Chennai

Phase III January, 1997 Low-leaded petrol Entire country Phase IV September,

1998 Ban of leaded petrol Delhi

Phase V September,1998

Unleaded andlow-leaded petrol

All other capitalsof state/union terri-tories and othermajor cities

Phase VI January, 1999 Unleaded petrol DelhiPhase VII After April,

2000Unleaded petrol Entire country

Black, grey and white colours of first column represent the leadedpetrol phase, the transitional phase and the unleaded petrol phase ofthe programme, respectively.

687A.K. Singh, M. Singh / Science of the Total Environment 368 (2006) 686–694

women as it acts as an abortifacient (Satin et al., 1991;Goyer, 1996; Ghai et al., 2003). The nervous system ofthe foetus is especially susceptible to lead, which cancross the placenta and penetrate the blood–brainbarrier. In children, the most frequent results of leadintoxication are irreversible damage to brain and thehindrance of body defence mechanisms. There iscurrently no lead level believed to be safe for infantsand young children (Dietrich et al., 1987; Bellinger etal., 1991, 1992; Bellinger and Needleman, 2003;Bellinger, 2004). As lead exposure is unsafe at anylevel, it has become a global health problem (Gava-ghan, 2002).

In developing countries, all children under 2 yearsand more than 80% of those between 3 and 5 years aresuspected of having blood-lead levels exceeding WorldHealth Organization standards (10 μg/dl). About 18million children in these countries may suffer perma-nent brain damage from lead poisoning (Michaelowa,1997). In India, the George Foundation published areport on blood-lead concentration in urban childrenaged below 12 years in Delhi and Kolkata and foundthat more than 50% of the children had blood-leadconcentrations ≥10 μg/dl in 1999 (George, 1999). InPakistan, 430 children from Karachi were investigatedand about 80% of the children had blood-leadconcentrations >10.0 μg/dl with an overall mean of15.5 μg/dl and were likely to suffer some degree ofintellectual impairment as a result of high lead exposureresulting from leaded petrol and other sources (Rahbaret al., 2002).

Environmental lead exposure is one of the worstthreats to human health in the world. Several studieshave demonstrated reduced lead exposure through useof unleaded petrol (Lovei, 1996, 1999; Thomas et al.,1999; Tong et al., 2000; Landrigan, 2002). Indiacompletely phased out the use of leaded petrol by theend of the 20th century. The aim of this study is toinvestigate the impact of the petrol-lead phase-outprogramme on the Indian environment. It is, therefore,important to compare lead concentrations in variousenvironmental components during the use of leadedpetrol with those observed after the use of unleadedpetrol.

1.1. Global petrol-lead phase-out programme

Populations in at least 100 countries, including India,are facing health problems related to environmental leadexposure. The growing awareness regarding toxiceffects of environmental lead exposure has led to aworldwide initiative to reduce lead content in petrol. It is

thus desirable to phase out lead from the environment,as quickly as possible, on the global scale (Gavaghan,2002). Leaded petrol is being replaced by unleadedpetrol in which ethanol or the heavy metal manganesecan be added instead of lead. The World HealthOrganization has been a leader in this global effort toreplace leaded petrol by unleaded petrol. Japan was thefirst country to reduce the lead content in petrol due tothe reporting of widespread lead contamination inTokyo in 1970. The United Nations commission calledon governments worldwide to switch from leaded tounleaded petrol in 1994. There have been severalsuccessful programmes of phasing out lead in thedeveloping world modelled on the programmes ofindustrialized countries (Michaelowa, 1997). Manydeveloping countries have been actively engaged insuch lead reduction programmes by replacing leadedpetrol with unleaded petrol. By the end of 1996, only 14countries had completely phased out the use of leadedpetrol and, on the other hand, in many Asian and Africancountries unleaded petrol was scarce, the lead content inpetrol reaching or exceeding 0.8 g/l at that time. Inrecent years, Bangladesh, China, Egypt, Haiti, Hon-duras, Hungary, Kuwait, Nicaragua, Malaysia andThailand have made successful efforts to phase outleaded petrol (Lovei, 1996, 1999).

In the second half of the 20th century, the urbanenvironment of India experienced a metamorphosis inwhich feudal towns changed into industrial cities, cities

Fig. 1. Map showing the Ganga River and other locations used in the present study.

