Heavy metals are basically the constituents of natural waters, usually present at low concentration. Heavy metals like copper, zinc, iron, molybdenum, vanadium, manganese and cobalt are essential for the living organisms within the permissible limits. These metal ions play a variety of functions in biological systems as important structural components in proteins. As a result of increased anthropogenic activities the concentration of heavy metals in water is exceeding, imposing serious environmental impacts.
The effluents discharged by the industrial and domestic sources are potential water pollutants (Aslam, 1998). These effluents generally have high values for the physico-chemical parameters like electrical conductivity; pH, hardness, alkalinity, and chemical oxygen demand etc. these effluents contain organic and inorganic waste. Organic waste includes fats, oil grease and inorganic waste includes mainly the heavy metals like iron, copper, zinc, manganese, cadmium, lead, arsenic, nickel and cobalt. Water contaminated by heavy metals is sometimes used for the irrigation of either food crops or medicinal plants. The heavy metals are accumulated in the soil and uptaken by the plants where they introduce the metal toxicity. Heavy metal toxicity is a result of the complex interaction of metal ions. (Latif et al, 2008).Metal ions by replacing the ions with metaloenzymes interferes the enzyme action. Cadmium shows the severe effects on plant seedling, length, dry weight and structural change in chloroplast (Latif et al, 2008). The plants containing heavy metals, consumed by the humans alter the biological system. Mostly the accumulation of toxic metals takes place in liver and kidneys, causing the disturbance of biochemical processes (WHO, 1992)
Industrialization is increasing in Pakistan and this has resulted in deterioration of water and the soil. It has been observed that a wide majority of industries discharge untreated effluent into river and only 10% industries had primary treatment plants (Dada 1997).The waste and effluents of the industries are discharged into the Nullah or rivers which then carry the effluents to the different compartments and contaminate the environment.
Nullah lai which originates from Islamabad and flow towards Rawalpindi finally enters in river soan, carrying different types of organic and inorganic waste from industries, residential commercial and sewage effluents. In Rawalpindi 65% of the wastewater is being disposed of into open drains that ultimately drain off into Nullah Lai (Islam-ul-Haqet al., 2007). Various industries are situated around the Nullah lai that includes oil refineries, textile mills, marble crushing units, flour mills, soap and detergent, hydrogenated oils, automobiles, steel and electroplating, steel re-rolling mills, pipe industries and rubber industries. The medicinal plants, frequently used by the local community like cannabis sativum and Parthenium hysterophorous are irrigated by the waste. These medicinal plants uptake the toxic metals accumulated in the soil. Most of the herbal plants are used by herbalist for the herbal therapy. (Adeel et. al 2013).
This study was conducted to assess the heavy metal concentration resulted from uptake by the medicinal plants and their transfer to the food chain which assist in evaluating the related health hazards linked with it. To compare the concentration of heavy metals in plants of different areas of the lai drain. To compare the concentrations of heavy metals with permissible limits set by WHO for heavy metals in medicinal plants.
2. EXPERIMENTAL METHODOLOGY
2.1 SITE DESCRIPTION
Study was conducted in different areas of Nullah lai. The elevation above sea level is about 425 meters. It lies between Latitude of 33??33'1.08" and Longitude 73??6'1.81. The Nullah lai passes from Islamabad and Rawalpindi and has a catchment area of 234.8 km2. Its upstream areas are located in Islamabad and the mid-stream includes areas of Islamabad and Rawalpindi and finally it enters into river soan that is the downstream of the Nullah Lai drain.
Study area was divided into upstream mid-stream and downstream areas. Four sampling sites were selected. In which there was 1 site for upstream areas that includes the area of saidpur village in Islamabad region. Site 2 and 3 were the mid-stream areas of lei drain that includes Kattarian Bridge (khayaban-e-sirsyed) and Gawal mandi. Mid-stream of the drain contains most of the pollutants coming from industrial area I-9 and I-10 which includes heavy metals like zinc, cadmium and copper. The 4th site was downstream area which includes area where lai drain merges into the river soan.
FIG 1 : SHAPE FILE OF SAMPLING AREA (NULLAH LAI)
2.2 SAMPLE COLLECTION
Total forty nine samples of three species (Parthenium hysterophorous, cannabis sativum and coronopus didymus) were taken from all four sites. Samples were taken randomly from all sites and stored in newspapers and polyethylene bags and were labelled. Those species were collected which were mostly common in all three sites in order to compare the concentration level of pollutants in plants growing on the edges of upstream, mid-stream downstream of the drain
2.3. SAMPLE PREPARATION
Fresh weight of plants was measured by using weighing machine (Sartorius P-319). Plants were sectioned into different parts i-e roots, stem and leave and were washed with tap water to remove soil and other visible contaminants and then with de- ionized water. Air drying of samples was done at room temperature for 24 hours. Further the samples were dried in drying oven (SNHZ-TECIT) for moisture removal from plants at 500C for 24 hours. Samples were ground using grinding machine (RETSCH) and were kept at 40C in Polyethene bags.
A total of 10 ml mixture of HNO3 and HCLO4 in 2:1 was added into 0.25g medicinal plants sample that was left for overnight digestion. It was heated on hot plate at temperature of 100-1500C, until brown fumes was changed into white fumes. The solution was filtered over filter paper no. 42 by raising the remaining volume with de-ionized distilled water up to the mark 50 ml and kept in plastic bottles at room temperature for heavy metals analysis.
