Heavy Metal Bioaccumulation in Highly Consumed Pelagic and Benthic Fish and Associated Health Risk.

The present study investigated the levels of Manganese (Mn), Cadmium (Cd), Copper (Cu), Zinc (Zn), Lead (Pb) and Iron (Fe) in the tissues of a benthic fish (Clarias gariepinus) and a pelagic fish (Oreochromis niloticus), which are highly consumed in Ghana. The fish were collected from the Weija reservoir, which is an important source of fishery and potable water in Accra, Ghana. The results indicate heavy metal accumulation in all the tissues (gills, liver and muscles) analyzed. The bioaccumulation of all the metals was lowest in the muscles compared to the liver and gills in both species. The bioaccumulation of the metals was generally higher in the tissues of the catfish, except for Fe and Zn. Fe was higher in the gills and liver of the tilapia, and Zn was higher in the liver of the tilapia. The analysis of relationships between metal levels in the different tissues and the size of the fish showed a few significant correlations. The results also showed that all metals showed no potential health risk to consumers, as THQs and TTHQs in tilapia and catfish were less than one, and the metal levels in both species were all below the FAO/WHO maximum permissible limits.

Microplastics prevalence in water, sediment and two economically important species of fish in an urban riverine system in Ghana.

Urban riverine systems serve as conduits for the transport of plastic waste from the terrestrial dumpsites to marine repositories. This study presented data on the occurrence of microplastics in water, sediment, Bagrid Catfish (Chrysichthys nigrodigitatus) and Black-chinned Tilapia (Sarotherodon melanotheron) from the Densu River, an urban riverine system in Ghana. Microplastics were extracted from the samples collected from both the lentic and lotic sections of the river. The results indicated widespread pollution of the Densu River with microplastics in all the compartments studied. The average numbers of microplastic particles deposited in the Dam (2.0 ± 0.58) and Delta (2.50 ± 0.48) sections of the river were not affected by the differences in their hydrology. However, the stagnant water system of the Dam promoted the floating of larger-sized microplastics while the flowing waters of the Delta did not show any selectivity in the deposition of microplastics between sediment and the water column. The number of microplastics ingestions by the Bagrid Catfish (2.88 ± 2.11) was similar to the Black-chinned Tilapia (2.38 ± 1.66) but both species ingested lower numbers of microplastics than reported for marine fish species in coastal Ghana.

Preliminary Assessment of Trace Metal Pollution and Their Bioaccumulation in Mollusks Inhabiting the Intertidal Sediments of the Atlantic Coast of Accra, Ghana.

The present study investigated the trace metal levels in sediments, enrichment in sediments, and its bioaccumulation in mollusks collected from the intertidal sediments of the coast of Accra, Ghana, which is influenced by anthropogenic activities. The metals (Fe, Mn, Cu, Cr, and Zn) were analyzed in sediments. The metals (Mn, Cu, Cr, and Zn) were analyzed in the soft tissue of the mollusks collected from the different coastal areas. The results indicate that although Accra is the capital city and the coast receives tons of anthropogenic wastes, trace metal levels were low and there was no enrichment for the metals analyzed except Cu which showed minor to moderate enrichment in the coastal sediments. There was bioaccumulation of the trace metals in the soft tissue of the mollusks, and the results suggest that the mollusks studied, the gastropods (Agaronia razetoi) and the bivalves (Tivela tripla), can be used for biomonitoring.

The effect of sediment characteristics on bioturbation-mediated transfer of lead, in freshwater laboratory microcosms with Lumbriculus variegatus.

While it has been well established that sediment bioturbators can affect the fate of metals in aquatic systems and that the fate of metals there can depend on sediment characteristics, the interaction between these influences is not well known. The present study therefore investigated whether the influence of a sediment bioturbator on the fate of metals is affected by sediment characteristics. This was investigated using two laboratory microcosm experiments with lead-contaminated sediment and the oligochaete Lumbriculus variegatus. The first experiment used sediment collected from five Toledo Bend reservoir sites that differed in sediment characteristics, and analyses looked at the influence of sediment organic matter, sediment silt/clay content, sediment pH, and pore-water pH. In the second experiment, organic matter and silt/clay content of Toledo Bend reservoir sediment were varied experimentally using alpha-cellulose and clay, and Pb transfer to the water column and bioaccumulation were again quantified. Both experiments were conducted with sediment spiked with Pb to a concentration of 100 µg/g, at an oligochaete density of 6279 ind./m². In the first experiment, the Pb concentrations in the water column and those in the worms at the end of the 14-day experiment differed among sediment-collection sites. Silt/clay content and sediment pH were the two most important variables influencing Pb transfer from sediment to the water column. A multiple regression model with these variables explained 58% of the variability in this lead transfer. For Pb accumulation by the worms, sediment organic matter and pore-water pH were the two most important variables. This regression model explained 85% of the variability in tissue Pb levels. In the second experiment, where the individual effects of the organic matter and silt/clay content on Pb transport and distribution were assessed, the use of sediment with more organic matter resulted in a reduction in both the Pb transfer to the water column and the accumulation in worms. The increase in the sediment's silt/clay content resulted in a reduction in Pb bioaccumulation only. Overall, the results of the present study demonstrate that sediment pH, pore-water pH, organic matter, and silt/clay content influence the bioturbation-mediated transfer and the environmental distribution of Pb.

The effect of lead contamination on bioturbation by Lumbriculus variegatus in a freshwater microcosm.

