Mercury May Pose Higher Ecological and Human Health Risks than Lead in Vegetables Cultivated on Solid Wastes Dumpsites Soils.

Vegetable cultivation on solid wastes dumpsites (SWD) soils is very common in developing countries though unsafe due to heavy metals pollution. In order to evaluate the ecological and human health risks of this practice, Talium triangulare and Lycopersicon esculentum were grown in a greenhouse on soils from two abandoned and active SWD, and control site. The SWD soils were acidic (pH 6.4-6.8), rich in organic matter (10.15%-15.35%) and the heavy metals content patterned Zn > Mn > Hg > Cu > Pb > Ni > Cd. Ecological risk was very high ([Formula: see text] = 396.40; RI = 400) for waterworks dumpsite (WWD) and was > 99% attributable to Hg. Pb was not accumulated in either vegetable but Hg levels exceeded FAO/WHO limits. HQ was mostly < 1 except for Hg (0.47-3.42) and Co (0-1.33) while THQ > 1 for T. triangulare and cancer risks exceeded 10-6-10-4 acceptable limits. Regular monitoring and outlawing of vegetable cultivation on SWD is advocated to avert Hg toxicity.

Combinations of cypermethrin and dimethoate alter behavior, hematology and histology of African Catfish, Clarias gariepinus.

Cypermethrin and dimethoate are pesticides frequently used in agriculture to eliminate pests. Contemporaneity of these and other pesticides in commercial preparations and several aquatic ecosystems is well known, though poorly studied. This study aims to evaluate the effect of sublethal concentrations of combinations of cypermethrin and dimethoate on juvenile catfish, Clarias gariepinus, given that the pesticides concomitantly occur in the floodplains were the fish breed. Behavioral, hematological and histopathological changes in juvenile fish exposed to sublethal concentrations were monitored for 96 hours. Pesticide exposed fish exhibited abnormal behaviors such as erratic swimming, frequent air gulping, sudden jerk movement and rapid opercula movement and these were more pronounced in higher concentrations. Significant reductions in erythrocytes (0.83-20.94%), hemoglobin (4.12-29.23%) and PVC (7.14-28.57%) and increase in leucocytes (4.84-9.32%) were observed (p<0.05). Mean corpuscular hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH) and mean cell volume (MCV) reduced significantly in the exposed groups compared to the control. Infiltration of inflammatory cells, distortion of cell architecture, hemorrhage and necrosis were the observed histopathological damages in the heart, brain, gill, liver, kidney and fin of exposed fish. These pathological damages were more severe than previously reported for either chemical. Therefore, the use of these chemicals in agriculture should be regulated, especially near fish breeding sites.

Evaluating Heavy Metals Pollution and Exposure Risk Through the Consumption of Four Commercially Important Fish Species and Water from Cross River Ecosystem, Nigeria.

In order to evaluate heavy metals exposure risk in the mid-Cross River, the concentrations of iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), lead (Pb) and chromium (Cr) in water and four commercially important fishes (Chrysichthys nigrodigitatus, Clarias anguillaris, Tilapia zillii and Mormyrus rume) were studied between February 2015 and August 2016. Iron (2.71 ± 0.5 mg/L), Mn (0.49 ± 0.06 mg/L), Pb (0.05 ± 0.04 mg/L) and Cr (0.06 ± 0.03 mg/L) in water were above permissible limits. The pattern of heavy metals concentration in fish was T. zillii > M. rume > C. anguillaris > C. nigrodigitatus except for Pb. The estimated daily intake of most heavy metals was below the tolerable daily intake values except Pb. Although the hazard quotient was below one, the total hazard quotient and the carcinogenic risk value for Cr were above acceptable ranges for all fishes.

Organ-dependent response in antioxidants, myoglobin and neuroglobin in goldfish (Carassius auratus) exposed to MC-RR under varying oxygen level.

Cyanobacterial bloom, a common phenomenon nowadays often results in the depletion of dissolved oxygen (hypoxia) and releases microcystin-RR (MC-RR) in the water. Information on the combined effects of MC-RR and hypoxia on the goldfish is lacking, therefore, this study is aimed at evaluating the effect of two doses of MC-RR on the antioxidants and globin mRNA of goldfish under normoxia, hypoxia and reoxygenation. The result showed that MC-RR at both doses (50 and 200 µg kg(-1) body weight) significantly (p<0.05) induced superoxide dismutase activities in the liver and kidney but catalase activities and total antioxidant capacity were low in these organs during hypoxia and reoxygenation compared to normoxia and control. Myoglobin and neuroglobin mRNAs in MC-RR group were significantly induced in the brain only and are believed to protect the brain from oxidative damage. However, other organs were unprotected and extensive damage was observed in the liver cells. Our results clearly demonstrated that MC-RR and hypoxia-reoxygenation transitions were synergistically harmful to the goldfish and could impair its adaptation to hypoxia, especially during reoxygenation.

