生態系と生態学のジャーナル

抽象的な

Ecological Health Status of the Fosu Lagoon, Southern Ghana II: Environmental and Human Health Risk Assessment

Frederick A. Armah, Isaac Luginaah, Markku Kuitunen and Paul Mkandawire

This study set out to assess the levels, distribution and human health risk of Pb, As, Cd, Mn and polycyclic aromatic hydrocarbons (PAHs) in sediments from the Fosu Lagoon in Ghana. This was coupled with environmental fate modeling to investigate biodegradation behaviour of PAHs in sediment. Generally, the order of heavy metal enrichment for the sampling locations was Mn>Cd>Pb>As respectively. Only Mn showed significant enrichment at all sites. The observed PAH contamination demonstrated potential anthropogenic impact. The phenanthrene-anthracene ratio was less than 10 indicating that the PAHs originate from combustion. Benzo[b]fluoranthrene is the only carcinogenic PAH that was detected in the study. Regarding heavy metals in children, the total Hazard Index (HI) for ingestion and dermal route was 3.4×10^-2 and 8.2×10^-3 respectively for Central Tendency Exposure (CTE) whereas it was 2.1×10^-1 and 1.0×10^-1 for the Reasonable Maximum Exposure (RME) scenario. In adults, the total HI was 1.0×10^-3 and 1.2×10-3, for ingestion and dermal routes respectively under the CTE scenario. For RME scenario, ingestion and dermal exposure had risk values of 2.2×10^-2 and 3.1×10^-2, respectively. Regarding PAHs, the total carcinogenic risk (RME) for children and adults were estimated as 1.02×10^-5 and 8.38×10^-6 respectively. The carcinogenic risk derived from the ingestion and dermal absorption of metals exceeded the generally acceptable risk level of 10^-6 for individual chemicals, being slightly above 10^-4. That risk level, basically due to the ingestion of As and Mn through sediments suggests potential harm to human health. The concentrations of PAHs in sediments did not present significant non-carcinogenic and carcinogenic risk for the local population. The fate modelling however, suggests that naphthalene, anthracene, benzo[b]fluoranthene, pyrene, fluorene and phenanthrene tend to sorb onto soil or sediment in the environment and biologically ‘‘do not degrade fast’’. This implies the need to implement long term monitoring of these compounds in order to sustain this fragile ecosystem.