The present study investigated the effect of lead (Pb) on bioturbation by the oligochaete worm Lumbriculus variegatus, using freshwater microcosms. The experiment used lead at "0", 140, 700, and 3500 µg/g in sediment, and used two different laboratory populations of L. variegatus. A molecular genetic analysis and bioassays were conducted to determine if the two populations differed genetically and whether they differed in Pb-sensitivity. The bioturbation of L. variegatus was estimated using luminophores placed at the sediment-water interface at the beginning of the experiment. After the 14 d experiment the luminophore profiles in sediment were used to estimate the biodiffusion and bioadvection coefficients, using the diffusion-advection model. The results showed that the biodiffusion and bioadvection coefficients were generally negatively related to the Pb concentrations in the sediment. Lead at 700 and 3500 µg/g reduced both coefficients, while Pb at 140 µg/g did not. Luminophore profiles in the "0" and 140 µg/g treatments were indicative of a non-local transport, while a diffusive transport was observed at the higher Pb levels. The two laboratory populations of L. variegatus used in the experiment differed in their sensitivity to Pb when mortality was used as the endpoint, but they did not differ in sediment bioturbation or the Pb-sensitivity of this process. Moreover, the genetic analysis did not detect any genetic differences between the populations. This study demonstrated that elevated levels of Pb can impact ecosystem functioning by decreasing the bioturbation activity of benthic organisms such as L. variegatus.

The effect of lead from sediment bioturbation by Lumbriculus variegatus on Daphnia magna in the water column.

The present study investigated the bioavailability and potential toxicity to Daphnia magna of lead released to the water column due to bioturbation by Lumbriculus variegatus. Experiments used microcosms with Pb-spiked sediment, with or without worms in the sediment, and with D. magna present in the water column. The daphniids were allowed free movement or were restricted to flow-through containers, in order to assess the influence of their direct contact with the contaminated sediment. A control group consisted of D. magna in clean moderately hard reconstituted water. At the end of the 12-day experiment, D. magna survival, reproduction, biomass, and Pb-bioaccumulation were determined. Water column turbidity and Pb levels were quantified to assess their influence on the Pb toxicity and bioaccumulation. The bioturbation by L. variegatus increased Pb levels and turbidity in the water column. While this resulted in an increased Pb bioaccumulation by the D. magna, the water column Pb levels and the Pb bioaccumulation were insufficient to bring about toxic effects for the survival, reproduction, and biomass of the daphniids. Contact of D. magna with the sediment resulted in an increase in their Pb bioaccumulation, with water turbidity and Pb data, suggesting that these crustaceans also acted as bioturbators. The increase in Pb bioaccumulation in D. magna as a consequence of bioturbation by L. variegatus demonstrates the potential for bioturbation to enhance contaminant toxicity to organisms in the water column, though this potential appeared relatively low in the case of lead.

The bioaccumulation and effects of selenium in the oligochaete Lumbriculus variegatus via dissolved and dietary exposure routes.

Aquatic organisms take up selenium from solution and from their diets. Many questions remain regarding the relative importance of selenium accumulation from these sources and resulting effects in benthic invertebrates. The present study addressed the toxicity and accumulation of Se via dissolved and dietary exposures to three different Se species, in the freshwater oligochaete Lumbriculus variegatus. Worms were exposed to 20µg/g dry weight of selenite (Se(IV)), selenate (Se(VI)), or seleno-l-methionine (Se-Met) in their diet (sediment) or to 15µg/L dissolved Se in water-only exposures. While the dissolved and sediment Se levels differed greatly, such levels may co-occur at a Se-contaminated site. Se accumulation, worm population growth, lipid peroxidation (as TBARS), and Na(+)/K(+)-ATPase activity were quantified at the end of the 2-week exposure. The sediment Se-Met exposure caused 100% mortality, while worm densities were reduced by the other exposures except the Se(VI) one. Se bioaccumulation was generally higher for the sediment-Se exposure than the dissolved-Se ones, and was higher for Se(IV) than Se(VI) in the dissolved-Se exposure but not the sediment-Se one. The Se accumulation was highest for Se-Met. The oligochaetes that accumulated Se had higher levels of lipid peroxidation and reduced Na(+)/K(+)-ATPase activity. The present study's findings of differences in Se accumulation and toxicity for the three Se species, with effects generally but not exclusively a function of Se body burdens, underscore the need for research on these issues in invertebrates. Moreover, the results imply that the dietary uptake route is the predominant one for Se accumulation in L. variegatus.

The effect of bioturbation by Lumbriculus variegatus on transport and distribution of lead in a freshwater microcosm.

The present study investigated the effect of bioturbation by the oligochaete worm Lumbriculus variegatus on the transport and environmental distribution of lead (Pb). Experiments used L. variegatus at densities of 0 ind./m(2), 2093 ind./m(2), and 8372 ind./m(2), in freshwater microcosms with Pb-spiked sediment. At the end of the 14-d experiment, Pb levels in the water column, tissues of L. variegatus, and sediment were determined, and bioturbation was quantified using luminophores. The bioturbation by L. variegatus increased Pb transport from the sediment to the water column. However, it did not significantly affect Pb bioaccumulation by L. variegatus or Pb levels in the sediment. The biodiffusion coefficient (Db) was positively related to worm density, but did not differ between Pb-spiked sediment and uncontaminated sediment. The latter finding suggests that Pb at the 100 µg/g concentration used in the present study did not affect L. variegatus bioturbation. The present study shows that bioturbation can enhance Pb transfer across the sediment-water interface and thus enhance Pb availability to organisms in the water column.