(Israr Ullah, islamabad)

Nickel (Ni) is widely distributed in nature and is found in animals, plants, and soil; the concentration of Ni in soil is approximately in the range of 4–80 ppm. Large amount of Ni is released in the atmosphere due to natural as well as anthropogenic activities including fossil fuel consumption, the industrial production (mining, smelting, and refining), use, and disposal of nickel compounds and alloys, and waste incineration. Human exposure to Ni results from Ni contaminated food ingestion, water, inhalation, and percutaneous absorption. According to International Agency for Research on Cancer evaluation, Ni compounds are carcinogenic to humans and are classified as Group 1. Mixtures of Ni metal and compounds cause cancers of the lung and of the nasal cavity and par nasal sinuses. The maximum permissible concentration for Ni set by WHO in drinking water is 0.07 mg/L, whereas National Standards for Drinking Water Quality, Pakistan (NSDWQ-Pak), suggest the guideline value of 0.02 mg/L. The concentration of Ni varies from <0.001–3.66 mg/L in ground water to <0.001–1.52 mg/L in surface water in Pakistan. It was observed that, in most of the cases, groundwater is contaminated with Ni beyond the contamination level set by NSDWQ-Pak or WHO. Similarly, 75% of the surface water samples from the largest city of the country (Karachi) exceed the limits. In a study from Lahore (North and East zone), the wastewater samples were collected to evaluate the waste water irrigation impact on vegetables. The Ni concentration was found to be the highest than the reported studies from Pakistan and ranged between 0.91 and 5.94 mg/L and exceeded the permissible limit of 1.0 mg/L set by National Environmental Quality Standards, Pakistan.

In soil, the highest concentration of Ni is 324 mg/kg (mean 172 mg/kg) from contaminated Lahore site, while mean reference value of 70 mg/kg (Pb-Zn sulfide horizon/mineralized site) in Kohistan region was found, which is far more than the permissible limits set by EU or USA standards of soil on which sewage sludge can be applied (30–75 and 210 mg/kg), respectively. This was attributed to the dispersion of metals due to mining and may pose potential threats to local communities of Kohistan region. Moreover, in another study conducted on soil of Jahangir Valley, Punjab province, the maximum total content of Ni was recorded as 81 mg/Kg (mean 31.93 mg/kg); the author concluded that these values do not pose any potential health hazard to the general population. In coastal sediments of the Arabian Sea along with the urban Karachi, the maximum concentration of 74 mg/kg Ni was found at the Lyari location at the most downstream part of the Malir River. Similarly, in another study the second highest value of 56.46 mg/kg was found at Karachi Port Trust (KPT) Boat Building Area. As per IARC, Ni compounds are human carcinogens by inhalation exposure; therefore, no safe level for nickel compounds can be recommended in air (assuming a linear dose-response). In the current analysis, the concentration of Ni in particulate matter was reported in the range of 0.001–0.15 μg/m3 and the highest of its content was reported in urban atmosphere of Islamabad. In vegetables, the concentrations of Ni ranging from <0.02 to 67.8 mg/kg with mean value of 30.1 mg/kg was observed in vegetables irrigated with sewage water in the suburbs of Peshawar city, KPK. The author reported the significant positive correlation of plant heavy metal with the given heavy metals in soil. In another research, the second highest mean Ni concentration of 28 mg/kg was observed in Spinach (Spinacia oleracea) irrigated by sewage water Hassan Abdal area, Punjab province.


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