Untersuchungen zur Speziation von verschmutzungsrelevanten Spurenmetallen in tropischen Ästuar- und Küstensystem (Südchina und Nord-Ost-Brasilien)

Abstract

This work investigated the concentrations, the distributions and the behaviors of five trace metals (nickel, cobalt, copper, cadmium and lead) plus iron in the aqueous and in the particulate phase in two tropical estuarine systems of China and Brazil, and estimated their contamination levels. The field work was carried out in the Wanquan Estuary and in the Wenchang-Wenjiao Estuary of the Southern Chinese island of Hainan as well as in the Mundaú Lagoon and in the Manguaba Lagoon of Northeast-Brazil, which are all characterised by relatively low contents of dissolved humics and DOC. The surface water samples were seperated into the dissolved (< 0.45 µm) and the particulate (> 0.45 µm) phase by conventional filtration followed by a further separation of the dissolved phase into two colloidal fractions (HMW "high molecular weight : 10 kDa - 0.45 µm; LMW "low molecular weight : 5 kDa - 10 kDa) and a fraction (TD: < 5 kDa) considered as "truly dissolved" fraction. The levels of these trace metals with high contamination riscs is generally higher in East-Hainan than in Northeast-Brazil. However, the estuarine behaviors of these metals in the two study areas are very similar. Dissolved cadmium appears more or less to be enriched in the dissolved phase, while dissolved iron and lead are rapidly removed from the dissolved phase when salinity increases. Nickel, cobalt and copper in solution, as well as all trace metals in particulate forms essentially follow a conservative mixing line. The relative significance of the truly dissolved fraction (< 5 kDa; TD) of the metals increased with increasing salinity. Dissolved iron, nickel and lead are mainly associated with the high molecular weight fraction (10 kDa - 0.45 µm; HMW), whereas dissolved cadmium predominantly occurs in the truly dissolved fraction. The truly dissolved fraction is also dominant for dissolved cobalt and copper; however, the high molecular weight fraction and the low molecular weight fraction (5 kDa - 10 kDa; LMW) cannot be neglected for these two metals. Despite the massive aquaculture industry in East-Hainan and the extensive cultivation of sugar cane in monocultural form in Northeast-Brazil as well as general anthropogenic activities, no significant impact of trace metals on the local environment could be detected in the two study areas. Although elevated metal concentrations occurred (in the Wenchang-Wenjiao Estuary and in the Mundaú Lagoon), they were leveled out effectively during estuarine processing. At high salinities, the metal concentrations in East-Hainan and in Northeast-Brazil are approximately at the same level. In comparison with averages of estuaries worldwide, both dissolved and particulate metal concentrations in the two study areas are similar or lower, except for iron probably originating from specific geographic settings.