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RESEARCH ARTICLE

Spatial distribution, source apportionment and ecological risk assessment of residual organochlorine pesticides (OCPs)

in the Himalayas

Ningombam Linthoingambi Devi1,2

& Ishwar Chandra Yadav3

& Priyankar Raha2

&

Qi Shihua4

& Yang Dan4

Received: 19 May 2015 /Accepted: 11 August 2015 /Published online: 25 August 2015# Springer-Verlag Berlin Heidelberg 2015

Abstract The Indian Himalayan Region (IHR) is one of the

important mountain ecosystems among the global mountainsystem which support wide variety of flora, fauna, human

communities and cultural diversities. Surface soil samples col-

lected from IHR were analysed for 23 organochlorine pesti-

cides (OCPs). The concentration of ∑OCPs ranged from 0.28

to 2143.96 ng/g (mean 221.54 ng/g) and was mostly dominat-

ed by DDTs. The concentration of ∑DDTs ranged from 0.28

to 2126.94 ng/g (mean 216.65 ng/g). Other OCPs such as

HCHs, endosulfan and heptachlor, Aldrin and dieldrin were

detected in lower concentration in IHR. Their concentrations

in soil samples ranged from ND to 2.79 ng/g for HCHs, ND to

2.83 ng/g for endosulfans, NDto 1.46 ng/g for heptachlor, ND

to 2.12 ng/g for Aldrin and ND to 1.81 ng/g for dieldrin.

Spatial distribution of OCPs suggested prevalence of DDTs

and HCHs at Guwahati and Itanagar, respectively. The close

relationship between total organic carbon (TOC) and part of OCP compounds (especially α - and γ-HCH) indicated the

important role of TOC in accumulation, binding and persis-

tence of OCP in soil. Diagnostic ratio of DDT metabolites and

HCH isomers showed DDT contamination is due to recent

application of technical DDT and dicofol, and HCH contam-

ination was due to mixture of technical HCH and lindane

source. This was further confirmed by principal component

analysis. Ecological risk analysis of OCP residues in soil sam-

ples concluded the moderate to severe contamination of soil.

Keywords Organochlorine pesticides . Itanagar . Guwahati .Tezpur . Dibrugarh

Introduction

Organochlorine pesticides (OCPs) can be transported globally

due to semi volatile in nature, which has the capability to

move from warmer areas to cooler areas (Wania and Mackay

1993). OCPs such as dichlorodiphenyltrichloroethane, hexa-

chlorocyclohexane, endosulfan, aldrins, dieldrin, heptachlor,

chlordane and other related compounds play an important role

in the contamination of environmental ecosystems (Deepa

et al. 2011; Bingham 2007; Gilliom et al. 2007; Oxynos

et al. 1989). These compounds have more capability to persist

for long time (UNEP 2002) and acute in living being (Colborn

1998; Dikshith et al. 1989). Due to the semi volatility and

persistence in nature, OCP used to detect at remote places

through long range atmospheric transport (LRAT) (Devi

et al. 2013). Although the productions and application of

DDTs and HCHs are banned in developed countries, still sev-

eral developing countries including India involved in

Responsible editor: Hongwen Sun

Electronic supplementary material The online version of this article

(doi:10.1007/s11356-015-5237-5) contains supplementary material,

which is available to authorized users.

* Ishwar Chandra Yadav

[email protected]

1 Central University of South Bihar, BIT Campus,Patna 800014, Bihar, India

2Department of Soil Science and Agricultural Chemistry, Institute of

Agricultural Sciences, Banaras Hindu University, Varanasi 221005,

India

3 State Key Laboratory of Organic Geochemistry, Guangzhou Institute

of Geochemistry, Chinese Academy of Sciences,

Guangzhou 510640, China

4 State key Laboratory of Biogeology and Environmental Geology,

School of Environmental Studies, China University of Geosciences,

388, Lumo Road, Wuhan 430074, China

Environ Sci Pollut Res (2015) 22:20154 – 20166

DOI 10.1007/s11356-015-5237-5

http://dx.doi.org/10.1007/s11356-015-5237-5http://crossmark.crossref.org/dialog/?doi=10.1007/s11356-015-5237-5&domain=pdfhttp://dx.doi.org/10.1007/s11356-015-5237-5


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productions and consumptions of DDTs and HCHs for do-

mestic and agricultural purposes (Yadav et al. 2015)