3. RESULTS AND DISCUSSIONS:
Concentrations of heavy metals found in all three species of medicinal plants which are under studied are given in Table 1.1, 1.2 and 1.3. Analysis of results shows that for Parthenium hysterophorous in upstream the mean concentration of the heavy metals decreases in the order of Zn>Mn> Cu> Cr> Cd> Ni >Pb. The zinc shows the higher concentration that is about 13.10 mg/g. In midstream regions the decreasing trend of heavy metal is like Mn> Zn> Cr> Cu> Ni> Cd >pb as 12.83 mg/g of Mn is recorded whereas in downstream the concentration of heavy metals decreases in order of Zn >Mn> Ni> Cu> Cr> Cd>pb with the concentration of Zn being recorded as 15.88 mg/g. (fig: 4 a) Mn showed the maximum SD values within 3 regions for Parthenium hysterophorous ranges between 1.0_1.33. The mean values with standard deviations are given in Table 2
The heavy metal concentration trend for coronopus didymus decreases in upstream in the order of Mn> Ni >Cr>Zn> Cu >Cd>Pb with 9.89 mg/g of Mn. In midstream decreasing order of metal concentration is like Mn> Cr > Ni> Zn >Pb> Cd > Cu with 13.93 mg/g of Mn where as in downstream it decreases in order of Mn> Ni>Cr>Zn>Cd>Cu>Pb with 12.23 mg/g of Mn is shown in graphical form in figure 4.0(b) Maximum standard deviation of 1.43-1.76 is shown by Mn in all the sites. Pb is found in least concentration in all three areas.
Decreasing order of cannabis sativum is like Zn> Ni >Mn> Cu>Pb> Cu>Cd in upstream areas. Whereas in mid-stream Zn has higher concentration it is followed by Cr> Ni>pb>Mn>Cu>Cd where as in downstream the decreasing trend of heavy metal concentration goes like Zn> Ni > Cr>Mn>Pb> Cu>Cd. Zn has shown maximum concentration in all three areas that ranges from 30.71 to 45.53 mg/g. (fig: 4.0 c) Upstream, midstream and downstream areas shows maximum concentrations of zinc and manganese accumulated in medicinal plants. The major sources of zinc and manganese are industrial effluents and sanitary wastes from nearby industrial and residential areas as the Nullah lai passes from nearby of these sources.
By comparison of mean values of samples all the three region , we get to know that for Parthenium hysterophorous species , there is overall less concentration of heavy metals accumulated in samples from upstream region whereas samples from midstream and downstream shows almost equal mean concentrations. A Coronopus didymus sample shows almost same range of their mean values from all regions. Cannabis sativa shows great variation in mean values of concentrations of accumulated heavy metals, less concentration for upstream region and higher concentration in mid-stream and downstream region. Higher concentration in mid region shows the entrance of high amount of industrial effluents and sanitary disposal in Nullah lai from different sources. Irrigation of plants by wastewater of Nullah lai is major source of accumulation of zinc and manganese in medicinal plants. Cannabis sativa shows the highest concentration of heavy metals among all species of medicinal plants as shown in Table 2. These variations can also be explained by varying uptake mechanisms and uptake efficiencies of different medicinal plants''
A concentration of all studied heavy metals (Ni, Cu, Mn, Cr, Pb, Zn and Cd ) for all the samples with permissible limits given by World health organization (WHO) for medicinal plants in mg/kg are given in Tables 3.1- 3.9 . Data represents the minimum and maximum ranges for heavy metal concentrations and permissible limits by WHO.
As shown in results Ni, Cr and Cd concentrations exceeds the permissible limits. Although, Mn and Zn show highest concentration of heavy metals, instead values lies within the permissible limits. According to WHO, permissible limit for Ni is 1.5 mg/kg, results shows that for concentration of Ni in Parthenium hysterophorous in upstream region lies in range of 0.22- 0.78 mg/kg i.e. within the limits . In midstream and downstream regions, a value ranges from 1.33- 1.65 mg/kg and 0.13- 1.67 mg/kg, which is above the permissible limits and able to pose health risk to human being. Permissible limit for Cr is 1.5 mg/kg, while its value ranges from 0.24 ' 1.64 mg/kg in upstream, 1.43-4.36 mg/kg in midstream and from 0.22-4.36 mg/kg in downstream region. This data show that Cr concentration is exceeded the permissible limits in all regions. Permissible limit for Cd is 0.3mg/kg. For Parthenium hysterophorous, its range in upstream region is 0.03-1.21 mg/kg, in midstream 0.99-1.67 mg/kg and for downstream, its range is 0.03-0.67 mg/kg. This range shows higher values as compared to permissible limits.
For Coronopus didymus and Cannabis sativa species, concentration founded in all three regions shows the exceeded concentration than limits. As permissible limits for Ni, Cr and Cd are 1.5 mg/kg, 1.5 mg/kg and 0.3 mg/kg. The actual founded values are 1.14-1.95 mg/kg for Ni in coronopus didymus in upstream, from 0.33-2.17mg/kg for Cr in cannabis sativa in upstream, 1.15-10-.55 mg/kg for Cd in cannabis sativa in midstream and 0.32-2.65 mg/kg for Cr in coronopus didymus in downstream.
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