Seasonal dynamics of phytoplankton in two tropical rivers of varying size and human impact in southeast Nigeria.

Phytoplankton occurrence and dynamics in rivers are mainly shaped by hydrophysical conditions and nutrient availability. Phytoplankton main structuring factors have been poorly studied in West African rivers, and this study was undertaken to identify these conditions in two tropical rivers that vary in size and human impact. For this, environmental variables and phytoplankton monthly samples were collected from the middle reaches of Asu and Cross rivers during an 18 months survey from March 2005-July 2006. Phytoplankton biomass (F=11.87, p=0.003), Shannon-Weiner diversity and species richness (F=5.93, p=0.003) showed significant seasonality in Asu but not in Cross River. Data was analyzed with Canonical correspondence analysis (CCA) and showed environmental differences between the two rivers, nitrate in Asu River (5.1-15.5 mg/L) was significantly higher than Cross River (0.03-1.7 mg/L), while PO4 (0.2-0.9 mg/L) was significantly lower in Asu River compared to Cross River (0.03-2.6 mg/L) (p < 0.05). Eutrophic factors (NO1) determined primarily phytoplankton dynamics in Asu River, especially during the dry season, whereas hydrophysical factors (depth, transparency and temperature) shaped phytoplankton in Cross River. Taxa indicative of an eutrophic condition, such as Euglena, Chlorella, Chlorococcus, Ceratium, Peridinium, Anabaena, Aphanizomenon, Closterium, Scenedesmus and Pediastrum spp., were frequently encountered in the shallow impounded Asu River, while riverine species, such as Frustulia rhomboids, Gyrosigma sp., Opephora martyr and Surirella splendida dominated Cross River. A succession pattern was observed in the functional groups identified: Na/MP-->TB-->P (rainy-->dry season) was observed in Asu River, whereas MP/D predominated in Cross River for both seasons. We concluded that, if nutrients predominate hydrophysical factors in shaping phytoplankton during dry season (half of the year) then, they are as important as hydrophysical factors structuring phytoplankton during rainy season (the other half).

Age, growth and mortality of Clarias gariepinus (Siluriformes: Clariidae) in the Mid-Cross River-Floodplain ecosystem, Nigeria.

Clarias gariepinus is a threatened highly prized species used for some elite ceremonies by the local communities. Artisanal fishers take advantage of this species annual breeding migration from the lower Cross River to the floodplain lakes in Mid-Cross River during the rainy season, and some migrant stocks are not able to spawn. Since there is a lack of information on this species population dynamics in the Mid-Cross area, this study aimed to evaluate the age, growth and mortality to support the development of effective management plans. For this, monthly overnight gill net catches (from 6 to 72mm mesh sizes) were developed between March 2005 and February 2007. Growth parameters were determined using the FiSAT II length-frequency distribution. A total of 1 421 fish were collected during the survey. The asymptotic growth (L(infinity)) was 80.24cm, growth rate (K) was 0.49/year while the longevity was 6.12 years. The annual instantaneous rate of total mortality (Z) was 2.54/year and the natural mortality (M) was 0.88. Fishing mortality (1.66/year) was higher than the biological reference points (F(opt) = 0.83 and F(limit) = 1.11) and the exploitation rate (0.66) was higher than the predicted value (E(max) = 0.64) indicating that C. gariepinus was over exploited in the Mid-Cross River-Floodplain ecosystem. Some recommended immediate management actions are to strengthen the ban of ichthyocide fishing, closure of the floodplain lakes for most of the year, restricted access to the migratory path of the fish during the flood period and vocational training to the fishers. In order to recover and maintain a sustainable harvest, I suggest that a multi-sector stakeholder group should be formed with governmental agents, community leaders, fishers, fisheries scientists and non-governmental organizations. These short and long term measures, if carefully applied, will facilitate recovery of the fishery.

Seasonal variation and diversity of rotifers in Ehoma lake, Nigeria.

The zooplankton and physicochemistry of Ehoma lake were studied from March 2005 to August 2006 in order to evaluate seasonal trend in species composition and abundance in relation to water quality. Forty two (42) species of rotifers dominated by Keratella tropica tropica were encountered. Species richness declined by nearly 50% from dry season values during the rainy season. Species richness was higher in the littoral zone during the dry season, the reverse was the case during the rainy season. Species abundance followed similar trend as species richness. Abundance was closely associated with dissolved oxygen, biological oxygen demand and width of the lake and these in turn varied significantly between seasons. Shannon-Weaver diversity varied from 2.2 to 3.8 bit ind(-1) and significantly between seasons (p<0.05). Anuraeopsis navicula navicula and Euchlanis dilatata dilatata Ehrenbreg were the only species gained during the flood periods.