Resolving mechanisms of toxicity while pursuing ecotoxicological relevance?

In this age of modern biology, aquatic toxicological research has pursued mechanisms of action of toxicants. This has provided potential tools for ecotoxicologic investigations. However, problems of biocomplexity and issues at higher levels of biological organization remain a challenge. In the 1980s and 1990s and continuing to a lesser extent today, organisms residing in highly contaminated field sites or exposed in the laboratory to calibrated concentrations of individual compounds were carefully analyzed for their responses to priority pollutants. Correlation of biochemical and structural analyses in cultured cells and tissues, as well as the in vivo exposures led to the production and application of biomarkers of exposure and effect and to our awareness of genotoxicity and its chronic manifestations, such as neoplasms, in wild fishes. To gain acceptance of these findings in the greater environmental toxicology community, “validation of the model” versus other, better-established often rodent models, was necessary and became a major focus. Resultant biomarkers were applied to heavily contaminated and reference field sites as part of effects assessment and with investigations following large-scale disasters such as oil spills or industrial accidents.

Over the past 15 years, in the laboratory, small aquarium fish models such as medaka (Oryzias latipes), zebrafish (Danio rerio), platyfish (Xiphophorus species), fathead minnow (Pimephales promelas), and sheepshead minnow (Cyprinodon variegatus) were increasingly used establishing mechanisms of toxicants. Today, the same organisms provide reliable information at higher levels of biological organization relevant to ecotoxicology. We review studies resolving mechanisms of toxicity and discuss ways to address biocomplexity, mixtures of contaminants, and the need to relate individual level responses to populations and communities.     

Differential developmental toxicity of naphthoic acid isomers in medaka (Oryzias latipes) embryos

Polycyclic aromatic hydrocarbons (PAHs) are widespread persistent pollutants that readily undergo biotic and abiotic conversion to numerous transformation products in rivers, lakes and estuarine sediments. Here we characterize the developmental toxicity of four PAH transformation products each structural isomers of hydroxynaphthoic acid: 1H2NA, 2H1NA, 2H3NA, and 6H2NA. Medaka fish (Oryzias latipes) embryos and eleutheroembryos were used to determine toxicity. A 96-well micro-plate format was used to establish a robust, statistically significant platform for assessment of early life stages. Individual naphthoic acid isomers demonstrated a rank order of toxicity with 1H2NA > 2H1NA > 2H3NA > 6H2NA being more toxic. Abnormalities of circulatory system were most pronounced including pericardial edema and tube heart. To determine if HNA isomers were AhR ligands, spatial-temporal expression and activity of CYP1A was measured via in vivo EROD assessments. qPCR measurement of CYP1A induction proved different between isomers dosed at respective concentrations affecting 50% of exposed individuals (EC50s). In vitro, all ANH isomers transactivated mouse AhR using a medaka CYP1A promoter specific reporter assay. Circulatory abnormalities followed P450 induction and response was consistent with PAH toxicity. A 96-well micro-plates proved suitable as exposure chambers and provided statistically sound evaluations as well as efficient toxicity screens. Our results demonstrate the use of medaka embryos for toxicity analysis thereby achieving REACH objectives for the reduction of adult animal testing in toxicity evaluations.     

Evidence for a 200 km thick diamond-bearing root beneath the Central Mackenzie Valley,Northwest Territories,Canada? Diamond indicator mineral geochemistry from the Horn Plateau and Trout Lake regions

The Central Mackenzie Valley (CMV) area of Northwest Territories is underlain by Precambrian basement belonging to the North American Craton. The potential of this area to host kimberlitic diamond deposits is relatively high judging from the seismologically-defined lithospheric thickness, age of basement rocks (2.2–1.7 Ga) and presence of kimberlite indicator minerals (KIMs) in Quaternary sediments. This study presents data for a large collection of KIMs recovered from stream sediments and till samples from two study areas in the CMV, the Horn Plateau and Trout Lake. In the processed samples, peridotitic garnets dominate the KIM grain count for both regions (> 25% each) while eclogitic garnet is almost absent in both regions (< 1% each). KIM chemistry for the Horn Plateau indicates significant diamond potential, with a strong similarity to KIM systematics from the Central and Western Slave Craton. The most significant issue to resolve in assessing the local diamond potential is the degree to which KIM chemistry reflects local and/or distal kimberlite bodies. Radiogenic isotope analysis of detrital kimberlite-related CMV ilmenite and rutile grains requires at least two broad age groups for eroded source kimberlites. Statistical analysis of the data suggests that it is probable that some of these KIMs were derived from primary and/or secondary sources within the CMV area, while others may have been transported to the area from the east-northeast by Pleistocene glacial and/or glaciofluvial systems. At this stage, KIM chemistry does not allow the exact location of the kimberlitic source(s) to be constrained.

