Long-term effects of chromium on morphological and immunological parameters of Wistar rats

Hexavalent chromium raises high concern because of its wide industrial applications and reported toxicity. Long-term (135 days) oral exposure of Wistar rats to chromium in the form of K₂Cr₂O₇ (exposed group~20 mg/kg/day) led to a decrease in thymus mass and thymocytes' number and caused structural and functional changes in the lymph nodes and spleen, namely lymphoreticular hyperplasia and plasmocytic macrophage transformation. Programmed cell death was increased in both thymocytes and splenocytes and decreased in lymphocytes in the T-zones of spleen and lymph nodes. Moreover, Cr (VI) administration decreased myeloid cells' and neutrophils' number, while it increased lymphoid and erythroid cells' number in bone marrow. Cr (VI) immune system effects seem to be related to oxidative stress induction, as depicted by the increased levels of diene conjugates and malondialdehyde in the spleen and liver and by the decreased activity of catalase and superoxide dismutase in rats' erythrocytes. In addition, exposure to Cr (VI) decreased copper, nickel and iron concentrations in blood and liver, while Cr levels in blood, spleen and liver were increased, as expected. The observed changes in the series of immunological parameters studied contribute to the development of new approaches for the prevention of low level Cr exposure toxicity.

Overview of the effects of chemical mixtures with endocrine disrupting activity in the context of real-life risk simulation: An integrative approach (Review)

Research over the past years has indicated that chronic human exposure to very low doses of various chemical species in mixtures and administered via different routes (percutaneous, orally, etc.) should be the main focus of new biochemical and toxicological studies. Humans have daily contact with various chemicals, such as food additives, pesticides from fruits/vegetables, antibiotics (and other veterinary drugs) from meat, different types of preservatives from cosmetics, to name a few. Simultaneous exposure to this wide array of chemicals does not produce immediate effects, but summative effect/s over time that may be clinically manifested several years thereafter. Classical animal studies designed to test the toxic outcome of a single chemical are not suitable to assess, and then extrapolate to humans, the effects of a whole mixture of chemicals. Testing the aftermath of a combination of chemicals, at low doses, around or below the no observed adverse effect is stressed by many toxicologists. Thus, there is a need to reformulate the design of biochemical and toxicological studies in order to perform real-life risk simulation. This review discuss the potential use of computational methods as a complementary tool for in vitro and in vivo toxicity tests with a high predictive potential that could contribute to reduce animal testing, cost and time, when assessing the effects of chemical combinations. This review focused on the use of these methods to predict the potential endocrine disrupting activity of a mixture of chemicals.

Indicator PCBs in farmed and wild fish in Greece - Risk assessment for the Greek population

Health benefits of fish consumption could be counterbalanced by the intake of contaminants after long term fish consumption, burdened even in trace levels. The presence of the indicator PCBs (NDL-PCBs and PCB 118) in farmed and wild seabream and seabass was evaluated. For the determination of PCB, a GC-MS method was developed and evaluated. The association of PCB accumulation in fish with seasonality, locality, production mode and species was also investigated. A new approach for the risk characterisation after exposure to NDL-PCB through fish consumption in Greece was developed, based on the real exposure and the permitted maximum levels of both aggregated dietary exposure and exposure through fish consumption. PCB levels determined in fish were below established permitted limits (6.24 ng/g 95th percentile), while PCB levels and congener distribution varied significantly between farmed and wild fish (p = 0.001). Seasonality was highlighted as an important factor affecting NDL-PCBs accumulation, with high levels coinciding with the reproduction period of each species. Differences were also depicted for sampling sites, with PCB 118 presenting significantly higher values in open seas while NDL-PCB congeners in closed seas. Risk assessment of NDL-PCB intake through fish consumption corrected for the aggregated exposure revealed no risk for the consumers.

Cadmium, lead and mercury in muscle tissue of gilthead seabream and seabass: Risk evaluation for consumers

Cadmium (Cd), lead (Pb) and mercury (Hg) presence was investigated in the muscle tissue of gilthead seabream and seabass, collected from various aquaculture sites of the Aegean and Cretan Sea as well as from the fish market (fisheries). Risk for the Greek population through consumption of these species was estimated using two approaches: Target Hazard Quotient (THQ) and Hazard Index (HI). All heavy metal levels in the fish tissue were below the established safe limits for consumption. Metal accumulation was found to differ amongst mode of production, species, location and seasonality. Seabass demonstrated higher Hg and lower Cd concentrations than seabream, Hg and Pb seem to be more accumulated in closed seas and Pb values displayed a linear increasing trend from warmer to colder periods. Regression analysis revealed that the main contributing factor to Cd accumulation is species (beta: -0.28, 95%CI: -0.48 to -0.09); lead is predominately affected by seasonality (beta: 0.44, 95%CI: 0.29 to 0.59), Hg accumulation is mainly affected by location (beta: -0.32, 95%CI: -0.61 to -0.03) while wild seabream accumulates greater levels for Hg and Pb than farmed. Risk analysis demonstrated that consumption of the studied species, is safe for all metals (HI < 0.460 and TTHQ < 0.299).

