Zinc distribution in the organs of adult Fundulus heteroclitus after waterborne zinc exposure in freshwater and saltwater

The influence of salinity and water chemistry on acute toxicity of cadmium to two euryhaline fish species

The euryhaline killifishes, Fundulus heteroclitus and Kryptolebias marmoratus inhabit estuaries that rapidly change salinity. Although cadmium (Cd) toxicity has been well characterized in fish inhabiting freshwaters, fewer studies have examined the toxic effects of Cd in estuarine and saltwater environments. Additionally, current environmental regulations do not account for organism physiology in different salinity waters even though metal sensitivity is likely to change in these environments. In this study, we investigated effects of changing salinity on acute Cd toxicity to larval (7-9 d old) F. heteroclitus and K. marmoratus. Median 96-h lethal concentrations (LC50) for Cd were calculated for both fish species at six different salinities. As salinity increased, metal toxicity decreased in both fish species up to 18 ppt salinity; and F. heteroclitus were more sensitive than K. marmoratus at salinities above 12 ppt. To determine which components of saltwater were protective against Cd toxicity, we investigated the influence of CaSO₄ (100 and 200 mg/L), CaCl₂ (200 mg/L), and MgSO₄ (300 mg/L) on Cd toxicity to K. marmoratus. The results demonstrated that both competition with calcium and complexation with chloride reduced the toxic effects of Cd to K. marmoratus. These findings could be used to improve marine/estuarine biotic ligand models for the determination of site-specific water quality criteria for Cd.

Performance of biomarkers metallothionein and ethoxyresorufin O-deethylase in aquatic environments: A meta-analytic approach

The preservation of natural environments guarantees the conservation of biodiversity and ecosystem processes. Biomonitoring programs in preserved sites can be carried out using molecular biomarkers, which reflect possible stresses that exist in the monitored location. The metallothionein (MT) proteins and isoenzyme Cytochrome P4501A (CYP4501A) are among the most used biomarkers and reflect the detoxification of metal and organic xenobiotics, respectively. This study aimed to assess the performance of these biomarkers in natural aquatic environments using a meta-analytic approach. The data search was conducted in ISI Web of Science™, considering papers published until August 2016. Studies included in this research needed to compare reference or control sites and sites under stress and be conducted in situ. In general, both biomarkers were useful when comparing control sites with sites under stress. Moreover, when the data were categorized into groups of organisms, mainly bivalves and fishes, there were differences between the groups and between the monitored environments, marine or freshwater. The use of these biomarkers in fish is suitable for freshwater environments, and bivalves are suitable for marine environments. We concluded that the concomitant use of vertebrate and invertebrate bioindicators is useful to develop an effective biomonitoring program and to avoid biases due the physiology of the selected bioindicator.

Kinetics for Zinc Ion Induced Sepia Pharaonis Arginine Kinase Inactivation and Aggregation

Arginine kinase is an essential enzyme which is closely related to energy metabolism in marine invertebrates. Arginine kinase provides a significant role in quick response to environmental change and stress. In this study, we simulated a tertiary structure of Sepia pharaonis arginine kinase (SPAK) based on the gene sequence and conducted the molecular dynamics simulations between SPAK and Zn²⁺. Using these results, the Zn²⁺ binding sites were predicted and the initial effect of Zn²⁺ on the SPAK structure was elucidated. Subsequently, the experimental kinetic results were compared with the simulation results. Zn²⁺ markedly inhibited the activity of SPAK in a manner of non-competitive inhibitions for both arginine and ATP. We also found that Zn²⁺ binding to SPAK resulted in tertiary conformational change accompanying with the hydrophobic residues exposure. These changes caused SPAK aggregation directly. We screened two protectants, glycine and proline, which effectively prevented SPAK aggregation and recovered the structure and activity. Overall, our study suggested the inhibitory effect of Zn²⁺ on SPAK and Zn²⁺ can trigger SPAK aggregation after exposing large extent of hydrophobic surface. The protective effects of glycine and proline against Zn²⁺ on SPAK folding were also demonstrated.

Assessment of metal contamination in the biota of four rivers experiencing varying degrees of human impact

Urbanization, agriculture, and other land transformations can affect water quality, decrease species biodiversity, and increase metal and nutrient concentrations in aquatic systems. Metal pollution, in particular, is a reported consequence of elevated anthropogenic inputs, especially from urbanized areas. The objectives of this study were to quantify metal (Cu, Al, Cd, Ni, and Pb) concentrations in the waters and biota of four streams in South Georgia, USA, and relate metal concentrations to land use and abiotic and biotic stream processes. Additionally, macrophytes, invertebrates, and fish were identified to assess biodiversity at each site. Metal concentrations in the three trophic levels differed among sites and species, correlating to differences in land use surrounding the rivers. The highest metal concentrations (except Al) were found in the streams most impacted by urbanization and development. Al concentrations were highest in streams surrounded by land dominated by forested areas. Metal content in macrophytes reflected metal concentrations in the water and was at least three orders of magnitude higher than any other trophic level. Despite metal concentration differences, all four streams contained similar water quality and were healthy based on macroinvertebrate community structure. This study provides insight into the impact of urbanization and the fate and effects of metals in river ecosystems with varying degrees of anthropogenic impact.

