Mercury distribution and its potential environmental risks : a case study at Phanom Pha gold mine, Phichit Province | |
| Author | Poranee Pataranawat |
| Call Number | AIT Diss. no.EV-07-07 |
| Subject(s) | Mercury--Toxicology--Thailand--Pichit Phanom Pha Gold Mine (Thailand)--Environmental aspects |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering and Management Inter-University Program on Environmental Toxicology, Technology and Management |
| Publisher | Asian Institute of Technology |
| Abstract | Mercury (Hg) contamination was assessed in environment near an amalgamation gold recovery operation located at a small scale mining operation (Phanom Pha) in Phichit Province, Thailand. Total mercury (THg) concentrations were determined in water, sediment, bivalves in the aquatic environment and as dry deposition or atmospheric fallout on surface soil and leaves of Neem tree (Azadirachta indica Juss. var. siamensis Valeton) near the mining operation. THg in surface soil, Neem flowers (edible part) and rice grain in surrounding terrestrial habitat and with distance from the mining area were also evaluated for possible contamination. Potential environmental risks were evaluated using the hazard quotient equation. Hg analyses conducted in the aquatic habitat showed that THg in water, sediment and bivalves (Scabies cripata Gould) ranged from 0.4 to 4 ug L⁻¹, 96 to 402 ug kg⁻¹ dry weight (dw) and 15 to 584 ug kg⁻¹ wet weight (ww), respectively. High concentrations of THg in water, sediment and bivalves were observed in the receiving water, the Khao Chet Luk Reservoir, near the mining operation. Whereas the THg concentration in water, sediment and bivalves from monitoring stations outside the gold mining operation (upstream and downstream), were considerably lower with the values of 0.4-0.8 ug L⁻¹, 96-140 ug kg⁻¹ dw and 88-658 ug kg⁻¹ dw, respectively. The elevated concentration of Hg found in the sediment near the mining operation was consistent with Hg accumulation measured in bivalves. The elevated Hg levels found in living bivalves collected from highly contaminated sites suggested that the sediment bound Hg was bioavailable. THg in surface soils, brown rice grain (Jasmine rice #105) and Neem flowers of terrestrial habitats were in the range of 16 to 180 ug kg⁻¹ dw, 190 to 300 ug kg⁻¹ dw, and 622 to 2150 ug kg⁻¹ dw, respectively. Elevated concentrations of mercury were found in Neem flowers with the concentration greater than 600 ug kg⁻¹ ww which exceeds the maximum permissible concentration reported for biota tissue (500 ug kg⁻¹ ww). An evaluation of air and soil pollution near the mining operations showed high concentrations of THg in dry deposit from atmospheric fallout (139 ug m⁻² d⁻¹), and in surface soil (10,564 ug kg⁻¹ dw) at station near where open burning of gold ore extracts using the amalgamation process, occurred. High or elevated concentration of THg (1172-1301 ug kg⁻¹ dw) in leaves of Neem tree was also measured near the mining operations. A survey of Hg in surface soil showed elevated Hg concentrations near the site which corresponded to the elevated THg concentration in dry deposition. These results suggested that atmospheric fallout is a major source of Hg to the area surrounding the mining or gold ore extraction. Results also suggest that Hg emitted into the air (estimated to be 60-150 g d⁻¹) from the gold mining activities (over past ten years) contaminated air, the aquatic environment, surface soil and biota in the area surrounding the gold mining operation. Using hazard quotient index (HQ) to estimate risk at the workplace and nearby, results showed that surface soil, surface water and sediment were found at risks with the HQ greater than 1. Likewise, Hg bioaccumulation was also found in bivalves and flowers of Neem trees again at the high concentrations of Hg with values around 584 and 602 ug kg⁻¹ ww, respectively, which exceeded the maximum permissible concentration for biota tissue. Such high values were exceeding the safe limits allowed for consumption. The screening toxicity test using modified Allium test (Shallot ascalonicum L.) was found to be very sensitive for Hg toxicity at the low level of concentration range from 180 ug L⁻¹ to 920 ug L⁻¹. Thus it might be developed/proposed as biomonitoring tool for Hg contamination in sediment at site. Regards to the toxic effects of Hg on seed germination and root elongation of Jasmine rice #105 (Oryza sativa L.) at the higher concentration range of 3 mg kg⁻¹ to 8 kg⁻¹, these toxicity tests might be developed/proposed for Mmonitoring Hg contamination in surface soil at workplace area. It can be concluded that Hg emitted into the air from gold mining activities nearly ten years of operation was proved to cause contamination in various environmental compartments as indicated in the air, water and sediment of the aquatic track, surface soil and even in biota. Although the retention of Hg by soil might help protecting the aquatic ecosystem from receiving such a full load of anthropogenic Hg deposition, stored Hg in the soil can be reemitted back into the atmosphere resulting in Hg accumulation in vegetation grown in the study area. This might pose a risk for the biota living within the influence of this store of Hg and for food chain in higher trophic level. The high elevated concentration of THg in edible parts of biota in the project area showed certain risk for local people being exposed to the hazardous Hg in the food chain as well. Thus the Hg contamination monitoring should be operated using the practical procedures of these toxicity screening tests that can be done locally. |
| Year | 2007 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Preeda Parkpian ;Mathuros Ruchirawat; |
| Examination Committee(s) | Chongrak Polprasert ;Vithet Srinetr; |
| Scholarship Donor(s) | Chulabhorn Research Institute ;Mahidol University ;Asian Institute of Technology Fellowship; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology - Chulabhorn Research Institute - Mahidol University, 2007 |