Soil media act as reservoir of OCPs because of their long

time retention capabilities (Wang et al. 2012; Miglioranza

et al. 2003). Over the span of time, they can gradually be

changed from a major sink to an important emission source

of OCPs to food and drinking water. Substantial amounts (be-

tween 20 and 70 %) of OCPs and their degradation productscan remain in soil after their application. Today, majority of

pesticides used in agricultural fields are synthetic organic

compounds which may pass into the soil by missing their

intended target, released during spraying in plants or through

surface and subsurface runoff from agricultural field (Yadav

et al. 2015). The movement and accumulation of OCP in the

soil are governed by soil properties, chemistry of the OCP

compound, cropping system, irrigation pattern and climatic

conditions (Agnihotri et al. 1994). The physicochemical prop-

erties of the soil such as organic carbon, porosity, texture,

structure and moisture contain appear to control the fate and

persistence of the organochlorine compounds in soil (Backeet al. 2004; Hippelein and Mclachlan 2000). Globally, organic

carbon present in soil plays a major role in the distribution and

persistence of OCPs in surface soil (Yang et al. 2012; Jiang

et al. 2009; Zhang et al. 2013).

Himalayas is the highest mountain range in the world and

has 9 out of 10 of the world’s highest peaks including Mount

Everest. The Indian Himalayan Region (IHR) is one of the

important mountain ecosystems among the global mountain

system (Singh 2006). Geologically, these are young moun-

tains and are significant from the perspective of climate and

as a life support, providing water to a large part of the Indian

subcontinent (Bahadur 2004). Physiographically, it starts from

foothill of south mountain range to Tibetan plateau in north,

since IHR is very high altitude and is strongly influenced by

seasonal fluctuation (Wang et al. 2007, 2010; Chen et al.

2008; Chatterjee et al. 2010; Liu et al. 2010; Gong et al.

2014; Liu et al. 2014). Hence, there is much possibility that

the organic pollutants may get transported and accumulated in

IHR during monsoon especially Indian monsoon through

LRAT mechanism (Wania and Westgate 2008; Qiu 2013;

Gong et al 2014; Liu et al. 2014). Summer Indian monsoon

starts from July through September and enter India from

south-west part (Krishnamurthy and Kinter 2002). Hence,

the air mass filled with great amount of moisture brought by

both monsoon as well as indigenous moisture cause snow fall.

After September, as the sun start receding to south, the north

land mass in Indian subcontinent gets cool fast. This brings

cold wind from north part (Himalayas and Indo-Gangetic

Plain) to the greater part of South Deccan peninsula including

Indian Ocean (Nagarajan 2010). Long range transport and

atmospheric deposition of OCPs get seriously affected by

such Indian monsoon changes (Wania and Westgate 2008;

Chatterjee et al. 2010; Qiu 2013). Hence, understanding the

fate and distribution of OCPs in IHR is matter of great

concern.

IHR has received much attention as it supports wide variety

of flora, fauna, human communities and cultural diversity

(Samant et al. 1998; Zobel and Singh 1997; Rao 1994). How-

ever, the role of IHR as recipient of POPs originating from the

plain is not much considered in the past. Recently, Mishra and

Sharma (2011) analysed human breast milk from Nagaon andDibrugarh and reported exceeding level of DDTs and HCHs.

They found that the local residents of the region are exposed to

high levels of OCP and stressed the need of detailed investi-

gation and monitoring of OCPs in human and environmental

media. Furthermore, evidence suggests that toxic chemicals

are accumulating in the Himalayas and Tibetan Plateau (Qiu

2013; Sheng et al. 2013; Wang et al. 2006, 2007, 2008, 2010)

and stress the need of comprehensive study to assess the level

of organic pollutants in the region. To the best of our knowl-

edge, studies on the assessment of OCPs residual level, their

distribution pattern and risk of OCPs from soil are very limited

in this region. Hence, present study aims to investigate theoccurrence, distribution pattern of OCPs and risk assessment

to ecological unities by residuals OCPs in surface soil from

IHR.

Materials and methods

Description of the study area

The study area (Guwahati, Tezpur, Dibrugarh and Itanagar) is

located in the eastern part of IHR. Guwahati, Tezpur and

Dibrugarh are the part of Assam (an Indian state) while Itangar

is the capital city of Arunachal Pradesh (another Indian state)

(Fig. 1). The Assam is located south of the eastern Himalayas

and comprises the Brahmaputra Valley and the Barak river

valleys along with the Karbi Anglong and the North Cachar

Hills. It is a temperate region and experiences heavy rainfall

and humidity. Guwahati, also the capital city of Assam, lies

between 26.11° N and 91.47° E. Tezpur is situated 175 km

north east of Guwahati and lies between 26.37° N and 92.50°

E, while Dibrugarh is positioned 439 km east of Guwahati and

lies between 27.29° N and 94.58° E (Fig. 1). Itanagar lies

between 27.1° N and 93.62° E. The mean temperature ranges

between 13.5 and 27.5 °C with lowest temperature in the

month of January. Annual rainfall in the area varies from

646 to 726 mm while relative humidity is around 88 %. De-

tails description of sampling sites is presented in Table S1.