Zinc bioaccumulation and ionoregulatory impacts in Fundulus heteroclitus exposed to sublethal waterborne zinc at different salinities

Exposure of Fundulus heteroclitus to an environmentally relevant Zn concentration (500 μg L⁻¹) at different salinities (0, 3.5, 10.5, and 35 ppt) revealed the following effects: (i) plasma [Zn] doubled after exposure at 0 ppt, a response which was eliminated at 35 ppt. Tissue [Zn] also increased in gill, liver, intestine, and carcass at 0 ppt. (ii) Both branchial and intestinal Ca2⁺ ATPase activities decreased in response to Zn at 0 ppt and were elevated at 35 ppt. Plasma [Ca] decreased by 50% at 0 ppt and by 30% at 3.5 ppt and increased by 20% at 35 ppt. Gill [Ca] decreased by 35% at 0 ppt and increased by about 30% at all higher salinities. (iii) Branchial Na⁺,K⁺ ATPase activity decreased by 50% at 0 ppt, increased by 30% and 90% at 10.5 and 35 ppt respectively. Intestinal Na⁺,K⁺ ATPase activity was reduced by 30% at 0 ppt. (iv) Plasma [Na] decreased by 30% at 0 ppt in Zn-exposed. Zn exposure also disturbed the homeostasis of tissue cations (Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺) in a tissue-specific and salinity-dependent manner. (v) Drinking rate was not altered by Zn exposure. In toxicity tests, acute Zn lethality (96-h LC50) increased in a close to linear fashion from 9.8 mg L⁻¹ at 0 ppt to 75.0 mg L⁻¹ at 35 ppt. We conclude that sublethal Zn exposure causes pathological changes in both Ca⁺⁺ and Na⁺ homeostases, and that increasing salinity exerts protective effects against both sublethal and lethal Zn toxicities.

Metal accumulation in wild nine-banded armadillos

Nine-banded armadillos (Dasypus novemcinctus) are widespread and abundant New World mammals with a lifestyle that entails prolonged, intimate contact with soils. Thus, armadillos would seem a promising candidate as a sentinel species to monitor chemical contamination in terrestrial ecosystems. Surprisingly, there have been virtually no toxicology studies on armadillos. Here, we provide the first analysis of metal contaminants for wild armadillos. Liver tissues were obtained from 302 armadillos collected at 6 sites in Georgia and Florida, USA that varied in their extent of human disturbance, from rural pine plantations to highly modified military/space installations. Data were stratified by age (juvenile and adult), sex, and site. Temporal (yearly) variation was examined at two of the sites that were sampled over three consecutive years. Concentrations of aluminum, cadmium, copper, nickel, lead, and zinc were measured in liver samples from each site. Although reference levels are not available for armadillos, accumulated metal concentrations were comparable to those reported for other mammals. We found no evidence of sex or age differences in the concentrations of any metal, except for Cd (age) and Pb (sex and age). However, concentrations of most metals varied substantially across sites and over time. Finally, concentrations of many metals were positively correlated with one another, suggesting that they likely co-occurred in some areas. Collectively, this study indicates the utility of armadillos as a sentinel species for studies of metal contamination in terrestrial systems, and highlights the need for further studies of other toxicants in these animals.

The influence of salinity on acute nickel toxicity to the two euryhaline fish species, Fundulus heteroclitus and Kryptolebias marmoratus

Nickel (Ni) is a common pollutant found in aquatic environments and may be harmful at elevated concentrations. Increasing salinity has been shown to decrease the bioavailability and toxicity of other metals to aquatic organisms. In the present study, acute Ni toxicity experiments (96-h) were conducted at various salinities (0-36 ppt) to determine the effects of salinity on Ni toxicity to 2 euryhaline fish species, Kryptolebias marmoratus and Fundulus heteroclitus. Nickel concentrations causing lethality to 50% of the fish ranged from 2 mg/L in moderately hard freshwater to 66.6 mg/L in 36 ppt saltwater. Nickel toxicity to F. heteroclitus decreased linearly with increasing salinity; however, Ni toxicity to K. marmoratus was only lowered by salinities above 6 ppt, demonstrating potential physiological differences between the 2 species when they are functioning as freshwater fish. Furthermore, the authors investigated the influence of Mg(2+) , Ca(2+) , Na(+) , and Cl(-) on Ni toxicity to F. heteroclitus. Freshwater with up to 120 mg/L Ca(2+) as CaSO4 , 250 mg/L Mg(2+) as MgSO4 , or 250 mg/L Na(+) as NaHCO3 did not provide protection against Ni toxicity. Alternatively, 250 mg/L Na(+) , as NaCl, was protective against Ni toxicity; and the extent of protection was similar to that demonstrated from salt water with the same Cl(-) concentration. These results suggest that Cl(-) is the predominant ion responsible for reducing Ni toxicity to K. marmoratus and F. heteroclitus in higher salinity waters.