Assessment of the toxicity toward Vibrio fischeri in sediments of a mining impacted estuary in the north of Spain

Increase in mercury and methylmercury levels with depth in a fish assemblage

Despite their remoteness, deep-sea species bioaccumulate mercury, mostly in the form of the neurotoxin methylmercury (MeHg). Although the concentration of MeHg in the water column is known to increase with depth down to a maximum found at the base of the permanent thermocline, the knowledge of the relationship between MeHg content in marine species and their depth of occurrence is limited. We analyzed total mercury (THg) and MeHg concentrations in 25 species of fish inhabiting the Avilés Submarine Canyon and its adjacent shelf (Cantabrian Sea, North-East Atlantic) between 50 and 1868 m depth. THg concentrations ranged from 0.03 μg g^-1 in wet weight (ww) in Chauliodus sloani and 4.0 μg g^-1 ww in Coryphaenoides guentheri. 65% of the species analyzed exceeded 0.5 μg g^-1 ww of MeHg, the maximum level for safe consumption recommended by FAO/WHO. THg and MeHg contents in muscle tissue increased with the depth of occurrence of fish and was influenced by their habitat so that demersal species had higher THg content than pelagic species inhabiting the same depth. MeHg accounted for an average 76 ± 3.9% of THg (mean ± SD), which is lower than that reported for other fish communities and can be explained by the high concentration of Hg present in sediments of the Nalón estuary, which discharges right off the Avilés Canyon head. The % of THg as MeHg was also strongly correlated with δ¹⁵N values, confirming that MeHg can be an indicator of the trophic identity of a species within the food web.

Toxicological characterization of produced water from the Permian Basin

Produced water (PW) is a hypersaline waste stream generated from the shale oil and gas industry, consisting of numerous anthropogenic and geogenic compounds. Despite prior geochemical characterization, the comprehensive toxicity assessment is lacking for evaluating treatment technologies and the beneficial use of PW. In this study, a suite of in vitro toxicity assays using various aquatic organisms (luminescent bacterium Vibrio fischeri, fish gill cell line RTgill-W1, and microalgae Scenedesmus obliquus) were developed to investigate the toxicological characterizations of PW from the Permian Basin. The exposure to PW, PW inorganic fraction (PW-IF), and PW salt control (PW-SC) at 30-50% dilutions caused significant toxicological effects in all model species, revealing the high salinity was the foremost toxicological driver in PW. In addition, the toxicity level of PW was usually higher than that of PW-IF, suggesting that organic contaminants might also play a critical role in PW toxicity. When comparing the observed toxicity with associated chemical characterizations in different PW samples, strong correlations were found between them since higher concentrations of contaminants could generally result in higher toxicity towards exposed organisms. Furthermore, the toxicity results from the pretreated PW indicated that those in vitro toxicity assays had different sensitives to the chemical components present in PW. As expected, the combination of multiple pretreatments could lead to a more significant decrease in toxicity compared to the single pretreatment since the mixture of contaminants in PW might exhibit synergistic toxicity. Overall, the current work is expected to enhance our understanding of the potential toxicological impacts of PW to aquatic ecosystems and the relationships between the chemical profiles and observed toxicity in PW, which might be conducive to the establishment of monitoring, remediation, treatment, and reuse protocols for PW.

Determination of heavy metal baseline levels and threshold values on marine sediments in the Bay of Biscay