Sample collection

A total of 69 surface soil samples were taken and combined

into 23 composite samples. After all, 23 composite samples

were collected (depth ranging from 0 to 20 cm) from all four

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sites, namely, Guwahati (GS1, GS2, GS3, GS4 and GS5),

Tezpur (TS1, TS2, TS3, TS4 and TS5), Dibrugarh (DS1,

DS2, DS3, DS4, DS5 and DS6) and Itangar (IS1, IS2, IS3,

IS4, IS5, IS6 and IS7). Each sample was composite of three

sub samples. Stainless steel scoops were used to collect sur-

face soil. The soil samples were then wrapped in aluminium

foil, packed into sealed polythene bags and kept in ice bag and

transported to laboratory. Hand gloves were used to avoid the

contamination during sampling. The soil samples were air

dried at room temperature. After proper drying, it was ground

to powder and sieved through 1-mm sieve and stored at −4 °C

until analysis.

Physicochemical characterizations

Physicochemical parameter of soil samples was estimated im-

mediately at laboratory of Soil Science and Agricultural

Chemistry, before storing in refrigerator. The pH and EC of

Fig. 1 Map of study area showing sampling locations

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the soil samples were recorded using portable pH/EC metre

(HANNA, H198303). The colour of the soils was identified

by Munsell soil colour chart (Munsell 1973). The percentage

total organic carbon content in soil samples was analysed by

titrimetric method (Walkley and Black 1934; Jackson 1973).

Bulk density (BD) and particle density (PD) were determined

by pycnometer method (Black 1965). Water holding capacity

(WHC) of soil samples was determined by methods of Keen box (Piper 1966).

Extraction and analysis

The required chemical reagents such as dichloromethane

(DCM), n-hexane and acetone were purchased from fisher

Scientific, USA and Tedia Co. USA. OCP standards 2, 4, 5,

6-tetrachloro-m-xylene (TCmX), decachlorobiphenyl (PCB

209) and 2, 2′, 6 , 6′-tetrachlorobiphenyl (PCB54) were bought

from Ultra Scientific. All the glassware was dipped in

K 2Cr 2O7-H2SO4 solution for 24 h and cleaned before experi-mentation. About 10 g of well-dried and homogenized soil

samples were soxhlet extracted for 24 h with DCM as solvent.

Prior to extraction, a known amount of 20 ng of TCmX and

PCB209 was added as surrogate standards. Small chips of

activated copper were added to collection flask to remove

the elemental sulfur. After soxhlet extraction, the extract was

concentrated to about 2 – 3 mL by a rotary evaporator. The

extracted samples were cleaned by alumina/silica column.

The column was packed from the bottom to the top, with

neutral alumina (3 cm, 3 % deactivated), neutral silica gel

(3 cm, 3 % deactivated), 50 % acid silica (3 cm) and anhy-

drous sodium sulfate (1 cm). The column was eluted with30 mL solvent of DCM/hexane (1:1). The eluted fraction

was concentrated and reduced to 0.2 mL on gentle nitrogen

stream. About 25 μ L of dodecane was added as a solvent

keeper. A known quantity of PCB-54 was added as an internal

standard prior to GC analysis. The eluted samples were

injected in to Agilent 6890A gas chromatograph equipped

with a Ni electron capture detector (GC-ECD). Details about

GC-ECD programme and injection time were described else-

where (Devi et al. 2013).

Quality assurance and quality control (QA/QC)

After every ten samples, a set of calibration standards were run

to check for interference and cross contamination. Analytical

grade chemicals reagent was used in this experiment. Field,

procedural and solvent blank were examined by same proce-

dure adopted for original sample analysis. The chromatogram

and peak of the blank solution and standard solution were not

overlapped and appeared clearly. The method detection limits

(MDLs) of OCPs were 3:1 signal versus noise value (S/N).

Surrogate recoveries in all samples for TCmX and PCB 209

were 80±15 %. OCP concentrations were expressed on dry

weight basis and were not corrected for recoveries.

Statistical analysis

Descriptive statistics, Pearson correlation and principal com-

ponent analysis (PCA) were performed using IBM SPSS sta-

tistics (version 21). Samples with BDL concentration were set as zero for calculation and analysis purposes.

