KARACHI, Feb 27: A research has found extremely high level of contamination with toxic metals especially that of mercury in the roadside soil along the National Highway.

The alarming level of toxicants, particularly the high level of mercury at all selected sampling sites, poses grave threat to public health and requires serious immediate remedial efforts, according to the research.

Karachi and Hyderabad are found to be the most polluted places in the network of the National Highway in the study which raises concern over the lack of a proper waste disposal system, especially for electronic waste.

The study, “Assessment of heavy metals toxicants in the roadside soil along the N-5, National Highway, Pakistan,” has recently appeared in the online edition of an international journal, Environment Monitoring and Assessment, this month.

The research has been conducted by Dr Nasiruddin Khan, M. Faisal Rasheed and Agha Arslan Wasim of Karachi University chemistry department and Anila Sarwar of the Fuel Research Centre of the Pakistan Council of Scientific and Industrial Research (PCSIR).

According to the study, the National Highway is significantly polluted with lead, copper, zinc and mercury.

The correlation between the elemental compositions of the main automobile components reveals vehicular traffic as the main non-point source of roadside soil pollution.

“Direct or indirect contact with toxic contaminants is harmful for both animals and humans. The toxic contaminants in the soil can contaminate underground water as well as the soil of the agricultural fields located along the highway.

“The contamination can also be transferred from the roadside to the fields by surface run-off by rain. Direct inhalation is also a major risk as these pollutants stay in the air in the form of suspended particles or dust,” Dr Nasiruddin Khan tells Dawn.

The nine selected sampling sites are located between Karachi and Lahore which comprises a major portion (around 70 per cent) of N-5 highway connecting Karachi to Peshawar. The maximum traffic density (1.3 million vehicles per month) has been estimated along the 1,260-km long road connecting Karachi to Lahore, the study says.

Findings

The most serious cause of concern, highlighted by the study, is the high levels of mercury found in the soil samples. The distribution of mercury levels in the study sites ranges from 61.50 to 144.05mg per kg with an average of 90.67mg per kg.

“This is around 45 times larger than the acceptable concentration in the soil. The maximum acceptable limit of mercury in soil in various countries is also much lower than found in this study.”

The analyses reveal that the soil samples are mostly contaminated with inorganic mercury. Identifying the potential sources for its contamination, the study says that the contamination is possibly caused by hospital waste (comprising broken thermometers, gastrointestinal tubes, sphygmomanometers, etc), discarded batteries, switches and fluorescent tubes.

“Various types of gasoline have also been found to be contaminated with mercury in another study. The interior lights of vehicles and headlights of high-intensity are also responsible for mercury pollution in the roadside soil. E-waste is another important source as a number of toxic elements are used in the manufacturing of computers,” the study says.

Among the nine sites that have been analysed, the maximum concentration of three metals (lead, zinc and copper) is found at Hyderabad.

Lead concentration along N-5 ranges from 12.30 to 176.05mg per kg with a mean of 36.45mg per kg. Its highest concentration (176.05mg per kg) is found at the bypass road of Hyderabad, which is almost seven times more than the second highest level found at Ubauro.

“The heavy traffic density at this point is one of the main reasons for this pollution caused by the use of lead-containing fuel and lubricants. Besides, roadsides along the highways are the places of unregulated incineration of huge quantities of solid waste, including plastic material mainly composed of polyethene and polyvinyl chloride and the dumping of demolition waste from the old buildings that were painted with lead-based paints.“A number of service areas for heavy transport are also located along the N-5 and causes metal pollution by various means. Unmonitored sale of low-quality smuggled leaded petrol is also another cause,” the study states while citing references from other reports.

“Like lead, the highest concentrations of zinc and copper were also found at the bypass road of Hyderabad. The maximum value of nickel was found in samples taken from Karachi which were also heavily polluted with mercury [127.38mg per kg] and cadmium [1.05mg per kg].

“This is expected because Karachi is an industrial area having a number of metallurgy-based factories; solid waste and emissions from these industries possibly contribute as the anthropogenic source of heavy metals,” the study says.

Regarding the health effects, the study says that heavy metals are accumulated in humans and animals through direct ingestion, inhalation of polluted soil, dermal contact or the intake of contaminated edible plants.

“Toxic effects of heavy metals are well documented. People living near polluted area have higher incidences of migraines, nausea, fatigue, miscarriage, and skin disorders.

“Long-term effects of pollution include cancer, leukaemia, reproductive disorders, kidney or liver damage, and failure of the central nervous system. Moreover, children suffer more severely as compare to adults,” it says.

Speaking specifically about human exposure to mercury, Dr Khan said that there was a long list of adverse effects on health that included impairment of the peripheral vision, disturbance in sensation, lack of coordination of movements, impairment of speech and hearing, muscle weakness, emotional changes and insomnia. He said that higher exposures might affect kidneys and cause respiratory failure and death.

“The presence of toxic metals in the roadside soil of highway records the contamination level outside the city. Since the traffic density is very low on the highway compared to inside the cities, one could expect much higher levels of toxic metals inside the city where the traffic density is too high and no proper method has been adopted for the proper disposal of waste especially e-waste,” Dr Khan remarked.