The Air−Sea Equilibrium and Time Trend of Hexachlorocyclohexanes in the Atlantic Ocean between the Arctic and Antarctica

Abstract

Hexachlorocyclohexanes (HCHs) were determined simultaneously in air and seawater during two cruises across the Atlantic Ocean between the Arctic Ocean (NyA°lesund/ Svalbard, 79°N; 12°E) and the Antarctic Continent (Neumayer Station/ Ekstroem Ice Shelf, 70°S; 8.2°W) in 1999/ 2000. The concentrations of R-HCH and γ-HCH in air and surface waters of the Arctic exceeded those in Antarctica by 1-2 orders of magnitude. The gaseous concentrations of γ-HCH were highest above the North Sea and between 20°N and 30°S. Fugacity fractions were used to estimate the direction of the air-sea gas exchange. These showed for R-HCH that the measured concentrations in both phases were close to equilibrium in the North Atlantic (78°N-40°N), slightly undersaturated between 30°N and 10°S and again close to equilibrium between 20°S and 50°S. γ-HCH has reached phase equilibrium in the North Atlantic as R-HCH, but the surface waters of the tropical and southern Atlantic were strongly undersaturated with γ-HCH, especially between 30°N and 20°S. These findings are significantly different from two earlier estimates around 1990 as a result of global emission changes within the past decade. Therefore, we investigated the time trend of the HCHs in the surface waters of the Atlantic between 50°N and 60°S on the basis of archived samples taken in 1987-1997 and those from 1999. A decrease of R-HCH by a factor of approximately 4 is observed at all sampling locations. No decrease of γ-HCH occurred between 30°N and 30°S, but there was a decrease in the North Atlantic, North Sea, and in the South Atlantic south of 40°S. The constant level of γ-HCH in the tropical Atlantic confirms the conclusion that the tropical Atlantic acts as a sink for γ-HCH at present time. The measured R-HCH seawater concentrations were compared with results from a global multimedia fate and transport model. Whereas the time trend over 13 years and the latitudinal gradient were well reproduced by the model, the absolute levels were too high by a factor of 4.5. This may be explained by the zonal averaging employed in the model as well as uncertain emissions and degradation rates.

A GIS model-based assessment of the environmental distribution of γ-hexachlorocyclohexane in European soils and waters

“…S9 of Supporting information). Our predictions underestimate MSCE-POP predictions and existing monitoring data (Lakaschus et al, 2002;Ilyina et al, 2006) within one order of magnitude in 1995, and two orders of magnitude in 2005 (Fig. 10).…”

“…Results from our model were compared with monitored inland and seawater concentraüons (EMEP, 2009;Buijsman and Van Pul, 2003;Wenzel et al, 2002;EIONET, 2009;Catalonian Water Agency datábase, 2009;von der Ohe, 2008;Lakaschus et al, 2002;Ilyina et al, 2006;Prevedouros et al, 2005) of which an extensive datábase was compiled for the different compartments. A map representing monitoring stations in Europe is included in the supporting information (Fig.…”

“…10). MAPPE evaluates concentration in the sea mixing depth with average valúes of 60 m, whereas monitoring data were sampled out at 11 m (Lakaschus et al, 2002) and 5 m (Ilyina et al, 2006) depth (no information about MSCE-POP model parameterization was available), which would explain up to one order of magnitude in the underestimation. On the other hand, from the comparison of estimated deposition data for the two models available for year 2005, underestimation can be partly explained by the observed underestimation in MAPPE calculations (Pistocchi and Galmarini, 2008) of atmospheric dry deposition, the dominant removal pathway above sea surfaces (Van Jaarsveld et al, 1997), with respect to MSCE-POP calculations.…”

“…However, y-HCH has been subject to extensive monitoring in European rivers as one of the identified priority hazardous substances under the WFD (Directive, 2000/60/EC) and few databases were created (EIONET, 2009;Catalonian Water Agency datábase, 2009;von der Ohe, 2008;ARGE-Elbe monitoring programme, 1995-2005 showing also a seasonal distribution and a trend of decreasing of concentrations along the years. Oceans are considered to be a sink of HCH's coming both from atmospheric deposition and continental loads from rivers, and a long-range transport médium (Wania and Mackay, 1999); as such, they have also been intensively monitored (Lakaschus et al, 2002;Ilyina et al, 2006). Several models have been used so far to describe environmental behavior of y-HCH in Europe and reflect a clear decrease in lindane mean concentrations in different media along the last decades.…”

Currently used pesticides, hexachlorobenzene and hexachlorocyclohexanes in the air and seawater of the German Bight (North Sea)

“…[17,18] The mean concentrations of a-HCH and g-HCH were 0.61 AE 0.55 and 1.4 AE 2.0 pg m À3 in March, 4.9 AE 2.3 and 8.9 AE 7.1 pg m À3 in May and 8.7 AE 5.7 and 27 AE 21 pg m À3 in July. The levels are at least six times lower than concentrations of HCHs measured in German Bight air in 1999 and 2001, [19] indicating a declining trend.…”