Results and discussion

Physicochemical characterization

Physiochemical characterization of surface soil samples was

estimated and presented in Table S2. The majority of soil

samples collected from Guwahati, Dibrugarh and Tezpur

showed yellowish to light brownish in colour while soil sam-

ples from Itanagar exhibit brownish yellow, light brownishgrey, light grey, light yellow and yellowish brown colour.

Water holding capacity (WHC) of the soil samples ranged

from 27.5 to 48.8 % with mean 39.7 %. The BD and PD of

all the soil samples irrespective of study sites showed more or

less similar result and ranged 1.1 – 1.5 mg/m3 and 2 – 2.6 mg/

m3, respectively. The mean pH of soil samples (6.92) showed

slightly acidic in nature and ranged from 4.6 to 8.6. Percentage

TOC content in soil samples was detected low and ranged

from 0.4 to 2.5.

OCP level in surface soil

Descriptive statistics (min, max mean and ±SD) of residual

OCPs analysed in surface soil are presented in Table 1. Ma-

jority of the OCPs compounds were identified in surface soil

of IHR except endrin aldehyde, endrin ketone, cis-nonachlor

and methoxychlor. The ∑OCP level in surface soil of IHR

ranged from 0.28 to 2143.96 ng/g. The OCPs concentration

measured in the present study was comparable with the OCPs

level observed in mountain forest soil in Czech Republic, but

far exceeding those in Mt. Qomolangma, China; Mount

Legnone, Italy; Pyrenees, Europe and Pico de Teide, Spain

(Table 2). Concentration of DDTs was higher than those of

HCHs, which is similar to many previous study reported in

mountain region of the world (Wang et al. 2007; Tremolada

et al. 2008; Xing et al. 2010; Holoubek et al. 2009; Gai et al.

2014). This is because the half-life of DDT (average 10 –

10.5 years) is more than the half life of HCH (average 20 –

50 days) (Harner et al. 1999). Therefore, DDTs are likely to be

more persistent and stay longer in soil as residues. Parent DDT

compound may degrade to DDE and DDD metabolites due to

photo-oxidation mechanism and are more persistent than par-

ent compounds (Miejer et al. 2001). The ∑DDTs accounted


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for more than 97 % of total OCPs, while ∑HCHs and

∑Endos accounted only 0.5 and 0.3 % of total OCP, respec-

tively. The concentration of overall OCPs compounds was

highest in Guwahati and ranged from 1309.4 to 3695.2 ng/g

(mean 2502.2 ng/g), followed by 6 to 1705.7 ng/g in Tezpur

(mean 365.3 ng/g), 5 to 1834.2 ng/g in Itanagar (mean

312.8 ng/g) and 2 to 97.5 ng/g in Dibrugarh (mean

35.7 ng/g) (Table S3). The concentration of OCPs detected

at all sites of present study area is much higher than the

OCPs level observed in soil of other location than mountain

(Table 2), indicating towards accumulation of OCPs at high

mountain Himalayas. This is because larger precipitation

rates and reduced volatilization at high altitudes enhance

atmospheric deposition of OCPs at high-elevation sites

(Blais et al. 1998). The use of DDT (the major component

in OCPs) was banned in India in the year 1985 (Yadav et al.

2015). The high concentration of DDT together with mod-

erate concentration of other OCPs in IHR suggests the

past use of OCPs compound and global distil lation effect

in the region.

Isomer concentration of DDT and HCH

The concentration of OCPs analysed in surface soil from IHR

is shown in Fig. 2. Comparatively, the ∑DDT (217 ng/g) and

∑HCH (1.12 ng/g) were most dominant OCP detected in soil

samples. The concentration of ∑DDT observed at present

study area is several folds higher than reported in Mount

Legnone, Italy (2.2 ng/g) (Tremolada et al. 2008) andRuoergai highland, China (1.63 ng/g) (Gai et al. 2014). The

higher concentration of DDTs is also comparable with other

region of the world (Table 2). Elevated level of DDTs suggests

current use of DDT in IHR. High level of DDT in this studies

area probably because of DDTapplication in tea crop, because

this region is leading producer of tea (Devi et al. 2013). An-

other possible reason may because it is close to agricultural

field of West Bengal India (Chakraborty et al. 2010). The

DDT were likely to be transported a short distance from the

source through atmospheric deposition, because DDT have

short residence time and favour deposition in soil (Qiu and

Zhu 2010; Ricking and Schwarzbauer 2012). The most use of DDTis because of an exception allowed for public health uses

in India. Several DDT metabolites such as p,p′-DDT; o,p′-

DDT; p,p′-DDD; o,p′-DDD; p,p′-DDE and o,p′-DDE were

also detected in soil samples. p,p′-DDT (148 ng/g), o,p′-

DDT (37 ng/g) and p,p′-DDD (13.56 ng/g) were mostly dom-

inant isomers found in present study. High concentration of p,

p'-DDT compared to o,p′-DDT and p,p′-DDD suggests fresh

input of DDT in current study area. The distribution of o,p′-

DDT and p,p′-DDD after p,p′-DDT in the present area indi-

cates active degradation of DDT in the soil and inputs of

already degraded DDT to the area (Hu et al. 2009).