688 A.K. Singh, M. Singh / Science of the Total Environment 368 (2006) 686–694

into metropolises, metropolises into megalopolises. Tosupport the need of the growing urban population,millions of people were exposed to lead via the use ofleaded petrol. The Ministry of Environment and Forests

Table 2Analytical techniques used for the estimation of lead content in the various

Environmentalcomponents

Reference studies Analytical techniqu

Ganga River Water Modak et al. (1992) Direct current plasmSarkar et al. (2003) Perkin Elmer–atomDutta et al. (2005) Atomic absorption

Lucknow urban air Singh et al. (1995) Anderson high voluspectrophotometer,

Kaul et al. (2003) High volume samspectrophotometer,graphite tube atomi

ENVIS (2003) –Dalbergia sissootree leaves

Singh et al. (1995) Flame atomic absor

Singh et al. (2005) Flame atomic absor(Perkin Elmer)

Urban children blood Tripathi et al. (1989) Differential pulse anG-PARC 174A

Kumar and Kesaree(1999)

Diathizone method

Raghunath et al. (1999) Differential pulse anG-PARC 174A

Tripathi et al. (2001) Differential pulse anG-PARC 174A

Bellinger et al. (2005) Lead care™ blood-Mahajan et al. (2005) Anodic stripping voAhamed et al. (2005) Graphite furnace at

along with the Ministry of Petroleum and Natural Gas,Government of India, had taken initiatives to introducethe use of low-leaded followed by unleaded petrol in aphased manner. In the initial stage, unleaded petrol was

environmental components in India

es used Reported leadconcentration (range)

a emission spectroscopy 10–115 μg/lic absorption spectrophotometer 2.3–3.9 μg/lspectrophotometer (GBC-902, Australia) 0.005–0.343 mg/lme sampler and flame atomic absorptionPerkin Elmer-2380

0.40–3.02 μg/m3

pler and flameless atomic absorption(Spectra Varian, Australia) equipped withzer (GTA) and with deuterium correction

0.04–3.91 μg/m3

0.02–0.34 μg/m3

ption spectrophotometer–Perkin Elmer 30–62.5 μg/g

ption spectrophotometer–Varian-250+ 2.1–12.3 μg/g

odic stripping voltammetry model EG and 1.1–47.7 μg/dl

and atomic absorption spectrophotometer 25.0–43 μg/dl



lead analyzer 2.5–38.3 μg/dlltammetry 2.0–12.6 μg/dlomic absorption spectrophotometer 2.8–15.0 μg/dl

Fig. 2. Lead content in the Ganga River Water at lower reaches in theGanga Delta region. (A) Bar diagram shows the increasing trendduring the leaded petrol phase and the declining in the transitional andunleaded petrol phases. (B) Reduction of lead content in the river waterfrom the leaded petrol phase (1988) to the unleaded petrol phase byseason (2001). [Data source: Modak et al., 1992; Sarkar et al., 2003;Dutta et al., 2005].


introduced in four metropolitan cities (Delhi, Mumbai,Kolkata and Chennai) from 1st April 1995; and then bystate capitals and other major cities from 1st June 1998,with coverage of the entire country by 1st April 2000(Ghose, 2002). The lead level was reduced from 0.56 g/l in leaded petrol through 0.15 g/l in low leaded petrol to0.013 g/l in unleaded petrol (Table 1). The petrol-leadphase-out programme can be sub-divided into the leadedpetrol phase (before 1996), the transitional phase(1996–2000) and the unleaded petrol phase (2000onwards) for the present study.

2. Materials and methods

2.1. Data

Several studies have reported lead concentrations invarious environmental components in India. After apreliminary survey, 14 internationally and one nationallypublished and recognised studies were found that met ourcriteria for inclusion in the data assessment. The GangaRiverWater, urban air ofMumbai andLucknow,Dalbergiasissoo tree species of Lucknow and urban children blood(collected from Mumbai, Chennai, Bangalore, Amritsarand Lucknow urban centres) were identified as the possibleenvironmental components for which data for lead contentswere available during the leaded petrol, transitional andunleaded petrol phases (Fig. 1). There have been significantimprovements in the analytical techniques used in the lasttwo decades to determine lead concentrations in variousenvironmental samples. The analytical techniques used indetermining lead content in the above selected studies arepresented in Table 2.

Modak et al. (1992), Sarkar et al. (2003) and Dutta et al.(2005) reported lead concentrations in the water of theGanga River, the biggest river system draining the northernpart of India. Tripathi et al. (2001) reported atmosphericlead in five urban localities in Mumbai in 1988 and 1996.Five studies (Tripathi et al., 1989; Kumar and Kesaree,1999; Bellinger et al., 2005; Mahajan et al., 2005; Ahamedet al., 2005) reported blood-lead levels of children fromMumbai, Chennai, Bangalore, Amritsar and Lucknowurban centres, respectively.

