212
R.V. Marins et aI.
Oil-fired plants are another significant source of Hg to the atmosphere over
Sepetiba Bay basin, although Hg content in oil is very small (0.02 to 0.08 g t- I
(Chu and Porcella 1995). Because the entire fuel supply is exposed to high flame
temperatures, essentially all of the Hg contained in the oil is vaporized and exits
the furnace with combustion gases to the atmosphere. Also, particle filters are not
particularly efficient to retain Hg vapour. The total contribution from this source
can range from 11 to 45 kg a-I.
Total estimated contributions of Hg from the industrial park and urban
sources to Sepetiba Bay basin range from 251 to 417 kg a -I. The major inputs are
to the atmosphere (167-201 kg a-I), and to soils (84-216 kg a-I). Direct inputs to
waterways are very small (less than 1.0 kg a-I). However, the large atmospheric
and soil load may contaminate fluvial systems through surface runoff. With the
recent control of Hg point sources throughout the world, similar situations have
been reported in many other coastal areas (Behrendt 1993; Mignon 1993; Pacyna
1995), highlighting the importance of evaluating diffuse sources of Hg to the
environment.
4
Mercury Inputs to Sepetiba Bay
4.1
Atmospheric Inputs
To check our estimates based on emission factors, bulk atmospheric deposition
of Hg over Sepetiba Bay was measured. Most of the near-surface atmospheric Hg
species over both the open ocean and coastal regions are in the vapour phase.
Measurements of Hg associated with particles [Hg(p)] in the air have been
limited over the past two decades. With the recent advances in instrumental
sensitivity and the application of clean techniques, knowledge of Hg(p)
concentrations and behaviour has improved. Recent measurements of particulate
Hg in several urban I industrial areas documented Hg on large particles and in
concentrations similar to those of the vapour phase Hg (ng m- 3 ). Therefore, bulk
deposition sampling techniques are the best way of evaluating total atmospheric
contribution of Hg to a given system (Marins et al. 1996).
Mercury concentrations in bulk precipitation over Sepetiba Bay ranged from
30 to 164 ng rl, with an average of 80 ng 1-1. This average concentration is from
two to three times higher than in pristine areas and suggests a moderate
contamination of Sepetiba Bay atmosphere.
Highest concentrations (up to 164 ng 1-1) occurred in summer (January and
February), whereas lowest concentrations (of 30 ng 1-1) occurred in winter (JulySeptember). Higher deposition also occurred in summer when highest Hg
concentrations and stronger and more frequent rains occur, leading to more
efficient washout of the atmosphere (Iverfeldt 1991). Similar behaviour was
reported for other metals in bulk precipitation over Sepetiba Bay (Pedlowiski
et al. 1991).
R.V. Marins et aI.
Oil-fired plants are another significant source of Hg to the atmosphere over
Sepetiba Bay basin, although Hg content in oil is very small (0.02 to 0.08 g t- I
(Chu and Porcella 1995). Because the entire fuel supply is exposed to high flame
temperatures, essentially all of the Hg contained in the oil is vaporized and exits
the furnace with combustion gases to the atmosphere. Also, particle filters are not
particularly efficient to retain Hg vapour. The total contribution from this source
can range from 11 to 45 kg a-I.
Total estimated contributions of Hg from the industrial park and urban
sources to Sepetiba Bay basin range from 251 to 417 kg a -I. The major inputs are
to the atmosphere (167-201 kg a-I), and to soils (84-216 kg a-I). Direct inputs to
waterways are very small (less than 1.0 kg a-I). However, the large atmospheric
and soil load may contaminate fluvial systems through surface runoff. With the
recent control of Hg point sources throughout the world, similar situations have
been reported in many other coastal areas (Behrendt 1993; Mignon 1993; Pacyna
1995), highlighting the importance of evaluating diffuse sources of Hg to the
environment.
4
Mercury Inputs to Sepetiba Bay
4.1
Atmospheric Inputs
To check our estimates based on emission factors, bulk atmospheric deposition
of Hg over Sepetiba Bay was measured. Most of the near-surface atmospheric Hg
species over both the open ocean and coastal regions are in the vapour phase.
Measurements of Hg associated with particles [Hg(p)] in the air have been
limited over the past two decades. With the recent advances in instrumental
sensitivity and the application of clean techniques, knowledge of Hg(p)
concentrations and behaviour has improved. Recent measurements of particulate
Hg in several urban I industrial areas documented Hg on large particles and in
concentrations similar to those of the vapour phase Hg (ng m- 3 ). Therefore, bulk
deposition sampling techniques are the best way of evaluating total atmospheric
contribution of Hg to a given system (Marins et al. 1996).
Mercury concentrations in bulk precipitation over Sepetiba Bay ranged from
30 to 164 ng rl, with an average of 80 ng 1-1. This average concentration is from
two to three times higher than in pristine areas and suggests a moderate
contamination of Sepetiba Bay atmosphere.
Highest concentrations (up to 164 ng 1-1) occurred in summer (January and
February), whereas lowest concentrations (of 30 ng 1-1) occurred in winter (JulySeptember). Higher deposition also occurred in summer when highest Hg
concentrations and stronger and more frequent rains occur, leading to more
efficient washout of the atmosphere (Iverfeldt 1991). Similar behaviour was
reported for other metals in bulk precipitation over Sepetiba Bay (Pedlowiski
et al. 1991).