The ∑HCHs (1.12 ng/g) was the next most abundant OCP

after DDTs detected in soil samples of IHR. The observed

concentration of ∑HCHs at present site is very much compa-

rable with the HCHs level in Manipur (Devi et al. 2013) and

several high mountain regionof the world (Table 2). However,

the HCHs level detected in IHR is much lower than Eastern

Tibetan Plateau, and Ruoergai highland in China (Xing et al.

2010; Gai et al. 2014). The elevated level of HCHs in this

study is may be because India is reported to be one of the

largest consumers of HCHs and most contaminated nations

in the world (Yadav et al. 2015). Paddy and cotton are the

two major crops grown India and requires about 29 and

27 % of the total pesticide consumption (Yadav et al. 2015).

Another possible reason was that HCHs used in other region

of India could be air transported and subsequently deposited

in IHR region (Wang et al. 2007; Xu et al. 2012). Among the

HCHs isomers, γ-HCH was most prevalent (0.72 ng/g) iso-

mer detected in soil (Fig. 2). High concentration of γ-HCH is

indicative of presence of lindane contamination. The concen-

tration levels of HCHs were observed in soils in the order γ-

HCH> δ-HCH>α -HCH >β-HCH.β-HCH has the lowest wa-

ter solubility and vapour pressure, which is the most stable and

Table 1 Descriptive statistics of OCPs (ng/g)

Compounds Minimum Maximum Mean Std. Dev.

α -HCH ND 0.33 0.21 0.09

β-HCH ND 0.29 0.06 0.08

γ-HCH ND 1.28 0.73 0.33

δ-HCH ND 0.89 0.13 0.20

∑ HCH ND 2.79 1.12 0.71

o,p-DDE ND 1.97 0.56 0.64

p,p-DDE ND 78.8 15.9 28.4

o,p-DDD ND 10.5 1.60 2.61

o,p-DDT ND 484 36.9 115

p,p-DDD ND 103 13.6 30.4

p,p-DDT 0.28 1448 148 355

∑ DDT 0.28 2127 217 532

α -Endo ND 0.54 0.22 0.16

β-Endo ND 1.26 0.20 0.29

Endosulfansulfate ND 1.03 0.19 0.28

∑ Endos ND 2.83 0.62 0.73

Heptachlor ND 1.46 0.75 0.45

Aldrin ND 2.12 0.60 0.59

Heptachlor-epoxide ND 0.27 0.08 0.08

trans-Chlordane ND 2.79 1.02 0.72

cis-Chlordane ND 0.50 0.14 0.13

trans-Nonachlor ND 0.97 0.10 0.23

Dieldrin ND 1.81 0.11 0.40

Endrin ND 1.21 0.31 0.30

HCB ND 0.27 0.03 0.06

∑OCP 0.28 2144 221 537

ND not detected


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relatively resistant to microbial degradation (Ramesh et al.

1991). Although the use of technical HCH was banned in

agriculture since 1997, but lindane is still allowed to use in

India in public health and in certain crop such as paddy rice

(Kumari et al. 2008; Kata et al. 2014; Yadav et al. 2015). The

presence of HCH and its isomers other than γ-HCH therefore

clearly indicates that these insecticides are still present in the

Indian environment.

Spatial distribution of OCPs

The distribution of OCPs in surface soil from IHR is shown in

Fig. 3. Based on spatial distribution map, high concentration

of OCPs, especially DDTs, was detected at GS2 site in

Guwahati (mean 1837 ng/g) and the lowest concentration

was detected at DS2 site in Dibrugarh (1.41 ng/g) (Fig. 3).