Lucknow, the capital city ofUttar Pradesh state, is one ofthe fastest growing urban centres located in northern India.Monitoring of lead concentration in Lucknow was carriedout in 1994, 1999, 2000 and 2002 (Singh et al., 1995;ENVIS, 2003; Kaul et al., 2003). The National BotanicalResearch Institute, Lucknow, had conducted the biomoni-toring of lead by selecting 15 plant species (Azadirachtaindica, Bougainvillea sp,Callistemon lanceolatum,Cassiafistula, Calotropis procera, D. sissoo, Delonix regia,

Eucalyptus sp, Ficus religiosa, Holoptelea integrifolia,Lantana camara, Polyalthia longifolia, Pongamia glabra,Tabernaemontana coronaria and Thevetia nerifolia) inLucknow and reported high lead concentrations in theseplant leaves as well as in the urban air (Singh et al.,1995). Tree species D. sissoo, which is commonly presentat all sites around Lucknow, was an ideal tree species tomonitor atmospheric lead concentrations as it showed avery strong correlation (r2=0.98) between lead in the treeleaves with lead in the urban air. Another biomonitoringstudy of the atmospheric environment was carried outduring the unleaded petrol phase by using the same treespecies in 2003 (Singh et al., 2005).

3. Results and discussion

3.1. The Ganga River Water

The Ganga River drains the Ganga Alluvial Plain, oneof the most densely populated, with uniformly


distributed urban centres and highly agriculturalisedregions, in the world. During the leaded petrol phase, theGanga River exhibited a wide range of total leadconcentration in its water (range: 10–115 μg/l; average:30.8 μg/l, n=27) in 1988 (Modak et al., 1992). Like theGanga River, the Indus River in Pakistan also exhibitedelevated total lead concentration (range: 13–160 μg/l;mean: 73 μg/l, n=10) in its water in 1991 (Tariq et al.,1996).

The Ganga River is characterised by high fluvialactivity in terms of water and sediment influxes duringthe monsoon season. Total lead concentrations in theGanga River Water at Uluberia during the monsoonseason from 1994 to 1998 show an increasing trendduring the leaded petrol phase and a decreasing trend in

Fig. 3. (A) Bar diagram showing reduction of atmospheric lead concentrationslead concentrations in the air of Lucknow in 1994, 1999–2000 and after the inTripathi et al., 2001; Kaul et al., 2003; ENVIS, 2003].

the transitional phase (Dutta et al., 2005). Fig. 2A showschanges in the lead concentrations in the Ganga RiverWater in the monsoon season from the leaded to theunleaded petrol phase.

Total lead concentrations of the Ganga River Water atUluberia in the Ganga Delta region varied seasonallyfrom 14 μg/l pre-monsoon to 19 μg/l during themonsoon and 21 μg/l post-monsoon. In the unleadedpetrol phase, total lead concentration in the Ganga RiverWater at Ganga Sagar was lower at 2.3 μg/l pre-monsoon, 3.9 μg/l during the monsoon and 3.1 μg/l post-monsoon (Modak et al., 1992; Sarkar et al., 2003).The higher monsoon lead concentration reflects fluvialtransportation of deposited atmospheric lead in andaround several urban centres of the Ganga River Basin

at urban localities in Mumbai. (B) Box and whisker diagram indicatingtroduction of unleaded petrol in 2002. [Data sources: Singh et al., 1995;

Fig. 4. Decline of lead concentrations in the Dalbergia sissoo treeleaves collected from Lucknow in 1994 and 2004. (A) Bar diagram oflead concentrations at selected sites and (B) Box and whisker diagramof lead concentrations at the urban centre. [Data source: Singh et al.,1995, 2005].


through the monsoon runoff by the Ganga River alongwith its tributaries (Singh et al., 2002). Fig. 2B showsthe significant reduction of lead concentration in theGanga River Water in all the seasons from 1988 and2001, a reflection of the use of unleaded petrol.

3.2. Mumbai and Lucknow urban air

Tripathi et al. (2001) studied average atmosphericlead concentrations in five urban sites (Colaba, Deonar,Goregaon, Khar and Sion) in Mumbai urban centre in1988 and 1996. Average atmospheric lead concentra-tions decreased at all these sites from the leaded petrolphase to the transitional phase as shown for Colaba(1988, 0.18 μg/m3; 1996, 0.11 μg/m3) in Fig. 3A.