Several international institutions have defined background or baseline levels to assess heavy metal concentrations on marine sediments in order to use these values as a reference for sediment quality indices. This criterion for marine sediment quality is applied to evaluate the potential risk of pollutants in aquatic ecosystems. However, those values were established using samples collected in large areas which present specific geochemical conditions. Then there may be a lack of accuracy in the results when using these parameters in other areas. In this context, 15 sediment cores (8 cm diameter; 2 m length) were recovered along the 400 km Asturian coastline, which is an area with representative lithological conditions for the Bay of Biscay, to determine more precise baseline levels for marine sediments from the Bay of Biscay. An evaluation of statistical and empirical methods was done to determine which method delivers the best results. Statistical methods such as mean±2SD and median±2* Median Absolut Deviation (MAD) are strongly influenced by outliers and data distributions which make these approaches less robust. Graphic techniques such as Cumulative Distribution Function (CDF) avoid the problems that asymmetrical data distributions may cause but introduce a certain level of subjectivity in the results due to the baseline values obtained depending on the researcher's experience. Finally, the Probability Curve (CP) method solves issues which may occur when using other techniques and allows one to establish baseline levels based on different percentiles. Regarding the features of the data analysed in this study, the baselines obtained via the CP method with the 95th percentile appear to be the most accurate for the Bay of Biscay. A wide variation has been found between the new baseline values and other international and national levels. Disparity between those levels and the baselines obtained in this study can be generated by granulometric and geological factors. The notable increase in Hg baseline values with respect to OSPAR Background Concentration values (BCs) (0.05 μg g^-1 and 0.6 μg g^-1 respectively) and the huge different with CEDEX levels and new threshold levels (0.35 μg g^-1 and 1.2 μg g^-1 respectively) emphasised the relevance of defining specific baselines and threshold levels, as the ones obtained in this study, not only to obtain more precise criteria for marine sediment quality to be used in environmental assessments, but also to propose new threshold levels for the evaluation of dredged material before dumping into ocean sites.

Study on simplified strategies for procedure of rapid detection of water toxicity

In this work, a simplified procedure of detection of water toxicity based on Pt ultramicroelectrode (UME) and mixed microorganism cultured without sterilization was the first proposed. A stable Pt UME was successfully prepared with a special glass tube as insulation and support material, which was used as working electrode in the biosensor. The Pt UME exhibits the typical cyclic voltammogram (CV) of Pt UME with sigmoid shape and possesses good stability, enlarged current response and tunable dimension. In addition, it was an effective and simple method for toxicity biosensor using mixed microorganisms cultured in unsterilized lysogeny broth (LB) as the bioreceptor. K₃[Fe(CN)₆] was used as an electron mediator. Under the optimal conditions of 30 mM K₃[Fe(CN)₆], OD₆₀₀ = 1 cell concentration, and 50 mM phosphate-buffered solution (PBS), the half-maximal inhibitory concentration (IC₅₀) values measured for Cd²⁺, Cu²⁺ and Ni²⁺ were 3.99 mg/L, 1.16 mg/L and 2.37 mg/L, respectively. The results indicated that the biosensor with large diameter Pt UME and mixed microorganisms cultured in unsterilized LB realized rapid and simple detection of water toxicity.

Ecological and probabilistic human health risk assessment of heavy metal(loid)s in river sediments affected by mining activities in Ecuador

Gold mining is a significant source of metal(loid)s released into the environment. It is an issue of concern due to the potential adverse health effects associated with exposure to toxic elements. This study aimed to assess the ecological and human health risk caused by heavy metal(loid)s exposure in river sediments in Ponce Enríquez, one of the most important mining sites in Ecuador. Concentrations of As, Cd, Cu, Pb, and Zn were evaluated in 172 sediment samples to determine the Potential ecological risk (R_I) and the carcinogenic (CR) and non-carcinogenic risk (HQ). The human exposure to polluted sediments during recreational activities was computed using Bayesian probabilistic models. Residents were randomly surveyed to adjust the risk models to the specific population data. More than 68% of the sampling stations pose a severe As and Cd ecological risk index ([Formula: see text] > 320). Likewise, residents exposed to river sediments showed a non-acceptable carcinogenic risk by incidental ingestion, being As the primary contributor to overall cancer in both children and adults receptors. Moreover, non-carcinogenic risk through the incidental ingestion of sediments was above the safe limit for children. This is the first study conducted in a mining region in Ecuador that reveals the severe levels of ecological and human health risk to which the population is exposed. These results can be applied as a baseline to develop public health strategies to monitor and reduce the health hazards of the residents of mining communities.

