INTRODUCTION:

Tea is one of the commonly consumed beverages in the world for its desirable aroma, taste and putative positive physiological functions^[1],[2]. The growing interest in drinking tea all over the world would be connected with polyphenol antioxidative activity, fighting the harmful influence of environmentally generated free radicals ^[3]. Tea leaves contain polyphenols which exhibit antioxidant ^[4], lowering cholesterol ^[5], hepatoprotective ^[6] and anticancer activities ^[7],[8]. Green tea possesses antibacterial, antitoxin, antiviral and antifungal activities ^[9]. The human body requires both metallic and non-metallic elements within the certain permissible limits for growth and good health ^[10]. Tea leaves are source of mineral elements such as copper, iron, manganese zinc, magnesium, sodium, potassium, phosphorous, iodine and fluorine ^[2]. Trace amount of copper is essential for human health ^[10].

Through Cu, Fe, Mn and Zn are known as the heavy metals but traces of these metals are essential for growth of the plant, therefore, these metals are treated as micronutrients.

High concentration of micronutrient metals may affect the ecosystem and human health. At low doses of some heavy metals are essential for plants, but the higher doses, they may cause metabolic disorders and growth inhabitation in most plant species ^[11]. Cu and Zn are trace elements that are essential for human health, but in high doses Cu can cause health problems such as anemia, liver and kidney damage, and stomach and intestinal irritation ^[12] and very high concentration of Zn can damage the pancreas and disturb the protein metabolism, and cause arteriosclerosis. Micronutrients present in the roadside soils and grasses may be transported through the food chain to the human body and have a significant toxicity to people^{[13], [14]}. The pollution of soils and vegetation by trace metals from automobile sources is a serious environmental issue ^[15]. With the rapid industrialization and urbanization trend, the increment of traffic activities substantially contributes to the accumulations of micronutrients discharged by vehicles in roadside environment. Road traffic activities are the major source of micronutrients emission to roadside soils ^[16]. Zn comes from tyre wear and galvanized parts such as fuel tanks ^[17]. Brake wear is the most important source for Cu. Micronutrient pollution in agricultural areas owing to traffic emissions may contaminate the crops growing near roadways ^[18]. In agricultural areas, uptake of micronutrients through the soil- crop system could play a predominant role

in human exposure to heavy metals ^[19]. Numerous previous studies have investigated the influencing mechanism of vehicle emissions on concentrations of micronutrients in roadside soils ^{[20], [21]}. The concentration of micronutrients decreases with increasing roadside distance ^{[22], [23]}. Therefore, determination of micronutrients in soil is essential for understanding their nutritive importance. Hence the aim of the study is to determine the concentration of Cu, Fe, Mn and Zn roadside tea cultivated soil.

MATERIALS AND METHODS:

Study Area:

This study was conducted in tea plantation areas inside the national highway. Tea estates are selected for study in the Dibrugarh district of Assam. Dibrugarh district is situated in the eastern part of Assam. The district extends from 27⁰05.38^/ N to 27⁰42.30^/ N Latitudes and 94⁰33.46^/ E to 95⁰29.80^/ E Longitudes. The geographical area covered by Dibrugarh district is 3381 sq km. The area of the Dibrugarh district experiences subtropical monsoon climate with mild winter, warm and humid summer. Rainfall decreases from south to north and east to west in the area. The average annual rainfall in this district is 276 cm with a total number of 193 rainy days.

Physico-chemical properties of soil:

The soils of the area are basically the products of the fluvial processes of the Brahmaputra and its tributaries. The plains are composed of alluvium which may be classified as new and old. The new alluvium varies mostly from clayey to sandy loam in texture and is slightly acidic in reaction. In certain parts, both the old and new alluvium are so combined that it is difficult to distinguish them. The pH ranges between 4.2 and 5.5. The new alluvium is less acidic as compared to the old alluvium. Its pH value varies from 5.5 to 9.9. Tea is abundantly grown in the old alluvium as it has high percentage of acid. The tea estates are located over relatively high lands with discernible slopes containing both old and new alluvium.

