TOTAL DISSOLVED INORGANIC CARBON AND PHYSICOCHEMICAL CHARACTERISTICS OF SURFACE MICROLAYER AND UPPER MIXED LAYER WATER FROM LAGOS LAGOON, NIGERIA

The carbonate and physicochemical characteristics of the surface microlayer and upper mixed layer of a tropical coastal lagoon were investigated. Data on the physicochemical parameters generally indicated a moderately polluted ecosystem. The influence of the ocean environment over the Lagoon system was evident by elevated salinity levels. The mean total dissolved inorganic carbon (DIC) for the surface microlayer (SML) and subsurface water (SSW) samples were 2626.6 and 2550.9 μmol kg-1 SW respectively. The dominant inorganic form of DIC in the lagoon water samples was HCO3- with a calculated average abundance >95.4% in the SML and >94% in the SSW. The bicarbonate species derived abundance varied between 1.6% (SML) and 8.4% (SSW), while the aqueous carbon dioxide were generally low in percentages ranging from 0.4 in SSW to 1.5 in SML water samples. In general, the occurrence of the carbonate species was in the order HCO3- > CO32- > CO2. Results showed that total alkalinity (AT) was relatively greater than the DIC. Long term monitoring studies in the coastal lagoon systems is needed to understand the coastal water chemistry and pollution status

Interseasonal distribution and partitioning of heavy metals in subtidal sediment of Qua Iboe Estuary and associated Creeks, Niger Delta (Nigeria)

An analysis of the distribution and chemical forms of selected metals: cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and lead (Pb) in subtidal sediments of Qua Iboe Estuary and adjourning creeks, collected between June 2000 and January 2001, were studied using a sequential chemical extraction method. The concentration of metals in each extracted fraction was determined using inductively coupled plasma spectrometer (ICP-AES). Pb, Cd and Cu appear to be the most abundant metal in the sediments of the systems, and are predominantly associated with the residual, organic and oxidisable phases. Results indicate that there are also insignificant components that are bound to both the exchangeable and carbonates fractions. Ni is largely associated with bioavailable phases with insignificant bound to organic matter and residual fractions. In general, an insignificant component of Cd and Pb are bound to organic matter phase. Moreover, speciation results indicate that metal contamination in the ecosystems investigated primarily comes from human-mediated sources. Thus, based on index of geoaccumulation calculated, sediments of these ecosystems have been classified as uncontaminated by Cr, Cu and Ni, strongly contaminated by Pb and extremely contaminated by Cd

New ecological risk indices for evaluating heavy metals contamination in aquatic sediment: A case study of the Gulf of Guinea

New indices – modified hazard quotient (m HQ) and ecological contamination index (ECI) – were developed for the evaluation of heavy metals contamination of sediment. Sequential extraction method was employed to determine the levels of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), and lead (Pb) in subtidal sediment samples from tropical ecosystems off the Gulf of Guinea. The results were used to assess the degree of contamination and estimate the extent of anthropogenic inputs from industrial activities. Results indicated that the concentrations of Cd, Cr, Cu, Ni and Pb ranged from 4.33 –5.67, 11.12– 28.52, 30.26–43.72, 2.02–2.60 and 162.0–190.37 mg/kg dw, respectively. The mean metal levels did not show significant variations among study sites during the wet and dry seasons. Spatial distribution and severity of sediment-associated contamination by heavy metals based on the newly developed indices (m HQ and ECI) were in good agreement with existing pollution indices and followed the descending sequence: Cd>Pb>Cu>Cr>Ni. Contamination severity index, mean hazard quotient and modified risk assessment code were also used to evaluate the sediment-heavy metal contamination, which generally indicated medium risk contamination of the investigated ecosystems. Aquatic pollution indicators (potential contamination index, ECI, hazard quotients, m HQ) revealed significant anthropogenic contamination by Cd and Pb, while Cr, Cu and Ni showed relatively low degree of contamination. Potential contamination index (PCI) generally followed the sequence Cd>Pb>Cu>Cr>Ni. A comparison of newly proposed indices with existing pollution indices revealed very good agreement. The contamination trends derived from the new indices were consistent and took into consideration site specificity, toxicity and a three-tier effect levels (threshold, mid-range and extreme effects guideline values) that support their reliability in evaluating contaminated aquatic ecosystems

Geochemical Speciation and Risk Assessment of Trace Metals in Sediments from Coastal Ecosystems off Equatorial Atlantic Ocean

The concentrations of Cd, Cr, Cu, Ni and Pb in estuarine benthic sediments were determined through multistep speciation scheme to evaluate their spatio-temporal distributions, selective fraction magnitude, degree of contamination and potential ecological risks. The results indicated that the metal fractionation percentages in the residual, oxidizable and reducible fractions are the most significant, while the exchangeable and carbonates bound trace metals are relatively low. High mobility and bioavailability was indicated for Cu, Cr and Ni, while Cd and Pb in sediments present low bioavailability for biota. Contamination factor (CFm), degree of contamination (DC), modified degree of contamination (mCd), geoaccumulation index (Igeo), risk assessment code (RAC), and potential ecological risk index (PERI) were used to assess trace metals sedimentary pollution. The results indicate a prevalent moderate to high contamination of most trace metals analyzed. The contamination ranking of trace metals based on percent contribution to DC was Cd>Pb>Cu>Cr>Ni. RAC values indicate medium risk for Cd and Ni at all studied sites during the wet and dry seasons. Cd and Pb show moderate and very high individual metal potential ecological risk, respectively, while multi-elemental potential ecological risk indices (RIs) indicate very high ecological risk in all the ecosystem

Geochemical fractionation and ecological risks assessment of benthic sediment-bound heavy metals from coastal ecosystems off the Equatorial Atlantic Ocean

This studydeterminesthepollution,fractionation,andecologicalrisksofsediment-boundheavymetals from coastalecosystemsofftheEquatorialAtlanticOcean.ContaminationFactor(CF),pollutionload index(PLI),andgeoaccumulationindex(Igeo) wereusedtoassesstheextentoftheheavymetalpol- lution, whilethepotentialecologicalriskwasevaluatedusingtherisksassessmentcode(RAC)and Håkanson potentialecologicalrisk.Theanalysisrevealedconcentrations(mg/g,dw)ofthecadmium(Cd), chromium (Cr),copper(Cu),nickel(Ni),andlead(Pb)insedimentsforwetanddryseasonsvaryfrom 4.40–5.08, 14.80–21.09,35.03–44.8,2.14–2.28, and172.24–196.39,respectively.Theresultsalsoshowed that themetalfractionationpercentagesintheresidual,oxidizable,andreduciblefractionsarethemost significant, whiletheexchangeableandcarbonateboundtracemetalsarerelativelylow.TheRACvalues indicate noriskforCdandNiandlowriskforothermetalsatallthestudiedsitesduringbothseasons. PotentialecologicalriskanalysisoftheheavymetalconcentrationsindicatesthatCdhadhighindividual potentialecologicalrisk,whiletheothermetalshavelowriskatallinvestigatedsites.Themulti-ele- mental potentialecologicalriskindices(R1) indicatehighecologicalriskinalltheecosystem