טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShoham-Frider Efrat
SubjectChemical Speciation of Mercury in Sewage Sludge before and
after Marine Disposal - Assessment of the Fate of
Mercury in the Marine Environment
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Gedaliahu Shelef
Dr. Nurit Kress


Abstract

The goal of this research was to determine the environmental fate of mercury discharged at sea as a trace component of sewage sludge. The environmental conditions which play a major role in mercury speciation were season-dependent: during the summer-autumn the sediment was oxidizing-anaerobic and reducing-anaerobic, correlated with the occurrence of sulfides, and during winter-spring the sediment was aerobic with no sulfides. Most of the mercury accumulated in the sediments, with maximum concentration of total mercury of 1003 ppb. High concentrations of methylmercury were measured in the sludge (40 ± 7 ppb) while in the affected sediments, the maximum concentration was 5.9 ppb. Total mercury and methylmercury concentrations decreased similarly from the surface of the sediments to deeper layers. At the depth of the sediment, where natural methylation is expected to occur, there was no methylmercury, indicating that it was introduced with the sewage sludge and not formed by natural processes. Selective extractions found that only 0.1-2.4% of the mercury in the sewage sludge and the affected sediments was present in water-soluble and human-stomach-acidity soluble fractions; 20-24% was attached to organic matter; 70-75% was attached to amorphic organic matter via sulfur bond, and 5-8% was present in the mercury-sulfide fraction. Therefore, more than 80% of the mercury was not directly accessible to the biota, nor available to methylation processes, but present as the most environmental stable species. And indeed, until today, no accumulation of mercury was found in marine biota from the disposal area.