Effects of carbon and silicon nanotubes and carbon nanofibers on marine microalgae Heterosigma akashiwo

The effect of carbon and silicon nanotubes (CNTs and SiNTs) and carbon nanofibers (CNFs) to microscopic marine algae Heterosigma akashiwo was studied, using algal growth inhibition for 3 days (acute effect) and 7 days (chronic effect) as toxicity endpoints. The criterion of the toxic effect was the statistically significant reduction of the number of algal cells in the exposed samples compared to the control. Samples did not demonstrate toxic effects at doses 1 mg/l and 10 mg/l. CNTs and SiNTs samples at 100 mg/l exhibited both acute and chronic toxic effects. We assume that the main cause of cell death in these samples was related to the mechanical damage of cell integrity. CNFs at concentrations of 100 mg/l did not inhibit algal growth, but cells with irregular shapes were observed, which were not observed after exposure to CNTs and SiNTs. Nickel impurities present in CNFs samples are presumably the main cause of observed cell deformations.

Oxidative Stress in Methylmercury-Induced Cell Toxicity

Methylmercury (MeHg) is a hazardous environmental pollutant, which elicits significant toxicity in humans. The accumulation of MeHg through the daily consumption of large predatory fish poses potential health risks, and the central nervous system (CNS) is the primary target of toxicity. Despite well-described neurobehavioral effects (i.e., motor impairment), the mechanisms of MeHg-induced toxicity are not completely understood. However, several lines of evidence point out the oxidative stress as an important molecular mechanism in MeHg-induced intoxication. Indeed, MeHg is a soft electrophile that preferentially interacts with nucleophilic groups (mainly thiols and selenols) from proteins and low-molecular-weight molecules. Such interaction contributes to the occurrence of oxidative stress, which can produce damage by several interacting mechanisms, impairing the function of various molecules (i.e., proteins, lipids, and nucleic acids), potentially resulting in modulation of different cellular signal transduction pathways. This review summarizes the general aspects regarding the interaction between MeHg with regulators of the antioxidant response system that are rich in thiol and selenol groups such as glutathione (GSH), and the selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (Gpx). A particular attention is directed towards the role of the PI3K/Akt signaling pathway and the nuclear transcription factor NF-E2-related factor 2 (Nrf2) in MeHg-induced redox imbalance.

Nonlinear responses to waterborne cadmium exposure in zebrafish. An in vivo study

Cadmium (Cd) has proved to be associated with numerous toxic effects in aquatic organisms via waterborne exposure. With a view to investigate Cd toxicity along a broad spectrum of exposures reaching from environmental to toxic, we employed adult zebrafish (Danio rerio) for an in vivo study. A number of 10 fish per tank were placed in 40L tanks and were exposed for 30 days to 0.0, 5.0, 25, 50, 75, 100 and 1000μgCd per liter. There were 2 tanks for each Cd exposure (duplicate experiment). Mortality was recorded daily, dead fish were collected and tissue samples were obtained for histologic observation, whereas remaining tissues were stored for Cd burden determination. Surviving fish were collected at the end of the experiment. Median overall survival (OS) in days was found to be 9.0, 11.0, 8.0 and 7.0 for 25μg/L, 50μg/L, 75μg/L and 100μg/L respectively, with all of them showing mortality greater than 50%. Remarkably, fish exposed to the highest Cd concentration (1000μg/L) survived the longest exhibiting a mean OS of 29.2 days. Cd determination in fish tissue was conducted with an in house ICP-MS method and levels ranged from 3.1 to 29.1ng/mg. Log Cd tissue levels were significantly correlated with the log Cd exposure levels (r = 0.535, p < 0.001). The highest Cd burden was determined for fish exposed to 1000μgCd /L (mean = 12.2ng/mg). Histopathology supported these results. Our findings disclose a deviation in toxic responses through the range of Cd concentrations, leading to nonlinear responses. These differentiated responses, could be linked to hormesis phenomena.