Increased Bioavailability of Mercury in the Lagoons of Lomé, Togo: The Possible Role of Dredging

Abstract

Surface sediments of the lagoons of Lomé, Togo, were analyzed for mercury, methylmercury, and trace elements. Concentrations were greater than typical for natural lagoon sediments, and with greater variability within the Eastern lagoon compared to the Western one. The Eastern lagoon is larger and has been dredged in the past, while the Western lagoon, which also receives major waste inputs, has not been dredged and shows less tidal flushing. Accordingly, one naturally believes that the Eastern lagoon is cleaner and probably safe to use due to its natural resources, including fishes to eat. Unexpectedly, we describe here that mercury methylation was greater in the Eastern lagoon, indicating increased bioavailability of mercury, as probably facilitated by past dredging that decreased solidphase retention of inorganic mercury. Urbanization has historically been more developed in the southern part of the lagoons, which is still reflected in contamination levels of sediment despite dredging, probably because sources of contamination are still more important there today. Such urban contamination emphasizes the need to regulate waste discharges and possible airborne contamination in growing cities of developing countries, and implements environmental and public health monitoring, especially in relation to misbelieves systematically associated with the cleansing effect of dredging activity.

Spatial and seasonal variations of trace elements concentrations in liver and muscle of round Sardinelle (Sardinella aurita) and Senegalese sole (Solea senegalensis) along the Senegalese coast

“…Arsenic is also naturally present in the environment especially in rocks and sediments and has a considerable tendency to accumulate in bottom sediments (Smedley and Kinniburgh, 2002). This fact could explain the relative lower contamination load in pelagic fish (sardinella) compared with benthic species (sole) (Tables 1 and 2) as previously observed (Gnandi et al, 2011;Perugini et al, 2014). The As found in this study may have both anthropogenic and natural sources and, the levels recorded generally agree with the literature.…”

“…The As found in this study may have both anthropogenic and natural sources and, the levels recorded generally agree with the literature. Concentration as high as 54.8 and 71.0 mg kg À1 were reported in fish from the Mediterranean sea (Perugini et al, 2014) and as high as 38.0 mg kg À1 in benthic fish species from coastal Togo (Gnandi et al, 2011). Total As concentrations have been found to be very high even in fish from remote areas of the Barents Sea with little known pollution (Julshamn et al, 2012).…”

Hospital Effluents Are One of Several Sources of Metal, Antibiotic Resistance Genes, and Bacterial Markers Disseminated in Sub-Saharan Urban Rivers

“…Freshwater resource pollution by various contaminants including toxic metals, persistent organic pollutants, pathogenic organisms, antibiotic resistant bacteria (ARB), and antibiotic resistant genes (ARGs) is still a major problem in many parts of the world (Poté et al, 2008 ; Knapp et al, 2012 ; Bréchet et al, 2014 ; Czekalski et al, 2014 ; Devarajan et al, 2015b ). The situation is particularly alarming in developing regions such as in Sub-Saharan Africa where most rivers, lakes, and lagoons are receiving untreated hospital and industrial effluent water, mining effluents, and urban storm water runoff affected by anthropogenic pollutants due to intensive and uncontrolled urbanization (Feng et al, 2004 ; Chatterjee et al, 2007 ; Gnandi et al, 2011 ; Atibu et al, 2013 ; Mwanamoki et al, 2014 , 2015 ).…”

The Geochemistry of Heavy Metals in the Mudflat of Salinas de San Pedro Lagoon, California, USA

“…Since trace metals occur naturally in the earth's crust, it cannot be assumed that an environment is automatically anthropogenically contaminated when trace metals are found in its sediments. We utilized the EF method, a widely used normalizing measure, to distinguish between natural and anthropogenic metal sources [26][27][28][29]. In EF calculation, Al was used as earth crust value by Turekian and Wedepohl, (1961) [30].…”