An integrative data-centric approach to derivation and characterization of an adverse outcome pathway network for cadmium-induced toxicity.

Cadmium is a prominent toxic heavy metal that contaminates both terrestrial and aquatic environments. Owing to its high biological half-life and low excretion rates, cadmium causes a variety of adverse biological outcomes. Adverse outcome pathway (AOP) networks were envisioned to systematically capture toxicological information to enable risk assessment and chemical regulation. Here, we leveraged AOP-Wiki and integrated heterogeneous data from four other exposome-relevant resources to build the first AOP network relevant for inorganic cadmium-induced toxicity. From AOP-Wiki, we filtered 309 high confidence AOPs, identified 312 key events (KEs) associated with inorganic cadmium from five exposome-relevant databases using a data-centric approach, and thereafter, curated 30 cadmium relevant AOPs (cadmium-AOPs). By constructing the undirected AOP network, we identified a large connected component of 18 cadmium-AOPs. Further, we analyzed the directed network of 59 KEs and 82 key event relationships (KERs) in the largest component using graph-theoretic approaches. Subsequently, we mined published literature using artificial intelligence-based tools to provide auxiliary evidence of cadmium association for all KEs in the largest component. Finally, we performed case studies to verify the rationality of cadmium-induced toxicity in humans and aquatic species. Overall, cadmium-AOP network constructed in this study will aid ongoing research in systems toxicology and chemical exposome.

A review of mesocosm experiments on heavy metals in marine environment and related issues of emerging concerns.

Mesocosms are real-world environmental science tools for bridging the gap between laboratory-scale experiments and actual habitat studies on ecosystem complexities. These experiments are increasingly being applied in understanding the complex impacts of heavy metals, ocean acidification, global warming, and oil spills. The insights of the present review indicate how metals and metal-bound activities impact on various aspects of ecological complexities like prey predator cues, growth, embryonic development, and reproduction. Plankton and benthos are used more often over fish and microbes owing to their smaller size, faster reproduction, amenability, and repeatability during mesocosm experiments. The results of ocean acidification reveal calcification of plankton, corals, alteration of pelagic structures, and plankton blooms. The subtle effect of oil spills is amplified on sediment microorganisms, primary producers, and crustaceans. An overview of the mesocosm designs over the years indicates that gradual changes have evolved in the type, size, design, composition, parameters, methodology employed, and the outputs obtained. Most of the pelagic and benthic mesocosm designs involve consideration of interactions within the water columns, between water and sediments, trophic levels, and nutrient rivalry. Mesocosm structures are built considering physical processes (tidal currents, turbulence, inner cycling of nutrients, thermal stratification, and mixing), biological complexities (population, community, and ecosystem) using appropriate filling containers, and sampling facilities that employ inert materials. The principle of design is easy transportation, mooring, deployment, and free floating structures besides addressing the unique ecosystem-based science problems. The evolution of the mesocosm tools helps in understanding further advancement of techniques and their applications in marine ecosystems.

Effect of sublethal gradient concentrations of nickel on postlarvae of Penaeus monodon, Perna viridis and Terapon jarbua: Enzyme activities and histopathological changes.

The present study evaluates the enzyme activities and histopathological changes in the post larvae (PL) of shrimp (Penaeus monodon), green mussel (Perna viridis) and fingerlings of crescent perch (Terapon jarbua) exposed to sublethal gradient concentrations of Nickel (Ni). The median lethal concentration (LC50) values were 2.49, 66.03 and 43.92 mg Ni L-1 derived for the PL of shrimp, green mussel and fish fingerlings respectively. No Observed Effect Concentration (NOEC), Lowest Observed Effect Concentration (LOEC) and chronic values of the PL of shrimp were 46.5, 73.0 and 58.3 µg Ni L-1 derived for the 21-d survival endpoint. The NOEC, LOEC and chronic values for the 30-d survival endpoint of the green mussels and fish fingerlings were 4.6, 6.32, 5.4 and 1.95, 2.6, 2.25 mg Ni L-1 respectively. The isoforms of esterase, superoxide dismutase and malate dehydrogenase activities in the whole body tissues of test organisms were studied by native polyacrylamide gel electrophoresis after exposure to Ni. Histological examination of compound eye sections of shrimp revealed deformation, compression, fusion and detachement in the corneal cells from the corneal facet of the ommatidia indicating cellular anomalies due to Ni toxicity. Gill sections of the green mussel witnessed reduced haemolymph in sinuses of gill filaments, degenerative changes in interfilamentous junction and necrosis of frontal ciliated epithelial cells with vacuoles after exposure to Ni. Nickel affects the vision of shrimp and fish fingerlings, gills and byssus of green mussels.

Toxicity of Nickel on the Selected Species of Marine Diatoms and Copepods.

Toxicity values for nickel on marine diatoms and copepods were derived based on bioassay tests. The 96 h IC50 of nickel on diatoms, Odontella mobiliensis and Coscinodiscus centralis were 0.31 ± 0.01 and 0.62 ± 0.02 mg/L and LC50 values on copepods, Oithona similis and Acartia danae were 2.78 ± 0.14 and 2.34 ± 0.32 mg/L, respectively. The species mean chronic values of nickel were 0.016, 0.17, 0.57 and 0.42 mg/L for O. mobiliensis, C. centralis, O. similis and A. danae, respectively. A hazardous concentration was derived and evaluated using the species sensitivity distribution (SSD) method. SSD indicated that 13 µg Ni/L is the maximum allowable concentration for protection of 95% plankton species in coastal and marine ecosystem of India. Diatoms are more sensitive to nickel than copepods by almost an order of magnitude. The toxicity values derived in the present study may be useful to calculate ambient water quality criteria/standard for nickel.