     

New constraints on the Messinian sealevel drawdown from 3D seismic data of the Ebro Margin,western Mediterranean

We present new 3D seismic and well data from the Ebro Margin, NW Mediterranean Sea, to shed new light on the processes that formed the Messinian Erosion Surfaces (MES) of the Valencia Trough (Mediterranean Sea). We combine these data with backstripping techniques to provide a minimum estimate of the Messinian sea level fall in the EBRO Margin, as well as coupled isostasy and river incision and transport modeling to offer new constraints on the evolution of the adjacent subaerial Ebro Basin. Four major seismic units are identified on the Cenozoic Ebro Margin, based on the seismic data, including two major prograding megasequences that are separated by a major unconfirmity: the MES. The 3D seismic data provide an unprecedented view of the MES and display characteristic features of subaerial incision, including a drainage network with tributaries of at least five different orders, terraces and meandering rivers. The Messinian landscape presents a characteristic stepped‐like profile that allows the margin to be subdivided in three different regions roughly parallel to the coastline. No major tectonic control exists on the boundaries between these regions. The boundary between the two most distal regions marks the location of a relatively stable base level, and this is used in backstripping analysis to estimate the magnitude of sea level drop associated with the Messinian Salinity Crisis on the Ebro Margin. The MES on the Ebro Margin is dominated by a major fluvial system, that we identify here as the Messinian Ebro River. The 3D seismic data, onshore geology and modeling results indicate that the Ebro River drained the Ebro Basin well in advance of the Messinian.     

Differential developmental toxicity of naphthoic acid isomers in medaka (Oryzias latipes) embryos

Polycyclic aromatic hydrocarbons (PAHs) are widespread persistent pollutants that readily undergo biotic and abiotic conversion to numerous transformation products in rivers, lakes and estuarine sediments. Here we characterize the developmental toxicity of four PAH transformation products each structural isomers of hydroxynaphthoic acid: 1H2NA, 2H1NA, 2H3NA, and 6H2NA. Medaka fish (Oryzias latipes) embryos and eleutheroembryos were used to determine toxicity. A 96-well micro-plate format was used to establish a robust, statistically significant platform for assessment of early life stages. Individual naphthoic acid isomers demonstrated a rank order of toxicity with 1H2NA>2H1NA>2H3NA>6H2NA being more toxic. Abnormalities of circulatory system were most pronounced including pericardial edema and tube heart. To determine if HNA isomers were AhR ligands, spatial-temporal expression and activity of CYP1A was measured via in vivo EROD assessments. qPCR measurement of CYP1A induction proved different between isomers dosed at respective concentrations affecting 50% of exposed individuals (EC50s). In vitro, all ANH isomers transactivated mouse AhR using a medaka CYP1A promoter specific reporter assay. Circulatory abnormalities followed P450 induction and response was consistent with PAH toxicity. A 96-well micro-plates proved suitable as exposure chambers and provided statistically sound evaluations as well as efficient toxicity screens. Our results demonstrate the use of medaka embryos for toxicity analysis thereby achieving REACH objectives for the reduction of adult animal testing in toxicity evaluations.     

Statistical approaches to the discrimination of mantle- and crust-derived low-Cr garnets using major and trace element data

Diamond exploration focuses on geochemical analysis of indicator minerals that are more abundant than diamond itself. Among such indicators, low-Cr (Cr₂O₃ < 1 wt%) garnets from mantle eclogites are problematic since they overlap compositionally with many lower-crust-derived garnets also transported by kimberlite. Misclassification of these garnets may create “false positive” mantle signatures and possible misdirection of exploration efforts. Statistical solutions using major elements in low-Cr garnet (Hardman et al. in J Geochem Explor 186:24–35, 2018) provide improved error rates for the discrimination of low-Cr crustal and mantle garnets recovered from kimberlite. In this study we analysed a large suite of garnets (n = 571) from both crustal and mantle settings, already characterised for major elements, for a wide range of trace elements by laser ablation inductively-coupled plasma mass spectrometry and use these new data along with literature data (n = 169) to evaluate the effectiveness of adding trace elements to garnet-based diamond exploration programs. A new garnet classification scheme, initially using a major-element based filter, uses garnet Sr contents and Eu anomalies to help identify low-Cr garnets that are misclassified using major element methods. Combined with existing methods, our new trace element classifiers offer improvement in classification error rates for low-Cr, crustal and mantle garnets to as low as 4.7% for calibration data.