E. García-Luque

Bioavailability of heavy metals bound to estuarine sediments as a function of pH and salinity values

Abstract The role of two key-variables such as pH and salinity in chemical speciation and bioavailability of heavy metals originated by mining activities bound to sediments was evaluated under estuarine conditions. Two sediment samples collected in two estuaries in southern Spain (Ría of Huelva and Guadalquivir estuary) together with dilution of toxic mud from the Aznalcóllar mining spill (April, 1998) were used to determine their chemical speciation and bioavailability at different pH (6.5, 7.5, 8.5) and salinity (10, 20, 35) values using the estuarine clam Ruditapes philippinarum. The chemical speciation was established by means of measurements of the mobilization of heavy metals from sediments to waters and determining in it pH, salinity, alkalinity and heavy metal concentration. The geochemical model MINTEQA2 was used to establish the thermodynamic species in the assays. To assess the bioavailability of the heavy metals the concentration of metallothioneins in the clam tissues and the mortality of this organism was measured at different pH and salinity values. The influence of both salinity and pH was detected in the chemical behavior of metals and in their associated biological responses established by metallothioneins and the percentage of mortality. At low values of both variables (pH=6.5 and S=10), the biological effects were highest, and it was related to the free ion Zn2+.

THE BEHAVIOUR OF HEAVY METALS FROM THE GUADALQUIVIR ESTUARY AFTER THE AZNALCÓLLAR MINING SPILL: FIELD AND LABORATORY SURVEYS

The spill at `Los Frailes’ caused a large input of metals intothe riverine, estuarine and coastal ecosystems. Metal behaviourin natural waters can be studied both by performing fieldmeasurements, and by undertaking laboratory simulationexperiments. Here is described the behaviour of the heavymetals Zn, Cd, Pb and Cu in the Guadalquivir estuary usingincubation experiments and the results compared to thoseobtained during field assessments. If the toxic waste water hadbeen discharged untreated into the environment, it could haveraised the heavy metal concentrations in the estuary water tohigh values, such as 20.65 μM for Zn and 40 × 10-3 μM for Cd. These values are several times higher than thoseobtained in samples collected in the area during the monitoringof the early impact. The metals present a non-conservative behaviour, with a high loss to waters of low salinity values.

Isolation and characterization of naphthalene-degrading bacteria from sediments of Cadiz area (SW Spain)

Petroleum hydrocarbon contamination of harbor sediments from shipping activity, fuel oil spills, and runoffs are becoming a great concern because of the toxicity and recalcitrance of many of the fuel components. Polycyclic aromatic hydrocarbons (PAHs) are of most concern due to their toxicity, low volatility, resistance to degradation, and high affinity for sediments. Microorganisms, especially bacteria, play an important role in the biodegradation of these hydrocarbons. The objective of the present study was to characterize and isolate PAH‐(naphthalene) degrading bacteria in the coastal sediments of Cadiz (SW Spain), since this area is mostly polluted by PAH occurrence. A total of 16 naphthalene‐utilizing bacteria were isolated from these sites. Introduction of bacteria isolated from contaminated sediments into mineral medium contributed to the increased rate of hydrocarbon utilization. The bacterial isolates obtained from these sites are very potent in utilizing naphthalene and crude oil. It would be interesting to assess if the selected naphthalene‐degrading isolates may degrade other compounds of similar structure. Hence these isolates could be very helpful in bioremediating the PAH‐contaminated sites. Further pursue on this work might represent eco‐friendly solution for oil contamination on sea surface and coastal area.