In Lucknow urban centre, leaded petrol (Pb, 0.56 g/l)was used as vehicular fuel in 1994. The urban air leadconcentration in Lucknow varied widely from 0.46 to2.96 μg/m3 and displayed an exponential relationship(r2 =0.98) with maximum traffic density during theleaded petrol phase in 1994 (Singh et al., 1995). Duringthe unleaded petrol phase, varying amounts of lead inthe urban air were reported during the summer (0.02–0.11 μg/m3) and winter (0.08–0.26 μg/m3) seasons(ENVIS, 2003). High lead concentrations in urban airduring the winter season are related to ground-basedinversion with strong stable atmospheric condition(Sadasivan et al., 1987; Tripathi, 1994). During 1999–2000, Kaul et al. (2003) reported lead concentrationsranging from 0.04 to 3.91 μg/m3 in the ambient air ofLucknow at ten sites. There was a strong linearcorrelation between air lead and petrol lead concentra-tions, indicating air lead response to a change in leadconcentration in petrol (Thomas et al., 1999). There wasa reduction of 87.5% in mean lead concentration in theair from 1.6 μg/m3 in 1994 to 0.2 μg/m3 in 2002 (Singhet al., 1995; ENVIS, 2003), reflecting the impact ofunleaded petrol in reducing the atmospheric leadconcentrations of Lucknow (Fig. 3B).

3.3. D. sissoo tree leaves

In Lucknow urban centre, high lead concentrations inthe urban air (0.46–2.96 μg/m3) as well as in D. sissootree leaves (9.0–30.4 μg/g dry wt.) were reported duringthe leaded petrol phase in 1994. In the unleaded petrolphase, lead concentrations in the leaves, collected fromeight urban sites, ranged from 2.1 to 12.3 μg/g dry wt. in2004 (Singh et al., 2005). Fig. 4A shows leadconcentrations in the leaves collected from three urbansites (Faizabad Road, University Road and M. G. Road)at Lucknow during the winter season in 1994 and 2004.

All three sites exhibited a reduction in average leadconcentration in the leaves from 18.4 to 7.1 μg/g drywt., despite a nearly three-fold increase of vehicularpopulation in the urban centre. In Lucknow, leadconcentrations in the leaves decreased by 56% from1994 to 2004, the mean lead concentration falling from18.7 to 8.3 μg/g dry wt. (Fig. 4B). This reduction of leadin the leaves of the urban centre again reflects the use ofunleaded petrol in Lucknow urban environment (Singhet al., 2005).

3.4. Urban children blood

It has been well established that there is a strongpositive relationship between lead in petrol/air andhuman population blood-lead levels. From a study basedon experimental and epidemiological data, it has beenestimated that an increase in air lead of 1 μg/m3 resultsin an increase in blood-lead of 3–5 μg/dl (Chamberlain,


1983; USEPA, 1986; Fergusson, 1990). Raghunath et al.(1999) observed a good correlation between air lead andthe blood-lead of 6–10 year-old children residing inMumbai (Fig. 5A). It was also reported that an increaseof 1 μg/m3 in air lead level corresponded to an increaseof 3.56 μg/dl lead in children blood concentration. In theUnited States, blood-lead levels decreased from about16 μg/dl to 10 μg/dl between 1976 and 1980 as the leadin petrol fell from 0.47 g/l to 0.3 g/l (Fergusson, 1990).Fig. 5B displays the decrease in blood-lead level ofchildren from urban localities in Mumbai from 1995 to1998, attributable to the use of unleaded petrol alongwith emission regulations and better transport and trafficmanagement policies (Tripathi et al., 2001).

Tripathi et al. (1989) studied the blood-lead concen-trations of 178 children from Mumbai during 1984–

Fig. 5. (A) Graph showing strong correlation between atmospheric-lead and thVariation in the blood-lead level of children from Mumbai during 1984 to 1998High–low and bar graph showing ranges and mean values of blood-lead in chilchildren blood-lead concentration after the change to unleaded petrol. Note that cal., 1989; Kumar and Kesaree, 1999; Raghunath et al., 1999; Tripathi et al., 20