High concentration of DDTs was found in soil samples mainly

Table 2 Comparison

table of ∑DDTand

∑HCH in surface soil

(ng/g) around the world

Location Country ∑DDT ∑HCH Reference

High mountain area

Ruoergai highland China 0.31 – 5.72 0.43 – 10.6 Gai et al 2014

Manipur, Northeast India India 0.49 – 5.68 0.01 – 2.85 Devi et al. 2013

Eastern Tibetan Plateau China 0.15 – 6.69 0.39 – 4.56 Xing et al 2010

Mountain forest soil CzechRepublic 8.80 – 1908 0.26 – 1.66 Holoubek et al 2009

Mount Legnone Italy 0.18 – 11.0 0.01 – 1.88 Tremolada et al 2008

Mt. Qomolangma China 0.39 – 6.06 ND Wang et al 2007

Wolong China 1.23 – 8.81 ND – 3.20 Zhang 2006

Pyrenees Europe 1.70 – 3.40 0.08 – 0.19 Grimalt et al 2004

Pico de Teide Spain 0.01 – 40.0 ND – 1.00 Ribes et al 2002

IHR India 0.28 – 2127 ND – 2.70 Present study

Other location

Hanoi Vietnam ND – 171 ND – 20.5 Toan et al. 2007

Hissar India 0.00 – 66.0 0.00 – 51.0 Kumari et al. 2008

Guangzhou China 7.60 – 663 0.20 – 104 Gao et al. 2008

KS Kaku Pakistan ND – 1538 ND – 119 Syed and Malik 2011

Chihuahua Mexico 1.00 – 788 – Diaz-Barriga et al. 2012

Kurushetra India 0.50 – 37.0 0.60 – 8.50 Kumar et al. 2013

Korba India 2.10 – 315 0.90 – 16.0 Kumar et al. 2014

ND not detected

Fig. 2 Concentration of DDTs and HCHs in surface soil



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from Guwahati. This is because of famous tea crops and veg-

etables production in this region which relatively uses high

OCPs (Muraleedharan 2006; Gurusubramanian et al. 2008).

State of Assam including Guwahati is the world’s largest tea

g ro win g re g io n , p ro d u c in g mo re th a n 4 0 0 mill io n

kilogrammes of tea annually (Asopa 2011). Highest concen-

tration of HCHs (2.12 ng/g) was detected at GS4 site also in

Guwahati and lowest (0.08 ng/g) at DS5 site in Dibrugarh.

The concentration of ∑HCH ranged from 0.52 to 2.12 ng/g

(mean 0.93 ng/g), 0.51 to 1.67 ng/g (mean1 17 ng/g), 0.08 –

1.44 ng/g (mean 0.91 ng/g) and 0.30 to 2.02 ng/g (mean

1.31 ng/g) in Guwahati, Tezpur, Dibrugarh and Itangar,

respectively.

Endosulfan is an organochlorine insecticide that was exten-

sively used around the world to protect vegetables and fruits,

cotton and ornamental plants. It is banned in India because of

its high toxicities. The total concentration of endosulfan in the

soil samples ranged between 0.37 and 2.81 ng/g (mean

1.09 ng/g), 0.22 to 1.73 ng/g (mean 0.73 ng/g), 0.09 to

0.71 ng/g (mean 0.39 ng/g) and 0.09 to 1.74 ng/g (mean

0.64 ng/g) in Guwahati, Tezpur, Dibrugarh and Itanagar, re-

spectively. The highest concentration of endosulfans was

found at Guwahati (Fig. 3). The concentration of β -isomer

was higher than theα -isomer in most of analysed soil samples

indicating the fast degradation of α -endosulfan in soil.

Other OCPs such as aldrin, dieldrin and endrin are all cy-

clodiene chemicals and are lipophilic. The most common

source of general population expose to aldrin, dieldrin and

endrin is through contaminated food products grown in con-

taminated soil. Aldrin, dieldrin and endrin were detected low

in soil samples from all sites. The concentration of aldrin

ranged from 0.07 to 0.73 ng/g, 0.09 to 2.12 ng/g, 0.03 to

1.16 ng/g and 0.02 to 1.95 ng/g in Guwahati, Tezpur,

Dibrugarh and Itangar, respectively. This indicates the histor-

ical use of these compounds before they were banned in India.

This could also be due to transport of air mass from other

Fig. 3 Spatial distributions of OCPs (ng/g) in the Indian Himalayas Region



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region by global distillation effect. Aldrin and endrin were

banned in 1996 and 1990, respectively, while dieldrin was

banned in 2003. Comparatively, higher concentrations of

Aldrin were detected in Tezpur.

