Background
In southern India blister blight incited by Exobasidium vexans Massee is the most important leaf disease in tea, causing heavy crop loss. The pathogen is an obligate parasite without any alternate host and it completes its life cycle within a short period of 11 to 28 days. Since climatic conditions prevailing during the monsoon are conducive for this pathogen, the crop has to be protected with periodical application of fungicides throughout the season. Earlier, only protectant fungicides were used to control blister blight. Later, a combination of protectant and eradicant fungicides and of late, systemic fungicides are used to control the disease. Among the protectant fungicides copper formulations have wide acceptance. Among the copper fungicides, (COC) copper oxychloride 50 WP (Wettable powder) is being used in tea plantations of south India against blister blight for the past five decades. Copper content was 50 per cent and suspensibility was 84 per cent in copper oxychloride. Under natural weather conditions, retention of copper oxychloride on the leaf surface was superior to other inorganic fungicides. The fungicides were regularly applied on the field grown susceptible clonal tea at an interval of 7 – 10 days. Hexaconazole, propiconazole and tridemorph are the recommended fungicides. In southern India, the disease is largely controlled by the use of triazole fungicides along with the combination of copper oxychloride (Hudson et al., 2002).

Based on the above observations and literature survey this study was undertaken. The present study was to determine the heavy metal, Pb in different brands of commercial grade copper oxychloride formulations. The Food and Agricultural Organization of United Nations give the specification of permissible amount of heavy metal impurities in copper oxychloride as 250 mg kg-1 to lead (FAO, 1991). The impurity profile study indicates that copper fungicides contain heavy metals. Lead is a major contaminant in copper oxychloride.

The heavy metals present in food and beverages are detrimental to human health and most countries restrict the concentration of metals like lead, cadmium etc. The non-edaphic factors that are potentially contributing to the occurrence of Pb in made tea have been investigated. A review on literature revealed that some work has been done on Pb accumulation in tea and are mainly attributed to industrial activity through the precipitation of atmospheric lead (Jin et al., 2005a) and surface dust contaminations through vehicular pollution (Han et al., 2006). Except for some work on these line carried out in plants like Tobacco on long term usage of copper fungicides (Semu and Singh, 1996), informations on tea is limited. An attempt has been made to investigate Pb contamination in tea due to application of COC formulation for the control of blister blight in tea plantations in south India.
 
1 Results and discussion
Elemental concentrations in the formulated fungicides are compared with FAO specifications. The results are summarized in Table 1. The results indicated that all the brands of copper oxychloride formulations tested contained impurities lower than the FAO specifications, except for four samples which showed slightly higher amount of Pb (<250 mg kg-1) and eight samples contained low amount of Pb (<50 mg kg-1).

As COC contained heavy metal impurities, its repeated application to control blister blight disease during monsoon months enhanced the heavy metal concentration, particularly Pb, in harvestable crop shoots. The first foliar application of COC had no significant Pb content in black tea (Table 2). But subsequent applications of COC increased Pb content in the harvested shoots. COC application along with hexaconazole showed a no increase in Pb content. Results indicated that repeated applications of COC singly or in combination with hexaconazole resulted in the accumulation of Pb. However, continuous application of COC did not show significant result in Pb accumulation beyond the threshold level in black tea. This may be due to the rainfall intensity during the application of COC and or higher leaf wetness which hindered the retention of foliar applied COC.

Jin et al. (2005b) reported that the increment in Pb concentration in black tea manufactured by CTC process may be attributed to the contamination of Pb impurity from the metal surface of the machine. The present study concluded that there is a strong possibility of Pd getting accumulated through the fungicide formulations. Application of impure copper fungicide formulations to tea leaves could increase the accumulation of heavy metals such as Pb in black tea, thus increasing the health hazards and the ecological risks due to excessive application of chemicals on tea.

2 Conclusions
As a practice, before application in the field, these agro inputs should be analysed by the estates for their suitability as per national standards.

3 Materials and methods
3.1 Sampling
Wettable powder formulations (50%) of four different brands consisting of thirty fungicide samples were collected from commercial market, local garden supply stores, and local tea gardens. All the samples were suitably labeled.

3.2 Field experiments
In tea, the contact fungicide COC is applied in combination with systemic fungicides to protect the plants from the incidence of blister blight disease caused by the fungus, Exobasidium vexans Massae (Chandra Mouli, 1993). Foliar application of COC is done at short intervals ranging from 5 to 7 days through out the monsoon period (Premkumar and Baby, 2005). COC is a source of Pb contamination. To generate information on the accumulation of Pb due to foliar application of COC, a field experiment was conducted at the Tea Experimental Farm, between July and September. Experimental plots were laid in randomized block design in a clonal tea field. Each plot measured 10 m x 10 m and plots were separated by three guard rows to prevent drift while spraying. There were three treatments, viz., COC 210 g ha-1, COC in combination with hexaconazole (210 g + 200 ml ha-1) and untreated control. All the treatments were replicated in seven plots. Foliar application was done using hand operated knapsack sprayer with a spray volume of 175 l ha-1. Two kg of the harvested crop was sampled from each plot on the seventh day after application and also before the next round of fungicide application. Sampled green leaf was processed into black tea in the mini manufacturing unit, as described earlier. The processed black tea samples were subjected to elemental analysis.

3.3 Sample preparation
The lead traces in the copper oxychloride fungicides were determined as reported by Franklin et al. (2005). About 1 g of solid or 1 ml of liquid sample was digested with 20 ml of aqua regia (HCl: HNO3, v/v 3:1) on a hot plate until a clear solution was obtained. The digested mixture was diluted with deionised water and made up to the mark in 100 ml pre-calibrated volumetric flasks. Samples were further diluted to 10 times with deionised water and analysed in GF-AAS. (Perkin Elmer AAnalyst 800, The Netherlands).

The tea samples were processed following the methodology as described in AOAC, 2000. In a washed clean dry crucible, 0.5g of sample (black tea) was weighed and kept in a muffle furnace at 450°C for 3 hours. After ashing 5 ml of 0.6 M HCl was added and the acid solution was allowed to evaporate in a hot plate. The residues filtered (using Whatmann filter paper No. 545) in 50 ml volumetric flask using 0.1 M HNO3. Simultaneously blank was also prepared without sample. All glassware and polyethylene sample containers were washed with tap water after each use, soaked (over night) in 6N HNO3 solution and rinsed several times with distilled water (Cabrera et al., 1994), in order to minimize the absorbance due to impurities.

Authors Contributions
SS conducted the field trials, sample preparation, metal analysis and interpreted the results. NM approved the protocol and drafted the manuscript.

Acknowledgements
The authors are grateful to Tea Board, Govt. of India for the financial assistance under Tenth five year plan.

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