Soil sampling and Laboratory analyses:

A total of 60 topsoil samples were collected from the roadside tea cultivated soils of Dibrugarh district of Assam during the January 2014. For each sampling site (both sides of road, NH 37), three topsoil ( 0-20 cm) samples were collected according to 100 m, 200 m and 300 m roadside distances. Composite soil samples were taken and prepared for necessary analysis in the laboratory ^[24],[25]. Samples from the control sites were collected following the same procedure. 1.0 g air dried sieved soil sample was placed in 100 ml beaker with 15 ml of concentrated HCl, 5 ml concentrated HNO₃ and 3 ml concentrated H₂SO₄ and heated at 95-100⁰ C on hot plate. After proper digestion, the digest was made up to 50 ml with deionised water. The extract was analysed using AAS (Varian Spectra AA 220). Same procedure was carried out on control soil sample. The locations of sampling stations were determined by using Global Positioning System (GARMIN e-Trex 30).

RESULT AND DISCUSSION:

The results of analysis of tea cultivated soil samples are presented in tables 1, 2, 3 and 4.The results of analysis of control soil is presented in table 5. There was wide variation in the micronutrient concentration of tea cultivated roadside soils. The results indicated that the concentration of of Cu,Fe, Mn and Zn in soil were different for the different soil sampling locations. The concentration of Cu measured in left and right sides of the national highway were 22.15±3.91 to 27.10±3.08 and 21.74±2.06 to 25.72±4.12 mg/kg respectively. The concentrations of Fe were 268.16±32.08 to 292.72±3014 and 266.48±28.14 to 290.68±30.22 mg/kg respectively. The concentrations of Mn were 244.36±32.05 to 322.18±48.06 and 322.18±48.06 to 242.94 to 308.25±40.28 mg/kg respectively. The concentrations of Zn were 32.58±2.74 to 48.24±2.48 and 30.56±2.34 to 46.52±3.02 mg/kg respectively. It was observed that manganese (Mn) has the highest concentration level in all the samples analysed followed by iron (Fe), then zinc (Zn) and copper (Cu). Therefore, the concentration of the micronutrients in decreasing order is given as Mn > Fe > Zn > Cu. These level agreement in the typical ranges of the average concentration in the Earth’s crust ^[26]. These levels are not as high as the ranges reported in roadside soils of England (Cu 15.5- 240.0 mg/kg, Zn 56.70- 480.0 gm/kg ) and Mn concentration in Malaysia soil is 200 mg/kg ^[27] which were higher than natural background levels reported for British soils ^[15]. All of the micronutrient concentrations show a declining trend with the increase of distance from the road (Fig. 1 to 8). The micronutrient concentration is higher near the roadside soil and gradually decreases as the distance increases. The possible accumulations of the roadside soil occur due to continual usage of the road by automobile. The micronutrients are emitted from various sources into the atmosphere. Most studies have used soil samples to monitor their metallic levels ^{[28], [29], [30]}.

Table 1. Concentrations of Cu and Fe in roadside tea cultivated soils in mg/kg (from Moran to Dibrugarh, NH 37 left side)

Variable	Level	Cu		Fe
Variable	Level	Range	SD	Range	SD
	100m	27.10±3.08	7.36	292.72±30.14	32.44
Distance		(24.02-30.28)		(262.58-322.86)
	200m	26.35±2.49	6.65	284.42±28.34	36.82
		(23.86-28.84)		(256.08-312.76)
	300m	22.15±3.91	7.25	268.16±32.08	40.24
		(18.24-26.06)		(236.08-300.24)

Table 2 . Concentrations of Mn and Zn in roadside tea cultivated soils in mg/kg (from Moran to Dibrugarh, NH 37 left side)
Variable	Level	Mn		Zn
Variable	Level	Range	SD	Range	SD
	100m	322.18±48.06	38.74	48.24±2.48	12.72
Distance		(274.12-370.24)		(45.76-50.72)
	200m	286.24±40.18	40.26	40.36±3.16	14.25
		(246.06-326.42)		(37.20-43.49)
	300m	244.36±32.05	42.78	32.58±2.74	17.06
		(212.31-276.41)		(29.84-35.32)

