In April 1997 and 1998 investigations of algae, Rotatoria, Cladocera, Copepoda and Hydracarina were conducted. The investigated localities were 8 small water bodies at around 800 m a.s.l., at Mali Krs, in the surrounding of Bor, Serbia (Yugoslavia). The aim was to examine composition of these groups and to give the evaluation of the quality of water. Among algae, according to the number of taxons, the dominant group was Bacillariophyta (45), then Chlorophyta (17), Cyanophyta (3), Euglenophyta (4), Xanthophyta (1) and Pyrrophyta (1). Rotatoria were present with the highest number of taxons among microfauna. In these investigations 48 taxons were present. The highest number of taxons was among Cephalodella, Corurella, and Trichocerca. Among Cladocera 4 taxons were present, and among Copepoda 9 taxons, and all the present species were found in our previous investigations. Hydracarina were present with 3 species, also with high diversity. Around two thirds of all taxons are oligosaprobionts, which indicates to the good quality of the water.

Diazinon is a common organophosphate pesticide widely used to control parasitic infections in agriculture. Excessive use of diazinon can have adverse effects on the environment and aquatic animal health. In the present study, the toxic effects of diazinon on the histology, antioxidant, innate immune and intestinal microbiota community composition of crucian carp (Carassius auratus gibelio) were investigated. The results showed that diazinon at the tested concentration (300 μg/L) induced gill and liver histopathological damages. Hepatic total superoxide dismutase (T-SOD), catalase (CAT), and glutathione S-transferase (GST) activities significantly decreased (P < 0.05) by 32.47%, 65.33% and 37.34%, respectively. However, the liver tissue malondialdehyde (MDA) content significantly (P < 0.05) increased by 138.83%. The 300 μg/L diazinon significantly (P < 0.05) downregulated the gene expression of TLR4, MyD88, NF-kB p100 and IL-8 but had no significant effect TNF-α (P = 0.8239). In addition, the results demonstrated that diazinon exposure could affect the intestinal microbiota composition and diversity. Taken together, the results of this study indicated that diazinon exposure can cause damage to crucian carp, induce histopathological damage in gill and liver tissues, oxidative stress in the liver, and innate immune disorders and alter intestinal microbiota composition and diversity.

Microcystin-LR (MC-LR) is the most abundant toxicant among microcystin variants produced by cyanobacteria. MC-induced toxicity is broadly reported to pose a threat to aquatic animals and humans and has been associated with the dysfunction of some organs such as liver and kidney. However, MC-induced neurotoxicity has not been well characterized after long-term exposure. This study was designed to investigate the neurotoxic effects after chronic oral administration of MC-LR. In our trial, C57/BL6 mice received MC-LR at 0, 1, 5, 10, 20 and 40 μg/L in drinking water for twelve months. Our data demonstrated that mitochondrial DNA (mtDNA) damage was evident in the damaged neurons as a result of chronic exposure. Histopathological abnormalities and mtDNA damage were observed in the hippocampus and cerebral cortex. Furthermore, MC-LR exerted distinct effects on these two brain regions. The hippocampus was more susceptible to the treatment of MC-LR compared with the cerebral cortex. However, no strong relationships were observed between the genotoxic effects and exposure doses. In conclusion, this study has provided a mtDNA-related mechanism for underlying chronic neurotoxicity of MC-LR and suggested the presence of differential toxicant effects on the hippocampus and cerebral cortex.

2,6-Dimethylphenol (2,6-DMP), an important chemical intermediate and the monomer of plastic polyphenylene oxide, is widely used in chemical and plastics industry. However, the pollution problem of 2,6-DMP residues is becoming increasingly serious, which is harmful to some aquatic animals. Microbial degradation provided an effective approach to eliminate DMPs in nature, which is considered as a prospective way to remediate DMPs-contaminated environments. But the 2,6-DMP-degrading bacteria is not available and the molecular mechanism of 2,6-DMP degradation is unclear as well. Here, a 2,6-DMP-degrading bacterium named B5-4 was isolated and identified as Mycobacterium neoaurum. M. neoaurum B5-4 could utilize 2,6-DMP as the sole carbon source for growth. Furthermore, M. neoaurum B5-4 could degrade 2,6-DMP with concentrations ranging from 1 to 500 mg L⁻¹. Six intermediate metabolites of 2,6-DMP were identified and a metabolic pathway of 2,6-DMP in M. neoaurum B5-4 was proposed, in which 2,6-DMP was initially converted to 2,6-dimethyl-hydroquinone and 2,6-dimethyl-3-hydroxy-hydroquinone by two consecutive hydroxylations at C-4 and γ position; 2,6-dimethyl-3-hydroxy-hydroquinone was then subjected to aromatic ring ortho-cleavage to produce 2,4-dimethyl-3-hydroxymuconic acid, which was further transformed to citraconate, and subsequently into TCA cycle. In addition, toxicity bioassay of 2,6-DMP in water using zebrafish indicates that 2,6-DMP is toxic to zebrafish and M. neoaurum B5-4 could effectively eliminate 2,6-DMP in water to protect zebrafish from 2,6-DMP-induced death. This work provides a potential strain for bioremediation of 2,6-DMP-contaminated environments and lays a foundation for elucidating the molecular mechanism and genetic determinants of 2,6-DMP degradation.