Microbial bioassays in environmental toxicity testing

Accidental spills and the misuse of chemicals may lead to current and legacy environmental contamination and pose concerns over possible (eco)toxicological secondary effects and risks toward non-target microbes and higher eukaryotes, including humans, in ecosystems. In the last decades, scientists and regulators have faced requests to thoroughly screen, prioritize and predict the possible deleterious effects of the huge numbers of existing and emerging xenobiotics, wastewaters and environmental samples on biological systems. In this context, it has become necessary to develop and validate (eco)toxicity bioassays based on microorganisms (e.g., bacteria, microalga, yeast, filamentous fungi, protozoa) as test-organisms whose data should be meaningful for environmental (micro)organisms that may be exposed to contaminated environments. These generally simple, fast and cost-effective bioassays may be preliminary and complementary to the more complex and long-term whole-organism animal-based traditional ecotoxicity tests. With the goal of highlighting the potential offered by microbial-based bioassays as non-animal alternatives in (eco)toxicity testing, the present chapter provides an overview of the current state-of-the art in the development and use of microbial toxicity bioassays through the examination of relatively recent examples with a diverse range of toxicity endpoints. It goes into the (eco)toxicological relevance of these bioassays, ranging from the more traditional microalga- and bacterial-based assays already accepted at regulatory level and commercially available to the more innovative microbial transcriptional profiling and gene expression bioassays, including some examples of biosensors.

Mercury and arsenic mobility in resuspended contaminated estuarine sediments (Asturias, Spain): A laboratory-based study

Estuarine sediments must be dredged to allow for navigation, and where these sediments are placed after dredging depends upon guidelines based only on the total concentration of contaminants. However, resuspension events could seriously affect the mobility and speciation of contaminants, including potentially toxic trace elements stored in sediments. The effects of resuspension on the cycling of mercury (Hg) and arsenic (As) between the sediment and water column was investigated in a mesocosm study. Four experiments were conducted in three estuaries in northern Spain based on samples collected from sites which have been impacted by decommissioned Hg and As mines and periodically subjected to dredging activities. Designed to mimic the resuspension of particles, each of the experiments revealed that the release of Hg and As species does not only depend on the total concentration in the sediments (16.3-50.9 mg kg^-1, for As and 0.52-5.01 mg kg^-1 for Hg). The contribution from porewaters and the subsequent reductive dissolution and/or desorption appear to be the main processes responsible for the abrupt increase in dissolved Hg and As species (maximum release of 427% and 125%, respectively). In some cases, As and Hg continued to remain at high concentrations in the water column even after the experiments were completed, thus testifying to their critical persistence in the dissolved form. Conversely, at the other sites, the restoration of pre-resuspension conditions was observed only a few hours after resuspension, mainly due to the role of Fe oxy-hydroxides which provides suitable surfaces for adsorption and/or co-precipitation involving dissolved Hg (maximum removal of -58%) and As (maximum removal of -25%) species. The results of this research could be helpful to take appropriate decisions regarding dredging especially at the Nalòn estuary, where the release of dissolved As(V) and MeHg appeared to be favoured by sediment resuspension.

Pollution and toxicity of sediment in potential dredging sites of the Marmara Sea, Turkey

This study aims to assess the impact of the sediment in the potential dredging areas of the Marmara Sea. To that aim, sediments were analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and heavy metals, sources were discussed, and toxicity tests were applied. For assessment, lower and upper limits of Turkish draft regulation (L_TR, U_TR) and UNEP-MAP's guidance document (LCT, UCT), and effects range low and median (ERL, ERM) were used. Total concentrations were found between 562 and 8643 µg kg^-1 for PAHs, 4-36 µg kg^-1 for PCBs, and 14-190 µg kg^-1 for OCPs. The highest ∑PAH concentrations were measured in Golden Horn, and none of the PAH compounds was above ERM. ERL and UCT were exceeded in İstinye and Golden Horn stations. The highest ∑PCBs and ∑OCPs levels were determined in İzmit Bay (IB). ΣPCBs in IB were higher than ERL and L_TR, while ΣDDT were found above ERM and UCT. High concentrations of chromium (∼190 mg kg^-1) and copper (∼180 mg kg^-1) in Golden Horn and mercury in IB (∼4 mg kg^-1) were detected. The highest toxicities were observed in İstinye and İzmit Bay. According to the regulations, none of the sediments can be dumped.