Methylation Potential of Mercury Impacted Pipeline Scale

Area of Science:

• Environmental Science
• Geochemistry
• Marine Biology

Background:

• Subsea oil and gas pipelines are often abandoned on the seafloor.
• Internal deposits (scale) in these pipelines can contain significant amounts of total mercury (THg).
• The environmental fate and methylation potential of mercury from abandoned pipelines require assessment.

Purpose of the Study:

• To assess the leachability of total mercury (THg) from abandoned subsea pipeline scale.
• To evaluate the potential for methyl mercury (MeHg) formation in sediments exposed to pipeline scale.
• To develop methods for assessing mercury release and methylation from pipeline deposits.

Main Methods:

• Static anaerobic microcosms simulating seafloor conditions.
• Exposure of mercury-contaminated pipeline scale to marine sediments for up to 28 weeks.
• X-ray fluorescence (XRF) for surface THg analysis.
• Measurement of THg and MeHg concentrations in sediments.

Main Results:

• Rapid release of THg from scale to sediments occurred within 6 weeks.
• Intact pipeline coupons released a higher percentage of THg at lower concentrations compared to higher concentrations.
• Peak MeHg concentrations in sediment were low (0.05% of sediment THg) and weakly correlated with sediment THg.
• Sediment MeHg positively correlated with leachable THg (filtered).

Conclusions:

• Mercury release from abandoned pipeline scale is rapid but the amount released depends on scale THg concentration.
• The methylation potential of released THg is limited, indicating mercury unavailability.
• Leachable THg is a useful indicator for assessing mercury release and methylation risk from pipeline deposits.