ENVIRONMENTAL IMPACTS OF MERCURY DISCHARGE FROM GOLD EXTRACTION ALONG INDUS, HUNZA AND GILGIT RIVERS IN NORTHERN PAKISTAN

Abstract

Humans are exposed to different toxic elements like lead, cadmium, arsenic and mercury (Hg). These metals are studied from long time and their adverse effects on humans are reported from throughout the world and also by the international bodies like World Health Organization (WHO). Globally, Hg is considered to be the worst pollutant that released from the natural as well as from anthropogenic sources and causes health problems for all biotic components of the environment. Hg is creating problems in both aquatic and terrestrial ecosystems and easily accumulates. It changes its forms (converts from inorganic into organic) in water, sediments, soil, plants and even biological tissues. In this research work focused on the release of Hg from gold extraction activity, contamination of water, sediments and plants with Hg, and its associated human health risk. This research work is divided into different parts to achieve the study objectives. The first study aimed to investigate the contamination of water and sediments with Hg, released from gold panning and extraction process in the northern areas of Pakistan. Water and sediment samples were collected from different sites along the rivers of Indus, Gilgit and Hunza. These rivers are very famous for extraction of gold in northern Pakistan. Sediments were divided into three groups such as wet sediments (WS) (collected just after amalgamation), fresh dry sediments (FDS) (collected after 1-2 h of amalgamation) and old dry sediments (ODS) (collected after 1-2 d of amalgamation). Water and sediment samples were prepared according to the standard procedures and analyzed for Hg concentrations using atomic absorption spectrophotometer (Perkin Elmer-700) equipped with mercury hydride system (MHS-15). Daily intake of Hg and its associated health risk through ingestion of drinking water were also calculated in this study. The sediments samples including WS (401 mg/kg), FDS (946 mg/kg) ix and ODS (22.9 mg/kg) were highly contaminated with Hg. In drinking water, the concentrations of Hg exceeded the maximum permissible limits set by World Health Organization, Pakistan Environmental Protection Agency, Canadian drinking water quality and US Environmental Protection Agency. The health risks results showed that the average daily dose for adults was 0.025 mg/kg-day with an average hazard quotient (HQ) value of 82.9, while for children the average daily dose was 0.03 mg/kg-day with HQ value of 92.7 which was many folds higher than the limit (1) which considers safe. The second part of this study was aimed to investigate Hg its species concentrations in human specimen and its negative impacts on the human beings involved in gold mining along the three rivers (Gilgit, Hunza and Indus) in the northern areas of Pakistan. Biological samples such as blood, urine, hair and nails were obtained from the gold miners including male and female and analyzed for Hg and its species concentrations. Total Hg concentrations in the blood, plasma, urine, hair and nails of male workers were 41 μg/L, 30.8 μg/L, 49.5 μg/L, 0.64 mg/kg and 0.46 mg/kg, respectively, while 44.4 μg/L, 36.8 μg/L, 41.5 μg/L, 1.1 mg/kg and 0.97 mg/kg, respectively in females. The results indicated that Hg in all (100%) samples exceeded the permissible limit set by US-EPA and WHO. Being a highly toxic metal, Hg exposure has caused several diseases such as inhalation problems, belly and neck pain, skin burn, stunted growth in children, teeth, heart, respiratory, kidney, joints and skin problems. Further investigation was also carried out to know the food chains (vegetables, grain, fruits and fish) contamination with Hg in Gilgit, Baltistan, Pakistan. The edible parts of vegetable and food plants were analyzed for contamination of Hg. The fish muscles were also analyzed to see the contamination of Hg. The results showed that the concentrations of Hg in food chains were higher than the critical value (2 μg/kg) determined by WHO. Soil samples were analyzed to find x out the Hg and its enrichment and transfer factors for different food items. Pollution load index showed the significantly higher concentration levels (ranged from 37-299) than the reference level (1.96). Daily intake and health risk index also showed that the population was at high risk in the study area.. Contaminated food is a major way of exposure of Hg for the local population of the study area. The final part of this research focused on Hg and its negative effects on wild plants collected from the study area. The results indicated that of the wild plants and their soil samples collected along the three rivers (Giligt, Hunza and Indus) were contaminated with Hg. In the study area, small-scale gold mining and weathering of rock were the main sources of Hg which contributed a lot of emission of Hg in to environment. Almost 75-80% samples in wild plants showed the higher Hg contamination, while 99% soil showed the higher Hg concentration than the recommended limits. The results showed that the mean concentration of Hg was 27 μg/g in plants, while 214 μg/g in soil. These findings indicated the Hg contamination was very high and varied from plant species to species. This study recommends that the control measures are needed to reduce the emission of Hg from gold extraction process to protect the environment from contamination and minimize the human health risk.