Heavy Metals sources and their concentrations in Pakistan

Heavy Metals in Pakistan: We find that out of the total 79.61 million hectares of geographical area of Pakistan, about 23.39 million hectares is under cultivation at present as compared to the 14.99 million hectares in 1949-50.

Heavy Metals sources and their concentrations in Pakistan

It means that the cultivated area has increased by about 56 percent over a period of 64 years at a rate of roughly less than one percent (0.9 %) per year. Agriculture farming throughout the Pakistan is not same. It differs from one region to other depending upon climatic conditions, cropping patterns and availability of surface and ground water supplies. However, about 60% of farmers depend upon groundwater to meet the crop water requirements.

Punjab agriculture has become heavily dependent on groundwater and its quality also greatly varies from place to place, due to variation in origin, source of recharge and patterns of groundwater movement. Keeping in view, further increase in agricultural production through enhancing cropping intensity would only have slim chances. Over-exploitation of existing land and water resources May result in further environment (soil, water) degradation.

Environmental pollution is a global and serious problem especially in industrial cities. Such  problem is more severe in developing countries like Pakistan where the disposal of untreated sewage coming from domestic uses, industrial effluents having  different  pollutants, effluent from animal husbandry and drainage of irrigated lands and run off. In developing countries disposal of untreated industrial effluents is disposed off on agriculture land in urban and peri urban areas, for the urban agriculture.

Usually, the city effluent is a potential source of microbes, organic matter, and inorganic nutrients and also has significant concentration of heavy metals (Fe, Mn, Cu, Zn, Pb, Cr, Ni, Cd and Co) which is being used for growing crops and vegetables around the cities. Phytotoxic concentration of heavy metals accumulates in crops and vegetables due to continue use of such untreated city industrial effluents. Which ultimately become a part of food chain that is hazardous to the plants, man and animals.

The growers are not aware of the toxic effects of metal ions that are being introduced into the food chain by growing crops and vegetables with city effluent. Therefore illiterate farmers use it as a potential source of irrigation and plant nutrients while on the other hand the administrators use this technique as a feasible option for removal of city (industrial) waste effluents.

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Such practice for a longer period of time causes contamination of soil. Due to excessive use of the industrial effluents, the soil capacity to retain the heavy metals is reduced heavy metals easily leach down in the ground water or increase the bio availability for plants. When such underground water use for drinking purposes it cause several water borne diseases like Hepatitis, malaria, cholera, typhoid, scabies, trachoma, typhus.

Definition of heavy metals

A metal having high density known as heavy metal in some literature density range is 3.5 to 7 gcm-3 where as in some other this range is 4.5 to 5gcm-3. There is no elemental effect of heavy metals on plants (valance state of 0) because plants take up any nutrient only in ionic form (solution).

Heavy Metals Sources

Naturally Heavy metals are present in the air, soil, water, food, and are widely used in manufacturing processes.  The  major contributor of heavy metals in the environment are batteries, household, Various  industries  such  as  metallurgy,  battery manufacturing,  metal  plating,  fertilizer  production, X-ray shielding devices, electroplating,  mining,  textile  dyeing Lead is used in the production of lead acid batteries, solder, alloys, cable sheathing, Pigments, rust inhibitors, ammunition, glazes and plastic stabilizers.

Tetraethyl And tetraethyl lead is important because of their extensive use as antiknock Compounds in petrol, etc. and are responsible for heavy metals contamination. For the metals derived from anthropogenic sources (human), this can strongly influence their speciation and hence bioavailability.

Effects

Now a day, world population is facing water Pollution caused by toxic heavy metals which is one of the major problems. The  high  concentrations  of  heavy  metals and particulate matter  in  industrial  effluents ultimately entering  and deteriorating the  soil and underground water and finally enter  in  food  chain which  affect  human  beings indirectly. It is investigated that the use of city industrial waste water for irrigation has increased the contamination of Cd, Pb, Co, Ar and Ni, in edible portion of vegetables causing potential health risk in the long term from this practice.

Heavy metals can also directly or indirectly damage genetic makeup (DNA or RNA) that may enhance the danger of cancer (skin, lungs, liver and bladder) called Genotoxicity. High intake of Nickel, manganese, chromium and cadmium cause the health  problems  like  as anemia,  kidney  disorder,  failure  in  nervous  system,  high blood  pressure.

Long-term exposure of Pb in adults can result in decreased performance in some tests that measure functions of the nervous system; weakness in fingers, wrists, or ankles. Cu toxic level can damage to mitochondrial, membranes bodies, metal fume fever, skin and hair discoloration and irritation of respiratory tract.

Nickel toxicity disturbs the insulin production of liver, lungs and nasal cancer, irritation of respiratory tract, skin rash and allergic reaction. Cobalt has synergistic effect with nickel and arsenic. High intake of cobalt can cause nausea, vomiting, cardiac and vision problems and can also damage to the thyroid gland functions.

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Similarly, higher manganese level affects the liver, brain, the developing fetus, and also affects the respiratory tract. The toxic effect of chromium is skin rash, ulcer, upset stomach, nose irritation; weaken immune system, nasal itch, lung cancer and liver damage.

Beyond  daily recommended intake   of lead can cause anemia, pale skin, abdominal pain, serve constipation ,hand grip strength reduction, paralysis of wrist joints and can also increase chances of miscarriage(the spontaneous or unplanned expulsion of a fetus from the womb before it is able to survive independently).

