Studies of the global baseline pollution XIII

Summary

High-volume air sampling by adsorption on silica gel on the island Réunion (21°S, 56°E) in the southern Indian Ocean was done for analyzing typical southern hemisphere air for semivolatile organohalogens such as α-hexachlorocyclohexane (13) and g-hexachlorocyclohexane (406), hexachlorobenzene (7), polychlorobiphenyls [PCB 28 (3.2); PCB 52 (4.9) PCB 101 (6.0); PCB 138 (5.0); PCB 153 (5.0); PCB 180 (1.5)], 4,4′-DDT (8), 4,4′-DDE (19), cis- (4) and trans-chlordane (9), trans-nonachlor (3) and heptachloroepoxide (6) in the lower troposphere. The values in parenthesis are mean concentrations in picogram per m³ air. Local input and long range transport could be distinguished in most cases. The 2,4-, 2,6-, 2,4,5-, 2,4,6-, the tetra- and pentachloro-congeners of the chloroanisoles (phenylmethyl-ethers) were detected. 2,3,5,6-Tetrachloro-1,4-dimethoxy-benzene was found in the 100–280 pg/m³ range, while 2,4,6-tribromoanisol was detected in the 8–30 pg/m³ range together with traces of 2,4- and 2,6-dibromoanisole. The sources and the fate of the latter compounds are not yet understood, since both anthropogenic emissions and biogenic origin are possible.

The ratios of the concentrations in the southern and northern hemisphere (south/north ratio) of the semivolatile organochlorine compounds are discussed. The south/north ratio ranges from 0.05 to 0.09 for HCB and α-HCH, respectively, to 0.74 for the PCBs and 0.9 for g-HCH, to 3 for 4,4′-DDE and up to 8 for 4,4′-DDT. This indicates that there is no significant interhemispheric exchange for compounds such as HCB and α-HCH in the atmosphere, and as a consequence the same must be true for other semivolatile compounds.