Mercury is a globally distributed toxicant to aquatic animals and mammals. However, the potential risks of environmental relevant mercury in terrestrial systems remain largely unclear. The metabolic profiles of the earthworm Eisenia fetida after exposure to soil contaminated with mercury at 0.77 ± 0.09 mg/kg for 2 weeks were investigated using a two-dimensional nuclear magnetic resonance-based (¹H-¹³C NMR) metabolomics approach. The results revealed that traditional endpoints (e.g., mortality and weight loss) did not differ significantly after exposure. Although histological examination showed sub-lethal toxicity in the intestine as a result of soil ingestion, the underlying mechanisms were unclear. Metabolite profiles revealed significant decreases in glutamine and 2-hexyl-5-ethyl-3-furansulfonate in the exposed group and remarkable increases in glycine, alanine, glutamate, scyllo-inositol, t-methylhistidine and myo-inositol. More importantly, metabolic network analysis revealed that low mercury in the soil disrupted osmoregulation, amino acid and energy metabolisms in earthworms. A metabolic net link and schematic diagram of mercury-induced responses were proposed to predict earthworm responses after exposure to mercury at environmental relevant concentrations. These results improved the current understanding of the potential toxicity of low mercury in terrestrial systems.

Due to their longevity and extensive migration areas, marine turtles are able to accumulate diverse contaminants over many years and as a consequence they represent an interesting bioindicator species for marine ecosystem pollution. Metals provoke toxicological effects in many aquatic animal species, but marine turtles have been under-investigated in this area. Thus, we have determined the presence of certain inorganic elements (As, Cd, Cu, Ni, Pb, Se and Zn) in olive ridley turtles (Lepidochelys olivacea) and related them to metallothionein (MT), superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) transcription and/or enzymatic activities. Gene expression of sod, cat and gr was found to be higher in blood than liver or kidney but most of the significant relationships were found in liver, not only for gene expression but also for enzyme activities. This must be related to the role the liver has as the first filter organ. Several positive relationships of sod, cat and gr gene expression in the different tissues were found in this population, as well as very high Cd concentrations. This could mean that these turtles are adapting to the metals-production of ROS and damage through a high transcription of these antioxidants. Multiple positive relationships with GR seem to be part of its compensatory effect due to the decrease of SOD production against the high and chronic exposure to certain xenobiotics. CAT, on the other hand, seems not to be used much, and glutathione detoxification of H₂O₂ may be more important in this species. Finally, despite the very high Cd concentrations found in this population, no significant relationship was found in any tissue with metallothionein gene expression. These results, along with very high Cd concentrations and a negative relationship with Cu, lead us to consider some kind of disruption in mt gene expression in these turtles.

Understanding the processes that regulate contaminant impacts in nature is an increasingly important challenge. For insecticides in surface waters, the ability of aquatic plants to sorb, or bind, hydrophobic compounds has been identified as a primary mechanism by which toxicity can be mitigated (i.e. the sorption-based model). However, recent research shows that submerged plants can also rapidly mitigate the toxicity of the less hydrophobic insecticide malathion via alkaline hydrolysis (i.e. the hydrolysis-based model) driven by increased water pH resulting from photosynthesis. However, it is still unknown how generalizable these mitigation mechanisms are across the wide variety of insecticides applied today, and whether any general rules can be ascertained about which types of chemicals may be mitigated by each mechanism. We quantified the degree to which the submerged plant Elodea canadensis mitigated acute (48-h) toxicity to Daphnia magna using nine commonly applied insecticides spanning three chemical classes (carbamates: aldicarb, carbaryl, carbofuran; organophosphates: malathion, diazinon, chlorpyrifos; pyrethroids: permethrin, bifenthrin, lambda-cyhalothrin). We found that insecticides possessing either high octanol-water partition coefficients (log Kow) values (i.e. pyrethroids) or high susceptibility to alkaline hydrolysis (i.e. carbamates and malathion) were all mitigated to some degree by E. canadensis, while the plant had no effect on insecticides possessing intermediate log Kow values and low susceptibility to hydrolysis (i.e. chlorpyrifos and diazinon). Our results provide the first general insights into which types of insecticides are likely to be mitigated by different mechanisms based on known chemical properties. We suggest that current models and mitigation strategies would be improved by the consideration of both mitigation models.