Comparison of different sources for heavy metals

The concentration of TSPs (total suspended particulates) is highest in the ambient air of two big cities of Pakistan Faisalabad and Gujranwala. The order of metal concentrations is (Cd > Pb> Zn) in these cities.

Table 1: Lahore vegetable leaves Heavy metals cone. (mg/kg)

Vegetables

Pb

Ni

Cd

Fe

Zn

Spinach

42-97.2

26.7-35

4.8-10.3

161-586

70.6-153.2

Cauliflower

36-68,4

12-35

3.9-6.5

98-370

38.9-121.3

Carrot

49-78.4

10.34.7

3.8-7.6

110-443

43.1-121.8

Tomato

31-59

10-29

2.9-5.7

61.227

38.4-119.17

The concentration of different heavy metals in different vegetables have been found in this order Fe>Zn>Pb>Ni>Cd grown in the vicinity of Lahore city by using industrial city effluents.

Table 2:  Lahore city Sewage water heavy metals concentration.

Heavy Metal

Range (water)

WHO safe limit (soil) mg/kg

WHO Safe limit(water) mgL-1

Pb

0.03-0.65

300

5

Ni

0.01-0.23

75

.2

Cd

0.001-0.21

3

0.01

Zn

0.1-1.07

300

2

Fe

0.27-0.94

140

.2

The safe limits of different heavy metals in soil from WHO (world health organization) is as Pb, Ni, Cd, Zn and Fe 300 ,75,3,300,140 mg/Kg respectively and of water is as 5.0,0.2,0.01,2.0 and 0.2 mL/L­ respectively.

Table 3: Heavy metals accumulation in leaves of different vegetable irrigated with industrial effluent.

Heavy metals

Concentration (mg/kg)

Pb

8.072-10.72

Cd

3.09-4.86

Cr

3.61-8.85

Ni

16.32-21.84

Table 4: Recommended daily intake

Metals

Daily Intake

Zn

15mg

Ni

<1mg

Fe

15mg

Cu

2mg

Mn

0.32 mg

Cr

120µg

Co

2µg

Pb

.36-5.5µg

According to WHO (world Health organization) daily recommended intake of different heavy metals is as Zn, Ni, Fe, Cu, Mn, Cr, Co and Pb is 15mg,<1mg,<15mg,2mg ,.32mg 120 µg ,2 µg and .36-5.5 µg /day respectively.

Table 5: Permissible limits of heavy metals in soil, plants and water

Sr. #

Heavy metals

Target value of soil(mg/kg)

Permissible value of plants (mg/kg)

Permissible value of water mg/L

1

Cd

0.8

0.02

0.1

2

Cr

100

1.30

0.10

3

Cu

36

10

0.20

4

Pb

85

2

5

5

Ni

35

10

0.2

interesting reading:  HEC needs to review its policy related to publication in international journals

The permissible limits of different heavy metals of soil are as Cd, Cr, Cu, Pb and Ni is 0.8,100, 36, 85 and 35 mg/Kg respectively. For Plants this limit is as 0.02, 1.30,10,2 and 10 mg/kg respectively and of water is as 0.1, 0.10, 0.20, 5.0 and 0.2 respectively.

Remedial measure of heavy metals

As air, soil, and Drinking water is mainly being polluted by toxic metal ions. Various methods have been engaged  for  the  removal  of  these toxic metal ions  from  the  polluted medium like chemical precipitation ,ion- exchange ,Phytoremediation (poultry, animals, plants, microbes and fisheries) and CaCo3.

Another bioremediation technique for heavy metals is feeding the feed staff (poultry, animals, fisheries) grown on heavy metal contaminated soils with industrial effluents. Because, the maximum cone. Of heavy metals may store in skin, liver, bones hooves and in their excretion litters and minimum conc. in the muscle which is being used as protein source by humans.

Basic Terms Used

  • TLV (Threshold Limit Values)

A TLV reflects the level of exposure that the typical worker can experience without an unreasonable risk of disease or injury. TLVs are not quantitative estimates of risk at different exposure levels or by different routes of exposure.

  • STEL (Short Term Exposure Limit)

The concentration to which workers can be exposed continuously for a short period of time without suffering from Irritation Chronic or irreversible tissue damage Narcosis of sufficient degree to increase the likelihood of accidental injury, impair self-rescue or materially reduce work efficiency.

For example, one cannot be exposed to an STEL concentration if the TLV-TWA (time weighted average for an 8 hour shift; see Permissible Exposure Limit (PEL)) would be exceeded. Workers can be exposed to a maximum of four STEL periods per 8-hour shift, with at least 60 minutes between exposure periods.

  • PEL (Permissible Exposure Limit)

It is the maximum amount or concentration of a chemical (gas, heavy metal, aerosol particles) that a worker may be exposed to under OSHA (Occupational Health and Safety Administration) regulations.

Ceiling values. At no time should this exposure limit be exceeded.

  • A8-hour Time Weighted Averages (TWA)

These are an average value of exposure over the course of an 8 hour work shift.mTWA levels are usually lower than ceiling values. Thus, a worker may be exposed to a level higher than the TWA for part of the day (but still lower than the ceiling value) as long as he is exposed to levels below the TWA for the rest of the day Limits.

Muhammad Nadeem1, Muhammad Zahaib Ilyas2, Tanveer Ahmad2

1 Soil and Water Testing laboratory, Hafizabad.

2 University of Agriculture Faisalabad.

 

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