Chlordane compounds are group of more than 140 differ-

ent components which include trans-chlordane, cis-chlordane,

heptachlor and trans-nonachlor in major proportion. Hepta-

chlor and chlordane are pesticides commonly used for termitecontrol. Heptachlor is also used in protecting plants seeds or

bulbs while nonachlor is a by-product of the manufacturing of

chlordane and heptachlor. In this study, concentration of hep-

tachlor was most dominant among chlordane compounds in

all sites. The concentration of heptachlor ranged from 0.07 to

1.46 ng/g, 0.34 to 1.44 ng/g, 0.03 to 1.1 ng/g and ND to

1.18 ng/g in Guwahati, Tezpur, Dibrugarh and Itanagar, re-

spectively. The concentration of trans-chlordane and cis-

chlordane was found higher in soil samples from Itanagar

and is comparable with the concentration detected in soil sam-

ple from UK (0.05 – 1.6 ng/g and 0.07 – 1.0 ng/g) (Miejer et al.

2001) and USA (mean 0.49 and 0.43 ng/g) (Aigner et al.1998).

Although HCB is not a registered pesticide in India, it

accounted about 30 % of total pesticides consumed in the

country (Yadav et al. 2015). The concentration of HCB was

detected low in all soil samples in the region. The highest

concentration of HCB was found in soil samples from Itana-

gar (0.27 ng/g).

Interrelationship of TOC and OCPs

TOC of the soil is an important factor that controls the fate and

distribution of OCP in soil (Yang et al. 2012). Organic carbon

in soil has affinity to bind OCPs because of their hydrophobic

nature (Jiang et al. 2009). Increase in organic content in soil

can provide more carbon source to microbial degradation of

OCPs. In present study, TOC content was positively and

weakly correlated with ∑DDTs (r 2=0.130) and ∑HCHs

(r 2=0.130) Fig. 4. Likewise, other OCP such as Endos and

Heptachlor were positively and weakly linked with TOC.

However, organic carbon was strongly and positively corre-

lated with α -HCH (r =0.765) and γ -HCH (r =0.612). The β -

and δ -HCH isomers were weakly and positively correlated

with organic carbon (Table S4). This indicates the soil organic

carbon may increase the accumulation OCP in soil. Majority

of the DDT metabolite and other individual OCP compounds

were weakly and positively correlated with organic carbon.

This suggests other factors such as land use type, particle size

and soil chemistry may also contribute towards the retention

of individual OCPs in soil (Zhang et al. 2013; Jiang et al.

2009). Our findings are consistent with the previous studies

(Zhang et al. 2013; Mishra et al. 2012; Jiang et al. 2009).

Furthermore, p,p′ -DDE was strongly and positively correlated

with o,p′-DDD (0.829), o,p′-DDT (0.565), p,p′ -DDD (0.863)

and p,p′ -DDT (0.811) (Table S4). γ -HCH was significantly

and positively correlated with HCB (0.683) and o,p′ -DDT

(0.731) suggesting similar sources of origin.

Source identification

The ratio of parent compound and their metabolite (also

known as diagnostic ratio (DR)) is used to identify the possible pollution source. p,p' -DDE and p,p' -DDD are the two

main metabolites of p,p' -DDT, and their ratio are used to in-

vestigate the extent of DDT degradation in the environment

(Eqani et al. 2011; Sarkar et al. 2008). DDTs are degradable

into DDD through reductive dechlorination under anaerobic

environment while into DDE under aerobic environmental

conditions. The DR of p,p' -DDT/( p,p' -DDD+ p,p' -DDE) >1

indicate fresh application, while


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Technical chlordane was mainly used to control termite, to

control weeds in field and kill insects in soil. Normally, cis-

chlordane to trans-chlordane ratio in technical chlordane

should be 0.79 (Rostad 1997; Dearth and Hites 1991). It is

fact that trans-chlordane degraded faster than cis-chlordane in

the environment. The cis-chlordane/trans-chlordane ratio >1

indicates the historical use of chlordane (Eitzer et al. 2001;

Bidleman et al. 2000). In our study, the ratios of cis-chlor-

dane/trans-chlordane in soils were


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γ -HCH can be explained by the isomerisation of γ -HCH

(Manz et al. 2001). PC 3 accounted for 15.48 % of variation

in OCPs data and was positively dominated by α-endosulfan

and ∑endos indicating the similar source of contamination.

PC4 represented 1.8 % of the total variance in OCPs data,

with high positive loading on β -endosulfan (0.809), Aldrin

(0.594) and dieldrin (0.704). The loading plot of first three

components (PC 1, PC 2 and PC3) which explained 57 %variation in OCPs data is shown in Fig. 5. It is evident from

Fig. 5 that heptachlor, heptachlor epoxide, cis – chlordane, en-

drin and trans-chlordane were separated from other OCPs

suggesting different source of origin. PC5, PC 6 and PC7

did not contain distinctive sources of variance in OCPs data

because of not having loading value greater than 0.50. Hence,

they are not considered and dropped from interpretation.