Chronic bioassay in benthic fish for the assessment of the quality of sediments in different areas of the coast of Spain impacted by acute and chronic oil spills

More and more, the coastal regions of the world suffer from the contamination of petroleum hydrocarbon [principally polycyclic aromatic hydrocarbons (PAHs)]. This contamination can be acute, as it happened in the Coast of Galicia (NW, Spain) by the oil spill from a tanker, or chronic by the existence of high maritime traffic and a lot of industries as it is the case of the Bay of Algeciras (BA) (SW, Spain). It is of a great concern due to the toxicity, especially in sediments and ecosystem associated to it. The objective of this study is to assess, through chronic bioassay, sediment toxicity in samples collected in different littoral areas of Spain and to compare the damage caused in benthic fish, Solea senegalensis, according to that which suffers acute spill (Coast of Galicia) or chronic spill (the BA) by means of histopathology methods and enzymatic activities studies. Organisms were exposed to different sediments from Galician Coast and the BA during 42 days and every sample was analyzed by triplicate in glass aquaria. At the end of the bioassay, histopathological diseases were analyzed in the gills, target organ. Likewise, stress parameters as ethoxyresorufin‐O‐deethylase (EROD) and the glutathione S‐transferases (GSTs) activities were determined in the liver. Results showed a significant positive correlation between the biomarkers of exposure (EROD and GST), biomarkers of effect (histopathology), and PAHs concentrations in the sediments.

Using a laboratory simulator in the teaching and study of chemical processes in estuarine systems

The teaching of Chemical Oceanography in the Faculty of Marine and Environmental Sciences of the University of Caidiz (Spain) has been improved since 1994 by the employment of a device for the laboratory simulation of estuarine mixing processes and the characterisation of the chemical behaviour of many substances that pass through an estuary. The equipment comprising the simulator is controlled by a computer system running the program OLE (Oceanography and LEarning), which was developed originally as a research tool in Chemical Oceanography (under Windows® environment). Later, on the initiative of several teachers, the handling of the simulator was simplified to allow its use as a didactic resource for teaching the various processes that take place in littoral systems.Since its initial development, many different natural environmental conditions have been simulated, and the behaviour of many chemical pollutants has been studied. On the basis of this favourable experience, the simulator designed appears to be a versatile tool that can be usefully employed in both academic learning and research work.

Aerobic biodegradation of linear alkylbenzene sulfonates and sulfophenylcarboxylic acids for different salinity values by means of continuous assays

Aerobic biodegradation of linear alkylbenzene sulfonates (LAS) and sulfophenylcarboxylic acids (SPCs) in water, at different salinity values, has been studied. Three experiments have been carried out employing a staircase model system with continuous dosage of LAS to the system and using concentrations of LAS of the same order as those detected in littoral waters receiving urban wastewater discharges. LAS biodegradation was observed to be almost complete (showing a great extent), and in all cases exceeds 98.4%. At the very low concentration values of LAS utilized in the experiments, no significant variations in the biodegradation of LAS due to the effect of the different salinity values assayed were observed. The biodegradation intermediates detected for all the cases were sulfophenylcarboxylic acids with carboxylic chains of between five and 13 carbon atoms. The detection of C13-SPC (which is only produced by C13-LAS) confirms the existence of ω-oxidation. The total disappearance of SPCs in all cases indicates that mineralization of LAS at the concentrations tested was complete.

Effects of Sediment Acidification on the Bioaccumulation of Zn in R. Philippinarum

Acidification resulting from the increase of carbon dioxide in the ocean is one of the main effects of global warming. Models predict that a decrease of pH in surface sediments results in higher mobility of metals in sediment pore water and overlying water. This hypothesis has been tested in an exposure sediment bioassay using the clam R. philippinarum. Different sediment samples (toxic mud from a mining spill; estuarine samples from the Ria de Huelva and Guadalquivir rivers, and sediments located in the Bay of Cadiz, all in Spain) were used to address the influence of pH values (6.5–8.5) in bioaccumulation of the metal Zn. Results show that there is a significant (p < 0.05) increase in bioaccumulation of this metal at lower values of pH (6.5 and 7.5) compared to the 8.5 value. These results indicate that modification of one unit in pH produces a significant effect in Zn bioavailability, which is also associated with adverse biological effects such us mortality. The results point out the importance of addressing the influence of sediment acidification and their implications in risk assessment in estuarine sediments or in special areas selected for carbon dioxide capture in marine environments.