Heavy Metal Contamination from Domestic Wastewater in Tropical Lagoon Sediments


This study by Fujita et al. (2014) investigates the contamination of heavy metals in the sediments of a tropical lagoon in Funafuti Atoll, Tuvalu. Sediment samples were analyzed from densely populated, sparsely populated, open dumping, and undisturbed sites along the islet. The highest concentrations of heavy metals and acid-volatile sulfates were found at the densely populated sites, where poorly constructed sanitary facilities are the cause of marine pollution due to domestic wastewater leakage. The currents were examined in order to see if they might have a role in the dispersal of heavy metals in the lagoon. Sediment samples were analyzed to measure acid-volatile sulfides, contamination factor, and pollution load index, and were analyzed using principal components analysis. Results showed that various types of grey wastewater were the primary source of contamination by heavy metals such as chromium, zinc, copper, lead, and cadmium. Manganese and nickel were found in higher concentrations at the open dumping site, supporting the idea that these contaminants are likely a result of disposed batteries. The prevalence of sanitary facilities and dumping sites such as the ones found on Funafuti across atolls in the Central and South Pacific poses significant ecological threats to the coastal sediment and coral reef environments that they support, as well as threats to human health and the availability of food resources.–Submitted by Dawn Barlow

Fujita, M., Ide, Y., Sato, D., Kench, P.S., Kuwahara, Y., Yokoki, H., Kayanne, H., 2014. Heavy metal contamination of coastal lagoon sediments: Fongafale Islet, Funafuti Atoll, Tuvalu. Chemosphere 95, 628 –634.

The study site selected by Fujita et al. was Fongafale Islet, Funafuti Atoll, Tuvalu, Central Pacific. The sediments found in the lagoon consist of gravel, sand, silt, benthic foraminifera, coral fragments, and shell fragments. At the densely populated urban settlement, 92% of the houses have access to sanitary facilities such as buried septic tanks that receive wastewater and pit toilets with a pour flush. However the septic tanks are not sealed against seepage, and so domestic wastewater leaks from these “bottomless” septic tanks into the lagoon, becoming the primary source of pollution in the region. Sediment samples were collected from the intertidal beach as well as in nearshore waters. Samples were also taken from a sparsely populated region to the north of the main settlement, and municipal solid waste open dumping site farther north. The fourth sampling site was even farther to the north, at a place which the authors deemed as close as possible to a comparable undisturbed natural environment. A current meter was installed there to measure nearshore patterns that may influence the dispersal of contaminants. Sediment samples (33 total) were measured for acid-volatile sulfide contamination, and heavy metal concentrations. The contamination factor (CF) was obtained by dividing the concentration of heavy metals in the sediment by the concentration at the background undisturbed natural environment site, and CF contamination values were categorized as low, moderate, considerable, or very high. The geoaccumulation index equation was used to interpret whether the sediments were “unpolluted,” “moderately polluted,” “moderately to heavily polluted,” “heavily polluted,” “heavily to extremely polluted,” “or extremely polluted.”

Fujita et al. did not find any significant current direction dependence, and the data from the current meter suggested that contaminants would only be transported during a small portion of the tidal cycle. Acid-volatile sulfides were detected in the densely populated area, both on the intertidal beach as well as in the nearshore zone, suggesting that this was probably because of wastewater leaking through the coastal sediment on the beach face. There was no detection of acid-volatile sulfides in the sparsely populated, open dumping, or undisturbed sites. Based on the CF values, the densely populated site was found to have “very high contamination” by heavy metals. The open dumping area followed the densely populated area in overall contamination, showing varying degrees of contamination for the different metals measured. The CF values of all the heavy metals tested for at the sparsely populated site indicated either considerable or moderate contamination. The highest values for the geoaccumulation index were measured in the densely populated area, except for nickel, which was found in the highest concentration in sediments at the open dumping zone. Because nickel and manganese are used in batteries, which are often dumped as a constituent of municipal solid waste, they are likely the culprits.

Fujita et al. discuss the idea that automobile traffic has been found to be a large contributor to heavy metal contamination in other studies and that nickel, copper, and zinc can be derived from traffic activities. However, because the nickel concentrations were lower in the densely populated region than the sparsely populated and the open dumping areas, it is unlikely that cars and traffic are the cause of the heavy metal contamination. In this study, the authors conclude that the most likely sources of heavy metal contamination are various types of grey wastewater, as domestic wastewater from households on Fongafale contains at least the heavy metals chromium, manganese, copper, zinc, cadmium, and lead. Both water pollution and heavy metal contamination have detrimental effects on the ecological health of the tropical reef ecosystems that thrive in this region. The degradation that results from such pollution can have a strong negative effect on not only the health of the reefs in the lagoon but also human health and the availability of food resources that are obtained from the reefs. Poorly constructed sanitary facilities such as the ones found on Fongafale Islet are common across atolls in the Central and South Pacific, and it is likely that these concerns surrounding heavy metal contamination apply to similar ecosystems in populated areas.


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