Table 3. Concentrations of Cu and Fe in roadside soils in mg/kg (from Moran to Dibrugarh, NH 37, right side)
Variable	Level	Cu		Fe
Variable	Level	Range	SD	Range	SD
	100m	25.72±4.12	6.92	290.68±30.22	30.36
Distance		(21.60-29.84)		(260.46-320.90))
	200m	23.06±3.78	7.68	282.04±26.64	36.78
		(19.28-26.84)		(255.40-308.68)
	300m	21.74±2.06	5.98	266.48±28.14	42.14
		(19.68-23.80)		(238.34-294.62)

Table 4. Concentrations of Mn and Zn in roadside soils in mg/kg (from Moran to Dibrugarh, NH 37, right side)
Variable	Level	Mn		Zn
Variable	Level	Range	SD	Range	SD
	100m	308.25±40.28	38.02	46.52±3.02	15.64
Distance		(267.97-358.53)		(43.50-49.54)
	200m	264.38±39.34	40.26	39.84±2.16	17.65
		(225.04-303.72)		(37.68-42.00)
	300m	242.94±30.74	42.78	30.56±2.34	16.42
		(212.20-273.68)		(28.22-32.90)

Fig 1. Concentration of Cu in mg/kg on the roadside (left) tea cultivated soil

Fig 2. Concentration of Fe in mg/kg on the roadside (left) tea cultivated soil

Fig 3. Concentration of Mn in mg/kg on the roadside (left) tea cultivated soil

Fig 4. Concentration of Zn in mg/kg on the roadside (left) tea cultivated soil

Fig 5. Concentration of Cu in mg/kg on the roadside (right) tea cultivated soil

Fig 6. Concentration of Fe in mg/kg on the roadside (right) tea cultivated soil

Fig 7. Concentration of Mn in mg/kg on the roadside (right) tea cultivated soil

Fig 8. Concentration of Zn in mg/kg on the roadside (right) tea cultivated soil

Cu concentration in tea cultivated soil ranged from 21.74±2.06 to 27.10±3.08 mg/kg and was recorded lowest of all the studied metals. Break dust recognized as a source of Cu which is used in brakes to control heat transport ^[31],[32]. Cu is usually present in soils within the range of 0 to 250 mg/kg ^[15]. The observed level is lower than 15.5 to 240.0 mg/kg reported in roadside soil of England ^[15].

Zn concentration in tea cultivated soil ranged 30.56±2.34 to 32.58±2.74 mg/kg. Normal concentration of Zn in soil ranges from 1.00 to 900 mg/kg (Akbar et al., 2006). The observed level is lower than Zn 56.7 to 480.0 mg/kg reported in roadside soil of England. Zn is used in brake linings because of their heat conducting properties and as such released during mechanical abrasion of vehicles, and from engine oil combustion and tyres of motor vehicles ^[15],[
32].

Mn concentration in tea cultivated soil ranges from 242.94±30.74 to 322.18±48.06 mg/kg. Normal concentration of Mn in soil in Malaysia is 200 mg/kg ^[27]. The observed level is higher than the normal which indicates that the soil of the study area is contaminated with Mn. When the concentration is low it is believed to be important for the function of enzymes system energy metabolism and oral supplementation is believed to be lower blood glucose levels ^[27].

Fe concentration in tea cultivated soil ranged 266.48±28.14 to 268.16±32.08 mg/kg. Fe form the composition of soils and their availability in a trace amount as obtained in this study could be due to local condition of soil weathering.

CONCLUSION:

The result of this work show that the concentration of the micronutrients in the tea cultivated roadside soil is comparatively high but lower the permissible limits. The micronutrient concentration is higher near the roadside soil and gradually decreases as the distance increases. The concentrations of the metals in the soils are in the order Mn > Fe > Zn > Cu. In the absence of any major industry in the sampling sites these observations suggest that motor vehicles on the roads were the may be sources of these metals to the roadside soils. Therefore regular monitoring of micronutrient metals in tea cultivated soil is essential.

ACKNOWLEDGEMENTS:

The author is gratefully acknowledging the financial support of MRP (No. F.5-28/2013-14/MRP/NERO/444) of UGC-NERO, Guwahati, Assam, India.

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Received on 14.11.2014 Modified on 01.12.2014

Asian J. Research Chem 8(1): January 2015; Page 30-35

DOI: 10.5958/0974-4150.2015.00007.3

Sl. No	Micronutrient	Concentration
1	Cu	12.34
2	Fe	126.42
3	Mn	138.78
4	Zn	20.52