Ecological risk assessment

To assess the potential ecological risk of OCP residues, theconcentration of DDTs and HCHs in soil was compared with

the related soil quality guideline. Standard guidelines for

OCPs compounds in surface soil are not available in India.

Hence, our results are compared with the soil quality guide-

lines recommended by U.S. National Oceanography and At-

mospheric Administration (NOAA), Canada government and

Chinese government. NOAA permits HCH level ranging from

50 ng/g in agricultural soil to 2000 ng/g in residential soil to

protect human health and environment (Buckman 1999). The

Canada government allows DDTconcentration up to 700 ng/g

in residential and agricultural soil and 1200 ng/g in commer-

cial and industrial soil. In our study, the level of HCH and

DDT was below the NOAA and Canada government recom-

mended guidelines.

The concentration of HCHs was observed in the present

study below the secondary standard value (500 ng/g dry wt.)

prescribed by Chinese government for safe agricultural farm-

ing (Wang et al. 2008). Likewise, DDTs’ concentration in all

soil samples except samples from Guwahati was below Chi-

nese standard value. DDTs’ concentration in soil samples

from Guwahati (1249.2 ng/g) showed twice as high as Chi-

nese standard value. This indicates that the soil at Guwahati iscontaminated with OCPs and is unsafe for agricultural farm-

ing. Similarly, primary standard values (50 ng/g dry wt. for

DDTs and HCHs) were set up by Chinese government to

protect environmental ecosystem and to maintain the quality

of background soil. In this study, six samples contained DDTs

higher level than the standard value. The level of HCHs in all

the soil samples was well within the limit of standard value.

The β -HCH level in all samples was below the critical level of

40 ng/g dry wt. This suggests soil in the study area is less

contaminated with β -HCH and is safe. The level of α -HCH

and γ-HCH in all soil samples was below the critical concen-

trations of 100 and 10,000 ng/g, respectively, (Urzelai et al.2000). Maximum concentration of DDTs allowed in soil is

10 ng/g in case of plant and invertebrate, 11 ng/g for small

birds and mammals and 190 ng/g for birds and animals (Qu

et al. 2015; Yu et al. 2013). In our study, the concentration

level of DDTs in eight soil samples were above the 11 ng/g dry

wt. limit, while only four samples exceed 190 ng/g concentra-

tion limit. Hence, it is concluded that the soil of the present

study area is partially contaminated with DDT and is modest

hazardous to plants, invertebrates, birds and mammal.

Conclusions

In the present study, high concentration of OCPs compounds

was detected in the soil samples. The concentration of ∑OCPs

ranged from 0.28 to 2143.9 ng/g, which was higher than the

OCP residues reported in plain region of India; hence, indicat-

ing accumulation of OCPs in IHR. The concentration of DDTs

(mean 216.6 ng/g) was mostly dominated among all OCPs.

Elevated concentration of DDTs in IHR suggested the current

use of DDT because of an exemption allowed for DDT use in

public health. Spatial distributions of OCPs suggested the

prevalence of DDTs at Guwahati (mean 2502.2 ng/g), while

Itanagar detected maximum concentration of HCHs. TOC

content in soil samples was strongly and positively correlated

with α -HCH (r =0.765) and γ-HCH (r =0.612) indicating the

role of organic carbon in accumulation of OCP in soil. Diag-

nostic ratio of DDT metabolite suggests the source of DDT

contamination in IHR due to recent use of technical DDT and

dicofol. The PCA analysis confirms the HCH pollution in the

IHR due to mixture of technical HCH and lindane. The eco-

logical risk of the OCPs in soil samples was assessed based on

soil quality guidelines recommended by Chinese government,Fig. 5 Loading plot of firstthreemajor components (PC1,PC2 andPC3)

of PCA showing distribution of individuals OCPs



11/13

Canada government and NOAA. Based on NOAA and Can-

ada government guidelines, the residual OCPs (DDT and

HCHs) in IHR may be classified as slightly contaminated

making them somewhat suitable for agricultural production.

However, the DDTs’ residue level in soil of Guwahati

exceeded the Chinese government ’s soil quality guideline in-

dicating the severe contamination of soil.

Acknowledgement NLD is thankful to University Grant Commission

(UGC), NewDelhi forfinancial assistance in theform of Dr. D.S. Kothari

Postdoctoral Fellowship.

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ESPR_Devi Et Al 2015