Hexavalent chromium exposure alters bone remodeling in the developing tooth alveolus and delays tooth eruption

Although it has been demonstrated that exposure of lactating rats to CrVI delays tooth eruption, the effects of CrVI exposure on bone remodeling in the developing alveolus during tooth eruption remain unknown. Our purpose was to analyze the effect of CrVI in the alveolus of the first lower molar of rats. Thirty-two suckling Wistar rats were divided into two groups. The experimental group received 12.5 mg/kg body weight/day of potassium dichromate dissolved in saline solution by oral gavage as of day 4 of the experiment; the control group received an equal dose of saline solution. Each group was divided into two sub-sets and euthanized at the ages of 9 and 15 days, respectively. Histochemical and histomorphometric studies of the bone surfaces of the developing tooth alveolus were performed. The percentage of bone formation surfaces was lower in experimental animals than in age-matched controls. The percentage of bone resorption surfaces was significantly lower in 9-day-old experimental rats than in controls and significantly higher in 15-day-old experimental rats than in controls. Exposure to CrVI during lactation alters the sequence of bone resorption and formation in the walls of the developing alveolus, both of which are necessary for tooth eruption, thus causing a delay.

CrVI and Trace Element Contaminated Groundwater Systems Connected with Ophiolitic Rocks

The level and distribution of chromium (as total chromium and CrVI) and other trace elements were investigated from surface and groundwater samples collected over three periods (n = 155) from Mersin (Turkey) in terms of their origins and potential health risk. The maximum total chromium is 41 µg/L and some of the samples have CrVI contents above 5 µg/L, which is the maximum permissible level of CrVI under Italian regulations. The dominant water facies are Ca-HCO₃ and Mg-HCO₃ types based on the Piper diagram. The Ca-HCO₃ type waters originate mainly from interaction with carbonate rocks, and the Mg-HCO₃ type waters originate from serpentinite dissolution. Chromium contents are higher in Mg-HCO₃ water types and the highest concentrations are found in samples from ophiolitic rocks and industrial areas. The As, Fe, Pb, Al, and Ni contents of some samples are above the EU limits in industrial areas.

Melanin-embedded materials effectively remove hexavalent chromium (CrVI) from aqueous solution

Background

Currently, it is recognized that water polluted with toxic heavy metal ions may cause serious effects on human health. Therefore, the development of new materials for effective removal of heavy metal ions from water is still a widely important area. Melanin is being considered as a potential material for removal of heavy metal from water.

Methods

In this study, we synthesized two melanin-embedded beads from two different melanin powder sources and named IMB (Isolated Melanin Bead originated from squid ink sac) and CMB (Commercial Melanin Bead originated from sesame seeds). These beads were of globular shape and 2–3 mm in diameter. We investigated and compared the sorption abilities of these two bead materials toward hexavalent-chromium (Cr^VI) in water. The isotherm sorption curves were established using Langmuir and Freundlich models in the optimized conditions of pH, sorption time, solid/liquid ratio, and initial concentration of Cr^VI. The FITR analysis was also carried out to show the differences in surface properties of these two beads.

Results

The optimized conditions for isotherm sorption of Cr^VI on IMB/CMB were set at pH values of 2/2, sorption times of 90/300 min, and solid-liquid ratios of 10/20 mg/mL. The maximum sorption capacities calculated based on the Langmuir model were 19.60 and 6.24 for IMB and CMB, respectively. However, the adsorption kinetic of Cr^VI on the beads fitted the Freundlich model with R² values of 0.992 for IMB and 0.989 for CMB. The deduced Freundlich constant, 1/n, in the range of 0.2–0.8 indicated that these beads are good adsorption materials. In addition, structure analysis data revealed great differences in physical and chemical properties between IMB and CMB. Interestingly, FTIR analysis results showed strong signals of –OH (3295.35 cm^− 1) and –C=O (1608.63 cm^− 1) groups harboring on the IMB but not CMB. Moreover, loading of Cr^VI on the IMB caused a shift of broad peaks from 3295.35 cm^− 1 and 1608.63 cm^− 1 to 3354.21 cm^− 1 and 1597.06 cm^− 1, respectively, due to –OH and –C=O stretching.

Conclusions

Taken together, our study suggests that IMB has great potential as a bead material for the elimination of Cr^VI from aqueous solutions and may be highly useful for water treatment applications.