1985. Blood-lead concentrations ranged from 1.1 to47.7 μg/dl and mean blood-lead concentration wasreported to be 11.3 μg/dl. In another study, Kumar andKesaree (1999) investigated blood-lead in 25 children inthe 5–15 year age group residing in Bangalore during1997–1998. The concentrations ranged from 25 to43 μg/dl with an average of 32 μg/dl. During 1998–1999, Bellinger et al. (2005) studied blood-leadconcentrations of 74 children (4–14 years) fromChennai. The range and mean blood-lead concentrationswere 2.5–38.3 μg/dl and 11.1 μg/dl, respectively. During2002 to 2004, Mahajan et al. (2005) measured the blood-lead concentration of 160 children (3 months–6 years)from Amritsar. Concentrations ranged from 2.0 to12.6 μg/dl with a mean of 7.3 μg/dl. In 2003, Ahamedet al. (2005) studied 62 children between 4 and 12 years

e blood-lead concentrations for 6–10 years old children in Mumbai. (B), showing a decline after the introduction of unleaded petrol in 1995. (C)dren from the urban centres of India. (D) Bar diagram showing decline ofhildren blood-lead is still above theWHO limit. [Data sources: Tripathi et01; Ahamed et al., 2005; Bellinger et al., 2005; Mahajan et al., 2005].

Fig. 6. Bar diagram showing response (in %) resulting from switch tounleaded petrol for lead in the various components of Indianenvironment.


in Lucknow observing a range and mean blood-leadconcentrations of 2.8–15.0 μg/dl and 7.5 μg/dl,respectively.

Fig. 5C displays the ranges and mean values ofblood-lead in children from Mumbai, Chennai, Banga-lore, Amritsar and Lucknow urban centres. It can beinferred that the mean blood-lead concentrations haddecreased from the transitional phase to the unleadedpetrol phase, probably attributable to the introduction ofunleaded petrol in India. In the same way, the reductionof mean blood-lead concentration in children fromKarachi, Pakistan, from 38 μg/dl in 1989 to 15.6 μg/dlin 2000 resulted from the decline leaded petrol use(Manser et al., 1990; Rahbar et al., 2002).

The United State Centres for Disease Control andPrevention in Atlanta, Georgia established the univer-sally accepted World Health Organization permissiblelimit of lead level in children blood on the basis ofneurological toxicity, as≤10 μg/dl (USCDC, 1991). Theaverage blood-lead concentration of urban Indianchildren in the unleaded petrol phase programme isstill above the permissible limit (Fig. 5D). This indicatesthat there could be the possibility of multiple sources oflead exposure, such as dietary intake, drinking water,cosmetics and lead-glazed ceramics, industrial emis-sions, lead-based paints, lead-based batteries and lead-soldered food cans etc. Much work needs to be done toreduce environmental lead exposure in millions ofpeople living in the urban centres of India. This can befurther achieved by reducing and phasing out the use oflead-based paints; eliminating the use of lead in foodcontainers; minimizing the dissolution of lead in watertreatment and distribution systems; improving controlover exposure to lead in workplaces; increasingemphasis on adequate nutrition, health care and attentionto socio-economic conditions (Tong et al., 2000).

4. Conclusions

The above data analysis provides a benchmark of theIndian experience in common with the global efforts inthe petrol-lead phase-out programme that has been a keycontributor to the drastic decrease of lead content invarious environmental components. It can be estimatedthat lead concentrations in the Ganga River Water,Lucknow urban air, D. sissoo leaves and urban childrenblood have decreased by 82.8%, 87.5%, 55.6% and33.5%, respectively, since the use of unleaded petrolfrom 2000 onwards (Fig. 6). Evidence from Europe,Japan, USA and Mexico also shows that phasing-outleaded petrol is the most effective way of reducingenvironmental lead exposure (Silbergeld, 1995). How-

ever, the remaining lead exposure of millions of peopleis also of serious concern in India. It is likely to remain asignificant public health problem because of rapidindustrialization and exponential urban growth alongwith the persistence of lead in the Indian environment. Acoordinated-approach shared by local, national andinternational agencies is still required for the completesolution of this problem in India and, indeed, severalother countries are still using leaded petrol.

Acknowledgements

The Department of Science and Technology, NewDelhi, financially supported this research through Fast-Track Research Project Scheme (SR/FTP/ES-47/2000).The authors express their gratitude to Prof. M. P. Singhand Prof. I. B. Singh from the Department of Geology,University of Lucknow for their encouragement andsupport in the study. We thank Dr. Ratan Kar, BirbalSahni Institute of Palaeobotany, Lucknow, and Ms AnjuSaxena, University of Lucknow for helpful commentson the initial draft. The editor and two anonymousreviewers are thanked for their helpful comments on themanuscript to improve the quality of presentation. Mr.Pramod Joshi is acknowledged for drawing figures.

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