Methylmercury Concentrations In Sediments Research Articles

A review of the potential risks associated with mercury in subsea oil and gas pipelines in Australia

Environmental context The oil and gas industry has a significant liability in decommissioning offshore infrastructure. Following decommissioning, subsea pipelines could be left on the seabed to provide artificial reefs. Mercury is a contaminant of concern which could remain within pipelines. There are gaps in our knowledge on how mercury moves through the marine environment. We review the current science and identify future research needs to understand potential impacts from mercury in subsea pipelines which will better inform decommissioning activities globally. Abstract In the coming years, the oil and gas industry will have a significant liability in decommissioning offshore infrastructure such as subsea pipelines. The policies around decommissioning vary depending on regional policies and laws. In Australia, the ‘base case’ for decommissioning is removal of all property and the plugging and abandonment of wells in line with the Offshore Petroleum and Greenhouse Gas Storage (OPGGS) Act 2006. Options other than complete removal may be considered where the titleholder can demonstrate that the alternative decommissioning activity delivers equal or better environmental outcomes compared to complete removal and meets all requirements under the OPGGS Act and regulations. Recent research has demonstrated that decommissioning in situ can have significant environmental benefits by forming artificial reefs, increasing marine biodiversity, and providing a potential fishery location. An issue, which has been given less attention, is around contaminants remaining within decommissioned infrastructure and their potential risks to the marine environment. Mercury is a contaminant of concern known to be present in some oil and gas pipelines, but the potential long-term impacts on marine ecosystems are poorly understood. We present a synthesis of information on mercury cycling in the marine environment including key drivers of methylation in sediments and ocean waters, existing models to predict methylmercury concentrations in sediments, and toxicological effects to marine biota. We discuss the applicability of existing water and sediment quality guidelines, and the associated risk assessment frameworks to decommissioning offshore infrastructure contaminated with mercury. Globally, research is needed to provide a comprehensive risk assessment framework for offshore infrastructure decommissioning. We recommend future areas of research to improve our understanding of the potential risks associated with mercury in subsea oil and gas pipelines.

Long-range effect of cyanide on mercury methylation in a gold mining area in southern Ecuador

Small-scale gold mining in Portovelo–Zaruma, Southern Equador, performed by mercury amalgamation and cyanidation, yields 9–10 t of gold/annum, resulting in annual releases of around 0.65 t of inorganic mercury and 6000 t of sodium cyanide in the local river system. The release of sediments, cyanide, mercury, and other metals present in the ore such as lead, manganese and arsenic significantly reduces biodiversity downstream the processing plants and enriches metals in bottom sediments and biota. However, methylmercury concentrations in sediments downstream the mining area were recently found to be one order of magnitude lower than upstream or in small tributaries. In this study we investigated cyanide, bacterial activity in water and sediment and mercury methylation potentials in sediments along the Puyango river watershed, measured respectively by in-situ spectrophotometry and incubation with 3H-leucine and 203Hg 2+. Free cyanide was undetectable (< 1 μg·L − 1 ) upstream mining activities, reached 280 μg·L − 1 a few km downstream the processing plants area and was still detectable about 100 km downstream. At stations with detectable free cyanide in unfiltered water, 50% of it was dissolved and 50% associated to suspended particles. Bacterial activity and mercury methylation in sediment showed a similar spatial pattern, inverse to the one found for free cyanide in water, i.e. with significant values in pristine upstream sampling points (respectively 6.4 to 22 μgC·mg wet weight − 1 ·h − 1 and 1.2 to 19% of total 203Hg·g dry weight − 1 ·day − 1 ) and undetectable downstream the processing plants, returning to upstream values only in the most distant downstream stations. The data suggest that free cyanide oxidation was slower than would be expected from the high water turbulence, resulting in a long-range inhibition of bacterial activity and hence mercury methylation. The important mercury fluxes resultant from mining activities raise concerns about its biomethylation in coastal areas where many mangrove areas have been converted to shrimp farming.

MERCURY IN WATER AND SEDIMENT OF STEAMBOAT CREEK, NEVADA: IMPLICATIONS FOR STREAM RESTORATION1

ABSTRACT: The objective of this study was to characterize the sources, concentrations, and distribution of total and methylmer‐cury in water, and channel and bank sediments of Steamboat Creek, Nevada. This information was needed to begin to assess the potential impacts of stream restoration on mercury pollution in this tributary to the Truckee River. The Truckee River flows into Pyramid Lake, a terminal water body home to one endangered and one threatened fish species, where stable pollutants will accumulate over time. Mercury in Steamboat Creek was originally derived from its headwaters, Washoe Lake, where several gold and silver mills that utilized mercury were located. In the 100 plus years since ore processing occurred, mercury‐laden alluvium has been deposited in the stream channel and on streambanks where it is available for remobilization. Total mercury concentrations measured in unfiltered water from the creek ranged from 82 to 419 ng/L, with greater than 90 percent of this mercury being particle‐bound (&gt; 0.45 (m). Mercury in sediments ranged from 0.26 to 10.2 μg/g. Methylmercury concentrations in sediments of Steamboat Creek were highest in wetlands, lower in the stream channel, and still lower in streambank settings. Methylmercury concentrations in water were 0.63 to 1.4 ng/L. A streambank restoration plan, which includes alterations to channel geometry and wetland creation or expansion, has been initiated for the creek. Data developed indicate that streambank stabilization could reduce the mercury loading to the Creek and that wetland construction could exacerbate methylmercury production.